Rabies history and symptoms

History and Symptoms

Micrograph with numerous rabies virions (small dark-grey rod-like particles) and Negri bodies, larger pathognomonic cellular inclusions of rabies infection

The virus is usually present in the nerves and saliva of a symptomatic rabid animal. The route of infection is usually, but not necessarily, by a bite. In many cases the affected animal is exceptionally aggressive, may attack without provocation, and exhibits otherwise uncharacteristic behaviour[1]. Transmission may also occur via an aerosol through mucous membranes; transmission in this form may have happened in people exploring caves populated by rabid bats. Transmission between humans is extremely rare, although it can happen through transplant surgery (see below for recent cases), or, even more rarely, through bites or kisses.

After a typical human infection by bite, the virus directly or indirectly enters the peripheral nervous system. It then travels along the nerves towards the central nervous system. During this phase, the virus cannot be easily detected within the host, and vaccination may still confer cell-mediated immunity to prevent symptomatic rabies. Once the virus reaches the brain, it rapidly causes encephalitis and symptoms appear. It may also inflame the spinal cord producing myelitis.

The period between infection and the first flu-like symptoms is normally two to twelve weeks, but can be as long as two years. The first symptoms of rabies may be nonspecific flu-like signs — malaise, fever, or headache, which may last for days. There may be discomfort or paresthesia at the site of exposure (bite), progressing within days to symptoms of cerebral dysfunction, anxiety, confusion, agitation, progressing to delirium, abnormal behavior, hallucinations, and insomnia. The acute period of disease typically ends after 2 to 10 days (6). Once clinical signs of rabies appear, the disease is nearly always fatal, and treatment is typically supportive. Disease prevention is entirely prophylactic and includes both passive antibody (immune globulin) and vaccine. Non-lethal exceptions are extremely rare. To date only six documented cases of human survival from clinical rabies have been reported and each included a history of either pre- or postexposure prophylaxis. The few humans who are known to have survived the disease were all left with severe brain damage, with the recent exception of Jeanna Giese (see below).