Bayesian Geostatistical Model-Based Estimates of Soil-Transmitted Helminth Infection in Nigeria, Including Annual Deworming Requirements

Abstract

BackgroundThe acceleration of the control of soil-transmitted helminth (STH) infections in Nigeria, emphasizing preventive chemotherapy, has become imperative in light of the global fight against neglected tropical diseases. Predictive risk maps are an important tool to guide and support control activities.MethodologySTH infection prevalence data were obtained from surveys carried out in 2011 using standard protocols. Data were geo-referenced and collated in a nationwide, geographic information system database. Bayesian geostatistical models with remotely sensed environmental covariates and variable selection procedures were utilized to predict the spatial distribution of STH infections in Nigeria.Principal FindingsWe found that hookworm, Ascaris lumbricoides, and Trichuris trichiura infections are endemic in 482 (86.8%), 305 (55.0%), and 55 (9.9%) locations, respectively. Hookworm and A. lumbricoides infection co-exist in 16 states, while the three species are co-endemic in 12 states. Overall, STHs are endemic in 20 of the 36 states of Nigeria, including the Federal Capital Territory of Abuja. The observed prevalence at endemic locations ranged from 1.7% to 51.7% for hookworm, from 1.6% to 77.8% for A. lumbricoides, and from 1.0% to 25.5% for T. trichiura. Model-based predictions ranged from 0.7% to 51.0% for hookworm, from 0.1% to 82.6% for A. lumbricoides, and from 0.0% to 18.5% for T. trichiura. Our models suggest that day land surface temperature and dense vegetation are important predictors of the spatial distribution of STH infection in Nigeria. In 2011, a total of 5.7 million (13.8%) school-aged children were predicted to be infected with STHs in Nigeria. Mass treatment at the local government area level for annual or bi-annual treatment of the school-aged population in Nigeria in 2011, based on World Health Organization prevalence thresholds, were estimated at 10.2 million tablets.Conclusions/SignificanceThe predictive risk maps and estimated deworming needs presented here will be helpful for escalating the control and spatial targeting of interventions against STH infections in Nigeria.

Trichuris trichiura infection and its relation to environmental factors in Mbeya region, Tanzania: A cross-sectional, population-based study

“…trichiura infection prevalence with increasing elevation was also found by other authors [30–33]. This effect is likely due to decreasing temperature at higher altitudes, which might negatively affect the development of T .…”

“…trichiura infections are transmitted by ingesting eggs, which develop in the soil [28], the finding of a positive association of A . lumbricoides infection with denser vegetation [29, 30] might also apply for T . trichiura .…”

“…trichiura infection is higher close to water bodies [30–32, 34]. This could be related to low altitude, moderated temperatures and high soil moisture near water.…”

A review of soil transmitted helminthiasis in Nigeria

“…In some cases, geographic information systems have been applied in order to gather supporting data for risk mapping and predictive studies [8]. However, molecular techniques in relation to identification and prevalence studies of species of STH are yet to be applied in epidemiological surveys in Nigeria.…”

Helminthiasis and chronic suppurative otitis media in Ijoun Community in Ogun State, Nigeria

“…Briefly, a prevalence of 16.8% obtained from estimated prevalence of soil transmitted helminths in Ogun State was used (Oluwole et al, 2015). Using a precision of 5% (0.05), a minimum sample size of 215 subjects was computed.…”