Newcastle disease virus pathotypes.

The clinical signs, mortality and postmortem findings following infection of six-week-old chicks with nine strains of Newcastle disease virus were studied. Although strains could be divided into four pathotypes the divisions were not clear-cut. The most prominent feature of disease following infection by two isolates from the post-1970 USA epidemic, a 1962 UK isolate and a 1972 UK isolate were haemorrhagic gut lesions. A virus isolate from the post-1970 UK epidemic, Lamb-Essex '70, rarely caused gut lesions in infected birds although this was the only strain to consistently induce oedema of the eye in infected birds.