Veterinary session

West Nile virus (WNV) is a worldwide zoonotic arbovirus that circulates in nature between vector mosquitoes and birds as maintenance hosts. Accidental hosts are mammalian species, with horses and humans being particularly important. Although in most cases, the disease is subclinical, infection with neuroinvasive symptoms may occur, which can even lead to death. Due to the high importance of WNV for human and animal health, the virus activity in vector and reservoir species is being monitored in many countries. The surveillance aims to detect the emergence of a possible epidemic before human cases occur so that appropriate measures can be taken in time to protect the residents. This is particularly important because there is currently no specific treatment for the disease, and vaccines are only available for horses.

Previous research has found exceptionally high mortality in New World corvid populations due to WNV infection; therefore, they are widely monitored. Although the WNV-susceptibility of European corvids seems to be lower, in Italy, where many human and horse infections are reported yearly, corvids are used in a complex active and passive surveillance system.

This thesis aims to monitor corvids' role in the epidemiology of West Nile fever in Hungary. In addition, we studied whether the same rate of mass mortality of crows as seen during previous WNV epidemics in the United States of America could be observed in our country.

The samples received were analysed using real-time reverse transcription (RT) PCR and ELISA. In 2022, 8 hooded crows (Corvus cornix) were found dead and examined within passive surveillance, and they tested positive. Four serological samples of the 50 birds tested in Debrecen within the active surveillance were WNV positive, corresponding to a seroprevalence of 8%. Despite detecting WNV in mosquitoes collected in the same area, the virus detection conducted simultaneously based on captured and euthanised corvids ended with negative results and did not predict an outbreak.

Therefore, it can be concluded that in our country, hooded crows are more likely to contribute to the passive monitoring of WNV activity. These findings are crucial for understanding the disease's dynamics. Furthermore, given the significant number of positive samples of magpies (Pica pica) detected in Italy, there is potential for this species to be used in active monitoring as well, offering hope for enhanced surveillance strategies in the future.