Modeling the risk of transmission of schistosomiasis in Akure North Local Government Area of Ondo State, Nigeria using satellite derived environmental data

Abstract

Schistosomiasis is a parasitic disease and its distribution, in space and time, can be influenced by environmental factors such as rivers, elevation, slope, land surface temperature, land use/cover and rainfall. The aim of this study is to identify the areas with suitable conditions for schistosomiasis transmission on the basis of physical and environmental factors derived from satellite imagery and spatial analysis for Akure North Local Government Area (LGA) of Ondo State. Nigeria. This was done through methodology multicriteria evaluation (MCE) using Saaty’s analytical hierarchy process (AHP). AHP is a multi-criteria decision method that uses hierarchical structures to represent a problem and makes decisions based on priority scales. In this research AHP was used to obtain the mapping weight or importance of each individual schistosomiasis risk factor. For the purpose of identifying areas of schistosomiasis risk, this study focused on temperature, drainage, elevation, rainfall, slope and land use/land cover as the factors controlling schistosomiasis incidence in the study area. It is by reclassifying and overlaying these factors that areas vulnerable to schistosomiasis were identified. The weighted overlay analysis was done after each factor was given the appropriate weight derived through the analytical hierarchical process. The prevalence of urinary schistosomiasis in the study area was also determined by parasitological analysis of urine samples collected through random sampling. The results showed varying risk of schistosomiasis with a larger portion of the area (82%) falling under the high and very high risk category. The study also showed that one community (Oba Ile) had the lowest risk of schistosomiasis while the risk increased in the four remaining communities (Iju, Igoba, Ita Ogbolu and Ogbese). The predictions made by the model correlated strongly with observations from field study. The high risk zones corresponded to known endemic communities. This study revealed that environmental factors can be used in identifying and predicting the transmission of schistosomiasis as well as effective monitoring of disease risk in newly established rural and agricultural communities.

Modelling local areas of exposure to Schistosoma japonicum in a limited survey data environment

“…The criterion used to assign the scale of judgement is the strength of the hypothetical link between the risk factors and exposure. The strength of the hypothetical link was evaluated based upon three studies that evaluated the risk factors associated with schistosomiasis infection [ 47 – 49 ].…”

“…Finally, Ajakaye et al . [ 49 ] evaluated physical and environmental risk factors to identify areas with suitable conditions for schistosomiasis transmission. They used Saaty’s comparison matrix to assign weights to each risk factor.…”

Schistosomiasis in Nigeria: Gleaning from the past to improve current efforts towards control

“…In 2013, a nationwide mapping and prediction of schistosomiasis in Nigeria was undertaken [ 42 ]. Others have been conducted in different states of the country [ 43 , 44 ]. Few studies have also identified schistosomiasis transmission foci by mapping out areas with abundance of freshwater snails that serve of intermediate hosts of schistosomes [ 45 , 46 ].…”

Statistical evaluation of spatial uncertainty in schistosomiasis mapping

“…The criterion used to assign the scale of judgement is the strength of the hypothetical link between the risk factors and exposure. The strength of the hypothetical link was evaluated based upon three studies that evaluated the risk factors associated with schistosomiasis infection (Ajakaye, Adedeji and Ajayi, 2017;Hu et al, 2017;).…”

“…As in the previous study, distance to water bodies was the most significant factor because of the smallest deviance, and elevation the least significant. Finally, Ajakaye et al (Ajakaye, Adedeji and Ajayi, 2017) evaluated physical and environmental risk factors to identify areas with suitable conditions for schistosomiasis transmission. They used Saaty's comparison matrix to assign weights to each risk factor.…”