The virus SARS-CoV-2 originated in Wuhan, China, in 2019 and has since spread worldwide, infecting humans and animals. Several reports have described the seroprevalence of antibodies in dogs and cats, but there are no reports from Mexico. This study aimed to evaluate the seroprevalence of neutralizing antibodies against the ancestral strain and Omicron BA.1 subvariant in dogs and cats in Mexico. A total of 1111 samples from dogs (n=1052) and cats (n=59) were collected in different regions of Mexico, and the presence of neutralizing antibodies (nAbs) was evaluated by a plaque reduction neutralization test (PRNT90) and microneutralization (MN). The results showed that 15.25% (9 of 59) of cats and 2.85% (30 of 1052) of dogs presented nAbs against the ancestral strain of SARS-CoV-2. However, the analysis of nAbs against Omicron BA.1 in cats showed the same percentage of positive animals but a reduction in the titer. In the case of dogs, 2.09% (22 of 1052) showed nAbs against Omicron BA.1. These results agree with previous reports showing that antibodies are more frequent in cats than in dogs and that these antibodies have a lower capacity to neutralize Omicron BA.1

SARS-CoV-2 is a virus that originated in Wuhan, China, in 2019 and has since spread worldwide, infecting people and animals. The objective of this study was to implement the plaque reduction neutralization test (PRNT90) and microneutralization (MN) to evaluate the presence of antibodies against SARS-CoV-2 in companion animals. First, a virus was isolated and sequenced, which showed a similarity of 99.9% with the original Wuhan strain. This virus had a titer of 3.55 DICC 50; for the PRNT90, it was adjusted to 30-40 plaque-forming units (PFU) and for the MN, at 100 DICC 50. For both assays, serial double dilutions of the sera were performed from 1:10 to 1:5120. Serum samples from people with negative and positive status were used as controls, as well as samples from companion animals (dogs and cats). In the case of human samples, the titers were from 1:10 to 1:5120 with PRNT and from 1:10 to 1:1280 with MN (r 2 = 0.957). Analysis of animal samples (dogs n = 521 and cats n = 29) revealed 10 positive samples, six from dogs and four from cats. Cats had higher titers than dogs. Titers ranged from 1:80 to 1:320 by MN and from 1:160 to 1:640 by PRNT90 for cats and from 1:10 to 1:40 by MN and from 1:10 to 1:80 PRNT90 for dogs (r 2 = 0.621). In both human and animal samples, the highest titers were observed with the PRNT90 test; however, the MN test is easier to perform than the PRNT90 test, so it is suggested as the test of choice for animal seroprevalence studies.

SARS-CoV-2 can infect pets under natural conditions, which raises questions about the risk factors related with susceptibility of these animals to infection. The status of pet infection by SARS-CoV-2 in Mexico it is not well understood. We aimed to estimate the frequency of positive household cats and dogs to viral RNA and antibodies for SARS-CoV-2 during the second wave of human infections in Mexico, and to recognize the major risk factors related to host and pet ownership behavior. We evaluated two study groups, cats and dogs from COVID-19 infected/suspected households (n=44) and those admitted for veterinary care for any reason at several veterinary hospitals in Puebla City, México (n=91). Using RT-PCR, we identified the presence of SARS-CoV-2 RNA in swabs of four dogs (18.2%) and zero cats in COVID-19 infected/suspected households, within this group 31.8% of dogs and 27.3% of cats tested IgG ELISA positive, and neutralizing antibodies were detected in one dog (4.5%) and two cats (9.1%). In the random group, 25.0% of dogs and 43.6% of cats were ELISA positive, only one cat shown neutralizing antibodies (2.6%). We identified no significant hematological and biochemical abnormalities as risk factors, but we found dynamic changes in leukocytes, lymphocytes, albumin/globulin rate, and creatinine. Pet age >4 years old, other pets at home, and daily cleaning of pet dish, were each associated with an increase of SARS- CoV-2 infection (p<0.05). Allowing face lick, sharing bed/food with pets, and owner tested positive or suspected of COVID-19 were not significant risk factors, but time (>4 hours) the owner spent out from home during the lockdown for COVID-19 (OR= 0.37, p= 0.009), and outdoor pet food tray (OR= 0.32, p= 0.011) were negative risks factors of SARS-CoV-2 infection in pets, suggesting that time the owner spends with their pet is an important risk factor.