Transmission
Any warm-blooded animal, including humans, may become infected with the rabies virus and develop symptoms. Indeed, the virus has even been adapted to grow in cells of poikilothermic vertebrates though natural transmission has only been documented among mammals. Most animals can be infected by the virus and can transmit the disease to humans. Infected bats, monkeys, raccoons, foxes, skunks, cattle, wolves, coyotes, dogs, mongoose (normally yellow mongoose) or cats present the greatest risk to humans. Rabies may also spread through exposure to infected domestic farm animals, groundhogs, weasels, bears and other wild carnivores. Rodents (mice, squirrels etc) are seldom infected.
The virus is usually present in the nerves and saliva of a symptomatic rabid animal. 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 behavior.
Transmission between humans is extremely rare. A few cases have been recorded through transplant surgery.
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. When the virus reaches the brain, it rapidly causes encephalitis. This is called the ''prodromal'' phase, and is the beginning of the symptoms. Once the patient becomes symptomatic, treatment is almost never effective and mortality is near 100%. Rabies may also inflame the spinal cord producing transverse myelitis.
Prevalence
The rabies virus survives in widespread, varied, rural fauna reservoirs. However, in Asia, parts of the Americas and large parts of Africa, dogs remain the principal host. Mandatory vaccination of animals is less effective in rural areas. Especially in developing countries, pets may not be privately kept and their destruction may be unacceptable. Oral vaccines can be safely distributed in baits, and this has successfully reduced rabies in rural areas of France, Ontario, Texas, Florida and elsewhere, like the City of Montréal, Québec, where baits are successfully used on raccoons in the Mont-Royal park area. Vaccination campaigns may be expensive, and a cost-benefit analysis can lead those responsible to opt for policies of containment rather than elimination of the disease.
There are an estimated 55,000 human deaths annually from rabies worldwide, with about 31,000 in Asia, and 24,000 in Africa. India has been reported as having the highest rate of human rabies in the world, primarily because of stray dogs. As of 2007, Vietnam had the second-highest rate, followed by Thailand; in these countries too the virus is primarily transmitted through canines (feral dogs and other wild canine species). Recent reports suggest that wild rabid dogs are roaming the streets. Because much cheaper pre-vaccination is not commonly administered in places like Thailand, the expense for lack of preparation with far more costly post-exposure prophylaxis can hit families hard. In the midwestern United States, skunks are the primary carriers of rabies, comprising 134 of the 237 documented non-human cases .
Further Reading
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