Rabies Pathology
The nature, cause, origin, and progress of Rabies.
Rabies is a viral disease. The virus is present in the saliva of infected animals. Thus, the most common mode of transmission Rabies is a viral disease. The virus is present in the saliva of infected animals. Thus, the most common mode of transmission is via a bite. The rabies virus is transmitted from the saliva (containing an infective dose) into the muscle and near nerve tissue of the victim.
More information about the virus - from CDC.
When the virus is introduced through a bite, it begins to replicate in the skin or muscle tissue before it works its way into the peripheral nerves. The virus travels along the peripheral nerves from the point of inoculation to the Central Nervous Systems (CNS). The time it takes the virus to go from the bite wound to the brain is the Incubation Period. The incubation period can range anywhere from 2 weeks to several months. The average time frame is 20 days to 3 months. Most prophylactic vaccination programs involve multiple shots spread out over this time period.
The location of the bite wound will determine the length of incubation. The dense concentration of sensory nerve endings in the head, face, neck and fingers accounts for the higher fatality rate observed when these areas are exposed. Similarly, the more extensive or severe the bite wounds, the higher the mortality, because more nerve tissue is exposed to an infective dose of rabies virus. In order to prevent infection of the CNS, wounds must be thoroughly cleaned and vaccination given as soon after the bite as possible.
Since the nervous tissue is stationary, the virus moves slowly as it jumps from nerve cell to nerve cell on its way to the brain. Though very small amounts of virus could enter the blood stream when the bite occurs, it would be unable to replicate there, so the blood from a rabid animal is not considered infectious.
It spreads through the CNS and into the peripheral nerves, which bring it to a variety of organs and tissues (including the skin, intestines, and salivary glands). In the salivary glands the virus replicates in abundance and is shed in the saliva. At this point the animal becomes infectious and can transmit the disease through a bite. There is a period of about 3 days that the animal will be actively shedding the virus but does not display any symptoms.
After this 3 day period, the virus in the brain has infected enough of the brain tissue that it begins to affect the animal's behavior (see symptoms of rabies).
