Seropositivity of main vector-borne pathogens in dogs across Europe

Abstract

Background: Canine vector-borne disease (CVBD) has been an area of increasing interest in Europe over the last few decades, and there have been changes in the prevalence and distribution of many of these diseases. Monitoring CVBD infections in Europe is often done by individual countries, but aggregated data for the European countries are helpful to understand the distribution of CVBDs.

Methods: We used an extensive retrospective database of results from point-of-care rapid enzyme-linked immunosorbent assay (ELISA) tests on dogs across Europe to identify distribution and seropositivity in animals tested for selected CVBDs (Anaplasma spp., Ehrlichia spp., Borrelia burgdorferi, Leishmania spp., and Dirofilaria immitis) from 2016 through 2020. Geographic distribution of positive tests and relative percent positive values were mapped by the Nomenclature of Territorial Units for Statistics classification for regions with sufficient test results for reporting.

Results: A total of 404,617 samples corresponding to 1,134,648 canine results were available from dogs tested in 35 countries over the 5-year study period. Over this period the number of test results per year increased whereas test positivity decreased. Leishmania spp. had the largest increase in total test results from 25,000 results in 2016 to over 60,000 results in 2020. Test positivity for Leishmania spp. fell from 13.9% in 2016 to 9.4% in 2020. Test positivity fell for Anaplasma spp. (7.3 to 5.3%), Ehrlichia spp. (4.3 to 3.4%), and Borrelia burgdorferi (3.3 to 2.4%). Dirofilaria immitis test positivity trended down with a high of 2.7% in 2016 and low of 1.8% in 2018. Leishmania spp. test positivity was highest in endemic areas and in several non-endemic countries with low numbers of test results. Co-positivity rates were significantly higher than expected for all pathogen test positive pairs except for Ehrlichia spp. with Borrelia burgdorferi and D. immitis with Borrelia burgdorferi.

Conclusions: This study represents the largest data set on CVBD seropositivity in Europe to date. The increase in the number of test results and decreasing test positivity over the study period may reflect changes in testing behavior and increased screening of healthy animals. The Europe-wide mapping of CVBD provides expected test positivity that can help inform veterinarians' decisions on screening and improve prevention and identification of these important, sometimes zoonotic, diseases.

Keywords: Anaplasma; Borrelia burgdorferi; Dirofilaria immitis; Dogs; Ehrlichia; Europe; Leishmania; Seropositivity.

Fig. 1

Anaplasma spp. antibody test positivity for NUTS regions or country over the study period (2016–2020. NUTS levels are shown with the most geographic detail allowed by the regional data. Gray regions did not have sufficient results for evaluation of region-specific test positivity analysis

Fig. 2

Ehrlichia spp. antibody test positivity for NUTS regions over the study period (2016–2020). NUTS levels are shown with the most geographic detail allowed by the regional data. Gray regions did not have sufficient results for evaluation of region-specific test positivity analysis

Fig. 3

Borrelia burgdorferi antibody test positivity for NUTS regions or country over the study period (2016–2020). NUTS levels are shown with the most geographic detail allowed by the regional data. Gray regions did not have sufficient results for evaluation of region-specific test positivity analysis

Fig. 4

Dirofilaria immitis antigen test positivity for NUTS regions or country over the study period (2016–2020). NUTS levels are shown with the most geographic detail allowed by the regional data. Gray regions did not have sufficient results for evaluation of region-specific test positivity analysis. Test positivity in the Canary Islands (a high endemic area) was added to the figure (not to scale) for reference

Fig. 5

Leishmania spp. antibody test positivity for NUTS regions or country over the study period (2016–2020). NUTS levels are shown with the most geographic detail allowed by the regional data. Gray regions did not have sufficient results for evaluation of region-specific test positivity analysis. Results from Germany and France are shown at NUTS level 1 since test results were restricted to a few areas within the country

Fig. 6

Yearly European test positivity for each pathogen. Positive percent of all tests and 95% confidence intervals (bars) are shown for each year. Non-overlapping confidence intervals support significant differences in test positivity between years