What is rabies?
Rabies is a relatively rare but deadly disease that is caused by a virus that attacks the nervous system.
Rabies is transmitted by contact with saliva of an infected animal, usually through a bite wound.
Rabies virus is not transmitted by blood or the spray of skunks
Which animals might have rabies?
All mammals, including humans, are susceptible. In Colorado, rabies occurs mainly in wild bats and skunks, and less frequently in foxes, raccoons, bobcats, coyotes, etc.
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, AND to keep pets currently vaccinated through their local veterinarian.
What are the signs of rabies?
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. Rabid animals may appear agitated and excited or paralyzed and frightened. Sometimes, rabid animals do not show any signs of illness before death from rabies.
Bats may be found on the ground, unable to fly.
Which animals should be submitted for rabies testing?
Any wild animal that has bitten or contacted a person or domestic animal.
Any carnivore that is showing neurologic signs (for example: seizures, staggering or circling)
Rabies is a viral disease normally transmitted by the bite of an 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 more likely to be sources of infection.
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, and the geographical distribution of rabies in these species has expanded. In Colorado and Wyoming, similar changes in the host species have occurred, except that rabies in raccoons has remained rare.
In Colorado, rabid bats have been reported most frequently from the densely populated counties, particularly around the Denver metropolitan area, although they have been reported from 27 counties and all sections of the state. Typically rabid bats are reported every year in Colorado with Boulder, Denver, El Paso and Larimer Counties having the highest number of rabies-positive bats each year. Other than rabies in bats each year, rabies in other species had been uncommon until 2007. In 2007, a rabies positive coyote and skunk were reported from Prowers County, and subsequent positive skunks from Washington, Mesa and Las Animas Counties also were detected. All were diagnosed with “South Central skunk strain” rabies, except the skunk from Mesa County, which could be strain typed due to the condition of the tissue. In 2008, 18 of 89 skunks positive with skunk strain rabies were submitted from Arapahoe, Baca, Powers, Cheyenne and Kiowa Counties. An additional rabies-positive skunk was found in Denver County that had bat strain rabies. In addition, a skunk strain rabies positive raccoon (first positive raccoon in Colorado since 1963) and a skunk strain rabies positive house cat (first positive cat in Colorado since 1985) were found in Cheyenne County.
The numbers of rabies-positive animals increased in 2009 with 103 animals representing five species being reported. Skunks were the most numerous (37) and were found in ten Counties east of I-25. Those counties were: Kiowa, Kit Carson, Lincoln and Prowers Counties (1 each); Otero County (2); Elbert, Arapahoe and Yuma Counties (5 each); El Paso and Morgan Counties (8 each). In addition rabid red fox were found in Prowers and El Paso Counties (1 each) and one mountain lion from El Paso County. El Paso County also reported a horse that tested positive for rabies. Rabies in bats was reported at 62 from 13 counties, similar to numbers reported in previous years.
To date (5/20/2010) the number of rabies cases in Colorado in 2010 is significantly higher than found during the same time period for 2009. A total of 43 rabies positive animals have been diagnosed, including 38 skunks, one horse, one muskrat, one mule deer, one red fox and one cat.
Rats, mice, squirrels and other rodents have been examined over the years, but have rarely been found to be rabid.
Rabies Virus and Transmission
Rabies virus in the saliva of the infected animal enters the tissue of the victim when bitten by the rabid animal. If the victim is susceptible, the virus travels slowly up nerve fibers to the part of the brain that controls the area bitten. 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 to be introduced by bite into another animal, thus perpetuating the virus in nature.
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. No arthropod vector is involved in the transmission of rabies virus. Not all infected animals will have rabies virus in their saliva as some die before the virus leaves the brain. It is important to note that 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. Rabies is not transmitted by the spray from skunks.
The length of the incubation period (period from the time the animal is bitten until clinical signs appear) varies from about ten days to several months and, in some cases, even longer. However, it usually takes 2-3 weeks. Once signs develop the disease progresses rapidly, and the animal dies within a few days. Signs of rabies are quite variable, and the type of behavior displayed cannot be regarded as diagnostic. Rabies should be suspected, however, whenever atypical behavior is observed in wild animals. Such behavior includes friendliness or loss of fear, unprovoked attacks, undue aggressiveness, bewilderment or, for some species, appearance in the daytime. Rabid bats will frequently be found fluttering on the ground unable to fly, and they may be aggressive when approached. One should be suspicious of bats flying during daylight hours because that is unusual behavior, although they could have been disturbed from their roosting site. In domestic animals (pets and livestock), a change in disposition or normal habits, such as failure to eat or drink, unusual behavior, or paralysis should cause one to suspect rabies. There is no clear distinction between the terms “furious” and “dumb” rabies since some rabid animals are both aggressive during early stages and become uncoordinated and paralyzed during later stages, although a rabid animal can display one form without the other. Some rabid animals will froth at the mouth in the last stages of clinical illness because they are unable to swallow due to paralysis of the throat muscles.
Distemper, another virus infection of wild and domestic animals, particularly carnivores, can cause similar signs and thus can be confused with rabies. Other viruses, some bacteria, like Listeria, and even parasitic worms can also infect the brain of animals and cause altered behavior. Nevertheless, rabies should be suspected in an animal exhibiting the signs described above. Until rabies is ruled out as a diagnosis, the animal should be handled as if it has rabies.
Reporting and Handling of Specimens
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 county health department should be notified so that it can take the necessary precautions. There is no test for rabies in live animals. Laboratory examination of the brain of the suspect animal by one of the state laboratories provides the only reliable diagnostic information. Examination of the brain is all that is necessary, since the virus is not present in the saliva without first occurring in the brain. The rapid and sensitive fluorescent antibody (FA) test can be performed immediately on the suspect animal. If human exposure (bite) results from an owned cat or dog, it may be quarantined and observed for ten days for onset of clinical rabies. Other animals should be sacrificed and tested immediately. In some circumstances, suspect animals will be submitted directly to the state laboratory for FA testing. In these cases care should be taken in acquiring and handling the suspect animal, and the specimen should be submitted as quickly as possible. The FA test for rabies will distinguish the rabies virus from other disease agents, such as those for distemper and Listeria that could be present in the animal’s brain. An FA test for identifying distemper virus in the brain is also available.
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. In killing the animal, one should avoid exposure to rabies. One should handle the dead animal while wearing gloves or use a plastic bag to pick up the carcass, turning the bag inside out over the animal so that it is contained inside the bag, and thus avoiding direct skin contact with the animal. The animal should be sealed in a double plastic bag and placed in a tight container, such as a cooler, for transport to the state laboratory. The gloves, area and other materials that were in contact with the suspect animal should be disinfected with a strong detergent. The specimen should be kept cool (but not frozen) at all times, during storage and transport to a laboratory. Freezing the carcass will both delay and complicate FA testing of the brain. Furthermore, unless a long delay (more than several days) before the carcass reaches the laboratory is expected, freezing is unnecessary. Identifying information (species, precise geographic data, dates, animal or human exposure etc.) about the specimen and the names, addresses, and telephone numbers of persons exposed to the suspect animal and for the person submitting the specimen should be included in or attached to the specimen package.
Prevention and Treatment for Exposure
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.
Following contact with a rabid animal, 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. Apply a strong first aid solution like iodine after thoroughly flushing the exposed site. Next, contact a physician, hospital emergency room or local health department to determine if rabies vaccine and antiserum are required. Bites from rodents which rarely have rabies, particularly those bites provoked while handling or trying to feed or catch rodents, do not usually indicate a risk and thus seldom require treatment with vaccine and antiserum. Information about the bite incident will aid in the determination of the risk of exposure. The following information is useful: the species of animal involved, whether the bite or attack was provoked by the victim, the behavior of the animal, and what first aid treatment was given. 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, and it is not legal in many states to sell wild animals as pets. In Colorado it is illegal to possess striped skunks and raccoons, all other live wildlife may not be possessed without proper permits. Striped skunks captured as nuisance wildlife must be killed or released at the capture site. Raccoons captured as nuisance wildlife must be killed or released within 2 miles of the capture site. The hazard of exposure to rabies, as well as the difficulty of providing proper care, is good reason for not keeping exotic or native wild animals as pets. Numerous multiple exposures to rabid pet skunks and other wild pet animals have occurred during the last few years.