Neglected Tropical Diseases in Sub-Saharan Africa: Review of Their Prevalence, Distribution, and Disease Burden

15 Sep 2009

Paul Chinnock

Source: PLoS Neglected Tropical Diseases (see original article or PDF)

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Citation: Hotez PJ, Kamath A (2009). Neglected Tropical Diseases in Sub-Saharan Africa: Review of Their Prevalence, Distribution, and Disease Burden. PLoS Negl Trop Dis 3(8): e412.

© 2009 Hotez, Kamath. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

A new analysis has concluded that, in sub-Saharan Africa, the infections categorised as “neglected tropical diseases” (NTDs) are collectively responsible for a disease burden equal to twice that caused by tuberculosis, half of that due to malaria, and a third of that resulting from HIV/AIDS. On the basis of this finding, the resources devoted to NTD control and research are woefully inadequate.

In a review published in PLoS Neglected Tropical Diseases Peter Hotez and Aruna Kamath searched the medical literature for prevalence data on all the diseases considered by the journal as being NTDs. (For the journal’s own NTD list, use this link.)

According to their analysis, approximately 85% of sub-Saharan Africa’s NTD disease burden results from infection with helminths (parasitic worms). Hookworm infection occurs in almost half of the region’s poorest people, including 40-50 million school-aged children and seven million pregnant women in whom it is a leading cause of anaemia. Schistosomiasis is the second most prevalent NTD after hookworm (192 million cases). Africa accounts for 93% of total cases worldwide. Lymphatic filariasis (46-51 million cases) and onchocerciasis (37 million cases) are also widespread. Each of these diseases is a significant cause of disability and has a major impact through reducing agricultural productivity.

The authors found that available data on non-helminth NTDs is very limited. Nevertheless, they estimate that protozoan infections (including sleeping sickness and visceral leishmaniasis) affect almost 100,000 Africans and that trachoma is the most common bacterial NTD (30 million cases).

Diseases on which the lack of data made it impossible for the authors to reach conclusions as to prevalence rates include: amoebiasis, toxoplasmosis, typhoid fever and non-typhoidal salmonellosis, tick-borne bacterial zoonoses, non-tuberculosis mycobaterial infections, and arboviral infections. It is likely therefore, as the authors acknowledge, that their estimates of the overall burden of Africa’s NTDs may considerably underestimate the actual position. They say that more research is needed to establish the true prevalence of all NTDs in order to help set Africa’s disease control priorities.

The authors also note that two countries – in Nigeria and the Democratic Republic of Congo – face a particularly high NTD burden. Together the two nations account for a third of the region’s helminth infections and a fifth of sleeping sickness case numbers.

It has become commonplace for AIDS, malaria and tuberculosis to be referred to as the “big three” infectious diseases of poverty. The findings of this review demonstrate that the NTDs constitute of fourth problem of comparable magnitude and should be given increased priority in funding for research and control activities.

The high proportion of the NTD burden due to helminths is extraordinary, given that effective treatments for these infections have been available for many years. With a relatively small increase in funding for control efforts, the disease burden could be considerably reduced. In the case of many of the non-helminth NTDs, however, there is still a lack of effective treatment; research efforts must therefore be stepped up.

Similar reviews of available data from other parts of the tropical world are also needed.