1. Parasitology

2. 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

3. 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 host’s immune response
Exhibit complex life cycles often with multiple hosts

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

5. 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

6. 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

7. Major Groups of Fish Parasites
Protozoa: single celled animals
Monogenetic Trematodes: Flukes (flatworms) with haptor (posterior attachment organ) and have a simple life cycle (no intermediate host)
Digenetic Trematodes: Flukes (flatworms) with oral/ventral suckers and exhibit complex life cycles (involve intermediate hosts)

8. 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 cylindrical or fattened with anterior end bearing elaborate hooked proboscis

9. 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 hyphae

10. External Protozoa Flagellates Ciliates Trichodinids Epistylis
Ichthyobodo (Costia)
Ciliates
Ichthyophthirius multifilis (“Ich”)
Trichodinids
Epistylis

11. 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

12. Internal Protozoa Myxobolus cerebralis (whirling disease)
Ceratomyxa shasta
Henneguya

13. Myxobolus cerebralis Infects cultured and wild salmonids
Specific tropism for cartilage
Infection can result in axial skeleton and neural damage

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

15. 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

16. Henneguya Myxosporea Ovoid, spherical, or lenticular spores
Usually cysts form around spores

17. 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

18. 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

19. Trematodes

20. Monogenetic Digenetic Gyrodactylus sp. 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

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

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

23. 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).

24. Nematodes
C. philippinensis egg
C. philippinensis adult

25. Capillaria philippinensis
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

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

27. Neoechinorhynchus rutili
Adult female
Adult male

28. Leeches (Hirudinea)
Leech with brood attached
Top view

29. 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

30. Hirudinea Problems Hemorrhaging Inflammation Edema Ulceration Fibrosis
Hyperplasia
Necrosis
Irritation
Weight loss
Some can be vectors of other parasites

31. Copepods
Lernaea sp.
Salmonicola sp.

32. 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

33. 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)

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

35. Glochidia attaching to gill tissue
Lampsilis reeveiana
Glochidia attaching to gill tissue

36. 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

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