Rabies

Definition

Rabies is a frequently fatal, acute viral infection which is transmitted to humans by infected animals (often dogs or bats) via a bite or by the exposure of broken skin to an infected animal's saliva.

Causes, incidence, and risk factors

Rabies is transmitted by infected saliva that enters the body through a bite wound or other open wound. The virus travels from the wound along nerve pathways to the brain, where it causes inflammation (irritation and swelling with presence of extra immune cells) that results in the symptoms of the disease.

The incubation period ranges from 10 days to 7 years, with the average being 3 to 7 weeks.

In the past, human cases in the U.S. usually resulted from a dog bite, but recently, more cases of human rabies have are linked to bats and there have not been any rabies cases caused by dog bites for a number of years.

Worldwide, dogs still pose a significant risk for transmitting rabies, however. Bats, skunks, raccoons, foxes, and other animals can also be sources of rabies virus. There are an estimated 15,000 cases of rabies worldwide each year.

Few cases occur in the US (only 3 reported in 1991 and 9 in 1994) because of extensive animal vaccination programs.

The United Kingdom has completely eradicated rabies, which is why Americans cannot bring pets or other animals to the UK without having them undergo a 6-month quarantine.

Symptoms

• low-grade fever (102 degrees F or lower)
  
• pain at the site of the bite
  
• exaggerated sensation at the bite site
  
• swallowing difficulty (drinking produces spasms of the larynx) or swallowing difficulty with liquids only
  
• restlessness
  
• excitability
  
• muscle spasms
  
• Convulsions
  
• Numbness and tingling
  
• loss of muscle function
  
• loss of feeling in an area of the body
  
• drooling
  
• anxiety, stress, and tension
  
• positive Babinski's reflex
  

Signs and tests

If a person has a history of animal bite, the animal will be observed for signs of rabies. Immunofluorescence (fluorescent antibody test) or necropsy (after death) performed on the suspect animal may show that the animal has rabies.