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• Immune Evasion
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• Immunocompromised
  Hosts
• Anti-malarial drug development
• Anti-parasitic drug development
• Conflict and Parasites
• Parasites of Bees
• Morgellons:
  Fact or Fiction?
• Eradication of
  Chaga’s Disease
• The world’s most successful parasite
• Guinea worm eradication

Parasites

Gang of 10

Video’s detailing some of these diseases further: http://www.who.int/tdr/media/video/b-rolls.htm

why these diseases matter

The outpour of support and funding for major diseases such as HIV/AIDS is well documented and receives substantial media attention. As more scholarship is published, correlations among health care, economic development, and political stability become clear. Disease is known to diminish a country’s economic output, and consequently is closely tied to armed conflict and the breakdown of governance. With the Big Three diseases tuberculosis, HIV/AIDs and malaria garnering the most attention, research, and funding, these parasitic infections can go unnoticed.

This neglect in the face of other huge problems stems in part from the fact that many infected people are clinically sub-symptomatic, making the total scope of the burden of disease hard to precisely quantify. Even asymptomatic infections can impact a child’s growth, cognitive function and contribute to malaise and lethargy (Hotez, et al.). Though hard to see immediately, these factors have a long-term dramatic impact on quality of life and overall diminishment of one’s potential. One specific concomitant disease burden is anemia, especially in pregnant women and fetal development. Iron deficiency anemia results in 12 million DALYs lost annually; it is the most common nutrition deficit worldwide. Stigma also surrounds several of these diseases. Leishmaniasis can result in horrible scarring, and the mucocutaneous form can destroy the sinuses of the face. Elephantitis caused by leishmaniasis results in grossly enlarged extremities or scrotum. 250,000 people with onchocerciasis have been rendered blind. These diseases usually afflict people who are already incredibly poor and resource-limited and further stifle their ability to improve their educational and socioeconomic status.

The multiple complications involved, the malnutrition resulting from intestinal infestation, the anemia and the potential of co-infection with other diseases (urologic shistosomiasis has been demonstrated to increase transmission risk of HIV 3-fold) result in 530,000 deaths annually. In light of this, considerable effort needs to be taken to further implement existing strategies and develop new ones (Stoever and Broder, et al.).

Clockwise from top left: woman with lymph edema due to lymph vessel damage from lymphatic filariasis infections; schistosomiasis; severe mucocutaneous leishmaniasis, child’s abdomen enlarged by roundworm infestation. Courtesy of Stoever.)

lack of funding priority

WHO reports indicate that control and elimination targets are falling woefully short. In 2006 it was estimated that control targets for schistosomiasis, lymphatic filariasis and onchocerciasis were only at 10%, 38% and 44%, respectively. In other words, only 62 cents is spent per DALY for the cohort of neglected tropical diseases, compared to $102/DALY for diabetes, $24/DALY for HIV/AIDS, and $6/DALY for malaria. Inexpensive and cost-effective approaches exist for NTDs; the will to organize and allot resources is simply lacking (UFS conference). However, the Gates Foundation’s huge endowment for NTDs signals great promise. Additionally, WHO has elaborated on the need for more funding for these diseases. The graph below demonstrates efforts to allocate research money where it would be most effective or is most needed. Augmented by new support from other sources, this money has allowed stalled research to begin anew and has promoted new drug discovery research (Remme, Feenstra).

Courtesy of Remme et al. Strategic emphases for tropical disease research: a TDR perspective.

The WHO report also categorized the most prevalent parasitic disease based off of epidemiological trends. They are listed as category I, II or III below and some of the research goals for each is summarized here.

current approaches: benefits & drawbacks

The three major approaches are

• Anthelmintic drug treatments (“deworming”): reduces morbidity by reducing the worm burden

• Drugs used: benzimidazole anthelmintics (BZAs); albendazole (single dose 400mg); mebendazole (single dose 500mg); levamisole; pyrantel pamoate
• Praziquantel (PZQ) (single dose 40mg/kg) is the major drug for schistosomiasis.
• Oxamniquine is used to treat S. mansoni infections in South Africa.
• The efficacy of Praziquantel and Oxamniquine is comparable (PZQ slightly better).
• BZAs and PZQ are inexpensive, have been rigorously tested, and pose few minor side effects.
• BZAs do not need dosage according to weight and are thus easier for population-based interventions.
• The use of proxy indicators (i.e. height-for-weight) has proved successful with PZQ
• In some cases the efficacy of mebendazole/albendazole on hookworm and Trichuris infection is low.
• Pyrantel pamoate has little effect on T. trichiura
• Deworming programs occur in three forms:
• universal treatment: the entire community is treated
• targeted treatment: treatment targets population groups irrespective of infectious status
• selective treatment: treatment targets individual-level application based on diagnosis or suspicion of current infection
• Benefits: periodic deworming in high-risk populations can keep levels of infection below those associated with morbidity, can prevent the development of irreversible consequences of diseases, and can reduce transmission over time.
• Drawbacks: low-efficacy of single-dose mebendazole for hookworm (re-infection w/in 4-6 mo), single-dose albendazole for trichuriasis; high areas of post-treatment re-infection in areas with high endemicity; diminished efficacy with frequent and repeated use (parasitic resistance?)

• Sanitation: reduce soil and water contamination
• Benefits: only definitive intervention against STH infections
• Drawbacks: needs to cover a high percentage of the population to be effective, therefore costs are high, especially in resource and infrastructure-poor areas; it can take years for it to be implemented/effective. Latrines can fall into disuse.

3. Health education: reducing transmission and re-infection by teaching healthy behaviors such as promoting use of latrines/hygienic behavior

• Benefits: can be provided simply and economically and the benefits go beyond control of parasitic infections
• Drawbacks: For example, in hookworm control, even if one wears shoes as barrier protection, Ancylostoma and Necator can still enter from other parts of the body. Agricultural practices/needs may require the use of nightsoil.