Rabies

Rabies is an infectious viral disease affecting human, domestic and wild animals. Human get this infection from infected animals, usually from the saliva of dog when it bites. Other rabid animals that can carry this virus are bat, monkey, cat, fox, raccoon, mongoose, pig and several other species. All reported rabies infections are from mammals.

Rabies human deaths are estimated to be 50,000 each year. But the actual infected population may be higher as no global rabies monitoring system exists.

The World Health Organization (WHO) reports:

99% of reported annual rabies deaths occur in Asia, Africa and South America.

90% deaths occurs in Asia.

60% deaths occurs in India; incidence is 3 in 1,00,000 population a year.

Rabies virus belongs to the Lyssavirus genus. There are 7 types in Lyssavirus, in which classic rabies virus represents the type 1. Once transmitted, the incubation period (time between exposure to the virus and symptoms become first apparent) is generally between 20 and 90 days, but it can also be of 4 days to several years in certain extremes cases.

Rabies virus is nuerotrophic which affects the nervous system of human and animals. As the virus spreads in the central nervous system (like brain), progressive inflammation of the brain (encephalitis) develops. The initial symptoms of rabies are often pain, mild fever or abnormal sensation of the skin like pricking, tingling or numbness (paraesthesia) of the limb. Once symptoms develop, rabies is fatal to both animals and humans, if not treated immediately. Advanced symptoms include hydrophobia (difficulty swallowing liquids), aerophobia (difficulties in inhalation, breathlessness), photophobia (excessive sensitivity to light and tendency to avoid light) and (or) paralysis.

Nerve Tissue Vaccines (inactivated rabies infected brain tissues from animals) is once a staple in rabies prevention and is being phased out as it has serious side effects human such as paralysis. Modern rabies vaccines such as, cell culture rabies vaccines (CCRV) and purified chick-embryo cell vaccine (PCECV) and purified Vero cell rabies vaccine (PVRV) are in common use and administered by intradermal (inside the skin)  or intramuscular (inside the muscle) routes.

Human rabies in Indian context

Most animal bites in India are due to dogs (92%), followed by monkeys (3%), cats (2%) and other mammals. Rural areas account for 76% of human rabies cases. In many cases the human victim follows dogs closely for symptoms of rabies. If dogs are non-symptomatic the human victim is unlikely to seek any medical advice. Approximately 59% of animal bite victims resort to faith healing, herbal therapy or self treatment. An Indian scientific report in 2008 suggests that rabies incidence is reducing from 3 in 1,00,000 to 2 in 1,00,000 (0.003 to 0.002%) in human.

Table 1. WHO compilation of  human rabies data in Asia for 2004.