Diphyllobothrium latum
Final hosts: Man and fish-eating mammals, such as the dog, cat, pig and polar bear
Life cycle: indirect
Predilection
site: Small intestine
Final
hosts: Man and fish-eating mammals, such as the dog, cat,
pig and polar bear
Intermediate
hosts: 1. Copepods. 2. Freshwater fish (pike, trout, perch)
Ø Eggs
are continuously discharged from the genital pores of the attached gravid
segments of the strobila and pass to the exterior in the faeces.
Ø They
resemble F. hepatica eggs being yellow and operculate, but are
approximately half the size.
Ø The
eggs must develop in water and within a few weeks each hatches to liberate a
motile ciliated coracidium, which, if ingested by a copepod, develops
into the first parasitic larval stage, a procercoid.
Ø When
the copepod is ingested by a freshwater fish, the procercoid
migrates to the muscles or viscera to form the second larval stage, the plerocercoid; this solid larval metacestode is about 5.0 mm
long and possesses the characteristic scolex.
Ø The
life cycle is completed when the infected fish is eaten raw, or insufficiently
cooked, by the final host. Development to patency is rapid, occurring within 4
weeks of ingestion of the plerocercoid.
Ø However,
if the infected fish is eaten by a larger fish, the plerocercoid has the
ability to establish itself in its new host.
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