Flaviviruses of the Japanese Encephalitis complex such as West Nile (WNV) and Usutu (USUV) viruses are emerging as causes of viral meningoencephalitis cases in animals and humans in Spain. Wild birds are natural reservoirs for WNV and USUV and, in liaison with competent mosquitoes, responsible for their maintenance and transmission. However, the intimate link between wild birds, domestic animals (horses), mosquitoes and humans in continental Spain is not yet well understood. With the goal of better understanding the ecology of flaviviruses at the wildlife-livestock-human interface, we captured birds in 2018/2019 in a decreasing wildlife-livestock interaction gradient in 5 horse farms. Birds were captured with mist nets at three sites per farm: (1) the farm; (2) a site 500-1,000m away from the farm; and (3) a site at a 3-5 km distance from the farm without livestock. We collected blood from the brachial vein, oral and cloacal swabs, and growing feathers from captured birds(N=580). The presence of Flavivirus antibodies in bird sera was estimated by a multispecies blocking ELISA that is highly specific for WNV, whereas a duplex quantitative real-time reverse transcription PCR allowed detecting Flavivirus infection. Twenty-eight of 451 sera were positive (6.2%) and the highest proportion of positives occurred in the farms (8.1%) in comparison to sites 2 and 3 (4.6% and 5.8%, respectively). Four of the 503 PCR tests (feathers/swabs) were positive (0.8%) but only one sample (Turdus merula) could be confirmed by sequencing as USUV (99.6% homology). PCR positive birds were only found in sites 1 and 2. These findings confirm the active circulation of flaviviruses in continental Spain and, especially, close to horse farms. The interaction with wild birds is high in the environment of the farms, so these results show that horses (and humans) are at risk of developing viral meningoencephalitis caused by WNV.

Resumen del póster presentado a la Joint Virtual Conference of the WDA and EWDA, celebrada del 31 de agosto al 2 de septiembre de 2021.

Peer reviewed