Rabies transmission

Rabies is usually transmitted through a bite from an infected animal.[1]

TEM micrograph with numerous rabies virions (small dark-grey rod-like particles) and Negri bodies (the larger pathognomonic cellular inclusions of rabies infection).

Transmission between humans is extremely rare, although it can happen through organ transplants, or through bites.

After a typical human infection by bite, the virus enters the peripheral nervous system. It then travels along the nerves towards the central nervous system by retrograde axonal transport. During this phase, the virus cannot be easily detected within the host, and vaccination may still confer cell-mediated immunity to prevent symptomatic rabies. Once the virus reaches the brain, it rapidly causes encephalitis and symptoms appear. This is called the "prodromal" phase and at this time, treatment is usually unsuccessful. Rabies may also inflame the spinal cord producing myelitis.

Animals
Dog with rabies virus
See also: Rabies and animals

Any mammal may become infected with the rabies virus and develop symptoms, but dogs are by far the main source of human rabies deaths — responsible for up to 99% of all rabies transmissions to humans.[2] Infected monkeys, raccoons, foxes, skunks, cattle, wolves, bats, and cats are also known to transmit rabies to humans. Rabies may also spread through exposure to infected domestic farm animals, groundhogs, weasels, bears and other wild carnivores. Small rodents such as squirrels, hamsters, guinea pigs, gerbils, chipmunks, rats, and mice and lagomorphs like rabbits and hares are almost never found to be infected with rabies and are not known to transmit rabies to humans.[3] Vampire bats can transmit rabies to humans in the 'new world' tropics.[4][5]

The virus is usually present in the nerves and saliva of a symptomatic rabid animal.[6][7] The route of infection is usually by a bite. In many cases the infected animal is exceptionally aggressive, may attack without provocation, and exhibits otherwise uncharacteristic behaviour.[8] (Note that "uncharacteristic behaviour" may include uncharacteristic friendliness as well as the stereotypically violent mode of rabies. Since rabies can be transmitted through contact with saliva, not just through bites, this "tame" mode of rabies is no less dangerous.) Transmission may rarely occur via an aerosol through mucous membranes; and might conceivably endanger people exploring caves populated by rabid bats.[9] However, aerosol transmission of rabies has not yet been well documented in the natural environment.[10]

References
  1. http://www.medicinenet.com/rabies_virus/article.htm
  2. WHO Rabies Fact Sheet http://www.who.int/mediacentre/factsheets/fs099/en/
  3. "Rabies. Other Wild Animals: Terrestrial carnivores: raccoons, skunks and foxes". Centers for Disease Control and Prevention (CDC). Retrieved 23 December 2010. Cite has empty unknown parameter: |month= (help)
  4. Pawan, J. L (2016). "The Transmission of Paralytic Rabies in Trinidad by the Vampire Bat (Desmodus Rotundus Murinus Wagner, 1840)". Annals of Tropical Medicine & Parasitology. 30 (1): 101–30. doi:10.1080/00034983.1936.11684921.
  5. Pawan, J. L (2016). "Rabies in the Vampire Bat of Trinidad, with Special Reference to the Clinical Course and the Latency of Infection". Annals of Tropical Medicine & Parasitology. 30 (4): 401–22. doi:10.1080/00034983.1936.11684948.
  6. The Merck Manual, Eleventh Edition (1983), p. 183
  7. The Merck manual of Medical Information. Second Home Edition, (2003), p. 484.
  8. Turton, Jenny (2000). "Rabies: a killer disease". National Department of Agriculture.
  9. Constantine, Denny G (1962). "Rabies Transmission by Nonbite Route". Public Health Reports. 77 (4): 287–9. doi:10.2307/4591470. JSTOR 4591470. PMC 1914752. PMID 13880956.
  10. Gibbons, Robert V (2002). "Cryptogenic rabies, bats, and the question of aerosol transmission". Annals of Emergency Medicine. 39 (5): 528–36. doi:10.1067/mem.2002.121521. PMID 11973559.

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