Abstract
Results of experiments evaluating the efficacy of three immunization strategies for the prevention of West Nile virus (WNV) encephalitis are reported. Immunization strategies evaluated included a killed virus veterinary vaccine, a live attenuated chimeric virus vaccine candidate, and passive immunization with WNV-immune serum; all were tested by using a hamster model of the disease. Each product protected the animals from clinical illness and death when challenged with a hamster-virulent wild-type WNV strain 1 month after initial immunization. The live attenuated chimeric virus vaccine candidate induced the highest humoral antibody responses, as measured by hemagglutination inhibition, complement fixation, and plaque reduction neutralization tests. Although the duration of protective immunity was not determined in this study, our preliminary results and the cumulative experience of other virus vaccines suggest that the live attenuated chimeric virus provides the longest lasting immunity.
Highlights
After the appearance of West Nile virus (WNV) in North America and the resulting human and equine cases of encephalitis, considerable efforts have focused on developing vaccines against this emerging viral pathogen
Convalescent-phase sera from some of these animals were used to prepare the WNV immune serum used in the passive immunization experiments described below
Each of the three immunization products evaluated in this study protected hamsters from clinical encephalitis and death upon subsequent challenge with the virulent wild-type WNV strain NY385-99
Summary
After the appearance of West Nile virus (WNV) in North America and the resulting human and equine cases of encephalitis, considerable efforts have focused on developing vaccines against this emerging viral pathogen. A number of different WNV vaccine candidates have been recently described and are in various stages of testing [1,2,3,4]. A formalin-inactivated veterinary vaccine (West Nile Virus Vaccine, Killed, Fort Dodge Animal Health, Fort Dodge, IA) was conditionally licensed by the U.S Department of Agriculture in August 2001 and has already been used in equines and exotic zoo birds in some areas of the country. We report the results of studies evaluating the efficacy of the killed veterinary vaccine, a live attenuated chimeric virus candidate, and passive immunization with immune serum for preventing WNV encephalitis in a hamster model of the disease [5,6]
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