Academic journal article Bulletin of the World Health Organization

Re-Evaluating the Burden of Rabies in Africa and Asia

Academic journal article Bulletin of the World Health Organization

Re-Evaluating the Burden of Rabies in Africa and Asia

Article excerpt

Introduction

More than 99% of all human deaths from rabies occur in the developing world (1), and although effective and economical control measures are available (2, 3) , rabies remains a neglected disease throughout most of these countries (4, 5). A major factor in the low level of political commitment to rabies control is a lack of accurate data on the true public health impact of the disease, it is widely recognized that the number of deaths officially reported greatly underestimates the true incidence of disease. Patients may not present to medical facilities for treatment of clinical disease; few cases receive laboratory confirmation; and clinical cases are often not reported by local authorities to central authorities (1, 6, 7).

These problems are not unique to rabies, and the recognized poor quality of much public health information from developing countries has prompted several investigations into the distribution of major infectious diseases and the mortality and morbidity attributable to them. Such studies are based on estimates of occurrence extrapolated from more readily quantifiable determinants of disease, such as vector distribution or host immunity (8-10). For rabies, a similar predictive approach has been used to estimate human deaths from rabies in the United Republic of Tanzania using a probability decision tree method to determine the likelihood of clinical rabies developing in a person bitten by a dog suspected to be rabid (6). Dog bites are reported proportionately more frequently than human cases of rabies and may provide an accessible data source from which human deaths from rabies can be inferred.

The objective of our study was to estimate the burden of rabies in Africa and Asia by applying data derived from these regions to this model and to thereby present a data-driven assessment of the human and economic costs of rabies in the developing world. We define Africa as all mainland countries on the continent plus Madagascar; Asia is defined as those countries falling under the WHO-defined South-East Asia Region and Western Pacific Region, including Pakistan. Only countries considered by WHO and the Office International des Epizooties as having endemic canine rabies were considered in this analysis. The list of all countries included in the study available from http://www.vet.ed.ac.uk/ctvm/Research/Appendices/ appendices.html.

Methods

Human rabies deaths

Full details of the methods used in the dog-bite probability model have been published elsewhere (6). Briefly, the model recognizes that not all bites from rabid dogs result in infection and that not every infection leads to clinical signs and 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 (11, 12). The model uses the distribution of injuries on the body together with the likelihood of the patient receiving successful treatment to predict the outcomes of bites from rabid dogs. The model thus allows the incidence of bites from suspected rabid dogs among the human population considered to be at risk to be used as a determinant of the number of human deaths from rabies.

The human population at risk from canine rabies was taken as the number of people living in areas affected by canine rabies where the density of the dog population exceeds the threshold density at which canine rabies is capable of being maintained endemically. Dog-population densities were inferred from human densities derived from two regional population density datasets (13, 14) with adjustments made to account for population growth (15). Associated dog-population numbers were calculated by dividing human figures by the regional average ratio of humans to dogs, based on values given in Table 1. The threshold density for rabies persistence was taken as 4.5 dogs/[km.sup.2], based on predictions produced from data on rabies transmission in rural Kenya (16); these data are consistent with empirical observations from elsewhere in Africa (17-20). …

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