Differential characteristics of Dirofilaria vs. Dipetalonema (Knotts).
Using the Knotts test Dirofilaria is differentiated from
Dipetalonema by the traits shown. Length, width and shape of the head
are the most valuable characteristics. Motility is checked on with a
direct smear. According to an LVMA report, Dipetalonema incidence is
low in Louisiana, on the order of 2% of microfilaria positive dogs. On
filter tests (eg .Difil), morphologic characters are similar but a different
fixation media is used than the Knotts test and measurements are not
the same. The Knotts test is used routinely by LSU Diagnostic Services.
The Knotts test ($.02) is about 1/10 to 1/20 the cost of filter tests to run.
Blood taken in late afternoon is preferable because of nocturnal
Note the slightly tapering head (a hemisphere on a cone) and the straight
Note the blunt head (a hemisphere on a cylinder) and the button hook
tail (present only 1/3 of the time).
D. Immitis and Dipetalonema microfilaria
Compare the anterior ends and the larger size of
Dipetalonema anterior end -close up.
Close up of buttonhook tail.
Dirofilaria in situ right heart
In about 25% of the cases, Dirofilaria is present but
microfilaria are not found (occult filariasis). Radiography and
clinical pathology findings are used to diagnose such infections.
Dirofilaria male worm.
Male worms are distinguished by their smaller
size and “cork screw” tail tail.
Babesiasis occurs sporadically in dogs in Florida
and other southern states and in tropical areas
in the world, but diagnosis is difficult because
organisms are seldom detectable except in acute
cases or after splenectomy. Serology is a more
accurate diagnostic method.
Note that B. cania is transmitted by the brown dog tick: (a
2-3 month L.C.). clinically affects puppies and young dogs
mainly. and causes classic haemolytic disease. Parasitemia
is notoriously low ( < 1 % RBC.s) in acute cases. Treatment
with Diaminamine aceturate ( Ganaseg. Squibb or -Berini1.
Hoechst-Roussel) has been effective at LSU .
Canine Visceral Leishmaniasis (Leishmania donovani.
This f1age1late parasite is diagnosed on occasion in dogs
returning from endemic areas in the Middle East or elsewhere.
The parasite is found intracellularly in macrophages in various
organs as seen in these impression smears. Note the nucleus and
kinetoplast. The disease is highly fatal in man but dogs develop a
more chronic disease and often have cutaneous manifestations.
Dogs act as a reservoir for Phebotomus infection in certain
endemic areas. Imported diseases such as Leishmania will likely
increase in incidence due to greater mobility of people and
animals. Several cases have been seen at LSU .
Cutaneous lesions in a poodle returned from Greece.
Biopsy smears may reveal organisms from skin lesions or other
organs. Serologic tests are available at CDC through state health
This disease is endemic in South America and Mexico where the dog
often serves as reservoir for infections in man. Intracellular
amastigotes are present in various tissues (especially cardiac. CNS)
Trypomastigotes (seen here) may be found in the blood during the
acute disease. but seldom in chronic infections. Giesma stain is best
for blood protozoa.
Amastigotes in cardiac musculature –T. cruzi histosection.
Note “nest” of organisms with distinct nucleus and
T. cruzi distribution in U.S.
A non-pathogenic strain of T. cruzi has been recognized in
wildlife in the U.S. for some time (in the shaded areas).
Clinical cases of acute canine T. cruzi have been reported in the
Southeast since 1972. Young animals (2 months -2 years) are
presented with acute heart failure (apparently due to cardiac
involvement) and die acutely without treatment. An
experimental Nitrofuran (Bayer) can be tried for treatment. but
90% of cases are fatal.
T. cruz.i characteristics
Recent cases have been reported from Texas. The brown dog
tick vector is ingested. Lameness (periosteal inflammation) is
the often presenting sign in chronic cases.
Recent cases in the Southeast of febrile hemolytic disease in
cats. RBC trophozoites, WBC schizonts. Unknown vector
(ticks?), probably Ixodes.
This “eyeworm” is endemic in mountainous areas of the
Western U.S. Residing under the eyelids and in conjunctival
sac, it causes surprisingly little damage. Eyeworms are often
hidden under lids and occasionally appear on the surface.
Surgical removal under anesthesia is indicated (20) .
(Giant kidney worm) occurs in dogs and is
diagnosed by finding eggs in urine sediment .
The parasite is often unilateral on the right
kidney and literally consumes the kidney
parenchyma, entirely filling the capsule.
Ova In situ
Capillaria plica egg
This non-pathogenic nematode of the urinary bladder is
sometimes found incidentally in urine sediment.
Capillaria plica: characteristics.
This parasite is similar to Dracunculus medenensis
the “fiery” serpent. of man in the Middle East. It is
found in raccoons in a sylvatic environment and
rarely may infest dogs.
This pentastome inhabits the nasal passages and sinuses of
dogs on rare occasion and is included here for convenience.
It attaches by anterior hooks to the mucosa and sucks
blood. Surgical removal is indicated but spontaneous cure
will occur after about 2 years.
L. serrata adult and young adults.
Note annulated, flat appearance.
Pneumonyssoides caninum. This large nasal mite is relatively
innocuous and occurs in the nasal passages of dogs and is
sometimes first noted when crawling out around the nostrils.
Ether or other noxious chemicals may stimulate movement.
Demodex. This is the causative agent of Demodectic or .red.
mange of dogs found in hair follicles. Deep scrapings with a scalpel
are needed for a mineral oil or KOH preparation. Mineral oil is
easier but KOH clears debris for easier mite identification
Demodectic mange lesions.
Dry scaley lesions with alopecia initially start on the face around the
lips and eyes and often clears up on its own without treatment at
this stage. If the disease progresses, a greater facial area is covered
and leg lesions may be present. Generalized mange becomes
pustular in certain individuals (immune defect?) and is often very
resistant to treatment.
Sarcoptes scabei var canis.
Causative agent of sarcoptic mange. Inhabit tunnels in the
stratum corneum and deep scrapings are imperative for diagnosis.
Often multiple scrapings from several areas must be before the
mite is found. Sarcoptes is more common in Louisiana than other
Sarcoptic mange lesions.
Sarcoptic mange begins on hairless areas such as the axilla or
inguinal area the callous of the elbow or the tips of the ears.
Untreated, it is quite pruritic (unlike Demodex) and may eventually
generalize (seen here). Dog often inflict self-trauma for relief of
This is the head mange mite of cats and resembles Sarcoptes a great
deal in morphology and life history .Note the smaller nymphal stages
near the adult. Eggs may be recovered from scrapings also, as with
Notoedres lesions -feline.
This mite has a predilection for the ears and head, leading to
crusty , grey alopecic lesions in the head area.
Chyletiella lesions in a cat.
This mite of dogs and cats causes flaky dry lesions
Scrapings reveal a characteristic mite with strong chewing
The ear mite of dogs and cats is very common. Cats get
an external otitis usually with black, dry crusty debris in
the ear .Dogs tend to have a blackish, more moist exudate.
An ear swab (wet with mineral oil) or an ear loop is used
to recover material to examine for mites.
Fleas are not highly host specific. C. felis, ,C. canis, Pulex
irritans and even Echidnophaga of poultry may be found on dogs
or cats. Keys may be used for identification
Flea dermatitis lesions.
Fleas can be diagnosed by finding adults and/or flea
debris (black fecal flakes) on the skin, particularly on the
tail, head and neck areas. Certain dogs become sensitized
(as do people) and develop a dermatitis secondary to flea
bites and subsequent scratching.
Lice are rare in dogs and cats and are essentially a disease of
neglect, in poorly nourished, debilataed animals
Linognathus setosus .
This sucking louse is one of three species of lice found in dogs
A chewing (biting) louse of dogs. A slide of Trichodectes
canis is not available. It is also a chewing louse
Lice and the nits that attach to hairs often occur in very large
numbers on infested dogs but seldom cause serious dermatitis
This is the only louse (chewing) of cats and is rare because of cats
self-grooming. Note the groove used to attach to hair shafts.
Heavy tick infection in a dog (Dermacentor variabilis). Note the
engorged ~ females (light grey) versus the engorged males
which retain their shape and color .
Five species of hard tick are common to dogs in the Southeastern
USA as follows. Ticks often found around the ears.
The brown dog tick requires only dogs for its life -f cycle. It often
establishes tenacious infestations in kennels, inside homes or in
areas frequented by dogs outside if warm weather is present. Note
the short mouthparts, the angle in the basis capitulum and the
plain brown color of both sexes.
Dermacentor variabilis( The American Dog Tick)
is widespread in the Eastern US as a “wood tick”. Adults
parasitize dogs primarily, small animal as larvae and nymphs.
Note the characteristic ornate scutum pattern of males and
females; and the short rectangular mouth parts. Vector of Rocky
Mountain spotted fever .
The black-legged shoulder tick parasitizes cattle in the adult
stage but may also attack dogs and cats. It is also a .wood tick.
acquired in field or brush. Note the very long mouthparts, the
inornate scutum. Black legs are generally clearly visible in
contrast to a yellowish or reddish body. Vector of Lyme disease
Ambylomma americanum (The Lone Star Tick )
is widespread in the Southeast in wooded, brushy areas and
often also attacks large animals or man. Note the long mouth
parts, the single ornate spot on the female scutum and the more
diffuse ornate male markings
Ambylomma maculatum( The “Gulf Coast Tick”)
occurs along the Gulf Coast and southeast atlantic
states. Note the more diffuse ornate markings on the
female scutum as compared to A. americanum and the
Otobius megnini ( The spinous ear tick )
occurs mainly in stabled cattle
and horses in the area South
West (West of Central Texas)
but may also attack dogs.
Unilateral infections are
common, are extremely
irritating, and may cause severe
head shaking and tortucollis