Question

The infective stage of Fasciola hepatica to sheep is
A) Sporocyst
B) Cercaria
C) Metacercaria
D) Hexacanth

Answer 1

Hint: Fasciola hepatica is a parasite that belongs to the class Trematode. These organisms are commonly known as Liver fluke. And infects the hepatocytes especially in animals such as cattle.

Complete answer:
The infective stage in the life cycle of these parasites is the Metacercaria stage present at the larval stage. These organisms exist as endoparasites within the body of animals such as sheep and cows. At this stage, the cercaria stage loses a rump and gets converted to metacercaria.
Considering the other given options:
A. Sporocyst is a separate parasite genus. The organisms belonging to it have two hosts to complete their life cycle. An example of a parasite belonging to the genus is the malarial parasite, the Plasmodium vivax. Thus it is not the right option.
B. In Fasciola hepatica the stage before the metacercaria is the cercaria stage. The developmental processes in this stage occur within the germinal cells. A cercaria has a tapering head along with huge penetration glands. It may or may not have an extended swimming "tail", banking on the species. Thus it is not the right option.
D. Hexacanth refers to the larval form of the parasite present as the Pork tapeworm. These organisms exist as an endoparasite in the intestines of human beings. The second host is the pigs. Thus it is not the right option.

Therefore, from the above-given options, the most appropriate and correct answer is C. That is the infective stage of Fasciola hepatica to sheep is the metacercaria stage.

Note:
These organisms can cause an infectious disease known as Fasciolosis. It can infect human beings too if consumed the meat or comes in contact with an infected cattle. Once infected, it can penetrate the gut of the host. In chronic cases, it can cause sudden death due to hemorrhage in cattle.