One Health Investigation of SARS-CoV-2 in People and Animals on Multiple Mink Farms in Utah

Abstract

From July−November 2020, mink (Neogale vison) on 12 Utah farms experienced an increase in mortality rates due to confirmed SARS-CoV-2 infection. We conducted epidemiologic investigations on six farms to identify the source of virus introduction, track cross-species transmission, and assess viral evolution. Interviews were conducted and specimens were collected from persons living or working on participating farms and from multiple animal species. Swabs and sera were tested by SARS-CoV-2 real-time reverse transcription polymerase chain reaction (rRT-PCR) and serological assays, respectively. Whole genome sequencing was attempted for specimens with cycle threshold values <30. Evidence of SARS-CoV-2 infection was detected by rRT-PCR or serology in ≥1 person, farmed mink, dog, and/or feral cat on each farm. Sequence analysis showed high similarity between mink and human sequences on corresponding farms. On farms sampled at multiple time points, mink tested rRT-PCR positive up to 16 weeks post-onset of increased mortality. Workers likely introduced SARS-CoV-2 to mink, and mink transmitted SARS-CoV-2 to other animal species; mink-to-human transmission was not identified. Our findings provide critical evidence to support interventions to prevent and manage SARS-CoV-2 in people and animals on mink farms and emphasizes the importance of a One Health approach to address emerging zoonoses.

Keywords: COVID-19; Neogale vison; One Health; SARS-CoV-2; animals; coronavirus; mink; zoonotic transmission.

Figure 1

Timeline of symptom onset and SARS-CoV-2 laboratory confirmation in farm workers and in mink relative to onset of increased mortality in mink on Farms A and B. * A1 left work early on 1 August with symptoms but was not tested for SARS-CoV-2 until 9 October (tested positive). ** A2 and A4 both had symptomatic household contacts that tested SARS-CoV-2-positive on 10 and 13 August, respectively. A2 would remain asymptomatic, but ultimately tested positive on 21 August. *** Reported clinical signs in mink included non-specific (e.g., inappetence, lethargy) and respiratory (e.g., sneezing, coughing, nasal and ocular discharge, labored breathing) symptoms. ^† B1 symptoms resolved on 9 August. NP swab was collected from B1 on 23 August, and the result on SARS-CoV-2 rRT-PCR was indeterminant. B1′s first positive result was not until 13 October.

Figure 2

Animal serology. Results of the mix-and-read assay are presented for each tested farm, species, and time-point. The dotted line indicates assay cut-off (2.5; 2.8 used for cats). Connected dots represent re-sampling of the same animal. Mink values are derived from diluted sample specimen results as described in methods. For mink, means of log-transformed values are shown by horizontal lines.

Figure 3

Panel (A) SARS-CoV-2 phylogenetic tree including 2250 randomly sampled sequences from human specimens in Utah and sequences from this study. Farm sequences fell onto two branches with zoom-in view of clades 20C group (Panel (B); Farms A and B) and 20A group (Panel (C); Farms C–F). Sequences are color-coded by farms of origin, and sequences from non-mink hosts are labeled in red with host species.