New serotype 2 and attenuated serotype 1 Marek's disease vaccine viruses: selected biological and molecular characteristics.
Two new Marek's disease vaccine viruses, Md11/75C/R2 (serotype 1) and 301B/1 (serotype 2), were evaluated in chickens with maternal antibodies (ab+) or without maternal antibodies (ab-). Strain Md11/75C/R2 was mildly pathogenic in ab--chickens, but this pathogenicity was markedly reduced in ab+ chickens. Md11/75C/R2 spread less by contact and replicated better, both in vivo and in vitro, than CVI988/C, another serotype 1 vaccine virus. Strain 301B/1 was similar to SB-1, another serotype 2 vaccine virus: both were nonpathogenic for ab--chickens, spread readily by contact, and replicated well in vivo. In vitro, 301B/1 grew more rapidly and produced larger plaques than SB-1. Notable characteristics of strain CVI988/C included absence of pathogenicity, poor replicative ability, and the absence of one epitope detected by a common serotype-1-specific monoclonal antibody. All four viruses could be distinguished from each other by restriction enzyme analysis of viral DNA. We conclude that Md11/75C/R2, although exceptionally protective, may require further attenuation. On the other hand, 301B/1, which in other studies induced higher levels of protection than SB-1, is nonpathogenic and may be considered for use as a commercial vaccine.
Witter
R L
RL
USDA, Regional Poultry Research Laboratory, East Lansing, Michigan 48823.
Silva
R F
RF
Lee
L F
LF
D000818:Animals; D002645:Chickens; D008381:Herpesvirus 2, Gallid / Q000145:classification / Q000276:immunology*; D008380:Marek Disease / Q000517:prevention & control*; D012703:Serotyping; D014611:Vaccination / Q000662:veterinary*; D014613:Vaccines, Attenuated; D014765:Viral Vaccines
D014613:Vaccines, Attenuated; D014765:Viral Vaccines