Covid 19 coronavirus: The virus kills mink, so they too may get a vaccine

Minks are known to have been infected with SARS-CoV-2, the pandemic virus, in a half-dozen countries around the world. Photo / 123rf

At least two American companies, as well as Russian researchers, are working on coronavirus vaccines for mink. The animals have grown sick and died in large numbers from the virus, which they have also passed back to people in mutated form.

Zoetis, a large veterinary pharmaceutical company in New Jersey with more than $6 billion in annual revenue in 2019, and Medgene Labs, a small company with about 35 employees that is based in South Dakota, are both testing vaccines in mink. They are seeking licensing of their products from the U.S. Department of Agriculture.

Both companies said their vaccine technologies are generally similar to the one used by Novovax for a human vaccine, which is in late-stage trials. That system involves making insect cells produce the spike protein on the coronavirus, which is then attached to a harmless virus that enters into the body's cells and trains the immune system to be ready for the real thing.

Minks are known to have been infected with SARS-CoV-2, the pandemic virus, in a half-dozen countries around the world.

All members of the weasel family are susceptible to infection and to developing some symptoms and passing on the virus, at least to others of their species. That is partly because of the proteins on the surfaces of their cells and because of the structure of their respiratory systems. Scientists don't know why mink in particular seem to get very sick, but the crowded, caged conditions on farms may result in exposure to higher amounts of virus.

The most serious outbreak was in Denmark, which has shut down mink farming until at least 2022 because of mutations to the virus that occurred in infected mink.

Late in the fall, Denmark ordered the slaughter of up to 17 million of the animals. Most of the dead mink were not allowed to be skinned for the fur trade. In average years, the country sells up to 17 million pelts, but last year's decision killed its breeding stock as well, and there are fears that the industry will not recover.

In the United States, by contrast, about 275 mostly small mink farms produce about 3 million pelts annually, according to an industry group, Fur Commission USA. Thousands of U.S. minks have been infected and have died, but states have dealt with the problem, quarantining some farms. The Agriculture Department has not become involved, and there have been no orders to kill mink populations, as in Denmark.

Still, the mink infections in the United States do pose a threat to public health. At least two minks that have escaped from the farms have tested positive. And one wild mink tested positive. Scientists worry that if the virus spreads to more wild mink or to other animals, it could become established in natural populations and form a reservoir from which it could emerge, perhaps in mutated form, to reinfect humans at another time.

So far the mutations observed in Danish mink have not turned out to be a problem. But mutations in the virus in infected humans have produced at least two variants that are more infectious. Allowing a second species, mink, to serve as another breeding ground for the virus adds to the chances of mutation as well as of escape into other animals. Consequently, a mink vaccine could have value beyond the industry. And although the Agriculture Department is not now considering any applications for vaccines for cats and dogs, that is a possibility that the companies are considering.

Zoetis produces many livestock and dog and cat vaccines. For pets, it makes vaccines for canine infectious respiratory disease, feline leukemia virus and others. The company began its work on an animal vaccine in February at the beginning of the pandemic.

"When we saw the first case of a dog getting infected in Hong Kong, we immediately put into action our normal procedures for developing an emerging infectious disease vaccine," said Mahesh Kumar, senior vice president of global biologics for Zoetis. "We decided to prepare a vaccine for dogs and cats."

Once the news of mink infections broke, however, the company approached the U.S. Agriculture Department and received permission to test the vaccine in minks. In the past, the path from testing to licensing for other vaccines took several months.

Kumar pointed out that veterinary coronavirus vaccines are common, such as those for avian infectious bronchitis. The disease was first identified in the 1930s, and a number of companies make vaccines.

Medgene, a small company in its early stages, began working on a technology for coronavirus vaccines for animals in response to a devastating disease that struck pigs in China in 2013, porcine epidemic diarrhoea virus. Mark Luecke, the company's chief executive, said that as soon as news of the pandemic had broken last year, and the coronavirus was identified and its genetic sequence described, a team "immediately started working on a vaccine that would be suitable for animals."

Because the company didn't know which animals would be susceptible, it began, as human vaccine developers usually do, testing it in mice. When it turned out mink were particularly susceptible, the company contacted people in the mink industry and started testing the virus. Luecke said it should be feasible to produce it this spring, pending licensing.

Outside the United States, other researchers are also working on mink vaccines. Researchers in Russia and Finland are pursuing animal vaccines that could be used for mink and other animals.

Written by: James Gorman
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