While its precise origins are unknown, rabies is thought to derive from rabhas, Sanskrit for "to do violence." Others trace its origins to Latin, rabis - "rage" or rabere - "to rave."
There are two forms of rabies. "Furious" rabies, the most common form, affects primarily the brain stem, causing the victim to become aggressive or excitable. The less common form, "paralytic" or "dumb" rabies, affects the spinal cord and can result in weakness, lethargy and the inability to move, speak or make sounds.
Rabies is most often transmitted as the result of a bite or scratch when the saliva of an infected animal enters the skin. The resulting viral infection attacks the victim's central nervous system.
The incubation period for rabies — the time between infection and the appearance of symptoms — can range from a few weeks to a year or longer in humans, although 30 to 50 days is more common. Animals usually develop symptoms 20 to 60 days after exposure. The incubation period depends on the dose of virus received and the location of the bite or contact.
Following infection, a series of worsening symptoms develop. Initial complaints resemble those of a cold or flu — fever, headaches, and muscle pain — but as brain function is affected, symptoms quickly worsen. The victim may experience agitation or irritability; loss of muscle control or paralysis, usually beginning in the legs; depression; and confusion.
When the virus affects the nerves of the salivary glands, it causes painful spasms of the throat and voice box. A sip of water can trigger these spasms, leaving the victim fearful of drinking — explaining why rabies is sometimes referred to as "hydrophobia," the fear of water. The infected salivary glands begin to produce too much saliva, which causes the appearance of foaming around the mouth associated with rabies. Coma and death usually occur within three to 20 days of the onset of symptoms. Once the rabies symptoms become apparent, no cure is known. The only palliative care is constant anaesthesia, to avoid the extremely painful spasms of all limbs.
Further information:
World Health Organization (WHO) Rabies Fact Sheet:
http://www.who.int/mediacentre/factsheets/fs099/en
National Institutes of Health (NIH) Medline Plus information on rabies:
http://www.nlm.nih.gov/medlineplus/rabies.html
