Rabies in dogs

Rabies is a fatal disease that occurs in nearly all warm-blooded animals, although rarely in rodents. In the United States, vaccination programs for dogs and other domestic animals have been remarkably effective. This has greatly reduced the risk of rabies in pets and their owners.

The major wildlife reservoirs for rabies (with substantial overlap) are the skunk in the Midwest, Southwest, and California; raccoons in New England and the East; foxes in New York, neighboring eastern Canada, Alaska, and the Southwest; and coyotes and foxes in Texas. Bats, which are distributed widely, also carry rabies.

The main source of infection for humans outside the United States continues to be a bite from an infected dog or cat. In India, for example, a country that lacks an effective rabies control program, it is estimated that several thousand people die of rabies each year. Travelers to countries where rabies is endemic should be aware of the risk of dog bites.

The rabies virus, which is present in infected saliva, enters the body at the site of a bite. Saliva on an open wound or disrupted mucous membrane also constitutes exposure. The average incubation period in dogs is two to eight weeks, but it can be as short as one week or as long as one year. The virus travels to the brain along the nerves. The more distant the bite is from the brain, the longer the period of incubation. The virus then travels back along the nerves to the mouth. Entry into the salivary glands occurs less than 10 days before symptoms appear—which means animals can be infectious before they show any signs of rabies (this is unusual but is possible).

Dogs can show either of two versions: the aggressive form, where they attack and act very boldly aggressive; or the “dumb” form, where they are ataxic (an inability to coordinate voluntary muscle movements) and may walk into objects. In both cases, you may notice extensive drooling due to paralysis of the muscles used for swallowing.

Any dog who is bitten by an animal who is not absolutely known to be free of rabies must be assumed to have been exposed to rabies, until proven otherwise. The National Association of State Public Health Veterinarians recommends that if the dog has previously been vaccinated against rabies, revaccinate immediately and observe the dog under leash confinement at home for 45 days. If the dog has not been vaccinated, either euthanize the animal or confine him under strict quarantine without direct handling by humans or contact with other animals for six months. Vaccinate him one month before he is released (that is, at five months after the bite). If this seems harsh, keep in mind that it would not have been necessary if the pet had been vaccinated. Different states may have their own specific quarantine and vaccination regulations for dogs who have been exposed to rabies.

Treatment: If you or your dog are bitten by any animal of unknown rabies status, it is extremely important to vigorously cleanse all wounds and scratches, washing them thoroughly with soap and water. Studies in animals have shown that prompt local wound cleansing greatly reduces the risk of rabies. The wound should not be sutured.

Prophylaxis in a previously vaccinated dog consists of a booster shot, which should be given as soon as possible (and certainly within 14 days of the lick or bite). Vaccination is not effective once signs of rabies infection appear.

The introduction of inactivated vaccines grown in human diploid cell cultures has improved the effectiveness and safety of postexposure vaccination for humans. Assuming the human bite victim did not have a preexposure rabies immunization, both passive rabies immune globulin and human origin active diploid cell vaccine should be given.

Prevention: Dogs should be vaccinated against rabies as early as 3 to 6 months of age, with a booster shot a year later and then again every one to three years, depending on the vaccine used and local and state ordinances.

Regardless of the dog’s age at the initial vaccination, a second vaccination should be given one year later.

When traveling with your pet, be sure to bring along proof of inoculation against rabies—ideally, a vaccination certificate signed by a veterinarian. If you enter a rabies quarantine area and are unable to prove your dog has been vaccinated, your pet could be impounded. In addition, you could be subject to a heavy fine.

Public health considerations: Do not pet, handle, or give first aid to any dog suspected of having rabies. All bites of wild animals, whether provoked or not, must be regarded as having rabies potential. If your dog is bitten by a wild animal or a domestic animal whose rabies status is unknown, wear gloves when handling your pet to clean his wounds. The saliva from the animal that is in and around the bite wound can infect a person if it gets into a cut or onto a mucous membrane.

Preventive vaccinations are available for high-risk groups of humans, including veterinarians, animal handlers, cave explorers, and laboratory workers.

Early laboratory confirmation of rabies in an animal is essential so that exposed humans can receive rabies prophylaxis as quickly as possible. The animal must be euthanized and his head sent in a chilled (not frozen) state to a laboratory equipped to diagnose rabies. Rabies is confirmed by finding rabies virus or rabies antigen in the brain or salivary tissues of the suspected animal. If the animal cannot be captured and his rabies status can’t be verified, you need to consult your physician, who may suggest prophylactic vaccinations.

Whenever you have physical contact with an animal who may conceivably be rabid, immediately consult your physician and veterinarian, and also notify the local health department. Biting dogs who appear healthy should be confined and kept under observation for 10 days. This is true even if the dog is known to be vaccinated for rabies.