Infection results most frequently from transmission of the virus from an infected animal to a human via a bite. Occasionally infection can also occur via an open wound, mucous membranes or even as the result of organ transplantation 1.
In developed countries, most cases are the result of bites from rabid bats, whereas in the developing world, rabid dogs are the main source of human infection 1.
Involvement of the CNS by rabies can take two forms 1:
- classic rabies encephalitis (80%)
- paralytic rabies (20%)
Classic rabies encephalitis
Encephalitis is by far the most common presentation of CNS involvement by rabies, accounting for 80% of cases. Symptoms are initially non-specific with general systemic symptoms, inspiratory spasms, autonomic dysfunction and altered mental status. With time classic symptoms and rabies encephalitis develop including: hydrophobia, aerophobia and hypersalivation 1.
Paralytic rabies is relatively uncommon accounting only for 20% of CNS infections in humans.