Hemorrhagic Enteritis of Turkeys: Influence of Maternal Antibody and Age at Exposure

The effect of maternal antibody (MAB) to hemorrhagic enteritis (HE) on the response of turkeys to infection with virulent and avirulent strains of HE virus (HEV) was examined. The influence of age at exposure and treatment with HEV antibody on development of clinical HE also was studied. MAB protected poults from clinical HE for up to 6 weeks of age. MAB also interfered with vaccination against the disease for at least 5 weeks after hatching, as indicated by absence of HEV antigen in spleens and by poor seroconversion at 6 days and at 3 weeks post-vaccination, respectively. The incidence of clinical HE in MAB-negative poults was significantly higher in poults inoculated with virus at 15 days of age or older than in poults inoculated at 1-13 days of age. Further, MAB-negative poults embryonally inoculated with virulent or avirulent strains of HEV did not develop disease; these poults developed antibody and resisted challenge with virulent virus at 6 weeks of age. Poults treated with HE antibody within 1 hour of challenge or at 1, 3, or 5 weeks before challenge with virulent virus were protected against lesions and mortality induced by HEV. These results suggest that MAB may influence susceptibility of turkeys to infection with HEV for at least 5 to 6 weeks after hatching, unlike the case with most other viral infections of poultry. The results confirm that early age resistance to clinical HE is independent of MAB and suggest that such resistance persists for up to 13 days of age. The data also suggest that turkeys lacking MAB can be immunized against HE by embryo vaccination. /// Se examinó el efecto de los anticuerpos maternales sobre la repuesta de pavos infectados con cepas virulentas y avirulentas del virus de enteritis hemorrágica. También se estudió la influencia de la edad de exposición y el tratamiento con anticuerpos contra el virus de enteritis hemorrágica sobre el desarrollo de la enfermedad clínica. Los anticuerpos maternales protegieron los pavitos contra el desarrollo de enfermedad clínica hasta las 6 semanas de edad, pero también interfirieron con la vacunación contra la enfermedad por un mínimo de 5 semanas después del nacimiento, como lo indicó la ausencia de antígeno en el bazo y la baja seroconversión a los 6 días y 3 semanas después de la vacunación, respectivamente. La incidencia de la forma clínica de enteritis hemorrágica en pavitos sin anticuerpos maternales fue significantemente mayor en los pavitos inoculados a los 15 días de edad