Rabies is a severe viral disease that attacks the central nervous system of mammals, including humans. The virus, typically transmitted through the saliva of an infected animal, travels along the nerves to the brain, causing inflammation of the brain and spinal cord. Once clinical symptoms appear, the infection is almost universally fatal, making prevention and identifying potential carriers a matter of public health importance.
Principal Wildlife Carriers
Wildlife species maintain the continuous cycle of rabies in the environment, acting as reservoirs that sustain the virus. In the United States, four groups of wild mammals are responsible for the vast majority of reported cases: bats, raccoons, skunks, and foxes. The specific variant of the virus often becomes adapted to one of these species, creating distinct terrestrial cycles across different geographic regions.
Bats are the species most commonly associated with human rabies cases in the US, accounting for about 70% of fatal infections. Their small bite marks can be easily missed, and their nocturnal nature means human contact can occur without a person realizing they have been exposed. The virus is maintained within bat populations and is scattered widely across the country.
Raccoons are the most frequently reported rabid terrestrial animal in the eastern US, while skunks dominate reported cases in the north-central and south-central states. These animals are high-risk because their behaviors often bring them into close proximity with human habitats, leading to potential confrontations with people or domestic pets. Foxes, including red and gray species, also serve as a significant regional reservoir, particularly in parts of Alaska, Arizona, and Texas. These four species are responsible for over 90% of all reported animal rabies cases in the US annually.
Domestic Animal Vulnerability and Prevention
Domestic animals, such as dogs, cats, and ferrets, become vulnerable to rabies almost exclusively through contact with infected wildlife carriers. Historically, dogs were the primary source of human rabies infections globally, and they still cause 99% of human cases in regions of Asia and Africa. Successful vaccination and animal control programs in the United States have eliminated the canine-specific rabies virus variant, shifting the disease burden almost entirely to wildlife.
The widespread vaccination of household pets acts as a crucial barrier, preventing the virus from jumping from wildlife into the human population. Many state and local laws mandate rabies vaccination for domestic dogs, cats, and sometimes ferrets, recognizing its importance as a public health tool. This legal requirement ensures that a buffer zone exists between the wild animal reservoir and people.
Livestock, including cattle and horses, are also susceptible to infection, typically after being bitten by a rabid wild animal. Unvaccinated stray or feral dogs and cats pose a continuous risk because they can interact with wildlife and then transmit the disease to people who attempt to rescue or handle them. Maintaining current vaccination status for all companion animals is the most effective way to prevent the disease from spreading to humans.
Animals Rarely or Never Infected
Certain animals are often incorrectly feared as rabies carriers, but scientific evidence shows they pose a minimal risk. Small rodents, including mice, rats, squirrels, chipmunks, hamsters, gerbils, and guinea pigs, are very rarely found to be infected with rabies. Rabbits and hares are also not known to transmit the disease to humans in the US.
These smaller animals are unlikely to survive an attack from a rabid predator long enough to transmit the virus themselves. If bitten, they often succumb to the injury or the infection quickly, preventing them from becoming circulating vectors. Therefore, bites from these animals rarely require post-exposure prophylaxis unless the circumstances are highly unusual.
The Virginia opossum is particularly resistant to rabies, which is attributed to its naturally lower body temperature, typically ranging from 94 to 97 degrees Fahrenheit. This cooler internal environment is less conducive for the rabies virus to thrive and replicate efficiently. Although opossums are mammals and theoretically capable of contracting the virus, confirmed cases of rabid opossums are exceedingly rare.