Several countries have reported instances of H5N1 avian flu infections in mammals, but now Spanish researchers have reported the first known outbreak in farmed mink. They described their investigation yesterday in Eurosurveillance.
The outbreak began in early October 2022 at a farm housing nearly 52,000 mink in Galicia region in northwest Spain. Farm workers noted a sharp increase in deaths, and nasopharyngeal swabbing of the mink revealed H5N1 avian influenza. The mortality rate increased each week, spreading from hot spots to the rest of the barns, peaking toward the end of October.
The mink were housed in partially open barns and were fed raw fish, poultry byproducts sourced from the same region, and other items.
Potential public health implications
A more detailed genetic analysis of the H5N1 virus found that it belonged to the current clade circulating in wild birds and poultry on multiple continents and is most closely related to a strain found in seabirds across Europe.
The scientists found that the H5N1 virus has an uncommon mutation that was seen only once before in a European polecat and that it could have arisen on its own in the mink. They said the mutation in the PB2 gene may have public health implications, given that it is present in the avian-like PB2 gene of the 2009 H1N1 pandemic flu virus and has characteristics that enable recognition by human airway receptor cells.
The virus was involved in wild bird deaths in Galicia in the weeks leading up to the mink farm outbreak, and the birds could have introduced the virus to the farm, given that the barns were partially open. The researchers said, however, that more sequencing is needed to confirm the connection. They added that no avian flu outbreaks had been reported at poultry farms that supplied byproducts to the mink farm.
No related human infections were found at the farm. Spanish mink farm workers are required to wear masks because of the risks of SARS-CoV-2 in those setting. The authors said more studies are under way to look at virulence and transmissibility of the virus. Since mink have been suggested as a possible mixing vessel for respiratory viruses, the group emphasized that interventions are needed to prevent contact between mink and wild animals and to control transmission between farm works and mink.