Hemagglutination inhibition (HI) assays indicated 7.25% of sera positive using equine H3N8, swine H3N2, and pandemic H1N1 antigens, with the most frequently detected immune response being to H3N2. colspan=”1″ H3N2 /th th align=”center” rowspan=”1″ colspan=”1″ H1N1pdm /th /thead HI positive1146204 Open in a separate window HI = hemagglutination inhibition. The seroprevalence of influenza in dogs in Europe has been studied in Italy and Germany. In Italy, the positive results obtained in a NP ELISA were 0.5C3.5%. HI positive reactions were obtained for H3N8, H3N2, and H1N1pdm subtypes of IAV (using canine H3N8, equine H3N8, swine H3N2, and H1N1pdm antigens).6,7,12 Seroprevalence was lower In Germany, 7 of 736 sera (0.95%) were positive in an NP ELISA, and antibodies against H1N1pdm were DB04760 detected.5 We found a reaction with the swine H1N1pdm strain in a small number of dogs (1.6%) in our current study; infections with H1N1pdm have been confirmed in Poland, both in swine and humans.11,13 Generally, in Europe, the percentage of dogs seropositive in NP ELISA is low, whereas the results of the HI test indicate a higher percentage of seropositive animals. The seroprevalence of CIV has been studied worldwide, notably in countries in which outbreaks of canine influenza have been reported, such as the United States or China. In a 2019 report of testing for canine H3N2 in pet dogs in the United States, 3.53% of sera were positive in ELISA and 2.21% in HI.8 Although only a low seroprevalence of canine influenza is usually recorded in the United States, seroprevalence can reach high levels in influenza-endemic areas.8,9 Studies carried out among dogs in Hong Kong have shown that seroprevalence rates of canine H3N2 or H3N8 (0.9%) were lower than those of human IAVs H1N1pdm or H3N2 (7.5%), indicating that humans may serve as the major source of exposure to IAV for dogs in a densely populated city.17 Among the ELISA-negative samples, we detected positive sera in the HI test. A similar tendency has been observed in previous studies.9,12,17 This divergence might arise from the kinetics of anti-NP and anti-HA antibodies; anti-NP titers detected by ELISA decrease over time, as observed for avian influenza.10,15 Additionally, ELISA for swine influenza detects mainly IgG antibodies, whereas the HI test detects IgM as well as IgG antibodies; hence the ELISA may not identify positive animals at the early stage of infection. 20 NP-based ELISA is therefore indicated as a suitable tool for surveillance purposes, but it can give false-negative results. On the other hand, not all sera positive in ELISA have been assigned DB04760 a specific serotype of IAV. It is possible that the strains used in HI are incompatible with strains circulating in the dog population. Given the limitations of the tests used, it seems advisable to use both tests in parallel to check the seroprevalence DB04760 of IAV in dogs. Although rather low seroprevalence is DB04760 noted generally, it seems advisable to monitor the seroprevalence of IAV infection in both BIRC3 pet and farmed dogs, especially in the context of H1N1pdm distribution. Given the population of dogs estimated at 700?million worldwide, the close contact between humans and dogs, and the susceptibility of dogs to infection by IAVs of both mammalian and avian origin, serosurveillance in dogs may be useful. Supplemental Material Supplemental_material C Supplemental material for Serologic investigation of influenza A virus infection in dogs in Poland:Click here for additional data file.(855K, pdf) Supplemental material, Supplemental_material for Serologic investigation of influenza A virus infection in dogs in Poland by Malgorzata Kwasnik, Marcin Smreczak, Jerzy Rola, Kinga Urbaniak and Wojciech Rozek in Journal of Veterinary Diagnostic Investigation Acknowledgments We thank Urszula Bocian for excellent technical assistance. Footnotes Declaration of conflicting interests: The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Funding: The study was supported by KNOW, Ministry of Science and Higher Education, Poland [05-1/KNOW2/2015 (K/02/1.0)]. ORCID iD: Malgorzata Kwasnik https://orcid.org/0000-0002-8689-6906 Supplementary material: Supplementary material for this article is available online..