Modeling the Spatial Distribution of Crimean-Congo Hemorrhagic Fever Outbreaks in Turkey

Abstract

The more than 1100 human cases of Crimean-Congo Hemorrhagic Fever (CCHF) reported in a continuing series of outbreaks that started in 2003 in Turkey constitute the largest epidemic of the disease since CCHF was first recognized in 1944. The spatial distribution of CCHF case reporting rates in Turkey was studied to look for clusters of disease. We applied the spatial scan analysis to test the hypothesis of whether there were areas with a higher than expected number of CCHF cases. The analysis was conducted through windows of 10, 20, 40 and 80 km in diameter[SR1] to determine whether clustering of cases was dependent on the size of the scanning window. At the largest window size, consistent patterns of significantly higher than expected numbers of CCHF cases were found in a total of 40 administrative districts. A predictive model to map the habitat suitability for the vector tick was developed from satellite-based climate data and high-resolution features of the vegetation from Landsat images covering the whole country. It was found that areas of higher risk (higher CCHF reporting) were correlated (p<0.05) with zones of high climate suitability for the tick together with a high rate of fragmentation of agricultural land interspersed between forest and shrub-type vegetation.

Species distribution and detection of Crimean Congo Hemorrhagic Fever Virus (CCHFV) in field-collected ticks in Ankara Province, Central Anatolia, Turkey

“…Since CCHFV activity in Turkey appear not to be limited to recurring foci, but has been expanding into new areas as well, data on tick densities and tick infection rates is crucial for the identification of high risk areas (Estrada-Pena et al 2007). Although there are indications that H. m. marginatum has outnumbered other tick species in the main recurrent foci of the current CCHF outbreaks, a systematic comparison between areas with and without the disease has not been carried out (Estrada-Pena et al 2007).…”

Trends in tick population dynamics and pathogen transmission in emerging tick-borne pathogens in Europe: an introduction

“…Examples of techniques and toolboxes are logistic regression, random forest, non-linear discriminant analysis, MaxEnt, and (boosted) regression trees. These modelling techniques have been applied to numerous tick-borne disease systems, such as TBE (Daniel et al 1998;, CCHFV (Estrada-Peña et al 2007), and Lyme borreliosis (Brownstein et al 2005;Swart et al 2014). A recent modelling attempt yielded a map of the global distribution of CCHFV (Messina et al 2015).…”

Ticks biting humans in the urban area of Istanbul

“…Only records for I. ricinus and H. aegyptium were used because they accounted for more than 75% of samples. We used already described protocols for the identification of clusters of high tick reporting as well as climate and vegetation variables defining such a clustering of reports (Estrada-Peña et al 2007). Observed clusters of reports for these two species are independent of the human population density (p<0.001).…”