Rabies

What Is Rabies?

Rabies is a disease humans may get from being bitten by an animal infected with the rabies virus. Rabies has been recognized for over 4,000 years. Yet, despite great advances in diagnosing and preventing it, today rabies is almost always deadly in humans who contract it and do not receive treatment.

Rabies can be totally prevented with appropriate treatment. You must recognize the exposure and promptly get appropriate medical care before you develop the symptoms of rabies.

  • While human rabies is quite rare in the United States (only 55 cases reported since 1990), in some areas of the world (for example, Southeast Asia, the Middle East, Africa, and Latin America), it is much more common. Worldwide, the majority of human rabies cases involve bites from rabid dogs, although this is extremely rare in the U.S., where wild animals such as raccoons and bats are the primary source of exposure.
  • The incidence of rabies in people parallels the incidence in the animal kingdom. The great strides that have been made in controlling the disease in animals in the United States and in other developed countries is directly responsible for the decline in human rabies in developed countries. The number of human deaths from rabies in the U.S. averages one or two cases per year, and deaths almost always occur when the affected person has delayed or failed to receive treatment.
    • Some regions of the country have more cases of rabies than others do.
    • Wild animals, rather than domestic animals, accounted for most reported cases of rabies in 2010.
  • Animals that carry rabies: Raccoons are the most common wild animals infected with rabies in the United States. Skunks, foxes, bats, and coyotes are the others most frequently affected.
    • Bats are the most common animals responsible for the transmission of human rabies in the United States, accounting for more than half of human cases since 1980 and 74% since 1990. Rabid bats have been reported in all states except Hawaii.
    • Cats are the most common domestic animals with rabies in the United States. Dogs are the most common domestic rabid animals worldwide.
    • Almost any wild or domestic animal can potentially get rabies, but it is very rare in small rodents (rats, squirrels, chipmunks) and lagomorphs (rabbits and hares). Large rodents (beavers, woodchucks/groundhogs) have been found to have rabies in some areas of the United States.
    • Fish, reptiles, and birds are not known to carry the rabies virus.
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What Is the Cause of Rabies?

  • For a human to get rabies, two things must happen.
    • First, you must have contact with a rabid animal.
    • Second, the contact must allow for the transmission of infected material, which will involve exposure to the saliva of the infected animal usually through a bite or scratch.
  • Contaminated tissue in the rabid animal includes saliva. Other potentially infectious tissue is in the brain or nerve tissue. The virus is transmitted only when the virus gets into bite wounds, open cuts in your skin, or onto mucous membranes (for example, into your eyes, nose, or your mouth). The virus then spreads from the site of the exposure to your brain and eventually spreads throughout your body's major organs.
  • Ways the virus is transmitted
    • Bites from infected animals are the most common source of transmission.
    • Scratches by infected animals are far less likely to cause infection but are still considered a potential source of rabies transmission.
    • Therefore, treatment might be necessary after a close encounter with a bat.
    • In the large majority of cases of human rabies associated with a bat, a definite history of a bat bite or scratch cannot be confirmed. It is unclear how the virus was transmitted in the other cases -- perhaps by an undetectable bite.
    • Rabies has rarely been transmitted by other means. Examples include organ transplantation, inhaling a large amount of bat secretions in the air of a cave, and inhaling the concentrated virus by laboratory workers studying rabies.

What Are Rabies Risk Factors?

Risk factors for rabies include participating in any outdoor activities or travel to areas that may involve contact with rabid animals. Lab workers who study the virus have an increased risk of accidental infection as do people that explore caves and those individuals that collect bat guano for fertilizer.

In the U.S., cats are the most common domestic animals to be infected with rabies.

Cause of Rabies

Animal Bites

Many different types of animals ranging from dogs, cats, hamsters, raccoons, ferrets, and squirrels can bite adults and children. Many times, bites are from the family pet.

Most states require that animal bites be reported, therefore, the person bitten will be asked to fill out a form with information about the bite or asked specific questions for reporting purposes when medical care is sought. Aside from simple data collection, this can be important in cases of rabies cases to help officials track location(s) and monitor a possible spread of the disease.

What Are Signs and Symptoms of Rabies?

  • Signs and symptoms in animals
    • Animals infected with rabies may appear sick, crazed, or vicious. This is the origin of the phrase "mad dog." However, animals infected with rabies may also appear overly friendly, docile, or confused. They may even appear completely normal.
    • Behavior of animals with rabies may be unusual. For example, seeing a normally nocturnal wild animal during the day (for example, a bat or a fox) or seeing a normally shy wild animal that appears strange or even friendly should raise suspicion that the animal may have rabies.
  • Signs and symptoms in humans
    • The average incubation period (time from infection to time of development of symptoms) in humans is 30-60 days, but it may range from less than 10 days to several years.
    • Most people first develop symptoms of pain, tingling, or itching shooting from the bite site (or site of virus entry).
    • Nonspecific complaints of fevers, chills, fatigue, muscle aches, and irritability may accompany these complaints. These symptoms may appear similar to those of the flu. Early on, these complaints may seem like any virus, except for the shooting sensations from the bite site.
    • Gradually, however, the affected individual becomes extremely ill, developing a variety of symptoms, including high fever, confusion, agitation, and eventually seizures and coma.
    • Typically, people with rabies develop irregular contractions and spasms of the breathing muscles when exposed to water (this is termed hydrophobia). They may demonstrate the same response to a puff of air directed at them (termed aerophobia). By this point, they are obviously extremely ill.
    • Eventually, the various organs of the body are affected, and the person dies despite support with medication and a respirator.
  • A rarer form of rabies, paralytic rabies, has been linked to vampire bat bites outside of the United States. In this form, the person who was bitten develops a paralysis, or inability to move the part of the body that was bitten. This spreads gradually throughout the body, and the person ultimately dies. Hydrophobia is less common in paralytic rabies than in classic rabies.

Is Rabies Contagious?

In general, rabies is acquired from the bite or scratch of an infected animal and is not contagious from person to person. Rabies has, however, rarely been transmitted by other means including organ transplantation, contamination of mucous membranes of the nose or mouth, inhaling a large amount of bat secretions in the air of a cave, and inhaling the concentrated virus by laboratory workers studying rabies.

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When to Seek Medical Care for Rabies

If you think an exposure to a rabid animal has occurred, call your doctor immediately.

  • The doctor should discuss both the animal's risk for having rabies and the risk of the exposure for transmission of the virus.
  • The doctor also should know if you have previously received vaccination against rabies, either because you're in a high-risk profession (for example, a veterinarian or zoo worker) or you have been exposed to a potentially rabid animal before. If you have been vaccinated previously, it will change the treatment that will follow after a new potential exposure.
  • Because rabies is such a rare disease, the doctor may be unfamiliar with the need for treatment or may not have the vaccine in the office for prompt administration. The local public health department is a good source of information in these cases, and a hospital's emergency department is a good place to seek medical care.

Any serious animal bite should be cared for as soon as possible in a hospital's emergency department.

  • In addition to the potential for transmission of rabies, other medical issues need to be checked:
    • Transmission of other infections, such as bacterial infections from the mouth of the biting animal
    • Need for an injection to maintain protection, or immunity, against tetanus (another type of infection that can be transmitted by bites or to open wounds)
    • Wound repair and cleansing
  • Even the most trivial bite can transmit rabies. Any bite or scratch by a rabid animal warrants the administration of rabies shots. Whether or not that animal is at risk for rabies depends somewhat on the region of the country and on the species of the animal. Any exposure to a bat where a bite cannot be ruled out must be considered a significant exposure even if you do not recall being bitten by the bat.

What Specialists Treat Rabies?

Rabies is a rare condition. If you believe you may have been exposed to rabies, it is appropriate to seek treatment at an emergency department, where you will be evaluated and treated by emergency-medicine specialists. You will likely be admitted to the hospital, where other specialists, such as infectious-disease specialists, will be consulted. If the disease develops in a person who did not receive appropriate treatment after exposure, critical-care specialists and other specialists as necessary will be involved in the care and management of the patient.

How Do Health-Care Professionals Diagnose Rabies?

  • Testing: No specific testing is needed because there is no way to detect if the rabies virus has been passed to you. It is not necessary to bring the animal itself to the emergency department because the doctors do not have the ability to test animals for rabies. The local health department will coordinate testing of the animal in question.
  • Examination: Your vital signs will be taken (temperature, heart rate, breathing rate, and blood pressure). You will be asked a series of questions about the animal and the exposure. The doctor will also ask questions about immunization you may have been given before against rabies and tetanus.
    • Certain medications used for the treatment of rheumatoid arthritis and the prevention and treatment of malaria (for example, chloroquine and mefloquine) can interact with the rabies vaccine should it be given. Bring a medication list or the pill bottles of all current medications you are taking to the emergency department.
    • If there is a concern that you may actually have rabies, it is important to tell the doctor about any history of jobs, hobbies, recent international travel, and exposure to animals.
  • Other illnesses: The diagnosis of rabies is complex and cannot be determined in the emergency department. Rabies can look very much like other serious illnesses, such as meningitis (infection of the fluid surrounding the brain and spinal cord). If the doctor is concerned about rabies or another form of central nervous system infection, you may be admitted to the hospital. You would be given a number of tests: blood tests and X-rays and a spinal tap to examine spinal fluid for evidence of infection.
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What Are Treatment Options for Rabies? Is Rabies Vaccination Effective?

  • Treatment to prevent rabies has three essential components if a high probability of viral transmission exists. Depending on the likelihood the animal has rabies and, in some cases, the availability of the animal for observation, your doctor may not initiate the latter two steps involving shots against the rabies virus.
    • Wound care involving soap and a virus-killing cleanser (this should always be done for any animal bite)
    • A onetime injection of human rabies immune globulin (or HRIG), which is a substance that provides rapid, short-term protection against rabies
    • Injection of the first of a series of vaccine doses to provide protection against rabies after an exposure
  • The decision to treat for rabies: The likelihood of an animal having rabies depends heavily on the species of the animal, its behavior, and where you were exposed to the animal. For example, in some areas of the country, such as the Texas-Mexico border, stray dogs have an extremely high likelihood of being rabid. In other areas, stray dogs may have little chance of being rabid.
    • Domestic dogs, cats, and ferrets have a well-defined incubation period for the rabies virus. If you have been bitten by one of these three animals, and the animal does not appear overtly ill at the time, then the animal will be observed by local health authorities for 10 days. If the animal remains well during that period, you will not need rabies shots.
    • If the animal has the potential for rabies and is available for sacrifice and immediate examination by the local health department, then treatment may be withheld pending the results of that test. This would include animals such as any wild animal, or an unwanted stray dog or cat, if you know where the animal is (dead or alive).
    • If the animal has the potential for rabies and is unavailable for sacrifice and examination, then you will be given rabies shots in the emergency department.
  • Special situations
    • Rabies vaccination and pregnancy: Both human rabies immune globulin (HRIG) and the various rabies vaccines are safe in pregnancy.
    • Immune suppression: If you are taking medicines (such as prednisone or steroids) or have a disease that interferes with the body's immune response to the rabies vaccine, discuss these situations with your doctor. The doctor will then determine if you will need additional blood tests to ensure that an adequate response to the vaccine has occurred and that protection against rabies is developing.

Are There Home Remedies for Rabies?

When bitten by an animal, you should always care for the wound immediately by washing it out with soap, water, and some sort of commercial antiseptic iodine solution, if available. This will help kill the common bacteria that may be passed by the bite but also has been shown to decrease the likelihood of transmission of the rabies virus, should the animal be rabid.

  • If the animal is a pet, get the owner's name, address, and phone number, if possible. This information will aid the local public health authorities as they monitor the animal.
  • If the animal is a wild animal, or stray dog or cat, contact the local animal-control authorities (your local humane society or city or county public health office) immediately. They will attempt to safely capture the animal for examination. The victim or other bystanders should not attempt to capture or subdue the animal. This might lead to further bites or exposures.
  • If the animal is a bat, and the exposure occurred in a building, the doors and windows should be shut in the room containing the bat after all other people are evacuated. If this cannot be done without risk of repeat exposure to the bat, then the most important thing is to minimize the chance of contact between that bat and other people. Once again, call local animal-control authorities, and they will capture the bat.
    • Bat exposures are different from any other animal. There does not necessarily have to be a detectable bat bite to constitute a significant exposure.
    • If a bat bite or direct contact cannot be ruled out, then there may have been a significant exposure, such as in the following circumstances:
      • A sleeping person awakens to find a bat in the room.
      • An adult sees a bat in the room of a previously unattended child, mentally disabled person, or intoxicated person.

What Medications Treat Rabies?

There are two types of rabies vaccine injections.

  • Injection of the human rabies immune globulin (HRIG) for immediate protection is based on your exact weight. This is not a situation where more is better. Therefore, you should not overestimate your weight. If the exact weight is not known, you will be weighed at the hospital.
    • Once the dose is determined, as much as possible is injected into and around the bite site. If the entire volume does not fit into the tissue in that area (for example, the tip of the finger), then the remaining volume will be injected into some other site in your body, such as the arm, leg, or buttocks. The doctor may use numbing medicine to decrease the pain associated with injection of HRIG into the tissues at the bite site.
    • If you have been previously immunized adequately against rabies, then the HRIG is not needed. You would need only the vaccine described in the next section.
  • Injection of the vaccine will begin during this initial visit to the emergency department and will proceed on a schedule over the next 14 days, with a total of four small injections.
    • There are two different types of rabies vaccines licensed for use in the United States (human diploid cell [HDCV] and purified chick embryo cell culture vaccine [PCECV]). If given properly and on schedule, both of types will protect you against rabies.
      • The dose for each is 1 cc, or milliliter, delivered into the muscle. This vaccine must be delivered into the deltoid, or shoulder muscle, in adults or older children. The front, outside aspect of the thigh muscle is acceptable in younger children. It must never be injected into the buttocks. Injection into the proper site ensures absorption. It must be administered in a site different from the remainder of the immune globulin that is not injected into the bite site.
      • If you have never been vaccinated against rabies, then vaccine shots will be given on the day of the visit (day zero), and again on days three, seven, and 14. If you have already been adequately immunized against rabies, a series of two booster vaccine injections will be given on day zero and again on day three only. This is sufficient to stimulate your body's immune system, or memory, and provide protection against rabies.

Follow-up for Rabies

If you have been exposed to rabies, maintain contact with the local health authorities and stick to the schedule of prescribed rabies vaccine shots. Contact your doctor after treatment in the emergency department. Your doctor may refer you for the additional doses of the vaccine if the doctor does not have them on hand.

Local discomfort at the site of the injection is expected. You may apply warm compresses and take over-the-counter pain remedies if needed. Any reactions differing from this should be discussed with your doctor.

How Can People Prevent Rabies?

Prevention of rabies depends on decreasing the disease in the animal kingdom. Avoid contact with wild animals and strays. Have your pets (including cats, dogs, and ferrets) vaccinated against rabies. Keep pets under control and away from wild animals and strays. Call animal-control services to remove stray animals from your neighborhood.

What Is the Prognosis for Rabies?

If you get timely, appropriate wound care and rabies shots, you will be virtually 100% protected against rabies.

  • To date, there have been no failures of this treatment in the United States.
  • Failures overseas, however, have occurred despite seeking medical care after exposure because doctors either failed to give wound care, did not inject the immune globulin around the bite or wound site, or did not give the vaccine in the correct spot (for example, vaccine was given in the buttocks).

For More Information About Rabies

For more detailed information about rabies, the reader should check the following site:

The Centers for Disease Control and Prevention, "Rabies"

Reviewed on 11/20/2017

REFERENCE:

United States. Centers for Disease Control and Prevention. "Rabies." Apr. 18, 2016. <http://www.cdc.gov/rabies/>.

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