Once SARS-CoV-2 emerged in humans, the search for other susceptible species was launched. Not only would additional reservoir species make the virus harder to control or eradicate, it could also provide the virus with additional evolutionary paths to follow.
The two biggest concerns were companion animals (primarily dogs and cats), and farmed livestock. Should SARS-CoV-2 flourish in poultry, or pigs, or cattle - or in household pets - then the COVID-19 pandemic would become much harder to contain.
In early April of 2020, in Susceptibility of Ferrets, Cats, Dogs & Other Domestic Animals to SARS-CoV-2, Dr. Hualan Chen - director of China's National Avian Influenza Reference Laboratory - published a paper on the susceptibility of a variety of animals to the SARS-CoV-2.
Hualan Chen et al.doi: https://doi.org/10.1101/2020.03.30.015347(Excerpt)We found that SARS-CoV-2 replicates poorly in dogs, pigs, chickens, and ducks, but efficiently in ferrets and cats. We found that the virus transmits in cats via respiratory droplets. Our study provides important insights into the animal reservoirs of SARS-CoV-2 and animal management for COVID-19 control.
While cats have not been shown to transmit the virus efficiently to others, the same cannot be said for mink - which are close relatives of ferrets - which have proven themselves quite susceptible to the virus.
As mink transmit the virus, over time SARS-CoV-2 can `adapt' to its new host, and new mutations can emerge (see Preprint: Recurrent Mutations in SARS-CoV-2 Genomes Isolated from Mink Point to Rapid Host-Adaptation) as illustrated in the serial passage graphic below.
So far, mink appear to be the biggest non-human reservoir of the virus, but there are many other mammals that have yet to be adequately tested. And some of the early reassuring test results on livestock are being repeated, since the virus continues to evolve.
Last fall much of our attention was focused on outbreaks in mink farms around the world - but most particularly in Denmark - where a mink variant appeared and began spreading in the population (see EID Journal: SARS-CoV-2 Transmission between Mink (Neovison vison) and Humans, Denmark).
While most of the mink farm outbreaks have been in Europe, last August (see USDA APHIS Confirms SARS-CoV-2 in Farmed Mink in Utah) the United States reported its first outbreak on two mink farms in Utah.
All of which brings us to an EID Journal research letter on the investigation into possible spillover of the virus from these Utah farms into local wildlife that is both reassuring and concerning at the same time.
Reassuring because there was no evidence of the establishment of SARS-CoV-2 in nearby wildlife, but concerning because 11 presumed `escaped' mink, living near the farms, tested positive for SARS-CoV-2 antibodies.
Meaning there were opportunities for a spillover into wildlife, even if none appeared to take hold. Follow the link to read this research letter in full, as I've only included some excerpts.
Volume 27, Number 3—March 2021
SARS-CoV-2 Exposure in Escaped Mink, Utah, USA
Susan A. Shriner , Jeremy W. Ellis, J. Jeffrey Root, Annette Roug, Scott R. Stopak, Gerald W. Wiscomb, Jared R. Zierenberg, Hon S. Ip1, Mia K. Torchetti1, and Thomas J. DeLiberto1
In August 2020, outbreaks of coronavirus disease were confirmed on mink farms in Utah, USA. We surveyed mammals captured on and around farms for evidence of infection or exposure. Free-ranging mink, presumed domestic escapees, exhibited high antibody titers, suggesting a potential severe acute respiratory syndrome coronavirus 2 transmission pathway to native wildlife.
We report a wildlife epidemiologic investigation of mammals captured on or near properties in Utah, USA, where outbreaks of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection occurred in farmed mink. Mink farms are relatively common in the United States, and most are small family farms. The US Department of Agriculture’s National Veterinary Services Laboratories (Ames, IA, USA) confirmed SARS-CoV-2 in mink at 2 Utah farms on August 17, 2020, after an investigation by the Utah Veterinary Diagnostic Laboratory and the Washington Animal Disease Diagnostic Laboratory (1).
SARS-CoV-2 outbreaks have subsequently been confirmed at multiple farms in Utah, Michigan, Wisconsin, and Oregon. Although epidemiologic investigations are ongoing, infected workers are the probable source of the virus’s introduction (2).
The first reported SARS-CoV-2 infection in mink occurred in the Netherlands in April 2020 (3). Since then, dozens of farms in Europe have experienced outbreaks, and more than a million mink have been culled (2). Genetic analyses suggest spillover from human infections, and potential zoonotic transmission from mink to a worker is suspected (4). Clinical data from mink infected with SARS-CoV-2 indicate the species is highly susceptible and that infections can range from asymptomatic to peracute (5).
We captured 102 mammals (78 rodents and 24 mesocarnivores). Rodent captures consisted of 45 deer mice (Peromyscus maniculatus), 5 Peromyscus spp. mice, 25 house mice (Mus musculus), and 3 rock squirrels (Otospermophilus variegatus).
Mesocarnivore captures consisted of 11 presumed escaped American mink (Neovison vison), 2 presumed wild American mink, 5 raccoons (Procyon lotor), and 6 striped skunks (Mephitis mephitis). Presumed escaped mink were closely associated with barns and designated as domestic escapees on the basis of location, behavior, and appearance. We identified wild mink by brown coat color and smaller size compared with farmed mink. All escaped mink and rodents, except for 4 deer mice and 1 rock squirrel, were caught on farm premises. All raccoons, the 2 presumed wild mink, and all but 1 striped skunk were captured off-property but within the buffer zone.
Serum samples from the 11 mink escapees tested positive for SARS-CoV-2 antibodies by virus neutralization (Table). No other animal had a detectable antibody response. Of the antibody-positive escaped mink, 3 also had high cycle threshold (Ct) detections by rRT-PCR of nasal swabs (range Ct 35.89–38.95) and 1 lung tissue specimen (Ct 39.2 for N1). A rectal swab specimen from a house mouse had a high Ct detection by rRT-PCR but was negative for SARS-CoV-2 antibodies. N1 alone was detected by rRT-PCR in 2 samples from deer mice (Ct 37.55 and 39.57).
Although we did not find evidence for SARS-CoV-2 establishment in wildlife, the discovery of escaped mink with the opportunity to disperse and interact with susceptible wildlife, such as wild mink or deer mice, is concerning.
Dr. Shriner is a wildlife epidemiologist at the US Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center. Her primary research interests are wildlife epidemiology and disease ecology.
One way it could conceivably do that is to adapt to, and establish itself, in other species.