Question

The use of intermediate hosts for development is a common feature of which parasitic group?

• A. Ciliated protozoans
• B. Monogeneans
• C. Nematodes
• D. Branchiurans

Hint:

Parasite Life Cycle Patterns:
1. Direct (One host): Protozoans, Monogeneans, Crustaceans.
2. Indirect (Multi-host): Nematodes, Cestodes, Digenean Trematodes.
Memory trick: "Monogeneans" $\rightarrow$ "Mono" means one $\rightarrow$ One host!

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks which group of parasites typically follows an indirect life cycle, involving one or more intermediate hosts (like copepods, mollusks, or other fish) before reaching the final (definitive) host.
Detailed Explanation:

• Indirect Life Cycles: Many parasites require multiple host species to complete different stages of their development (larval vs. adult).

• Nematodes (Roundworms): Most parasitic nematodes of fish (e.g., Anisakis, Camallanus) have complex, indirect life cycles. They often use small crustaceans (like copepods or amphipods) as intermediate hosts. The fish usually becomes the definitive host after eating the infected crustacean.

• Analysis of other options:
• Ciliated Protozoans (e.g., Ich): Have direct life cycles (spread directly from fish to fish via water).

• Monogeneans (e.g., Dactylogyrus): Known for having direct life cycles (no intermediate host needed; often called "the direct flukes").

• Branchiurans (e.g., Argulus): Crustacean parasites (fish lice) that have direct development.

Step 3: Final Answer:
Nematodes (along with digenean trematodes and cestodes) are known for using intermediate hosts.