Rabies

The bite of a rabid animal can transmit the rabies virus to a human.

• The rabies virus causes rabies.
• Rabid animals transmit the virus via a bite or saliva exposure.
• Early signs and symptoms of rabies mimic those of a viral flu-like infection.
• People should start post-exposure prophylaxis (PEP) treatment as soon as they suspect an exposure.
• In the U.S., two to three people die from rabies each year.
• Animal vaccinations and post-exposure prophylaxis protocols have nearly eradicated rabies in the U.S.

Rabies is a viral illness spread via the saliva of an infected animal by the rabies virus (genus Lyssavirus). Rabies exposure occurs usually through biting a human or another infected animal. Transmission can also occur through saliva touching an open wound or touching mucous membranes.

The rabies virus causes rabies. The virus infects the brain and ultimately leads to death. After a rabid animal bites someone, the virus is deposited in the muscle and subcutaneous tissue. For most of the incubation period (which is usually one to three months), the virus stays close to the exposure site. The virus then travels via peripheral nerves to the brain and from there, again via peripheral nerves, to nearly all parts of the body.

Any warm-blooded animal can spread rabies. In the United States, the saliva of rabid bats, coyotes, foxes, raccoons, and skunks most often transmits rabies. In the developing world, stray dogs are the most likely animal to transmit rabies. The virus has also been found in cows, cats, ferrets, and horses.

The local health department will usually have information on which other animals in your area have been found to carry the rabies virus.

Any activity that brings someone in contact with possibly rabid animals, such as traveling in an area where rabies is more common (Africa and Southeast Asia) as well as outdoor activities near bats and other possible rabid animals, increases one's risk of getting infected with rabies.

Symptoms of human rabies can occur as fast as within the first week of the infection.

The early symptoms of rabies are very generalized and include weakness, fever, and headaches. Without a history of potential exposure to a rabid animal, these symptoms would not raise the suspicion of rabies as they are very similar to the common flu or other viral syndromes.

The disease can then take two forms:

1. With paralytic rabies (approximately 20% of cases), the patient's muscles slowly become paralyzed (usually starting at the site of the bite). This is the less common form and ends in coma and death.
2. With furious rabies (about 80% of cases), the patient exhibits the classic symptoms of rabies, such as:
   • anxiety and confusion (The patient is often overly active.);
   • encephalitis, causing hallucinations, confusion, and coma;
   • hypersalivation;
   • hydrophobia (fear and avoidance of water);
   • aerophobia (fear of fresh air);
   • difficulty swallowing.

Once the clinical signs of rabies occur, the disease is nearly always fatal.

In the U.S., there is one reported case of a patient surviving rabies without vaccination (Jeanna Giese), which led to the development of the so-called Milwaukee treatment protocol. Physicians don't recommend this protocol as a treatment alternative.

In animals, healthcare professionals diagnose rabies by detecting the rabies virus in any affected part of the brain. This requires the euthanization of the rabid animal. Testing a suspected animal will help avoid extensive testing in human contact (if the test is negative) and unnecessary treatments.

In humans, healthcare professionals diagnose rabies by testing saliva, blood samples, spinal fluid, and skin samples. Multiple tests may be necessary. The tests rely on the detection of proteins on the surface of the rabies virus, the detection of the genetic material of the virus, or the demonstration of an antibody (immune) response to the virus.

Medical care is recommended if a health care professional thinks that someone was exposed to a potentially rabid animal.

If the animal is a pet or farm animal that has no symptoms, the animal can be isolated and observed for 10 days. Wild animals that can be captured can be killed and tested for the virus. If the animal can't be found, it is best to consult with the health department.

The U.S. Centers for Disease Control and Prevention (CDC) recommends prophylaxis (protective treatment) after a wildlife bite from an animal suspected to have rabies.

The general pathway to determine post-exposure prophylaxis for rabies requires the following information:

• Bite: Did a bite occur, and where is the location of the bite? (Any penetration of the skin is considered a bite; although bites to the face and hands carry the highest risk, all bites need to be considered for prophylaxis.)
• Non-bite incident: Did the saliva touch an open wound or a mucous membrane?
• Animal risk factors: No cases of rabies infection have been reported in the U.S. from fully vaccinated domestic animals (dogs or cats). If bitten, it is important to determine if the bite was provoked or unprovoked. A provoked bite includes any circumstances during which the person touched, threatened, scared, fed, or otherwise interacted with the animal before the bite. If no such interaction occurred, the bite is considered unprovoked, and it increases the likelihood that the animal may have rabies.
• Bats: A healthcare professional should evaluate any contact with a bat that leads to a potential scratch, bite, or mucous membrane exposure to saliva. If prolonged exposure to a bat is discovered (sleeping in a room where a bat is found), postexposure prophylaxis needs to be considered.

As rabies is a fatal disease, if it is suspected, it is often best to start treatment until further information is available.

A healthcare professional administers a series of injections. The first is a rabies immune globulin (human rabies immune globulin [HRIG]), which health care professionals only give to previously unvaccinated individuals, as well as the rabies vaccine. Those who have been previously vaccinated or are already receiving pre-exposure vaccination should only receive the vaccine. Over the next 2 weeks, healthcare professionals administer three additional rabies vaccine injections during follow-up visits on days 3, 7, and 14. Healthcare professionals give the first of these vaccines as soon as possible after exposure. Doctors give these rabies vaccinations as intramuscular injections, and the vaccines help the body fight the virus.

The treatment regimen for previously vaccinated individuals is different, with no HRIG given and only two doses of the rabies vaccine.

The incubation period for rabies can range from a few days to several years. The incubation period refers to the time it takes for symptoms to appear from the time of exposure to a virus. Rabies typically has an incubation period of 1-3 months in humans; however, this time can be shorter or longer depending on a number of factors.

Once the symptoms of rabies start, the disease is nearly universally fatal if left untreated. Eventually, respiratory failure and paralysis occur, which leads to death.

Rabies prevention is mostly about good pet care and outdoor behavior. Vaccinate pets and keep them away from outdoor and wild animals. Don't approach wild animals. Keep bats out of the home, and stay away from areas with bats (caves).

About 5,000 cases of animal rabies are reported annually to the CDC, with most of these cases occurring in wildlife.

When traveling, be aware of stray animals.

If spending significant time in a country where rabies is common, one should consider a rabies vaccination.