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 origins 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. To date, there is no evidence of natural
SARS-CoV-2 infection in rats and experimental studies suggest rats are
likely not susceptible to ancestral SARS-CoV-2. However, as variants
emerge, new species have been identified as competent hosts, as
demonstrated by the susceptibility of rats to the SARS-CoV-2 Alpha
variant of concern (VOC). 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, including the two
seropositive samples, were collected prior to the emergence of VOCs, and
22 were collected while the Alpha variant 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) testing
was conducted on presumptive positive samples. We did not detect
SARS-CoV-2 RNA in any samples tested. Two out of eleven samples positive
by sVNT had neutralizing antibodies by PRNT (1:40 and 1:320 PRNT70). 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.