Seroprevalence, biogeographic distribution and risk factors for Aelurostrongylus abstrusus infections in Swiss cats.

The metastrongyloid nematode Aelurostrongylus abstrusus is a worldwide occurring feline lungworm. The spectrum of clinical signs in infected cats ranges from mild (e.g. nasal discharge or cough) to severe respiratory distress. The aim of this seroepidemiological study was to define prevalence and risk factors for A. abstrusus infections in Swiss cats, to assess the biogeographic distribution and to investigate the influence of temperature and altitude on the occurrence of this parasite. Sera of 4067 domestic cats were collected from all over Switzerland, tested for the presence of antibodies against A. abstrusus by a novel ELISA and the results correlated with biogeographic aspects. A subsample of 1000 datasets was used for risk factor analyses. Overall, 10.7% (434/4067, 95% confidence intervals [CI]: 9.7-11.7%) of the cats were tested positive, with variations from 0.0% to 20.0% among ten different biogeographic regions. Differences were significant between the Western (13.9%, CI: 11.4-16.7%) and the Eastern (9.2%, CI: 8.0-10.5%) Swiss Plateau, possibly attributable to the suitability of the areas for intermediate hosts. In total 90.3% (392/434) of the seropositive cats originated from regions lower than 700 m above sea level. Correspondingly, 98.9% (429/434) of positive samples were obtained from regions with a mean temperature higher than -2 °C in January, suggesting altitude and temperature being limiting factors for A. abstrusus infections in Switzerland. Concerning individual risk factors, prevalence was higher in intact (15.5%, CI: 9.5-23.4%) than in neutered cats (5.8%, CI: 7.9-10.4%). Young adult cats (aged 11-22 months) were significantly more often seropositive (10/76, 13.2%, CI: 6.5-22.9%) than kittens aged 1-10 months (1/34, 2.9%, CI: 0.1-15.3%) or adult and senior cats > 22 months (58/889, 6.5%, CI: 5-8.4%). Outdoor cats and cats presenting respiratory signs tend to be more often positive than indoor cats (p =  0.077) and animals without respiratory signs (p = 0.086), respectively. We here confirm that the use of a serological test can contribute to improve the identification of infected animals, through evaluation of risk factors on a population level and for a better management on an individual level, overcoming the challenges represented by faecal examinations and the correlated underestimation of the occurrence of A. abstrusus in cats.