The Neglected Tropical Diseases (NTDs)
Many of the infectious diseases that are endemic in the developing world have earned the label “neglected” because health-care markets in the afflicted countries are insufficient to attract biopharmaceutical industry investment in research and development (R&D).Most of the R&D investment devoted to neglected diseases is deployed through public-private, not-for-profit, product development partnerships (PDPs). Since 1996, several PDP organizations have arisen to tackle the development of new vaccines, drugs, and diagnostics for developing-world diseases. In addition, several research institutes, a few large pharmaceutical companies, and a handful of biotechnology companies have initiated their own programs, in many cases working with PDPs.
Every year more than US $70 billion is spent worldwide on health R&D by the public and private sectors. An estimated 10% of this is used for research into 90% of the world's health problems. This is what is called "the 10/90 gap". The consequences of this unequal allocation of the world’s health resources, is that diseases that afflict the world’s poorest people have been largely ignored. According to Doctors Without Borders, of the 1,393 new drugs approved from 1975 to 1990, just 13 drugs (barely 1%) were for infectious diseases that disproportionately affect the developing world.
NTDs comprise mainly parasitic and bacterial infections and are the most common afflictions of humankind. The WHO has prioritised its efforts on controlling the following 14 NTDs:
- Buruli Ulcer
- Chagas disease (American trypanosomiasis)
- Dengue/dengue haemorrhagic fever
- Dracunculiasis (guinea-worm disease)
- Human African trypanosomiasis (HAT)
- Lymphatic filariasis
- Soil transmitted helminthiasis
NTDs have afflicted humanity for millennia and, in their long histories, have acquired notoriety as disabling and deforming diseases. In the past, their serious impact on health and productivity led to considerable knowledge about the diseases. Much of this understanding came from the pioneering work of Scottish physicians and scientists such as Dr David Livingston, Sir Patrick Manson, Sir David Ross, Sir David Bruce and Dr William Leishman.
As a result of a greater understanding of these diseases and as living conditions improved, opportunities for transmission were drastically reduced. As a result, these diseases are now rarely seen in populations that enjoy good access to health services and a reasonable standard of living. Today, NTDs are a symptom of poverty and disadvantage. Those most affected are the poorest populations often living in remote, rural areas, urban slums or in conflict zones. With little political voice, NTDs have a low profile and status in public health priorities. Although medically diverse, NTDs share features that allow them to persist in conditions of poverty, where they cluster and frequently overlap.
The global health crisis in relations to the NTDs, demands a comprehensive and integrated response, with faster delivery of existing drugs, vaccines, and diagnostics to those most in need. While programmes to ensure access to current medicines can yield substantial benefits, they will not offer complete solutions. Many of the treatments available today are decades old and are often limited by problems of drug resistance, inadequate safety, and efficacy. For example, current treatments for river blindness (onchocerciasis) only kill immature parasitic worms in early stages of infection and are ineffective for advanced disease. Chagas disease has received proportionately little attention from medical science, yet this devastating illness, the world’s third most prevalent parasitic disease, is a leading health concern throughout South and Central America. Between 16 and 18 million people are infected, and 100 million more are at risk of contracting the parasite, which kills an estimated 45,000 people a year. There is currently no effective treatment available for Chagas disease.
Another neglected disease is leishmaniasis. The most deadly form of this parasitic illness, called visceral leishmaniasis, afflicts some 1.5 million people, primarily in the Indian subcontinent, Ethiopia, Kenya, Sudan and Brazil. Untreated, the disease is more than 90% fatal. In India alone, as many as 200,000 die every year. Also deadly if untreated is African trypanosomiasis, or sleeping sickness, a parasitic disease that infects half a million people worldwide and causes 50,000 deaths annually. Although drugs have been developed to treat it, growing drug resistance has rendered many of them ineffective. As is true for almost all neglected diseases, there has been little interest in researching and developing alternatives.
Dengue is the most common mosquito-borne viral disease of humans that in recent years has become a major international public health concern. Globally, 2.5 billion people live in areas where dengue viruses can be transmitted. Due to climate change, the increased geographical spread of both the mosquito vectors and the viruses has led to the global resurgence of epidemic dengue fever and emergence of dengue hemorrhagic fever (dengue/DHF) which causes an estimated 50,000 deaths annually. There is currently no effective treatment for Dengue.
In summary, there is a critical need for novel, safe, and affordable therapeutics to treat these and many other infectious diseases of the developing world.