Surveillance for SARS-CoV-2 in Norway Rats (Rattus norvegicus) from Southern Ontario

Abstract

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from wildlife has raised concerns about spillover from humans to animals, the establishment of novel wildlife reservoirs, and the potential for future outbreaks caused by variants of wildlife origin. Norway rats (Rattus norvegicus) are abundant in urban areas and live in close proximity to humans, providing the opportunity for spillover of SARS-CoV-2. Evidence of SARS-CoV-2 infection and exposure has been reported in Norway rats. We investigated SARS-CoV-2 infection and exposure in Norway rats from Southern Ontario, Canada. From October 2019 to June 2021, 224 rats were submitted by collaborating pest control companies. The majority of samples were collected in Windsor (79.9%; n = 179), Hamilton (13.8%; n = 31), and the Greater Toronto Area (5.8%; n = 13). Overall, 50.0% (n = 112) were female and most rats were sexually mature (55.8%; n = 125). Notably, 202 samples were collected prior to the emergence of variants of concern (VOC) and 22 were collected while the Alpha variant (B.1.1.7) was the predominant circulating VOC in humans. Nasal turbinate (n = 164) and small intestinal (n = 213) tissue samples were analyzed for SARS-CoV-2 RNA by RT-PCR. Thoracic cavity fluid samples (n = 213) were tested for neutralizing antibodies using a surrogate virus neutralization test (sVNT) (GenScript cPass); confirmatory plaque reduction neutralization test (PRNT) was conducted on presumptive positive samples. We did not detect SARS-CoV-2 RNA in any samples tested. Two out of eleven samples positive on sVNT had neutralizing antibodies confirmed positive by PRNT (1 : 40 and 1 : 320 PRNT70); both were collected prior to the emergence of VOC. It is imperative that efforts to control and monitor SARS-CoV-2 include surveillance of rats and other relevant wildlife species as novel variants continue to emerge.

Figure 1

Rat collection counts and human COVID-19 cases per 100,000 people by date from January 1, 2020 to June 22, 2021 in (a) Ontario, (b) Windsor, and (c) Hamilton. Collection dates of seropositive rats (PRNT70) are indicated by black diamonds.

Figure 2

Map of Southern Ontario with the locations of rats collected by pest control companies from October 2019 to June 2021. Collection location data are superimposed on a choropleth map of human population density (per km²) by regional county municipalities.

Figure 3

Sample types collected for rats submitted by pest control companies in Southern Ontario for the (a) prepandemic group (n = 75) collected between October and December 2019 and the (b) pandemic group (n = 149) collected between January 2020 and June 2021.