Animals get rabies almost exclusively through bites from other infected animals. The rabies virus lives in saliva, and when an infected animal bites another, the virus enters the wound and begins working its way toward the brain. This cycle has persisted for centuries across wildlife populations worldwide, with different species serving as the primary carriers in different regions.
How a Bite Transmits the Virus
Rabies virus concentrates in the saliva of infected animals. When a rabid animal bites, its teeth puncture the skin and deposit saliva containing the virus directly into muscle tissue. From there, the virus can replicate in muscle cells or immediately latch onto nearby nerve endings. Once it reaches a nerve, it begins traveling toward the brain at roughly 3 millimeters per hour, crawling along the nerve fibers like a slow-moving train on a track.
This is why bite location matters so much. A bite on the face or neck, close to the brain and packed with nerve endings, leads to a much shorter incubation period than a bite on a paw or leg. In dogs, most clinical cases develop within 21 to 80 days after exposure, but the timeline can stretch considerably longer depending on where the bite occurred and how much virus was deposited.
Once the virus reaches the brain, it multiplies rapidly and then travels back outward along nerves to the salivary glands. This final step is what makes the infected animal capable of spreading the virus to the next host. The entire cycle, from bite to brain to saliva, is what keeps rabies circulating in animal populations.
Which Animals Carry Rabies
Different wildlife species serve as reservoirs for the virus in different parts of the world. In the United States, the major carriers are bats, raccoons, skunks, and foxes. Bats are the most widespread, found carrying rabies in every U.S. state except Hawaii. Raccoons maintain the virus across the eastern seaboard from Canada to Florida. Skunks are the primary reservoir across most of the Midwest and West, while foxes carry it in the Southwest (gray foxes) and Alaska (arctic foxes). In Puerto Rico, mongooses are the main wildlife reservoir.
Globally, domestic dogs are by far the most important carrier. Dogs cause 99% of human rabies deaths worldwide, according to the World Health Organization. In much of Africa and Asia, where stray dog populations are large and vaccination coverage is low, dog-to-dog transmission keeps the virus cycling through communities. Dogs also bridge the gap between wildlife and people: a dog bitten by a rabid raccoon or bat can then pass the virus to its owner or other pets.
Any mammal can contract and transmit rabies, but smaller mammals like squirrels, rabbits, and mice are rarely found infected. Their size means they’re unlikely to survive an attack from a larger rabid animal long enough to develop the disease themselves.
Non-Bite Transmission Is Extremely Rare
While bites account for the vast majority of transmission, the virus can technically enter through any break in the skin or through mucous membranes (eyes, nose, mouth) if they come into contact with infected saliva or nervous tissue. A deep scratch from a rabid animal could theoretically transmit the virus if saliva was present on the claws, though this is uncommon.
Aerosol transmission, where the virus travels through the air, has been demonstrated in laboratory settings but has never been well documented in nature. Cases of human rabies linked to bats where no bite was remembered are now thought to involve bites that were simply too small to notice. Bat teeth are tiny enough that a sleeping person might not realize they were bitten.
One unusual route does exist: organ and tissue transplantation. Since the virus lives in nerve-rich tissues, transplanted organs from an unknowingly infected donor can transmit rabies to recipients. The CDC has documented four such events in the United States since 1978, affecting 13 recipients total. This remains vanishingly rare but illustrates how the virus can hide in the body during its long incubation period.
Why the Virus Dies Quickly Outside a Host
Rabies virus is fragile once it leaves an animal’s body. It is no longer infectious once the material containing it dries out, and it breaks down within minutes at temperatures above 50°C (122°F). Even at room temperature, the virus survives no more than a few hours. Sunlight destroys it quickly. This means animals cannot pick up rabies from contaminated surfaces, water bowls, or the environment. Transmission requires direct, fresh contact with an infected animal’s saliva or nervous tissue.
When an Infected Animal Becomes Contagious
An animal isn’t contagious for the entire incubation period. The virus only appears in saliva after it has completed its journey to the brain and then traveled back out to the salivary glands. This means an animal that was bitten last week and is incubating the virus but showing no symptoms is almost certainly not yet shedding virus in its saliva. The dangerous window begins shortly before symptoms appear and lasts until the animal dies, which typically happens within days of the first signs of illness.
This biology is the basis for the standard 10-day quarantine observation period used for dogs, cats, and ferrets that have bitten someone. If the animal is still healthy after 10 days, it was not shedding virus at the time of the bite.
How Vaccination Breaks the Chain
Vaccination is the main tool for preventing rabies from spreading through animal populations. For domestic pets, the first rabies vaccine is typically given between three and six months of age and provides one year of protection. After the initial dose, booster shots given with a three-year vaccine extend immunity for three years at a time. Animals with unknown vaccination histories are treated as if they’ve never been vaccinated and given a one-year duration for their first dose.
Wildlife vaccination programs also play a role. In parts of the U.S. and Europe, oral vaccine baits are distributed by air over large areas to immunize raccoons, foxes, and coyotes. These programs have successfully pushed raccoon rabies back from expanding westward and eliminated fox rabies from several European countries. Without vaccination, the virus simply continues cycling through susceptible populations indefinitely, passed from one animal to the next through bites, generation after generation.