Prospects for the Control of Neglected Tropical Diseases by Mass Drug Administration

Henk L. Smits

Disclosures

Expert Rev Anti Infect Ther. 2009;7(1):37-56. 

In This Article

Control Through Mass Drug Administration

Control programs for STH, schistosomiasis, LF, onchocerciasis and trachoma became possible by the availability of inexpensive (often donated by the main pharmaceutical companies), effective and safe drugs that can be administered to affected communities during annual or biannual mass drug administration (MDA) programs. These essential drugs are albendazole (ALB) or mebendazole for the treatment of STH, praziquantel (PZQ) for schistosomiasis, ALB and diethylcarbamazide (DEC) or ALB and ivermectin (IVM) for LF, IVM for onchocerciasis and azithromycin (AZM) for trachoma.[9,10,11,12,13] Many countries have successfully implemented MDA programs with one of the success nations being Morocco, formerly one of the 55 countries endemic for blinding trachoma that successfully controlled the disease in 2006. The mass administration of these drugs is attractive as it can be performed through school teachers, local drug dispensaries or public-health teams after some training.

Fundamental to the expected success of the MDA programs is the assumption that once the prevalence of infection is reduced to below a critical threshold level, transmission will remain low and re-emergence of the disease as a public-health problem is unlikely and may be controlled by other factors, such as natural immunity. Although MDA is the cornerstone of the control programs, they all require additional measures, such as vector control, improved hygiene and environmental sanitation and health education and information.[14,15] These complementary measures may be more difficult and expensive to implement than drug administration and results usually are difficult to gauge. The importance of these measures and, in particular, health education and information should not be underestimated. Most MDA programs appear to be less effective than originally planned and, depending on the initial disease prevalence, need to be continued during a much longer period, a situation that in view of the risk of the development of drug resistance is also highly undesirable. Mathematical modeling has demonstrated that coverage is the most critical factor determining the effectiveness of MDA. Different studies have demonstrated that the coverage of MDA programs is too low and that health education and information, together with community participation and mobilization, are important tools for improvement of coverage and that improved hygiene. Sanitation and vector control are essential to prevent re-emergence of the infection after successful drug administration.[16] Therefore, health-education and community-participation programs should be initiated at a very early stage, and other accompanying measures should be started as soon as the disease prevalence is reduced by MDA. In this respect, it may be recalled that some of the NTDs were once very common in Europe and some other developed countries where they have disappeared as a result of economic development and improved hygiene, sanitation and changes in lifestyle.[17] It is fundamental to understand that poor hygiene and poor sanitation are not synonymous with poverty and that, by simple changes in lifestyle through education, major changes can also be achieved also in resource-poor communities.

The importance and effectiveness of vector control, improved hygiene and environmental changes and the role of public-health education therein can be illustrated by the success of the control program for dracunculiasis (guinea worm), a nematode parasitic infection caused by Dracunculus medinensis. This poverty-related disease that affects mostly communities without safe potable water supplies has been successfully eliminated from almost half of the endemic countries. This was achieved by improving water supplies and filtration of water, control of the copepod (water fleas) intermediate host and larvae using temephos insecticides and case containment allied with health education.[18,19] Currently, the total number of cases has been reduced by over 99% with probably less than 10,000 cases remaining, most of them in remote rural areas in Sudan and Ghana. These remaining cases appear to be limited to nomadic communities who still rely on unsafe stagnant pools or wells for their drinking water supplies.[20] Although complete control of this disease may not be achieved within the next few years, it can be a reality in the near future, provided that sufficient resources remain available to eliminate the remaining foci.

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