The discovery and documentation of rabies dates all the way back to antiquity. Even Aristotle mentioned this deadly virus-caused disease in his writings. The rabies virus has been found worldwide, except in Antarctica and a few other isolated regions such as Japan. Limited to mammals including bats, rabies is usually transmitted by a bite or scratch of a rabid animal. Less common modes of transmission are by inhalation, for example, the air in bat caves where high levels of virus particles are present, or by ingestion of infected meat. Although the virus lives less than 24 hours after the death of an infected animal, carcasses should be handled with caution. This applies especially to those handling wild animals, such as hunters and trappers. When a rabid animal bites, the virus, which is present at high levels in saliva, enters the bite wound and passes into the tissues of the victim. Replication takes place in the muscles. It then migrates to the victim’s nerves, for example, the nerves of the leg. From there it spreads to the brain and the salivary glands. A bite from a rabid animal does not always lead to infection. In fact, it has been said that only about 15% of exposed humans will contract the disease. However, this figure is mere speculation. Humans, dogs and cats are not nearly as susceptible to the disease as are skunks, raccoons, foxes, and bats. Even among these species there are variations in susceptibility to the different strains of the virus, and only about one percent of bats actually carry it. Federal health authorities recently reported a small victory in the war against rabies. The canine-specific strain has been eliminated in the US. However, other animals can still infect dogs. The incubation period from the time of contact to manifestation of symptoms is slow, usually from 3 to 8 weeks in dogs, 2 to 6 weeks in cats and 3 to 6 weeks in people. Variations have been reported, listing incubation periods as long as 6 months in dogs and 12 months in people.The symptoms of rabies consist of three phases. An animal may go through just one or all of these. Skunks sometimes do not show any symptoms, but they may become lifelong carriers. During the first or prodromal phase which lasts 2-3 days in most dogs, the animal will exhibit apprehension, anxiety, nervousness, and may withdraw. A fever may also be present. Friendly dogs may become irritable and bite, while aggressive animals may suddenly be affectionate and docile. Many will continuously lick the site of the bite. The prodromal phase in cats usually only lasts 1-2 days. Their behavior tends to be more erratic than that of dogs.The prodromal phase is usually followed by the furious phase, which typically lasts from 1 to 7 days in dogs. The animals are very irritable and are highly responsive to auditory and visual stimuli. The irritability and restlessness continue to increase and the dog may become vicious and bite, even attacking their enclosure if crated or fenced in. This behavior will progress to disorientation and seizures and end in the death of the animal.The third phase is called the paralytic or dumb phase. Some animals may enter this phase directly from the prodromal phase, omitting the furious phase. The nerves of the head and throat are affected first, leading to salivation. This appears similar to pictures of big dogs foaming at the mouth. The foaming is caused by an inability to swallow. As the diaphragm and face muscles become increasingly paralyzed, the dog may make a choking sound as if there was something stuck in its throat. This eventually leads to respiratory failure and death. Some animals exhibit a combination of the above phases.Although these symptoms leave no doubt as to the condition, a definitive diagnosis of rabies can only be made by microscopic examination of the brain. Some newer testing methods which use skin or blood samples are being evaluated, but these are not yet routinely used. If an animal bites a person, the animal is usually quarantined and observed for at least 10 days to watch for possible symptoms of rabies. Quarantine requirements vary according to the rules of different communities as well as the vaccination status of the animal involved. There is no treatment for rabies. Once the disease develops in humans, death is a certainty. A few very rare cases of dogs surviving the infection have been reported. People exposed to a rabid animal may receive a 5-shot series of Human Rabies Immune Globulin to prevent infection. Three injections of a prophylactic vaccine (Human Diploid Cell Vaccine) may be considered for people at high risk of contracting the disease, i.e., wildlife veterinarians, cave explorers, and travelers to developing countries where rabies incidence is high and post-exposure vaccine may not be readily available.This deadly disease can be prevented by proper vaccination. Unfortunately, many dogs are never vaccinated, and very few cats ever receive vaccinations.It is best to give an initial vaccination to puppies and kittens at 4 months of age, and then again at a year of age. The second shot can be the 3-year vaccine, which is considered to be effective. However, some states require vaccination yearly or once every two years. Most veterinarians agree that the vaccines have been adequately tested and that they should be given in accordance with the manufacturer’s instructions. The text of the National Association of State Public Health Veterinarians (NASPHV) Rabies Compendium, the national rabies control standard, states that vaccines used in state and local rabies control programs should have at least a 3-year duration of immunity, and that “No laboratory or epidemiologic data exist to support the annual or biennial administration of 3- or 4- year vaccines following the initial series.” Rabies vaccines are also available for large animals, such as cattle and sheep. However, there are no specific vaccines for most exotic animals. According to the NASPHV Compendium, the efficacy of parenteral vaccination of wildlife and hybrids against rabies has not been established. Attempts are sometimes made to use canine vaccine on some species such as wolf hybrids, in order to offer some protection. Keeping wild animals as pets is never advisable.Over the past decades the United States and Canada have seen a marked decrease in the incidence of rabies in people and domestic animals. However, most states have reported increases of the disease in wild animals such as raccoons, skunks, foxes and bats. In Canada, the once-dominant Arctic fox strain decreased markedly due to baited-vaccine programs. However, the raccoon strain is now on the increase.Alaskan mushers have special cause for vigilance as in recent years the number of cases of rabies infections in animals has increased. In 2006, 18 cases were confirmed, and 35 cases have already been reported during the first six months of 2007. No rabies infections have been reported in people. It must be noted that these numbers represent only confirmed cases. Since many exposures may go unreported every year, these numbers may not represent the full extent of rabid animals in the state. Most of the occurrences were in the northern region of the state, involving predominantly red and arctic foxes, and a few dogs. No rabies-positive wolves or wolf hybrids were reported. Experimental oral rabies vaccines have been studied in captive arctic foxes in Alaska over the last two decades. Two vaccines proved effective but trials have not yet been conducted in the field. There are plans to evaluate another vaccine that is currently being used in gray foxes and coyotes in the southwestern US.In the Russian arctic, as in other Arctic regions, foxes are most implicated as carriers of the rabies virus. Unprovoked attacks by wolves or wolf-dog hybrids on people have been described in reports from Russia in recent times, but confirmed rabies were not mentioned. While foxes predominate in northern regions, skunks, raccoons and bats are major carriers of the disease in the lower 48 states. In one Wisconsin county five bats were determined to be rabies positive this year, and numbers are up statewide in 2007 compared to 2006. A Madison, Wisconsin man and young child were recently bitten by bats. The man found the bat in his bed and woke up when the bat bit him in the arm. The child was bitten by a bat that fell off of a barn roof. Both had to undergo post-exposure shots. Coyotes are sometimes involved, and groundhogs, bobcats, otters, opossum, deer and beavers may contract the disease. These cases are very rare. In 2006, two fatal cases of rabies in people, one in Indiana and the other in Texas, were associated with bat exposure. The World Health Organization (WHO) reports that more deaths occur worldwide from rabies than from any other infectious disease. Of the approximately 50,000 human rabies deaths reported every year, it is estimated that over 30,000 take place in the Indian sub-continent. In Africa, Asia and Latin America, transmission of the disease is nearly always blamed on dog bites. China has registered huge rabies outbreaks over the recent decades. Dogs are the most frequently implicated carriers of the disease, and they are blamed for the large number of human deaths that occur in that country every year. There is very little public awareness of the disease and few vaccinations are given, especially in rural areas. Instead, the country frequently responds with massive culling of dogs. For example, media reports state that authorities of Jining, provincial capitol of the Shandong province, recently ordered that all dogs within a three-mile radius of every rabies case would be slaughtered. Public health representatives in Mouding, a county in Yunnan province, clubbed, electrocuted or buried alive 50,000 dogs in an attempt to control the disease. Whether vaccinated or not, no dog was spared except police and army dogs. Animal protection groups are outraged, and even the World Health Organization deems these measures as excessive. Among South American countries, Colombia has responded to the rabies threat in a more humane manner than China. For example, the City of Bogotá conducts massive annual free vaccinations of its large dog and cat populations, consisting of about 6,000 to 7,000 vaccinations per month. As a result, no rabies-positive dogs were reported in 2006, and no human infection has occurred in Bogotá since 1982. Vaccinations are accompanied by public education about the virus and what to do if exposed. Raised public awareness and free vaccinations in major cities have done much to bring the problem of rabies somewhat under control in Colombia. Unfortunately, vaccination is not mandatory and control measures have not yet reached all areas of the country, especially outlying communities. Due to space limitations, this article can not cover all countries. The bottom line for mushers is this: make sure your rabies vaccinations are up to date. Know your local regulations in regard to handling of wild critters following suspected exposure of a dog, and rush the dog to the clinic for a booster shot regardless of the present vaccination status. If you yourself are bitten, wash the wound and see a physician immediately.Karen Gadke, PhD (Health Science) is a clinical study specialist, medical writer, author and lecturer. She has been mushing and racing since 1979. She owns both Siberians and Alaskans.
