Horses and Donkeys Used as Sentinal Animals for Crimean-Congo Hemorrhagic Fever in Europe

As part of a “One Health” approach, to track the circulation of the Crimean-Congo hemorrhagic fever virus in Southeast and Central Europe, a study analyzed blood samples from horses and donkeys in Bulgaria (579 equines), in Romania (1,534), and in the Czech Republic (576) using the ELISA method to detect any specific antibodies. This virus, which is transmitted primarily through the bite of ticks of the genus Hyalomma, can cause severe hemorrhagic fever in humans, with a case fatality rate ranging from 10 to 40%. The likelihood of detecting Hyalomma ticks is higher in horses because they receive daily care and are in close proximity to humans, and these ticks are easily identifiable by their morphology, even in photographs. Consequently, numerous reports of these ticks have been documented in horses across Central, Western, and Northern Europe, particularly in the Czech Republic, Austria, Hungary, Poland, the Netherlands, the United Kingdom, Sweden, and Norway. Despite growing concerns about the spread of this fever in Europe, seroepidemiological data on equine exposure to the virus remain limited. No serological survey has been conducted, which constitutes a gap in surveillance and prevents early warning. The objective of this study was to determine the seroprevalence of antibodies against this virus in the 2,689 serum samples analyzed, in order to assess its potential spread from Southeast Europe to Central Europe using equines as sentinel animals.  

A marked variation in seroprevalence

The study reports a marked variation in seroprevalence from the southeast to the northwest: specific antibodies were detected in donkeys and horses in Bulgaria, with an overall seroprevalence of 14.5%. In Romania, 23 of the 1,534 equine serum samples tested were seropositive, representing an overall seroprevalence of 1.5%. In the Czech Republic, serological screening of 576 horses showed no antibodies, resulting in a seroprevalence of 0%. These results correlate with regional environmental conditions and vector distribution and indicate a northward expansion of Hyalomma ticks. This also suggests that climate change and land use are creating conditions conducive to the circulation of the Crimean-Congo hemorrhagic fever virus in regions previously considered low-risk.  

What is happening in Europe is already evident elsewhere

This study represents the largest serological survey of the Crimean-Congo hemorrhagic fever virus conducted in equines in the region and provides essential baseline data for anticipating the future spread of this virus in non-endemic areas. Developments in Europe reflect similar ecological changes observed elsewhere, particularly in certain regions of North America, underscoring the importance of global surveillance and preparedness for the disease. As the range of vectors expands, the United States and other non-endemic countries will need to assess their own risks of animal and human exposure and invest in proactive strategies based on the “One Health” approach.  

An Environment Conducive to Ticks

Climate change, environmental degradation, and globalization have led to the proliferation of many vectors and a reduction in transmission barriers, increasing the risk of vector-borne diseases in previously free areas. The introduction and establishment of Hyalomma ticks in non-endemic regions of Europe—likely facilitated by migratory birds and climate-induced environmental changes—demonstrate the need for robust surveillance systems and integrated monitoring strategies. This study can serve as a model for non-endemic regions to proactively combat new vector-borne threats by using equine sentinels as early indicators of viral circulation, as part of a cross-border “One Health” approach… before human cases emerge.