Academic journal article Bulletin of the World Health Organization

Estimating Human Rabies Mortality in the United Republic of Tanzania from Dog Bite Injuries. (Research)

Academic journal article Bulletin of the World Health Organization

Estimating Human Rabies Mortality in the United Republic of Tanzania from Dog Bite Injuries. (Research)

Article excerpt


Globally, rabies is considered to be a relatively insignificant human disease, accounting for only 1% of deaths attributable to infectious diseases (1). However, there is widespread recognition that the number of deaths officially reported in much of Africa does not reflect the true incidence of the disease. There have been many inconsistencies in the reported incidence of human rabies. For example, the 1996 World Survey of Rabies (2) recorded a global total of 33 212 cases, of which 238 were in Africa and 32 772 in Asia. In Ethiopia, 464 human cases were reported in Addis Ababa between 1992 and 1993 (3), whereas in the entire country only 26 and 35 cases were officially reported to the World Health Organization in 1992 (4) and 1993 (5) respectively.

Several explanations for underreporting have been proposed: patients with clinical rabies may stay at home or seek treatment from local healers; most cases do not receive laboratory confirmation; causes of death may be recorded locally but are not transmitted to the central authorities; a small proportion of deaths attributable to rabies may not be recognized as such by medical staff (1, 6-9).

Many of these problems are clearly not unique to rabies. The poor quality of much public health information in sub-Saharan Africa has prompted several recent investigations into the distribution of major infectious diseases and the mortality and morbidity attributable to them. For example, climatological data together with models of acquired immunity have been used to estimate malaria mortality in sub-Saharan Africa (10). In countries with relatively poor data on tuberculosis, a consensus process has been used to provide plausible estimates of mortality caused by this disease (11). Other extrapolative work has been carried out in order to quantify the populations at risk from diseases such as meningitis and filariasis. This has involved the use of environmental and climatological surrogates from which the distribution and burden of disease have been inferred (12, 13).

Attempts to estimate the true scale of human mortality caused by rabies have been carried out only in India (2), Ethiopia (3) and a few other countries, and they are generally considered to have involved making well-informed guesses. We describe an approach to estimating human rabies mortality in the United Republic of Tanzania, using empirical data on the incidence and distribution of dog bite injuries, the accuracy of rabies recognition and the levels of post-exposure treatment, together with published data on the proportion of bite victims that develop clinical disease.

The fear of developing rabies provides a powerful incentive for people to report animal bite injuries to hospitals, particularly when human post-exposure treatment is available (14, 15). Records of bite injuries from rabid animals may thus provide an accessible source of epidemiological data on rabies, which, in the United Republic of Tanzania, are routinely reported from district hospitals to the central authorities.

Not all bites from rabid dogs result in rabies. Not every bite results in infection and not every infection leads to death. One of the principal factors influencing the outcome of a bite from a rabid dog is the location of the bite on the body. Bites on the head, face and neck, for example, carry a much higher risk than bites on a foot or leg (8, 16-20). We use the distribution of injuries to predict the outcomes of bites of rabid dogs.


The calculation of the predicted number of human rabies deaths in the United Republic of Tanzania is based on a series of probability steps, P1 to P10 (Fig. 1).


Step 1: Incidence of animal bite injuries

Incidence data for animal bite injuries were obtained from national statistics held by the Ministry of Agriculture and Cooperatives (1990-96) for the whole of the United Republic of Tanzania (21, 22) and from 24 villages within the Mara Region in the north-west of the country where rabies awareness had been improved through community-based active surveillance and education programmes (15). …

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