Conquering Switzerland: the emergence of in foxes over three decades and its rapid regional increase in prevalence contrast with the stable occurrence of lungworms.

Angiostrongylus vasorum, Crenosoma vulpis and Capillaria aerophila are the most common lungworms of domestic and wild canids. We investigated the short- and long-term lungworm prevalence changes in the Swiss fox population with a focus on A. vasorum. Between 2012 and 2017, lungs and hearts of 533 foxes from north-eastern Switzerland were necropsied and blood samples tested for circulating A. vasorum antigen. Angiostrongylus vasorum prevalence increased steadily from 21.5% in 2012 to 81.8% in 2017. In contrast, C. aerophila and C. vulpis prevalences fluctuated between 41.8 and 74.7%, and 3.6 and 14.9%, respectively. Based on 3955 blood samples collected between 1986 and 2017 from three geographic areas and during four time periods, antigen seropositivity increased from 2.4 to 62.0%. In north-eastern Switzerland, seropositivity was initially low (1.9 and 1.7% in the first two time periods) but increased in the following two decades to 22.2 and 62.0%, respectively. Our findings depict the spectacular expansion of A. vasorum in the past three decades. Regionally, the prevalence in foxes increased 4-fold within 6 years in some regions. This underpins the important role of foxes as reservoir hosts, likely explaining the increasing number of cases of canine angiostrongylosis in Switzerland. Our findings are representative of central Europe and may help anticipating future developments in areas where A. vasorum is present but (still) infrequent.