EFFECT OF AGE ON LOUPING-ILL ENCEPHALITIS IN HAMSTER

Syrian hamsters developed symptoms of neurological disease following intracerebral inoculation with louping-ill virus at from 3 to 25 days of age, or intraperitoneal inoculation at from 3 to 10 days of age. In older animals inoculated intraperitoneally the disease was asymptomatic. The severity of neuron necrosis decreased as the period of inoculation by both routes increased to 14 days. Four day old hamsters inoculated intraperitoneally showed persistent viraemia and death at 7 or 8 days post inoculation. High titres of virus were found in the brain and there were spreading foci of cellular necrosis associated with P.A.S. positive granules. Older inoculated hamsters generally had a subclinical infection. Lower levels of viraemia were detected for about 6 days and the low titres of virus in the brains of 22 day old hamsters tended to disappear at about 11 days after inoculation. Vascular inflammatory foci of lymphocytes were seen from about 6 days after inoculation. © 1969.