Rabies

Description

Rabies, an acute, fatal encephalomyelitis caused by neurotropic viruses in the family Rhabdoviridae, genus Lyssavirus, is almost always transmitted by an animal bite that inoculates the virus into wounds. Very rarely, rabies has been transmitted by nonbite exposures that introduce the virus into open wounds or mucous membranes. All mammals are believed to be susceptible, but reservoirs are carnivores and bats. Although dogs are the main reservoir in resource-poor countries, the epidemiology of the disease differs sufficiently from one region or country to another to warrant the medical evaluation of all mammal bites.

Occurrence

Rabies is found on all continents except Antarctica. In certain areas of the world, canine rabies remains highly endemic, including (but not limited to) parts of Brazil, Bolivia, Colombia, Ecuador, El Salvador, Guatemala, India, Mexico, Nepal, Peru, the Philippines, Sri Lanka, Thailand, and Vietnam. The disease is also found in dogs in most of the other countries of Africa, Asia, and Central and South America, except as noted in Table 3–13, which lists countries that have reported no cases of rabies during the most recent 2-year period for which information is available (formerly referred to as “rabies-free countries”).

Additional information can be obtained from the World Health Organization, local health authorities of the country, the embassy, or the local consulate's office in the United States.

Risk for Travelers

Travelers to rabies-endemic countries should be warned about the risk of acquiring rabies, although rabies vaccination is not a requirement for entry into any country. Travelers with extensive unprotected outdoor, evening, and nighttime exposure in rural areas, such as might be experienced while bicycling, camping, or engaging in certain occupational activities, might be at high risk even if their trip is brief.

Clinical Description

The disease progresses from a nonspecific prodromal phase to paresis or paralysis; spasms of swallowing muscles can be stimulated by the sight, sound, or perception of water (hydrophobia); delirium and convulsions can develop, followed by coma and death.

Prevention

Preexposure vaccination with human diploid cell rabies vaccine (HDCV), purified chick embryo cell (PCEC) vaccine, or rabies vaccine adsorbed (RVA) may be recommended for international travelers based on the local incidence of rabies in the country to be visited, the availability of appropriate antirabies biologicals, and the intended activity and duration of stay of the traveler. Preexposure vaccination may be recommended for veterinarians, animal handlers, field biologists, spelunkers, missionaries, and certain laboratory workers. Table 3–14 provides criteria for preexposure vaccination. Preexposure vaccination does not eliminate the need for additional medical attention after a rabies exposure, but simplifies postexposure prophylaxis in populations at risk by eliminating the need for rabies immune globulin (RIG) and by decreasing the number of doses of vaccine required. Preexposure vaccination is of particular importance for travelers at risk of exposure to rabies in countries where locally available rabies vaccines might carry a high risk of adverse reactions. Preexposure vaccination can also provide protection when there is an unapparent or unrecognized exposure to rabies and when postexposure prophylaxis might be delayed.

Purified equine rabies immune globulin (ERIG) has been used effectively in developing countries where human rabies immune globulin (RIG) might not have been available. If necessary, such heterologous product is preferable to no RIG administration in human rabies postexposure prophylaxis. The incidence of adverse reactions after the use of these products has been low (0.8%–6.0%), and most of those that occurred were minor. However, such products are neither evaluated by U.S. standards nor regulated by the U.S. Food and Drug Administration, and their use cannot be unequivocally recommended at this time. In addition, unpurified antirabies serum of equine origin might still be used in some countries where neither human RIG nor ERIG are available. The use of this antirabies serum is associated with higher rates of serious adverse reactions, including anaphylaxis.

Travelers should be advised that any animal bite or scratch should receive prompt local treatment by thorough cleansing of the wound with copious amounts of soap and water and a povidone-iodine solution if available; this local treatment will significantly reduce the risk of rabies. Travelers who might have been exposed to rabies should be advised to always contact local health authorities immediately for advice about postexposure prophylaxis and should also contact their personal physician or state health department as soon as possible thereafter.

Tables 3–15 and 3–16 provide information on preexposure and postexposure prophylaxis. Routine serologic testing is not necessary for travelers who receive the recommended preeexposure or postexposure regimen with HDCV, PCEC, or RVA vaccines. Exposed travelers previously vaccinated with noncell culture vaccines should receive the complete postexposure regimen unless they have developed a laboratory-confirmed antibody response to the primary vaccination. Serologic testing is still recommended for travelers whose immune response might be diminished by drug therapy or by diseases. Rabies preexposure prophylaxis might not be indicated for travelers to the countries in Table 3–13, and postexposure prophylaxis is rarely necessary after exposures to terrestrial animals in these countries.

Adverse Reactions

Travelers should be advised that they can experience local reactions such as pain, erythema, and swelling or itching at the injection site, or mild systemic reactions, such as headache, nausea, abdominal pain, muscle aches, and dizziness. Approximately 6% of persons receiving booster vaccinations with HDCV can experience an immune complex-like reaction characterized by urticaria, pruritus, and malaise. Once initiated, rabies postexposure prophylaxis should not be interrupted or discontinued because of local or mild systemic reactions to rabies vaccine.

Precautions and Contraindications

Pregnancy. Pregnancy is not a contraindication to postexposure prophylaxis.

Age. In infants and children, the dose of HDCV, PCEC, or RVA for preexposure or postexposure prophylaxis is the same as that recommended for adults. The dose of RIG for postexposure prophylaxis is based on body weight (Table 3–16).

For more information about rabies, see the CDC rabies site at http://www.cdc.gov/ncidod/dvrd/rabies

— Charles Rupprecht