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  • Topic: Rabies, Nervous system, Central nervous system
  • Pages : 6 (2026 words )
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  • Published : October 23, 2005
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Though rabies has been documented since before the birth of Christ, the recent deaths from rabies of four people in the United States, who had received transplanted organs from a man infected but not actively suffering from the disease, show that the rabies continues to be a virulent and silent killer of people. Scientists speculate that rabies first appeared in Africa or Asia as five other viruses related to rabies are isolated there. As early as 2,300 B.C. there were laws in Babylonia that required the owner of a rabid dog to pay a fine if the dog bit someone. Writings have been found in Greece in the fifth and fourth centuries B.C. that described rabies in domestic animals as well as dogs. There are accounts of rabies epidemics in wolves in western Europe in 1271 and it is believed that rabies was brought to the New World in 1753 when dogs brought to the Virginia colony were found to be infected. In 1998, there were from 30,000 to 50,000 deaths worldwide from rabies, but only one in the United States, though 18,000 in the U.S. received rabies vaccine after being bitten by infected animals.1

It has been widely accepted that people who had access to the vaccine were essentially safe from the disease. However, the death of the fourth person in the U.S. in the course of a week from rabies contracted through organ transplants made national headlines on July 8, 2004 2 because no one had suspected the 20 year old male donor had been infected. This event brought the threat of rabies to the forefront again as one of the trademarks of rabies is that it shows no symptoms until it is too late for a vaccine to be effective. The reason there are no early symptoms is because of the way rabies is transmitted and the way it affects the human body. Rabies is caused by a rhabdovirus similar to those that cause encephalitis. However, the rabies virus requires the involvement of the central nervous system as part of its lifecycle. Rabies virus is usually transmitted through the saliva of a rabid animal via a bite that punctures the skin of the victim. In more infrequent cases it can be contracted via saliva entering an existing wound or through inhalation in a cave with a dense, long term population of infected bats. Once the bullet shaped virus breaks through the protective epithelium, it reaches the central nervous system via peripheral nerves by exploiting retrograde axoplasmic transport or transsynaptic transmission.3 There is an incubation period averaging three to seven weeks (minimum of 10 days, maximum of several years) during which time the virus may amplify in peripheral tissue, particularly the skeletal muscle. The incubation period is somewhat connected to the distance of the point of infection to the brain. The virus gains access to the central nervous system via motor and sensory nerves. Early symptoms include fever, headache and a sore throat. Once the virus reaches the brain, the first area to be infected is the limbic system (the portion of the brain involved in emotions). The rabies sufferer grows nervous, restless and unusually sensitive to light and sound. Abnormalities in behavior become pronounced, including delirium and biting behavior, alternating with periods of calm, widespread brain dysfunction and impairment of respiratory and autonomic nervous systems. Attempts at drinking cause laryngeal spasms which give rise to a violent reaction to even the site of water (hydrophobia). As the infection becomes widespread and often includes the brain stem, spinal cord, hippocampus, basal ganglia, cortex and related structures. The virus then migrates along efferent nerves to the salivary glands. This form is referred to as furious rabies. Less common is the paralytic or dumb form where acute ascending paralysis resembling Guillain-Barre syndrome predominates with relative staring of higher cortical functions internally. Both forms progress to coma, autonomic nervous system dysfunction and death....
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