Will COVID-19 Establish an Animal Reservoir?
Minks farmed for their fur are acquiring SARS-CoV-2 from humans and transmitting it back, a classic scenario for a possible genetic mutation that could create a mismatch with some vaccines under development, the World Health Organization (WHO) reported.
“Since June 2020, 214 human cases of COVID-19 have been identified in Denmark with SARS-CoV-2 variants associated with farmed minks, including 12 cases with a unique variant, reported on 5 November,” WHO stated. “All 12 cases were identified in September 2020 in North Jutland, Denmark. The cases ranged in age from 7 to 79 years, and eight had a link to the mink farming industry, and four cases were from the local community.”1
While the clinical presentation in humans was similar to other COVID-19 infections, WHO reported a so-called “cluster 5” variant with a combination of previously unobserved mutations.
“Preliminary findings indicate that this particular mink-associated variant identified in both minks and the 12 human cases has moderately decreased sensitivity to neutralizing antibodies,” WHO reported. “Further scientific and laboratory-based studies are required to verify preliminary findings reported and to understand any potential implications of this finding in terms of diagnostics, therapeutics, and vaccines in development.”
To head off the threat, Danish officials are culling more than 17 million farmed minks and will conduct mass PCR testing of the human population in the Jutland area. They are increasing surveillance of the local population to detect all COVID-19 cases, including through population-wide mass PCR testing for the region of North Jutland. Officials also will conduct genetic sequencing of human and mink SARS-CoV-2 to identify the mutated strain. Mitigation efforts include limiting transportation and movement between Jutland and other cities.
“Minks were infected following exposure from infected humans,” WHO reported. “Minks can act as a reservoir of SARS-CoV-2, passing the virus between them, and pose a risk for virus spillover from mink to humans. People can then transmit this virus within the human population. Additionally, spillback (human-to-mink transmission) can occur.”
At the time of this report, Denmark, the Netherlands, Spain, Sweden, Italy, and the United States have reported SARS-CoV-2 in farmed minks.
While the general scientific consensus is epidemic coronaviruses arise from bats, the original severe acute respiratory syndrome (SARS) in 2002 found an intermediate host in palm civets sold at Chinese wet markets.2 Similarly, Middle East respiratory syndrome (MERS) has established a reservoir in camels. Palm civets were aggressively culled, and SARS disappeared. The first MERS cases emerged in 2012, and the link to dromedary camels is now well-established. Due to their central cultural role in the region, camels have not been culled, and MERS still sporadically spread.3
Finding SARS-CoV-2 in minks and, to a lesser extent, other animals, raises the possibility that coronavirus will eventually become endemic through an animal reservoir.
Research on Animals and COVID-19
In addition to minks, the CDC reports ongoing research on a variety of other animals and COVID-19.
“These findings were based on a small number of animals, and do not show whether animals can spread infection to people,” the CDC stated.4
The studies thus far reveal:
- Cats, dogs, ferrets, fruit bats, hamsters, and tree shrews can become infected. They can spread the infection to other animals of the same species in laboratory settings.
- Data suggest dogs can become infected but might not spread the virus to other dogs as easily as cats and ferrets can spread it to other animals of the same species.
- Researchers have studied nonhuman primates as models for human infection. Rhesus macaques, cynomolgus macaques, Grivets, and common marmosets can become infected and sick in lab settings.
- Lab mice, pigs, chickens, and ducks do not appear to catch or spread infection.
- The CDC, the U.S. Department of Agriculture, state public health and animal health officials, and academic partners are working to conduct active surveillance of SARS-CoV-2 in pets, including cats, dogs, and other small mammals, that had contact with a person with COVID-19. The animals are tested for infection and to see whether the pet develops antibodies.
The WHO recommended detailed analyses and scientific studies to better understand the reported mutations. Other key points recommendations in the report:
- “The sharing of full genome sequences of human and animal strains will continue to facilitate detailed analyses by partners.
- “This event highlights the important role that farmed mink populations can play in the ongoing transmission of SARS-CoV-2 and the critical role of strong surveillance, sampling, and sequencing SARS-CoV-2, especially around areas where such animal reservoirs are identified.
- “The preliminary findings by Denmark are globally relevant, and WHO recognizes the importance of sharing epidemiological, virological, and full genome sequence information with other countries and research teams, including through open-source platforms.
- “All countries should enhance surveillance for COVID-19 at the animal-human interface where susceptible animal reservoirs are identified, including mink farms.
- “Strengthen farming biosafety and biosecurity measures around known animal reservoirs to limit the risk of zoonotic events associated with SARS-CoV-2. This includes infection prevention and control measures for animal workers, farm visitors, and those who may be involved in animal husbandry or culling.
- “WHO advises against the application of any travel or trade restrictions for Denmark based on the information currently available on this event.”1
REFERENCES
- World Health Organization. SARS-CoV-2 mink-associated variant strain — Denmark. Nov. 6, 2020. https://www.who.int/csr/don/06-november-2020-mink-associated-sars-cov2-denmark/en/
- World Health Organization. Severe acute respiratory syndrome (SARS). https://www.who.int/health-topics/severe-acute-respiratory-syndrome#tab=tab_1
- World Health Organization. Middle East respiratory syndrome coronavirus (MERS-CoV). https://www.who.int/health-topics/middle-east-respiratory-syndrome-coronavirus-mers#tab=tab_1
- Centers for Disease Control and Prevention. Coronavirus disease 2019: COVID-19 and Animals. Updated Nov. 18, 2020. https://www.cdc.gov/coronavirus/2019-ncov/daily-life-coping/animals.html
Minks farmed for their fur are acquiring SARS-CoV-2 from humans and transmitting it back, a classic scenario for a possible genetic mutation that could create a mismatch with some vaccines under development, the World Health Organization reported.
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