The virus, a highly pathogenic avian influenza A (H5N1), killed 4.3% of all the mink on the farm in the Galicia region in a single week during the outbreak. In response to the outbreak, which occurred in October last year, the Galician government culled 52,000 mink on the farm. The farm’s 11 workers tested negative for the virus.

Just weeks before the mink started dying, 27 seabirds were found dead or sickened by a similar virus in the same area. The same strain has also infected wild birds and poultry across Europe.

Spanish scientists conducted genomic analysis of the viruses, which showed that the virus could have passed from a wild bird to the mink, and evidence supported that the virus mutated to be able to spread from mink to mink.

The virus’s ability to jump from birds to mammals is spreading alarm as mink could serve as a “mixing vessel” for the virus so it could eventually spill over into humans. Experimental studies are still ongoing to further explore the transmissibility of the viruses detected in Spain.