Rabies
Cause
The rabies virus, a lyssavirus of the family Rhabdoviridae.
Transmission
Rabies is a zoonotic disease affecting a wide range of domestic and wild mammals, including bats. Infection of humans usually occurs through the bite of an infected animal as the virus is present in the saliva. In developing countries, transmission is usually through dog bites. Transmission may occasionally also occur through other contact with a rabid animal, for example following a penetrating scratch with bleeding or licking of broken skin and mucosa. Person-to-person transmission other than via organ transplant has not been laboratory-confirmed.
Nature of the disease
An acute viral encephalomyelitis, which is almost invariably fatal. The initial signs include a sense of apprehension, headache, fever, malaise and sensory changes around the site of the animal bite. Excitability, hallucinations and abnormal fear of drafts of air (aerophobia) are common, followed in some cases by fear of water (hydrophobia) due to spasms of the swallowing muscles, progressing to delirium, convulsions and death a few days after onset. A less common form, paralytic rabies, is characterized by paralysis and loss of sensation, weakness and pain.
Disease burden
Rabies is present in mammals in many countries worldwide (Map). Most of the estimated 55 000 human rabies deaths per year occur in Africa and Asia. More information on rabies is available at http://www.who.int/rabies/ rabnet/en.
Risk for travellers
The risk to travellers in areas countries and areas at risk for rabies (Map, or http://www.who.int/rabies/rabnet/en) is proportional to the probability of contact with potentially rabid mammals. In most developing countries, the estimated ratio of dogs, both owned and ownerless, to humans is 1:10 and an average 100 suspected rabid dog bites per 100 000 inhabitants are reported annually. According to a recent survey conducted in India, 1.6% of the total population received a dog bite during a 12-month period. As rabies is a lethal disease, medical advice should be sought immediately at a competent medical centre – ideally, the rabies treatment centre of a major city hospital. First-aid measures should also be started immediately (see “Post-exposure prophylaxis”, below).
Travellers should avoid contact with free-roaming animals, especially dogs and cats, and with wild, free-ranging and captive animals. For travellers who participate in caving or spelunking, casual exposure to cave air is not a concern, but cavers should be warned not to handle bats. In most countries of the world, suspect contact with bats should be followed by post-exposure prophylaxis.
The map shows the WHO categories of risk, from no risk (rabies-free) countries or areas to countries or areas of low, medium and high risk (dog rabies). Categorization is based primarily on the animal host species in which the rabies virus is maintained in a country or area, e.g. bats and/or other wildlife and/or dogs and on the availability of reliable laboratory-based surveillance data in these reservoir species. Access to proper medical care and the availability of modern rabies vaccines have also been taken into consideration on a country basis. In countries or areas belonging to categories 2–4, pre-exposure immunization against rabies is recommended for travellers with certain characteristics:
Category 1: no risk.
Category 2: low risk. In these countries or areas travellers involved in activities that might bring them into direct contact with bats (for example, wildlife professionals, researchers, veterinarians and adventure travellers visiting areas where bats are commonly found) should receive pre-exposure prophylaxis.
Category 3: medium risk. In these countries or areas, travellers involved in any activities that might bring them into direct contact with bats and other wild animals, especially carnivores, (e.g., wildlife professionals, researchers, veterinarians and travellers visiting areas were bats and wildlife are commonly found) should receive pre-exposure prophylaxis.
Category 4: high risk. In these countries or areas, travellers spending a lot of time in rural areas involved in activities such as running, bicycling, camping or hiking should receive pre-exposure prophylaxis. Prophylaxis is also recommended for people with significant occupational risks, such as veterinarians, and expatriates living in areas with a significant risk of exposure to domestic animals, particularly dogs, and wild carnivores. Children should be immunized as they are at higher risk through playing with animals, particularly with dogs and cats; they may receive more severe bites and are less likely to report contact with suspect rabies animals.