Changing patterns of soil-transmitted helminthiases in Zanzibar in the context of national helminth control programs

Helminth control programs have been implemented in Zanzibar for over a decade. In June/July 2007, approximately 6 months after the last school-based anthelmintic treatment, a cross-sectional survey was carried out in two schools, and results were compared with data obtained in the same schools in 1994. Multiple stool samples collected from 368 school children were subjected to the Kato-Katz, Koga agar plate, and Baermann methods. The prevalence of Trichuris trichiura, hookworm, Ascaris lumbricoides, and Strongyloides stercoralis was 46.6%, 21.6%, 16.9%, and 10.2%, respectively. Infection intensities were generally low. Compared with 1994, the prevalence of S. stercoralis, hookworm, A. lumbricoides, and T. trichiura decreased by 81.0%, 80.5%, 70.6%, and 48.6%, respectively. Infection intensities decreased by > 95% for all helminth species studied. Our study confirms that preventive chemotherapy successfully reduces the level and intensity of helminth infections. To consolidate achievements made, additional control measures such as health education and environmental sanitation are needed.