Unraveling the Ecological Complexities of Tick-Associated Crimean-Congo Hemorrhagic Fever Virus Transmission: A Gap Analysis for the Western Palearctic

Abstract

This review aims to summarize the current knowledge of the eco-epidemiology of Crimean-Congo hemorrhagic fever (CCHF) virus transmission reviewing the most recent scientific advances in the last few decades of epidemic and non-epidemic ("silent") periods. We explicitly aim to highlight the dynamics of transmission that are still largely unknown. Recent knowledge gathered from research in Africa and Europe explains the very focal nature of the virus, and indicates that research on the ecology of the virus in the inter-epidemic periods of the disease has not yet been addressed. Hyalomma spp. ticks have been incriminated in the transmission of the virus under field conditions, but the role of other ticks found infected in nature remains to be tested under experimental conditions. Published evidence suggests that the increase in human cases reported in the Balkans, Turkey, and Russia is perhaps less due to the effect of changes in climate, but rather result from the impact of yet unexplored mechanisms of amplification that might be supported by wild animal hosts. Assessment of the available data suggests that epidemics in Eastern Europe are not the result of a spreading viral wave, but more likely are due to a combination of factors, such as habitat abandonment, landscape fragmentation, and proliferation of wildlife hosts that have exacerbated prevalence rates in tick vectors. There is an urgent need to empirically demonstrate these assumptions as well as the role of birds in introducing infected ticks, and also to evaluate the potential for survival of introduced ticks. Either a replacement of the pathogenic virus in the western Mediterranean or a lack of westward dissemination of infected tick populations may explain the absence of the virus in Western Europe.

Crimean-Congo hemorrhagic fever: History, epidemiology, pathogenesis, clinical syndrome and genetic diversity

“…The geographic distribution of each CCHFV-competent tick vector is therefore defined by the range of its vertebrate hosts and the environmental conditions required for it to reach adulthood. At any given location, the vector's population density will change from year to year, depending on the availability of vertebrate hosts, weather conditions, changes in vegetation and other factors that affect the success of molting and egg production (Estrada-Pena et al, 2012b).…”

Molecular and Serological Detection of Crimean-Congo Hemorrhagic Fever Virus in Sulaimani Province, Iraq

“…This is of special interest because the main tick vector Hyalomma marginatum is abundant in places like Spain and Southern Italy, as well as in Mediterranean and African countries where neither the disease nor the virus have been reported [25]. Thirty-six years ago, CCHF was endemic in the study area where clinical cases were reported, but since 1997 there have been no reports of human infection cases of the disease in Sulaimani province according to data from the directorate of health and protection in Sulaimani province.…”

Risk of vector‐borne diseases for the EU: Entomological aspects – Part 1

“…Livestock are at particularly high risk of importing Hyalomma marginatum adults as they can support large infestations. It is not uncommon for up to 100 Hyalomma adult ticks to be found on one animal (Estrada-Pena, Jameson et al 2012). With potential infection rates between 2 and 15%, importation of the virus via this route should be taken into consideration.…”