Rabies (cont.)

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What is the history of rabies, and what is the cause of rabies?

Rabies has been reported in historical documents since about 2300 BC. Ancient texts recorded that owners of rabid dogs were cautioned against getting bitten. The word rabies is derived from the Latin word rabies, which meant "madness or rage." For many centuries, it was common practice to kill any animal or human that showed symptoms of the disease because tradition had taught people that the disease could be easily passed on to other people and isolation or death of the afflicted could prevent transmission of the disease. In the 15th century, Italian physician Girolamo Fracastoro studied rabies and concluded that it was a communicable disease transmitted to people by direct contact with saliva from infected animals. He termed the disease rabies. In 1895, after studying the data presented by Fracastoro centuries before, Louis Pasteur and Emile Roux were able to produce a vaccine against the disease-causing viruses without actually discovering or isolating the viruses.

Rabies has been a problem in many countries, even into the 21st century as China developed a "one-dog" rule for people in Beijing to better control an increasing rate of dog rabies in 2006. Although the U.S. has had no people infected by dogs in years, there is an increasing incidence in wild animals (for example, bats and raccoons), especially in the southern states since the 1970s.

The virus that causes rabies is Lyssavirus (Lyssa is the Greek goddess of madness, rage, and frenzy) rabies, a cylindrical or bullet-shaped virus that is enveloped and contains a negative-sensed RNA that makes up its genetic material.

Picture of the longitudinal view of the viral structure.
Picture of cross-sectional view of the viral structure.
Figure 2: CDC diagrams of the bullet-shaped rabies virus. The top image is the longitudinal view, and the bottom image is the cross-sectional view of the viral structure. SOURCE: CDC

The virus is termed a neurotropic virus because it proliferates in nerve tissues, especially the brain tissues of humans and animals. It proceeds from the bite or entrance wound along nerves to eventually infect the brain. The treatment use of human immune globulin and vaccine is designed to interrupt and kill the virus before it makes the journey to the brain. The virus enters nerve cells, takes over the cells systems, and develops virus replicating sites (termed Negri bodies, that can be seen microscopically inside cells) that produce new viruses to continue viral spread to other body sites like the brain and, most important for spreading the viruses to other animals, the salivary glands. The rabies life cycle is relatively simple; the virus is transmitted to a wild animal by bites or saliva, the virus replicates in the bitten animal that, in turn, bites another animal and the cycle is completed. Humans are incidentally infected and rarely transmit the virus so humans play almost no role in the rabies life cycle.

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