Spatial analysis and risk mapping of Crimean-Congo hemorrhagic fever in sub-Saharan Africa

Crimean-Congo hemorrhagic fever (CCHF) is a re-emerging tick-borne zoonosis that is caused by the CCHF virus.

The geographical distribution of the disease and factors that influence its occurrence are poorly known.

Researchers from the International Livestock Research Institute (ILRI) and Freie Universität Berlin analyzed historical records on its outbreaks in various countries across sub-Saharan Africa (SSA) to identify hotspots and determine socioecological and demographic factors associated with these outbreaks.

Their findings are published in Scientific Reports (Jan 2025).

They used data from historical outbreaks that were reported between 1981 and 2022 in various countries in SSA.

To develop a common framework for merging the outbreak data and potential explanatory variables, they generated a common shapefile that combined Level 2 administrative units in all the countries.

Several climatic, environmental, socioecological data were obtained from on-line GIS databases and extracted using the shapefile.

The data were analyzed using an approximate Bayesian hierarchical model using the R-INLA package.

The outcome was a Boolean variable which indicated whether an administrative unit in the shapefile was affected in a given year or not.

A neighborhood structure was also generated and used to account for spatial autocorrelation in the analysis.

The final model that was obtained from the analysis was used to build a CCHF risk map.

Disease outbreaks

A total of 54 CCHF outbreaks were compiled across 414 districts in nine SSA countries.

Factors that were positively associated with CCHF outbreaks included human population density, land area under grassland, bare soil cover and shrub cover.

Conversely, high precipitation during wet months, elevated mean temperature and slope had negative effects.

The risk map generated shows that CCHF occurrence risk is higher in arid and semi-arid lands of West Africa, the Sahelian region, Central Africa, and the Eastern and Southern Africa region.

The analysis identified ecological and demographic factors that are associated with CCHF outbreaks in SSA.

This finding suggests the need to improve surveillance for the disease, especially in the grasslands where the human population is increasing.

Citation
Ilboudo, A.K., Oloo, S.O., Sircely, J., Nijhof, A.M. and Bett, B. 2025. Spatial analysis and risk mapping of Crimean-Congo hemorrhagic fever (CCHF) in sub-Saharan Africa. Scientific Reports 15: 2292.

Photo: Tick research in ILRI’s biotechnology labs in Nairobi, Kenya (ILRI/David White)