Persistence of Parental Infectious Bursal Disease Antibody and Its Effect on Susceptibility of Young Chickens

SUMMARY The influence on subsequent infection to infectious bursal disease virus (IBDV) in chicks was studied in two trials. In the first trial, gross and histologic examination of the bursa of Fabricius at 3 and 5 days postinfection showed a modifying influence through the 7th week by the parental antibody on lesions produced. In groups challenged up to 3 weeks of age, 17/17 of the unimmune chicks showed bursal atrophy, compared with 5/18 of the parentally immune groups. In a second trial, any influence of parental antibodies had disappeared by the 5th week of age. The reduction in virus neutralizing titers tended to parallel the loss of protection to challenge virus. The presence of parental antibodies and the massive destruction of the lymphoid tissue of the bursa of Fabricius did not seem to interfere with the development of an active immunity. Neither the fully susceptible chicks nor the parentally immune chicks showed clinical signs of the disease when challenged before three weeks of age. There appears to be an early age resistance to IBDV infection.