Tests indicate that West Nile virus and Usutu virus circulate widely among birds and horses in Catalonia, northeastern Spain.

The tick-borne encephalitis virus has also been detected sporadically in horses, Sebastian Napp and his fellow researchers reported in the journal. Virus.

Their study looked at the incidence of flaviviruses in horses and birds in the region between 2010 and 2019.

Flaviviruses include important pathogens capable of infecting humans, such as dengue virus, yellow fever virus, West Nile virus, tick-borne encephalitis virus, and encephalitis virus Japanese.

Like West Nile virus, other viruses of the genus, such as Usutu virus and Bagaza virus, can cause serious illness in animals. They are transmitted to susceptible animals by mosquitoes or ticks which feed on blood.

In recent years, areas of Europe reporting flavivirus infections, especially those caused by West Nile virus, Usutu virus or tick-borne encephalitis virus, have increased significantly, the authors noted.

“Many of these viruses are currently endemic in several parts of the continent. “

Of the 3,791 serum samples taken from birds in Catalonia between 2010 and 2019, 380, or 10 percent, were positive for a flavivirus.

Of these, there was sufficient serum in 205 cases for a more precise analysis. A total of 118 showed specific antibodies for West Nile virus, 19 for Usutu virus and 68 were classified as undetermined flavivirus. None have been classified as Bagaza virus.

Of the 1,856 serum samples taken from horses during the same period, 182, or 9.8 percent, tested positive. Of these, 164 had enough serum for further testing. Ninety-two were found positive for West Nile virus, 11 were found for Usutu, four were found for tick-borne encephalitis virus and 57 were classified as infected with an unknown flavivirus.

The authors said there may have been some bias in selecting animals for the study. In the case of birds, some species were over-represented either because they were useful for West Nile monitoring (such as chickens or magpies), or were found in wildlife recovery centers (such as raptors) , or because samples were routinely collected as part of other surveillance activities. programs.

In horses, sample distribution may have been influenced by proximity to the Equine Veterinary Hospital. Finally, some regions, mainly areas where West Nile traffic was detected, were also over-represented due to specific inventories implemented there.

The researchers noted that a third of the samples tested were inconclusive by the microneutralization test in terms of identifying the specific virus, highlighting the limitations of current diagnostic techniques.

“Our results highlighted the widespread circulation of flaviviruses, in particular West Nile virus, but also Usutu virus, and suggest that chickens and horses could serve as sentinels for both viruses,” they said.

They noted that so far no human infection with West Nile, Usutu or tick-borne encephalitis viruses has been reported in Catalonia.

“However, given that these viruses have been circulating for some time in different regions of Catalonia, this means that they need to be monitored, and the most effective way to do this is in the context of one health.

“This includes educating physicians (clinicians) to take these infections into account in the differential diagnosis of patients with compatible clinical symptoms. “

Considering the wide distribution of West Nile virus and Usutu virus in Catalonia, microneutralization tests for both viruses should be included as a routine technique for the correct diagnosis of flavivirus infections. “Failure to do so results in both under-detection and misclassification,” they said.

“In view of the sporadic detection of tick-borne encephalitis virus, further studies on the risk of introduction and establishment would be needed. “

Napp, S .; Llorente, F .; Beck, C .; José-Cunilleras, E .; Soler, M .; Pailler-García, L .; Amaral, R .; Aguilera-Sepúlveda, P.; Pifarré, M.; Molina-Lopez, R .; Obon, E .; Nicolas, O.; Lecollinet, S .; Jiménez-Clavero, M.Á .; Busquets, N. Widespread circulation of flaviviruses in horses and birds in northeastern Spain (Catalonia) between 2010 and 2019. Viruses 2021, 13, 2404. https://doi.org/10.3390/v13122404

The study, published under a Creative Commons License, can be read here.