Know your Immunity – Stay Protected from Rabies Rabies is a deadly but preventable viral disease that affects the brain and nervous system. Once symptoms appear, it is almost always fatal — that’s why prevention and early monitoring are crucial. The Rabies Virus Antibody IgG Test measures the level of specific antibodies (IgG) in your blood that protect you against the rabies virus. This helps ensure your vaccination has worked and that you are still protected.