Rabies transmission

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

Rabies is mostly transmitted to humans, and between animals, through the saliva of infected animals. Transmission is generally through a bite from any infected animal.[1]

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. 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

Any mammal may become infected with the rabies virus and develop symptoms, including humans. But dogs are, by far, the main source of human rabies deaths, contributing up to 99% of all rabies transmissions to humans according to the World Health Organization.[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, but not necessarily, 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.) It has been suggested that transmission may very rarely occur via an aerosol through mucous membranes; and that transmission in this form might conceivably endanger people exploring caves populated by rabid bats.[9] However, non-bite transmission of rabies is very rare, and aerosol transmission has never 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 2010-12-23.
  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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