A recent study published in the One Health Advances Journal discussed influenza A virus (IAV) infections in minks, emphasizing their contribution/role as an intermediate host.
Study: Mink infection with influenza A viruses: an ignored intermediate host? Image Credit: shauttra/Shutterstock.com
IAVs infect different hosts, including humans, birds, and marine mammals. Studies have demonstrated mink infection with IAV subtypes and viral transmission via aerosols. Mink infection with avian H5N1, H9N2, H5N6, and human or swine H1N1 and H3N2 viruses has been reported.
Sequence data from the Global Initiative for Sharing Avian Influenza Data (GISAID) repository shows that the rate of IAV detection in mink has increased considerably over the past decade.
Although minks are highly susceptible to IAV infection, outbreaks with severe outcomes are rare. Studies suggest that animal feed containing pork and poultry by-products might be responsible for mink infection with swine/avian IAVs.
In contrast, mink infection with the human influenza virus could be due to transmission from farm workers. In the present study, the authors summarized the evidence on mink infections with IAVs, focusing on their role as intermediate hosts.
Mink infection with emergent viruses
China has witnessed multiple outbreaks of viral infections in mink farms since 2010. A novel orthoreovirus was detected in Hebei, with a mortality rate of 5%. In 2014, a swine pseudorabies outbreak was documented in Shandong, with a high rate of mortality estimated at 87%. Newcastle disease virus was responsible for pneumonia and hemorrhagic encephalitis in mink in 2014.
In 2015, the highly pathogenic avian influenza virus (HPAIV) H5N1 caused outbreaks in two farms in China, with mortality estimated at 56% and 64%, respectively. Mink infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has increased, particularly in North American and European countries.
Moreover, SARS-CoV-2 transmission from infected minks to humans was documented in Denmark and the Netherlands. Reassortment and adaptation are suggested as critical for zoonotic influenza viruses in humans. In addition, co-infection with different viruses in animals/humans might result in novel strains with pandemic potential.
Pigs are considered the mixing vessel as they harbor receptors for human and avian influenza viruses. Likewise, minks exhibit a similar feature, as they have both sialic acid α2,3-galactose (SA α2,3-Gal) and SA α2,6-Gal receptors for avian and human strains, respectively. Therefore, minks could represent another mixing vessel for novel strain(s).
Mink farms and infectious diseases
Neovison vison, the American mink, is an important species for the fur-farming industry. China, Poland, Denmark, and the Netherlands are the major fur-producing countries. Most minks (80%) in China are farmed in the Shandong province.
Minks are densely populated on these farms and likely sheltered in a single facility/building. Thus, infectious diseases occur due to intensive farming, inadequate biosecurity, and poor sanitation.
Aleutian mink disease virus (AMDV) is notable for its devastating effects on the adult reproductive system and the subsequent impact on fur quality.
Gastroenteric and respiratory symptoms are caused due to canine distemper virus (CDV), SARS-CoV-2, and mink enteritis virus (MEV). Bacteria such as Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa are implicated in hemorrhagic pneumonia.
Molecular and serologic features of influenza virus infection in minks
Sequences from the GISAID repository show that IAVs detected in minks are phylogenetically related to prevailing human, avian, and swine strains.
H9N2 and H5N6/H5N1 have been the predominant mink influenza virus subtypes in China since 2013. Genetic analyses revealed that all H9N2 viruses detected in minks belonged to G9/Y280 lineage, prevalent in poultry.
All H5N1 and H5N6 subtypes detected in China and Spain, except for one H5N1 subtype in Sweden, were likely introduced in minks from infected poultry.
Molecular analyses revealed mammalian adaptive signatures (D701N and E627K substitutions) in the polymerase basic 2 (PB2) gene. Numerous studies have assessed the seroprevalence of avian IAVs in minks.
Seropositivity was the highest for H9N2 among all subtypes in minks, ranging between 20% and 47.5% during 2013-19, and much lower for H5N6 and H5N1. Seroepidemiologic data show that minks in China are highly exposed to human and avian influenza viruses, increasing the risk of novel variants due to co-infection.
Taken together, high susceptibility to and receptors for human and avian influenza viruses in minks meet the prerequisites to serve as the intermediate host for interspecies influenza transmission.
Therefore, routine surveillance of IAVs in minks and preventive measures should be implemented. Vaccination against influenza should be introduced in the mink populations for public health and industrial benefits.