Rabies is a frightening viral infection and the only infectious disease that carries a 100% mortality in any species (including humans) once it is contracted. World Rabies Day is observed every year on 28 September to help raise awareness about rabies prevention and the impact of the disease on both humans and animals.

Young people are the most commonly affected age group, and exposure to infected dogs is the most common reason for human infections. Rabies can be prevented by vaccination, and while there is a relatively expensive treatment available to humans who have been exposed, it is one that needs to be applied correctly and soon after exposure in order to be effective. There is an astounding lack of awareness, among the public and within the medical fraternity, of how to manage post-exposure patients. This is typical of most countries in which rabies is prevalent.

The virus particle does not survive for very long outside of an infected host and is quickly deactivated by sunlight and lack of moisture. All warm-blooded animals are vulnerable to infection, but only mammals are known vectors and reservoirs; birds have a very low susceptibility. The disease is almost always transmitted by saliva from the bite of an infected animal. The ingestion of infected material can also transmit the disease.

Worldwide, more than 55 000 people die of rabies every year (with about 30 000 occurring in India alone). More than 27 000 cases of animal rabies are reported each year, but the estimated number of actual cases is much higher. More than 70% of these cases are in children and young adults, with 40% of people who are bitten by suspected rabid animals are children under the age of 15. Dogs are the source of 99% of human death from rabies; wildlife is a very rare source of infection. The most affected areas are India and South East Asia, then Africa, South America and finally, Russia.

In the northern hemisphere, rabies is mostly a sylvatic disease among wildlife. In the southern hemisphere, however, the feral urban dog is the primary species involved in transmission. The current host species in SA are the domestic dog, black-backed jackal, bat-eared fox and yellow mongoose. The distribution of the disease by host species is illustrated below:

Source: Nel et al., 1997

It is clear that the domestic dog is the prime animal host in SA; cats account for 3.8% of animal cases and are thus a less important host. If the disease could be controlled in dogs, the battle would largely be won. Although canine rabies has been called “urban rabies”, in SA, canine rabies is essentially a rural phenomenon. Families in rural environments could own up to 10 dogs per family (with an average of seven). Affected dogs show obvious changes in behaviour as the hallmark sign. These usually include unusual aggression, fear of water, excessive salivation (saliva contains the virus), mental dullness and ultimately death (usually within five days of showing signs).

In order to significantly affect transmission rate, there would need to be a vaccine coverage of about 70% vaccinated (Coleman and Dye, 1996; Meltzer and Rupprecht, 1998). Exactly what the coverage in these rural populations of dogs is, is unknown. Unfortunately, in the two provinces with the highest number of rabid dog cases, vaccine coverage was below 10%.

Each human death could be regarded as a health system failure. Although there is no treatment for someone who is infected and showing signs of the disease, there is an effective prophylactic treatment that will prevent people who are exposed to the infection from developing rabies.

First aid following a bite from an infected dog should include vigorous wound hygiene. This should be followed with the administration of a hyperimmune serum at a hospital as soon as possible. Sadly, poor hospital readiness and doctors that are insufficiently informed about the disease have resulted in many preventable deaths. People who work with dogs, such as veterinarians and animal healthcare workers, should all be vaccinated against rabies and should keep these vaccinations current. The clinical signs of rabies in people include headache, nausea, vomiting, agitation, anxiety, confusion, hyperactivity, difficulty swallowing, excessive salivation, fear of water, hallucinations and partial paralysis.

The elimination of feral dog populations alone has proven to be ineffective, very unpopular and expensive, and eliminating wildlife is impossible. Vaccination remains the most practical measure that can be taken to prevent the occurrence and spread of rabies.

Professor Andrew Leisewitz works in the Department of Companion Animal Clinical Studies in the Faculty of Veterinary Science at the University of Pretoria

References:

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