Seroprevalence of IgG Antibodies Against Borrelia burgdorferi Sensu Lato, Anaplasma phagocytophilum, and Tick-Borne Encephalitis (TBE) Virus in Horses in Southern Norway

<i>Ixodes ricinus</i> ticks play a crucial role as carriers of diseases, transmitting pathogens to vertebrate hosts, including horses. This study aimed to investigate the seroprevalence of IgG antibodies against <i>Borrelia burgdorferi</i> sensu lato (s. l.), <i>Anaplasma phagocytophilum</i>, and tick-borne encephalitis virus (TBE-virus) in equine sera collected in southern Norway. In total, sera from 331 horses stabled in four counties (Agder, Vestfold and Telemark, Vestland, and Viken) were analyzed by immunoblot. In total, 66% of the horses were IgG-seropositive for antibodies against one or multiple tick-borne pathogens. The highest seroprevalence was detected against <i>B. burgdorferi</i> s. l. (47%), followed by <i>A. phagocytophilum</i> (34%) and TBE-virus (10%). A significant difference between the counties regarding IgG antibodies against <i>A. phagocytophilum</i> was found, with the highest seroprevalence in horses stabled in the coastal areas of Agder and Vestland. In conclusion, the study demonstrates that horses in southern Norway are at high risk of contracting tick-borne infections.