Epidemic Tremor in Young Chickens

During the last 4 years there has appeared in New England flocks a disease of young chickens hitherto unrecognized. This disease was described in a preliminary report (Jones, 1932) as "An encephalomyelitis in the chicken." Its increasing frequency among commercial flocks in the last 2 years has made necessary the use of a more descriptive name. In view of the striking symptom which differentiates it from other nervous disorders, and because of its appearance in large numbers of chickens within a flock, the name "epidemic tremor of chickens" has been chosen. The present paper is a report of studies carried on in field epidemics and in the laboratory since its first appearance. The disease has been transferred experimentally to normal chickens by intracerebral inoculation of suspensions of brain and spinal cord. During the course of twenty passages, the virulence has been materially increased. Whereas in early experiments only a few of the inoculated birds contracted the disease, in recent transfers it has not been unusual for an entire series to become infected. The average incubation period has likewise been shortened in the course of these passages, and the severity of the brain lesions has increased. The condition has many of the characteristics of a virus disease and has been tentatively classed as such.