Neglected tropical diseases

Abstract

These diseases could be controlled or eliminated in our lifetimes if efforts are better coordinated

In 2002 one of us wrote an editorial in the BMJ entitled “The world's most neglected diseases,” referring to 13 ancient tropical infections of the poor (box).¹ These diseases are disabling, disfiguring, and stigmatising; they impair children's physical and cognitive growth; they promote poverty; and many of the drugs used to treat them are toxic, difficult to administer, and are more than 50 years old.² Five years ago, there was little good news to report. But recently there has been a silent revolution in the attention being paid to these diseases.^{2 3} We see several reasons for optimism.

Main neglected tropical diseases

Protozoan infections

• Human African trypanosomiasis

• Visceral leishmaniasis

• Chagas disease

Helminth infections

• Soil transmitted helminths: hookworm, ascariasis, trichuriasus

• Schistosomiasis

• Lymphatic filariasis

• Onchocerciasis

• Dracunculiasis

Bacterial infections

• Trachoma

• Leprosy

• Buruli ulcer

Firstly, the long held belief that it is not economically feasible to develop drugs, diagnostic methods, and vaccines specifically for the neglected tropical diseases has now been shattered.⁴ Although these conditions exclusively affect the world's poorest people, product development partnerships have been established for at least six neglected tropical diseases in the past seven years without commercial markets or conventional business models, and several new drugs and vaccines are in the pipeline.^{5 6}

This increase in drug development activity is not a passing trend. Moran and colleagues surveyed the landscape of drug development for neglected tropical diseases and found that 63 drug projects were under way at the end of 2004 (although some of these were for malaria and tuberculosis, diseases that are not considered to be among the most neglected).⁴ On the basis of standard attrition rates, and assuming ongoing funding, we can expect to see eight or nine new drugs for neglected tropical diseases within the next five years. This increased pharmaceutical activity by public-private partnerships is now being complemented by the development capabilities of the so called “innovative developing countries,” such as Brazil, India, and China.⁷ These countries have spent decades building infrastructures for developing their own drugs, vaccines, and diagnostics, with minimal financial or technical help from the rich world.

Furthermore, the moral duty to scale up use of the existing tools for controlling neglected diseases is becoming clearer. “A scientist who is also a human being,” said Albert B Sabin, who developed the oral polio vaccine, “cannot rest while knowledge which might reduce suffering rests on the shelf.” For some of the neglected tropical diseases, the current drugs, if administered to everyone at risk, could certainly reduce suffering. Indeed, the World Health Assembly's targets for controlling five of the neglected tropical diseases (lymphatic filariasis, onchocerciasis, trachoma, soil transmitted helminth diseases, and schistosomiasis) emphasise mass drug administration. The African programme for onchocerciasis control is a good example—by the end of this year, treatment with ivermectin will have reached 65 million people (www.worldbank.org/afr/gper).

Given that the neglected tropical diseases often occur in the same geographical areas, and given evidence that a drug used by one disease specific vertical programme could simultaneously affect other diseases, there is now great interest in rolling out an integrated package of disease control. For example, a package of four drugs (albendazole, ivermectin, azithromycin, and praziquantel) could integrate the control of seven major neglected tropical diseases for 500 million people in Africa and could be delivered for about $50 (£25; €36) per person each year.² Furthermore, tackling neglected parasitic diseases could enhance the effectiveness of antiretroviral therapy in endemic regions.⁸

The penny has finally dropped among donors—they have realised that because chronic parasitic diseases leave people mired in poverty, controlling these diseases will help to achieve the Millennium Development Goal of halving the proportion of people living on less than a dollar a day by 2015 (www.undp.org/mdg/). Lymphatic filariasis, for example, is responsible for the loss of 0.63% of India's gross national product,⁹ while the global annual loss of productivity related to impaired vision and blindness from trachoma is as high as $5.3bn.¹⁰

The United States Agency for International Development has recently awarded a $100m grant to scale up integrated control of neglected diseases in Africa.¹¹ This amount, however, is still less than 10% of the funds needed in sub-Saharan Africa alone for widescale implementation of interventions for neglected tropical diseases.¹²

One problem facing the community working on controlling neglected tropical diseases is the lack of communication between the various players—researchers, policymakers, clinicians, public-private partnerships, donors, and patient advocacy groups. Finally, we have an online tool for such communication—the world's first journal specifically devoted to these diseases. The Bill and Melinda Gates Foundation has awarded the Public Library of Science a grant of $1.1m to launch in October 2007 PLoS Neglected Tropical Diseases (www.plosntds.org), an open access, non-profit journal. One unusual feature of the journal is that, unlike other tropical medicine journals,¹³ 40% of the editors who handle peer review are from countries where the neglected tropical diseases are endemic.