Rabies is not a public health problem as it used to be, but it continues to command respect for its dire consequences. The viral disease is transmitted almost exclusively through animal bites and, if left untreated, can cause severe neurological symptoms such as fever, headache, excessive salivation, muscle spasms, paralysis, and confusion .
A series of injections, started immediately after the bite, can help unvaccinated people prevent illness. Unfortunately, the disease is almost always fatal once symptoms appear .
According to statistics from the Centers for Disease Control and Prevention (CDC), from 2008 to 2017, only 23 cases of human rabies were reported in the United States.
Rabies can be prevented with one of two FDA-approved vaccines.
Symptoms of rabies
In the early stages of infection, there may be few symptoms other than fever or headache, if any.
The time between exposure and the onset of disease symptoms, known as the incubation period, can average from 20 to 90 days.
As the infection progresses and spreads to the brain, symptoms of encephalitis (inflammation of the brain) and meningitis (inflammation of the tissues around the brain and spine) will develop. In this later stage of the disease, a person may begin to experience a progressive and often dramatic variety of physical and neuropsychiatric symptoms, including
- Loss of appetite
- Nausea and vomiting
- Sensitivity to light
- Excessive salivation
- Anxiety and excitement
- Abnormal behavior (including assault and terrorist attacks)
- Hydrophobia (insatiable thirst with inability to swallow or panic when presented with a drink)
- Partial paralysis
From this point on, the disease can progress rapidly and cause delirium, coma, and death within 7 to 10 days. Once prodromal symptoms appear, treatment is rarely effective.
The disease was once called hydrophobia (fear of water) because of the symptom of the same name.
Rabies is caused by a class of viruses known as lyssaviruses , of 14 strains that are specific to animals. The virus itself can in high concentrations, it is found in saliva and nerve cells of an infected animal or person. Animal bites are the predominant mode of transmission, although the infection can also be transmitted through contact with dead animals. Person-to-person transmission is extremely rare.
After a bite, scratch, or contact with infected body fluids (through the eyes, nose, mouth, or damaged skin), the virus travels along the nerves of the peripheral central system to the spinal cord and brain.
In the United States , bat bites are the most common route of transmission of the virus from animal to human, followed by mad dog bites. Other commonly infected North American animals include raccoons, skunks, foxes, cattle, coyotes, and house cats.
To date, there are no tests available to diagnose human rabies before symptoms appear. Therefore, treatment will likely start if a person has been bitten by a wild animal or any animal suspected of having rabies. Given the deadly nature of rabies infection, there really is no reason to wait.
That said, if the suspect animal is dead, tests can be done to confirm the infection by taking tissue samples from the brain. If there is an asymptomatic animal, the control group will position it so that brain tissue can be removed for testing.
Time is of the essence if a rabies infection is expected. Treatment includes four rabies shots and a dose of a drug called human rabies immunoglobulin (HRIG). HRIG contains immune antibodies that immediately inactivate the rabies virus and control it until the vaccine begins to work.
HRIG is only prescribed to people who have not been previously vaccinated against rabies. It is injected directly into the wound. Any remaining vaccine will be injected into a muscle away from the vaccine injection site. (Injecting HRIG too close to the vaccination site can interfere with the immune response.)
Two HRIGs are approved for this purpose:
- Imogam Rabies-HT (Human Rabies Immunoglobulin)
- HyperRabTM S / D (Human Rabies Immunoglobulin)
Treatment should start immediately after exposure : the first injection of HRIG and the rabies vaccine is given immediately; three additional vaccines are given three, seven, and 14 days later.
Side effects are usually mild and can include injection site pain and a mild fever.
There are two rabies vaccines approved for use in the United States, both made with an inactivated virus that cannot cause infection:
- Imovax (human diploid cell vaccine)
- RabAvert (purified chicken embryonic cell vaccine)
Both are injected into the shoulder muscle in three doses. After the initial injection, the second is prescribed seven days later and the third is prescribed 14-21 days later.
Although side effects are usually mild (including injection site pain, dizziness, headache, and nausea), some people are known to experience a serious and life-threatening allergic reaction known as anaphylaxis .
Due to the risk of anaphylaxis, the use of RabAvert should be avoided in people with a known allergy to eggs and replaced with Imovax.
Generally speaking, a rabies vaccination series provides 10 years of immune protection. For those at high risk of contracting rabies, boosters can be given every six months to two years if necessary. High-risk people include:
- Those who have frequent contact with wildlife in areas known to be at risk of contracting rabies (including wildlife officials, veterinarians, animal handlers, and spelunkers)
- International travelers who may have contact with animals in parts of the world where rabies is endemic
If you have other questions or concerns about rabies risk and prevention, use the discussion guide below for healthcare professionals to start a conversation with your doctor.
Rabies Discussion Guide for Healthcare Providers
Get our printed guide to your next doctor's appointment to help you ask the right questions.
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The success achieved by public health officials in fighting rabies in the United States is due in large part to the widespread vaccination of pets. All states have rabies vaccination laws, with the exception of Kansas, Missouri, and Ohio. However, among those who do this, laws can vary depending on the timing of vaccinations, the need for booster shots, and whether dogs need them and cats don't.
Regardless of what the laws in your state say, it is important to protect your pet and follow the rabies vaccination guidelines provided by the American Association of Animal Hospitals (AAHA).
To this end, all dogs, cats, and ferrets should receive a single dose of rabies vaccine no earlier than three months of age, followed by booster shots one year later and additional boosters every three years thereafter.
By protecting your pet, you also protect your family and your community.