Mink culling over SARS-CoV-2 – better safe than sorry?
Author: Ivana Mišová, PhD.
Published at: 12/01/2020
The mass culling of farmed minks due to the spread of the novel coronavirus came as a shock to most. Was it a necessary measure or a better-safe-than-sorry precaution? Should we be wary of not only other people but animals as well?
Can animals get infected?
Coronavirus infection is no novelty in the animal kingdom, as several coronaviruses have been identified in many species. What determines the host range of a virus is the compatibility of the receptors on the virus surface and those on the host cell. SARS-CoV-2 uses its spike protein on the viral surface interacting with ACE-2 as the virus receptor molecules for infection. The similarity of ACE-2 sequences between species is key for SARS-CoV-2 infection – and analysis has shown high sequence similarity among many species, including multiple primates, rodents, and companion, domestic and wild animals, raising an alert on a potential interspecies transmission of SARS-CoV-21.
Human-to-animal transmission of SARS-CoV-2
Soon, the first indications of cross-species transmission emerged. In May, several dogs from households with a confirmed human case of COVID-19 were found to be infected with SARS-CoV-2, although they remained asymptomatic2. There were other sporadic cases of SARS-CoV-2-positive animals living with infected humans3. Even a tiger at a zoo tested positive for SARS-CoV-2 and showed respiratory symptoms4. These occurrences have led to a panic negatively impacting the welfare of pets, although there is no evidence that pets play a significant role in spreading COVID-195.
The case of minks
SARS-CoV-2 infection in mink farms was first reported in April in the Netherlands6. Viral sequence analysis pointed to humans – mink farm workers infected with SARS-CoV-2 – as the probable source of the initial infection. Later, the virus spread among the minks, which even displayed respiratory symptoms, and six more countries have since reported SARS-CoV-2 in farmed minks6,7. However, the virus spreading in minks was subsequently transmitted back to humans. In Denmark, 214 human cases of COVID-19 associated with farmed minks have been identified8. Several of them had a unique variant, referred to as the “Cluster-5” variant.
A combination of mutations with unforeseen impact
With time, viruses – including SARS-CoV-2 – can accumulate mutations and change. What needs to be determined is the impact of these mutations on the virus's characteristics and the subsequent disease. Depending on the type and location of the mutations (read more), it might make no difference in the virus's behavior. However, these mutations could also make the virus more transmissible, deadlier, or potentially jeopardize the effectiveness of COVID-19 therapeutics and vaccines being developed. Cross-species transmission could have led to a unique combination of mutations, like the cluster-5 variant.
In the case of the cluster-5 variant of SARS-CoV-2, preliminary findings indicate that it has moderately decreased sensitivity to neutralizing antibodies8. This suggests that the variant could be less responsive to antibody treatments or vaccines, which led to the decision to cull the farmed minks. Fortunately, the variant hasn't spread widely9. One mink-related mutation – Y453F, leading to an amino acid change in the virus's spike protein – has spread more widely. While data suggests that a SARS-CoV-2 with Y453F mutation partially escapes detection by a commercial antibody, it does not necessarily mean that the mutation will hinder the therapeutic drug's effect9.
The aftermath of the mink culling
With a potential threat to the multiple promising vaccines just around the corner, it is not shocking that the more radical measures have been taken. Nevertheless, the legally unsupported decision to order about 15 million minks to be killed cost the Danish agriculture minister his position10. Yet, a thorough analysis is essential so that the preliminary data is not given too much weight. While we need to be mindful of other potential sources of SARS-CoV-2 infection, human-to-human transmission remains the main threat.
- Li, S. Qiao, and G. Zhang, “Analysis of angiotensin-converting enzyme 2 (ACE2) from different species sheds some light on cross-species receptor usage of a novel coronavirus 2019-nCoV,” Journal of Infection, vol. 80, no. 4. W.B. Saunders Ltd, pp. 469–496, 01-Apr-2020.
- Sit, T.H.C., Brackman, C.J., Ip, S.M. et al. Infection of dogs with SARS-CoV-2. Nature 586, 776–778 (2020). https://doi.org/10.1038/s41586-020-2334-5
- M. A. Parry, “COVID-19 and pets: When pandemic meets panic,” Forensic Sci. Int. Reports, vol. 2, p. 100090, Dec. 2020.
- Oreshkova et al., “SARS-CoV-2 infection in farmed minks, the Netherlands, April and May 2020,” Eurosurveillance, vol. 25, no. 23, p. 2001005, Jun. 2020.