UPSC MainsZOOLOGY-PAPER-I202015 Marks
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Q11.

With the help of labelled diagrams only, explain the different larval stages in the life cycle of Fasciola hepatica (No description is required).

How to Approach

This question requires a purely diagrammatic answer, focusing on the morphological changes during the life cycle of *Fasciola hepatica*. The approach should be to sequentially illustrate each larval stage – miracidium, sporocyst, redia, cercaria, and metacercaria – with clear, labelled diagrams. No descriptive text is permitted within the diagrams themselves. Accuracy in depicting the key features of each stage is crucial. The diagrams should be arranged in a logical order representing the life cycle progression.

Model Answer

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Introduction

*Fasciola hepatica*, commonly known as the liver fluke, is a parasitic trematode that infects the liver of mammals, including humans. Understanding its complex life cycle is crucial for effective control and prevention of fascioliasis. The life cycle involves multiple larval stages, each adapted for survival and transmission between intermediate and definitive hosts. This answer will visually represent these stages, adhering strictly to the question’s requirement of labelled diagrams only, without any accompanying descriptive text.

Life Cycle of *Fasciola hepatica* – Diagrammatic Representation

1. Miracidium:

Miracidium

Labels: Cilia, Gut, Penetration Gland

2. Sporocyst:

Sporocyst

Labels: Germ Balls, Gut, Body

3. Redia:

Redia

Labels: Oral sucker, Gut, Eye spot, Tail

4. Cercaria:

Cercaria

Labels: Tail, Gut, Oral sucker, Penetration gland

5. Metacercaria:

Metacercaria

Labels: Body, Suckers, Cyst wall

The life cycle continues with the ingestion of metacercariae by the definitive host, leading to the development of adult flukes in the liver.

Conclusion

The life cycle of *Fasciola hepatica* is a complex process involving multiple larval stages, each adapted for survival and transmission. Understanding these stages is vital for developing effective control strategies, including targeting intermediate snail hosts and implementing proper livestock management practices. Continued research into the parasite’s biology is crucial for mitigating the impact of fascioliasis on both animal and human health.

Answer Length

This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.

Additional Resources

Key Definitions

Fascioliasis
An infectious disease caused by *Fasciola hepatica* or *Fasciola gigantica*, affecting the liver and bile ducts of mammals, including humans.
Miracidium
The first larval stage of trematodes, a free-swimming, ciliated larva that hatches from the egg and seeks out a snail intermediate host.

Key Statistics

Globally, an estimated 2.4 million people are infected with fascioliasis, with the highest prevalence in Southeast Asia, South America, and parts of Europe.

Source: WHO (as of knowledge cutoff 2023)

Economic losses due to fascioliasis in livestock are estimated to be over $3.2 billion annually worldwide (based on 2015 estimates).

Source: FAO (as of knowledge cutoff 2023)

Examples

Outbreak in Iran

In 2018, Iran experienced a large outbreak of fascioliasis linked to the consumption of contaminated watercress. This highlighted the importance of food safety measures and public health education.

Frequently Asked Questions

What is the role of the snail in the life cycle of *Fasciola hepatica*?

The snail acts as the intermediate host for the miracidium and sporocyst stages. The miracidium penetrates the snail, undergoes asexual reproduction to form sporocysts, and eventually rediae, which are released into the water.

Topics Covered

ZoologyParasitologyFasciola hepaticaLife CycleParasitic Worms