Tapeworms of
Dogs and Cats
"Tapeworms" are members of the Class Cestoda which are
included under the Phylum Platyhelminthes (the
flatworms) along with the Class Trematoda (the flukes).
Of the several orders of cestodes which occur as
parasites in the animal kingdom, only two are of
veterinary importance, the Order Cyclophyllidea and the
Order Pseudophyllidea. Most of the important cestodes
of domestic animals and man are cyclophyllidean
tapeworms. Only two pseudophyllidean genera are of any
importance in dogs or cats. Distinct morphological and life
cycle patterns differentiate cyclophyllidean and
pseudophylidean tapeworms.
Order Cyclophyllidea
Cyclophyllidean larval stages
The eggs of cyclophyllidean tapeworms develop within themselves
spherical embryos characterized by the presence of three pairs of
claw-like hooks. These embryos are known as oncospheres or
hexacanth embryos. Oncospheres remain passively in the eggs until
ingested by a proper intermediate host in which they are destined
to develop. The intermediate host may be either a vertebrate or an
invertebrate, and the larval form eventually to develop will be
either a cysticercus, coenurus, hydatid, or a cysticercoid. After
ingestion of the egg, the oncosphere will penetrate the gut wall of
the intermediate host, migrate to one or more specific organs and
develop into one of the above intermediate stages. This constitutes
the infective stage of cyclophyllidean tapeworms, and is dependent
upon the species of cestode. Upon ingestion of either a cysticercus,
coenurus, hydatid, or cysticercoid (larval forms) by a final host, the
bladder-like structure disintegrate and only scolices survive. These
turn right side out (evaginate), attach themselves to the mucosal
lining of the intestine, and grow into mature tapeworms. This
occurs within the alimentary canal of the final host, and at this site
the mature worm develops and hermaphroditic fertilization occurs.
Dipylidium caninum
Dipylidium caninum is cosmopolitan in distribution and
is the most common tapeworm of dogs and cats. It may
also occur in wild carnivores and very rarely may infect
man. D. caninum resides in the small intestine.
Identification characteristics of tapeworms
Tapeworms that occur as the adult form in dogs and
cats may be differentiated from one another by
morphology of the scolex (head) , the neck, the
individual segments (proglottides) and characteristics
of the entire strobila (body).
D. caninum scolex
The length of mature D. caninum specimens vary from 5 cm to 70
cm and the scolex is extremely small (1/4 - 1/2 mm in width). As
with all cyclophyllidean tapeworms, immature segments "bud off”
from the neck, pushing the older segments posteriorly where
they become progressively mature and then" gravid" toward the
caudal portion of the strobila.
The scolex of Dipylidium caninum has four circular suckers and a
mobile, retractable rostellum which is "armed" with a number of
small spines. These "hold-fast" organs serve as the means of
attachment to the intestinal mucosa with the strobila extending
freely into the lumen.
D. caninum - Mature proglottid
Because of the unusual shape of the segments, which resemble
cucumber seeds when relaxed in water, D. caninum is often referred
to as the "cucumber worm". The reproductive organs are double in
each segment and can be seen grossly as two dense, whitish areas
which terminate at a genital pore on the lateral margin of either
side. Tapeworms are hermaphroditic; both male and female organs
occur in each set of reproductive organs.
Dipylidium gravid proglottid
When segments become gravid,
the uterus grows and becomes
convoluted and packed with
eggs.
Shedding segment diagram
Entire gravid segments are continuously shed from the caudal end
of the strobila. They remain motile and are found in the feces or on
the perineal area of the host after having crawled from the anus.
Eggs are seldom shed individually, but are contained in "packets"
within mature proglottids. Dipylidium infections are therefore
usually diagnosed by identification of shed proglottids rather than
by finding eggs by fecal examination. Segments which dry on the
perineum of a dog leads to often observed "rice granules" on dogs
infected with cyclophyllidean tapeworms.
Egg of Dipylidium
Eggs may be found by preparing "squash preparations" of
gravid segments, and are less commonly found upon stool
examination. The membrane surrounding egg packets is
derived by "pinching" off a portion of the uterus and
contains up to 20 eggs in a gelatinous matrix.
Flea intermediate host
Motile proglottids crawl away from stools or from the
perineum to other areas such as bedding in the host's
environment. When dry, proglottids rupture, releasing
packets of eggs. Further development depends on the
presence of fleas or biting lice as intermediate hosts.
Flea larva
Infection of fleas is possible only at the larval
stage which has biting mouth parts for feeding
on organic matter and debris. By the time the
flea has become an adult, the onchosphere has
developed to an infective cysticercoid.
Biting louse
Biting lice (Trichodectes canis)
serve as less frequent intermediate
hosts. Onchospheres penetrate into
the body cavity of lice or fleas and
develop to infective cysticercoids in
about thirty days
Cysticercoids
This larval form has a single depressed, (not invaginated)
scolex in a small solid cyst without a cyst cavity. Upon
ingestion by the definitive host (while chewing on fleas), the
scolex emerges and the rest is digested off. Dipylidium
caninum reaches maturity in a susceptible dog or cat host in
approximately three weeks.
Public health
Dipylidium very rarely may infect man.
Approximately 40 cases have been recorded in the
U.S. and nearly all of these have been in children,
that accidentally ingest fleas that fall off dogs or
cats or possibly as a result of being licked on the
face by a dog which has just crushed an infected
flea. Human infections are not considered
pathogenic, although vague intestinal disturbances
or colic have been associated with infections.
Taenia Generalized life cycle
A number of species of Taenia occur as adults in the small intestine
of dogs and cats. Eggs have a thick striated shell (embryophore)
which surrounds a hexacanth embryo. Taenia life cycles involve a
Cysticercus larval stage in one or more mammalian intermediate
hosts and infection of the final host occurs by ingestion. The
following table lists important characteristic of the Taenia species
that occur in dogs, cats or man. Taenia saginata and T. solium of man
are covered in a separate handout.
Adult Prime Final Larva Prime Larval
Host Intermediate Predilection
Host Site
T. pisiformis dog Cysticercus Rabbit peritoneum
pisiformis
T. hydatigena dog Cysticercus Sheep, Ox, Pig peritoneum
tenuicollis
T. ovis dog Cysticercus Sheep muscle
ovis
T. (Hydadigera) cat Cysticercus Rodents liver
taeniaeformis fasciolaris
T. saginata man Cysticercus Ox muscle
bovis
T. solium man Cysticercus Pig, man muscle
cellulosae
The intermediate stages of Taenia spp. all have their
own generic and specific names because they were
originally supposed to be distinct organisms with their
own identities. Only in the past century has their
relationship to the adult tapeworms been established,
and the special names have persisted though there is
now no real need for them. The practice also persists
in the trematodes, where there are many cercariae
whose final form is not known, and which are still
designated as belonging to the hypothetical genus
Cercaria.
Taenia pisiformis in situ
Taenia pisiformis occurs in the small intestine and
next to Dipylidium caninium, is the most common
tapeworm of dogs in the Southeast. It also occurs in
cats, foxes, wolves and related carnivores. Taenia
spp. are more robust tapeworms than Dipylidium and
segments are more rectangular in shape.
T. pisiformis Scolex
The scolex is distinctly larger than Dipylidium and
bears four suckers and a rostellum armed with a
double row of hooks arranged in a circular pattern.
T. pisiformis mature segment
The genitalia of Taenia spp. are single in each
segment, and the genital pores occur in irregular
alternating sequence on either lateral margin.
T. pisiformis gravid segment
Gravid segments contain a branched, convoluted uterus packed
with individual eggs. Like Dipylidium and other cyclophyllidean
tapeworms, gravid segments detach and are passed in the stool.
It is unusual to find eggs in the feces and diagnosis is usually
made by finding motile proglottids or dry “rice granules”.
Placement of the genital pore on proglottids and finding typical
eggs on a “squash preparation” allows identification of Taenia
species. Identification of cestode species is necessary to
knowledge of the probab1e source of infection and subsequent
prevention recommendations.
Taenia eggs
Eggs of Taenia spp. are small
(about 4Ou) and spherical
and the embryophore or
shell consists of two layers,
an outer vitelline layer which
is brown and pitted and an
inner chitinous layer . Tne
embryophore has a typical
radial striation, owing to the
presence of cemented
hexagonal prisms which form
much of its thickness. The
oncoshere contains 6 hooks
(hexacanth embryo).
T. pisiformis cysticerci
Rabbits are the most common intermediate host to T. pisiformis; it is
found to a lesser extent in rodents and squirrels. Upon ingestion of eggs,
the embryophore is digested off and very active onchospheres are
carried to the liver via the hepatic portal blood. Here they migrate in the
parenchyma for about a month before breaking through the capsule to
the peritonium, where they grow to cysticerci. As the name indicates, the
larva Cysticerci pisiformis is only pea-sized and usually occurs in bunches
in the omenta, mesentery or other serosa1 surface. During the wandering
phase in the liver, tissue
damage occurs (similar to
juveni1e Fasciola migrations)
and a condition called
“hepatitis cysticercosa” may
result in the intermediate
host. Cysticerci become
infective in approximately 2
months.
Cysticerci consist of a single scolex invaginated into a fluid
filled bladder.
T. pisiformis cysticerci
When ingested by the final host, the scolex everts,
the bladder structures are digested away, the
scolex attaches to the mucosa and goes on to
maturity .
The prepatent period before passage of eggs or
segments is approximately 2 months.
Taenia hydatigena
Bovine intermediate host
Cattle, sheep and swine are
the primary intermediate
hosts for Taenia hydatigena.
T. hydatigena is one of the
largest Taenia species in
dogs and may reach 5 meters
in length.
Cysticercus tenuicollis
Oncospheres carried to the liver in the portal blood stream,
and wander in the parenchyma for about a month before
they break through G1isson's capsule and attach to the
peritoneum. Here they grow singly or in bunches to very
large cysts of 7-8 cm diameters on the abdominal serosal
surface, particularly on the omentum and mesentery .
Damage due to migration in the liver may lead to “hepatitis
cysticercosa”, as with T. pisiformis in rabbits.
Infection of dogs and closely
related carnivores occurs by
ingestion of cysticerci in offal
from cattle, sheep or pigs. It
is not a common parasite in the
Southeast. The prepatent
period, from ingestion of eggs
to passage of gravid
proglottids is 2 months as with
other Taenia species.
Taenia ovis
T. ovis is found in the small intestines of dogs and
measures about one meter in length when mature. After
ingestion of eggs by sheep or goats, the oncosheres are
bloodborne to the musculature. T. ovjs is similar in its
development to T. saginata or T. solium, except that the
dog, rather than man, harbors the adult tapeworms.
T. ovis cysticercus
T. ovis infections in sheep are referred to as “sheep measles” and are
similar in size and morphology to “beef measles” or “pork measles”.
The most common sites leat sites of infection are the heart and
diaphragm but they occur also in striated muscle anywhere in the
body. Little is known regarding the effect on sheep, although one
worker produced death experimentally by feeding as few as 10 gravid
segments. The major losses due to T. ovis involve condemnation of
carcasses at meat inspection.
Farm dogs are of greatest
importance in transmitting T.
ovis, and this species is
restricted mainly to Western
USA where most of the sheep
and goat industry is found.
Again, the prepatent period is 2
months.
Taenia taeniaformis - cat host
T. taeniaformis is the most
common cestode of cats and is
widely distributed throughout
the U.S. It may also be found
in the small intestines of dogs
and related carnivores.
T. taeniaformis strobilocercus I rat liver
This species has a relatively wide intermediate host range with rats,
mice, and also rabbits, squirels, and other rodents being capable of
harboring cysticerci. When blood-borne oncosperes arrive in the liver,
they do not wander, but develop to encapsulated “strobilocerci” which
are infective in about 2 months. Strobilocerci occur tightly packed in
pea-sized cysts, embedded inliver tissue. Their identity is revealed
upon opening the cysts, when they burst out.
Strobilocerci teased from
rat liver
The scolex of strobilocerus is not invaginated, and is seperated from a
cyst or bladder by a chain of asexual proglottids. Upon ingestion by the
final host, the entire larval structure except the scolex is digested off.
Tapeworms of this larval type therfore make strobila twice in their life
cycles.
T. taeniaformis egg
The prepatent period of 16 to 18 days before passage of
gravid segments or eggs is short as compared to other
members of the genus.
Multiceps spp.
Multiceps spp. are basically similar to Taenia in life history except that the larval
stage is a coenurus. A coenurus differs from a cysticercus only by the presence of
several scolices (rather than one) invaginated from its wall. Some authorities
include Multiceps spp. in the genus Taenia. Key characteristics of the two
Multiceps species of dogs are as follows.
Prime Prime larval
final intermediate predilection
Adult host Larva host site
Multiceps dog Coenurus sheep central nervous
(=Taenia) cerebralis system
multiceps
Multiceps dog Coenurus rabbit connective
(=Taenia) serialis tissue
serialis
Taenia saginata life cycle
T. saginata is the "beef tapeworm of humans" and is one of the
largest cestodes, with an average length of 5-10 meters. Cattle
become infected when their feed, or pastures are contaminated
with feces of humans infected with T. saginata. Eggs swallowed by
cattle hatch in the duodenum and the liberated onchospheres
enter the lymphatics or blood vessels of the hepatic portal
system and are blood-borne to the
muscles via the general circulation.
They develop to oval infective
cysticerci in 60 to 75 days. After
ingestion by man in inadequately
cooked beef, cysticerci attach and
grow to sexually mature tapeworms in
about 3 months.
Taenia Cysticercosis
Two cyclophyllidian tapeworms parasitize the small
intestine of man in the adult stage, Taenia saginata
and Taenia solium. The larval stage (cysticerci) of
these parasites occur in meat from cattle ("beef
measles") and swine ("pork measles") respectively.
T. saginata gravid segment
Gravid, actively crawling segments are
detached from the strobilus in the
intestines of infected humans and these
eggs containing segments are passed in the
stool. Individual eggs are difficult to find
by fecal flotation procedures for this
reason. The number of eggs available for
cattle infection may be great, since an
infected person often expels 8 to 9
segments daily, each of which contain
80,000 to 100,000 eggs. Eggs do not
survive desiccation well, but retain
infectivity well in moist situations on
pastures for 60- 70 days at 2OC and 180
days at lOC.
T. saginata egg
Note the contained onchosphere with six
(...hexacanth) hooks which will be released by the
digestive process and migrate to muscles (usually
within 24 hours).
T. saginata free cysticerci
Cysticerci (formerly called Cxsticercus bois
develop as small oval structures which are at first
transparent but later white and opaque from
encapsulation. They measure 7-10 mm by 4-6 mm in
diameter at 60 to 75 days. Note the single scolex
and transparent cysts for each cysticercus.
T. saginata cysticerci in situ
Sites of localization in order of
decreasing importance are: heart,
masseter muscles, shoulder, tongue, and
other skeletal muscles. A "measly beef"
carcass may contain many thousand
cysticerci. Cysticerci are thought to
remain infective for about two years,
after which they calcify. Prenatal
infection of calves with blood-borne
onchospheres has been documented and is
not uncommon in high incidence areas.
Criteria for rejection of infected beef
carcasses or acceptance with trimming has
been covered previously under
Cysticerci in muscle. "Disposition of Carcasses". Cysts are
destroyed by freezing at -15F for 15
consecutive days or heating to 140F.
T. saginata cysticerci in tongue
T. saginata scolex
T. saginata in man is easily identified by the lack of
both hooks and a rostellum. It is the only "unarmed"
tapeworm that occur in man.
T. saginata mature proglottid
Note the single lateral genital pore of Taenia spp opposed to the
central genital pore of Diphyllobothrium latum segments. In the
United States, 12,000 to 16,000 infected cattle were discovered
by meat inspectors annually from 1959 through 1967. Many cases
occur as "outbreaks" in the Southwestern US and most are traced
to infected migratory farm workers. Human T.saginata infections
are far more prevalent in the US than T. solium.
Taenia solium - Life Cycle
The life history of Taenia solium is essentially similar to T. saginata except
that cysticerci occur in swine. Man is infected by pork eaten in a cured
form (such as sausage) or inadequately cooked condition.
T. solium scolex
Fully developed worms measure up to 7 meters long. It can be
distinguished from T.saginata by the presence of an armed
rostellum.Note the double crown of 22 to 32 rostellar hooks
T. solium cysticercus in ventricular
myocardium
Massive infections are usual in swine and cysticerci show little
predilection for specific muscle sites. In light infections, greater
numbers are found in muscles of the upper limbs, abdomen, and
diaphragm. Cysticercus cellulosae is sometimes used to refer to the
larval stage in "pork measles".
Surgical removal of cysticerous from
human
Taenia solium is unique among taenoid cestodes in having
the potential for internal autoinfection of humans
harboring adult worms. In some regions infection with the
larval stage is as common as infection with the adult worm.
Cysticercus infection with T. solium can occur by two methods:
1. by food or water contaminated by human feces, or self infection
by transfer of eggs from the anal region to the mouth, and
rarely, reverse peristalsis results in gravid proglottids being
carried to the stomach of humans harboring the adult worm. The
eggs are induced to hatch, and thousands of onchospheres are
disseminated via the circulation. Massive infections and even death
has been documented, particularly in immunosuppressed or
weakened individuals. Adult worms in the intestine of man generally
cause no serious damage for either T. solium or T. saginata but may
result in loss of weight and mild digestive disturbances.
Praziquantel is used to treat adult Taenia spp. in man. Yomesan and
a number of older preparations were used with mixed success in
the past. In some underdeveloped countries such as Mexico and
Kenya, cerebral cysticerci are a major cause of CNS symptoms and
death. T. solium has an apparent predilection for brain localization
in humans, especially after massive autoinfection .
Coenurus cerebralis in situ in sheep brain
The larval stage of Mu1ticeps multiceps, designated Coenurus
cerebralis, arrives in the central nervous system as a blood-borne
oncosphere. The coenurus is slow growing, and reaches maturity in 7
or 8 months at which time it may measure up to 5 cm in diameter.
Signs are due to pressure necrosis, and a number of clinical effects
may be seen depending on the site of the coenurus. Locomotor
disturbances are the most common and include continuous or
intermittent incoordination, exaggerated gait and circling, a condition
commonly referred to as “gid” or “sturdy” by sheep raisers. Other
signs may include blindness, head
pressing, anorexia, and depression.
Eventually recumbency and death
ensue. “Gid” must be differentiated
from listeriosis or louping-ill.
Coenurus cerebralis in situ in sheep brain
Dogs become infected by ingestion of infected brain or spinal
cord tissues. Each scolex may develop to a mature tapeworm
in the intestinal tract in 3-4 weeks. Multiceps multiceps is
found primarily in the Western U.S. and in countries with
large sheep populations.
Multiceps serialis - Coenurus in situ - rabbit
connectiove tissue
The life history of this cestode is esentially similar to M.
multiceps, except that the intermediate host is a rabbit and the
coenurus is located in the subcutaneous tissues. It differs from
Coenurus cerebralis by the arrangement of the scolices in a line
radiateing from a central point (thus “serialis”), and also by its
propensity for both extemal and intemal budding. The adults are
found in dogs and related canidae. Little is known of the
geographic distribution in the U.S., but it has been occasionally
reported in the Southeast.
Echinococcus
Another important genus of the “taeniid” cestodes is one
of the smallest tapeworms (up to 6mm) and consists of a
scolex and three or four segments. Because of its small
size, this tapeworm is difficult to find at necropsy. The
scolex is similar to that of Taenia spp. With a double row
of hooks on the rostellum.
Echinococcus
There is one immature, one or two mature, and one
gravid segment. There are two important species, E.
granulosus and E. multilocularis.
Echinococcus life cycle
The eggs, about 30 by 38u, are
indistinguishable from those of dog
Taenias. From the feces of dogs,
wolves, or foxes they gain access to
their intermediate hosts through
contaminated forage or water. In
addition to the animals noted above,
pigs, horses, rabbits, and many
other herbivores are susceptible.
Human infection usually results from
too intimate association with dogs;
children are especially liable to
infection by allowing dogs to lick
their faces with a tongue which, in
view of tbe unclean habits of dogs,
is an efficient means of transfer of
tapeworm eggs. Eggs transferred by
the hands from an infected dog’s
fur may also lead to infection.
The intermediate host for Echinococcus granulosus
include most of the domestic animals and man. The
most important host is the sheep, in which the
highest proportion of the cysts are fertile. Cattle
and swine also serve as intermediate hosts, but
many of the hydatid cysts in these animals are
sterile. In the United States, moose and deer are
not infrequently infected.
Echinococcus Hydatid Cyst
The larval stage of Echinococcus is the hydatid, tbe most complex of
tapeworm larval forms. Germinal epithelium produce individual
scolices, brood capsules or daughter cysts. In older cysts, there is a
granular deposit consisting of liberated brood capsules and free
scolices called “hydatid sand”.
Echinococcus hydatid cysts in situ
After ingestion of eggs, the oncosphere becomes blood-borne and is
filtered out in small capillary beds in any organ including the liver or
lungs (the most frequent localization sites) or in other tissues such
as the brain, bone marrow, or other organs.
Hydatid cysts in sheep lung
Hydatid cysts in horse liver
Echinococcus hydatid cysts of various sizes
Hydatid cysts grow very slowly.
The young larvae becomes a
hollow bladder, around which the
host adds an enveloping, fibrous
cyst wall. At the end of a month
cysts measure only 1mm; in 5
months they are about 10 mm and
their inner surface begins
producing brood capsules. As the
cyst grows larger, brood capsules
differentiate further and
daughter cysts may be produced.
Hydatids may eventually reach
orange size or larger. After 10 or
20 years, they may contain many
quarts of fluid and thousands of
scolices.
Echinococcus hydatid cyst - histosection
Note the brood capsules budding off from the delicate
germinal epithelium and the thick connective tissue wall
produced by the host.
E. granulosus egg
When cysts are ingested by dogs, very heavy infections with hundreds or
thousands of adult E. granulosus results and patency occurs at 4-6 weeks.
Clinical signs are minimal even when large numbers of adults are present. Due
to the relatively short life of domestic animals and the long periods required
for hydatids to mature, Echinococcus is of little economic importance to the
livestock industry and its main importance is a public health hazard to man.
New Zealand and Iceland have successfully controlled human echinococcosis by
requiring frequent vermifuges for dogs and proper disposal of offal from
livestock. In the U.S., Echinococcus is of highest incidence in Basque
sheepherders in western mountain
areas. Incidence in Argentina is 2-4.6
per hundred thousand people and 8.3
per hundred thousand in Greece. The
greatest danger of human hydatidosis
is loss of respiratory function in lung
infections, and anaphylaxis from
rupture of a cyst due to
hypersensitivity to cyst antigens. The
latter is an important consideration
during surgical excision of cysts.
E. multilocularis - exogenous budding
E. multilocularis is closely related to E. granulosus and occurs in
subarctic regions of Canada, Alaska, Europe and Asia as a parasite of
wild and domestic canidae. It has been found as far south as the
Dakotas and Illinois of the U.S. and there is concern this species is
extending its range into the U.S. and also in Europe and may soon
exceed E. granulosus as a public health problem. The basic
intermediate host is the vole. Recent spread may be due to re-
establishment of former numbers and range of foxes, other canidae.
E. multilocularis differs from E. granulosus by exogenous budding to the
outside of the cyst (as diagrammed here) rather than the endogenous
budding of E. granulosus.
E. multilocularis - histosection of vole liver
Due to exogenous budding E. multilocularis has a growth pattern
much like that of a neoplasm. This species is highly invasive and
metastases from primary liver hydatids may occur in distant organs.
Although most domestic and wild animals are refractory to this
parasite, man may be infected. The species is a very severe zoonotic
disease transmitted from dogs to people in the endemic area. It
initiates a highly invasive process in the liver and other body organs
which is exceptionally difficult to treat, since there is no drug
available that affects the cyst stage.
Order Pseudophyllidea
Two species of pseudophyllidian tapeworms occur to
a limited extent in dogs and cats in the U.S.,
Diphyllobothrium latum and Spirometra mansonoides.
Both are covered in a handout entitled “Meat, Fish
and Water-borne Diseases of Public health
Significance.”
Several key characteristics may be used to identify
and diagnose pseudophyllidian tapeworms.
D. latem - scolex
The scolex is very small and has two slit-like
bothria (rather than four circular suckers) which
serve as hold fast organs.
D. latum - segment
Segments are retained and not shed continuously by
pseudophyllidian tapeworms. Proglottids are of nearly uniform
size and maturity and passage of individual operculated eggs
rather than segments are the means of egg dispersal. Genital
structures and the genital pore are located centrally on each
segment (as seen here) and may be seen grossly.
Diphyllobothrium latum life cycle
Diphyllobothrium latum is a pseudophyllidian tapeworm which is
commonly known as the "broad fish tapeworm " of man and other
fish-eating mammals such as dogs, cats, bears, etc. The life cycle
involves two intermediate hosts, small fresh water crustaceans
known as "copepods" and various fresh water fish.
Operculate eggs hatch outside the final hosts' body in water in
about 2 weeks, liberating the first larval stage, a free-swimming,
ciliated coracidium. After ingestion by certain copepods (i.e.
Cyclops) the coracidium develops in another two weeks to the
procercoid stage. When the copepod is eaten by fish, the second
intermediate host, the procercoid migrates to the muscles and
other organs and develops to the plerocercoid stage. The
plerocercoid is about 5mm long and is visible in exposed muscle
of infected fresh-water fish, including pike, perch, trout, salmon
and others. If small fish infected with plerocercoids are
ingested by larger fish, the larval tapeworms, having paratenic
tendencies, migrate to the muscles and viscera of the new host
and re-encyst, a process that can be repeated in a long series of
fish hosts. Man and other hosts are infected by ingestion of the
plerocercoid in uncooked, pickled or "cured" fish.
Diphyllobothrium latum life cycle
Diphyllobothrium latum is a pseudophyllidian tapeworm which is
commonly known as the "broad fish tapeworm " of man and other
fish-eating mammals such as dogs, cats, bears, etc. The life cycle
involves two intermediate hosts, small fresh water crustaceans
known as "copepods" and various fresh water fish.
Operculate eggs hatch outside the final hosts' body in water in
about 2 weeks, liberating the first larval stage, a free-swimming,
ciliated coracidium. After ingestion by certain copepods (i.e.
Cyclops) the coracidium develops in another two weeks to the
procercoid stage. When the copepod is eaten by fish, the second
intermediate host, the procercoid migrates to the muscles and
other organs and develops to the plerocercoid stage. The
plerocercoid is about 5mm long and is visible in exposed muscle
of infected fresh-water fish, including pike, perch, trout, salmon
and others. If small fish infected with plerocercoids are
ingested by larger fish, the larval tapeworms, having paratenic
tendencies, migrate to the muscles and viscera of the new host
and re-encyst, a process that can be repeated in a long series of
fish hosts. Man and other hosts are infected by ingestion of the
plerocercoid in uncooked, pickled or "cured" fish.
Diphyllobothrium egg
The egg is oval, yellowish and operculated, and is
somewhat similar to Fasciola hepatica in appearance but is
much smaller (70u by 45u). A posterior "knob" is
sometimes visible opposite the operculated end (as seen
here).
Diphyllobothrium latum life cycle
Diphyllobothrium latum is a pseudophyllidian tapeworm which is
commonly known as the "broad fish tapeworm " of man and other
fish-eating mammals such as dogs, cats, bears, etc. The life cycle
involves two intermediate hosts, small fresh water crustaceans
known as "copepods" and various fresh water fish.
Operculate eggs hatch outside the final hosts' body in water in
about 2 weeks, liberating the first larval stage, a free-swimming,
ciliated coracidium. After ingestion by certain copepods (i.e.
Cyclops) the coracidium develops in another two weeks to the
procercoid stage. When the copepod is eaten by fish, the second
intermediate host, the procercoid migrates to the muscles and
other organs and develops to the plerocercoid stage. The
plerocercoid is about 5mm long and is visible in exposed muscle
of infected fresh-water fish, including pike, perch, trout, salmon
and others. If small fish infected with plerocercoids are
ingested by larger fish, the larval tapeworms, having paratenic
tendencies, migrate to the muscles and viscera of the new host
and re-encyst, a process that can be repeated in a long series of
fish hosts. Man and other hosts are infected by ingestion of the
plerocercoid in uncooked, pickled or "cured" fish.
Diphyllobothrium egg
The egg is oval, yellowish and operculated, and is
somewhat similar to Fasciola hepatica in appearance but is
much smaller (70u by 45u). A posterior "knob" is
sometimes visible opposite the operculated end (as seen
here).
D. latum coracidium emerging from egg
The coracidium is an apparent biologic analogy to the
trematode miracidium, but consists of a hexacanth
onchosphere with a ciliated coat.
Diphyllobothrium latum life cycle
Diphyllobothrium latum is a pseudophyllidian tapeworm which is
commonly known as the "broad fish tapeworm " of man and other
fish-eating mammals such as dogs, cats, bears, etc. The life cycle
involves two intermediate hosts, small fresh water crustaceans
known as "copepods" and various fresh water fish.
Operculate eggs hatch outside the final hosts' body in water in
about 2 weeks, liberating the first larval stage, a free-swimming,
ciliated coracidium. After ingestion by certain copepods (i.e.
Cyclops) the coracidium develops in another two weeks to the
procercoid stage. When the copepod is eaten by fish, the second
intermediate host, the procercoid migrates to the muscles and
other organs and develops to the plerocercoid stage. The
plerocercoid is about 5mm long and is visible in exposed muscle
of infected fresh-water fish, including pike, perch, trout, salmon
and others. If small fish infected with plerocercoids are
ingested by larger fish, the larval tapeworms, having paratenic
tendencies, migrate to the muscles and viscera of the new host
and re-encyst, a process that can be repeated in a long series of
fish hosts. Man and other hosts are infected by ingestion of the
plerocercoid in uncooked, pickled or "cured" fish.
Diphyllobothrium egg
The egg is oval, yellowish and operculated, and is
somewhat similar to Fasciola hepatica in appearance but is
much smaller (70u by 45u). A posterior "knob" is
sometimes visible opposite the operculated end (as seen
here).
D. latum coracidium emerging from egg
The coracidium is an apparent biologic analogy to the
trematode miracidium, but consists of a hexacanth
onchosphere with a ciliated coat.
Cyclops- lst intermediate host
Like miracidia, the coracidium requires a water
environment and must be ingested by a copepod
intermediate host within 24 hours or it dies.
Diphyllobothrium latum life cycle
Diphyllobothrium latum is a pseudophyllidian tapeworm which is
commonly known as the "broad fish tapeworm " of man and other
fish-eating mammals such as dogs, cats, bears, etc. The life cycle
involves two intermediate hosts, small fresh water crustaceans
known as "copepods" and various fresh water fish.
Operculate eggs hatch outside the final hosts' body in water in
about 2 weeks, liberating the first larval stage, a free-swimming,
ciliated coracidium. After ingestion by certain copepods (i.e.
Cyclops) the coracidium develops in another two weeks to the
procercoid stage. When the copepod is eaten by fish, the second
intermediate host, the procercoid migrates to the muscles and
other organs and develops to the plerocercoid stage. The
plerocercoid is about 5mm long and is visible in exposed muscle
of infected fresh-water fish, including pike, perch, trout, salmon
and others. If small fish infected with plerocercoids are
ingested by larger fish, the larval tapeworms, having paratenic
tendencies, migrate to the muscles and viscera of the new host
and re-encyst, a process that can be repeated in a long series of
fish hosts. Man and other hosts are infected by ingestion of the
plerocercoid in uncooked, pickled or "cured" fish.
Diphyllobothrium egg
The egg is oval, yellowish and operculated, and is
somewhat similar to Fasciola hepatica in appearance but is
much smaller (70u by 45u). A posterior "knob" is
sometimes visible opposite the operculated end (as seen
here).
D. latum coracidium emerging from egg
The coracidium is an apparent biologic analogy to the
trematode miracidium, but consists of a hexacanth
onchosphere with a ciliated coat.
Cyclops- lst intermediate host
Like miracidia, the coracidium requires a water
environment and must be ingested by a copepod
intermediate host within 24 hours or it dies.
Adult Diphyllobothrium latum
D. latum attaches to the mucosa of the small intestine and is the
longest known cestode, reaching a length of 15 meters and consisting
of more than 4000 segments. It is a very fast-growing cestode and can
reach a length of a meter in three weeks. The first eggs appearing in
the feces in about four weeks after ingestion of pleurocercoids and
the worm may survive ten years or more. As a rule eggs can be found in
the feces of the definitive host, in contrast to infection with
cyclophyllidian tapeworms in
which eggs are released in
gravid segments passed from
the body . D. latum segments
are shed only when they are
old and no longer capable of
producing eggs. The majority
of segments are in the same
stage of development and are
more uniform in size than
cyclophyllidian tapeworms.
Diphyllobothrium latum life cycle
Diphyllobothrium latum is a pseudophyllidian tapeworm which is
commonly known as the "broad fish tapeworm " of man and other
fish-eating mammals such as dogs, cats, bears, etc. The life cycle
involves two intermediate hosts, small fresh water crustaceans
known as "copepods" and various fresh water fish.
Operculate eggs hatch outside the final hosts' body in water in
about 2 weeks, liberating the first larval stage, a free-swimming,
ciliated coracidium. After ingestion by certain copepods (i.e.
Cyclops) the coracidium develops in another two weeks to the
procercoid stage. When the copepod is eaten by fish, the second
intermediate host, the procercoid migrates to the muscles and
other organs and develops to the plerocercoid stage. The
plerocercoid is about 5mm long and is visible in exposed muscle
of infected fresh-water fish, including pike, perch, trout, salmon
and others. If small fish infected with plerocercoids are
ingested by larger fish, the larval tapeworms, having paratenic
tendencies, migrate to the muscles and viscera of the new host
and re-encyst, a process that can be repeated in a long series of
fish hosts. Man and other hosts are infected by ingestion of the
plerocercoid in uncooked, pickled or "cured" fish.
Diphyllobothrium egg
The egg is oval, yellowish and operculated, and is
somewhat similar to Fasciola hepatica in appearance but is
much smaller (70u by 45u). A posterior "knob" is
sometimes visible opposite the operculated end (as seen
here).
D. latum coracidium emerging from egg
The coracidium is an apparent biologic analogy to the
trematode miracidium, but consists of a hexacanth
onchosphere with a ciliated coat.
Cyclops- lst intermediate host
Like miracidia, the coracidium requires a water
environment and must be ingested by a copepod
intermediate host within 24 hours or it dies.
Adult Diphyllobothrium latum
D. latum attaches to the mucosa of the small intestine and is the
longest known cestode, reaching a length of 15 meters and consisting
of more than 4000 segments. It is a very fast-growing cestode and can
reach a length of a meter in three weeks. The first eggs appearing in
the feces in about four weeks after ingestion of pleurocercoids and
the worm may survive ten years or more. As a rule eggs can be found in
the feces of the definitive host, in contrast to infection with
cyclophyllidian tapeworms in
which eggs are released in
gravid segments passed from
the body . D. latum segments
are shed only when they are
old and no longer capable of
producing eggs. The majority
of segments are in the same
stage of development and are
more uniform in size than
cyclophyllidian tapeworms.
D. latum is easily recognized
by its large size, central
genital pore in square
segments
and long unarmed
scolex with two
elongate, groove-like
suckers called bothria.
Genital pores are lateral in cyclphyllidian tapeworms.
Diphyllobothrium latum life cycle
Diphyllobothrium latum is a pseudophyllidian tapeworm which is
commonly known as the "broad fish tapeworm " of man and other
fish-eating mammals such as dogs, cats, bears, etc. The life cycle
involves two intermediate hosts, small fresh water crustaceans
known as "copepods" and various fresh water fish.
Operculate eggs hatch outside the final hosts' body in water in
about 2 weeks, liberating the first larval stage, a free-swimming,
ciliated coracidium. After ingestion by certain copepods (i.e.
Cyclops) the coracidium develops in another two weeks to the
procercoid stage. When the copepod is eaten by fish, the second
intermediate host, the procercoid migrates to the muscles and
other organs and develops to the plerocercoid stage. The
plerocercoid is about 5mm long and is visible in exposed muscle
of infected fresh-water fish, including pike, perch, trout, salmon
and others. If small fish infected with plerocercoids are
ingested by larger fish, the larval tapeworms, having paratenic
tendencies, migrate to the muscles and viscera of the new host
and re-encyst, a process that can be repeated in a long series of
fish hosts. Man and other hosts are infected by ingestion of the
plerocercoid in uncooked, pickled or "cured" fish.
Diphyllobothrium egg
The egg is oval, yellowish and operculated, and is
somewhat similar to Fasciola hepatica in appearance but is
much smaller (70u by 45u). A posterior "knob" is
sometimes visible opposite the operculated end (as seen
here).
D. latum coracidium emerging from egg
The coracidium is an apparent biologic analogy to the
trematode miracidium, but consists of a hexacanth
onchosphere with a ciliated coat.
Cyclops- lst intermediate host
Like miracidia, the coracidium requires a water
environment and must be ingested by a copepod
intermediate host within 24 hours or it dies.
Adult Diphyllobothrium latum
D. latum attaches to the mucosa of the small intestine and is the
longest known cestode, reaching a length of 15 meters and consisting
of more than 4000 segments. It is a very fast-growing cestode and can
reach a length of a meter in three weeks. The first eggs appearing in
the feces in about four weeks after ingestion of pleurocercoids and
the worm may survive ten years or more. As a rule eggs can be found in
the feces of the definitive host, in contrast to infection with
cyclophyllidian tapeworms in
which eggs are released in
gravid segments passed from
the body . D. latum segments
are shed only when they are
old and no longer capable of
producing eggs. The majority
of segments are in the same
stage of development and are
more uniform in size than
cyclophyllidian tapeworms.
D. latum is easily recognized
by its large size, central
genital pore in square
segments
and long unarmed
scolex with two
elongate, groove-like
suckers called bothria.
Genital pores are lateral in cyclphyllidian tapeworms.
Diphyllobothrium latum is unusual among cestodes in being
pathogenic in the adult stage. The capacity of D.latum for depriving
its human host of vitamin B12 to produce pernicious anemia
(macrocytic, hyperchromic) is well documented. It does this by two
mechanisms: (1) it interferes with absorption of B12 by blocking the
combination of B12 and an intrinsic factor from the gastric mucosa
and (2) it absorbs and binds large amounts of B12 in its own tissues.
D. latum contains 15 times as much B12 as other cestodes and a
powdered preparation of its segments may actually be used to treat
victims of an active infection.
Infection rates are highest in cultural groups which traditionally eat
roe or fresh water fish raw, lightly salted, or pickled without
cooking. Incidence is highest in the US in people of Scandinavian
extraction in the Great Lakes region. Eskimos in Alaska and Jewish
people fond of gefilte fish (spiced minced fish) are also prone to
infection. Plerocercoids are killed in fish subjected to freezing at -
l0°C for 24-48 hours or cooking at over 56 °C for 5 minutes.
Diphyllobothrium latum life cycle
Diphyllobothrium latum is a pseudophyllidian tapeworm which is
commonly known as the "broad fish tapeworm " of man and other
fish-eating mammals such as dogs, cats, bears, etc. The life cycle
involves two intermediate hosts, small fresh water crustaceans
known as "copepods" and various fresh water fish.
Operculate eggs hatch outside the final hosts' body in water in
about 2 weeks, liberating the first larval stage, a free-swimming,
ciliated coracidium. After ingestion by certain copepods (i.e.
Cyclops) the coracidium develops in another two weeks to the
procercoid stage. When the copepod is eaten by fish, the second
intermediate host, the procercoid migrates to the muscles and
other organs and develops to the plerocercoid stage. The
plerocercoid is about 5mm long and is visible in exposed muscle
of infected fresh-water fish, including pike, perch, trout, salmon
and others. If small fish infected with plerocercoids are
ingested by larger fish, the larval tapeworms, having paratenic
tendencies, migrate to the muscles and viscera of the new host
and re-encyst, a process that can be repeated in a long series of
fish hosts. Man and other hosts are infected by ingestion of the
plerocercoid in uncooked, pickled or "cured" fish.
Diphyllobothrium egg
The egg is oval, yellowish and operculated, and is
somewhat similar to Fasciola hepatica in appearance but is
much smaller (70u by 45u). A posterior "knob" is
sometimes visible opposite the operculated end (as seen
here).
D. latum coracidium emerging from egg
The coracidium is an apparent biologic analogy to the
trematode miracidium, but consists of a hexacanth
onchosphere with a ciliated coat.
Cyclops- lst intermediate host
Like miracidia, the coracidium requires a water
environment and must be ingested by a copepod
intermediate host within 24 hours or it dies.
Adult Diphyllobothrium latum
D. latum attaches to the mucosa of the small intestine and is the
longest known cestode, reaching a length of 15 meters and consisting
of more than 4000 segments. It is a very fast-growing cestode and can
reach a length of a meter in three weeks. The first eggs appearing in
the feces in about four weeks after ingestion of pleurocercoids and
the worm may survive ten years or more. As a rule eggs can be found in
the feces of the definitive host, in contrast to infection with
cyclophyllidian tapeworms in
which eggs are released in
gravid segments passed from
the body . D. latum segments
are shed only when they are
old and no longer capable of
producing eggs. The majority
of segments are in the same
stage of development and are
more uniform in size than
cyclophyllidian tapeworms.
D. latum is easily recognized
by its large size, central
genital pore in square
segments
and long unarmed
scolex with two
elongate, groove-like
suckers called bothria.
Genital pores are lateral in cyclphyllidian tapeworms.
Diphyllobothrium latum is unusual among cestodes in being
pathogenic in the adult stage. The capacity of D.latum for depriving
its human host of vitamin B12 to produce pernicious anemia
(macrocytic, hyperchromic) is well documented. It does this by two
mechanisms: (1) it interferes with absorption of B12 by blocking the
combination of B12 and an intrinsic factor from the gastric mucosa
and (2) it absorbs and binds large amounts of B12 in its own tissues.
D. latum contains 15 times as much B12 as other cestodes and a
powdered preparation of its segments may actually be used to treat
victims of an active infection.
Infection rates are highest in cultural groups which traditionally eat
roe or fresh water fish raw, lightly salted, or pickled without
cooking. Incidence is highest in the US in people of Scandinavian
extraction in the Great Lakes region. Eskimos in Alaska and Jewish
people fond of gefilte fish (spiced minced fish) are also prone to
infection. Plerocercoids are killed in fish subjected to freezing at -
l0°C for 24-48 hours or cooking at over 56 °C for 5 minutes.
Diphyllobothrium Treatment
Although dogs, cats, and other mammals may be
infected the importance of wild and domestic
animals as reservoirs is unknown and man is thought
to be the main host for D. latum. There are
differing opinions on the capacity of eggs produced
in animals to hatch and infect copepods. Quinicrine
(®Atabrine) and niclosamide (®Yomesan) are
effective treatments in man. Dogs may be
successfully treated with arecoline preparations
(®Nemural) and cats may be treated with kamala.
Praziquantel at 3 times label dose is the treatment
of choice for dogs, cats and man.
Diphyllobothrium latum life cycle
Diphyllobothrium latum is a pseudophyllidian tapeworm which is
commonly known as the "broad fish tapeworm " of man and other
fish-eating mammals such as dogs, cats, bears, etc. The life cycle
involves two intermediate hosts, small fresh water crustaceans
known as "copepods" and various fresh water fish.
Operculate eggs hatch outside the final hosts' body in water in
about 2 weeks, liberating the first larval stage, a free-swimming,
ciliated coracidium. After ingestion by certain copepods (i.e.
Cyclops) the coracidium develops in another two weeks to the
procercoid stage. When the copepod is eaten by fish, the second
intermediate host, the procercoid migrates to the muscles and
other organs and develops to the plerocercoid stage. The
plerocercoid is about 5mm long and is visible in exposed muscle
of infected fresh-water fish, including pike, perch, trout, salmon
and others. If small fish infected with plerocercoids are
ingested by larger fish, the larval tapeworms, having paratenic
tendencies, migrate to the muscles and viscera of the new host
and re-encyst, a process that can be repeated in a long series of
fish hosts. Man and other hosts are infected by ingestion of the
plerocercoid in uncooked, pickled or "cured" fish.
Diphyllobothrium egg
The egg is oval, yellowish and operculated, and is
somewhat similar to Fasciola hepatica in appearance but is
much smaller (70u by 45u). A posterior "knob" is
sometimes visible opposite the operculated end (as seen
here).
D. latum coracidium emerging from egg
The coracidium is an apparent biologic analogy to the
trematode miracidium, but consists of a hexacanth
onchosphere with a ciliated coat.
Cyclops- lst intermediate host
Like miracidia, the coracidium requires a water
environment and must be ingested by a copepod
intermediate host within 24 hours or it dies.
Adult Diphyllobothrium latum
D. latum attaches to the mucosa of the small intestine and is the
longest known cestode, reaching a length of 15 meters and consisting
of more than 4000 segments. It is a very fast-growing cestode and can
reach a length of a meter in three weeks. The first eggs appearing in
the feces in about four weeks after ingestion of pleurocercoids and
the worm may survive ten years or more. As a rule eggs can be found in
the feces of the definitive host, in contrast to infection with
cyclophyllidian tapeworms in
which eggs are released in
gravid segments passed from
the body . D. latum segments
are shed only when they are
old and no longer capable of
producing eggs. The majority
of segments are in the same
stage of development and are
more uniform in size than
cyclophyllidian tapeworms.
D. latum is easily recognized
by its large size, central
genital pore in square
segments
and long unarmed
scolex with two
elongate, groove-like
suckers called bothria.
Genital pores are lateral in cyclphyllidian tapeworms.
Diphyllobothrium latum is unusual among cestodes in being
pathogenic in the adult stage. The capacity of D.latum for depriving
its human host of vitamin B12 to produce pernicious anemia
(macrocytic, hyperchromic) is well documented. It does this by two
mechanisms: (1) it interferes with absorption of B12 by blocking the
combination of B12 and an intrinsic factor from the gastric mucosa
and (2) it absorbs and binds large amounts of B12 in its own tissues.
D. latum contains 15 times as much B12 as other cestodes and a
powdered preparation of its segments may actually be used to treat
victims of an active infection.
Infection rates are highest in cultural groups which traditionally eat
roe or fresh water fish raw, lightly salted, or pickled without
cooking. Incidence is highest in the US in people of Scandinavian
extraction in the Great Lakes region. Eskimos in Alaska and Jewish
people fond of gefilte fish (spiced minced fish) are also prone to
infection. Plerocercoids are killed in fish subjected to freezing at -
l0°C for 24-48 hours or cooking at over 56 °C for 5 minutes.
Diphyllobothrium Treatment
Although dogs, cats, and other mammals may be
infected the importance of wild and domestic
animals as reservoirs is unknown and man is thought
to be the main host for D. latum. There are
differing opinions on the capacity of eggs produced
in animals to hatch and infect copepods. Quinicrine
(®Atabrine) and niclosamide (®Yomesan) are
effective treatments in man. Dogs may be
successfully treated with arecoline preparations
(®Nemural) and cats may be treated with kamala.
Praziquantel at 3 times label dose is the treatment
of choice for dogs, cats and man.
Spirometra (sparganosis)
Spirometra spp. are pseudophyllidian tapeworms that
occur in the adult stage in the intestine of cats, dogs
and certain wild carnivores. The life cycle is similar
to Diphyllobothrium. Unlike D. latum, it is the
opportunistic plerocercoid stage which is of
importance as a public health problem, not the adult
stage. The plerocercoid larvae of worms of the genus
Spirometra were designated as Sparganum spp.
before the adult forms and life cycle became known.
"Sparganosis" is still used to refer to infection by
plerocercoids of Spirometra.
Diphyllobothrium latum life cycle
Diphyllobothrium latum is a pseudophyllidian tapeworm which is
commonly known as the "broad fish tapeworm " of man and other
fish-eating mammals such as dogs, cats, bears, etc. The life cycle
involves two intermediate hosts, small fresh water crustaceans
known as "copepods" and various fresh water fish.
Operculate eggs hatch outside the final hosts' body in water in
about 2 weeks, liberating the first larval stage, a free-swimming,
ciliated coracidium. After ingestion by certain copepods (i.e.
Cyclops) the coracidium develops in another two weeks to the
procercoid stage. When the copepod is eaten by fish, the second
intermediate host, the procercoid migrates to the muscles and
other organs and develops to the plerocercoid stage. The
plerocercoid is about 5mm long and is visible in exposed muscle
of infected fresh-water fish, including pike, perch, trout, salmon
and others. If small fish infected with plerocercoids are
ingested by larger fish, the larval tapeworms, having paratenic
tendencies, migrate to the muscles and viscera of the new host
and re-encyst, a process that can be repeated in a long series of
fish hosts. Man and other hosts are infected by ingestion of the
plerocercoid in uncooked, pickled or "cured" fish.
Diphyllobothrium egg
The egg is oval, yellowish and operculated, and is
somewhat similar to Fasciola hepatica in appearance but is
much smaller (70u by 45u). A posterior "knob" is
sometimes visible opposite the operculated end (as seen
here).
D. latum coracidium emerging from egg
The coracidium is an apparent biologic analogy to the
trematode miracidium, but consists of a hexacanth
onchosphere with a ciliated coat.
Cyclops- lst intermediate host
Like miracidia, the coracidium requires a water
environment and must be ingested by a copepod
intermediate host within 24 hours or it dies.
Adult Diphyllobothrium latum
D. latum attaches to the mucosa of the small intestine and is the
longest known cestode, reaching a length of 15 meters and consisting
of more than 4000 segments. It is a very fast-growing cestode and can
reach a length of a meter in three weeks. The first eggs appearing in
the feces in about four weeks after ingestion of pleurocercoids and
the worm may survive ten years or more. As a rule eggs can be found in
the feces of the definitive host, in contrast to infection with
cyclophyllidian tapeworms in
which eggs are released in
gravid segments passed from
the body . D. latum segments
are shed only when they are
old and no longer capable of
producing eggs. The majority
of segments are in the same
stage of development and are
more uniform in size than
cyclophyllidian tapeworms.
D. latum is easily recognized
by its large size, central
genital pore in square
segments
and long unarmed
scolex with two
elongate, groove-like
suckers called bothria.
Genital pores are lateral in cyclphyllidian tapeworms.
Diphyllobothrium latum is unusual among cestodes in being
pathogenic in the adult stage. The capacity of D.latum for depriving
its human host of vitamin B12 to produce pernicious anemia
(macrocytic, hyperchromic) is well documented. It does this by two
mechanisms: (1) it interferes with absorption of B12 by blocking the
combination of B12 and an intrinsic factor from the gastric mucosa
and (2) it absorbs and binds large amounts of B12 in its own tissues.
D. latum contains 15 times as much B12 as other cestodes and a
powdered preparation of its segments may actually be used to treat
victims of an active infection.
Infection rates are highest in cultural groups which traditionally eat
roe or fresh water fish raw, lightly salted, or pickled without
cooking. Incidence is highest in the US in people of Scandinavian
extraction in the Great Lakes region. Eskimos in Alaska and Jewish
people fond of gefilte fish (spiced minced fish) are also prone to
infection. Plerocercoids are killed in fish subjected to freezing at -
l0°C for 24-48 hours or cooking at over 56 °C for 5 minutes.
Diphyllobothrium Treatment
Although dogs, cats, and other mammals may be
infected the importance of wild and domestic
animals as reservoirs is unknown and man is thought
to be the main host for D. latum. There are
differing opinions on the capacity of eggs produced
in animals to hatch and infect copepods. Quinicrine
(®Atabrine) and niclosamide (®Yomesan) are
effective treatments in man. Dogs may be
successfully treated with arecoline preparations
(®Nemural) and cats may be treated with kamala.
Praziquantel at 3 times label dose is the treatment
of choice for dogs, cats and man.
Spirometra (sparganosis)
Spirometra spp. are pseudophyllidian tapeworms that
occur in the adult stage in the intestine of cats, dogs
and certain wild carnivores. The life cycle is similar
to Diphyllobothrium. Unlike D. latum, it is the
opportunistic plerocercoid stage which is of
importance as a public health problem, not the adult
stage. The plerocercoid larvae of worms of the genus
Spirometra were designated as Sparganum spp.
before the adult forms and life cycle became known.
"Sparganosis" is still used to refer to infection by
plerocercoids of Spirometra.
Spirometra Life Cycle
As with D. latus, eggs laid in water hatch to coracidia, are ingested by fresh
water copepods, in which development to the procercoid stage occurs. When
infected copepods are swallowed by mice, water snakes or amphibians
(depending on the species of Spirometra) the plerocercoid stage develops.
Cats or dogs may become infected by ingesting infective plerocercoids and
begin passing operculated eggs in about 2 weeks. Spirometra mansonoides has
a wide distribution in wild and feral cats in the Eastern USA and uses wild
species of mice for the plerocercoid (spargana) stage. Man on rare occasion
enters this life cycle as an accidental host, as can a wide variety of other
warm or cold blooded animals. While procercoids and adult Spirometra are
restrictive in the copepods or definitive host(s) they can develop in, the
plerocercoids have the capacity to develop in almost any animals and almost
indefinite serial plerocercoid transmission may occur (frog, mouse --- snake --
pig --- man, etc.). Man and other animals therefore act as paratenic hosts for
plerocercoids (spargana) in which the parasite is unable to develop beyond
this stage to sexual maturity . Plerocercoids of Spirometra mansonoides
enter the human gut migrate to body tissues and appear as spargana. Animals
incriminated in transmission to man include poorly cooked tissues of domestic
and feral pigs, chickens and other fowl, frogs and snakes. An alternate mode
of infection for some Spirometra spp. is by ingestion of infected copepods in
water in which case development to migrating plerocercoids occurs. In Asia,
infections occur by migration of spargana from raw flesh of frogs which are
applied to wounds as poultices by local inhabitants.
Spirometra mansonoides plerocercoid
In this species which occurs
in the Eastern USA,
"spargana" are found in SQ
tissues and musculature of
mice.
The scolex occurs in the
blunt, thicker anterior
end.
Dracunculus medinensis
Dracunculus medinensis (guinea worm, fiery serpents).
This nematode has been known since ancient times and is
referred to in the Bible as the "fiery serpents"
afflicting the Israelites by the Red Sea. They occur as
very long (2-4 feet) worms coiled in the subcutaneous
tissues, especially on the extremities. Toxic materials
are excreted which cause a blister which ulcerates.
Under the stimulus of contact with water, female worms
eject milky fluid, containing myriads of larvae from the
uterus into the water. If ingested by copepods, larva
develop to infective larvae which may then infect a new
host by ingestion in drinking water. A similar species,
Dracunculus insignia occurs in raccoons and occasionally
dogs in the USA.
Anasakis
Another nematode which occurs in marine fish is
Anasakis marina. This parasite causes severe
eosinophilic granulomas or ulceration in the
gastrointestinal tract of man following accidental
ingestion of encapsulated larvae (2 cm long) in the
viscera and flesh of raw, salted or pickled herring,
cod, mackeral and other fish. Marine mammals,
(dolphins, porposes, seals) are thought to serve as
the normal definitive host for the adult stage of
Anasakis. Larvae are killed by deep freezing (-2OC
for 24 hours). Infections occur mainly in Japan and
the Netherlands who customarily eat raw marine fish.
Taenia Cysticercosis
Two cyclophyllidian tapeworms parasitize the small
intestine of man in the adult stage, Taenia saginata
and Taenia solium. The larval stage (cysticerci) of
these parasites occur in meat from cattle ("beef
measles") and swine ("pork measles") respectively.
Pseudophylidian operculated egg
Individual eggs develop in water to produce a ciliated coracidia. Eggs
of Diphylobothrium and Spirometra are very similar in size and
appearance and are easily overlooked in routine fecals because they
approximate the size of a hookworm egg (see Sloss p. 68). Eggs of
both species float with NaNO3 solution. Diphyllobothrium latum is not
thought to occur in dogs and cats in the Southeast, but Spirometra
mansonoides is widespread in wild animals in the eastern U. S .,
including the Gulf Coast States.
The life cycle of Spirometra mansonoides is similar to
that of D. latum, except for the second intermediate host.
Plerocercoids develop primarily in mice and snakes rather
than fish. Infections occur in cats (to a lesser extent in
dogs) by ingesting infected tissues. The bobcat is thought
to be the primary definitive host. Adult Spirometra are
relatively small in comparison to D. latum and they seldom
exceed 1 meter in length.
Mesocestoides spp.
Mesocestoides is a seldom reported tapeworm of dogs and other
carnivores (Williams et al (1975), JAVMA 166, 997). The
classification, life cycle and transmission of Mesocestoides is
controversial but these tapeworms seem to occupy a position
interposed between the cyclophyllidean and pseudophyllidean
tapeworms. Two intermediate hosts are thought to be required, an
arthropod (possibly orbatid mites) and a vertebrate (birds, small
rodents, reptiles). Unique larval forms occupy the serous cavities
and when ingested by the final host, develop to maturity in about 3
weeks.
The clinical features of the infections and gross appearance of
shed proglottids may lead to diagnositic confusion with Dipylidium.
Eggs are seldom shed; squash preparations of segments reveal
individual thin shelled eggs containing a hexacanth embryo (see
Sloss). The genital opening is centrally (not laterally) placed on
segments and the scolex of adults has four suckers but no hooks.
Clinical Signs and Diagnosis
Despite their dramatic impact on clients and their frequently large size,
adult tapeworms in general cause very little harm in dogs and cats and
their importance is often exaggerated. Competition with the host for
nutrients by tapeworms (by direct absorption through the tegument)
occurs, but is serious only with Diphyllobothrium latum (B12 deficiency
results). Usually, the signs due to the common tapeworms consists only of
vague gastrointestinal upsets, perhaps with diarrhea and emaciation due to
mild enteritis with heavy infections. Gravid segments of cyclophyllidean
tapeworms may migrate through the anal sphincter onto the perineum
causing pruritis. Affected animals assume a sitting position and scoot on
the ground to relieve irritation. (A far more common cause of scooting,
however, is impacted anal glands). Rarely, segments may cause impaction by
lodging in the anal glands.
It is important to identitfy tapeworms to species or atleast genus level to
be able to identify the probable source of infection and to make sound
recommendations on control measures. This can be done by identifying eggs
in fecal flotation of squash preparations, by finding proglottids or “rice
granules” on the perineum, or by identification of whole worms passed
after treatment. The latter is best done by placing segments in water in
the refrigerator overnigth to “relax” proglottids (or “unwrap” rice
granules) to allow them to assume typical shape.
Treatment and Control of Common Cestodes Qf
Dogs and Cat
For many years the only treatment available for cestodes
were old-time drug preparations of vegetable origin (Kamala,
Kousso, felix mas, arecoline hydrobromide), organic heavy
metal preparations, (Nemura1; Anthelin) or combinations of
these drugs. These drugs act by purgation
(parasympathomimetic), have little or no efficiency against
other helminths, have low safety margins, and often result in
only shearing the strobila off, leaving the scolex to
regenerate. Two commercial products, Yomeson (no longer
available) and Scolaban act on the scolex with a high safety
margin in dogs and cats. Praziquantil (Droncit) and
Epsiprantel (Cestex) are the most effective and widely used
cesticide in current use. Tapeworms are killed and digested
after treatment and are therefore not often found in the
stool (unlike the more dramatic passage of tapeworms with
vermifuges).
The following may be used in dogs for Taenia spp. and or
Dipylidium. A repeat treatment should be given in 2-4 weeks.
1. Di-phenthane- 70- (in ® Vermiplex) "Aid in Removal Only"
2. Di-phenthane - 70 plus arecoline hydrobromide
3. ®Nemura1 (brand of Drocarbil-Winthrop Labs;
an organic arsenical combined with arecholine = “vermifuges”
4. ® Anthelin (an organic antimonial with arecholine)
5. ® Yomesan (Niclosamide) - Removed from market
6. ® Scolaban (Bunamidine HCL) – Removed from market
7. Fenbendazole (®Pancur), febantel (® Rintal)
Affects taeniid tapeworms only.
8. ® Droncit (praziquantel) - Cyclophyllidian & Pseudophyllidian;
current drug of choice for human schistosomiasis - (®Drontal is
pyrantel + praziquantel ± febantel)
9. ®Cestex (Epsiprantel) - Enteric tapeworms only
Checklist: Tapeworms of Domesticated Animals
Adult Definitive Larval Intermediate Larval
Parasite Host Stage Host Predilection
Site
Taenia hydatigena Dog Cysticercus tenuicolli Sheep, Cattle, Pig Peritoneum
Taenia pisiformis Dog Cysticercus pisiformis Rabbit Peritoneum
Taenia ovis Dog Cysticercus ovis Sheep Muscle
Multiceps multiceps Dog Coenurus cerebralis Sheep C.N.S.
Multiceps seralis Dog Coenurus seralis Rabbit Connective
tissue
Taenia taeniaformis Cat Cysticercus fasciolaris Mouse, Rat Liver
Echinococcus granulosus Dog, Cat, Hydatid cyst Cattle, Sheep, Pig Liver, Lungs
Canids
(Continued on Next Slide)
Adult Definitive Larval Intermediate Larval
Parasite Host Stage Host Predilection
Site
Dipylidium caninum Dog, Cat, Fox Cysticercoid Flea ( dog or cat) Body Cavity
Mesocestoides spp. Dog, Cta, Canids Cysterceroid 1 st: Mite Peritoneum
and 2nd: Mammals , Pleura
Birds, Reptiles
Spirometra spp. Dog, Cat, Canids Procercoid 1 st: Cyclops Body Cavity
Plerocercoid 2 nd: Mammals and SubQ
Amphibians, Reptiles
Diphyllobothrium latum Man, Dog, Cat, Procercoid 1 st: Cyclops Body Cavity
Pig Plerocercoid 2 nd: Fresh water fish Muscle
Moniezia expansa Sheep, Cattle, Goats Cysticercoid Orbatid mites Body cavity
Moniezia expansa Sheep, Cattle Cysticercoid Orbatid mite Body cavity
Thysanosoma actinioides Sheep, Goats, Cysticercoid Orbatid mite Body cavity
Cattle
( CONTINUED ON NEXT SLIDE)
Adult Definitive Larval Intermediate Larval
Parasite Host Stage Host Predilection
Site
Anoplocephala perfoliata Horses Cysticercoid Orbatid Mite Body Cavity
Anoplocephala magna Horses Cysticercoid Orbatid Mite Body Cavity
Paranaplocephala mamillana Horses Cysticercoid Orbatid Mite Body Cavity
Taenia saginata Man Cysticercus bovis Cattle Muscle
Taenia solium Man Cysticercus cellulosae Swine Muscle
Hymenolepis spp. Rat, Man, Mouse Cysticercoid Grain Beetles Body Cavity