SARS-CoV-2 Adaptation in Mink Farms Raises Concerns of Spillover and Evolution

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The intricate interplay between viruses and their hosts has been a subject of ongoing scientific scrutiny. The emergence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its subsequent global spread, causing the COVID-19 pandemic, brought into sharp focus the dynamics of zoonotic transmission.

The transmission of SARS-CoV-2 from humans to animals, and the potential for reverse spillover, has been extensively documented [11-13]. Following the mass culling of mink in Denmark and the Netherlands due to SARS-CoV-2 outbreaks, the mink industry landscape shifted.

Poland emerged as the prominent mink producer in Europe and the second-largest globally, a surprising feat despite the pandemic’s impact on mink production. This article delves into the detection of a novel, cryptic lineage of SARS-CoV-2 on mink farms in Poland, shedding light on its implications for both animal and human health.

Mink Farms and the Emergence of a Cryptic Lineage

The spotlight turns to Poland, where mink farms have witnessed an unexpected turn of events. Over the span of three months, separate instances of SARS-CoV-2 infections were identified on two mink farms situated in close proximity. Strikingly, the viral strains recovered from these infections exhibited nearly identical genetic sequences, characterized by distinctive mutations such as F486L and N501T in the spike protein.

These mutations raise compelling suspicions of mink adaptation, hinting at the intricate process of viral evolution within a novel host environment.

Intriguingly, the genetic makeup of the identified mink SARS-CoV-2 variant revealed its closest kinship with B.1.1.307 viruses detected in humans across diverse parts of Europe, more than two years prior to its discovery on the mink farms. This temporal disconnect sparks curiosity about the intermediate hosts that could have facilitated this lineage’s establishment in mink populations.

Remarkably, the possibility of wild animal involvement, such as cats or other carnivores, cannot be excluded, especially considering the plausible opportunities for contact between domesticated and wild animals.

Unraveling the Source and Evolution

Efforts to trace the origin of this cryptic lineage face numerous complexities. All mink farms within the region, as well as farm workers and their families, consistently tested negative for the virus, challenging the assumption of a human-mediated introduction. While one hypothesis suggests the introduction of the virus from free-living mink populations observed around farms, empirical validation remains pending [14,15].

The elusive nature of the source animal reservoir complicates pinpointing the exact moment of virus introduction into the mink farms. The relatively modest 40 nucleotide differences from the nearest human virus imply a rapid evolutionary journey within mink populations, underscoring the potential for swift adaptation in novel host environments.

Silent Evolution: Implications for Animal and Human Health

Curiously, the mink on the SARS-CoV-2-positive farms exhibited no overt signs of disease, casting a shadow of uncertainty over the virus’s adaptation process. The absence of disease symptoms raises the possibility of independent viral evolution, potentially giving rise to future outbreaks with novel strains. This phenomenon not only underscores the virus’s adaptability but also the complexity of assessing its impact on animal health.

As of now, spillback of the cryptic SARS-CoV-2 lineage into the human population remains undetected. However, prudence dictates a robust surveillance system to monitor mink and human populations on these farms more rigorously. This should be augmented with molecular and serological testing of wild animals like feral mink, cats, martens, polecats, and foxes. Such an integrated approach aims to preemptively identify potential transmission pathways and ensure prompt containment measures in the event of cross-species transmission.

Conclusion

The case of the cryptic SARS-CoV-2 lineage detected in mink farms in Poland illuminates the intricate dance between viruses and their hosts. The convergence of factors, including the mink industry’s resurgence amid a pandemic-driven decline, underscores the need for vigilant monitoring and understanding of zoonotic transmission dynamics.

While the exact origin and evolutionary trajectory of this lineage remain enigmatic, its existence necessitates a comprehensive approach to surveillance, testing, and mitigation, aimed at safeguarding both animal and human health. As we venture further into the uncharted territory of viral evolution and host adaptation, this case serves as a poignant reminder of the urgency of interdisciplinary collaboration and proactive measures in the face of emerging infectious threats.


B.1.1.307 is a lineage of SARS-CoV-2, the virus that causes COVID-19. It was first identified in humans in late 2020 and early 2021, and was most common in Europe. However, it has not been seen in humans in over two years.

In late 2022, B.1.1.307 viruses were detected on three mink farms in Poland. The viruses were closely related to B.1.1.307 viruses that had been detected in humans in the same region two years earlier, but they had 40 mutations that were not found in the human viruses. These mutations could have occurred during circulation in mink, or they could have been acquired from an unknown animal reservoir.

It is not yet known whether B.1.1.307 viruses are more transmissible or virulent than other SARS-CoV-2 variants. However, the fact that they have been able to circulate in mink for two years suggests that they may be more adapted to animal hosts than to humans.

The discovery of B.1.1.307 viruses in mink farms in Poland is a reminder that SARS-CoV-2 can continue to circulate in animals, and that it is possible for it to jump back to humans. It is important to continue to monitor the virus for new variants, and to take steps to prevent its spread between animals and humans.

Here are some additional links that you may find helpful:

  • Cryptic SARS-CoV-2 lineage identified on two mink farms as a possible result of long-term undetected circulation in an unknown animal reservoir, Poland, November 2022 to January 2023: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10283451/
  • Study identifies an unknown SARS-CoV-2 lineage on three mink farms in Poland: https://www.news-medical.net/news/20230424/Study-identifies-an-unknown-SARS-CoV-2-lineage-on-three-mink-farms-in-Poland.aspx
  • Researchers detect 2 new SARS-CoV-2 strains on Polish mink farms: https://www.cidrap.umn.edu/covid-19/researchers-detect-2-new-sars-cov-2-strains-polish-mink-farms

reference link: https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2023.28.16.2300188

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