During its life-cycle, Fasciola hepatica (liver fluke) infects its intermediate host and primary host at the following larval stage respectively :
A
Redia and miracidium
B
Cercaria and redia
C
Metacercaria and cercaria
D
Miracidium and metacercaria
The answer is D.
Solution
The liver fluke has two hosts: the primary (definitive) host is the sheep (or cattle), and the intermediate host is a freshwater snail (Lymnaea). Eggs pass out with the faeces of the sheep and hatch in water into ciliated miracidium larvae. The miracidium bores into the snail; so the miracidium is the stage infective to the intermediate host. Inside the snail it develops through sporocyst, redia and cercaria stages. Cercariae leave the snail, encyst on grass or aquatic plants, and become metacercariae. When a sheep eats this grass, the metacercaria infects it; so the metacercaria is the stage infective to the primary host. So the stages are miracidium (intermediate host) and metacercaria (primary host).
ConceptInfective stages of Fasciola
Animal Kingdom in past papers
123 questions from this chapter have appeared across 27 exam years.
