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.

Figure 1. Flowchart detailing study participation in the schools surveyed in Unguja (A) and Pemba (B) in January till March, 2012.

Figure 2. S. haematobium prevalence in adults in 45 study shehias in Unguja (A) and Pemba (B).

Map indicating the S. haematobium prevalence in the adult population of the 45 study shehias in Unguja (A) and Pemba (B) at the baseline survey conducted in November/December 2011, surveyed schools in all 45 study shehias per island and sites in the 15 snail control shehias per island, where Bulinus spp. snails were found. Shehias in Unguja and their assigned intervention: Biannual mass drug administration with praziquantel: 1 = Cheju, 2 = Donge Mnyimbi, 3 = Fuoni Kibondeni, 4 = Gamba, 5 = Kama, 6 = Kiboje Mkwajuni, 7 = Kitope, 8 = Mbuzini, 9 = Mchangani, 10 = Mfenesini, 11 = Mkwajuni, 12 = Muungano, 13 = Mwakaje, 14 = Mwanyanya, 15 = Ubago; biannual mass drug administration with praziquantel plus snail control: 16 = Bandamaji, 17 = Chuini, 18 = Donge Mchangani, 19 = Fujoni, 20 = Jendele, 21 = Jumbi, 22 = Kandwi, 23 = Kianga, 24 = Kilimahewa Juu, 25 = Kinyasini, 26 = Mafufuni, 27 = Miwani, 28 = Mtopepo, 29 = Nyerere, 30 = Welezo; biannual mass drug administration with praziquantel plus behaviour change interventions: 31 = Chaani Kubwa, 32 = Dole, 33 = Donge Mtambile, 34 = Kilombero, 35 = Koani, 36 = Mahonda, 37 = Melinne, 38 = Mgambo, 39 = Mtoni, 40 = Mwanakwerekwe, 41 = Mwera, 42 = Pale, 43 = Sebleni, 44 = Upenja, 45 = Uzini. Shehias in Pemba and their assigned intervention: Biannual mass drug administration with praziquantel: 1 = Chanjaani, 2 = Kangani, 3 = Kiwani, 4 = Konde, 5 = Matale, 6 = Ole, 7 = Pandani, 8 = Selemu, 9 = Tibirinzi, 10 = Tumbe, 11 = Ukutini, 12 = Uwandani, 13 = Wambaa, 14 = Wawi, 15 = Wesha; Biannual mass drug administration with praziquantel plus snail control: 16 = Finya,17 = Kangagani, 18 = Kinowe, 19 = Kisiwani, 20 = Kwale, 21 = Makangale, 22 = Makombeni, 23 = Mbuzini, 24 = Mgogoni, 25 = Mkanyageni, 26 = Msuka, 27 = Piki, 28 = Shumba Viamboni, 29 = Vitongoji, 30 = Ziwani; biannual mass drug administration with praziquantel plus behaviour change interventions: 31 = Chambani, 32 = Jadida, 33 = Kengeja, 34 = Kinyasini, 35 = Kizimbani, 36 = Mchangamdogo, 37 = Michenzani, 38 = Mtambile, 39 = Mtambwe Kusini, 40 = Ng'ambwa, 41 = Ng'ombeni, 42 = Ngwachani, 43 = Pujini, 44 = Shungi, 45 = Sizini.

Figure 3. S. haematobium prevalence in first-year school children in 45 study shehias in Unguja (A) and Pemba (B).

Map indicating the S. haematobium prevalence in first-year school children in the 45 study shehias in Unguja (A) and Pemba (B) at the baseline survey conducted in January-March 2012, surveyed schools in all 45 study shehias per island and sites in the 15 snail control shehias per island, where Bulinus spp. snails were found. Shehias in Unguja and their assigned intervention: Biannual mass drug administration with praziquantel: 1 = Cheju, 2 = Donge Mnyimbi, 3 = Fuoni Kibondeni, 4 = Gamba, 5 = Kama, 6 = Kiboje Mkwajuni, 7 = Kitope, 8 = Mbuzini, 9 = Mchangani, 10 = Mfenesini, 11 = Mkwajuni, 12 = Muungano, 13 = Mwakaje, 14 = Mwanyanya, 15 = Ubago; biannual mass drug administration with praziquantel plus snail control: 16 = Bandamaji, 17 = Chuini, 18 = Donge Mchangani, 19 = Fujoni, 20 = Jendele, 21 = Jumbi, 22 = Kandwi, 23 = Kianga, 24 = Kilimahewa Juu, 25 = Kinyasini, 26 = Mafufuni, 27 = Miwani, 28 = Mtopepo, 29 = Nyerere, 30 = Welezo; biannual mass drug administration with praziquantel plus behaviour change interventions: 31 = Chaani Kubwa, 32 = Dole, 33 = Donge Mtambile, 34 = Kilombero, 35 = Koani, 36 = Mahonda, 37 = Melinne, 38 = Mgambo, 39 = Mtoni, 40 = Mwanakwerekwe, 41 = Mwera, 42 = Pale, 43 = Sebleni, 44 = Upenja, 45 = Uzini. Shehias in Pemba and their assigned intervention: Biannual mass drug administration with praziquantel: 1 = Chanjaani, 2 = Kangani, 3 = Kiwani, 4 = Konde, 5 = Matale, 6 = Ole, 7 = Pandani, 8 = Selemu, 9 = Tibirinzi, 10 = Tumbe, 11 = Ukutini, 12 = Uwandani, 13 = Wambaa, 14 = Wawi, 15 = Wesha; Biannual mass drug administration with praziquantel plus snail control: 16 = Finya,17 = Kangagani, 18 = Kinowe, 19 = Kisiwani, 20 = Kwale, 21 = Makangale, 22 = Makombeni, 23 = Mbuzini, 24 = Mgogoni, 25 = Mkanyageni, 26 = Msuka, 27 = Piki, 28 = Shumba Viamboni, 29 = Vitongoji, 30 = Ziwani; biannual mass drug administration with praziquantel plus behaviour change interventions: 31 = Chambani, 32 = Jadida, 33 = Kengeja, 34 = Kinyasini, 35 = Kizimbani, 36 = Mchangamdogo, 37 = Michenzani, 38 = Mtambile, 39 = Mtambwe Kusini, 40 = Ng'ambwa, 41 = Ng'ombeni, 42 = Ngwachani, 43 = Pujini, 44 = Shungi, 45 = Sizini.

Figure 4. S. haematobium prevalence in 9–12-year-old school children in 45 study shehias in Unguja (A) and Pemba (B).

Map indicating the S. haematobium prevalence in 9- to 12-year school children in the 45 study shehias in Unguja (A) and Pemba (B) at the baseline survey conducted in January-March 2012, surveyed schools in all 45 study shehias per island and sites in the 15 snail control shehias per island, where Bulinus spp. snails were found. Shehias in Unguja and their assigned intervention: Biannual mass drug administration with praziquantel: 1 = Cheju, 2 = Donge Mnyimbi, 3 = Fuoni Kibondeni, 4 = Gamba, 5 = Kama, 6 = Kiboje Mkwajuni, 7 = Kitope, 8 = Mbuzini, 9 = Mchangani, 10 = Mfenesini, 11 = Mkwajuni, 12 = Muungano, 13 = Mwakaje, 14 = Mwanyanya, 15 = Ubago; biannual mass drug administration with praziquantel plus snail control: 16 = Bandamaji, 17 = Chuini, 18 = Donge Mchangani, 19 = Fujoni, 20 = Jendele, 21 = Jumbi, 22 = Kandwi, 23 = Kianga, 24 = Kilimahewa Juu, 25 = Kinyasini, 26 = Mafufuni, 27 = Miwani, 28 = Mtopepo, 29 = Nyerere, 30 = Welezo; biannual mass drug administration with praziquantel plus behaviour change interventions: 31 = Chaani Kubwa, 32 = Dole, 33 = Donge Mtambile, 34 = Kilombero, 35 = Koani, 36 = Mahonda, 37 = Melinne, 38 = Mgambo, 39 = Mtoni, 40 = Mwanakwerekwe, 41 = Mwera, 42 = Pale, 43 = Sebleni, 44 = Upenja, 45 = Uzini. Shehias in Pemba and their assigned intervention: Biannual mass drug administration with praziquantel: 1 = Chanjaani, 2 = Kangani, 3 = Kiwani, 4 = Konde, 5 = Matale, 6 = Ole, 7 = Pandani, 8 = Selemu, 9 = Tibirinzi, 10 = Tumbe, 11 = Ukutini, 12 = Uwandani, 13 = Wambaa, 14 = Wawi, 15 = Wesha; Biannual mass drug administration with praziquantel plus snail control: 16 = Finya,17 = Kangagani, 18 = Kinowe, 19 = Kisiwani, 20 = Kwale, 21 = Makangale, 22 = Makombeni, 23 = Mbuzini, 24 = Mgogoni, 25 = Mkanyageni, 26 = Msuka, 27 = Piki, 28 = Shumba Viamboni, 29 = Vitongoji, 30 = Ziwani; biannual mass drug administration with praziquantel plus behaviour change interventions: 31 = Chambani, 32 = Jadida, 33 = Kengeja, 34 = Kinyasini, 35 = Kizimbani, 36 = Mchangamdogo, 37 = Michenzani, 38 = Mtambile, 39 = Mtambwe Kusini, 40 = Ng'ambwa, 41 = Ng'ombeni, 42 = Ngwachani, 43 = Pujini, 44 = Shungi, 45 = Sizini.