Causes of Rabies Symptoms

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The rabies virus is of the genus Lyssavirus, of which there are more than eighty species. There are actually ten different viruses in the rabies serogroup, but of these ten it is the rabies virus which most often causes infection in humans. Other viruses in the rabies serogroup include Mokola virus, Kotonkan virus, and European bat Lyssavirus.

Throughout the world, unvaccinated dogs remain the main reservoir of rabies virus. This group includes non-domesticated canine species such as wolves, jackals, and coyotes. In the United States, the main reservoir animals are raccoons, skunks, and bats.

Rabies is normally transmitted via a bite from an infected animal. Death is a near-certainly if treatment is not administered before the onset of symptoms.

Symptoms of Rabies

Rabies symptoms include headache and fatigue and fever. These initial symptoms are quickly followed by anxiety, confusion and hallucinations.

Other characteristic symptoms include excessive production of saliva, difficulty swallowing, fear of water, and partial paralysis.

What causes Rabies Symptoms?

Rabies is a viral disease which primarily affects the central nervous system. The virus is a neurotropic virus, which means it has an affinity for the CNS. This is, in fact, how the virus avoids being recognized by the immune system. The central nervous system is an immune “privileged” site, which means it is protected from immune system activity that might cause damaging inflammation. This privilege allows the virus to escape detection by the immune system.

Once entering the CNS, the virus remains in an incubation phase for between twenty and ninety days. Cases have been recorded where incubation lasts a year or longer, but this is rare. During incubation, the virus begins to multiply.

Following incubation, the virus begins to enter CNS sensory and motor axons. This is known as the prodromal period, and is the time in which the first symptoms begin to appear. One of the hallmark symptoms of this period is pain or numbness at the inoculation site (such as a bite wound), which begins as virus particles begin entering the spinal ganglion. As the virus begins to invade the nervous system, symptoms such as headaches, fever, fatigue, insomnia, agitation, and depression may appear.

As the virus invades the nervous system in greater numbers, the infection enters the acute neurologic period. At this point the virus begins to spread rapidly throughout the central nervous system. Disruption of nervous system function causes a wide range of symptoms, including more several agitation, hallucinations, confusion, and other mood changes and neurological symptoms.

At this point the virus spreads to salivary glands as well as the peripheral nervous system. The disruption of the salivary glands causes excessive saliva production, another hallmark of late-stage infection. As nervous system involvement increases, the body becomes increasingly unstable. Tachycardia, hypertension, hypoventilation, and other symptoms are common. Respiratory failure, coma, and death usually occur within a week or ten days of the onset of neurological symptoms.

References

Centers for Disease Control Rabies Topic Site

National Institute of Health MedlinePlus Rabies Information

Sandra G Gompf, MD, FACP, FIDSA. Rabies information at eMedicine

World Health Organization Rabies Fact Sheet