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Eimeria maxima: a comparison of two laboratory strains with a fresh isolate
Abstract:
Oocysts of the Weybridge and Houghton strains of Eimeria maxima and a fresh field isolate were similar and measured on average 30-9 X 22-4 mum. The Weybridge strain and the field isolate produced similar pathogenic effects in 6-week-old chickens, high doses causing 50-80% mortality and severe weight loss. The Houghton strain was slightly less pathogenic and few birds died but more oocysts were produced. With each strain, a single dose gave complete immunity to a light challenge with the homologous strain. Two or 3 immunizing doses gave complete immunity to a heavy homologous challenge but were not sufficient to protect against heterologous challenge.
Insights
Eimeria maxima strains showed varying pathogenicity in chickens. Vaccination with homologous strains provided protection against homologous challenges, but not heterologous ones.
Area of Science:
- Veterinary Parasitology
- Avian Health
- Immunology
Background:
- Eimeria maxima is a significant protozoan parasite affecting poultry.
- Different strains of Eimeria maxima exhibit varying levels of pathogenicity and host immune responses.
- Understanding strain-specific pathogenicity and immune responses is crucial for effective disease control in chickens.
Purpose of the Study:
- To compare the pathogenicity of different Eimeria maxima strains (Weybridge, Houghton, and a field isolate) in chickens.
- To evaluate the efficacy of homologous vaccination against homologous and heterologous challenges.
- To assess the dose-dependent effects of Eimeria maxima infection on mortality and weight loss.
Main Methods:
- Oocysts from Weybridge, Houghton, and a field isolate of Eimeria maxima were characterized morphologically.
- Groups of 6-week-old chickens were infected with varying doses of each Eimeria maxima strain.
- Pathogenicity was assessed by monitoring mortality, weight loss, and oocyst production.
- Vaccination trials involved single or multiple immunizing doses followed by homologous or heterologous challenge infections.
Main Results:
- Oocyst morphology was similar across all tested Eimeria maxima strains.
- Weybridge strain and field isolate caused high mortality (50-80%) and severe weight loss.
- Houghton strain was less pathogenic, resulting in fewer deaths but higher oocyst production.
- A single immunizing dose conferred immunity to a light homologous challenge.
- Two or three immunizing doses provided complete immunity against heavy homologous challenge but not heterologous challenge.
Conclusions:
- Eimeria maxima strains differ in their pathogenicity, impacting chicken health and productivity.
- Homologous vaccination is effective against homologous Eimeria maxima challenge, with dose-dependent protection.
- Cross-protection against heterologous Eimeria maxima strains is limited, highlighting the need for strain-specific control strategies.