Parasitology

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Parasitology
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What is a parasite?

• Definition
• An animal which lives in (endoparasite) or on
  (ectoparasite) another animal (the host).
• Is almost always a different species from the
  host
• Depends on the host for food an causes some
  degree of injury

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General characteristics

• Tremendous reproductive capabilities
• Have physical adaptations that enhance attachment
  to the host (i.e. suckers, hooks or clamps)
• Possess various mechanisms for avoiding the
  hosts immune response
• Exhibit complex life cycles often with multiple
  hosts

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Typical Indirect parasite life cycle
Primary Host Adult stage parasite infects host
Egg/Spore Stage Transmission and spread into the
environment
Infective larvae Able to infect primary host
Intermediate host Growth and developmental stage
(may not cause damage to the host)
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Negative affects on the host

• Direct damage to host
• inducing tissue and organ damage
• Indirect effects
• Stress causes an increase susceptibility to
  secondary infections
• Direct damage can act as a portal for secondary
  infection
• Parasite may serve as a carrier/vector for
  another viral/bacterial pathogen

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Signs of Parasitic infections

• Fish at surface gulping or piping
• Suggests parasites on gills
• Fish rolling/flashing
• suggests protozoan or worm infestation (internal
  or external)
• Lethargy or listlessness
• Suggests gill parasite

• Fish at bottom
• Suggests gill parasite, especially Ich
• Fin erosion/Lesions
• Indicative of external parasite
• Flared gills
• Indicative of gill parasite
• Excess mucus, fish shimmies/quivers, or is off
  feed
• General indication of disease

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Major Groups of Fish Parasites

• Protozoa single celled animals
• Monogenetic Trematodes Flukes (flatworms) with
  haptor (posterior attachement organ) an have
  simple life cycle (no intermediate host)
• Digenetic Trematodes Flukes (flatworms) with
  oral/ventral suckers and exhibit complex life
  cycles (involve intermediate hosts)

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Major Groups of Fish Parasites

• Cestodes (Tapeworms) worms with
  flattened/segmented bodies, head usually has
  suckers/hooks/suctional grooves
• Nematodes (Roundworms) Thin elongated worms with
  cylindrical bodies covered by a rigid cuticle
• Acanthocephala (Spiny-headed worms) bodies
  cylindical or fattened with anterior end bearing
  elaborate hooked proboscis

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Major Groups of Fish Parasites

• Copepods crustaceans (sea lice) that may appear
  louse, worm, or grub like
• Leeches flattened or cylindrical, body segmented
  with anterior/posterior suckers
• Glochidia larval freshwater clams
• Fungi either as spores or as fungal hyphie

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External Protozoa

• Flagellates
• Ichthyobodo (Costia)
• Ciliates
• Ichthyophthirius multifilis (Ich)
• Trichodinids
• Epistylis

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External Protozoa

• Common and usually occur in low numbers
• Dense populations can cause serious epizootics
  (usually caused by some form of stress)
• Symptoms include
• -Irritation (flashing) -Erosion of scales
• -Erythema (reddening) -Hemorrhaging
• -Excess mucus production -white spots on skin
• Control by chemical treatment

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Internal Protozoa

• Myxobolus cerebralis (whirling disease)
• Ceratomyxa shasta
• Henneguya

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Myxobolus cerebralis

• Infects cultured and wild salmonids
• Specific tropism for cartilage
• Infection can result in axial skeleton and neural
  damage

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Ceratomyxa shasta

• Myxosporea
• Found in marine and freshwater environments
• Only infects salmonids
• Susceptibility varies
• Clinical signs vary among infected salmonid
  species
• Identified by spore size, shape, and location

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Henneguya

• Myxosporea
• Ovoid, spherical, or lenticular spores
• Usually cysts form around spores

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General Myxosporidean lifecycles

• landmark discovery by Wolf Markiw in 1984

• a fish myxosporean alternates with an
  actinosporean from an oligochaete worm

• both spore types represent alternate lifecycle
  stages of the one organism

• morphologically distinct spores are genetically
  identical

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General Diagnostic Procedure

• Presumptive ID
• Wet preparation
• Histology
• Site of infection
• Spore morphology

• Confirmation of ID
• Molecular methods
• Any level of infection, all stages, definitive

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Trematodes
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• Monogenetic
• Gyrodactylus sp.

• Digenetic
• Bolbophorus damnificus
• is often referred to as the catfish trematode
• Misnomer because there are about 30 trematodes
  found in the channel catfish and because it is
  also found in the fathead minnow

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Digenetic Trematodes

1. Adult flukes reside in fish, birds, or mammals
2. Flukes lay eggs that pass through the definitive
   host, eggs hatch to a ciliated miracidia
3. The miracidia will develop to a cercariae if in
   contact with a snail or mussel
4. If the cercariae contacts invertabrate of fish
   hose it will encyst as a metacercaria

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Cestodes

1. GI tract of fish, bird or Mammal
2. Eggs are laid to water and are eaten or hatch
   into a coracidium (C) and are then eaten by an
   invertabrate host
3. Larval development to a proceroid or a
   pleroceroid occurs invertabrate
4. Final host becomes infected by ingesting
   invertebrate

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• A. colex of Bothriocephalus acheilognathii from
  carp, Transvaal, South Africa (by courtesy of
  J.G. Van As).
• B. B. acheilognathii, whole worm (living) from
  farmed carp, Israel.
• C. Embryonated eggs of b.
• D. Ligula sp. from Rastrineobola argenteus from
  L. Victoria. Infected fish are recognized by
  their inflated abdomen (top fish) and may
  accommodate even three worms (bottom group).

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Nematodes
C. philippinensis egg
C. philippinensis adult
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• Unembryonated eggs are passed in the stool (1)
  and become embryonated in the environment (2)
  after ingestion by freshwater fish, larvae hatch,
  penetrate the intestine, and migrate to the
  tissues (3).  Ingestion of raw or undercooked
  fish results in infection (4).  The adults reside
  in the human small intestine mucosa (5).  The
  females deposit unembryonated eggs (can become
  embryonated) (6).  Also infects fish eating birds
  (7).

Capillaria philippinensis
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Acanthocephala

• A) GI tract of Fish, Acanthor larva released
• B) Eaten by invertabrates and produces a
  cystacanth (C)
• If eaten by suitable host, the cystacanth will
  develop into an adult

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Neoechinorhynchus rutili
Adult female
Adult male
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Leeches (Hirudinea)
Leech with brood attached
Top view
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Leech Characteristics

• Primarily occur in freshwater
• Most are predators or scavengers which feed on
  fluids or soft tissues of live or dead
  invertebrates
• Generally have 34 body segments and an anterior
  and posterior sucker
• Parasitic leeches attach temporarily
• Cause little noticeable harm

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Hirudinea Problems

• Hemorrhaging
• Inflammation
• Edema
• Ulceration
• Fibrosis
• Hyperplasia

• Necrosis
• Irritation
• Weight loss
• Some can be vectors of other parasistes

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Copepods
Lernaea sp.
Salmonicola sp.
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Copepods are a subclass of Crustaceans

• Sexes are usually separate with sexual
  dimorphism present
• Heavy infections can cause severe damage to skin,
  muscle, and gill tissues
• Can also lead to secondary infections, anemia,
  emaciation, and mortality

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Copepoda

• Mature copepods release eggs (B) that hatch to
  larvae (C)
• D) After molting a copepod stage is formed and
  may attach to a host (E)

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Glochidia

• Larvae attach to gills or skin
• Live as parasites then drop off and live
  independently
• Some modify mantle tissue to help find host

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Glochidia
Lampsilis reeveiana
Glochidia attaching to gill tissue
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Fungi

• Saprolegnia water molds
• Worldwide in freshwater
• Appear as whitish cottony-like growths
• Considered secondary invaders
• Can attach to eggs and fish
• Can be controlled with chemicals

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Aphanomyces invadans
Hyphae
Germination
Sporangia
Cyst
Sporulation
1 Zoospore
2 Zoospore
1º cyst