MLT GlobeParasitology: Trematodes (flukes)
25 Parasitology MCQs on Trematodes (flukes) with answers and explanations.
A stool concentrate shows a large oval egg with a prominent LATERAL spine. Which schistosome produced it?
S. mansoni eggs have a lateral spine and are found in faeces. S. haematobium eggs have a terminal spine (urine), S. japonicum a tiny knob, and Fasciola eggs are operculated without a spine.
Schistosomes live in the mesenteric or vesical venous plexuses. Which common name reflects this?
Adult schistosomes live in blood vessels, hence 'blood flukes'. Fasciola/Clonorchis are liver flukes, Paragonimus a lung fluke and Fasciolopsis an intestinal fluke.
A person swimming in a freshwater lake becomes infected with Schistosoma. Which stage penetrated the skin?
Fork-tailed cercariae released from snails penetrate human skin. Miracidia hatch from eggs and infect snails; metacercariae are infective stages of food-borne flukes such as Fasciola.
Which of the following helminths is a trematode rather than a nematode?
Schistosoma is a fluke (trematode). Ascaris, hookworms and Trichuris are roundworms (nematodes).
A urine sample collected around midday from a patient with haematuria shows eggs with a TERMINAL spine. Which parasite is present?
S. haematobium lives in the vesical plexus and releases terminal-spined eggs in urine, peaking around midday. S. mansoni eggs have a lateral spine and appear in stool.
Which name does not belong to a human Schistosoma species?
Buski refers to Fasciolopsis buski, the giant intestinal fluke. S. haematobium, S. mansoni and S. japonicum are the main human blood flukes.
Operculated brown eggs in sputum from a patient with chronic cough and hemoptysis suggest:
The lung fluke Paragonimus lays eggs in the lungs that are coughed up in sputum or swallowed and passed in stool. It is often misdiagnosed as tuberculosis.
Terminal hematuria in a patient from an endemic area suggests infection with:
S. haematobium adults live in the vesical venous plexus, and eggs penetrate the bladder wall, causing bleeding at the end of urination. S. mansoni affects the intestine and liver.
The main public health measure to interrupt the life cycle of most trematodes (flukes) is control of:
Almost all flukes need a freshwater snail as the first intermediate host, so molluscicides and habitat control reduce transmission. Insect vectors do not transmit flukes.
The sheep liver fluke that can infect humans who eat raw watercress is:
Metacercariae of F. hepatica encyst on water plants like watercress; adults live in bile ducts. Clonorchis comes from raw fish and Fasciolopsis is an intestinal fluke.
The Chinese or Oriental liver fluke is:
C. sinensis is acquired from raw freshwater fish in East Asia and lives in bile ducts. Opisthorchis felineus is the cat liver fluke and Paragonimus is the lung fluke.
The routine specimen for diagnosing Fasciola hepatica infection is:
Large operculated eggs are passed in stool or found in duodenal aspirate; serology helps in the early phase. Blood is not the diagnostic specimen.
Which host is needed for schistosomes to develop from miracidium to cercaria?
Miracidia enter specific snails, where they multiply into cercariae. Humans are the definitive host.
Chronic urinary infection with Schistosoma haematobium is associated with which cancer?
Long-standing egg deposition in the bladder wall causes chronic inflammation that predisposes to squamous cell bladder cancer.
Humans acquire the Chinese liver fluke Clonorchis sinensis by eating:
Metacercariae encysted in freshwater fish are eaten raw; watercress transmits Fasciola.
Lung fluke (Paragonimus) infection is acquired by eating raw or undercooked:
Metacercariae of Paragonimus develop in freshwater crustaceans eaten raw, pickled or undercooked.
Which fluke, the largest intestinal fluke of humans, is acquired by eating raw water plants such as water chestnuts?
Fasciolopsis buski lives in the small intestine; metacercariae encyst on aquatic plants that are peeled with the teeth.
After swimming in a lake frequented by birds, a person develops an itchy papular rash that resolves without systemic illness. Cause?
Swimmer's itch (cercarial dermatitis) is due to non-human schistosome cercariae that penetrate but die in human skin. Hookworm causes ground itch from soil, not water.
Which statement correctly describes trematodes (flukes)?
Flukes are acoelomate flatworms with leaf-shaped unsegmented bodies. Cylindrical bodies with a pseudocoelom describe nematodes, and segmented ribbons describe cestodes.
Generalized lymphadenopathy is least characteristic of which infection?
Lymph node enlargement is prominent in toxoplasmosis, African trypanosomiasis (Winterbottom sign) and kala-azar. Chronic schistosomiasis mainly causes granulomas around eggs in the liver, gut or bladder.