Agent factors
The virus is excreted in the saliva of affected animals.

Reservoir of Infection
Rabies exist in 3 epidemiological forms: urban rabies, wild life (sylvatic) rabies and bat rabies.

Urban Rabies
The transfer of infection from wild life to domestic dogs result in the creation of urban cycle which is maintained by the dog and is responsible for 99% of human cases in India.

Wild life rabies
The wild life cycle is perpetuated by the jackal, fox, hyena and other wild life carriers which are the main reservoir and transmitters of rabies.

Bat rabies
In certain Latin American countries (e.g. Brazil, Venezuela, Mexico, Trinidad, Tobago) and parts of U.S.A. the vampire bat is an important host and vector of rabies.

Sources of Infection
In dogs and cats, the virus may be present in the saliva for 3–4 days (occasionally 5–6 days) before the onset of clinical symptoms and during the course of illness till death.

Animal bites
In India most of the human rabies cases have resulted from dog bites. Transmission of man is particularly through rabid dog bites. As a prerequisite to transmission, the saliva of the dog (or the biting animal) must contain the virus at the time of bite.

Licks
Licks on abraded skin and mucosa (abraded or unabraded) can transmit the disease.

Person to person
Man to man transmission, although rare, is possible.

Incubation period of Rabies
The incubation period in man is highly variable, commonly 3–8 weeks following exposure but may vary from 4 days to many years. In general, incubation period tends to be shorter in severe exposures and bites on face, head, neck and upper extremities and bites by wild animals.

Pathogenesis of Rabies
Rabies virus replicates in muscle or connective tissue cells at or near the site of introduction before it attaches to nerve endings and enters peripheral nerves. It spreads from the site of infection centripetally via the peripheral nerves towards the central nervous system.