The coverage and frequency of mass drug administration required to eliminate persistent transmission of soil-transmitted helminths

Abstract

A combination of methods, including mathematical model construction, demographic plus epidemiological data analysis and parameter estimation, are used to examine whether mass drug administration (MDA) alone can eliminate the transmission of soil-transmitted helminths (STHs). Numerical analyses suggest that in all but low transmission settings (as defined by the magnitude of the basic reproductive number, R0), the treatment of pre-school-aged children (pre-SAC) and school-aged children (SAC) is unlikely to drive transmission to a level where the parasites cannot persist. High levels of coverage (defined as the fraction of an age group effectively treated) are required in pre-SAC, SAC and adults, if MDA is to drive the parasite below the breakpoint under which transmission is eliminated. Long-term solutions to controlling helminth infections lie in concomitantly improving the quality of the water supply, sanitation and hygiene (WASH). MDA, however, is a very cost-effective tool in long-term control given that most drugs are donated free by the pharmaceutical industry for poor regions of the world. WASH interventions, by lowering the basic reproductive number, can facilitate the ability of MDA to interrupt transmission.

The Impact of Two Semiannual Treatments with Albendazole Alone on Lymphatic Filariasis and Soil-Transmitted Helminth Infections: A Community-Based Study in the Republic of Congo

“…Mathematical modeling studies recently suggested that, in such settings, community MDA and more frequent treatments are more likely to achieve a significant impact (and possibly, interrupt transmission of STHs) than programs using selective MDA for school children only on an annual basis. 26,27 Our preliminary results tend to support the modelers' predictions. In Seke Pembe, the first two rounds of MDA with ALB at high coverage had a significant impact on STH infection levels, with increasing effectiveness for T. trichiura, A. lumbricoides, and hookworm.…”

Prospects for elimination of soil-transmitted helminths

“…This is especially true in communities where hookworm is the predominant infection, as prevalence of hookworm infection peaks in adulthood [30]. Modeling of STH transmission under repeated rounds of MDA suggests that due to continued transmission at the community level, PSAC-targeted and SAC-targeted deworming programs will need to continue indefinitely -or at least until economic development, access to adequate water and sanitation, and other sociodemographic changes occur -to maintain benefit [10,31].…”

“…Models (and some empiric data) suggest that transmission interruption may be possible through chemotherapy alone, provided that the treated population is expanded to all age groups and high coverage is achieved [8][9][10]31,33,34]. Experience from the Global Alliance to Eliminate Lymphatic Filariasis, which provides community-wide MDA with a package of drugs, including albendazole, has demonstrated that achieving high treatment coverage through community delivery of MDA is possible [35].…”

“…Models of STH transmission under repeated rounds of community-wide MDA suggest that transmission interruption in a variety of transmission settings may be possible through chemotherapy alone [31,34]. STH species cannot autoinfect, meaning that successful reproduction requires at least one male and one female worm within a single human host [56].…”

The science of infectious diseases

“…These are drugs for bacterial [9] and helminth infections [10,11], vaccines for pathogens of all kinds [12], and insecticides [13] and the manipulation of heritable characteristics for mosquito control [14].…”