A report co-authored by Fraser Health Medical Health Officer Dr. Emily Newhouse and published by the Public Health Agency of Canada sheds light on the public health response to COVID-19 outbreaks at mink farms.
When workers at mink farms in the Fraser Valley first tested positive for COVID-19 in late 2020, public health teams were already aware that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) had spread rapidly during earlier outbreaks within mink farms in the Netherlands and Denmark.
An investigation of mink farm outbreaks in Fraser Health found SARS-CoV-2 was likely transmitted from humans to mink (anthropogenic transmission) as well as from mink to humans (zoonotic transmission).
In two outbreaks where both human and mink infections were detected, farm staff were symptomatic before detection in the minks. As well, the viral makeup from mink and human-derived samples was closely related.
“We found that SARS-CoV-2 was most likely introduced into farmed mink by farm staff, where it then evolved in the mink before being reintroduced into humans,” says Dr. Newhouse.
The evidence gathered from the mink farm outbreaks — the first such outbreaks documented in Canada — suggested that the risk of humans acquiring COVID-19 from minks can last for months during longer outbreaks in mink herds.
According to the report, quarantine of infected farms, isolation of infected workers and their close contacts and enhanced infection control practices helped to break the chains of transmission. And while vaccination of farm workers and enhanced biosecurity practices reduced the risk of transmission on farms, those measures did not fully eliminate mink-to-human transmission.
“What this means is that conditions in the environment enabled the virus to persist in the mink herd and potentially spread to humans,” says Dr. Newhouse. “The information we gathered during the course of the public health response to the COVID-19 outbreaks at mink farms will help to inform our response to zoonotic diseases in the future.”
The public health response to the mink farm outbreaks took a “One Health” approach, with multiple agencies all contributing expertise. A working group which included a Fraser Health medical health officer, environmental health officer, communicable disease nurse coordinator, cluster investigator and analyst helped guide the outbreak response.
