Seroprevalence of SARS-CoV-2 (COVID-19) exposure in pet cats and dogs in Minnesota, USA

Abstract

The COVID-19 pandemic caused by the coronavirus SARS-CoV-2 is continuing to spread globally. SARS-CoV-2 infections of feline and canine species have also been reported. However, it is not entirely clear to what extent natural SARS-CoV-2 infection of pet dogs and cats is in households. We have developed enzyme-linked immunosorbent assays (ELISAs) using recombinant SARS-CoV -2 nucleocapsid (N) protein and the receptor-binding-domain (RBD) of the spike protein, and the SARS-CoV-2 spike-pseudotyped vesicular stomatitis virus (VSV)-based neutralization assay to screen serum samples of 239 pet cats and 510 pet dogs in Minnesota in the early phase of the COVID-19 pandemic from mid-April to early June 2020 for evidence of SARS-CoV-2 exposures. A cutoff value was used to identify the seropositive samples in each experiment. The average seroprevalence of N-and RBD-specific antibodies in pet cats were 8% and 3%, respectively. Among nineteen (19) N-seropositive cat sera, fifteen (15) exhibited neutralizing activity and seven (7) were also RBD-seropositive. The N-based ELISA is also specific and does not cross react with antigens of common feline coronaviruses. In contrast, SARS-CoV-2 antibodies were detected at a very low percentage in pet dogs (~ 1%) and were limited to IgG antibodies against SARS-CoV-2 N protein with no neutralizing activities. Our results demonstrate that SARS-CoV-2 seropositive rates are higher in pet cats than in pet dogs in MN early in the pandemic and that SARS-CoV-2 N-specific IgG antibodies can detect SARS-CoV-2 infections in companion animals with higher levels of specificity and sensitivity than RBD-specific IgG antibodies in ELISA-based assays.

Recombinant SARS-CoV-2 Nucleocapsid Protein: Expression, Purification, and Its Biochemical Characterization and Utility in Serological Assay Development to Assess Immunological Responses to SARS-CoV-2 Infection

“…To compare N(−RNA) and N(+RNA) in the application of an N-based IgG ELISA to detect anti-SARS-CoV-2 N antibody in clinical serum samples, we used 31 cat serum samples, including 17 seropositive and 14 seronegative ones, that were previously confirmed by both the SARS-CoV-2 receptor-binding domain (RBD) and N-based IgG ELISAs as well as in an established COVID-19 neutralization assay [ 27 ]. Each cat serum sample was added in an equal amount into the wells of a 96-well plate and tested in an ELISA plate under three conditions, uncoated, N(+RNA) coated, and N(−RNA) coated.…”

“…Given the increasingly high vaccination rates for COVID-19 in the general populations, the N-based COVID-19 serological assays provide a valuable tool to distinguish natural SARS-CoV-2 infection from vaccination, because all current vaccine formulations use the viral spike (S) protein but not N as an antigen. Using the N(−RNA), we set up a new N-based IgG ELISA to screen a relatively small number of the already confirmed household cat sera as part of a larger study to survey pet cats and dogs admitted to the Veterinary Medical Center at the University of Minnesota that demonstrated a higher seroprevalence of SARS-CoV-2 infection of pet cats than of pet dogs in the early phase of the COVID-19 pandemic in the state of Minnesota [ 27 ].…”

“…A similar ELISA method as described above was used to evaluate 31 cat serum samples that were determined to be either positive or negative for anti-N antibody seroprevalence through various assays [ 27 ]. Briefly, a 96-well MaxiSorp plate was either uncoated or coated with 100 ng of the purified N(+RNA) or N(−RNA) protein, in duplicate, incubated overnight at 4 °C, and blocked with 5% nonfat milk in PBST buffer for 1 h at 37 °C.…”

“…The seropositive and seronegative cat serum samples in this study were from our previously published study [ 27 ]. These pet cats were presented to the veterinary medical center for various medical conditions or wellness checks.…”

Report of One-Year Prospective Surveillance of SARS-CoV-2 in Dogs and Cats in France with Various Exposure Risks: Confirmation of a Low Prevalence of Shedding, Detection and Complete Sequencing of an Alpha Variant in a Cat

“…Importantly, those cat-to-cat transmissions were possible even between asymptomatic cats [11]. There are more than 100 million cats and 90 million dogs in Europe [12], with a relatively high seroprevalence revealed by a rate of seroconversion starting from 0.2% and reaching 14.69% in the general companion animal population, and reaching from 21-53% in those living in SARS-CoV-2-infected households [6,[13][14][15][16][17][18][19][20][21]. Altogether, these observations led us to consider that the role of pets, albeit limited in the global SARS-CoV-2 epidemiology, might be more significant when humans come in close contact with animals living in SARS-CoV-2-positive households.…”