Rabies is an acute disease, caused by a virus (rhabdovirus), that can infect all warm-blooded animals, and is usually fatal. Certain carnivorous mammals and bats are the usual animal hosts. Rabies occurs throughout most of the world; only Australia and Antarctica are free of it. Most human cases have been contracted from rabies-infected dogs. In the United States, human cases have decreased to an average of one person per year (75% of cases are acquired outside the United States). Reduction in human rabies is likely linked with the intensive control of dog rabies during the 1950s and 1960s through massive vaccination campaigns, stray dog control programs, and improvement in human treatment following exposure. Nevertheless, thousands of people in the United States continue to receive treatment every year for possible exposure to rabies virus by animal bites. Most of the treatments are still due to dog and cat bites; however, these pet species have the lowest occurrence of reported rabies among all animal species tested.
Rabies in wildlife increased dramatically during the 1960s and now accounts for most of the reported animal rabies cases (91% in 1991). Some of the increase in reporting was due to real increases in the number of cases, and some was due to an increased awareness of wildlife rabies, particularly in striped skunks, raccoons, and bats. In 1991, 6,975 cases of animal rabies were reported in 49 states, the District of Columbia, and Puerto Rico. Raccoons (44.2%), striped skunks (29.7%), and various species of bats (9.9%) continued to be the major hosts. Red and gray foxes (4.6%), other wildlife species (2.8%), and domestic animals (8.9%) comprise the remainder of hosts. During the last 2 years, raccoons replaced striped skunks as the major wildlife host in the United States because of the continued expansion of raccoon rabies in the northeastern United States. Animal cases are reported throughout the year, although the number of cases reported reaches a seasonal peak for skunks in March and April, for raccoons in April, and for bats in August.
Clinical Signs. Rabies is considered almost 100% fatal once clinical signs develop. The disease progresses rapidly following the appearance of clinical signs, and the animal dies within a few days. Although abnormal behavior is not diagnostic for rabies (other diseases, like distemper, cause similar behavioral changes), atypical behavior and signs develop following brain infection, and rabies should be suspected whenever wild animals display unusual behavior.
Infected animals usually display either “furious” or “dumb” rabies, although some animals progress through both stages. Skunks, raccoons, foxes, and other canids usually have furious rabies and are unduly aggressive before convulsions and paralysis set in. Some animals, however, have dumb rabies and proceed to tremors and convulsions without agitation or aggression. Other behavioral changes include friendliness or loss of fear, appearance in the daytime for some typically nocturnal species (skunks, bats), unprovoked attacks on anything that moves (including inanimate objects), bewilderment, and aimless wandering. Unusual barking, crying, and frothing at the mouth are additional signs, which are the result of paralysis of the throat muscles. Occasionally, rabid bats are encountered prostrate or fluttering on the ground, unable to fly; they should be handled with care because they can still bite and transmit rabies. Some rabid bats, particularly solitary species like the hoary bat, are aggressive and have been known to attack people. In domestic animals, rabies should be suspected if there is any change in normal habits, such as sudden change in disposition, failure to eat or drink, running into objects, or paralysis.
Transmission. Rabies virus is transmitted primarily via the saliva during the bite of a rabid animal. However, other methods of transmission are possible. Accidental exposure of wounds or cuts to the saliva or tissues of infected animals can occur. The virus is also present in various body organs of infected animals, especially the brain and salivary glands, which poses a health hazard to persons who are field dressing or performing necropsies on these animals. In addition, aerosol exposure has occurred, although rarely, in caves containing very large populations of infected bats. Transmission between animals also occurs by ingestion of infected tissues and by transplacental passage to offspring.
Avoid exposure to any sick or dead animals that are suspected to have rabies. Handle any dead animal with gloves or with a plastic bag that can be turned inside-out to cover and contain the animal. Avoid direct skin contact with the animal. For large animals such as skunks and raccoons, remove the head cautiously and seal it in a plastic bag, avoiding contact or aerosol exposure. Seal the whole animal or head inside an additional plastic bag (double) and keep it cool at all times. Do not freeze the specimen unless a delay of several days is anticipated before it is examined for rabies. Disinfect gloves or knives that were in contact with the animal with a strong detergent or bleach or dispose of them.
Prevention and Treatment. The best treatment for rabies is prevention. Individuals at high risk of exposure to rabies, such as wildlife biologists, game wardens, animal control officers, animal handlers, and veterinarians should be vaccinated before potential exposure. Safe and highly effective vaccines are available through a physician or the local health department.
First aid should immediately be provided to a person who has been bitten by or had contact with a potentially rabid animal. Scrub the exposed site, including bite wounds, with soap and water or water alone and flush thoroughly. Then apply a strong first aid solution (iodine) or cream. First aid treatment is the most effective method of preventing infection by the rabies virus but should not preclude medical attention from a physician, hospital emergency room, or the local health department. Contact your physician or health department as soon as possible to determine dosage of rabies vaccine and whether antirabies serum is required. Inform the health care professionals about the rabid animal and the circumstances of the exposure (species of animal involved and its behavior, if the attack or bite from the animal was provoked, and what type of first aid was administered).
