Address for correspondence: Mertyn Malkinson, Ph.D., Kimron Veterinary Institute, Beit Dagan, Israel 50250. Voice: +972.3.968.1691; fax: +972.3.968.1739.
martinm{at}moag.gov.il
The recent epizootic of West Nile fever in Israel affected predominantly
young domestic geese between three and eight weeks old. Clinically,
the birds presented paralytic signs while morbidity and mortality
were severe in affected flocks. The condition was encountered
from early September through late November on goose farms located
throughout the country. Losses incurred by goose flocks were
sufficiently great as to warrant investigation of ways to protect
young geese against the neurological form of the disease. We
have conducted a series of vaccination trials in which three-week
old geese were immunized with an attenuated, commercial flavivirus
vaccine derived from Israel turkey meningoencephalitis virus
(TME). Birds were challenged two weeks later with a low Vero
cell passage of West Nile virus by the intracerebral route.
In a second group of experiments, inactivated and live TME vaccines
were given in tandem at an interval of two weeks and challenged
two weeks later. The third vaccination trial was based on West
Nile virus (WNV) harvested from infant mouse brain, inactivated
with formalin and oil adjuvanted. A single injection given either
subcutaneously or intramuscularly resulted in 75% protection
of the vaccinated groups, while two injections spaced two weeks
apart resulted in 94% protection. Groups of geese, vaccinated
at the farms and challenged under controlled conditions in the
laboratory, showed levels of protection ranging from 39% to
72% for TME vaccine and 52% and 80% for WNV vaccine. The lower
levels of protection are attributable to flocks being affected
with intercurrent infections at the time of vaccination.
