Question

Given below are two statements:
Statement I: Heavy infection of Eimeria bovis causes bloody diarrhoea in calves below 1 month of age
Statement II: Gamonts are the most pathogenic stage in the life cycle of Eimeria bovis
In light of the above statements, choose the correct answer from the options given below:

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Hint:

To remember the pathogenesis of Eimeria: Schizonts multiply in the small intestine with minimal clinical signs, but Gamonts destroy the large intestinal mucosa, causing severe hemorrhaging and bloody diarrhea.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Bovine coccidiosis, caused primarily by Eimeria bovis and Eimeria zuernii, is an important enteric disease of calves.
The pathogenicity of coccidiosis is directly linked to the destruction of epithelial cells during the asexual (schizogony) and sexual (gametogeny) stages of the life cycle.

Step 2: Detailed Explanation:
Let us analyze the statements individually:
1. Statement I: Heavy infection of Eimeria bovis causes bloody diarrhoea in calves below 1 month of age
This statement is incorrect.
Clinical coccidiosis is rarely observed in calves under 3 to 4 weeks of age.
This is because Eimeria bovis has a long prepatent period of approximately 18 to 21 days.
Additionally, maternal antibodies and age-associated exposure dynamics mean that clinical cases with bloody diarrhea typically occur in calves aged 1 to 6 months.
Diarrhea in calves under 3 weeks of age is usually caused by other pathogens such as Rotavirus, Coronavirus, enterotoxigenic E. coli (ETEC), or Cryptosporidium.
Therefore, Statement I is false.
2. Statement II: Gamonts are the most pathogenic stage in the life cycle of Eimeria bovis
This statement is correct.
During the life cycle of Eimeria bovis, the first-generation schizonts grow to giant sizes in the endothelial cells of the lacteals in the small intestine.
However, the sexual phase (gametogeny) occurs in the epithelial cells of the cecum and colon.
The development and maturation of millions of gamonts (macrogametocytes and microgametocytes) destroy large areas of the large intestinal mucosa.
This massive epithelial destruction causes severe hemorrhagic enteritis, sloughing of the mucosa, and the classic clinical sign of bloody diarrhea.
Therefore, the sexual gamont stages are the most pathogenic stage of the parasite.
Thus, Statement II is true.

Step 3: Final Answer:
Statement I is false because clinical coccidiosis occurs in older calves, while Statement II is true because gamonts cause the most severe tissue destruction.
Therefore, the correct answer is option (D).