CIENCIASMEDICASNEWS: Ahead of Print - Survey of Crimean-Congo Hemorrhagic Fever Enzootic Focus, Spain, 2011–2015 - Volume 25, Number 6—June 2019 - Emerging Infectious Diseases journal

During 2011–2015, we conducted a Crimean-Congo hemorrhagic fever virus (CCHFV) survey in captured ticks that were feeding mainly on wild and domestic ungulates in Spain, where presence of this virus had been reported previously. We detected CCHFV RNA in Hyaloma lusitanicum and H. marginatumticks for 3 of the 5 years. The rate of infected ticks was 2.78% (44/1,579), which was similar to those for other countries in Europe with endemic foci for CCHFV (Kosovo, Bulgaria, and Albania). These data confirm the established spread of CCHFV into western Europe. Phylogenetic study of the small RNA segment showed Africa-3 clade as the only genotype identified, although we observed cocirculation of genetic variants during 2011 and 2015. We could not rule out genetic reassortments because of lack of sequence data for the medium and large RNA segments of the virus genome.

Crimean-Congo hemorrhagic fever virus (CCHFV), an RNA virus of the family Nairoviridae, is the most widespread tickborne virus affecting humans. It causes Crimean-Congo hemorrhagic fever (CCHF), which has a high mortality rate in humans (1) in many countries in Asia, the Middle East, eastern Asia, Africa, and Europe (2,3). Recently, CCHF has been detected in Spain, indicating its spread into western Europe (4,5).

CCHF is a zoonosis maintained between ticks and vertebrate animals. Ticks are both the vector and the natural reservoir of CCHFV. Ticks transmit CCHFV to large and small mammals, which act as amplifier hosts without signs of illness. Birds are predominantly refractory to CCHFV infection (6–8). The virus has been isolated from several genera and species of ixodid ticks (9). However, most data are for ticks collected while feeding, which provides an unrealistic view of the actual species vectors (10).

The main vectors involved in CCHFV transmission are ticks of the genus Hyalomma (11–14). Immature ticks acquire the virus by feeding on infected small vertebrates or by the transovarial route. Once infected, they remain infected throughout their development and, when they are mature, transmit the infection to large animals, such as livestock. Transovarian and venereal transmission pathways have also been demonstrated (2). Another transmission mechanism is cofeeding, which results from spreading of the virus in tick saliva directly to other ticks feeding nearby (13).

In disease-endemic areas, CCHF is sporadic and is transmitted to humans by tick bites or contact with viremic animals or humans and occurs mainly in remote or agricultural regions (15–21). CCHF is seasonal in association with the life cycle and activity levels of local tick populations. CCHF outbreaks and nosocomial transmission has also been reported most often when an infectious case is not suspected early enough to permit use of proper containment protocols (22). Persons at risk are most frequently found among farmers and their families, as well as slaughterhouse and healthcare workers, veterinarians, and military personnel (23).

Thumbnail of Study site locations in the Iberian Peninsula in which Crimean-Congo hemorrhagic fever virus was detected: Cáceres, Toledo, Segovia, and Huesca Provinces. Square shows presence of CCHFV in humans bitten by a tick bite, star shows presence of CCHFV in ticks with positive results by PCR, circle indicates region where serum samples positive for CCHFV were detected in Portugal, and white area show regions in 4 localities (Cáceres, Ávila, and Toledo Provinces and Madrid) in Spain where C

Figure 1. Study site locations in the Iberian Peninsula in which Crimean-Congo hemorrhagic fever virus was detected: Cáceres, Toledo, Segovia, and Huesca Provinces. Square shows presence of CCHFV in humans bitten by a...

Only 2 autochthonous human cases of CCHF have been reported in Spain in an episode with tick and nosocomial transmission. The cases occurred in 2016, and the viruses isolated from these patients were included in the Africa-3 clade (genotype III) (5,24), the same clade that was found in local ticks (4,25) and 1 of the 6/7 genetic clades in which CCHFV strains are grouped on the basis of small (S) RNA segment sequence homology (26,27). Previously, the CCHFV genome was detected in ticks collected in 2010 from red deer in Cáceres, Spain (4), which is 300 km from the area (Ávila Province) where the index case-patient acquired the disease through tick bite transmission. After autochthonous human cases were detected, a surveillance study on ticks was conducted to investigate the spread of CCHFV in Spain. Results showed 4 geographic regions with CCHFV-positive results (Figure 1) and the presence of CCHFV in 128 (3.2%) of 3,959 pools of ticks collected from wild and domestic animals (28). All CCHFV-positive ticks were collected while they were feeding on wild animals.

These data highlighted the emerging threat for CCHF in Spain and potentially all of western Europe. A new case of CCHF also linked to tick bite transmission occurred in August 2018 in Spain. A study of the presence of CCHFV in Spain was initiated in 2011 to analyze principally its circulation in the region of original detection. We report the results of a survey covering 5 years of collection.