Napp et al.
Widespread circulation of flaviviruses in horses and birds in northeastern Spain (Catalonia) between 2010 and 2019.
Viruses. 2021; 13(12):2404. doi:10.3390/v13122404
In recent years, the areas in Europe reporting flavivirus infections and specifically West Nile virus (WNV), Usutu virus (USUV) and TBE virus has significantly increased.
In 2018, Europe experienced the largest number of WNV infections to date with more than 2000 human cases, and in Spain, the 2020 season resulted in an unprecedented increase in the number of human cases with 77 cases reported. Austria was the first European country where USUV was detected (in 2001). In 2006, this virus was detected in Spain, in mosquitoes in a wetland near Barcelona. Although most USUV infections occur in birds, a total of 46 human cases have been recorded in Europe up to 2019 (most, however, were asymptomatic infections detected in blood donors). Another flavivirus, Bagaza virus (BAGV) was detected in birds in Catalonia in chickens by serology in 2018.
To better understand flavivirus circulation in Catalonia, serum samples from birds and horses were analyzed by a pan-flavivirus competition ELISA and by a microneutralization assay against different flaviviruses. Samples from horses were tested for antibodies specific for WNV, USUV and BAGV and also for TBE virus.
The results show a widespread circulation of flaviviruses in Catalonia, especially WNV and USUV, while BAGV could not be detected.
TBE antibodies (microneutralization titers) were detected in four horses. Further investigations revealed that all animals had stayed at some point outside Catalonia (e.g., in Germany and Switzerland [Sebastian Napp, personal communication]), and thus the possibility of imported infections could not be ruled out. It should be noted here that TBE antibodies have previously been detected in dogs from western and southern Spain and in a horse from the island of Mallorca. Thus, further investigations are warranted to analyze if TBE virus is endemic in Spain.