Effect of Eimeria tenella infection on the production of Salmonella enteritidis-contaminated eggs and susceptibility of laying hens to S. enteritidis infection.

Experiments were conducted to determine the effect of Eimeria tenella infection on the production of Salmonella enteritidis-contaminated eggs and susceptibility of egg-laying hens to S. enteritidis infection. The dose of sporulated oocysts of E. tenella used in the present study was 2 x 10(5) per chicken. When hens were infected with 10(6) colony-forming units (CFU) of S. enteritidis, E. tenella infection resulted in a significant increase (P < 0.05) of S. enteritidis contamination in the shells of fresh eggs but not in the egg contents of fresh eggs and stored eggs. Significant effects of coccidial infection on the contamination of eggs (shells and contents) were not observed when hens were infected with 10(4) CFU of S. enteritidis. Surface-disinfected eggs pooled within each week from individual chickens infected with 10(4) CFU of S. enteritidis and E. tenella showed significantly (P < 0.05) more S. enteritidis contamination in eggshells, but not in egg contents, than did those from hens infected with S. enteritidis alone. Coccidial infection resulted in a significant increase of S. enteritidis in the cloacal swabs of hens infected with 10(4) CFU of S. enteritidis. In all the experiments, chickens infected with S. enteritidis and E. tenella showed significantly higher positive rates and counts of cecal S. enteritidis than did chickens infected with S. enteritidis alone. No significant differences of S. enteritidis-positive rates in ovary, oviduct, liver, and spleen were noted whether the hens were infected with a combination of E. tenella and S. enteritidis or with S. enteritidis alone.