Absence of IgG antibodies among high-risk contacts of two confirmed cases of Crimean-Congo haemorrhagic fever in the autonomous region of Madrid (Spain)

Changes in the epidemiology of Crimean-Congo hemorrhagic fever: Impact of travel and a One Health approach in the European region

BACKGROUND

The World Health Organization has identified Crimean-Congo hemorrhagic fever (CCHF) as a priority disease for research and development in emergency contexts. The epidemiology of CCHF is evolving and this review highlights travel-associated cases and focuses on the need for a One Health approach in Europe.

METHODS

For this narrative review, two searches were performed in PubMed and Google Scholar for the period 1980-October 2024. The first search identified travel-associated CCHF cases globally, additional cases were identified in the ProMED mail database and through healthmap.org. The second search, with a focus on the European region, aimed to analyse reports of CCHF virus (CCHFV) detected in ticks, CCHF seroprevalence studies in animals and/or humans, and autochthonous CCHF cases.

RESULTS

Seventeen cases of imported CCHF, the majority acquired in Africa, were identified. Importation to European countries accounted for eight of the cases. Most patients presented with fever and hemorrhagic manifestations and the estimated case fatality rate was 35 %. In the WHO European region, at least 13 countries have reported ticks infected with different genotypes of CCHFV; 17 countries were found to have animals/humans with positive CCHF serology. Finally, 16 countries in the WHO European region have notified human cases of CCHF. The Russian Federation, Turkey, and several former USSR countries are considered highly endemic, followed by the Balkanic region, with sporadic cases emerging in Bulgaria, Greece, Spain, and recently Portugal.

CONCLUSIONS

Travel-associated CCHF is infrequent. However, given the recently reported increased geographical distribution in ticks and animals in the European region, additional human cases may be anticipated in the near future. Europe receives over half of all international tourist arrivals annually, so healthcare professionals should be aware of risk factors and current protocols for the management of suspected and confirmed cases.

Epidemiological Aspects of Crimean-Congo Hemorrhagic Fever in Western Europe: What about the Future?

Crimean-Congo hemorrhagic fever virus (CCHFV) is an arthropod-borne virus (arbovirus), mainly transmitted by ticks, belonging to the genus Orthonairovirus (family Nairoviridae, order Bunyavirales). CCHFV causes a potentially severe, or even fatal, human disease, and it is widely distributed in Africa, Asia, eastern Europe and, more recently, in South-western Europe. Until a few years ago, no cases of Crimean-Congo hemorrhagic fever (CCHF) had been reported in western Europe, with the exception of several travel-associated cases. In 2010, the CCHFV was reported for the first time in South-western Europe when viral RNA was obtained from Hyalomma lusitanicum ticks collected from deer in Cáceres (Spain). Migratory birds from Africa harboring CCHFV-infected ticks and flying to Spain appear to have contributed to the establishment of the virus (genotype III, Africa-3) in this country. In addition, the recent findings in a patient and in ticks from deer and wild boar of viral sequences similar to those from eastern Europe (genotype V, Europe-1), raise the possibility of the introduction of CCHFV into Spain through the animal trade, although the arrival by bird routes cannot be ruled out (Africa-4 has been also recently detected). The seropositive rates of animals detected in regions of South-western Spain suggest an established cycle of tick-host-tick in certain areas, and the segment reassortment detected in the sequenced virus from one patient evidences a high ability to adaptation of the virus. Different ixodid tick genera can be vectors and reservoirs of the virus, although Hyalomma spp. are particularly relevant for its maintenance. This tick genus is common in Mediterranean region but it is currently spreading to new areas, partly due to the climate change and movement of livestock or wild animals. Although to a lesser extent, travels with our pets (and their ticks) may be also a factor to be considered. As a consequence, the virus is expanding from the Balkan region to Central Europe and, more recently, to Western Europe where different genotypes are circulating. Thus, seven human cases confirmed by molecular methods have been reported in Spain from 2016 to August 2020, three of them with a fatal outcome. A One Health approach is essential for the surveillance of fauna and vector populations to assess the risk for humans and animals. We discuss the risk of CCHFV causing epidemic outbreaks in Western Europe.