Rabies Health Article

Definition

Rabies is a viral illness that can affect any mammal but is most common in carnivores (flesh-eaters). It is sometimes referred to as a zoonosis, or disease of animals that can be communicated to humans. Rabies is usually transmitted in the saliva through a bite wound. The virus attacks the central nervous system, and is fatal once symptoms begin, with very rare exceptions.

Description

Rabies, also known as hydrophobia, belongs to the rhabdovirus family. Fewer than 10% of animal cases reported in the United States in 1998 were in domestic animals. Raccoons accounted for the largest number of cases in wild animals. Cases of rabies in humans are very infrequent in the United States, averaging one or two a year (down from over 100 cases annually in 1900), but the worldwide incidence is estimated to be between 30,000 and 50,000 cases each year. These figures are based on data collected by the World Health Organization (WHO) in 1997 and updated in 2002. Rabies is most common in developing countries in Africa, Latin America, and Asia, particularly India. Dog bites are the major origin of infection for humans in developing countries, but other important host animals may include the wolf, mongoose, and bat. Most deaths from rabies in the United States result from bat bites; the most recent victim was a man in Iowa who died in September 2002.

People whose work frequently brings them in contact with animals are considered to be at higher risk than the general population. This would include those in the fields of veterinary medicine, animal control, wildlife work, and laboratory work involving live rabies virus. People in these occupations and residents of or travelers to areas where rabies is a widespread problem should consider being immunized.

In late 2002, rabies re-emerged as an important public health issue. Dr. Charles E. Rupprecht, director of the World Health Organization (WHO) Collaborating Center for Rabies Reference and Research, has listed several factors responsible for the increase in the number of rabies cases worldwide:

• Rapid evolution of the rabies virus. Bats in the United States have developed a particularly infectious form of the virus.
• Increased diversity of animal hosts for the disease.
• Changes in the environment that are bringing people and domestic pets into closer contact with infected wildlife.
• Increased movement of people and animals across international borders. In one recent case, a man who had contracted rabies in the Philippines was not diagnosed until he began to feel ill in the United Kingdom.
• Lack of advocacy about rabies.

Causes & symptoms

The most common way to contract rabies is from the bite of an infected animal. Although bats are the most frequent source of human infection in the United States, dogs are the primary vector of rabies in most parts of the world. The disease may also be transmitted by tissues and body fluids other than saliva. Rare cases have occurred as a result of infection through corneal transplantation.

Rabies travels from the site of the bite along the peripheral nerves to the brain. The average incubation period in humans is 30–50 days, although it varies from 10 days to over a year. The initial symptoms are flu-like and nonspecific. They may include fever, headache, muscle pain, sore throat, fatigue, nausea, and vomiting. Altered sensation and muscle twitching in the area of the bite are signs that are more suspicious of rabies. When the virus reaches the brain, signs related to encephalitis (local or general inflammation of brain tissue) appear. This typically involves agitation, progressing to confusion,

combativeness, seizures, and localized areas of paralysis. There may also be hypersensitivity to light, sound, and touch. The patient may be coherent at times, but less so as the disease progresses. Many viruses causing encephalitis may produce similar signs. The next stage is dysfunction of the brainstem. The well-known phenomenon of foaming at the mouth is caused by excessive saliva production combined with difficulty swallowing. Many patients will refuse liquids at this point due to the painful muscle contractions caused by swallowing. This is how rabies came to be known as hydrophobia, which means "fear of water." Coma ensues soon after brainstem involvement, and death occurs when the respiratory center is affected. The course of the disease is four to 20 days after symptoms appear, unless life support is used.