SARS-CoV-2 Transmission from Human to Pet and Suspected Transmission from Pet to Human, Thailand

Abstract

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been the cause of human pandemic infection since late 2019. SARS-CoV-2 infection in animals has also been reported both naturally and experimentally, rendering awareness about a potential source of infection for one health concern. Here, we describe an epidemiological investigation of SARS-CoV-2 infection in 639 cats and 224 dogs throughout multiple waves of COVID-19 outbreaks in Thailand. To indicate the potential source of infection, we performed SARS-CoV-2 genomic sequencing of samples obtained from pets and contacted humans, combined with in-depth interviews to support the epidemiological investigation. In the tested animals, SARS-CoV-2 RNA was present in 23 cases (19 cats and 4 dogs). Whole-genome sequencing of selected samples showed various SARS-CoV-2 variants of concern, which included the original European lineage (B.1), Alpha (B.1.1.7), Delta (B.1.617), and Omicron (BA.2). Among SARS-CoV-2-positive pets, 34.78% had evidence of contact with infected humans. Together with genomic analysis and an overlapping timeline, we revealed evidence of viral transmission from infected humans as the primary source, which spread to household cats via an undefined mode of transmission and most likely circulated between cohoused cats and caretakers within the weeks before the investigation. The SARS-CoV-2 surface glycoprotein (spike gene) obtained from caretakers of individual cats contained sequence signatures found in the sequences of infected cats, indicating possible exposure to the virus excreted by cats. Although pet-to-human transmission of SARS-CoV-2 is considered relatively rare, our study provides suspected episodes of human infection from animals that were initially infected through contact with infected humans.

Keywords: COVID-19; SARS-CoV-2; animal; cat; coronavirus; zoonotic infections.

FIG 1

Geographic and schematic overviews of sample collection and SARS-CoV-2-positive samples. Shown are the geographic distribution of samples collected in this study (left) and the total numbers of samples collected during the first to fifth COVID-19 waves in Thailand (right). The number of collected samples in each region is labeled according to a red color range that corresponds to the graph in panel B (blue line).

FIG 2

Phylogenetic analysis of SARS-CoV-2 sequences from humans in Thailand from April 2020 to June 2022 and sequences obtained from previously reported animals using the maximum likelihood method. Whole-genome sequences derived from SARS-CoV-2-positive animals from this study are indicated by red dots and are clustered within various VOCs of human SARS-CoV-2 sequences, as indicated by the different colors. The scale bar of 0.00050 indicates units of substitutions per site.

FIG 3

Schematic timeline of events of SARS-CoV-2 infection in scenario A. Dates are presented for the corresponding events. Symbols in turquoise, purple, and indigo indicate events affecting humans, cats, and both cats and humans, respectively.

FIG 4

Phylogenetic analysis of animal-related human SARS-CoV-2 surface glycoprotein gene sequences detected in this investigation. Sequences derived from Alpha (B.1.1.7) (A) and Omicron BA.1 and 2 (B) VOCs indicated a sequence cluster between humans and animals. Sequences derived from cats and humans in scenario A are indicated in purple, and the red labels indicate sequences obtained from cat BKK100 at different sampling times. Sequences obtained from infected dog BKK-ST023.1 and veterinarian BKK-ST023.8 are indicated in light green. The scale bars indicate units of substitutions per site in each tree.