Rabies is a viral disease that causes inflammation of the brain, and in the vast majority of cases, death. Most cases of rabies infection occur through the bite of an infected animal, when the virus enters the body in the animal’s saliva. According to the World Health Organization, proper cleaning of the wound and rapid immunization can halt the disease in practically 100 percent of cases, if carried out before the rabies infection progresses into its later stages.
Incubation Stage
During the incubation stage, the virus attaches itself to muscle or nerve cells at specific locations called nicotinic acetylcholine receptors. The virus may remain in muscle cells for a long period while it replicates, notes Richard Hunt, on the University of South Carolina School of Medicine's Microbiology and Immunology On-Line website. The infection does not cause any symptoms to appear during this stage, which may last up to several months.
The rate of progress of the disease depends on the number of viral pathogens injected, the number of nerve endings in the bite area, the proximity of the site to the brain, and the general health of the person’s immune system. The Centers for Disease Control and Prevention notes that the hands and face have a large number of nerve endings and a bite in these areas carries a higher risk of rapid progression of the infection to the next stage.
Prodromal Phase
The Centers for Disease Control and Prevention points out that that the virus does not enter the bloodstream, but must be picked up by a nerve synapse in order to make its way to the brain. Professor Hunt explains that the virus proceeds along the axons of the nerves toward the central nervous system, using a process known as retrograde transport. It eventually reaches and penetrates the spinal ganglia and the spinal cord, then spreads into the brain. There, it can infect different brain cells, including those in the cerebellum and the hippocampus. This period in the progression of the infections is called the prodromal phase.
Treatment During Early Stages
The CDC warns that the virus must be prevented from entering peripheral nerves, if the disease course is to be halted. The disease is fatal after the appearance of symptoms and only early treatment can prevent eventual death from rabies. The Merck Manual explains that proper treatment involves thorough cleansing of the site of the bite with benzalkonium chloride, or soap and water. If the bite wound is deep, it should be washed with soapy water with a medium degree of pressure. After cleansing, the wound should be left uncovered. Post exposure prophylaxis involves an injection of rabies immune globulin into the wound site in order to provide antibodies that can neutralize the virus in situ. In addition, a series of injections of rabies vaccine serves to activate and accelerate the body's own immune response. Hunt notes that the body's response is usually slow and becomes effective in neutralizing the virus only after the virus has entered the brain, when it is too late to provide any chance for survival.
