Question

Which of the following is NOT true for precocious line of Eimeria?

• A. It can revert to parent strain
• B. It is highly immunogenic
• C. Schizogony is skipped by precocious line
• D. It is an early producer of oocysts

Hint:

For vaccine safety, live-attenuated strains must be genetically stable.
The defining biological advantage of precocious coccidial vaccine strains is that they are stable and cannot revert to their virulent parental strains.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Precocious lines of Eimeria are attenuated strains developed by selecting for the first excreted oocysts over successive generations.
These lines are widely utilized in live coccidiosis vaccines (e.g., Paracox) because they exhibit reduced virulence while retaining protective immunogenicity.

Step 2: Detailed Explanation:
Let us review the characteristics of precocious lines:
- Precocious trait stability: A fundamental safety feature of vaccine-certified precocious lines is that their attenuation is genetically stable.
They are incapable of reverting back to the virulent, wild-type parent strain.
Therefore, stating that it "can revert to parent strain" is false (not true).
- Immunogenicity: Precocious lines retain the surface antigens of the parent strain and undergo replication within the host, making them highly immunogenic.
Thus, this statement is true.
- Truncated life cycle: These lines achieve a shortened prepatent period (early oocyst production) primarily because they omit or skip one or more rounds of asexual replication (schizogony/merogony).
Thus, this statement is true.
- Early production: By definition, precocious lines are selected for rapid development and are early producers of oocysts.
Thus, this statement is true.

Step 3: Final Answer:
The false statement is (A), as precocious lines do not revert to the parent strain.