Biology 625
ANIMAL PARASITOLOGY
Fall semester lecture note outline

Updated: 24 September 1999

1. This order often placed as a superfamily of the order Echinostomatiformes
2. Composed of amphistomes (acetabulum at or near posterior end)
3. Usually thick, fleshy worms
4. Ovary usually post-testicular

Megalodiscus temperatus (family: Diplodiscidae)

1. This species, and related species and genera, parasites in rectum and urinary bladder of anurans worldwide
2. One of the most commonly encountered species of amphistome
3. life-cycle
   1. adults in urinary bladder or rectum (ca 6 x 2.3 mm)
   2. eggs into water
   3. hatch almost immediately; miricidium penetrate snails of the genus Helisoma.
   4. one sporocyst and three redial generations
   5. cercariae liberated; positively phototactic
   6. contact frog
      1. encyst on skin as metacercaria
      2. during molting, frogs commonly eat skin and trematodes enter body
      3. metacercariae excyst in rectal area
      4. mature in 1-4 months
   7. eaten by tadpole
      1. encyst in stomach as metacercariae
      2. excyst when reaches rectal area
      3. as tadpole undergoes metamorphosis into frog, flukes migrate back up to the stomach and then migrate back to the rectum.

Paramphistomum cervi (family: Paramphistomidae)

1. Cosmopolitan in distribution
2. Adults in rumen of domestic animals, pickish in color
3. Pathogenic; in large numbers can cause intestinal ulceration and death; secondary bacterial infections
4. life-cycle
   1. adults in rumen
   2. eggs out with feces
   3. mature in water
   4. miricidium hatches; penetrates multiple genera of snail hosts
   5. one sporocyst and two redial generations
   6. cercariae encyst on aquatic vegetation
   7. eaten by herbivore
   8. excyst in duodenum; penetrate gut; migrate through tissues to abomasum
   9. enter lumen and migrate anteriorly to rumen
   10. mature in 2-4 months

Stichorchis subtriquetrus (family: Paramphistomidae)

1. Similar life-cycle to Paramphistomum cervi
2. Occurs in the caecum of beavers worldwide
3. Metacercariae encyst on aquatic vegetation (especially bark)
4. Over 95% of all beavers in Kansas are infected
5. Can cause pathology and mortality, although large numbers may occur in beaver without overt clinical signs

The definitive taxonomic work to date on this group is as follows: Sey, O. 1991. CRC Handbook of the Zoology of Amphistomes. CRC Press, Boca Raton. ISBN 0-8493-3624-4.