Vaccination against Marek's disease: possible causes of failure of herpesvirus of turkeys (strain FC126) to protect chickens against Marek's disease
Okazaki, W.; Purchase, H.G.; Burmester, B.R.
American Journal of Veterinary Research 34(6): 813-817
1973
ISSN/ISBN: 0002-9645 PMID: 4350544 Document Number: 59176
Chickens from commercial flocks which had been vaccinated with herpesvirus of turkeys (HVT) vaccine against Marek's disease (MD), but which had eventually developed lesions of MD, were examined to find the cause of the MD or MD-like lesions. Only 62% of these chickens had present or past infection with HVT. Thus, some losses may occur because HVT did not become established in chickens, although most chickens had become infected with HVT. Probably, in some chickens, infection with MD virus occurred before immunity could be developed. Evidence was not seen that an MD virus capable of breaking through the HVT vaccination was responsible for the disease, nor was there any evidence of involvement of leucosis/sarcoma or reticuloendotheliosis viruses.