Para Lab 6

PARASITOLOGY LABORATORY 6 – Lung Flukes USTMED ’07 Sec C – AsM; Photos provided by JV.N.

Paragonimus westermani ova

PARAGONIMUS WESTERMANI CLASSIFICATION

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Trematode

DISEASE

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Paragonimiasis, Oriental lung fluke infection

GEOGRAPHICAL DISTRIBUTION

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Asia

LOCATION IN HOST

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encapsulated in parenchyma of lung

MORPHOLOGY

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Adult worms: These thick, robust, ovoid flukes, measuring 7.5-12.0 mm by 4-6 mm, are hermaphroditic, with a lobed ovary located anterior to two branched testes. The testes lie side by side in the posterior part of the body. Eggs: The moderately large, broadly ovoid, thickshelled, golden-brown eggs are unembryonated when passed in sputum or in feces. The eggs may measure 80120 u by 45-70 u. At the abopercular (?) end of the egg, the shell is somewhat thickened.

Paragonimus westermani

Paragonimus westermani Adult

LIFE CYCLE

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Unembryonated eggs passed in feces enter the water and undergo development to the miracidial stage. The egg hatches and the miracidium must find an appropriate freshwater snail intermediate host. Following a developmental period of two to three months, cercariae emerge from the snail and come in contact with various crustaceans, such as crabs and crayfish, penetrating into the viscera and musculature, and encysting to the metacercarial stage. Infection is acquired by ingestion of raw, infected crustaceans. In the mammalian host, the metacercariae migrate from the intestine through the body cavity and the diaphragm where they then enter the parenchyma of the lung. Adult worms become encapsulated in lung tissue, usually two worms per each capsule. The prepatent period is five to six weeks, and adult worms may live for up to 20 years.

Heterophyes heterophyes

DIAGNOSIS

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Detection of eggs in feces or in sputum Diagnostic problems. – the eggs of this species frequently are confused with the eggs of the broad fish tapeworm, Diphyllobothrium latum. However, the eggs of the latter are smaller (58-75 u long by 40-50 u) and they have an abopercular knob on the shell. In Paragonimus, the abopercular end of the thickened shell has no knob.

COMMENTS

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HETERPHYSE HETEROPHYES

METAGONIMUS YOKOGAWAI Metagonimus yokogawai

It now is well recognized that a number of Paragonimus species may parasitize humans, and almost all of these occur in canine or feline reservoir hosts. P. westermani matures in dogs and cats. The other species of Paragonimus have been described from various parts of southeast Asia, Africa, and Latin America. The eggs of these other species, though varying in size, have generally similar morphology.

Paragonimus westermani, Eggs.

ECHINOSTOMA ILOCANUM Echinostoma ilocanum

The eggs of the lung fluke, P. westermani, are large, have a moderately thick dark shell, a prominent operculum at the broad end, and a thickened abopercular end. They are unembryonated when discharged from the body in feces or in sputum. These eggs illustrate the wide variation in shape that is characteristic of the species.

Paragonimus westermani (more slides)

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