Mapping survey of schistosomiasis and soil-transmitted helminthiases towards mass drug administration in The Gambia

Background A national mapping survey of schistosomiasis (SCH) and soil-transmitted helminthiases (STH) was conducted in The Gambia in May, 2015. The survey aimed at establishing endemicity of schistosomiasis and soil-transmitted helminthiases to inform decisions on program planning and implementation of mass drug administration (MDA). Methodology/Principal findings A cross-section of 10,434 eligible school aged children (SAC), aged 7 to 14 years old were enrolled in the survey. The participants were randomly sampled from 209 schools countrywide using N/50, where N = total eligible children per school. Stool, and urine samples were provided by each child and examined for schistosomiasis and soil-transmitted helminthic infections using double Kato-Katz, urine filtration, dipstick techniques and CCA rapid test kits. Data were managed using online LINKS system enabling real-time data availability and access. Epi Info version 3.5.3 and health mapper version 4.3.2 were used to generate outputs of endemicity and distribution. Descriptions of mapped districts for MDA eligibility and frequency were done with reference to WHO PC strategy recommendations. Mapping results indicated that nationally, the prevalence of schistosomiasis (SCH) and soil-transmitted helminthiases (STH) was 4.3% and 2.5% respectively. In terms of distribution STH are more common in Western Region One (WR1) at 4.1% prevalence, then Lower River Region (LRR) 3.6%, and Western Region Two (WR2) 3.0%. In contrast, SCH indicated much higher prevalence in Central River Region (CRR) at a rate of 14.2%. This is within medium prevalence range, and is followed by Upper River Region (URR) at 9.4%, which is within low prevalence range. At the district level, schistosomiasis prevalence seems to be highest in Niani district (22%) in CRR. Banjul island, the capital city, seems to have the highest prevalence of STH (up to 55%), followed by Kombo South with 22% prevalence. Schistosoma haematobium characterised by haematuria, was the most dominant infection of schistosomiasis discovered followed by Schistosoma mansoni which reported in 0.1% of infections. Out of 42 districts mapped 14, or 38%, of them are co-endemic for soil-transmitted helminthiases (ascariasis, trichuriasis, and hook-worm infections) and schistosomiasis (S. haematobium and S. mansoni). Conclusions We identified that 24/42(57%) districts mapped in The Gambia are endemic for schistosomiasis expressing the need for preventive chemotherapy. Twenty (47%) of the districts mapped are endemic for STH. However, only two STH endemic districts namely Banjul (55%) and Kombo South (22%) were within rates eligible for mass drug administration.
Author summary The Gambia joined the international community in the fight against neglected tropical diseases (NTDs), in order to enable control and eventual elimination by year 2020. This goal is in line with Africa regional targets for NTDs control and elimination. This decision was the driving force for a tabletop analysis of the existing NTD situation in the country, culminating in the development of a comprehensive five-year NTD Master plan 2015–2020, and an Annual Work Plan 2016. The World Health Organisation regional office for Africa’s Regional Program Review Group (WHO/AFRO RPRG) supported this work by granting approval for the mapping of schistosomiasis (SCH) and soil-transmitted helminthiases (STHs) across the country in May 2015. In this publication, we describe the purpose of the survey, how the survey was conducted, and how data and specimens were collected, handled, analyzed and interpreted. We have discovered that schistosomiasis exists in twenty-four districts in the country. Most of these districts are located in the eastern half of the country in Upper and Central River Regions. This means that communities in the affected districts require treatment to reduce the burden of disease. Treatment for schistosomiasis is unlike soil-transmitted helminthiases because all districts with schistosomiasis are eligible for treatment irrespective of the level of prevalence and endemicity according to the guidelines of the World Health Organisation (WHO). In comparison to STH, mass drug administration is not required for low STH endemic communities where the prevalence was less than 20%. Instead such communities will benefit from case by case treatment STH. Mass treatment will be required in district where STH prevalence was at least moderate or 20% and above. Soil-transmitted helminthiases were found in twenty districts. However, it is important to highlight that only two of these districts, with prevalence of 22% and 55%, respectively were eligible for mass drug administration in accordance with WHO guidelines. The guidelines recommend that districts with a prevalence of soil-transmitted helminthiases of less than 20% do not require mass community treatment in order to achieve disease elimination.