SARS-CoV-2 in a Mink Farm in Italy: Case Description, Molecular and Serological Diagnosis by Comparing Different Tests

Abstract

This study described a SARS-CoV-2 infection in minks on an Italian farm. Surveillance was performed based on clinical examination and a collection of 1879 swabs and 74 sera from dead and live animals. The farm was placed under surveillance for 4.5 months, from the end of July 2020, when a man working on the farm tested positive by RT-PCR, till mid-December 2020 when all the animals were sacrificed. Clinical examination revealed no clinical signs or increased mortality rates attributable to SARS-CoV-2, while diagnostic tests detected only four weak PCR-positive samples, but 100% of sera were positive for SARS-CoV-2 anti-S antibodies. The phylogenetic analysis of two SARS-CoV-2 sequences from two minks and the sequence of the worker showed that they belonged to different clades. It could be therefore assumed that two distinct introductions of the virus occurred on the farm, and that the first introduction probably occurred before the start of the surveillance period. From the data collected, and especially from the detection of specific antibodies through the combination of different tests, it can be postulated that syndromic surveillance combined with genome detection by PCR may not be sufficient to achieve a diagnosis in asymptomatic animals. In particular, the serological approach, especially when using tests directed towards the S protein, may be useful for improving the traceability of virus circulation in similar environments.

A comparison of sampling and testing approaches for the surveillance of SARS-CoV-2 in farmed American mink

“…This is particularly important given that outbreaks may not be associated with any clinical signs or increased mortality in infected mink. 2,24 We found that there was a small but significant difference between RT-rtPCR assays targeting the SARS-CoV-2 E versus RdRp gene. Both assays were clearly capable of detecting the 3 different strains of virus circulating on the 3 infected farms and in different sample types.…”

“…The clinical presentation and epidemiology of these outbreaks have been somewhat variable. In some, infection of mink on affected farms has occurred in the absence of visible disease 2,24 ; in other cases, there has been increased mortality as well as clinical signs including reduced feed intake, nasal discharge, respiratory distress, and diarrhea. 4,23,33 Postmortem examinations of naturally and experimentally infected mink have indicated that SARS-CoV-2 primarily affects the respiratory tract causing rhinitis and interstitial pneumonia.…”

“…To date, the World Organisation for Animal Health recommends against the selling of raw pelts because of biosecurity risks. 24 However, there are very few reports of SARS-CoV-2 on the fur or pelts from infected mink. 1,4 The degree to which pelts from infected animals are contaminated is important because this is the purpose for which mink are produced, and the inability to sell pelts as a result of bio-security risks has adverse economic impacts on infected farms.…”

“…Serology is often used in partnership with RT-rtPCR testing given that seropositivity can indicate that animals have been exposed to SARS-CoV-2 even if they are RT-rtPCR–negative. 2,24 The correlation between RT-rtPCR and serology results appears to vary based on the timeline of an outbreak, with RT-rtPCR–positive animals being more common than seropositive animals during the prodromal period and period of disease, whereas the reverse is true during periods of decline and convalescence. 4 However, little is known about the correlation between RT-rtPCR and serology results within an individual animal.…”

SARS-CoV-2 and animals, a long story that doesn't have to end now: What we need to learn from the emergence of the Omicron variant

“…In certain cases, human-to-animal transmission led to onward epizootic circulation of SARS-CoV-2, as in the case of farmed American minks reported from many European and American Countries ( 39 , 54 – 56 ), and of white-tailed deer ( Odocoileus virginianus ) in North America ( 11 , 12 ) ( Figure 1 ). Transmission within animal populations may promote the origin of new variants as a consequence of evolutionary changes in the virus.…”