The only data given was the postal code of the veterinary clinic that took the serum sample

The only data given was the postal code of the veterinary clinic that took the serum sample. federal government agency responsible for disease control and prevention. As in most European countries, the first wave of SARS-CoV-2 infections in the human population was detected from February to March 2020 [3]. In August of 2020, cases of SARS-CoV-2 infections started to rise again, hitting a high at the end of November, when the overall case reports had doubled within one month [4]. Strict measures concerning the social activity Rosiglitazone maleate of citizens [5] led to a decline in registered infection until February 2021 [4]. During this so-called second wave between August 2020 and February 2021, the occurrence of variants of concern of SARS-CoV-2 [6], and the changes in transmissibility that came along [7], were reported. Ever since the start of the pandemic, the role of Rosiglitazone maleate cats in the transmission of SARS-CoV-2 was questioned [8]. The susceptibility of cats to a SARS-CoV-2 infection and the transmission of the virus to cohoused uninfected cats Rosiglitazone maleate were shown in animal trials [9,10,11,12]. Further, first case reports of naturally infected cats [13,14,15,16,17,18,19,20] and serological surveys [21,22,23,24] proved the occurrence of natural SARS-CoV-2 infections in cats. A survey on serum samples from German domestic cats, conducted during the first wave of the pandemic, showed that trans-species transmission from infected humans to their cats happened on a regular, though infrequent, basis [25]. Since the higher number of human infections might also lead to CASP8 a higher risk in trans-species transmission, the collection of serum samples from domestic cats from all over Germany during the second wave of the pandemic was continued. 2. Materials and Methods From September 2020 to February 2021, serum samples were collected from domestic cats during the clinical examination from the attending veterinarian. They were sent to the Synlab company, located in Augsburg, Germany, for hematology testing, which kindly provided the superfluous sera for the presented study. The samples were chosen randomly. Neither the health status of the cats nor the SARS-CoV-2 infection status of the owners was known. The only data given was the postal code of the veterinary clinic that took the serum sample. Overall, 1173 serum samples were tested for antibodies against SARS-CoV-2 by an indirect ELISA against the receptor-binding domain (RBD). The indirect ELISA was already validated before [26]. Samples with a positive or borderline result were additionally tested in an indirect immunofluorescence assay (iIFA) in order to confirm the ELISA result. Only serum samples that were positive in both the ELISA and the iIFA test were regarded as positive for SARS-CoV-2 antibodies. In addition, samples with positive or borderline results in the ELISA were tested for neutralizing antibodies by the use of a virus neutralization test (VNT). Both tests were described before and are based on the usage of Vero E6 cells (L 0929, Collection of Cell Lines in Veterinary Medicine (CCLV), Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany), and the 2019_nCoV Muc-IMB-1 SARS-CoV-2 isolate [25,27]. Further, cross-reactivity of the aforementioned tests with sera that contain antibodies against feline coronavirus (FCoV) was ruled out during the previous SARS-CoV-2 surveillance study on the German cat population [25]. 3. Results and Discussion The overall seroprevalence in the sampled cat sera during the second wave of human SARS-CoV-2 infections was 1.36% (16/1173) (see Table 1 and Figure 1), which is nearly twice as high as the prevalence during the first wave of virus circulation between April and September 2020 (0.65%) [25]. For comparison, the amount of registered human infections rose from 289,189 cases at the end of September 2020 to 2,442,336 at the end of February 2021, which accounts for a more than eightfold increase of overall registered human cases in Germany during the second wave of the pandemic [4]. Open in a separate.