Description

Fatal acute viral encephalomyelitis transmitted from animals to humans through bites or exposure to saliva or nervous tissue from a rabid animal. Only mammals are able to contract and transmit the disease.

Epidemiology

• An estimated 59,000 deaths are due to rabies every year in the world, most of them in Asia and Africa. Many of the affected countries do not have proper surveillance systems for rabies.
• Only 1 to 3 human cases reported annually in the United States. Imported cases infected overseas add 1 to 3 more cases annually.
• The dog is the main animal reservoir in most of world. In the United States and most developed countries, canine rabies had been eliminated.
• Wildlife such as bats, raccoons, skunk, and foxes are main reservoirs in North America, with frequent spillover to cats, dogs, and other domestic animals.
• All of the continental United States is enzootic for bat rabies, whereas transmission among terrestrial reservoirs occurs in specific geographic regions such as the Eastern United States (raccoon); south central, north central areas, and the state of California (skunk); south west (fox); Alaska (Arctic fox); and Puerto Rico (mongoose).
• Hawaii is considered rabies-free.

Risk Factors

• Travel to areas where canine rabies is endemic
• Recent scratch or bite from known animal reservoir species including bats or other wildlife; exposure from an unvaccinated domestic animal (e.g., cat, dog) without the ability for appropriate management
• Transmission from transplanted corneas, vessels, and solid organs has occurred.
• Working with animals (e.g., veterinarians) or working in a laboratory with the virus
• Outdoor occupations and recreational activities that increase contact with high-risk species
• Mass exposures to potentially rabid animals (e.g., bats, cats) may occur in summer camps, county fairs (e.g., rabid goat), petting zoos (e.g., rabid sheep), schools, and public events.

General Prevention

• Targeted to humans and domestic animals
• Immunoprophylaxis: Preexposure rabies prophylaxis (Pre-EP) is offered to those at high risk (e.g., veterinarians, animal handlers, trappers, travelers to high-risk regions).
• Avoid unnecessary contact with wild animals in the United States and overseas.
• Pets should be vaccinated and kept updated on their immunizations.

Pathophysiology

• Except for rare cases, the rabies virus enters the body through a bite that breaks the skin and introduces infected saliva:
  • From there, the virus gains access to muscle, where it is sequestered.
  • The virus then enters the peripheral nerves, where it moves centripetally to the CNS at a rate of ~3 mm/h.
  • Once in the CNS, infection spreads rapidly throughout many areas of the brain.
  • Neurologic manifestations progress rapidly from sensorial alterations to coma.
  • Leads to autonomic instability, the mechanisms of which are still poorly understood, which leads to acute death
• Average incubation period is 2 to 3 weeks to 2 to 3 months and, in rare cases, is suspected to be several to many years, with the longest documented incubation being 8 years.

Etiology

• The 14 known members of the Lyssavirus genus, rhabdovirus family (rabies virus, Lagos bat virus, Mokola virus, Duvenhage virus, Aravan virus, Irkut virus, Khujand virus, European bat lyssavirus types 1 and 2, West Caucasian bat virus, Australian bat lyssavirus, Shimoni bat virus, Ikoma virus, and Bokeloh virus) are suspected to be capable of causing human rabies death.
• Lyssaviruses are single-stranded RNA viruses and all except Mokola had been associated with bats.
• Most cases are due to the rabies virus, with rare cases due to the other lyssaviruses.