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Two-way transmission of coronavirus confirmed between humans and minks

Genetic studies of SARS-CoV-2 outbreaks on 16 mink farms in the Netherlands have revealed two-way virus transmission between humans and minks. The authors of the AAAS study found that the virus was initially introduced by humans, and has since evolved. 

“More research in minks and other mustelid species is important to understand if these species are at risk of becoming a reservoir of SARS-CoV-2,” wrote the experts.

The coronavirus has been confirmed in farmed minks across six known countries so far, including Spain, Sweden, Italy, the Netherlands, Denmark. and the United States, according to the World Health Organization (WHO).

Even after more than 1.2 million people have died from COVID-19, the animal that initially transmitted the coronavirus to humans has not been identified. At the same time, several animals have been shown to be susceptible to the virus. 

“Available evidence suggests that the virus is predominantly transmitted between people through respiratory droplets and close contact, but there are also examples of transmission between humans and animals,” wrote the WHO. “Several animals that have been in contact with infected humans, such as minks, dogs, domestic cats, lions and tigers, have tested positive for SARS-CoV-2.”

“Minks were infected following exposure from infected humans. 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, spill-back (human to mink transmission) can occur.” 

The WHO said that it is a serious concern when any animal virus spills into the human population, or when an animal population could contribute to amplifying and spreading a virus affecting humans.

“As viruses move between human and animal populations, genetic modifications in the virus can occur. These changes can be identified through whole genome sequencing, and when found, experiments can study the possible implications of these changes on the disease in humans.”

After the coronavirus was first diagnosed on two mink farms in late April of 2020, the Dutch national response system for zoonotic diseases was activated. A team of experts led by Dr. Bas Oude Munnink set out to investigate using SARS-CoV-2 diagnostics, whole-genome sequencing, and in-depth interviews with farm workers. 

By the end of June, nearly 70 percent of the mink farm residents, employees and/or contacts that were tested had SARS-CoV-2 infection. The analysis of the mink virus genomes on these farms revealed a diversity of sequences. 

According to the researchers, large clusters of infection were initiated by human COVID-19 cases with viruses that bear the D614G mutation. The genetic sequencing also revealed that some people were infected with strains of the virus that had an animal signature, which provides direct evidence of animal to human transmission. 

The researchers did not find any indication of spillover to people living in close proximity to mink farms. They concluded that it is imperative that the fur production and trading sector does not become a reservoir for future spillover of SARS-CoV-2 to humans.

The study is published in the journal Science.

By Chrissy Sexton, Staff Writer

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