Lauren Mekalian
CRA

Disease
Rabies

Almost always fatal, Rabies is a viral infection that affects the central nervous system of mammals, causing encephalitis (def) with or without paralysis.

Causative Agents

The classic rabies virus belongs to the genus Lyssavirus of the Rhabdoviridae family. Among the 80 other members of the genus Lyssavirus are 9 others belonging to the rabies serogroup (def): Obodhiang virus, Kotonkan virus, Mokola virus, Duvenhage virus, Rochambeau virus, European bat virus 1 and 2, and Australian bat virus.

Rabies virions, like all viruses classified in the Rhabdoviridae family, are bullet-shaped and about 180 nm long and 75 nm wide. The bullet is  encapsulated by a peplos (def) with 10 nm spike-like glycoprotein peplomers (def). The single-stranded, non-segmented, antisense RNA found inside the virion's helical capsid codes for nucleoprotein, phosphoprotein, matrix protein, glycoprotein and polymerase.

Epidemiology

Cases of rabies have been documented worldwide, and it is estimated by the World Health Organization that rabies is responsible for about 55,000 deaths each year. In actuality, the number of deaths is probably much higher since rabies is more prevalent in developing countries, where many cases likely go unreported.

Approximately ten million people receive post-exposure prophylaxis (def) every year after exposure to animals potentially infected by rabies. In the U.S., most fatal human rabies cases are from bat strains of the virus; globally, rabies fatalities are most commonly from infected dog bites. Almost half of those fatalities are children under 15 years old, and 95 percent of human deaths from rabies occur in Africa and Asia.

Transmission

Rabies virus is transmitted in saliva of infected individuals or animals, and is most often passed on in bite wounds. Though not as common, it can also be transmitted by being scratched, being licked over a mucous membrane or an open wound, and through aerosolized mucous or feces (especially in bats). Rabies can also be transmitted through exposure to tears, cerebrospinal fluid and neurological tissue of an infected mammal.

Though any mammal is susceptible to the virus, not all animals live long enough with the virus to be able to spread it. Raccoons, dogs, foxes and bats are the most common carriers to infect humans.

Though very rare, there have been cases of transmission from human corneal and organ transplants.

Signs and Symptoms

Upon exposure, the rabies virus infects peripheral neurons and works its way to the central nervous system.

Early symptoms of rabies include headache, fever, general weakness, and discomfort, which are common symptoms associated with a variety of illnesses. On occasion, tingling is present at the bite site.

Symptoms more unique to rabies occur within 2 to 10 days as the disease advances. These indicative symptoms include insomnia, confusion, slight or partial paralysis, hallucinations, agitation, excitation, increased salivation, hydrophobia, difficulty swallowing, and anxiety. Unfortunately when these symptoms become evident, death usually follows within a matter of days.
 
Prevention and Treatment

The onset of rabies in almost one hundred percent of exposures can be prevented by wound cleansing and immunizations done immediately following contact with infected animals. Animal rabies vaccinations have greatly reduced cases of rabies in developed countries. Whenever possible, the infected animal is caught and humanely sacrificed to avoid more exposures.

Once exposure happens, the point of contact is cleaned and disinfected (soap and water or iodine solution for ten minutes), and the anti-rabies vaccine is administered to exposures involving broken skin. As much as possible of the 20 IU/kg dose of HRIG (human rabies immunoglobulin) is administered at the wound, and the remaining amount is administered intramuscularly at the gluteus. One milliliter of the vaccine (HDCV, RVA, or RabAvert) is administered intramuscularly at the deltoid or thigh on the day of the exposure, and the 3rd, 7th, 14th and 28th days after exposure.

HDCV (human diploid cell vaccine), RVA (rabies vaccine adsorbed) and RabAvert are each inactivated forms of the virus that cause an active immune response. HRIG is produced from humans who have been vaccinated.

Bibliography
Gompf, Sandra G. and Charurut Somboonwit. Rabies. updated October 3, 2008. eMedicine.com. Retrieved April 9, 2010 from http://emedicine.medscape.com/article/220967-overview.

Merlin, Mark A. and Peter W. Pryor II. Rabies. updated May 11, 2009. eMedicine.com. Retrieved April 9, 2010 from http://emedicine.medscape.com/article/785543-overview.

Fisher, Donna J. Rabies. Updated October 9, 2008. eMedicine.com. Retrieved April 9, 2010 from http://emedicine.medscape.com/article/968262-overview.

CDC. U.S. Department of Health and Human Services. Rabies Vaccine Information Statement. 10/6/2009. Retrieved April 12, 2010 from http://www.cdc.gov/vaccines/pubs/vis/downloads/vis-rabies.pdf

CDC. National Center for Zoonotic, Vector-borne, and Enteric Diseases, Division of Viral and Rickettsial Diseases. The Rabies Virus. Last updated March 22, 2010. Retrieved April 12, 2010 from http://www.cdc.gov/rabies/transmission/virus.html

Wikipedia. Rabies. Last modified April 11, 2010. Retrieved April 12, 2010 http://en.wikipedia.org/wiki/Rabies.

World Health Organization. Retrieved April 12, 2010 from http://www.who.int/rabies/human/en/.

Northwest Center for Public Health Practice & Washington State Department of Health. Human Rabies Vaccines. Retrieved April 12, 2010 from http://www.nwcphp.org/docs/rabies/humanvaccine.html.