Nov 13 2020
While animal coronavirus research in the Whittaker lab is centered on felines and FIP, our studies also extend to other species, with mustelids of particular interest. Mustelids include ferrets and mink, and are the only other species to have an FIP-like disease; in ferrets this is called ferret systemic coronaviral disease or FSCD, with systemic mink diseases remaining unexplored. We have recently reported on FCSD, and one open question is whether the ferret coronavirus undergoes “internal mutation” that gets selected to become a systemic virus as with feline coronaviruses—current data are far from clear on this.
Along with cats, mustelids are of interest in connection to the COVID-19 pandemic and their ability to be infected with SARS-CoV-2. As described in our article earlier this year, the human and feline versions of the SARS-CoV-2 receptor (ACE2) are quite close, suggesting a route for the “spillover” seen—but this does not apply to mustelids. Ferrets are as susceptible as cats in experimental challenge, with animal-animal but likely not animal-human transmission occurring in both cases. Mink are a very different story; they have been linked to “spill-back” events earlier in the summer in the Netherlands, and most dramatically a widespread outbreak in mink in Denmark had led to the documented spill-back infections of humans, a regional lock-down and the order to euthanize the entire mink population of Denmark (approximately 15 million animals). This draconian approach was fueled by fears that mink harbored a mutant virus that would not be susceptible to the COVID vaccine. Thankfully, the order to cull is being reconsidered based in part on a more rational understanding of the “mutant” virus.
As proposed in a recent commentary, we need to realize that viruses mutate all the time and are really better referred to as “variants”. What is important is that most mutants (or variants) are less successful as viruses—they are less “fit”. Some are neutral and a few are “fitter”. These variants should not be ignored, and it important to track and understand variants when they arise, but not to automatically assume a doomsday scenario when viruses change (which they do all the time). The sequences of the SARS-CoV-2 viruses found in mink are summarized here. Two of these variants have some evidence of functional effects in that they may improve receptor binding and/or help to evade certain antibodies This does not necessarily mean that they will reduce vaccine efficacy. Most of these variants are also found in humans across the world and on balance are likely to be only modestly different to other SARS-CoV-2 viruses.
There are many arguments for eliminating mink ranches, but the uncontrolled culling of massive numbers of animals in a very short space of time under the guise of a public health vaccine-failure emergency, should not be one of them. It is more important to improve biosecurity and testing measures to ensure that transmission to other animal species, especially free-ranging wildlife, does not occur.