Seroepidemiological survey and spatial analysis of the occurrence of Angiostrongylus vasorum in Swiss dogs in relation to biogeographic aspects.

Angiostrongylus vasorum is a metastrongyloid nematode living in the pulmonary arteries and in the right heart causing potentially fatal respiratory distress, coagulopathies and a wide range of other clinical signs in dogs. The aim of this study was to investigate the seroprevalence and distribution of A. vasorum in Swiss dogs and to identify correlations with biogeographic aspects. A total of 6136 dog sera from all over the country submitted by veterinarians for haematological or chemical analyses were examined for the presence of circulating A. vasorum parasite antigen and specific antibodies against A. vasorum by ELISA. The combined seroprevalence for both specific antibodies and antigen was 0.96% (95% confidence intervals: 0.7-1.2%), while the overall antibody prevalence was 3.08% (CI: 2.7-3.5%) and the antigen prevalence 2.17% (CI: 1.8-2.6%). The highest prevalence for dogs identified as positive in both ELISAs was detected in Western Switzerland (around Geneva, 2.21%, CI: 0.7-5.1%), representing a new endemic area. Known endemic regions in Southern Switzerland (Ticino, 2.17%, CI: 1.0-4.0%) and in the High Rhine area (northern Switzerland, 1.11%, CI: 0.4-2.4%) were confirmed. Spatial analysis identified a cluster with a radius of approximately 30 km in Sisseln, located in this latter region at the German border, for antibody positive dogs, which interestingly corresponded to the location of historical cases of canine angiostrongylosis diagnosed 12-16 years previously. In total 96.6% (57/59) of the antigen- and antibody positive samples originated from areas with a mean temperature warmer than -2 °C in January. Correspondingly, most of the samples (53/59, 89.8%) positive in both ELISAs originated from areas below 700 meters above sea level (m asl), suggesting the altitude being a limiting factor for A. vasorum transmission in Switzerland. This study confirms previously known endemic areas for A. vasorum in Switzerland, and additionally identifies positive dogs in virtually all bioregions. As asymptomatic dogs may suddenly develop a critical clinical status with potentially fatal outcome, disease awareness has to be maintained for dogs from across Switzerland at altitudes below 700 m asl.