Prevalence of soil-transmitted helminth infections, schistosomiasis, and lymphatic filariasis before and after preventive chemotherapy initiation in the Philippines: A systematic review and meta-analysis

Objective: To estimate the impact of preventive chemotherapy on the prevalence and intensity of soil-transmitted helminth (STH) infections, schistosomiasis, and lymphatic filariasis in the Philippines, using systematic review and meta-analysis. Methods: We included reports reporting prevalence of STH infections, schistosomiasis, or lymphatic filariasis in the Philippines published until 31 March 2021. Peer-reviewed studies were identified in electronic databases. Grey literature reports by the University of the Philippines and the Department of Health were also included. Pooled infection prevalence, before and after the initiation of preventive chemotherapy, stratified by age group, was calculated using the inverse variance heterogeneity model. Findings: A total of 109 reports were included in the review and meta-analysis. Overall prevalence of moderate-heavy intensity Ascaris lumbricoides (6.6%) and Trichuris trichiura (2.7%) infection after initiation of preventive chemotherapy were significantly lower than the prevalence prior to initiation (23.6% for A. lumbricoides and 12.2% for T. trichiura). Prevalence reductions were also found in school and preschool-age children for A. lumbricoides and T. trichiura. Studies conducted after preventive chemotherapy initiation had significantly lower overall prevalence of moderate-heavy intensity schistosomiasis (3.1% vs 0.2%) and of schistosomiasis in school-age children (30.5% vs 1%). Pooled prevalence of lymphatic filariasis prior to preventive chemotherapy initiation was 3.2% across 12 provinces, while currently only two provinces still have prevalence of more than 1%. There were no published studies reporting prevalence of lymphatic filariasis after initiation of preventive chemotherapy. Heterogeneity was high with I2 mostly above 90%. Conclusion: The burden of STH infections and schistosomiasis in children were significantly lower in studies conducted following the initiation of preventive chemotherapy. Eliminating morbidity and interrupting transmission, however, may require expanded control initiatives including community-wide treatment, and improved water, sanitation, and hygiene. Lymphatic filariasis burden has decreased since the implementation of preventive chemotherapy, with all but two provinces having reached the elimination of lymphatic filariasis as a public health problem. Author summary: Mass treatment with anti-parasitic medications is a key control and elimination strategy for several helminth infections, namely intestinal worm infections, schistosomiasis, and lymphatic filariasis, which are common in the Philippines and other endemic countries. To gain insight into the impact of such a strategy that has been in place for more than 14 years, we used systematic review and meta-analysis to compare the prevalence of each of these helminth infections in the Philippines before and after the initiation of mass treatment. The review included 109 reports, composed of peer-reviewed studies and grey literature. The pooled overall prevalence of heavy intensity and the prevalence in children of intestinal worm infection and schistosomiasis were significantly lower in studies conducted after initiation of mass treatment. The studies included are highly heterogenous reflecting variability in sampling procedures, diagnostic tests, study sites, and years of data collection. Eliminating morbidity and interrupting transmission may require expanded control initiatives including community-wide treatment, and improved water, sanitation, and hygiene. The same significantly lower prevalence after initiation of mass treatment was observed for lymphatic filariasis where only two out of the initial 12 endemic provinces still require mass treatment due to prevalence above 1%.