rabies
(rā'bēz 
)
[L. rabies, rage]
A fatal infection of the central nervous system (CNS) caused by the rabies virus. Human infection occurs as the result of a bite from a wild animal in which the virus is present. It may occasionally be transmitted by inhalation of infectious aerosol particles or contamination of conjunctiva or other mucous membranes by the saliva of an infected animal. The long incubation period, before signs of rabies appear, is 3 to 12 weeks; this means that wild animals that are displaying no signs of the disease may still be infected, thereby increasing the risk of human infection. SYN: hydrophobia (1).
SEE: immune globulin; rabies vaccine.
Incidence: In 2013, the WHO estimated that 61,000 deaths from rabies occur each year. Most cases are in Asia or Africa, and almost all result from dog bites. Deaths caused by rabies are rare in the U.S., where the disease is identified in one or two people annually.
Causes: Rabies is found almost exclusively in wild animals (raccoons, skunks, coyotes, foxes, and bats), which serve as reservoirs for infection. Domestic animal infections have been rare in the U.S. since 1960, but dogs and cats in developing countries may be infected. After infection, the virus replicates in the animal for several days to months; this period stimulates an immune response to viral antigens. The virus then spreads through the cytoplasm of peripheral nerve axons to the CNS.
Symptoms and Signs: Early symptoms in humans are usually nonspecific and include fever, malaise, and headache. Progressive signs of cerebral infection are those of encephalitis (anxiety, confusion, insomnia, agitation, delirium, hallucinations, hypersalivation, hyperactive reflexes, and convulsions). Periods of stupor alternate with episodes of extreme agitation. The classic symptom of hydrophobia is probably related to the painful contracture of the pharyngeal muscles that occurs during swallowing. Once clinical signs occur, the disease is usually fatal within days.
Diagnosis: The diagnosis of rabies is made in animals by a direct fluorescent antibody test on brain tissue. In humans, brain biopsies, skin biopsies from the nape of the neck, corneal impression tests, and /or spinal fluid, blood, or salivary antibody tests are conducted.
Prevention: Veterinarians, animal hand lers, and those who come in frequent contact with wild animals should receive preexposure prophylaxis with rabies vaccine. The vaccine does not prevent infection with rabies but simplifies treatment because it eliminates the need for immune globulin and decreases the amount of rabies vaccine required after exposure.
To decrease the spread of rabies, the CDC recommends that all domestic animals be vaccinated routinely (consult local veterinarian and public health department) and that contact between pets and wild animals be minimized. Control of rabies in pets through vaccination and elimination of contact with stray animals significantly reduces the risk of human infection. Garbage containers should be designed to prevent attracting raccoons and skunks. Physical contact with raccoons, skunks, foxes, coyotes, and bats should be reported immediately.
Treatment: Treatment after exposure is highly successful in preventing rabies if treatment is administered promptly (within 10 days of infection). Thorough washing of the wound as soon as possible with soap and water for approx. 5 min effectively reduces viral particles. If available, a virucide, e.g., povidone-iodine, or alcohol (ethanol) should be applied after washing. Exposed mucous membranes (eyes, nose, mouth) should be thoroughly flushed with water.
The CDC recommends that patients receive one dose of human rabies immunoglobulin (HRIG) and four doses of rabies vaccine over a 14-day period. The first dose of rabies vaccine is given as soon as possible after exposure, with further doses on days 3, 7, and 14 after the first. Patients who have already received preexposure vaccination do not receive the immunoglobulin, just the postexposure vaccinations on days 0 and 2. No cases of rabies have occurred when postexposure prophylactic regimen has been followed promptly after exposure.
Modern cell-based vaccines are similar to flu shots in terms of pain and side effects. The older nerve-tissue-based vaccinations, which require several painful injections into the abdomen with a large needle, are inexpensive but are being replaced by affordable intradermal vaccination regimens of the WHO.
Patient Care: Physicians should contact the local or state health department to determine the need for postexposure prophylaxis. All wounds must be thoroughly cleaned. Most fatalities occur when people do not seek medical assistance because they are not aware of the possibility of rabies infection.