Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): Eimeria tenella is the most pathogenic coccidia of chickens and causes heavy mortality in broilers managed under deep liter system.
Reason (R): Mortality in caecal coccidiosis usually occurs due to the presence of large number of gametogenic stages in the caecal epithelium of infected birds.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

The second-generation schizont is the "killer" stage of *Eimeria tenella*.
It is exceptionally large and causes severe hemorrhage when it ruptures, releasing thousands of merozoites and destroying the surrounding blood vessels.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Eimeria tenella is a highly pathogenic coccidian parasite affecting chickens, localized specifically in the ceca.
Understanding the pathology caused by the different life cycle stages of the parasite is necessary to evaluate these statements.
Detailed Explanation:
Let us evaluate both statements:
Assertion (A): Eimeria tenella is indeed the most pathogenic coccidian species in chickens.
It causes acute cecal coccidiosis, characterized by bloody diarrhea, severe dehydration, and high mortality.
This disease is especially prevalent in broilers kept on deep litter systems, where high stocking density and moisture favor the survival and ingestion of sporulated oocysts.
Thus, Assertion (A) is true.
Reason (R): The severe hemorrhaging and subsequent mortality in cecal coccidiosis are primarily caused by the rupture of the second-generation schizonts (meronts) in the lamina propria of the cecum, not the gametogenic stage.
The second-generation schizonts grow very large, causing severe mechanical disruption of epithelial cells and mucosal capillaries as they rupture on day 4 and 5 post-infection.
The gametogenic stage (sexual stage) also causes cell destruction, but it is not the main driver of the acute, fatal hemorrhage.
Thus, Reason (R) is false.
Therefore, Assertion (A) is true, but Reason (R) is false.

Step 2: Final Answer:
The correct option is (C).