Response of the Syrian Hamster to the Virus of Newcastle Disease

Summary A California strain of Newcastle virus (No. 11,914) was carried serially by intracerebral inoculation through 200 passages in Syrian hamsters. The virus produced symptoms of irritability followed by involuntary motor reactions and paralysis. During the state of paralysis and while moribund, a large percentage of the infected hamsters showed marked labored breathing. The incubation period decreased gradually from 2 to 6 days in the early passages to approximately 12 hours after the 190th passage. Despite the apparent increased infectivity with progressive passages, the hamster-adapted Newcastle virus of the 200th passage titered only slightly higher in 4-week-old hamsters than that of the 49th or 72nd passages. After the 92nd passage the hamster-adapted Newcastle disease virus was non-pathogenic for chickens when inoculated intramuscularly or subcutaneously.