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Neglected tropical diseases

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The Neglected Diseases are a group of tropical infections which are especially endemic in low-income populations in developing regions of Africa, Asia, and the Americas. Different groups define the set of diseases differently. Together, they cause an estimated 500,000 to 1 million deaths annually and cause a global disease burden equivalent to that of HIV-AIDS. Some of these diseases have known preventive measures or acute medical treatments which are available in the developed world but which are not universally available in poorer areas. In some cases, the treatments are relatively inexpensive. For example, the treatment for schistosomiasis is USD $0.20 per child per year.[1]

These diseases are contrasted with the big three diseases (HIV/AIDS, tuberculosis and malaria), which generally receive greater funding and research funding. The neglected diseases can also make HIV/AIDS and tuberculosis more deadly.[2]

List of diseases

A young boy from Panama suffering from Chagas disease. It has manifested as an acute infection with swelling of the right eye (chagoma).

Leprosy, tuberculosis, cholera and yellow fever are not exclusively tropical diseases (they have occurred everywhere), but their highest incidence is in the tropics.

Trypanosomal parasites

  • Kala-azar (visceral leishmaniasis, a severe form of leishmaniasis) - Treatments exist, most of them costly and/or toxic. Resistance to pentavalent antimonials is spreading in parts of India. Disease is fatal if untreated. Vaccines are under development as of 2006. Infection is spread by the bite of sandflies.
  • African Sleeping Sickness (African trypanosomiasis) - Disease was nearly eradicated in the 20th century, but relaxation in control methods has led to resurgence. Treatments exist, but are highly toxic and resistance is spreading. This disease is always fatal if untreated. Infection is spread by the bite of the tsetse fly.
  • Chagas disease (American trypanosomiasis) - No vaccine exists for Chagas disease. Treatment for early infection exists but is uneconomical and not authorized as such, current drugs have severe side effects. Chagas disease does not kill victims rapidly, instead causing years of debilitating chronic symptoms. Bites from South American assassin bugs allow the disease to spread.

Worm (helminth) parasites

  • Schistosomiasis - Inexpensive praziquantel can treat this disease, but cannot prevent reinfection. Other treatments are harder to obtain in the developing world. Multiple vaccines are under development. Schistoma species have a complex life cycle that alternates between humans and freshwater snails; infection occurs upon contact with contaminated water. This disease is unique in that damage is not caused by the worms themselves, but rather by the large volume of eggs that the worms produce.[3]
  • Lymphatic Filariasis (causes elephantiasis) - Possible antihelminthic treatments under investigation
  • Onchocerciasis (river blindness) - Antihelminthic treatment exists, prevention involves insect control
  • Drancunculiasis (guinea worm) - Eradication goal is 2009, as of 2007

Soil-transmitted helminthiases:

  • Ascariasis (roundworm) - Antihelminthic treatments exist, prevention involves food and sewage sanitation
  • Trichuriasis (whipworm) - Antihelminthic treatments exist, prevention involves food and sewage sanitation
  • Hookworm - Antihelminthic treatments exist, prevention involves food and sewage sanitation

Bacterial infections

  • Leprosy - Antibiotic treatments exist which can clear the infection; BCG vaccine has some preventative effect.
  • Buruli ulcer - Surgical and antibiotic interventions are recommended
  • Trachoma - Antibiotic treatments exist, prevention involves interpersonal hygiene
  • Cholera - Cholera is caused by Vibrio cholerae bacteria living in contaminated drinking water. The disease presents with severe, watery diarrhea after a short incubation period lasting from zero to five days. Cholera is especially dangerous because it can kill patients in less than 24 hours from rapid dehydration. Antibacterial treatments can cure the disease, but most effective is isotonic fluid replacement therapy, which reduces deaths to 1% of cases. Cholera can be prevented with limited efficacy by two oral vaccines, but access to clean drinking water provides a guarantee of prevention.

Viral infections

  • Yellow fever - A vaccine exists for Yellow fever. Yellow fever, like some other neglected diseases, is caused by a flavivirus
  • Dengue fever - Dengue fever is also caused by a flavivirus, and is spread by the bite of the A. Aegypti mosquito. Dengue fever is not usually fatal, but infection with one of four serotypes can increase later susceptibility to other serotypes, resulting in the highly dangerous Dengue hemorrhagic fever (DHF). No treatment for either type of disease exists beyond palliative care.
  • Japanese Encephalitis - Japanese encephalitis is also caused by a flavivirus. The disease is spread by Culex tritaeniorhynchus mosquitoes.

Incentives for treating diseases

The Priority Review Voucher is an incentive for companies to invest in new drugs and vaccines for neglected tropical diseases. A provision of the Food and Drug Administration Amendments Act (HR 3580) awards a transferable “priority review voucher” to any company that obtains approval for a treatment for a neglected tropical disease. This provision adds to the market based incentives available for the development of new medicines for Neglected Diseases.

The prize was proposed by Duke University faculty Henry Grabowski, Jeffrey Moe, and David Ridley in their 2006 Health Affairs paper: "Developing Drugs for Developing Countries."[4] In 2007 United States Senators Sam Brownback (R-KS) and Sherrod Brown (D-OH) sponsored an amendment to the Food and Drug Administration Amendments Act of 2007. President George W. Bush signed the bill in September 2007.

See also

References

  1. ^ NPR: Making the Case to Fight Schistosomiasis
  2. ^ SciDev.Net. 'Beat neglected diseases' to fight HIV, TB and malaria. Mike Shanahan. 31 January 2006 [1]
  3. ^ Division of Parasitic Diseases - Schistosomiasis Fact Sheet
  4. ^ Developing Drugs For Developing Countries - Ridley et al. 25 (2): 313 - Health Affairs
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