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Neglected Tropical Diseases

Neglected tropical diseases comprise several parasitic, bacterial and viral infections and are the most common afflictions of humankind. They affect the world's poorest, an estimated 3 billion people, who subsist on less than $2 per day. Neglected tropical diseases are thought to cause 500,000 deaths each year, yet their greatest impact lies in the way they promote poverty, stigmatize, disable and inhibit individuals from being able to care for themselves or their families. Together, neglected tropical diseases cause as much disease and suffering as malaria or tuberculosis. They are the 4th most important group of communicable diseases, behind lower respiratory infections, HIV/AIDS, and diarrhoeal diseases. Children, women and those living in remote areas without any access to an effective health care system are most vulnerable. An increasing body of evidence also indicates that co-infection with one or more of the neglected tropical diseases adversely affects the natural history and progression of malaria and HIV/AIDS.

Neglected tropical diseases and Malaria

Several studies point to the increasing severity of clinical malaria that results from helminth co-infection. There is enhanced risk or increased incidence of clinical falciparum malaria resulting from either soil-transmitted helminth or schistosome infections, and increased susceptibility to malaria in patients with soil-transmitted helminth infections. In addition to increased susceptibility to malaria, the helminths, especially hookworm and schistosomiasis, exacerbate the anaemia caused by malaria.

To make matters worse, many African populations experience further reductions in haemoglobin because of sickle cell disease and thalassaemia, as well as nutritional deficits in iron and folate. The severe anaemia resulting from helminth polyparasitism and malaria produces several adverse health consequences among particularly important African subpopulations: children and pregnant women.

Neglected tropical diseases and Intermittent Preventive Therapy (IPT) for Malaria

There is an urgent need to expand our knowledge base on the interactions between malaria and helminth co-infections and there is also an urgency to examine the impact of neglected tropical disease control on intermittent preventive therapy (IPT) with antimalarials.

School-aged children are an important yet understudied population in terms of the health impact of malaria, with some studies indicating that up to 50% of African school-aged children experience an attack of clinical malaria each year, and up to 20% of the mortality from malaria occurs in school-aged children. Like helminth infections, malaria also adversely affects cognition and education. In pregnancy, IPT (IPTp) protects against maternal anaemia and low birth-weight, especially in primigravidae and secundigravidae.

The importance of helminth co-infections in exacerbating malaria in older children (beyond infancy) and in pregnancy, together with evidence that IPT in older children and in pregnant women will greatly reduce morbidity from malaria, suggests that there are multiple opportunities to link neglected tropical disease control with malaria control

Key Points:

  • Estimates suggest that neglected tropical diseases cause more than half a million deaths a year.
  • They confer a far greater burden, in terms of morbidity, on poor populations than this number suggests.
  • Co-infection with another disease exacerbates infection.
  • There is enhanced risk of clinical malaria if the patient has a pre-existing helminth infection.
  • As children are more likely to harbour a helminth infection, serious consideration should be given to intermittent preventive treatment in this cohort.

Malaria Consortium implements programmes to address neglected tropical diseases in Uganda and Southern Sudan. This includes operational research on visceral leishmaniasis and lymphatic filariasis in Uganda and interventions to strengthen case management and prevention of visceral leishmaniasis in hard-to-reach areas of southern Sudan. Malaria Consortium is also carrying out situation analyses on the potential for integrated control of neglected tropical diseases in various countries in eastern Africa.

References:

1. Kolaczinski J, Kabatereine N, Onapa A, Ndyomugyenyi R, Kakembo A, Brooker S. (2007) Neglected tropical diseases in Uganda: the prospect and challenge of integrated control. Trends in Parasitology [Forthcoming in October Issue]

2. Yamey, G & Hotez P. (2007) Neglected tropical diseases. BMJ 336 (7614) 269-270.

3. Brooker S & Utzinger J. (2007) Integrated disease mapping in a polyparasitic world. Geospatial Health 2, 141-146.

4. Brady, M., Hooper, P., Ottesen, E., 2006. Projected benefits from integrating NTD programs in sub-Saharan Africa. Trends Parasitol. 22, 285-291.

5. WHO, 2006. Preventive chemotherapy in human helminthiasis. Coordinated use of anthelminthic drugs in control interventions: a manual for health professionals and programme managers. World Health Organization, Geneva. [Available from: http://whqlibdoc.who.int/publications/2006/9241547103_eng.pdf]

6. WHO (2006) Neglected Tropical Diseases: Hidden successes, emerging opportunities. WHO/CDS/NTD/2006.2