An Overview of Rabies

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Rabies is not the public health concern that it once was, but it continues to command respect due to its serious consequences. The viral disease is transmitted almost exclusively by animal bites and, if left untreated, can cause serious neurological symptoms including fever, headache, excessive salivation, muscle spasms, paralysis, and mental confusion. Rabies can be prevented with one of two FDA-approved vaccines. A series of shots started immediately after a bite, can help unvaccinated individuals avert the disease. Unfortunately, once symptoms appear the disease almost always fatal.

According to statistics from the Centers for Disease Control and Prevention (CDC), only 23 cases of human rabies have been reported in the U.S. from 2008 to 2017.

Symptoms

During the early stages of infection, there may be few, if any, symptoms other than a fever or a headache. The time between exposure and disease symptoms, known as the incubation period, can run anywhere from 20 to 90 days on average.

As the infection progresses and makes its way toward the brain, symptoms of encephalitis (inflammation of the brain) and meningitis (inflammation of the tissues surrounding the brain and spinal column) will develop. During this later stage of disease, a person can begin to experience a progressive and often dramatic range of physical and neuropsychiatric symptoms, including

  • Loss of appetite
  • Nausea and vomiting
  • Sensitivity to light
  • Excessive salivation
  • Anxiety and agitation
  • Paranoia
  • Abnormal behavior (including aggression and bouts of terror)
  • Hallucinations
  • Hydrophobia (unquenchable thirst with an inability to swallow or show panic when presented with fluids to drink)
  • Seizures
  • Partial paralysis

From this point, the disease can rapidly progress, leading to delirium, coma, and death in seven to 10 days. Once prodromal symptoms appear, treatment is almost never effective.

The disease was actually once called hydrophobia (fear of water) due to the namesake symptom.

Causes

Rabies is caused by a virus class known as the lyssavirus, of which there are 14 animal-specific strains. The virus itself can be found in high concentrations in saliva and the nerve cells of an infected animal or human. Animal bites are the predominant mode of transmission, although the infection can also be passed by handling dead animals. Transmission between humans is extremely rare.

Once a person is bitten, scratched, or exposed to infected body fluids (either through the eyes, nose, mouth, or broken skin), the virus will travel through the nerves of the peripheral central system to the spinal cord and brain.

In the United States, bat bites are by far the most common route of animal-to-human transmission, followed by bites from rabid dogs. Other North American animals commonly infected include raccoons, skunks, foxes, cattle, coyotes, and domestic cats. 

The states with the highest rate of animal rabies are Texas, Virginia, Pennsylvania, New York, Maryland, New Jersey, Georgia, and California. 

Diagnosis

To date, there are no tests available to diagnose human rabies before the onset of symptoms. As such, treatment will be started presumptively if a person has been bitten by a wild animal or any animal suspected of having rabies. Given the deadly nature of a rabies infection, there is really no reason to wait.

What that being said, if the suspected animal is dead, tests can be performed to confirm the infection by taking tissue samples from the brain. If there is ​an asymptomatic animal, animal control will put it down so that brain tissue can be extracted for testing.

Treatment

Time is of the essence if a rabies exposure is expected. Treatment involves four shots of the rabies vaccine and one shot of a drug called human rabies immunoglobulin (HRIG). HRIG contains immune antibodies that immediately inactivate and control the rabies virus until the vaccine can begin to work.

HRIG is only given to people who have not been previously vaccinated for rabies. It is injected directly into the wound. Any leftover would be injected into a muscle far away from where the vaccine shots are delivered. (Injecting HRIG too close to the vaccination site may interfere with the immune response.)

There are two HRIG preparations approved for this purpose:

  • Imogam Rabies-HT (human rabies immune globulin)
  • HyperRab TM S/D (human rabies immune globulin)

Treatment should be started without delay and no later than 10 days after exposure. The first shot of HRIG and the rabies vaccine is given immediately; three additional vaccine injections are given three, seven, and 14 days later.

The side effects are generally mild and may include injection site pain and mild fever.

Prevention

There are two rabies vaccines approved for use in the United States, both of which are made with an inactivated virus that cannot cause infection:

  • Imovax (human diploid cell vaccine)
  • RabAvert (purified chicken embryo cell vaccine)

Both are delivered by injection into the muscle of the upper arm in three doses. After the initial shot, the second is given seven days later, and the third is given 14 to 21 days after that.

While side effects tend to be mild (including injection site pain, dizziness, headache, and nausea), some people have been known to experience a severe and potentially deadly allergic reaction known as anaphylaxis. It is for this reason that RabAvert should be avoided in people with a known egg allergy and substituted with Imovax.

Generally speaking, a rabies vaccination series provides you with 10 years of immune protection. For those at high risk of rabies exposure, booster shots can be given every six months to two years, as needed. Persons at high risk include:

  • Those who come into frequent contact with wildlife in areas where rabies risk is known (including wildlife officers, veterinarians, animal handlers, and cave spelunkers)
  • International travelers who are likely to come into contact with animals in parts of the world where rabies is endemic

A Word From Verywell

The success that public health officials have had in controlling rabies in the United States is due in no small part to the widespread vaccination of domesticated pets. Every state has rabies vaccination laws with the exception of Kansas, Missouri, and Ohio. That said, among those that do, the laws can vary by the timing of the vaccination, the need for booster shots, and whether dogs need them but cats don't.

Irrespective of what your state's laws say, it important to protect your pet and follow the rabies vaccination guidance provided by the American Animal Hospital Association (AAHA).

To this end, all dogs, cats, and ferrets should be given a single dose of the rabies vaccine no earlier than three months of age, followed by a booster shot a year later, and additional booster shots given every three years thereafter.

By protecting your pet, you will also be protecting your family and your community.

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