Ticks on the run: A mathematical model of Crimean-Congo Haemorrhagic Fever (CCHF)-key factors for transmission

TL;DR

This paper presents a mathematical model of Crimean-Congo Haemorrhagic Fever transmission, highlighting key factors like tick survival and transmission stages, to inform control strategies amid changing climate and vector invasion risks.

Contribution

The study develops a nonlinear ODE model incorporating tick, livestock, and human interactions, with sensitivity analysis and empirical calibration across countries to identify effective disease control measures.

Findings

Decreasing tick survival time can effectively eradicate CCHF.

Tick co-feeding and transstadial/transovarial transmission sustain the disease cycle.

Different countries exhibit distinct parameter sets influencing disease spread.

Abstract

Crimean-Congo haemorrhagic fever (CCHF) is a tick-borne zoonotic disease caused by the Crimean-Congo hemorrhagic fever virus (CCHFV). Ticks belonging to the genus \textit{Hyalomma} are the main vectors and reservoir for the virus. It is maintained in nature in an endemic vertebrate-tick-vertebrate cycle. CCHFV is prevalent in wide geographical areas including Asia, Africa, South-Eastern Europe and the Middle East. Over the last decade, several outbreaks of CCHFV have been observed in Europe, mainly in Mediterranean countries. Due to the high case/fatality ratio of CCHFV in human sometimes, it is of great importance for public health. Climate change and the invasion of CCHFV vectors in Central Europe suggest that the establishment of the transmission in Central Europe may be possible in future. We developed a compartment-based nonlinear Ordinary Differential Equation (ODE) system to model the disease transmission cycle including blood sucking ticks, livestock and human. Sensitivity analysis of the basic reproduction number $R_0$ shows that decreasing in the tick survival time is an efficient method to eradicate the disease. The model supports us in understanding the influence of different model parameters on the spread of CCHFV. Tick to tick transmission through co-feeding and the CCHFV circulation through trasstadial and transovarial stages are important factors to sustain the disease cycle. The proposed model dynamics are calibrated through an empirical multi-country analysis and multidimensional scaling reveals the disease-parameter sets of different countries burdened with CCHF are different. This necessary information may help us to select most efficient control strategies.