Biology 625
ANIMAL PARASITOLOGY
Fall semester lecture note outline

Updated: 05 March 2001

1. Adults are quite diverse in this order, and many do not resemble one another
2. Larvae and juveniles share more similarities than adults
3. Wall of excretory bladder epithelial
4. Cercariae with simple tail and dorsal finfold
5. Oral stylet usually present (xiphidiocercariae)
6. Most species have small eggs and most (but not all) have eggs that must be eaten by snail to hatch
7. Tend to be medium-small worms; most intestinal (but a number of exceptions)
8. Below are some representative species:

Dicrocoelium dendriticum (family: Dicrocoeliidae)

1. Synonyms include Dicrocoelium lanceolatum and Distoma dendriticum
2. Medium sized, elongate, and flattened worms ("lancet fluke") (ca 6-10 x 1.5-2.5 mm)
3. Body pointed at both ends
4. Cecae simple; ovary post-testicular
5. Common in Europe and Asia; introduced into Australia and NE portion of North America 5)Life-cycle
   1. adults in bile ducts, gall bladder, and pancreatic ducts of sheep, cattle, goats, pigs, cervids, lagomorphs, some rodents, and rarely humans
   2. eggs passed embryonated out with feces
   3. eaten by land snails, and about 55 different species of snails have been shown to be suitable hosts (in USA, especially Cionella lubrica or Zebrina detrita)
   4. hatch
   5. two sporocyst generations
   6. xiphidiocercariae accumulate in pulmonary chamber of snail
   7. cercariae aggregate as massess and secrete thin cyst wall. Snail then coats cercariae with mucus, and deposits slime balls containing numerous cercariae (dozens to hundreds) in slime trails
   8. slime balls eaten by ants. About 17 species and several genera of ants have been found to be suitable second intermediate hosts (in USA, Formica fusca); ants love to eat slime balls and even feed them to the larval ants
   9. most metacercariae encyst in hemocoel and are infective to final host; however, 1-2 encyst in depression between roots of subesophageal nerves leading to mouthparts (never become infective)
   10. as temperature decreases in the evening, ants climb up grass and clamp down with mandibles. Uninfected ants return to colony. Paralyzed ants found only at temperatures under 20 C
   11. mandibles release when ants warm up the next morning
   12. ruminants graze in evenings and mornings, ingesting these exposed ants
   13. metacercariae excyst in duodenum, migrates up common bile duct
6. A closely related species, Dicrocoelium hospes, is found in portions of Africa and infects ruminants and occasionally humans.
7. A similar species, Brachylecithum mosquensis, infects robins in North America and utilizes carpenter ants, Campanotus spp., which wander aimlessly in brightly lit areas when infected.

Haematoloecus spp. (family: Haematoloechidae)

1. Parasitic in the lungs of anurans
2. Relatively transparent, large worms about 8 x 1.2 mm
3. Over 40 known species worldwide, 4-6 species in midwest (i.e. H. medioplexus, H. longiplexus, H. varioplexus, H. complexus)
4. Key to species 1981, Can J Zool 59: 1836-1846.
5. Uterus with many eggs, often obscuring many internal details
6. Vitellaria in clusters along lateral margin of body
7. Life-cycle
   1. adults in lungs (2-3 per frog/toad typical; occasionally many)
   2. eggs up trachea; out with feces; passed fully embryonated
   3. ingested by snails (i.e. Planorbula armigera for H. medioplexus)
   4. miricidium hatches
   5. sporocyst in hepatic gland of snail
   6. cercariae escape from snail
   7. many sucked into rectal branchial chamber of dragonfly nymphs; some (but not all) species can also penetrate intersegmental membranes and can utilize other hosts; some species penetrate caudal gills of damselflies
   8. metacercariae
   9. dragonfly metamorphoses into adult
   10. ingested by frog or toad
   11. excystation; migrate anteriorly up gut, through glottis, into repiratory tract
8. select references: 1994, J Parasitol 80: 1052-1055; 1996, J Parasitol 82: 94-99.

Prosthogonimus macrorchis (family: Prosthogonimidae)

1. Most species in family live in oviducts, bursa, or intestine of birds (about 30 species in the genus; i.e. P. pellucidus)
2. All members of the family tend to be quite transparent, and internal details are easily seen
3. Life cycle
   1. adults in oviduct of domestic fowl and many wild birds
   2. ca 8 x 5 mm
   3. eggs out with feces; sink to bottom of pond
   4. eaten by snail (Amnicola spp.)
   5. hatch
   6. sporocysts in digestive gland of snail
   7. xiphidiocercariae
   8. sucked into rectal brancial chamber of dragonfly nymph
   9. metacercariae in muscles of body wall
   10. dragonfly metamorphoses into adult
   11. eaten by bird
   12. excyst in intestine; migrate posteriorly and mature; in male birds, the worms die during the migration

Nanophyetus salmincola (family: Troglotrematidae)

1. Small, ovioid, and with a spiny tegument
2. Adults 0.8-2.5 x 0.3-0.8 mm
3. Infect wide variety of mammals and even fish eating birds; hundreds can be recovered from the intestinal tract of a single animal
4. Life-cycle
   1. adults live embedded in crypts in wall of small intestine
   2. eggs are passed unembryonated; out with feces
   3. eggs embryonate in environment; 3-8 months
   4. hatch
   5. miricidia penetrate snails (Juga plicifera; syn. Oxytrema silicula; they keep changing the name on this snail so who knows what it really is this year)
   6. at least one redial generation and probably two
   7. xiphidiocercariae exit
   8. penetrates skin of fish, predominately salmonids affected (over 30 species of fish can be infected; some river drainages with over 70% prevalence of infections). Lamprey, tadpoles, and even the Giant Pacific salamander may also harbor infective metacercariae.
   9. metacercariae in tissues throughout body
   10. young fish may die due to heavy metacercarial infections; heavy infections have also been shown to increase fish morbidity and mortality to viral infections
   11. infected fish ingested by definitive host
   12. worms mature in gut of definitive host
5. Skunk and raccoon main hosts, although over 30 species of mammals and some birds have been shown to be suitable hosts. Little damage to definitive hosts except in very heavy infections. Heavy infections in humans may result in intestinal discomfort and diarrhea. One infection in a cougar, where 650,000 worms were recovered, revealed marked mucosal thickenings of the duodenum and jejunum, enteritis, and malnutrition (1979, J. Wildlf. Dis. 15: 419-420).
6. Flukes may be infected with a rickettsia, Neorickettsia helminthoeca.
7. Rickettsia pathogenic for canids only, causing up to 90% mortality in dogs ("salmon poisening") (I've been told, but have never seen a paper describing this, that a second rickettsial species may also exist. This species causes fever in canids but is not fatal).
8. The rickettsia is passed transovarianly (in eggs)
9. Northwest North America, Siberia
10. In Russia, the name Nanophyetus salmincola schikhobalowi is sometimes used. Other synonyms include Nanophyetus schikhobalowi and Troglotrema salmincola.
11. References: 1964, J Parasitol 50: 588-589; 1966, J Parasitol 52: 54-59; 1968, J Parasitol 54: 770-774; 1989, Am J Trop Med Hyg 36: 586-591

Paragonimus kellicotti (family: Troglotrematidae)

1. Nearly 50 known species in the genus; this particular species is found in North America
2. Large, fleshy worms that live in the lungs
3. Found in canids, pigs, felids, raccoons, goats, muskrats, mustelids, skunk, opossum, and even two reports from humans also
4. Life-cycle
   1. adults encysted in pairs in lungs
   2. eggs up trachea; out with feces
   3. mature in environment in several weeks
   4. hatch
   5. miricidium penetrates snail (Pomatiopsis lapidaria)
   6. sporocyst and two redial generations
   7. cercariae either emerge and penetrate crayfish (i.e. Cambarus spp.) , or snail with cercariae eaten by crayfish. Other Paragonimus spp. may use freshwater crabs or other crayfish species.
   8. metacercariae in gills, muscle
   9. eaten by definitive host
   10. bores through gut wall; through diaphragm and penetrates lung directly
   11. maturation into adults
5. Select references: 1975, J Wildlf Dis 11: 136-141; 1978, J Parasitol 64: 998-1002; 1978, Parasitology 77: 13-18; 1978, JAVMA 173: 734-742; 1979, Vet Parasitol 5: 325-337; 1986, Am J Clin Pathol 86: 685-687 (human); 2000, Acta Cytol 44: 75-80 (human)