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Rabies

Rabies is a disease that is spread by a rhabdovirus, a virus from the viral family Rhabdoviridae. The rabies virus is the only member of this family that is known to cause disease in humans; it primarily targets members of the plant and animal family. This virus is composed of RNA material inside a capsule, which means that it releases its RNA in the host cell and proceeds to replicate itself.
The rabies virus is spread through the saliva, primarily as a result of being bitten by an infected animal; however, there are some instances in which it has been spread by inhalation of aerosol particles or contamination of the mucus membranes from contact with the saliva of an infected animal. Once contact has occurred there is a three to twelve week incubation before symptoms begin to manifest; during this time the animal will be able to spread the virus to other non-infected hosts. For this reason it is vitally important that following a bite by a wild animal the bite site be washed thoroughly and the animal tested.

The virus will begin to replicate at the site of the bite first, but will quickly spread to the CNS, or central nervous system, comprised of the brain and spinal cord. The CNS is the body system which controls the majority of the body’s activities. Once it is established in the brain the virus will spread to the salivary glands, kidneys, heart, hair follicles and cornea.

Early symptoms of rabies are fairly non-specific. The infected host will suffer from fever, malaise and headache. The ensuing encephalitis, or swlling of the brain, will result in anxiety, confusion, insomnia, agitation (this results in the abnormally aggressive behavior seen in animals with rabies), delirium, hallucinations, hypersalivation (slobbering), hyperactive reflexes and convulsions. The host will also display a severe hydrophobia, or fear of the water (this symptom is classic with rabies cases but the exact cause is, as yet, unknown). Once symptoms have manifested, death usually occurs within a matter of days.

The virus itself is diagnosed by a direct fluorescent antibody test on the brain of an animal or, in humans, a biopsy of tissue from the brain or the skin from the nape of the neck. An antibody test, done on the spinal fluid, blood or saliva of an infected human may also be done.  Antibodies are the body’s defense system against viruses, and the presence of a rabies antibody in an animal which has demonstrated symptoms or in a human who has been exposed is considered to be diagnostic. An antibody will not be present unless the host has been exposed to the virus.

The ability of an antibody to fight viruses is beneficial because it has allowed veterinarians to manufacture a vaccine. This vaccine is comprised of an inactive form of the virus which will stimulate the body to create antibodies which will then attack the virus should the animal be exposed again. It is vitally important that every pet owner ensure that their pet receives a rabies vaccine.

A post-exposure prophylaxis has been developed to treat humans who have been exposed to rabies. The body will be injected with both a rabies virus vaccine, stimulating the body’s own immune system to stimulate production of antibodies, and injection of pre-formed antibodies to begin fighting the virus immediately. Four doses of the vaccine will occur on days three, seven, fourteen and twenty eight following exposure. No cases of rabies have occurred when this has been done immediately after exposure, further demonstrating the need for immediate treatment following exposure.

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