a minute intestinal fluke (and the smallest human fluke).
fully embryonated eggs each with a fully-developed miracidium, and eggs
are passed in the hostís feces
After ingestion by a suitable snail (first intermediate host), the eggs
hatch and release miracidia which penetrate the snailís intestine
Snails of the genus Semisulcospira are the most frequent
intermediate host for Metagonimus yokogawai. The miracidia
undergo several developmental stages in the snail, i.e. sporocysts
Many cercariae are produced from each redia. The cercariae are released
from the snail
encyst as metacercariae in the tissues of a suitable fresh/brackish
water fish (second intermediate host)
The definitive host becomes infected by ingesting undercooked or salted
fish containing metacercariae
After ingestion, the metacercariae excyst, attach to the mucosa of the
mature into adults (measuring 1.0 mm to 2.5 mm by 0.4 mm to 0.75 mm)
In addition to humans, fish-eating mammals (e.g., cats and dogs) and
birds can also be infected by M. yokogawai
Mostly the Far
East, as well as Siberia, Manchuria, the Balkan states, Israel, and
The main symptoms
are diarrhea and colicky abdominal pain. Migration of the eggs to
extraintestinal sites (heart, brain) can occur, with resulting symptoms.
The diagnosis is
based on the microscopic identification of eggs in the stool. However,
the eggs are indistinguishable from those of Heterophyes heterophyes
and resemble those of Clonorchis and Opisthorchis.
Specific diagnosis is based on identification of the adult fluke
evacuated after antihelminthic therapy, or found at autopsy.
the drug of choice.
* This drug is
approved by the FDA, but considered investigational for this purpose.