A Study of Asymptomatic Newcastle Disease in a Breeding Flock

An asymptomatic form of Newcastle disease which was diagnosed by chance by means of the haemagglutination inhibition test is described. No evidence of transmission of the virus was found following contact exposure of susceptible chickens for as long as 179 days to asymptomatic but infected birds. Newcastle disease virus could not be isolated from serologically reacting chickens, from embryos of eggs laid by the hens, or from the progeny of the breeding flock.