Scientists from Pennsylvania are pleased with initial studies of a live, but greatly weakened, rabies virus vaccine designed for the immunization of raccoons, stray dogs, and other wildlife.

Lab studies indicate that the vaccine is stable, doesn’t cause disease, produces strong immunity, and can be mass-produced, Dr. Marie-Luise Dietzschold of Molecular Targeting Technologies in West Chester and colleagues at Thomas Jefferson University in Philadelphia report.

Over the last 10 years, oral immunization of wildlife with live vaccines such as the vaccinia-rabies virus vaccine known as VRG has proven to be a safe and effective way to control rabies in the U.S, the researchers note in the medical journal Vaccine.

More than 15 million VRG-containing baits have been distributed to local rabies-control programs, with no adverse effects to humans.

However, in September 2000, an individual who came in contact with the vaccine developed severe local inflammatory reactions, raising concerns about the safety of VRG and fueling interest in developing safer rabies vaccines for wildlife.

To this end, Dietzschold’s group genetically engineered a vaccine that overexpresses the rabies virus G protein. They found that mice immunized with the vaccine developed high levels of protective immunity.

Other tests showed that the vaccine is safe, and survives in the environment even with long exposure to extremes of temperature.

The new vaccine “is an excellent candidate for immunization of stray dogs and wildlife,” Dietzschold and colleagues conclude, adding that it has recently been shown to protect dogs against a lethal dose of rabies virus.

SOURCE: Vaccine, December 2004.