Monitoring for the possible introduction of Crimean-Congo haemorrhagic fever virus in Italy based on tick sampling on migratory birds and serological survey of sheep flocks

Crimean-Congo haemorrhagic fever (CCHF), endemic in Africa, Asia, Eastern Europe and the Middle East, is caused by a tibovirus (CCHFV) transmitted in particular by the Hyalomma genus of the Ixodidae family that can remain attached to the host for up to 26 days, which in case of migratory birds allows long distance carriage. Although CCHF in domestic ruminants is usually subclinical, they may become reservoirs and act as sentinels for the introduction and/or circulation of CCHFV. In this study, possible CCHFV introduction and circulation in Italy were monitored by tick sampling on migratory birds and by a serosurvey conducted on sheep. While bird tick sampling was conducted in thirteen ringing sites of Central and Southern Italy, the serosurvey was performed on flocks grazing in coastal provinces of Central Italy that are stop over areas for birds flying from Africa, where Hyalomma ticks and CCHFV are endemic, to Central and Northern Europe. A total of 282 ticks (80.8% were Hyalomma spp.) were collected from 139 (0.28%) migratory birds of the 50,325 birds checked with 0.22% infested by Hyalomma spp., involving 22 avian species with a mean number of 1.6 Hyalomma spp. per infested bird. For the serosurvey, 540 sheep sera were randomly collected that resulted all negative when examined by an indirect IgG ELISA, employing a recombinant antigen coded by the CCHFV S gene. While the present study confirmed the introduction of CCHFV potential vectors in Central Italy, transported by migratory birds arriving from endemic areas, the serosurvey results did not put in evidence the concomitant arrival of the virus in the study area during the survey period. In general, in areas potentially at risk of CCHFV introduction and circulation, structured serological monitoring of susceptible domestic animals represents a rational system for an early detection of virus circulation.