Rabies in animals
In animals, rabies is a viral zoonotic neuro-invasive disease which causes inflammation in the brain and is usually fatal. Rabies, caused by the rabies virus, primarily infects mammals. In the laboratory it has been found that birds can be infected, as well as their cell cultures. The brains of animals with rabies deteriorate. As a result, they tend to behave bizarrely and often aggressively, increasing the chances that they will bite another animal or a person and transmit the disease.
In addition to irrational aggression, the virus can induce hydrophobia —wherein attempts to drink water or swallow cause painful spasms of the muscles in the throat or larynx—and an increase in saliva production. This aids the likelihood of transmission, as the virus multiplies and accumulates in the salivary glands and is transmitted primarily through biting. The accumulation of saliva can sometimes create a "foaming at the mouth" effect, which is commonly associated with rabies in animals in the public perception and in popular culture; however, rabies does not always present as such, and may be carried without typical symptoms being displayed.
Rabies kills an average of 70,000 people a year worldwide. Dogs are the primary cause of the virus infecting humans in most parts of the world, but in some countries, such as the United States and Canada, bats are the principal vector.
Stages of disease
Three stages of rabies are recognized in dogs and other animals.- The first stage, known as the prodromal stage, is a one- to three-day period that occurs once the virus reaches the brain, and enters the beginning of encephalitis. Outwardly, it is characterized by behavioral changes such as restlessness, deep fatigue, and pain indications such as self-biting or itching. Some animals demonstrate more social behavior, while others conversely self-isolate; this is an early warning sign of the pathogen changing the hosts’ behavior to speed up transmission. Physical shifts such as fever, or nausea may also be present. Once this stage is reached, treatment is usually no longer viable. The onset of the prodromal stage can vary significantly, which can be attested to factors such as the strain of the virus, the viral load, the route of transmission, and the distance the virus must travel up the peripheral nerves to the central nervous system. The incubation period can be between months to years in humans but typically averages down to weeks or as little as a day in most mammals.
- The second stage is the excitative stage, which lasts three to four days. It is this stage that is often known as furious rabies due to the tendency of the affected animal to be hyperreactive to external stimuli and bite at anything near.
- The third stage is the paralytic or "dumb" stage and is caused by damage to motor neurons. Incoordination is seen due to rear limb paralysis and drooling and difficulty swallowing is caused by paralysis of facial and throat muscles. This disables the host's ability to swallow, which causes saliva to pour from the mouth. This causes bites to be the most common way for the infection to spread, as the virus is most concentrated in the throat and cheeks, causing major contamination to saliva. Death is usually caused by respiratory arrest.
Treatment
Mammals
Bats
Bats throughout North and South America carry the classical rabies virus, while in other parts of the world they carry other lyssaviruses. Rabies in bats was first closely studied in Trinidad in the West Indies. This island was experiencing a significant toll of livestock and humans alike to rabid bats. In the 10 years from 1925 and 1935, 89 people and thousands of livestock had died from it—"the highest human mortality from rabies-infected bats thus far recorded anywhere."In 1931, Dr. Joseph Lennox Pawan of Trinidad in the West Indies, a government bacteriologist, found Negri bodies in the brain of a bat with unusual habits. In 1932, Dr. Pawan discovered that infected vampire bats could transmit rabies to humans and other animals. In 1934, the Trinidad and Tobago government began a program of eradicating vampire bats, while encouraging the screening off of livestock buildings and offering free vaccination programs for exposed livestock.
After the opening of the Trinidad Regional Virus Laboratory in 1953, Arthur Greenhall demonstrated that at least eight species of bats in Trinidad had been infected with rabies; including the common vampire bat, the rare white-winged vampire bat, as well as two abundant species of fruit bats: Seba's short-tailed bat and the Jamaican fruit bat.
Recent data sequencing suggests recombination events in an American bat led the modern rabies virus to gain the head of a G-protein ectodomain thousands of years ago. This change occurred in an organism that had both rabies and a separate carnivore virus. The recombination resulted in a cross-over that gave rabies a new success rate across hosts since the G-protein ectodomain, which controls binding and pH receptors, was now suited for carnivore hosts as well.
Cryptic rabies refers to unidentified infections, which are mainly traced back to particularly virulent forms in silver-haired and tricolor bats. These are generally rather reclusive species, so the relative degree of infection and similarities between their strains is unusual. Both are independent rabies reservoir species but make up a large number of bites. This absence of typical symptoms can often cause major delays in treatment and diagnosis in both animals and humans, as the required post-exposure prophylaxis and dFAT tests may not be run.
Bears
It is extremely rare for bears to be rabid, although it is possible. In 2025, a bear which attacked a man in Pennsylvania was confirmed to be rabid. The first confirmed rabies case in a polar bear occurred in 1989 in Northwest Territories in Canada.Cats
In the United States, domestic cats are the most commonly reported rabid animal. In the United States,, between 200 and 300 cases are reported annually; in 2017, 276 cats with rabies were reported., in every year since 1990, reported cases of rabies in cats outnumbered cases of rabies in dogs.Cats that have not been vaccinated and are allowed access to the outdoors have the most risk for contracting rabies, as they may come in contact with rabid animals. The virus is often passed on during fights between cats or other animals and is transmitted by bites, saliva or through mucous membranes and fresh wounds. The virus can incubate from one day up to over a year before any symptoms begin to show. Symptoms have a rapid onset and can include unusual aggression, restlessness, lethargy, anorexia, weakness, disorientation, paralysis and seizures. Vaccination of felines by a veterinarian is recommended to prevent rabies infection in outdoor cats.
Cattle
In cattle-raising areas where vampire bats are common, fenced-in cows often become a primary target for the bats, due to their easy accessibility compared to wild mammals. In Latin America, vampire bats are the primary reservoir of the rabies virus, and in Peru, for instance, researchers have calculated that over 500 cattle per year die of bat-transmitted rabies.Vampire bats have been extinct in the United States for thousands of years, thus United States cattle are not currently susceptible to rabies from this vector. However, 2 cases of rabies in dairy cows in the United States, in which people have been exposed through unpasteurized milk, have occurred since 1996. In both of these incidents it is likely that the cows received the virus from raccoons. In 1998, a cow with rabies was milked 12 times within the week before it died. This milk was mixed with milk from other cows and distributed for consumption. 66 people who drank the milk were found and all received PEP. The other incident occurred in 1996 and 14 people were treated with PEP.
Vaccination programs in Latin America have been effective at protecting cattle from rabies, along with other approaches such as the culling of vampire bat populations.
Coyotes
Rabies is common in coyotes, and can be a cause for concern if they interact with humans.Dogs
s represent by far the most common animal involved in the transmission of rabies to humans. At a global level, dog bites and scratches are responsible for 99% of human rabies cases.Rabies has a long history of association with dogs. The first written record of rabies is in the Codex of Eshnunna, which dictates that the owner of a dog showing symptoms of rabies should take preventive measure against bites. If a person was bitten by a rabid dog and later died, the owner was fined heavily.
Dog mediated rabies is defined as "any case caused by rabies virus maintained in the dog population independently of other animal reservoir species, as determined by epidemiological studies". Most Western countries have eliminated dog mediated rabies, but it remains prevalent in developing countries. In countries where dog-mediated rabies has been eliminated, unvaccinated dogs can still contract rabies from being bitten by a rabid animal, such as a fox, coyote, jackal, raccoon and skunk. In the United States, in 2022, 50 dogs tested positive for rabies.
Dog-mediated rabies is still very common in countries in Africa and Asia. In India, dog-mediated rabies is endemic; with rabies being primarily transmitted to humans from dogs, followed by cats, jackals, mongooses, and others.
The incubation period from rabies in dogs can be anywhere from a week to several months. Many dogs develop dumb rabies which can go ignored and many other dogs die before being diagnosed. Symptoms of the disease in dogs include, personality changes, raised temperature, dilated pupils, a nictitating membrane, and excessive salivation.