Biology 625
ANIMAL PARASITOLOGY
Fall semester lecture note outline

Updated: 05 February 2001

Trichuris (= Trichocephalus) spp. (Order: Trichurida; Family: Trichuridae) (whipworms)

1. Most speciose genus in the family
2. All with direct life-cycles
3. Most species cosmopolitan
4. Adults in large intestine, rectum, caecum of mammals; elongate (thread-like) at anterior end, becoming thick posteriorly; stichosome present
5. Eggs with bipolar plugs (50-55 x 22-23 um)
6. Typical life-cycle
   1. Adults with anterior ends threaded in gut wall
   2. Females produce 3,000-5,000 eggs per day following copulation
   3. Eggs out with feces; embryonate in about 3 weeks
   4. Ingestion of eggs
   5. Hatch; juveniles enter crypts of Lieberkuhn
   6. Penetrate cells; tunnel through mucosa back to luminal surface; grow and undergo molts in the process
   7. As worms become mature, large posterior end breaks out of mucosa and protrudes; completes maturation
7. Pathology includes diarrhea, anemia, prolapsed rectum, finger clubbing in humans, growth retardation. Secondary bacterial infections can occur due to contamination of lesions produced by worms
8. Various species (60-70 known species)
   1. Trichuris discolor (cattle)
   2. Trichuris felis (felids)
   3. Trichuris leporis (rabbits)
   4. Trichuris muris (rats)
   5. Trichuris ovis (cattle, sheep)
   6. Trichuris trichiura (primates)
   7. Trichuris suis (swine)
   8. Trichuris vulpis (canids; rarely humans)

Calodium (Capillaria) hepaticum (Order: Trichurida; Family: Capillariidae)

1. This genus, and other genera in the family, infect numerous organs of all classes of vertebrates. All are thin, delicate worms that thread themselves through a mucosa. They are similar in appearance to Trichuris spp., except that the transition between the anterior and posterior portions is much more gradual.
2. Over 300 named species within the Capillariidae, but taxonomy very difficult and many classification schemes.
3. Calodium hepaticum lives in the liver, predominately in rodents, but many mammalian species can be infected
4. Typical life-cycle of Calodium hepaticum:
   1. Adults in liver parenchyma
   2. Female produces eggs that are encapsulated as masses and retained in liver
   3. Adults die and degenerate; female releases more eggs in this process that are also encapsulated
   4. Eggs exit liver either when host dies and is scavenged upon, or when host eaten by predator. Eggs pass through feces and are liberated into the environment in 1-4 cell stage. Some eggs may be liberated after a host dies and decomposes, but most eggs fail to embryonate under such circumstances
   5. Embryonation while in soil; moisture and oxygen critical. Eggs require about 6 weeks at room temperature for embryonation, and can then remain viable for well over 1 year. Eggs may also survive sub-zero temperatures.
   6. Eggs then eaten and hatch in intestine; L1 larvae liberated
   7. Larvae penetrate gut wall
   8. Migrate to liver; all molts and maturation in liver
   9. Time of larval penetration of intestine until eggs begin to appear in liver ranges from 2.5-3.5 weeks
   10. Most important hosts for Calodium hepaticum (in order of importance):
       1. Rattus norvegicus (primary host, with prevalences ranging from 9-94%)
       2. Other Rattus spp. (prevalences 1-58%)
       3. Other rodent genera and species (i.e. Apodemus, Arvivola, Bandicota, Clethrionomys, Microtus, Mus, Ondatra, Peromyscus, Sigmodon, etc.) with prevalences of 0.3-80%, but mainly in the 5-25% range
       4. Other animals (i.e. carnivores, horses, insectivores, marsupials, primates, rabbits, ruminants, etc.) mainly with incidental reports
5. Other related species/genera in the Capillariidae.
   1. Anatrichosoma spp. (in tissues of old world primates, a few rodents, and in the opossum)
   2. Aonchotheca (Capillaria) caudinflata (small intestine of galliform and anseriform birds; earthworms intermediate hosts)
   3. Baruscapillaria obsignata (=Capillaria columbae) (small intestine of galliform and columbiform birds)
   4. Capillaria oesophagealis (intestine of crows; earthworms as intermediate hosts)
   5. Eucoleus (Capillaria) aerophilia (lives in lungs of carnivores; occasionally found in primates)
   6. Eucoleus (Capillaria) annulatus (in esophagus and crop of various galliform birds; earthworms used in live cycle as a definitive host)
   7. Eucoleus (Capillaria) contortus (in esophagus and crop of many bird species worldwide; eggs directly infective for birds)
   8. Paracapillaria (Calodium, Capillaria) philippinensis (small intestine of fish eating birds and primates; fish used as intermediate hosts)
   9. Pearsonema (Capillaria) plica (kidneys and urinary bladder of canids; earthworms capable of transmitting infections)

Trichinella spp. (Order: Trichurida; Family: Trichinellidae)

1. World's largest intracellular parasite
2. Adults intramulticellular, in intestinal epithelium
3. Larvae reside in skeletal muscle fibers
4. Same host serves both as definitive and intermediate host
5. Life-cycle of Trichinella spiralis
   1. Adults threaded through mucosal cells along gut
   2. After copulation, males soon die
   3. Over a 2-4 month period, females release 500-1,500 L1 larvae
   4. L1s travel through lymphatics and blood stream, enter skeletal muscles
   5. Enter muscle fiber; in most species the muscle cell becomes modified to support the larvae and is termed a nurse cell.
   6. L1 coiled and dormant in nurse cell
   7. Eventually eaten; then hatches
   8. Larvae molt 4x very rapidly, often within 1.5 days
   9. Mature into adults
      1. males 1.4-1.6 mm long; slender
      2. females 3-4 mm long; slender
6. Actor Yul Brenner (The Magnificent Seven, The King and I, Westworld, The Ten Commandments, etc.) acquired trichinosis in a famous New York restaurant in the 1980's by eating undercooked pork
7. Actor Morris Ankrum (General Hanley in Earth vs the Flying Saucers) died of trichinosis in 1964
8. It has been hypothesized that Wilfgang Amadeus Mozart (1756-1791) may have died of trichinosis after consuming infected pork cutlets (1986, Parasitol Today 2: 117-119). There is disagreement over this hypothesis
9. Eight named species (1992, J Parasitol 78: 654-659; 2000, J Parasitol 86: 134-139; 2000, Vet Parasitol 93: 293-307). There are also at least 3 genotypes of unknown taxonomic status: T-6, T-8, and T-9. T-8 and T-9 may represent Trichinella britovi that were introduced into Africa and Japan, respectively. However, T-6 appears to be a separate North American species most closely related to Trichinella nativa.
   1. Trichinella britovi
      1. synonym: genotype T-3
      2. temperate regions of Palaearctic in Europe and Asia
      3. introduced into portions of Africa
      4. low reproduction in rats and pigs; presence in domestic swine rare
      5. low resistance to freezing
      6. produces a nurse cell
      7. one unique alloenzyme; 4 coils of encysted larva
      8. primarily sylvatic; infects many animals, especially carnivores like the fox, felids, other canids, bear; sometimes horses, rodents, insectivores, and humans
      9. species description 1992, J Parasitol 78: 654-659
      10. genotypes T-8 and T-9 from southern Africa and Japan, respectively, are capable of interbreeding with this species (it is likely that T-8 and T-9 are Trichinella britovi that were introduced with domestic animals)
   2. Trichinella murrelli
      1. synonym: genotype T-5 (in part)
      2. North America (USA and BC, Canada)
      3. reproduction in mice, rats and pigs lower than for T. spiralis
      4. no freezing resistance
      5. produces a nurse cell
      6. 2 unique alloenzymes
      7. most similar to T. britovi and isolate T-9 from Japan
      8. in carnivores; humans
      9. species description 2000, J Parasitol 86: 134-139.
   3. Trichinella nativa
      1. synonym: genotype T-2
      2. arctic and subarctic (Holarctic)
      3. low reproduction in rats and pigs
      4. high resistance to freezing
      5. produces a nurse cell
      6. 2 unique alloenzymes; 5 coils of encysted larva
      7. sylvatic; bear, walrus, seals, felids, mustelids; rare in swine; numerous reports in sylvatic rodents; very pathogenic to humans
      8. some isolates have survived freezing at -18 C for 4 years (1999, J Parasitol 85: 144-147)
      9. species description 1972, Vest Akad Nauk SSR 28: 27-32
      10. genotype T-6 occurs in southern Canada and the northern and western U.S. It is very similar to T. nativa, is capable of interbreeding with T. nativa, and is also fairly resistant to freezing but there are slight differences between the two. T-6 overlaps Trichinella nativa, T. spiralis, and T. murrelli.
   4. Trichinella nelsoni
      1. synonym: genotype T-7
      2. Southern Africa
      3. low reproduction in rats and pigs
      4. no freezing resistance
      5. produces a nurse cell
      6. 4 unique alloenzymes
      7. sylvatic, in numerous wild african animals and occurs mainly in carnivores; however, a number of reports in sylvatic swine (warthog, brush pig) causing human infections; rare in rodents
      8. species description 1972, Vest Akad Nauk SSR 28: 27-32
   5. Trichinella papuae
      1. synonym: genotype T-10
      2. Papua New Guinea
      3. originally isolated from swine; also found in crocodiles
      4. low to moderate infectivity in rodents
      5. low resistance to freezing
      6. no nurse cell produced
      7. unable to infect birds
      8. experimentally transmitted to a variety of reptiles, i.e. caimans, varanids, pythons (poorly) and turtles (poorly), with the highest reproductive rate in varanids
      9. large ribosomal subunit has differences separating this from other species
      10. species description 1999, Int. J. Parasitol. 29: 1825-1839; other biological data 2004, Parasitology 128: 333-342; 2004, Emerg. Inf. Dis. 10: 1507-1509.
   6. Trichinella zimbabwensis
      1. Zimbabwe, Mozambique, Ethiopia
      2. originally isolated from Crocodylus niloticus in Zimbabwe
      3. infects both reptiles (crocodiles, caimans, varanids, pythons, turtles) and mammals. Very high reproductive rate in varanids.
      4. does not infect birds
      5. similar morphologically to Trichinella papuae, although 3 allozymes are diagnostic between the two
      6. cross transmission studies with Trichinella papuae show that viable offspring can be produced, although the F1 offspring go on to produce very few and less viable F2 larvae
      7. no nurse cell produced
      8. species description 2002, Int. J. Parasitol. 32: 1787-1799. Other aspects of biology 2004, Parasitology 128: 333-342.
   7. Trichinella pseudospiralis
      1. synonym: genotype T-4
      2. cosmopolitan
      3. very low reproduction in pigs; high reproduction in rats
      4. broad host range; infects birds (especially raptors) most commonly, but also infects marsupials, rodents, swine, carnivores, primates (including humans)
      5. several outbreaks in humans recorded (i.e. 1997, Wiad Parazytol 43: 287-288; 1988, Clin Inf Dis 26: 111-115; 2000, Emerg Inf Dis 6:543-7), commonly attributed to eating undercooked pork
      6. no freezing resistance
      7. no nurse cell produced
      8. 12 unique alloenzymes separating this from T. spiralis; primarily a parasite of raptors and rodents
      9. species description 1972, Veterinariya 10: 90-91
   8. Trichinella spiralis
      1. synonym: genotype T-1
      2. cosmopolitan
      3. high reproduction in rats and pigs
      4. no freezing resistance
      5. produces a nurse cell
      6. 6 unique alloenzymes
      7. infects numerous wild and domestic animals
      8. species description 1835, Trans Zool Soc London 1: 315-324
10. Pathology of Trichinella spiralis
    1. 12 hr to 2 days after ingestion, females begin to penetrate gut. Also worm waste products. Inflammation, pain, diarrhea, fever, nausea, sweating, occasionally respiratory difficulty and red blotches on skin.
    2. Facial edema and fever 5-7 days post-infection due to worm waste products
    3. During larval migration, blood vessel damage resulting in edema, petechia, pneumonia, encephalitis, pleurisy, meningitis, nephritis, deafness, peritonitis, eye damage, brain damage. Occasionally death due to myocarditis due to local necrosis and inflammation of heart muscles
    4. About the 9-10th day post-infection, juveniles begin penetrating skeletal muscle fibers. Muscle pain, difficulty in swallowing, difficulty in breathing, weakening of pulse and blood pressure which can result in heart damage, swelling of esophagus, swelling of masseters. Can lead to respiratory failure because damage to diaphragm and intercostals.
11. Common method to sample includes tongues/tongue biopsis, and placing tissues in 1:1 solution of HCl/trypsin. Tissue digests away and thrashing larvae left.

Dioctophyme renale (Order: Dioctophymatida; family Dioctophymatidae) (giant kidney worm)

1. Generally a parasite of wild mustelids, especially mink; also reported in canids, bear, raccoon, otter, seals, domestic animals such as horses, cattle, and swine, and humans. Individual reports in a seal and a rat are not verified.
2. Both Dioctophyme and Dioctophyma are used in the literature. The International Commission on Zoological Nomenclature has ruled that the former is the correct generic usage (1987, Bull. Zool. Nomen. 44: 237-239).
3. cosmopolitan
4. Life-cycle
   1. Adults in kidney, usually right kidney
      1. males 20 cm long x 6-8 mm wide
      2. females up to 1 meter long x 1.2 cm wide
   2. Female produces eggs that pass out with urine; fertilized eggs in the 2 cell stage heavily mammilated except at poles; unfertilized eggs may also be passed
   3. Eggs embryonate in 2 weeks to 3 months
   4. Eaten by aquatic oligochaete; hatch
   5. Penetrate ventral blood vessels
   6. Develop to L3 larvae
   7. Paratenic hosts (fish or frogs) may ingest oligochaetes; (juveniles cross gut, encyst in muscle or viscera)
   8. Eaten by definitive host (either eats infected oligochaetes or paratenic host)
   9. juveniles penetrate gut wall
   10. migrate to liver; mature over period of about 50 days in liver parenchyma
   11. migrate to kidney directly
   12. Mature and may remain alive for 5 years
5. Prevalence may be as high as 50% in mink in some areas, such as in portions of Ontario. In some areas of the world, domestic dogs, marten, coyote, and golden jackals may also have high levels of infection
6. Experimental infection often results in violent vomition due to worms invading the stomach wall and heavy infections (i.e. a couple dozen larvae) can kill a mink. Generally, however, animals are infected only with low numbers of worms (1-3) at a time. Further clinical signs, including weight loss, irritability, anemia, weakness, and increased frequency of urination may or may not be present.
7. Pathology is due to pressure necrosis and feeding by adult worms; kidney becomes atropied, non-functional and thin-walled, and calcification of necrotic tissue sometimes occurs.
8. Worms occasionally penetrate renal capsule and wander in peritoneal cavity.
9. Rarely, the adults may attempt to migrate through the ureters causing severe pain and irritation

Eustrongylides spp. (Order: Dioctophymatida; Family: Dioctophymatidae)

1. About 11-12 species that live in tumors in wall of proventriculus of fish eating birds.
2. Typical life-cycles
   1. Nematodes liver in hyperplastic tumors in proventriculus wall; eggs out through tiny aperatures
   2. Embryonate in water
   3. Eaten by aquatic oligochaetes; hatch
   4. Migrate to ventral blood vessels; molt twice to L3 (2-4 months; larvae become bright red)
   5. If eaten by fish, migrate across gut and encapsulate in viscera and on intestinal serosa
   6. Molt to L4
   7. Eaten by fish eating birds
   8. Embed in gut wall; overgrowth of host tissue to form tumor
   9. Transform into adults
3. Similar genera, Hystrichis in proventriculus of some birds

Order: Mermithida

1. This order contains numerous nematodes that are free-living as adults, but whose larval stages are parasitic in invertebrates (especially arthropods)
2. Anterior and posterior ends of worms taper
3. Buccal cavity absent
4. Esophagus very long
5. Typical life-cycles
   1. Adults free-living; do not feed and no gut (utilize a food storage organ for survival, temed a trophosome)
   2. Copulate and females produce eggs
   3. Usually larvae hatch, either as L2 or L3 depending upon the species (few have larvae remaining in eggs that are ingested)
   4. Penetrates cuticle of arthropod with stylet (some species ingested)
   5. Cross gut and enter hemocoel
   6. Worm gradually grows and molts; 10 days to 3 month life-cycles
   7. In some species, the L3 emerges, and the L4 and adults are free-living in the environment. In other species, adults emerge.
   8. Generally, the nematode consumes the arthropod during development, and usually kill the arthropod during emergence. Most emergence when arthropod contacts water
   9. Typical genera include Mermis, Hydromermis, Capitomermis