# Influence of High Eimeria tenella Immunization Dosages on Total Oocyst Output and Specific Antibodies Recognition Response in Hybrid Pullets (Gallus gallus)—A Pilot Study

## TL;DR

This study compares high doses of E. tenella in chickens to understand how they affect immunity and oocyst output.

## Contribution

The study identifies optimal immunization dosages for E. tenella that enhance immunity and oocyst collection in pullets.

## Key findings

- A 10K oocyst dose reduced oocyst output but caused severe clinical signs and low antibody titers.
- A 5K oocyst dose improved oocyst collection and early sterilizing immunity with strong antigen recognition.
- The 5K dose group showed better antigen recognition after the first booster dose.

## Abstract

Background: Two high primary-immunization doses of a wild-type E. tenella strain were assessed in healthy pullets (5K versus 10K sporulated oocysts/bird) to understand the effects of coccidia infection. Methods: Acquired immunity was evaluated following primary immunization and two booster doses with the homologous strain. Total oocyst shedding, clinical signs, and viability of every bird/group after each immunization/booster were recorded. Indirect ELISA measured the time course of humoral responses from each immunization group against sporozoite and second-generation merozoite of E. tenella. Antigen pattern recognition on these two asexual zoite stages of E. tenella was analyzed using Western blotting with antibodies from each immunization program. Afterwards, antigen recognition of specific life-cycle stages was performed using individual pullet serums from the best immunization program. Results: A primary-immunization dose of 1 × 104 oocysts/bird reduced the oocyst output; however, all pullets exhibited severe clinical signs and low specific antibodies titers, with decreased polypeptide recognition on both E. tenella asexual zoite stages. In contrast, immunization with 5 × 103 oocysts/bird yielded the best outcomes regarding increased oocyst collection and early development of sterilizing immunity. After the first booster dosage, this group’s antisera revealed a strong pattern of specific antigen recognition on the two assayed E. tenella life-cycle stages. Conclusions: The E. tenella-specific antibodies from the 5 × 103 oocysts/bird immunization program can aid in passive immunization trials and further research to identify B-cell immunoprotective antigens, which could help in the development of a genetically modified anticoccidial vaccine.