Genetic Resistance to Marek's Disease. Delineation of the Response of Genetically Resistant Chickens to Marek's Disease Virus Infection

Abstract

SUMMARY Genetically resistant chickens (Line 6) were inoculated at one day old with a cloned preparation of the JM strain of Marek's disease virus (MDV), and their response was compared, on a chronologic basis, with that of similarly inoculated genetically susceptible (Line 7) chickens. The susceptible chickens developed severe clinical Marek's disease (MD) and died within 8 weeks of inoculation. Many had gross lesions and all examined after 2 weeks postinoculation had microscopic lesions in the nerves. In contrast, the resistant chickens showed no overt signs of clinical disease throughout the observation period of 14 weeks. None had gross or microscopic nerve lesions characteristic of MD although they developed low levels of persistent viremia. Thus: a) regression of lesions was not a major factor involved in resistance to MD; and b) the presence or absence of microscopic nerve lesions 3 weeks postinoculation or later may be a qualitative genetic marker of MD response in Line 7 and Line 6 chickens. Although the resistant and susceptible chickens had no striking differences in precipitating antibody levels, they differed markedly in virus-neutralizing (VN) antibody response. Both lines acquired passive VN antibody which disappeared by the 5th week of hatching. Line 6 chickens began to develop active VN antibody by the 6th week and maintained high levels through the 14th week, whereas Line 7 chickens developed no detectable active VN antibody. The possible role of VN antibody in resistance to MD is discussed. 894