Rabies is a zoonotic viral disease that causes acute and severe encephalitis in humans and other mammals. It was historically referred to as hydrophobia ("fear of water") because most of its victims panic when offered liquids to drink as a result of uncontrollable, painful spasms in their throat muscles when they swallow. Early symptoms can include fever and abnormal sensations at the site of exposure, which are followed by nausea, vomiting, violent movements, uncontrolled excitement, fear of water, an inability to move parts of the body, confusion or loss of consciousness. Once symptoms appear, the result is virtually always death. The time period between contracting the disease and the start of symptoms is usually one to three months but can vary from less than one week to more than one year. The time depends on the distance the virus must travel along peripheral nerves to reach the central nervous system. Rabies is caused by lyssaviruses, including the rabies virus and Australian bat lyssavirus. It is spread when an infected animal bites or scratches a human or other animals. Even in the absence of a bite or a scratch, saliva from an infected animal coming into contact with the eyes, mouth, or nose can transmit rabies. Rabies can also be transmitted through tears and nervous tissues. The transmission of rabies by drinking unpasteurized milk from an infected animal is theoretically possible, although not supported by scientific empirical evidence, which excludes anecdotes. Globally, dogs are the most common animal involved. In countries where dogs commonly have the disease, more than 99% of rabies cases in humans are the direct result of dog bites. In the Americas, bat bites are the most common source of rabies infections in humans, and less than 5% of cases are attributed to dogs. Rodents are very rarely infected with rabies. The disease can be diagnosed only after the start of symptoms, but prompt prophylactic treatment is recommended for anyone who has had contact with a rabid animal. Animal control and vaccination programs have decreased the risk of rabies from dogs in a number of regions of the world. Immunizing people before they are exposed is recommended for those at high risk, including those who work with bats or who spend prolonged periods in areas of the world where rabies is common. In people who have been exposed to rabies, the rabies vaccine and sometimes rabies immunoglobulin are effective in preventing the disease if the person receives the treatment before the start of rabies symptoms. Washing bites and scratches for 15 minutes with soap and water, povidone-iodine, or detergent may reduce the number of viral particles and may be somewhat effective at preventing transmission. As of 2016, only fourteen people were documented to have survived a rabies infection after showing symptoms. However, research conducted in 2010 among a population of people in Peru with a self-reported history of exposures to vampire bats (commonly infected with rabies) found that seven out of 73 subjects whose blood serum was tested had rabies virus-neutralizing antibodies, though only one reported prior rabies vaccination. These findings suggest previously undocumented cases of infection and viral replication followed by abortive infection, indicating that some people exposed to the virus can thereby develop natural antibodies without treatment. Rabies causes about 59,000 human deaths worldwide per year, about 40% of which are in children under the age of 15. More than 95% of human deaths from rabies occur in Africa and Asia. Rabies is present in more than 150 countries and on all continents but Antarctica. More than 3 billion people live in regions of the world where rabies occurs. A number of countries, including Australia and Japan, as well as much of Western Europe, do not have rabies among dogs. Many Pacific islands do not have rabies at all. It is classified as a neglected tropical disease. The global cost of rabies is estimated to be around US$8.6 billion per year in lost lives and livelihoods, medical care, and associated costs, besides uncalculated psychological trauma.
Etymology The name rabies is derived from the Latin rabies, meaning 'madness'. The Greek word λῠ́σσᾰ (lyssa, 'madness'), derived either from a feminine form of λῠ́κος (lykos, 'wolf') or from the Proto-Indo-European root *lewk- ('light'), is used in the genus name of the rabies virus, Lyssavirus.
Signs and symptoms
The incubation period between infection and the first symptoms is typically one to three months in humans. Initial symptoms of rabies are often nonspecific, such as fever and headache. As rabies progresses and causes inflammation of the brain and meninges, symptoms can include slight or partial paralysis, anxiety, insomnia, confusion, agitation, abnormal behavior, paranoia, terror, and hallucinations. The infected person may also fear drinking water. The symptoms eventually progress to delirium and coma. Death usually occurs two to ten days after first symptoms. Survival is almost unknown once symptoms have presented, even with intensive care.
Two forms of the disease are recognized, furious rabies and dumb rabies. The furious form affects 80% of rabies victims. This form of rabies causes irrational aggression in the host, which aids in the spreading of the virus through animal bites. This form of rabies has also been called hydrophobia ("fear of water"; see also aquaphobia) throughout its history. In the later stages of a furious infection, the victim has difficulty swallowing, often panics when presented with liquids to drink, and cannot quench their thirst. Saliva production is greatly increased, and attempts to drink, or even the intention or suggestion of drinking, may cause excruciatingly painful spasms of the muscles in the throat and larynx. Since the victim cannot swallow saliva and water, the virus has a much higher chance of being transmitted, because it multiplies and accumulates in the salivary glands and is transmitted through biting. Such overproduction of saliva and inability to swallow it may cause "foaming at the mouth," much associated with rabies in the public perception and in popular culture. The remaining 20% of rabies victims often experience the dumb form, a progressive paralytic condition marked by muscular weakness, loss of sensation, and paresis that resembles Guillain–Barré syndrome in its symptomatology. This form of rabies does not usually cause fear of water.
Cause
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