Use of live and inactivated vaccines in the control of West Nile fever in domestic geese.

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.