Rabies overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Rabies is a viral zoonotic disease that causes acute encephalitis (inflammation of the brain) in mammals. In non-vaccinated humans, rabies is almost invariably fatal after neurological symptoms have developed, but prompt post-exposure vaccination may prevent the virus from progressing. There are only six known cases of a person surviving untreated rabies. [1]
Historical Perspective
Rabies is a disease that has been classically associated with infected animals, mainly dogs. The first written record was from approximately 1930 BC when the owner of a dog with Rabies symptoms was told to take preventative measures against bites. If a person died from being bitten by a rabid dog, the owner was fined heavily. Although dogs are viewed as the main culprit of rabies, rabies is also associated with animals such as possums, skunks, and more importantly, bats.
Pathophysiology
The rabies virus is categorized as a Lyssavirus. The molecular biology of rabies consists of bullet shaped virus with helical symmetry that has a length of approximately 180 nm. Rabies typically has its greatest effect on the brain. It is typically defined by encephalitis and myelitis. It is very important to avoid being bitten by a rabid animal because the virus is typically transmitted through the saliva of an infected organism.
Differentiating Rabies from other Diseases
The differential diagnosis for rabies deals with eliminating diseases with similar symptoms from the diagnosis. There are many viruses that can appear similar to rabies such as encephalitis and the herpes simplex virus. It is very important to rule out certain diseases such as echovirus and poliovirus. Rabies is a serious disease that needs to be treated quickly if someone is suspected to be infected with the virus.
Epidemiology and Demographics
The epidemiology of rabies addresses several questions: what animals have rabies and in what regions of the country, how many people get rabies and from what animals, and what are the best strategies for preventing rabies in people and animals. Epidemiologic information is often presented as statistical data (e.g., numbers or percentages in graphs and on maps). For example, in 2001, 7,437 cases of rabies were reported in the United States. Raccoons accounted for almost 40% of reported cases.
Risk Factors
A bite from an infected animal is the biggest risk factor. People that live in an area, or travel to an area that has a large incidence for rabies, are at a high risk for acquiring rabies from a rabid animal. Handling certain wild animals such as bats or raccoons will put a person at a higher risk.
Diagnosis
Symptoms
When a person contracts rabies, they do not show symptoms immediately. The disease take a period of time to manifest in the body which is know as its period of incubation. Once symptoms arise, the patients condition deteriorates rapidly. There is not a great deal of time available to perform a routine physical examination. A patient will most likely present with some severe symptoms that may be misdiagnosed as diseases such as Guillain-Barre syndrome.
Laboratory Findings
Several tests are necessary to diagnose rabies ante-mortem (before death) in humans; no single test is sufficient. Tests are performed on samples of saliva, serum, spinal fluid, and skin biopsies of hair follicles at the nape of the neck. Saliva can be tested by virus isolation or reverse transcription followed by polymerase chain reaction (RT-PCR). Serum and cerebrospinal fluid are tested for antibodies to rabies virus. Skin biopsy specimens are examined for rabies antigen in the cutaneous nerves at the base of hair follicles.
References
- ↑ VIROLOGY - CHAPTER TWENTY RABIES pathmicro.med.sc.edu