RABIES
Rabies is a viral brain disease that is almost always fatal if it is not prevented with prompt treatment. The disease, which typically spreads to humans from animals through a scratch or a bite, causes inflammation of the brain. The disease is also called hydrophobia (meaning fear of water) because it causes painful muscle spasms in the throat that prevent swallowing. In fact, this is what leads to most fatalities in untreated cases: victims become dehydrated and die. Carriers of rabies include dogs, cats, bats, skunks, raccoons, and foxes; rodents are not likely to be infected. About 70% of rabies cases develop from wild animal bites that break the skin. Though a vaccine used first in 1885 is widely used, fatalities still occur due to rabies. Most fatalities take place in Africa and Asia, but some also occur in the United States. The cost of efforts to prevent rabies in the United States may be as high as __BODY__ billion per year.
While many animal diseases cannot be passed from animal to man, rabies has long been known as an easy traveler from one species to the next. The disease was known among ancient people. The very name rabies, Latin for rage or madness, suggests the fear with which early men and women must have viewed the disease. For centuries there was no treatment, and the disease was left to run its rapid course leading to death.
Rabies is described in medical writings dating from 300 B.C., but the method of transmission or contagion was not recognized until 1804. In 1884, the French bacteriologist Louis Pasteur developed a preventive vaccine against rabies, and modifications of Pasteur's methods are still used in rabies therapy today. The Pasteur program, or variations of it, has greatly reduced the fatalities in humans from rabies. Modern treatment, following a bite by a rabid or presumed rabid animal, consists of immediate and thorough cleansing of the bite wound and injection into the wound and elsewhere of hyper-immune antirabies serum. Post exposure treatment consists of five injections of vaccine given over a one-month period, along with one dose of rabies immune globulin injected near the wound and intramuscularly.
The standard vaccine contains inactivated rabies virus grown in duck eggs. It is highly effective but causes neuroparalysis in about one in 30,000 persons receiving it. In the 1970s, a new vaccine was developed in France and the United States that contains virus prepared from human cells grown in the laboratory. This vaccine is safer and requires a shorter course of injections. With the widespread use of vaccine, rabies cases in the U.S. declined to fewer than five per year.
The transmission of rabies is almost invariably through the bite of an infected animal. The fact that the virus is eliminated in the saliva is of great significance, and unless saliva is introduced beneath the skin, the disease is seldom transmitted. The virus has been demonstrated in the saliva of dogs 3–8 days before the onset of symptoms. However, it has also been reported that only about 50–60% of the infected dogs shed the virus in the saliva. Rare cases of rabies have been reported where only clawing and scratching occurred, or where the skin was contaminated with saliva. The virus is most concentrated in the central nervous system and saliva, but it has also been demonstrated in various organs of the body and milk from infected animals.
In humans, the rabies virus, in addition to entering the body by the usual route through skin broken by a bite or scratch, can enter the body through intact mucous membranes, can be inhaled as an aerosol, and can be transplanted in an infected corneal graft. These four cases are the only virologically documented examples of transmission of rabies from one person to another. Vertical transmission from mother to fetus and from lactating mother to suckling young has been described in nonhuman mammals.
The incubation period in natural cases of rabies is variable. In general, the quantity of virus introduced into the wound is correlated with the length of incubation before symptoms occur. In dogs, the minimum period is ten days, the average 21–60 days, but may be as long as six months. In man, the incubation period is one to three months, with the minimum of ten days.
Rabies is caused by a number of different viruses that vary depending on geographic area and species. While the viruses are different, the disease they cause is singular in its course. The bullet-shaped virus is spread when it breaks through skin or has contact with a mucous membrane. The virus begins to reproduce itself initially in muscle cells near the place of first contact. At this point, within the first five days or so, treatment by vaccination has a high rate of success.
Once the rabies virus passes to the nervous system, immunization is no longer effective. The virus passes to the central nervous system, where it replicates itself in the system and moves to other tissues such as the heart, the lung, the liver, and the salivary glands. Symptoms appear when the virus reaches the spinal cord.
A bite from a rabid animal does not guarantee that one will get rabies; only about 50% of people who are bitten and do not receive treatment ever develop the disease. If one is bitten by or has had any exposure to an animal that may have rabies, medical intervention should be sought immediately. Treatment virtually ensures that one will not come down with the disease. Any delay could diminish the treatment's effectiveness.
In humans and in animals, rabies may be manifest in one of two forms: the furious (agitated) type or the paralytic (dumb) type. Furious rabies in animals, especially in the dog, is characterized by altered behavior such as restlessness, hiding, depraved appetite, excitement, unprovoked biting, aimless wandering, excessive salivation, altered voice, pharyngeal paralysis, staggering, general paralysis, and finally death. Death usually occurs within three to four days after the onset of symptoms. The paralytic form of rabies is frequently observed in animals inoculated with fixed virus, and is occasionally observed in other animals with street virus contracted under natural conditions. Animals showing this type usually show a short period of excitement followed by uncoordination, ataxia, paralysis, dehydration, loss of weight, followed by death.
In humans, furious rabies patients typically show bizarre behavior, ranging from episodes of severe agitation to periods of depression. Confusion becomes extreme as the disease progresses, and the patient may become aggressive. Hydrophobia is always seen with this type of disease, until the patient becomes comatose while showing intermittently uncontrollable inspiratory spasms. This type of rabies is also characterized by hypersalivation, from 1–1.6 qt (1–1.5 L) of saliva in 24 hours, and excessive sweating.
The paralytic form of rabies in humans is often indistinguishable from that of most viral encephalitis, except for the fact that a patient suffering from rabies remains conscious during the course of the disease. Paralysis usually begins at the extremity exposed to the bite and gradually involves other extremities finally affecting the pharyngeal and respiratory muscles.
The dog is a most important animal as a disseminator of rabies virus, not only to man but also to other animals. Wild carnivora may be infected and transmit the disease. In the United States, foxes, raccoons and skunks are the most commonly involved. These animals are sometimes responsible for infecting domestic farm animals.
The disease in wildlife (especially skunks, foxes, raccoons, and bats) has become more prevalent in recent years, accounting for approximately 85% of all reported cases of animal rabies every year since 1976. Wildlife now constitutes the most important potential source of infection for both human and domestic animals in the United States. Rabies among animals is present throughout the United States with the exception of Hawaii, which has remained consistently rabies-free. The likelihood of different animals contracting rabies varies from one place to the next. Dogs are a good example. In areas where public health efforts to control rabies have been aggressive, dogs make up less than 5% of rabies cases in animals. These areas include the United States, most European countries, and Canada.
However, dogs are the most common source of rabies in many countries. They make up at least 90% of reported cases of rabies in most developing countries of Africa and Asia and many parts of Latin America. In these countries, public health efforts to control rabies have not been as aggressive. Other key carriers of rabies include the fox in Europe and Canada, the jackal in Africa, and the vampire bat in Latin America.
In the United States, 60% of all rabies cases were reported in raccoons. The high number of cases in raccoons reflects an animal epidemic, or, more properly, an epizootic. The epizootic began when diseased raccoons were carried from further south to Virginia and West Virginia. Since then, rabies in raccoons has spread up the eastern seaboard of the United States. Concentrations of animals with rabies include coyotes in southern Texas, skunks in California and in south and north central states, and gray foxes in southeastern Arizona. Bats throughout the United States also develop rabies. When rabies first enters a species, large numbers of animals die. When it has been around for a long time, the species adapts, and smaller numbers of animals die.
There are few deaths from rabies in the United States. Between 1980 and the middle of 1994, a total of 19 people in the United States died of rabies, far fewer than the 200 Americans killed by lightning, for example. Eight of these cases were acquired outside the United States. Eight of the 11 cases contracted in the United States stemmed from bat-transmitted strains of rabies.
Internationally, more than 33,000 people die annually from rabies, according to the World Health Association. A great majority of cases internationally stem from dog bites. Different countries employ different strategies in the fight against rabies. The United States depends primarily on vaccination of domestic animals and on immunization following exposure to possibly rabid animals. Great Britain, in which rabies has never been established, employs a strict quarantine for all domestic animals entering the country.
Continental Europe, which has a long history of rabies, developed an aggressive program in the 1990s of airdropping a new vaccine for wild animals. The vaccine is mixed with pellets of food for red foxes, the primary carrier there. Public health officials have announced that fox rabies may be eliminated from Western Europe by the end of the decade. The World Health Organization is also planning to use the vaccine in parts of Africa.
Though the United States have been largely successful in controlling rabies in humans, the disease remains present in the animal population, a constant reminder of the serious threat rabies could become without successful prevention efforts.
