What is rabies?

Updated: Jun 21, 2019
  • Author: Sandra G Gompf, MD, FACP, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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Rabies is caused by a neurotropic virus of the family Rhabdoviridae, genus Lyssavirus, subgroup rabies virus.

The virus is commonly transmitted via saliva that contaminates bites, scratches, and wounds, and, recently, via mucosal exposure. [1] Rabies transmission via transplanted neurologic tissues (corneas) and solid organs has also been documented. [2, 3, 4] One case of rabies was reported in China after exposure of an open wound to the blood of a person bitten by a dog; the exposed person succumbed to rabies after seeking no medical care, while the bitten individual received postexposure prophylaxis and did not develop rabies. [5]

Animal species that present the highest transmission risk to humans include canines (dogs, foxes, coyotes), cats, raccoons, and bats. In the case of bats, exposure may go unrecognized by a sleeping individual; thus, postexposure prophylaxis (PEP) is recommended whenever a bat is discovered in the room of a sleeping or incapacitated person. [6]

The lowest-risk species is the opossum, in which the virus does not replicate because of its low body temperature.

Human-to-human rabies virus transmission via saliva is theoretically possible. While it has not been documented, a mucosal, scratch, or bite exposure to saliva or blood of a person (or any other mammal) suspected of having rabies would be managed in a manner similar to that of any other exposure, with rabies PEP.

Standard precautions are recommended in the care of patients with rabies in healthcare settings, including use of personal protective equipment during activities that may pose a risk of salivary contamination of mucosa or break in the skin. [7]

Rabies PEP should begin as soon as possible following an exposure, but no specific time frame has been defined, nor is it ever "too late" for PEP. Rabies is almost invariably fatal once symptoms begin, regardless of treatment, while PEP is safe and nearly 100% effective if administered before onset. Although the incubation period of rabies is typically 1-3 months, this may be hastened to a few days if inoculation occurs on the head and neck or may be prolonged if inoculation occurs on a site more distant from the central nervous system. It may also be delayed by very many years.

The fatal madness of rabies has been described throughout recorded history, and its association with rabid canines is well known. For centuries, dog bites were treated prophylactically with cautery, with predictable and unfortunate results. In the 19th century, Pasteur developed a vaccine that successfully prevented rabies after inoculation and launched a new era of hope in the management of this uniformly fatal disease. (See Treatment and Medications.)

Rabies is a viral disease that affects the central nervous system (CNS). The genus Lyssavirus contains more than 80 viruses. Classic rabies, the focus of this article, is the prototypical human Lyssavirus pathogen. (See Etiology.)

There are 10 viruses in the rabies serogroup, most of which only rarely cause human disease. The genus Lyssavirus, rabies serogroup, includes the classic rabies virus, Mokola virus, Duvenhage virus, Obodhiang virus, Kotonkan virus, Rochambeau virus, European bat Lyssavirus types 1 and 2, and Australian bat Lyssavirus. (See Etiology.) Five antigenic variants of rabies strains are recognized in the United States (see the image below).

Distribution of the 5 strains of rabies virus and Distribution of the 5 strains of rabies virus and the associated wildlife in the United States.

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