Epidemiology - Rabies Virus

Epidemiology

Rabies is a recognized zoonotic disease worldwide.

◗ Geographical distribution

Rabies has been recognized for over 4000 years. Today it is found in most countries, except many Australian islands, Great Britain, Japan, Hawaii, and most of the Caribbean islands. The risk of rabies is highest in countries with hyperendemic canine rabies, including most of Asia, Africa, and Latin America.

Rabies is endemic in India. It has been estimated that more than 30,000 people die of rabies in India every year. More than 70,000 people in India receive antirabies vaccination per year. With the dog population of over 16 million, the problem of rabies is huge. The virus is usually transmitted from a rabid animal to humans mostly by bites or other forms of traumatic contacts.

◗ Reservoir, source, and transmission of infection

Rabies is a zoonotic disease. Dogs are the important reservoir of infection. Other animal reservoirs include silver-haired bats, eastern pipistrella, raccoons, skunks, foxes, or cats, ferrets, cattle, opossums, fowl, etc. Foxes are more infectious than dogs and other animals, because larger amounts of virus (up to 106 infectious doses/mL) are present in their saliva.

The virus is excreted in saliva of infected dogs, foxes, wolves, jackals, vampire bats, raccoons, and skunks. The virus is found in the salivary gland of these infected animals. Infected saliva or infected CNS tissue, including corneal transplants in humans, are the sources of infection. The virus is transmitted to humans by following ways:

·           Bite of a rabid dog or other infected animals is the main route of transmission of infection.

·           Contact of saliva with broken skin or with mucous mem-branes, exposure to aerosolized secretions from an infected animal, and contact with unpasteurized milk from dairies are very uncommon modes of transmission.

·           Corneal transplants: The only documented cases of rabies caused by human-to-human transmission occurred in eight recipients of transplanted corneas. Currently, donated cor-neas are not accepted if the donor died from encephalitis that may be consistent with rabies. In India, few such cases have also been documented.

With the exception of corneal transplants, man-to-man infec-tion is rare.