Parasites

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					Protozoans/Parasites
         What We Will Cover:
            Parasitemias
•   Flagellated protozoans (P. Mastigophora)
•   Flagellated algae (C. Dinoflagellida)
•   Ciliates (protozoans)
•   Myxozoans (protozoans)
•   Digenetic Trematodes (flukes)
•   Cestodes (tapeworms)
     (1) Flagellated Protozoans
• Flagellates are protozoans: simple, single-celled
  animals (over 50,000 recognized species)
• very small (15-30 M), body elongate, leaf-like
  appearance, up to 975,000/mL of blood
• flagellum arises posteriorly and can be connected
  to other parts of body, pulls animal through the
  blood
• most famous are Trypanasoma, Trypanoplasma,
  Ichthyobodo necatur
         Ichthyobodo necatur
• A Mastigophoran, but a member of Class
  Diplomonadea
• also small, but flat and ovoid when swimming
• has 2-4 flagella arising from a basal body
  (kinetosome) at anterior end
• obligate parasite, poor swimmer, attaches to gills,
  but not good at attaching
• uses a sucking organelle to penetrate host
• tissue penetrated becomes necrotic
         Icthyobodo necatur
• Largely affects young, undernourished carp
  and trout
• can also parasitize frogs/tadpoles
• wild fish/frogs serve as reservoirs, found
  everywhere
• seasonality affect resulting from salmonid
  hatchery stocking seasons (April - May)
• affects smolts by attaching to gills and not
  allowing them to adapt to seawater
        Ichthyobodo necatur

• Pathogenicity: dull spots on body (blue
  slime), pale gills, hemorrhaging, fin
  necrosis, loss of appetite, flashing,
  moribund fish
• Control: salmonids need prophylaxis with
  formalin (1:4000 for 1 hr); carp need 1%
  salt bath 30 minutes repeated 3-4 times
Ichthyobodo necatur
Ichthyobodo necatur
       (2) Flagellated algae:
        Oodinium/Amylodinium

• Members of Subkingdom Protozoa, Phylum
  Mastigophora (flagellates), Class
  Dinoflagellida (dinoflagellates)
• Two major genera: Oodinium (freshwater)
  and Amylodinium (saltwater)
• Both attach to skin and gills causing
  condition known as velvet or rust disease
  (from chlorophyll in parasite)
     Morphology of Oodinium,
          Amylodinium
• Parasitic stage
  (trophont) is spherical
  or pyriform
• cytoplasm is foamy in
  appearance due to
  presence of small
  granules or droplets
• attachment via root-
  like rhizoids
           Life Cycle of
       Oodinium/Amylodinium
• Parasitic trophont found on fish for about one
  week feeding on cytoplasm
• eventually retracts rhizoids, drops off and encysts
• encysted form known as “tomont”, hard to kill
  with chemicals
• tomont undergoes mitotic division (8), ultimately
  producing up to 256 dinospores
• one dinospore can equal 1 billion new parasites
• dinospores break out of cyst and seek new hosts
 Life Cycle of Oodinium,
       Amylodinium




tomont        trophont   dinospores
     Host/parasite Relationship
• Broad specificity: sea bream, sea bass,
  mullet, tilapia, striped bass
• wide geographic distribution (here in Gulf
  of Mexico)
• cause little problem in nature, usually result
  of crowding
• outbreaks can be very explosive, Gulf Coast
  Research Lab lost almost all striped bass to
  this in 1976
           Pathology/Control
• Damage due to penetration of rhizoids
• Affects epithelium of skin, gills, nasal cavities,
  eyes and mouth
• Parasites produce lytic excretion causing
  inflammation, sometimes necrosis, secondary
  infections with bacteria/fungi
• Control: difficult due to rapid reproduction, no
  apparent acquired immunity, can encyst
• Treatment: copper (fair), metronidazole (14
  mg/L)
Pathology: lysis, necrosis of gill
           epithelia
    (3)Ciliates: Ichthyophthirius
           multifilis (ICH)
• Another single-celled protozoan type
• adult is round in shape, up to 1 mm in diameter, known
  as “trophont” (rem? Same as Amylodinium)
• short cilia in rows over entire cell, obvious as free-living
  stages “tumble” through the water
• Life Cycle: the trophont attaches to gills or skin, after
  7-10 days, the trophont drops off and is called a
  “tomont” (same, also), tomont attaches to substrate and
  encysts, cyst ruptures releasing swarmers known as
  “theronts”
• theronts are the parasites (have perferatorium), also
  use hyaluronidase, only for less than 20 hrs, displace
  normal tissue as they grow
  Ichthyophthirius multifilis (ICH)
• Signs: white pustules in advanced cases,
  sometimes called white spot disease; if found on
  gills, not found on body
• Behavioral changes: fish scratch against bottom
  (flash), hide in corners, twitching fins
• death in 20-26 days, thought to be due to
  osmoregulatory failure in most cases
• Host/parasite range: broad, mainly in
  catfish/salmonids
 Ichthyophthirius multifilis (ICH)
• Control: prevention (once in, difficult to
  treat)
• chemotherapy requires treating water, not
  the fish (cysts, stages in fish unaffected)
• formalin: around 250 ppm, goes up as temp
  goes up
• malachite green: 1.25 ppm daily for 30 min
  (Nox-Ich, Ich-out)
• remove fish, raise temp to 90oF
Ichthyophthirius multifilis (ICH)




          Cell embedded in tissue
Ichthyophthirius multifilis (ICH)




                    Theronts (swarmers)
Ichthyophthirius multifilis (ICH)
Ichthyophthirius multifilis (ICH)
         Cryptocaryon irritans
• Similar to ICH
• primarily marine
• trophozoite similar to
  ICH
• life cycle similar to
  ICH
• primarily problem for
  mariculture facilities
  and marine aquaria
                Epistylus sp.
• Colonial, stalked
  ciliate
• possess ciliary spiral
  around cytostome
• usually on skin
• causes flashing, which
  can lead to harm
• really just a bother,
  little apparent harm
                 Trichodina sp.
• Body shaped like hockey
  puck
• also spiral cilia around
  cytostome
• makes them fly through
  the water like a flying
  saucer
• lives on gills, skin mainly
• have rings of chitinous
  teeth
Stop here: next time, myxozoans and P.
Platyhelminthes!
    (4) Myxozoans: Myxobolus
            cerebralis

• Rather odd, exclusively endoparasites
• could be Cnidarians (Phylum Cnidaria)
• multicellular during adult life, with various
  cell types
• now don’t know what to call them
• anyhow, we will discuss whatever they are
  in the context of what they cause: whirling
  disease (Salmonid Whirling Disease)
     Salmonid Whirling Disease
• Important characteristic: can produce spore that is
  highly resistant (15 yrs dessication), associated
  with dispersal
• Life Cycle: infective stage gets into fish upon
  contact with skin, produces amoebula known as
  “trophozoite”, site attacked is species specific,
  most visible stage is the spore, spore released to
  environment, consumed by oligochaete, grow and
  released to environment
• fish eats oligochaete or encounters free spores
     Salmonid Whirling Disease
• Usually found in salmonids, but not a contagious
  parasite
• Pathology: development in cartilage, usually
  young fish, can have carriers showing no signs,
  fish exhibits whirling (tail chasing) when feeding
  or alarmed, whirling caused by destruction of
  inner ear by spores
• can cause “blacktail” by controlling production of
  chromatophores in spinal column, also pugnose,
  skeletal deformities
    Salmonid Whirling Disease

• Diagnosis: remove gill arch, grind and
  allow to settle, check supernatant for spores
• other methods: cook head/plankton centri-
  fuge, pepsin-trypsin digestion/centrifuge
• Fluorescent Antibody Test (FAT) w/rabbit
• Transmission: direct during first year,
  indirect via annelid, contamination (cyst)
• Hosts: trout, salmon, char, grayling
    Salmonid Whirling Disease

• How did it get here? Came from Europe via
  Danish frozen trout in the 50’s
• Control: non-treatable, avoidance critical,
  UV of incoming/recirc water, filtration to
  less than 10 µM
• Accomodation: incubate eggs and rear fry
  separately in UV water, check new ponds
  with sentinels
Salmonid Whirling Disease




     Various forms of spores
Salmonid Whirling Disease




                mature spores
  sporoblast
Salmonid Whirling Disease
      Phylum Platyhelminthes

• Class Turbellaria (turbellarians)
• Class Monogenea (flukes)
• Class Cestoidea (tapeworms)
  – S.C. Cestodaria
  – S.C. Eucestoda (true)
• Class Trematoda (flukes)
      (5) Cestodes: tapeworms
• Tapeworms are members of the Phylum
  Platyhelminthes which includes the classes
  Turbellaria, Monogenea, Trematoda and
  Cestoidea (tapeworms)
• the tapeworms are unique in that they have
  no digestive tract and, thus, are parasitic of
  many invertebrates
• we are concerned with the Subclass
  Eucestoda, the true tapeworms
                 Cestodes
• Occur in all classes of vertebrates and some
  invert’s, common in wild fish, mainly
  unsightly
• all have three different body regions:
  scolex (attachment), neck (buds off
  proglotids), strobila (remainder)
• proglottids formed by the asexual budding
  of neck
• all proglottids develop both male and
  female sexual organs
  Cestode Anatomy




proglottids         scolex
                 Cestodes

• Gravid proglottids are usually full of eggs,
  gonads degenerated
• Egg release: apolysis (release of whole
  proglottids) or anapolysis (eggs extruded
  through a common pore)
• Morphology: no gut; have nervous,
  osmoregulatory, reproductive systems for
  both males and females (male develops
  first)
Tapeworm Life Cycle
      Diphyllobothrium latum
• Broad fish tapeworm
  of humans
• has three hosts:
  copepod, fish, humans
• fish hosts: pike,
  perch, turbot, lake
  trout, eel
• distribution depends
  on what we eat
      Life Cycle of Diphyllobothrium latum (a
            zoonosis, transmitted to man)
                                               Canids, Felids, bear, seals, etc.
                                   Adults
                                   in Man

                                                Chunks of proglottids
                                                shed in feces
        Eats infected flesh,
        liver or roe
                               ZOONOSIS
                                                Incubate 5d-weeks. Hatch
                                                and release coracidium
              Fish

                                               Copepod
Pike, perch, walley,
turbot, lake trout, eel        Eaten by fish                  Diaptomus,
                                                              Cyclops
       Diphyllobothrium latum

• Effects on humans: abdominal pain,
  blockage of gut, vit B12 deficiency
• Effects on fish: visceral adhesion, sterility,
  decreased market value
• Control: cook fish, proper freezing
    (6) Class Trematoda: flukes
• Also members of Phylum Platyhelminthes
• Class Trematoda: all parasitic, mainly in digestive
  system, found in all classes of vertebrates
• Subclass Digenea: at least two hosts in life cycle,
  first host typically a mollusc
• Subclass Aspidogastrea: only one host, usually a
  mollusc, mature in fish/turtles, intermediate host
  can be lobster
• Subclass Didymozoidea: tissue dwelling parasites
  of fish, no complete cycle known
            Class Trematoda




Subclass Digenea    Subclass Aspidogastrea
       Digenetic Trematodes:
           Morphology
• Attachment Organs: most have oral sucker and
  ventral sucker (acetabulum)
• Digestive System: mouth, prepharynx, pharynx,
  esophagus, intestinal cecae; feeding is suctorial
• Reproductive System: genital pore for both sexes;
  male has testes, vas def; female has ovary,
  oviduct, Mehlis gland ???, ootype (egg shell
  formation), uterus, vitellaria, vitelline ducts,
  vitelline reservoir; copulation generally by cross-
  fertilization
Trematode Morphology




     Notice arrangement of suckers
      Life Cycle of Trematodes
• Adult parasite: sexually reproducing stage of the
  parasite
• Definitive host: host of adult parasite
• Intermediate hosts: all hosts in life cycle other than the
  definitive host (usually numbered, starting with first
  after definitive host)
• adults live mainly in digestive tract, but also in blood,
  gall bladder, muscle, other organs
• eggs leave adult via feces, some ready to hatch after
  entering water, most need period of development
• in most cases eggs must be laid in water
     Life Cycle of Trematodes
• Larval stage hatching from egg is known as
  miracidium (ciliated, free-swimming), only goal is
  to find/penetrate intermediate host
• first host is usually a snail; miracidia find
  intermediate host via photoreception,
  chemoreception, tangoreception, statoreception;
  snail mucus is attractive
• Asexual Reproduction: occurs in first
  intermediate host as either sporocysts (thin-walled
  germinal sac) or rediae (same, but with pharynx
  and gut); browse through tissues of snail
      Life Cycle of Trematodes
• Goal: produce large numbers of cercaria, making up
  for losses in complex life cycle
• This is the difference between monogenetic and
  digenetic trematodes: monogenetic = one offspring;
  digenetic = produce cercaria = many offspring
• Cercariae: the second free-living larval stage, their fate
  depends on species
   – penetrates or is ingested by definitive host and develops into
     adult (Sanouinicola)
   – penetrates or is eaten by second intermediate host and encysts
     as metacercariae
   – encysts on substrate and waits to be eaten by definitive host
    Life Cycle of Trematodes

• Metacercariae: quiescent or resting stage,
  arrested development until definitive host
  eats secondary host, morphology varies
  with species
• after consumption, metacercariae excyst and
  develop into adults in relatively short period
  of time
        Life Cycle of Trematodes


egg




                                 sporocysts
               miracidium




                               metacercaria


      rediae        cercaria
                 Crepidostomum
• Adults in intestines of
  salmonids
• can be very frequent in certain
  areas; however, death unusual
• eggs passed with feces of fish
• miracidia hatch and penetrate
  fingernail clams
• cercariae released and
  penetrate mayfly nymphs or
  amphipods
• salmonids infected when they
  eat the above
                Sanguinicola
• Lacking suckers, ceca are X or H-shaped,
  numerous testes
• adults live in cyprinids, salmonids, etc.
• found in bulbous arteriosus, ventral aorta, gill
  vessels, kidneys
• eggs released in bloodstream, hatch in gill
  capillaries, release miracidiae
• miracidiae penetrate Oxytrema snail, produce
  sporocysts
                 Sanguinicola
• cercariae released from
  sporocysts, directly
  penetrate fish host (no
  metacercaria)
• build-up of eggs in gills
  may obstruct flow of
  blood, signs of oxygen
  distress result
• many eggs washed to
  kidney, can become
  encapsulated, impairs flow
  of blood to kidney
                                cercaria
Sanguinicola




Build-up of eggs in gills

				
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