Question

Metacercaria of liver fluke is
A) Free swimming stage
B) Encysted stage
C) Non encysted nonmotile stage
D) Free-Floating stage

Answer 1

Hint: Metacercariae of the Clinostome family occurs in both encysted and non-encysted forms.Liver fluke disease (fasciolosis) is caused by the parasite of trematode Fasciola hepatica.

Complete Answer:
Disease can result from the migration of large numbers of immature flukes through the liver, or from the presence of adult flukes in bile ducts, or both. Liver fluke can infect all grazing animals (and humans), but it primarily affects sheep and cattle. It's the most pathogenic in cattle.
Fasciola parasites grow into adult flukes in the bile ducts of infected mammals that move through immature fasciola eggs in their faeces. After a few weeks, the egg hatch releases a parasite type known as miracidium, which then infects the snail host. It is a free-swimming ciliated larva.
Adult fluke lay eggs that have been transferred to pasture in the faeces. At sufficient temperatures, miracidium grows within the egg, hatches and migrates in thin moisture film, actively searching the snail host.
 Miracidia will only live outside the snail for a few hours. Within the snail, they undergo two further stages of development, including multiplication, eventually becoming infective cercariae, which emerge from the snail when temperature and humidity levels are sufficient.
The cercariae migrate to the wet herbage, encysting as metacercariae, the highly resilient infective stage of the liver fluke. After ingestion, young flukes migrate to the liver, into which they tunnel, causing substantial tissue damage.
The infection is patented roughly 10-12 weeks after the ingestion of the metacercaria. It takes 18-20 weeks for the whole cycle.

Thus the correct Answer is option(B) Encysted stage.

Note:In sheep, liver fluke disease occurs in three major clinical forms: acute, subacute, and chronic fasciolosis. The type occurs depending on the amount of infective metacercariae ingested and the time span during which they are ingested. Recent milder winters and rainy summers have seen improvements in trends of parasite epidemiology and disease reported earlier seasonal acute disease reports.