Rabies

Definition

Rabies is a viral infection of the central nervous system. Rabies is almost always fatal unless treated before symptoms appear.

The Nervous System

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Causes

A virus found in infected, warm-blooded animals causes rabies. Animals that commonly carry the virus include:

  • Bats
  • Raccoons
  • Skunks
  • Foxes
  • Coyotes

The rabies virus is present in the saliva, brain, or nerve tissue of infected animals. Usually, humans contract rabies through a bite or scratch from an infected animal. The virus may also be transmitted if infected tissue comes into contact with human mucus membranes, such as in the eyes, nose, or mouth.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition. The only risk factor for contracting rabies is contact with an infected animal. In most parts of the United States any contact with a bat may be considered a rabies risk factor. Seek medical advice if you find a bat anywhere inside your home.

Symptoms

After exposure, the rabies virus may incubate for 10 days to one or more years in humans before symptoms appear. Usually, symptoms develop within 3 to 7 weeks, after which treatment will not stall the progression of the infection. Death usually occurs within a week after symptoms appear.

Symptoms in humans may include:

  • Pain, tingling, or itching at the site of the bite wound or other site of viral entry
  • Stiff muscles
  • Increased production of thick saliva
  • Flu-like symptoms, such as headache, fever, fatigue, nausea
  • Painful spasms and contractions of the throat when exposed to water (called hydrophobia)
  • Erratic, excited, or bizarre behavior
  • Paralysis

Symptoms in animals may include:

  • Erratic behavior, often overly aggressive or vicious
  • Disorientation (eg, nocturnal animal such as a bat or fox appearing in daylight)

Diagnosis

If you think you have been exposed to rabies, see a doctor or contact a public health official immediately.

If the animal is available and appears well, it will be kept under observation for 7 to 10 days. If no symptoms develop, you are not at risk for rabies. If the animal is sick or dead, it's head will be shipped to a special facility where its brain will be examined for the presence of the virus. In the meantime, you may be advised to begin treatment.

If the animal is unavailable, treatment may often be recommended depending on the animal's species, where the encounter took place, and other factors.

Treatment

If an animal has bitten you, immediately do the following:

  • Wash the wound immediately with plenty of soap and water to remove saliva; this is the most important first step you can take in preventing rabies.
  • Call your doctor or seek care in an emergency room.

If it is likely that you have been exposed to rabies, your doctor will recommend postexposure prophylaxis. This involves two injections:

Human Rabies Immune Globulin (HRIG)

This should ideally be given within 24 hours after exposure. It contains large quantities of antibodies to the rabies virus. In most cases, half of the dose should be injected into the wound and surrounding tissue. The remainder is given intramuscularly. If you have previously received rabies vaccine, you may not need the HRIG shot.

Other Rabies Vaccines

Unlike the HRIG, rabies vaccines cause your own immune system to develop protective antibodies against the rabies virus. These antibodies will live in your body for many years. There are three types of rabies vaccines available:

  • Human diploid cell vaccine (HDCV)
  • Rabies vaccine adsorbed (RVA)
  • Purified chick embryo cell culture (PCEC)

Over the next four weeks, your doctor will give you five shots of one of these vaccines. The vaccine will be injected into your upper arm muscles.

Certain medications may interfere with your body's response to the rabies vaccine. Be sure to tell your doctor about all medications or herbs that you take on a regular basis.

Prevention

To help prevent rabies:

  • Vaccinate house pets.
  • Avoid contact with wild animals.
  • Do not touch any wild animal, even if it appears to be dead.
  • Seal basement, porch, and attic openings to prevent an animal from entering your home.
  • Report any animal to your local animal control authorities that is acting strangely or appears sick.
  • If you regularly come in contact with animals, have the rabies vaccine prior to any exposure to rabies (pre-exposure prophylaxis). Booster doses are often required.

RESOURCES:

Centers for Disease Control and Prevention (CDC)
http://www.cdc.gov

National Institute of Allergy and Infectious Diseases, National Institutes of Health
http://www.niaid.nih.gov

CANADIAN RESOURCES:

Public Health Agency of Canada
http://www.phac-aspc.gc.ca/new_e.html

Safe Canada
http://www.safecanada.ca/

References:

Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/ncidod/dvrd/rabies . Accessed October 14, 2005.

Hankins DG and Rosekrans JA. Overview, prevention, and treatment of rabies. Mayo Clin Proc . 2004 May;79(5):671-6.

Rabies. DynaMed website. Available at: http://www.dynamicmedical.com/dynamed.nsf . Accessed October 14, 2005.



Last reviewed December 2007 by David L. Horn, MD, FACP

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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