Influence of infectious bursal disease on the development of immunity to Eimeria tenella.

Specific-pathogen-free (SPF) chicks infected with infectious bursal disease (IBDV) virus at one day of age or midway (7 days) through a two-week immunization program for Eimeria tenella showed significantly less (P less than or equal to 0.05) protection against coccidal challenge as measured by lesion scores than chicks given IBDV after 14 days of coccidial immunization. The chicks showed complete protection to later coccidial challenge administered on Day 21. Bursae were markedly smaller from IBDV-infected chicks than from uninfected controls, and pathological changes were extensive. Virus-neutralization tests demonstrated that titers to IBD were higher in chicks exposed to the virus than in unexposed controls.