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Rabies is a viral disease of mammals and is transmitted primarily through bites. Annually, 7,000 to 8,000 rabid animals are detected in the United States, with more than 90 percent of the cases in wild animals. Rabies is found naturally in Missouri, occurring primarily in bats and skunks, although other animals are also found rabid each year, including domestic species such as dogs, cats, horses, and cattle. The annual number of rabid animals reported in Missouri during the ten-year period 1995 through 2004 ranged from 26 to 59 (average of 40 cases per year). Although rabies is transmitted to humans almost entirely through bites from rabid animals, contamination of open wounds or mucous membranes with saliva or nervous tissue from a rabid animal could potentially constitute an exposure. Rabies in humans is almost invariably fatal. Fortunately, human deaths in the United States have become relatively rare because: (1) effective vaccinations have been available for dogs and cats since the 1950s, (2) public health practices such as animal quarantine and testing are aggressively pursued, and (3) improved anti-rabies shots have been developed for persons exposed to rabies. Many Missourians receive the anti-rabies series of shots each year. The Centers for Disease Control and Prevention (CDC) estimates that 40,000 persons in the United States receive the anti-rabies series of shots annually. Rabies in both animals and humans in Missouri is reportable to the Missouri Department of Health and Senior Services¹. Tragically, in 2008, a human rabies fatality occurred in Missouri in an individual who did not seek medical advice or treatment following a bat bite. Before this, the last human rabies infection in the state was reported in 1959.
Rabies in Animals
The incubation period (time from exposure to signs of illness) of rabies in domestic animals such as dogs and cats can be quite variable, but averages three to six weeks. The first sign of rabies in animals is often a change in temperament or behavior. For example, a friendly dog may become reclusive (or vice versa) and nocturnal wild animals such as skunks may become active during the daytime. In the next stage, classically referred to as “furious” rabies, the animal will attack and bite other animals, objects, or people. The final stage is referred to as “dumb” rabies, and at this point the animal is partially or completely paralyzed and close to death. Often, there is paralysis of the throat muscles, resulting in an inability to swallow and profuse salivation. The animal may want to drink water, but painful throat muscle spasms prevent this. Excess salivation may result in “frothing at the mouth,” but this characteristic is often observed in animals dying from other causes as well. An animal may go through all of these stages or only some of them. Death is virtually certain within ten days of onset of signs. A dog, cat, or ferret may be infectious (have rabies virus in its saliva) for several days before it develops any outward signs of disease. Whether this is true, and for what time period, is unknown for other animal species.
Vaccination of Animals
Effective rabies vaccines are available for dogs, cats, ferrets, sheep, cattle, and horses. Vaccination of cats and dogs is crucial, since vaccinated pets are a protective barrier between the people who own and interact with them and rabid wild animals with which the pets might have contact. Dogs and cats whose owners consider them to be “indoor animals” should also be vaccinated because these pets often have exposures to other animals, either by the dog or cat being unintentionally released to the outdoors, or by wild animals such as bats getting into the house. Vaccinations must be administered by a licensed veterinarian. Primary and booster vaccinations should be obtained in accordance with recommendations from licensed veterinarians and in accordance with local animal control ordinances. There is no postexposure treatment available for animals as there is for humans. Information pertaining to animal rabies vaccines as well as the prevention and control of rabies in animals is available in the Compendium of Animal Rabies Prevention and Control, 2008².
Testing Animals for Rabies
Animals that bite or otherwise potentially expose a human or pet to rabies may be tested for this disease. Testing an animal for rabies requires that it be euthanized, since sections of the brain must be examined for the presence of the rabies virus. Most testing is accomplished at the State Public Health Laboratory (SPHL) in Jefferson City. Rabies testing is no longer available through SPHL branch laboratories. Typically, the head of the suspect animal (wild or domestic) is removed by a veterinarian, placed in a specially designed shipping container, and transported via contracted courier to the SPHL for testing. The courier service picks up rabies (and other specimens) from local public health agencies and other facilities each weekday. Rabies test results are normally available within one day after specimen arrival at the laboratory. There is no charge for shipping containers, courier service, or testing. Additional information regarding rabies testing is available from the SPHL³. The laboratory of the Springfield-Greene County Public Health Center also offers rabies testing. This agency may be contacted for information pertaining to specimen submission and cost.
Bats and Rabies
Bites from bats are the main source of rabies in humans in the United States today. Although the vast majority of bats do not have rabies, any potential encounter with a bat must be assessed for the possibility of rabies transmission. It is not possible to tell if a bat has rabies just by observing it; rabies can be confirmed only by having the animal tested in a laboratory. However, any bat that is active by day, is found in a place where bats are not usually seen (for example in rooms in the home or sitting on the lawn), or is unable to fly, is far more likely than others to be rabid. Such bats are often the most easily approached. Therefore, it is best never to handle any bat. If bitten by a bat, or if infectious material (such as saliva) from a bat gets into the eyes, nose, mouth, or a wound, wash the affected area thoroughly and seek medical attention immediately. Whenever possible, the bat should be captured and sent to a laboratory for rabies testing. People usually know when they have been bitten by a bat. However, because bats have small teeth which may leave marks that are not easily seen, there are situations in which a person should seek medical advice even in the absence of an obvious bite wound. For example, if a person awakens and finds a bat in the room, sees a bat in the room of an unattended child, or sees a bat near a mentally impaired or intoxicated person, he/she should seek medical advice and have the bat tested. It is not possible to contract rabies from just seeing a bat in an attic, in a cave, or at a distance, nor is it transmitted through contact with bat guano (feces).
Rabies in Humans
The incubation period of rabies in people is also variable (depending upon factors such as the site and severity of the bite), but averages three to eight weeks. Following an exposure to rabies, there is normally a window of opportunity (usually measured in days) in which the patient can receive a series of shots to keep him/her from developing disease. Once symptoms begin, the outcome is almost always death. Early symptoms of rabies often include sensory changes at the site of the bite (numbness or tingling), fever, headache, and a general feeling of discomfort. As the infection progresses, the patient may exhibit excitability, anxiety, aerophobia (abnormal aversion to air in motion), and hydrophobia (abnormal fear of water). Other neurological symptoms may include mental confusion, paralysis, delirium, and convulsions. Without medical intervention, death usually occurs within two to six days. With medical intervention, the course of disease may be prolonged to several weeks before death ensues. The diagnosis of rabies in humans may be complicated since other diseases that affect the brain produce similar symptoms. Diagnosis is also difficult in the early stages of disease when tests for rabies may not yet be positive. Specimens obtained for testing include saliva, blood, cerebral spinal fluid, and biopsied nerve tissue. Additional information pertaining to prevention of rabies in humans is available in Human Rabies Prevention – United States, 2008, Recommendations of the Advisory Committee on Immunization Practices (ACIP)⁴.
Actions Following a Potential Rabies Exposure
The following actions should be taken if a person is bitten or otherwise possibly exposed to a rabid animal:
- Domestic animals: Identify and, if possible, confine the biting animal. Dogs, cats, and ferrets may be quarantined for ten days (if healthy and depending on other circumstances), or they may be euthanized and tested for rabies. Other domestic animals are handled on a case-by-case basis.
- Wild animals: Identify and, if possible, confine the biting animal for rabies testing. No quarantine period is recognized for wild animals.
- Wash the wound immediately and thoroughly with soap and water for 10 to 15 minutes.
- Consult with a physician to: (1) check the tetanus immunization status, (2) determine if antibiotic treatment is needed for bacterial infection, (3) determine if other medical procedures are necessary, such as sutures in the case of disfiguring wounds, and (4) have a rabies risk assessment accomplished, including determining if the anti-rabies series of shots is warranted.
Anti-Rabies Series of Shots for Humans
- Postexposure: The current series of shots is very effective if given soon after the exposure, and is fewer in number with far less side effects than the anti-rabies regimen given prior to 1980. However, the current series is not without some discomfort and risk, and averages several thousand dollars per series per patient. The shots are not effective once symptoms develop. Persons who have never been vaccinated against rabies receive two different products: human rabies immunoglobulin (HRIG) and human rabies vaccine. The dose of HRIG depends upon the weight of the person, and is generally infiltrated by needle and syringe at the site of the bite. These persons also receive four intramuscular doses of vaccine over the next 14 days⁵. Persons with altered immunocompetence (and not previously vaccinated) should receive a five-dose vaccination regimen with one dose of RIG. Persons who are exposed to a rabid animal but have been previously vaccinated require only two booster doses of vaccine three days apart.
- Preexposure: Preexposure vaccinations are recommended for persons in high-risk groups such as veterinarians and animal control officers. The preexposure series consists of three intramuscular doses of vaccine administered over a 21- or 28-day period. These vaccinations are administered for several reasons. First, although preexposure vaccination does not eliminate the need for additional therapy after a rabies exposure, it simplifies therapy by eliminating the need for HRIG and decreasing the number of doses of vaccine needed – a point of particular importance for persons who might be at high risk for adverse reactions. Second, preexposure vaccination might protect persons whose postexposure therapy is delayed. Finally, it might provide protection to persons at risk for inapparent exposures to rabies.
- Ensure dogs and cats are up-to-date on rabies vaccinations. Vaccinations are also available for ferrets, horses, cattle, and sheep. The effectiveness of animal vaccines is the main reason for the nationwide decline in rabies cases among people and domestic animals.
- Keep pets under control; do not allow them to run loose.
- Avoid contact with stray pets and wild animals; do not keep wild animals or wild animal crosses as pets.
- Report wild animals exhibiting unusual behavior or stray pets to animal control officials.
Tips for Children
Children suffer a disproportionate number of bites from animals, often resulting in serious injury to the face, head, and neck. The following tips can help children avoid being bitten, and the resulting physical/mental trauma and potential exposure to rabies and other diseases that accompany bites:
- Never touch unfamiliar or wild animals. Enjoy wild animals from afar.
- Avoid direct contact with stray animals. Stray cats and dogs may not have been vaccinated against rabies.
- Never adopt wild animals or bring them into the home.
- Do not try to nurse sick animals to health. It is common to want to rescue and nurse a hurt wild animal, but that animal may have rabies. Ask an adult to call an animal control officer or animal rescue group for help with the sick animal.
- Make sure that trash cans and pet foods are secured so that they do not attract wild animals.
- Do not disturb a dog that is sleeping, eating, or caring for puppies.
- If bitten, report the bite to an adult immediately.
- Reporting Communicable, Environmental and Occupational Diseases. 19CSR20-20.020. http://s1.sos.mo.gov/cmsimages/adrules/csr/current/19csr/19c20-20.pdf
- Compendium of Animal Rabies Prevention and Control, 2008. National Association of State Public Health Veterinarians, Inc., Topeka, KS. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5702a1.htm
- Rabies Testing. Missouri State Public Health Laboratory, Jefferson City, MO.
- Human Rabies Prevention – United States, 2008, Recommendations of the Advisory Committee on Immunization Practices (ACIP). Centers for Disease Control and Prevention, Atlanta, GA. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5703a1.htm
- Use of a Reduced (4-Dose) Vaccine Schedule for Postexposure Prophylaxis to Prevent Human Rabies, Recommendations of the Advisory Committee on Immunization Practices, Centers for Disease Control and Prevention, Atlanta, GA. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5902a1.htm