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 already knew that mink were a potential reservoir for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Earlier outbreaks in the Netherlands and Denmark revealed the virus could spread rapidly within mink farms.  

An epidemiological investigation of mink farm outbreaks in Fraser Health found SARS-CoV-2 was likely transmitted from humans to mink (anthropogenic transmission) and from mink to humans (zoonotic transmission).

In two outbreaks where both human and mink infections were detected, mink farm staff were symptomatic before detection in the minks, and the viral makeup from mink and human-derived samples were 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 the risk of humans acquiring COVID-19 from mink 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. While vaccination of farmworkers and enhanced biosecurity practices reduced the risk of transmission on farms, those measures did not fully eliminate mink-to-human transmission from the established “mink
reservoir.”

“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 to help minimize the impact. 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.