Rabies
Rabies
Disease History, Characteristics, and Transmission
Introduction
Rabies, from the Latin word rabies for mad, has long been one of the most-feared of diseases. It was described by the Greek philosopher Aristotle (384–322 BC) who realized that humans could contract rabies through being bitten by infected dogs, which is still the most common way the disease is transmitted. Rabies claims the lives of around 55,000 people around the world each year, mainly in rural parts of Africa and Asia.
Rabies is an acute viral illness which affects the brain and nervous system. Left untreated, it is invariably fatal. The symptoms are dramatic, including seizures, hallucinations, foaming at the mouth, and violent throat spasms. Rabies is a zoonosis—a disease of animals which can affect humans. Wild mammals are the reservoir of the rabies virus and they can, in turn, affect domestic animals like cats and dogs. Humans usually become infected through a bite from a wild or domestic animal with rabies. Fortunately, an effective vaccine against rabies is available and this can be used either before or after exposure to the virus.
Disease History, Characteristics, and Transmission
The rabies virus belongs to the rhabdovirus group and is a bullet-shaped enveloped RNA virus (that is, its genetic material is RNA, rather than DNA). The incubation period of the virus is between ten days and as long as one year. Early symptoms are vague and may resemble flu—and include fatigue, headache and nausea.
Once the rabies virus reaches the brain and nervous system, dramatic neurological symptoms set in. These include hallucinations, agitation, muscle spasm, paralysis, and seizures. Foaming at the mouth is a classic symptom of rabies and is a combination of increased salivation and difficulty in swallowing. The latter produces another classic symptom—hydrophobia, or fear of water, where extreme throat spasms may be induced by even the sight of water. Sometimes rabies dominated by agitation is known as furious rabies, while that dominated by paralysis is called dumb rabies.
Within days of the onset of symptoms, a person with rabies will enter a coma and death is usually by paralysis of the respiratory muscles. Survival is extremely rare— there have been only six documented cases and all of these individuals had been protected to some extent by vaccination before or after exposure to the rabies virus.
The rabies virus eventually passes through the nervous system to the salivary glands and it is the saliva of an infected animal which transmits the disease to other animals and to humans. Exposure to the rabies virus usually occurs from a bite by an infected animal, although the virus might also sometimes be transmitted through a scratch or lick from the animal. Infections have also occurred through inhaling aerosols from the droppings of infected bats.
Wild carnivorous mammals, including skunks, foxes, wolves, jackals, raccoons and coyotes, act as a reservoir for rabies virus. The infection may be passed to domestic animals—that is, dogs and cats. Humans can be infected by direct contact with either wild or domestic mammals. The former is sometimes known as sylvatic rabies, the latter as urban rabies. An animal with rabies virus will not be infectious all the time—only when the virus is in their saliva which can happen late on in the incubation period, because it has to pass from the muscle, where infection occurs, through the nervous system to the salivary glands.
Insectivorous and vampire bats can also transmit rabies. Rodents, such as rats, mice, and hamsters, and lagomorphs, such as rabbits and hares, hardly ever get infected with rabies and have never been shown to transmit it to humans. However, woodchucks and groundhogs were responsible for 86 per cent of 368 cases of rabies among rodents reported to the Centers for Disease Control and Prevention (CDC) between 1985 and 1994. Other herbivorous mammals including cattle, horses, and deer can become infected with rabies but very rarely infect humans.
Human to human transmission of rabies is rare, but not unknown. There have been eight cases recorded among recipients of transplanted corneas and three in recipients of solid transplanted organs. In theory, bites could also transmit rabies from one person to another, although no such cases are known. Casual contact, such as touching or contact with non-infectious fluids, does not carry a risk of infection with rabies virus.
Scope and Distribution
Rabies is a global problem which has been recognized for at least 3,000 years. At the turn of the twentieth century, there were over one hundred cases of rabies in the United States each year. Now that number is fewer than five. The disease is notifiable to the CDC and states also collect data on cases. According to a survey carried out by the World Health Organization (WHO) in 2004, there are around 55,000 deaths from rabies each year worldwide, most of them in rural Africa and Asia. Around half of all cases of rabies from dog bites occur among children under the age of 15.
WORDS TO KNOW
INCUBATION PERIOD: Incubation period refers to the time between exposure to disease causing virus or bacteria and the appearance of symptoms of the infection. Depending on the microorganism, the incubation time can range from a few hours (an example is food poisoning due to Salmonella) to a decade or more (an example is acquired immunodeficiency syndrome, or AIDS).
NOTIFIABLE: By law, occurrences of some diseases must be reported to government authorities when observed by health-care professionals. Such diseases are called notifiable diseases or reportable diseases. Cholera and yellow fever are examples of notifiable diseases.
RESERVOIR: The animal or organism in which the virus or parasite normally resides.
SYLVATIC: Sylvatic means pertaining to the woods and refers to diseases such as plague that are spread by animals such as ground squirrels and other wild rodents.
ZOONOSES: Zoonoses are diseases of microbiological origin that can be transmitted from animals to people. The causes of the diseases can be bacteria, viruses, parasites, and fungi.
There is marked geographical variation in the mammal species that pose a threat of rabies. In the United States, sylvatic rabies accounts for most cases and urban rabies is rare; the reverse is true in developing countries. Bats are the most common reservoirs of the disease in Latin America and the wolf in Eastern Europe.
Treatment and Prevention
There is no specific treatment for rabies once the symptoms have begun. A rabies vaccine was first developed by Louis Pasteur in the late 1880s. This was a crude preparation made from the dried spinal cord of infected rabbit. Similar vaccines are still in use in some countries, although WHO does not recommend them. Rabies vaccines made in cell culture are preferred for safety reasons.
Rabies vaccine can be given either before or after exposure to the virus. Pre-exposure vaccine should be given where a person's occupation brings them into contact with wild animals or with the virus itself—for instance, veterinarians, animal handlers, and certain laboratory workers. Travelers to regions where rabies is common and children living in these countries should also be vaccinated.
Post-exposure vaccination is needed if someone has been potentially exposed to rabies virus through an animal bite or other contact. Each year, over one million Americans receive an animal bite and these must always be taken seriously. But only a few of these will pose any risk of rabies infection, so each case must be carefully evaluated. An important part of this is having an expert examine the animal involved for symptoms and signs of rabies.
Vaccination of domestic animals against rabies plays an important role in keeping the disease at bay. Some European countries, such as France, Switzerland, and Belgium, have eliminated rabies in their wildlife through vaccination campaigns, and this is being tried in places where the disease is more common such as India and South Africa.
Impacts and Issues
In 2004, WHO was informed of a case of rabies in a dog owned by a resident of the city of Bordeaux, in France. Many people had handled this dog over a five-week period when the animal was potentially infectious. WHO had to put out a call for these individual to come forward for assessment and possible post-exposure vaccination. The dog had been imported illegally from Morocco and had not been vaccinated against rabies.
This incident shows the importance of taking animal import and quarantine regulations seriously. By flouting these on entry to France, the dog's owner put many people's lives at risk. Responsible owners get their pets vaccinated against rabies. And, when it comes to wildlife, it is best to admire from afar and never to handle or touch an animal that you do not know.
Wisconsin teenager Jeanna Giese became the first person known to have survived symptomatic rabies without vaccination. In September 2004, Giese contracted rabies after being bitten on the finger by a bat. One month after the bite, she was admitted to the hospital. Rabies was considered always fatal in unvaccinated patients, but physicians and Giese's family chose an experimental treatment. Physicians put Giese into a drug-induced coma for a week, at the same time giving her several strong antiviral drugs (amantadine and ribavirin). Giese's immune system fought the infection. She returned to school the following academic year after several months of recovery and intense physical therapy. Physicians and medical researchers continue to debate whether Giese survived because of the experimental treatment, or whether other factors, such as a stronger-than-average immune system or a weaker-thanaverage strain of rabies, played a larger role.
Following the Geise case, there was an increased focus on bats as potentials vectors of disease. Though bats are beneficial in controlling mosquito and insect populations, researchers estimate that 1% of bats in the United States carry rabies. Bats rarely bite humans and cause only minor injury at the location of the bite. It is possible for bites on sleeping victims to go undetected. In August 2006, over 1,000 young girls were advised to obtain rabies vaccinations after attending a Girl Scout camp where bats were present in sleeping quarters. Not all of families opted for vaccination, but none of the girls have developed rabies.
Cases of rabies are increasing, even in developed urban environment. In 2006, the Chinese government passed a law that forbid dogs in many in public places and limited dog ownership to one animal per household. Rabies is endemic in China, and is one of the nation's leading causes of death from infectious disease. However, officials cited the popularization of pet ownership and the failure of many pet owners to vaccinate dogs as primary causes for the resurgence of rabies, especially in the nation's cities.
LOUIS PASTEUR AND THE RABIES VACCINE
By 1880 French scientist Louis Pasteur (1822–1895) had shown that vaccination against anthrax worked in animals. He used a weakened, or attenuated, form of a culture of the anthrax bacterium as the vaccine and found it protected animals against the disease, compared to control animals that had not been vaccinated. In 1880, he decided to turn his attention to rabies a feared disease with a high mortality rate. Pasteur showed that a vaccine made from an attenuated form of the rabies virus could protect dogs that had been bitten by rabid animals. He hesitated, however, before trying his vaccine on humans.
Pasteur's first human patient was a young boy called Joseph Meister who was brought to him from Alsace on July 6, 1885. Joseph had been bitten fourteen times by a rabid dog on his hands, legs, and thighs. Clearly, his life was in danger and Pasteur administered the first dose of vaccine the next day. He used the dried-out spinal cord from a rabid rabbit as the source of vaccine. The drying process allowed the virus to lose much of its virulent character and helped allay safety fears. The boy was given increasingly strong doses of vaccine over the next twelve days and was soon able to return to Alsace in good health, having developed no symptoms of rabies, nor any ill effects from the vaccination.
The development of an effective rabies vaccine was the final, and most dramatic, success of Pasteur's long and distinguished career in medicine, chemistry, and microbiology. Pasteur's work on rabies led to the establishment of the now world-famous Pasteur Institute in Paris. The Institute was funded through public contributions and was initially devoted to rabies vaccination. Since its launch in 1888, the Institute has been home to many distinguished scientists, including several Nobel Prize winners.
See AlsoAnimal Importation; Zoonoses.
BIBLIOGRAPHY
Books
Wilson, Walter R. and Merle A. Sande. Current Diagnosis & Treatment in Infectious Diseases. New York: McGraw Hill, 2001.
Web Sites
Center for Diseases Control and Prevention (CDC) National Center for Infectious Diseases. “Rabies.” January 7, 2005 <http://www.cdc.gov/ncidod/dvrd/rabies> (accessed Apr 19, 2007).
World Health Organization. “Rabies.” <http://www.who.int/mediacentre/factsheets/fs099/en> (accessed April 19, 2007).
Susan Aldridge