The major human helminthiases, including schistosomiasis and the soil-transmitted helminth (STH) infections, represent the leading neglected tropical diseases (NTDs) in terms of their global prevalence and ability to inflict tremendous disease burdens and disability. Recent estimates from the Global Burden of Disease Study 2017 indicate that almost 1 billion people are infected with STHs, whereas 140 million people have schistosomiasis, with most living in the world’s low- and middle-income countries. In response to the adverse health, educational, and economic effects of pediatric helminth infections, the World Health Organization (WHO) and other international development organizations have taken an active role in trying to lower the disease burden and improve child health through the use of preventive chemotherapy (PC), with a goal of reaching at least 75% of at-risk population and up to 100% of school-aged children. By 2015, nearly 1 billion PC treatments were delivered by NTD PC programs globally.
Although the benefits of deworming programs for children have been known since the early 20th century, the modern framework for global deworming began with transmission modeling studies conducted by Anderson and May during the 1980s, which identified school-aged populations at greatest risk for heavy worm burdens, followed by work led by Bundy, Savioli, and others who provided proof-of-concept of the benefits of deworming through schools. Later, the economists Miguel and Kremer conducted a key study in 2004, which analyzed a randomized experiment conducted in Kenya in the late 1990s, and the results showed the significant effects of PC to improve child health and school attendance. More importantly, the effect was observed not only for the dewormed children but also other children in neighboring schools who did not directly get the treatments. Along with the “spillover” effect, authors suggested that PC is not only effective but highly cost-effective with a single treatment costing a few pennies. In many countries, deworming for STH infections and schistosomiasis has since been integrated with other mass treatment approaches that target lymphatic filariasis, onchocerciasis, trachoma, yaws, and other NTDs.
"Since the original findings highlighted above, multiple studies have confirmed that PC for STH infections and schistosomiasis leads to reduced worm burden, improved public health and DALYS and high economic returns. However, in 2012, and again in 2015, a Cochrane review found little to no evidence for the benefits of PC for STH on nutritional indicators, hemoglobin, and school performance. Subsequently, a group of epidemiologists and researchers replicated and reanalyzed the original Miguel and Kremer study. The authors argued that there is little to no evidence for the benefits of PC on externalities, studies which were confirmed by an additional systematic review. Yet another analysis argued that studies claiming the benefits of PC showed methodological biases. The media quickly picked up on this issue, and the deworming/PC debate became a heated debate in the scientific community. The key study findings since 2000s by economists and epidemiologists that support and do not support PC are summarized in S1 Table. In this paper, we critically evaluate the “worm wars” literature, highlighting gaps in the current discourse on deworming, which have been ignored by both economists and epidemiologists. For the rest of this article, we mostly use the term mass drug administration (MDA) instead of PC because the former is the more commonly used term in the debates.
Read the full article in PLOS Neglected Tropical Diseases.