Case Scenario 01

Going global: estimating rabies underreporting in Africa and Asia

A major factor in the low level of political commitment to rabies control has been a lack of accurate data on the true public health impact of the disease and a lack of information on the costs and benefits of disease control. Despite the often distinctive and distressing clinical signs of disease in people, it is well recognized that the number of human deaths officially reported vastly under-estimates the true incidence of disease. Several explanations for under-reporting have been proposed, such as a lack of laboratory confirmation of cases, absence of reporting from local to central authorities and the fact that many victims do not present to medical facilities. This may occur because people prefer to seek treatment from local healers, they may be too ill to travel or the clinical signs may be interpreted as “bewitchment” rather than disease. A predictive approach to estimating human deaths in the United Republic of Tanzania has been developed, 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. The advantages of using dog-bite injury data are considerable: (a) the incidence of dog bites is relatively high in comparison with cases, (b) dog bite injuries, when they occur, are often reported to medical authorities as people recognize the need for post-exposure prophylaxis (PEP) following rabid dog bites, and (c) the data are generally notified to central authorities. Dog bite injuries thus constitute a valuable and accessible source of rabies epidemiological data in many countries of Africa and Asia.

Using this probability-tree approach and detailed data on dog-bite injuries from the northern part of the United Republic of Tanzania, the incidence of human rabies cases in that country was estimated to be 100 times higher than officially recorded, with 1 499 (95% confidence interval 891- 2 238) human deaths annually in comparison with the 10-20 human cases typically reported each year by central authorities. Adopting this approach in a revaluation of the rabies burden in Africa and Asia, a total of 55 000 (24 000- 93 000) human deaths were estimated to occur annually in these regions and deaths due to rabies responsible for 1.74 million disability-adjusted life years (DALYs) lost each year. Model outputs have been validated through data subsequently collected in China, India and the Philippines. Additional components of rabies disease burden include (a) the side-effects of nerve-tissue vaccines which are still used widely in parts of Asia and contribute 0.04 million DALYs to the disease burden, (b) economic losses, which amount to US$ 583 million annually, largely due to the direct and indirect costs of human post exposure vaccination, (c) the fear and anxiety associated with receiving a bite from a suspected rabid dog, which could account for as many as 165 000 DALYs not included in the total above, (d) an animal welfare burden as a consequence of public attitude and treatment of animals in areas where dog rabies is endemic and (e) the extinction threat posed by dog rabies to several endangered wildlife populations.