SARS-CoV-2 monitoring on mink farms in Poland

Abstract

Introduction Many countries have reported severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infections in mink, and transmission back to humans has raised the concern of novel variants emerging in these animals. The monitoring system on Polish mink farms detected SARS-CoV-2 infection first in January 2021 and has been kept in place since then. Material and Methods Oral swab samples collected between February 2021 and March 2022 from 11,853 mink from 594 farms in different regions of Poland were screened molecularly for SARS-CoV-2. Isolates from those with the highest loads of viral genetic material from positive farms were sequenced and phylogenetically analysed. Serological studies were also carried out for one positive farm in order to follow the antibody response after infection. Results SARS-CoV-2 RNA was detected in mink on 11 farms in 8 out of 16 Polish administrative regions. Whole genome sequences were obtained for 19 SARS-CoV-2 strains from 10 out of 11 positive farms. These genomes belonged to four different variants of concern (VOC) – VOC-Gamma (20B), VOC-Delta (21J), VOC-Alpha (20I) and VOC-Omicron (21L) – and seven different Pango lineages – B.1.1.464, B.1.1.7, AY.43, AY.122, AY.126, B.1.617.2 and BA.2. One of the nucleotide and amino acid mutations specific for persistent strains found in the analysed samples was the Y453F host adaptation mutation. Serological testing of blood samples revealed a high rate of seroprevalence on the single mink farm studied. Conclusion Farmed mink are highly susceptible to infection with SARS-CoV-2 of different lineages, including Omicron BA.2 VOC. As these infections were asymptomatic, mink may become an unnoticeable virus reservoir generating new variants potentially threatening human health. Therefore, real-time monitoring of mink is extremely important in the context of the One Health approach.

SARS-CoV-2 Outbreaks on Mink Farms—A Review of Current Knowledge on Virus Infection, Spread, Spillover, and Containment

“…Accordingly, the first outbreak of SARS-CoV-2 on mink farms in Poland was detected on 30 January 2021 on one mink farm in North Poland as a result of testing 28 mink farms between November 2020 and January 2021 [ 55 , 56 , 83 ]. Another 13 SARS-CoV-2-positive mink farms were detected through July 2022 [ 56 , 85 ], and an additional 3 positive farms were detected between September 2022 and January 2023 [ 56 ]. Strict biosecurity measures were put in place, and farm workers, owners, and visitors were required to be tested for SARS-CoV-2 regardless of their health status [ 85 ].…”

“…Another 13 SARS-CoV-2-positive mink farms were detected through July 2022 [ 56 , 85 ], and an additional 3 positive farms were detected between September 2022 and January 2023 [ 56 ]. Strict biosecurity measures were put in place, and farm workers, owners, and visitors were required to be tested for SARS-CoV-2 regardless of their health status [ 85 ].…”

“…The source is not clear for most outbreaks in Poland, except one outbreak that occurred in December 2021 that is possibly linked to human introduction [ 85 ]. However, possible zoonotic spread of the virus from infected mink to farm workers was also detected [ 83 , 85 ].…”

“…The source is not clear for most outbreaks in Poland, except one outbreak that occurred in December 2021 that is possibly linked to human introduction [ 85 ]. However, possible zoonotic spread of the virus from infected mink to farm workers was also detected [ 83 , 85 ]. In September 2022 and January 2023, a cryptic variant of SARS-CoV-2 with ≥40 nucleotide changes was detected on two mink farms in close proximity [ 56 ].…”

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

“…From December 2021, all mink farms in Poland were tested for the presence of SARS-CoV-2 according to the scheme which stipulates sampling when disease symptoms or increased mortality were detected in the animals or when workers on the farm were SARS-CoV-2-positive (sample size designed to detect a 50% or 5% prevalence, respectively, with 95% confidence) [5]. The implemented system resulted in the identification of the first positive farm in January 2021, another 13 farms in the following months up to July 2022 [6,7]. These Omicron (21L, one farm, BA.2).…”