Dogs and Cats Are Less Susceptible to the Omicron Variant of Concern of SARS-CoV-2: A Field Study in Germany, 2021/2022

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused a pandemic of unprecedented extent. Besides humans, a number of animal species can be infected; however, in some species, differing susceptibilities were observed depending on the virus variant. Here, we serologically investigated cats and dogs living in households with human COVID-19 patients. The study was conducted during the transition period from delta as the dominating variant of concern (VOC) to omicron (BA.1/BA.2) to investigate the frequency of virus transmission of both VOCs from infected owners to their pets. The animal sera were tested by surrogate virus neutralization tests (sVNT) using either the original receptor-binding domain (RBD), enabling the detection of antibodies against the delta variant, or an omicron-specific RBD. Of the 290 canine samples, 20 tested positive by sVNT, but there were marked differences between the sampling time and, related thereto, the virus variants the dogs had contact to. While in November 2021, infected owners led to 50% seropositive dogs (18/36), only 0.8% (2/254) of animals with household contacts to SARS-CoV-2 between December 2021 and April 2022 tested positive. In all cases, the positive reaction was recorded against the original RBD. For cats, a similar pattern was seen, as in November 2021, 38.1% (16/42) tested positive, and between December 2021 and March 2022, only 5.0% (10/199). The markedly reduced ratio of seropositive animals during the period of omicron circulation suggests a considerably lower susceptibility of dogs and cats to this VOC. To examine the effect of further omicron subvariants, sera taken in the second and third quarter of 2022 from randomly selected cats were investigated. 2.3% (11/372) tested seropositive, and all of them showed a stronger reaction against the original RBD, further supporting the assumption of a lower susceptibility of companion animals to the omicron VOC.

Figure 1

Periods at which samples were taken in the present study and shares of variants of concern (VOCs) detected in human samples in Germany (data retrieved from https://www.rki.de/DE/Content/InfAZ/N/Neuartiges_Coronavirus/Daten/VOC_VOI_Tabelle.html). The sampling period in COVID-19 households is indicated in red, and the two time frames at which randomly selected cats were sampled are marked by black bars.

Figure 2

Serological results of dogs kept in COVID-19 households. In the upper panel, the shares of positive (red) and negative (grey) results are given; the animals are sorted into the month in which their owner tested SARS-CoV-2 positive. In the lower panel, the values as measured in the surrogate virus neutralization test are shown individually for each canine sample. In November 2021, before the omicron variant of concern was detected for the first time in the human population of Germany, the canine sera were tested only against the original RBD. From December 2021 onwards, the samples were tested in parallel using the original as well as the omicron RBD, and the results of individual samples are connected by a black line. The cutoff is indicated by a horizontal dashed line.

Figure 3

Serological results of cats kept in COVID-19 households. In the upper panel, the shares of positive (red) and negative (grey) results are given; the animals are sorted into the month in which their owner tested SARS-CoV-2 positive. In the lower panel, the values as measured in the surrogate virus neutralization test are shown individually for each feline sample. In November 2021, before the omicron variant of concern was detected for the first time in the human population of Germany, the feline sera were tested only against the original RBD. From December 2021 onwards, the samples were tested in parallel using the original as well as the omicron RBD, and the results of individual samples are connected by a black line. The cutoff is indicated by a horizontal dashed line.

Figure 4

Results of the surrogate virus neutralization test for the positive control sera. All control samples were tested against the original as well as the omicron RBD, and the results of individual samples are connected by a line. The cutoff of the test is indicated by a horizontal dashed line.

Figure 5

Results of the surrogate virus neutralization test for randomly selected cats sampled in calendar weeks 11 to 23 of 2022 (a) or in calendar weeks 31/32 of 2022 (b). All samples were tested against the original as well as the omicron RBD, and the results of individual samples are connected by a line. The cutoff of the test is indicated by a horizontal dashed line.