Elimination of Schistosomiasis Transmission in Zanzibar: Baseline Findings before the Onset of a Randomized Intervention Trial

Abstract

Background

Gaining and sustaining control of schistosomiasis and, whenever feasible, achieving local elimination are the year 2020 targets set by the World Health Organization. In Zanzibar, various institutions and stakeholders have joined forces to eliminate urogenital schistosomiasis within 5 years. We report baseline findings before the onset of a randomized intervention trial designed to assess the differential impact of community-based praziquantel administration, snail control, and behavior change interventions.

Methodology

In early 2012, a baseline parasitological survey was conducted in ∼20,000 people from 90 communities in Unguja and Pemba. Risk factors for schistosomiasis were assessed by administering a questionnaire to adults. In selected communities, local knowledge about schistosomiasis transmission and prevention was determined in focus group discussions and in-depths interviews. Intermediate host snails were collected and examined for shedding of cercariae.

Principal Findings

The baseline Schistosoma haematobium prevalence in school children and adults was 4.3% (range: 0–19.7%) and 2.7% (range: 0–26.5%) in Unguja, and 8.9% (range: 0–31.8%) and 5.5% (range: 0–23.4%) in Pemba, respectively. Heavy infections were detected in 15.1% and 35.6% of the positive school children in Unguja and Pemba, respectively. Males were at higher risk than females (odds ratio (OR): 1.45; 95% confidence interval (CI): 1.03–2.03). Decreasing adult age (OR: 1.04; CI: 1.02–1.06), being born in Pemba (OR: 1.48; CI: 1.02–2.13) or Tanzania (OR: 2.36; CI: 1.16–4.78), and use of freshwater (OR: 2.15; CI: 1.53–3.03) showed higher odds of infection. Community knowledge about schistosomiasis was low. Only few infected Bulinus snails were found.

Conclusions/Significance

The relatively low S. haematobium prevalence in Zanzibar is a promising starting point for elimination. However, there is a need to improve community knowledge about disease transmission and prevention. Control measures tailored to the local context, placing particular attention to hot-spot areas, high-risk groups, and individuals, will be necessary if elimination is to be achieved.

Author Summary

Schistosomiasis is a chronic and debilitating disease caused by parasitic worms. It negatively impacts on the health and wellbeing of mainly rural dwellers in tropical and sub-tropical countries. The World Health Organization recently put forward an ambitious goal for the year 2020: to control schistosomiasis globally. Interruption of transmission and elimination of schistosomiasis are encouraged whenever resources allow. After careful consideration, the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) selected the Zanzibar archipelago to learn how best to eliminate schistosomiasis. We report the baseline findings of a 5-year program. Parasitological examination of about 20,000 people on Unguja and Pemba islands revealed a low overall prevalence of Schistosoma haematobium (7%). Nevertheless, hot-spots with high prevalence (>20%) and high-risk groups (males, young adults, people born in Pemba or mainland Tanzania, and people using natural freshwater) were identified. The community knowledge about schistosomiasis transmission and prevention was poor. Few of the collected intermediate host snails shed S. haematobium cercariae. A multi-arm randomized trial is now being implemented to determine the differential impact of mass deworming, snail control, and behavior change interventions. Lessons learned from this schistosomiasis elimination program will be important for other settings.