Sunday, May 19, 2013
Rabies is a viral disease of mammals normally transmitted between animals by the bite of an infected animal. The virus affects the brain and is usually fatal. All warm-blooded animals are susceptible to rabies, but certain carnivorous mammals and bats are most likely to be sources of infection. Rabies is a relatively rare but uniformly fatal disease that is caused by a virus that attacks the nervous system.
The major host species for animal rabies in the United States has changed during the last 40 years with a marked decline of reported cases in dogs, cats, and foxes. At the same time, reported cases in skunks, raccoons, and bats have increased. In Idaho, the primary host species for rabies are bats.
In Idaho, rabid bats have been reported most frequently from the densely populated areas including Lewiston, Boise, Twin Falls, Pocatello and Idaho Falls. Rabid bats have been reported from many rural areas especially in the southern part of gthe state. Rabid bats are reported every year in Idaho, generally with between 10-20 cases per year.
Rabies virus is transmitted by contact with saliva of an infected animal, usually through a bite wound. The virus in the saliva of the infected animal enters the tissues of the victim when bitten by the rabid animal, and if the victim is susceptible, the virus travels slowly up nerve fibers to the brain. The virus multiplies and spreads to other parts of the brain, eventually causing a variety of signs in the infected animal. At the same time, the virus spreads from the brain to the salivary glands and is released in the saliva where it could be introduced by bite into another animal.
The virus can also be transmitted by contamination of cuts and abrasions of the skin with infected saliva or virus-infected tissues. Oral transmission by eating infected animals or tissues has also been demonstrated in certain animal species. Transmission by aerosol where animals and humans acquired rabies infections by breathing the air in bat caves has only been reported in Texas. Not all infected animals will have rabies virus in their saliva as some die before the virus leaves the brain, but the virus will rarely be present in the salivary glands or saliva without first occurring in the brain. With the possible exception of several species of bats, the virus is present in the saliva of the infected animal for no more than a few days before clinical signs appear.
All mammals, including humans, are susceptible. In Idaho, rabies occurs mainly in wild bats. Wild animals including bobcats and foxes in Idaho have been found with the bat form of rabies. Cats, dogs and livestock can also become infected with rabies if they are bitten by rabid wild animals, and they have not been vaccinated. Rodents such as rats, mice, gerbils, guinea pigs and squirrels are not likely to be infected with rabies. Herbivores such as deer, elk, and sheep are susceptible but unlikely to be infected with rabies.
The best way for the public to protect themselves is to avoid touching, handling or adopting wild or stray animals. All cats and dogs that venture outside and may have contact with wild animals should be vaccinated for rabies. Vaccination schedules and advice can be obtained from local veterinarians.
The first sign of rabies is usually a change in the animal’s behavior. Nocturnal animals like skunks, raccoons and bats may be out during the day. Rabid animals may stagger, tremble or seem weak (dumb rabies) or may appear agitated and excited or paralyzed and frightened (furious rabies). Sometimes, rabid animals do not show any signs of illness before death from rabies.
Most bats affected by rabies are found on the ground, unable to fly during daylight. But rabies should be considered if bats are encountered in newly opened cabins, or in rooms where people that are sleeping may not have been aware of the bat.
Any wild animal, especially carnivores or bats, which has bitten or contacted a person or domestic animal and which is showing aggressiveness without being provoked, or that is showing neurologic signs like seizures, staggering or circling should be considered as a rabies suspect.
Domestic or wild animals which exhibit the signs of rabies should be considered rabid, and if there is any risk of exposure to humans or domestic animals, the Idaho Department of Fish and Game, the Idaho Department of Health and Welfare or the local Health District Office should be notified so that the necessary precautions can be taken to retrieve the animal and get it sent to the laboratory for testing.
Caution must be taken in approaching a suspected rabid animal, since many rabid animals are very aggressive and can still bite even when they appear to be paralyzed. If the suspect animal is still alive, it should be killed as humanely as possible, without damage to the head. During euthanasia and handling of rabies suspects, care should be taken to avoid exposure to rabies. Rubber or latex gloves or a plastic bag turned inside out should be used to handle animals to avoid direct skin contact with the animal. The animal should be placed in a double plastic bag and placed in a leak proof container for transport to the laboratory.
The best protection against rabies is pre-exposure vaccination of persons at high risk of exposure to rabid animals, such as veterinarians, wildlife biologists, wildlife rehabilitators and animal handlers. Safe vaccines are available, but several injections in the arm over a few months’ period are required for initial protection against exposure. Information about pre-exposure immunization can be obtained through the local health department or a physician.
If a rabid animal is contacted, the exposed person should apply or receive first aid treatment. The immediate, thorough scrubbing of the exposed skin or body surface, including a bite wound, with soap or detergent and water, or water alone, is the most effective means of preventing infection with rabies virus. The patient should be seen by their physician as soon as possible to determine if rabies vaccine and antiserum are required. If the exposed person is known to have been previously immunized and has antibody against rabies, the physician, at his discretion, may reduce the vaccine treatment.
The vaccination of pets is important in reducing potential human exposure to rabies since pets are more likely than people to come in contact with rabid wild animals and can subsequently expose people. Appropriate vaccines should be administered to pets by a veterinarian. None of the animal vaccines have been approved for use in wild animals. In Idaho it is illegal to possess striped skunks, foxes or raccoons without proper permits, primarily due to concerns about rabies.