Rabies still presents a public health threat causing more than 70,000 human deaths each year. Humans get infected with the rabies virus mostly through bites from rabid domestic and wildlife animals. Controlling rabies virus infection in domestic and wildlife animals, therefore, not only reduces the mortality in these animals but also reduces the risks of human exposure. Pre-exposure vaccinations for people who are constantly at risk further prevent human rabies, as do post-exposure immunizations for people who are bitten by rabid or suspected rabid animals. Currently, inactivated rabies virus vaccines are used to immunize domestic animals, particularly pets. Purified and inactivated rabies virus vaccines are used for humans in the pre- or post-exposure settings. A recombinant vaccinia virus expressing rabies virus glycoprotein (VRG) has been used to control rabies in wildlife. Although these vaccines are effective, annual vaccinations are required to maintain adequate immunity in pets. For humans, multiple doses of the inactivated tissue culture vaccines are required to stimulate optimal immune responses. Furthermore, current tissue culture vaccines are expensive; thus most people in need of vaccinations (in developing countries) cannot afford them. Hence, there is a need to develop more efficacious and affordable rabies virus vaccines. We propose to develop avirulent live rabies virus vaccines by constructing mutant virus with reduced ability to spread in the nervous system (by mutation of the glycoprotein G) and with reduced rate of viral replication (by mutation and/or rearrangement of genes within the rabies virus genome). This will be accomplished by using the state-of-the-art reverse genetics technology. Our proposal is based on recent findings from us as well as others showing the following. 1) Mutation of the phosphorylated serine at 389 of the N to alanine reduced the rate of viral replication by more than five-fold and virus production by more than 10,000 times. 2) Mutation of the G at residue 333 reduced dramatically the virulence and pathogenicity of rabies virus. 3) Rearrangement of the genes within the vesicular stomatitis virus genome resulted in attenuation and enhancement of immune responses. The rationale for constructing mutated or rearranged rabies viruses is that such altered viruses most likely will be further attenuated than currently available attenuated rabies virus (still induce rabies in neonatal animals). If the further attenuated rabies viruses no longer causes diseases in animals at any age and by any route of inoculation, yet remain immunoqenic, they can be developed as modified live rabies vaccines for humans and animals.
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