Study population and setting
Following an outbreak of SARS-CoV-2 on a mink farm in Utah, USA that was confirmed on August 17, 2020, researchers sampled wild mammals around the farm premises and on public lands within a 3.5 km radius. Between August 22 and 30, 2020, 102 animals were captured, including 45 deer mice (Peromyscus maniculatus), 5 Peromyscus spp. mice, 25 house mice (Mus musculus), 3 rock squirrels (Otospermophilus variegatus), 11 presumed escaped American mink (Neovison vison) and 2 presumed wild American mink, 5 raccoons (Procyon lotor), and 6 striped skunks (Mephitis mephitis). Escaped mink were distinguished from wild mink based on their close association with barns and differences in coat color and size. Samples from each animal included oral, nasal, and rectal swabs or washes; tissue specimens; and blood specimens. Samples were tested for the presence of SARS-CoV-2 RNA with two real-time reverse transcription PCR (rRT-PCR) assays targeting the N1 and N2 genes; samples were considered positive only if both N1 and N2 were detected. The presence of SARS-CoV-2 antibodies in sera was tested using a virus neutralization assay in Vero E6 cell culture.
Summary of Main Findings
Of the 11 escaped mink captured on the farm premises, 3 had detectable SARS-CoV-2 in nasal swabs or lung tissue specimens; all animals had detectable neutralizing antibodies against SARS-CoV-2. None of the other captured animals had detectable antibodies, including the wild mink. One rectal swab specimen from a house mouse capture on the farm premises was PCR-positive, but with a high Ct value indicating a low quantity of viral RNA likely resulting from excretion following ingestion of contaminated material rather than from infection. Two deer mice individuals collected from farm premises were positive for SARS-CoV-2 RNA in oral or rectal swabs, although only the N1 gene was detected.
The detection of both SARS-CoV-2 RNA and neutralizing antibodies helps to distinguish between animals with current infection and past exposure to SARS-CoV-2.
Due to the very small sample size and limited geographical scope, it is not possible to know how frequently mink infected with SARS-CoV-2 escape from farms, and how frequently they interact with other wildlife species on or off farm premises. More data is necessary to assess the risk of SARS-CoV-2 establishing ongoing transmission in susceptible wildlife species. Additionally, no sequence data was produced, which would have been useful for comparing with sequences from infected mink inside the farms, although such information is not yet available.
SARS-CoV-2 outbreaks have been reported on mink farms in multiple European countries and several US states, including Utah, Michigan, Wisconsin, and Oregon. There is concern that infected farms may spread the virus to other farms through movement of animals, people, or materials, including via incidental infection of domestic or wild animals on farm premises. This paper demonstrates that escaped mink had evidence of current or past SARS-CoV-2 infection. While some deer mice captured on farms may have been infected, thereby confirming experimental evidence showing this species is susceptible to infection, SARS-CoV-2 detection was only successful for one target gene and thus may not represent a true infection.
This review was posted on: 12 March 2021