Geographical distribution of soil transmitted helminths and the effects of community type in South Asia and South East Asia – A systematic review

Background: Soil-transmitted helminth (STH) infections are among the most prevalent neglected tropical diseases (NTD) worldwide. Since the publication of the WHO road map to combat NTD in 2012, there has been a renewed commitment to control STH. In this study, we analysed the geographical distribution and effect of community type on prevalence of hookworm, Trichuris and Ascaris in south Asia and south east Asia. Methodology: We conducted a systematic review of open-access literature published in PubMed Central and the Global Atlas of Helminth Infection. A total of 4182 articles were available and after applying selection criteria, 174 studies from the region were retained for analysis. Principal findings: Ascaris was the commonest STH identified with an overall prevalence of 18% (95% CI, 14–23%) followed by Trichuris (14%, 9–19%) and hookworm (12%, 9–15%). Hookworm prevalence was highest in Laos, Vietnam and Cambodia. We found a geographical overlap in countries with high prevalence rates for Trichuris and Ascaris (Malaysia, Philippines, Myanmar, Vietnam and Bangladesh). When the effect of community type was examined, prevalence rates of hookworm was comparable in rural (19%, 14–24%) and tribal communities (14%, 10–19%). Tribal communities, however, showed higher prevalence of Trichuris (38%, 18–63%) and Ascaris (32%, 23–43%) than rural communities (13%, 9–20% and 14%, 9–20% respectively). Considerable between and within country heterogeneity in the distribution of STH (I2 >90%) was also noted. When available data from school aged children (SAC) were analysed, prevalence of Ascaris (25% 16–31%) and Trichuris (22%, 14–34%) were higher than among the general population while that of hookworm (10%, 7–16%) was comparable. Conclusions/Significance: Our analysis showed significant variation in prevalence rates between and within countries in the region. Highlighting the importance of community type in prevalence and species mix, we showed that tribal and rural communities had higher hookworm infections than urban communities and for ascariasis and trichuriasis, tribal populations had higher levels of infection than rural populations. We also found a higher prevalence of ascariasis and trichuriasis in SAC compared to the general population but comparable levels of hookworm infections. These key findings need to be taken into account in planning future MDA and other interventions. Author summary: Soil transmitted helminth infections (hookworms, Trichuris and Ascaris) are highly prevalent across south Asia and south east Asia and recently several large initiatives have been launched to control or interrupt transmission. We conducted a systematic review of STH infections to identify the communities in south Asia and south east Asia that will benefit the most from intervention programs. Our analysis showed that Ascaris is the most prevalent STH in the region but there was considerable geographic variation in the region. We found that tribal and rural communities in these countries had higher prevalence of STH compared to urban populations. We also found a higher prevalence of Ascaris and Trichuris in school aged children compared to the general population but comparable levels of hookworm infections. These key findings are important for future planning of intervention strategies for control of STH.