Serological Evidence of Exposure to EBHSV and RHDV2 in Brown Hare (Lepus europaeus Pall. 1778) in Poland: Insights into Lagovirus-Host Interaction and Population Dynamics

The long-term decline in European hare populations across Europe is linked to both environmental and anthropogenic factors. Among the factors influencing the population dynamics of lagomorphs, lagoviruses play a significant role. This study evaluated population indices and the presence of antibodies against EBHSV and RHDV2 in hares in Poland. A total of 109 individuals were examined from five regions where population density allowed for game management. Population indices were assessed, and the presence of antibodies was determined using ELISA tests with monoclonal antibodies. Body mass of hare was similar across all regions but differed significantly between juveniles and adults. Population growth rates were positive, while reproductive rates remained relatively low. Antibodies specific to EBHSV in hare were detected in all five regions—with an overall seroprevalence of 78.9%—indicating widespread prior exposure to this virus among the hares studied. RHDV2-reactive antibodies were found in 10.1% of the individuals. Given the risk of cross-reactivity and individual immune responses, results regarding RHDV2 should be regarded as serological evidence of possible exposure requiring further investigation. The findings provide serological evidence of lagovirus exposure in the examined hare populations even in areas with population densities sufficient for game management. These results underscore the importance of integrated hare population monitoring that combines traditional population metrics with serological surveillance, particularly regarding lagoviruses such as EBHSV and RHDV2.