Rabies - Hydrophobia

Rabies is caused by a bite from an infected animal but occasionally by other forms of contact. In some countries it is a significant killer of livestock. The rabies virus makes its way to the brain by following the peripheral nerves.

RABIES OR hydrophobia is a viral neuroinvasive disease that causes acute encephalitis (inflammation of the brain) in warm-blooded animals. It is zoonotic (ie transmitted by animals), most commonly by a bite from an infected animal but occasionally by other forms of contact. It is fatal if left untreated. In some countries it is a significant killer of livestock.

The rabies virus makes its way to the brain by following the peripheral nerves. The incubation period of the disease depends on how far the virus must travel to reach the central nervous system, usually taking a few months. Once the infection reaches the central nervous system and symptoms begin to show, the untreated infection is usually fatal within days. In the beginning stages of rabies, the symptoms are malaise, headache and fever, while in later stages it includes acute pain, violent movements, uncontrolled excitements, depressions and the inability to swallow water (hence the name hydrophobia).


In the final stages, the patient begins to have periods of mania and lethargy, and coma. Death generally occurs due to respiratory insufficiency. The term is derived from the Latin rabies, "madness." This, in turn, may have come from the Sanskrit rabhas, "to do violence.

The Greeks derived the word "lyssa," which is derived from "lud" or "violent," this terminology is used in the name of the genus of rabies lyssavirus. The rabies virus is the type species of the Lyssavirus genus, which encompasses other similar viruses.

Lyssa-viruses have helical symmetry, with a length of about 180nm and a cross-sectional diameter of about 75nm. These viruses are enveloped and have a single stranded RNA genome with negative-sense. The genetic information is packaged as a ribonucleoprotein complex, in which RNA is tightly bound by the viral nucleoprotein.

The RNA genome of the virus encodes five genes whose order is highly conserved. These genes are nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G) and the viral RNA polymerase (L). From the point of entry, the virus travels quickly along the neural pathways into the central nervous system (CNS) and then further into other organs. The salivary glands receive high concentrations of the virus thus allowing further transmission.