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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 organizations define the set of diseases differently. In sub-Saharan Africa, the impact of these diseases as a group is comparable to malaria and tuberculosis.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. Nevertheless, control of neglected diseases is estimated to require funding of between US$2 billion to US$3 billion over the next five to seven years.
These diseases are contrasted with the big three diseases (HIV/AIDS, tuberculosis and malaria), which generally receive greater treatment and research funding. The neglected diseases can also make HIV/AIDS and tuberculosis more deadly.. However, some pharmaceutical companies have committed to donating all the drug therapies required and mass drug administration have successfully accomplished in several countries.
List of diseases
Neglected tropical diseases include in order of decreasing prevalence: roundworm (ascariasis), whipworm (trichuriasis), hookworm (necatoriasis, ancylostomiasis), snail fever (schistosomiasis), elephantiasis (lymphatic filariasis), trachoma, Kala-azar black fever (leishmaniasis), Chagas disease (American trypanosomiasis), leprosy, African sleeping sickness (African trypanosomiasis), Guinea worm (dracunculiasis), and buruli ulcer.
- 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 have not changed much since colonial times due to lack of further research. The current forms of treatment are ineffective, highly toxic and resistance is spreading. This disease is always fatal if untreated but the outcome is often the same with the existing treatment. 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. Schistosoma 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.
- Lymphatic Filariasis (causes elephantiasis) - Effective antihelminthic treatments have been widely used in a cost-effective manner 
- Onchocerciasis (river blindness) - Antihelminthic treatment exists, prevention may also involve insect control
- Drancunculiasis (guinea worm) - Eradication goal is 2009, as of 2007
- 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
- Strongyloidiasis - Antihelminthic treatments exist, prevention involves sewage sanitation and prevention of malnutrition
- 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.
- 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 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 one of the listed diseases. The voucher can later be used to accelerate review of an unrelated drug. This program is for all tropical diseases and includes medicines for malaria and tuberculosis. The first voucher given was for Coartem, a malaria treatment. It does not use or define the term "neglected" though most of the diseases listed are often included on lists of 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." 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.
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- ^ "Making the Case to Fight Schistosomiasis". National Public Radio. http://www.npr.org/templates/story/story.php?storyId=7806977. Retrieved 2008-12-01.
- ^ "How To Cure 1 Billion People? -- Defeat Neglected Tropical diseases". Scientific American. http://www.scientificamerican.com/article.cfm?id=a-plan-to-defeat-neglected-tropical-diseases. Retrieved 01 January 2010.
- ^ Mike Shanahan (31 January 2006). "Beat neglected diseases to fight HIV, TB and malaria". SciDev.Net. http://www.scidev.net/News/index.cfm?fuseaction=readNews&itemid=2629&language=1.
- ^ Reddy M, Gill SS, Kalkar SR, et al. Oral drug therapy for multiple neglected tropical diseases.JAMA 2007;298(16):1911-1924
- ^ "Control of Neglected Tropical Diseases (NTD)". World Health Organization. http://www.who.int/neglected_diseases/en/. Retrieved 2008-11-30.
- ^ "Schistosomiasis Fact Sheet". CDC, Division of Parasitic Diseases. http://www.cdc.gov/ncidod/dpd/parasites/schistosomiasis/factsht_schistosomiasis.htm. Retrieved 2008-12-03.
- ^ [Mohammed KA, Hail HJ, Gabrielli AF. et al. Triple co-administration of ivermectin, albendazole and praziquantel in Zanzibar: a safety study. PLoS Negl Trop Dis 2(1):e171.doi:10.1371/journal.pntd.0000171]
- ^ "FDA Approves Coartem Tablets to Treat Malaria". USFDA. http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm149559.htm. Retrieved 11 December 2009.
- ^ Developing Drugs For Developing Countries - Ridley et al. 25 (2): 313 - Health Affairs
- Global Network for Neglected Tropical Diseases
- Neglected Tropical Disease Control Program RTI/USAID $100,000,000 Program to Treat 40,000,000 People
- The Global Network for Neglected Tropical Diseases (Sabin Vaccine Institute)
- Taking on The Neglected Diseases, WorldChanging
- Nigeria's Neglected Disesaes, National Public Radio, 3-part series. March 12-13, 2007.
- International Trachoma Initiative,
- Cure for Neglected Diseases: Funding
- Malaria, the Mostly Forgotten Killer
- Whose health revolution?
- Public Library of Science NTDs, open-access journal on Neglected Tropical Diseases
- Drugs for Neglected Diseases initiative, a non-profit product development partnership for the R&D of new treatments for the most neglected diseases