Trematodes and Parasitic Life Cycles Review

Comprehensive question-and-answer practice flashcards covering general trematode biology, life cycles, diagnostics, vaccine adjuvants, Paragonimus westermani, Fasciolopsis busci, Fasciola hepatica, and Echinostoma.

What was the only adjuvant available for human use for a very long period of time?

Alum salts.

Why do live attenuated vaccines and mRNA vaccines not require an added adjuvant?

The vaccine component or mRNA itself acts as its own adjuvant by being recognized directly by innate immune pattern recognition receptors.

How do trematodes, nematodes, and cestodes differ in the structure of their digestive systems?

Trematodes have a mouth but no anus (a blind gut), nematodes have both a mouth and an anus, and cestodes have neither and absorb nutrients through their skin.

What distinguishes a definitive host from an intermediate host in a parasitic life cycle?

The definitive host is where the sexual cycle of the parasite occurs, whereas the intermediate host is where the asexual cycle takes place.

What is the name of the ciliated stage that hatches from a trematode egg to find a snail intermediate host?

Miracidium.

How do schistosomes differ from the trematodes covered in Chapter 1 in terms of sex determination and intermediate hosts?

Schistosomes are dioecious (have separate male and female worms living in copula) and lack a second intermediate host, whereas the other trematodes are hermaphrodites and require a second intermediate host.

What is an operculum on a trematode egg?

A lid-like hatch or door on the egg through which the miracidium is released.

What is the most common species of lung fluke responsible for human paragonimiasis?

Paragonimus westermani.

What serves as the second intermediate host for Paragonimus westermani?

Crustaceans, specifically crabs and crayfish.

What role do pigs play in the life cycle of Paragonimus westermani?

Pigs serve as a paratenic host, harboring dormant larval stages that can infect humans if undercooked pork is consumed.

What diagnostic specimen uniquely contains Paragonimus westermani eggs compared to other helminths?

Sputum (saliva or spit).

Is pairing required for Paragonimus westermani worms to reproduce?

No, because Paragonimus westermani are hermaphrodites capable of self-fertilization, although they are frequently found in pairs within lung cysts.

What severe ectopic involvement occurs in 90% of Paragonimus cases among individuals under age 15 in Korea?

Cerebral involvement (cerebral paragonimiasis).

What do Charcot-Leyden crystals in microscopic tissue samples indicate?

The historical presence and breakdown remnants of eosinophils.

What is the largest trematode species discussed in the lecture, and where does it reside in the definitive host?

Fasciolopsis busci, which resides primarily in the small intestine.

How does the role of pigs in the life cycle of Fasciolopsis busci differ from their role in Paragonimus westermani?

Pigs serve as a true reservoir host for Fasciolopsis busci, whereas they act as a paratenic host for Paragonimus westermani.

How do humans contract a Fasciolopsis busci infection?

By ingesting metacercariae attached to aquatic plants (such as water chestnut, water caltrop, water bamboo, or water hyacinth) or by drinking contaminated water.

What prominent morphological feature distinguishes adult Fasciola hepatica from Fasciolopsis busci?

A cephalic cone.

Which water plant is most commonly linked to human infection with Fasciola hepatica?

Watercress.

Where in the human body do adult Fasciola hepatica flukes localize, and what clinical presentation do they often mimic?

They reside in the bile ducts of the liver and often mimic gallstones (cholelithiasis).

What is the drug of choice for treating Fasciola hepatica infections, and how does it differ from other trematodes?

Triclabendazole (triclobenzole); it is the exception to the rule because almost all other trematodes are treated with praziquantel.

Why can stool egg microscopy fail to identify a specific infection among Fasciola hepatica, Fasciolopsis busci, and Echinostoma?

Their eggs are morphologically indistinguishable (all are large, operculated, brownish trematode eggs).

What organisms act as second intermediate hosts for Echinostoma species?

Snails or frogs.

Why did researchers investigating Fasciola hepatica in Cambodia initially make a diagnostic misidentification?

They observed abundant large trematode eggs in stool samples and assumed it was Fasciola hepatica, but further analysis revealed the eggs belonged to Echinostoma.

What distinct morphological feature allows Schistosoma mansoni eggs to be definitively identified?

A prominent lateral spine (a single spike on the side of the egg).