Characterization of H5N1 highly pathogenic mink influenza viruses in eastern China

Exploring Potential Intermediates in the Cross-Species Transmission of Influenza A Virus to Humans

The influenza A virus (IAV) has been a major cause of several pandemics, underscoring the importance of elucidating its transmission dynamics. This review investigates potential intermediate hosts in the cross-species transmission of IAV to humans, focusing on the factors that facilitate zoonotic events. We evaluate the roles of various animal hosts, including pigs, galliformes, companion animals, minks, marine mammals, and other animals, in the spread of IAV to humans.

Characterization of neurotropic HPAI H5N1 viruses with novel genome constellations and mammalian adaptive mutations in free-living mesocarnivores in Canada

The GsGd lineage (A/goose/Guangdong/1/1996) H5N1 virus was introduced to Canada in 2021/2022 through the Atlantic and East Asia-Australasia/Pacific flyways by migratory birds. This was followed by unprecedented outbreaks affecting domestic and wild birds, with spillover into other animals. Here, we report sporadic cases of H5N1 in 40 free-living mesocarnivore species such as red foxes, striped skunks, and mink in Canada. The clinical presentations of the disease in mesocarnivores were consistent with central nervous system infection. This was supported by the presence of microscopic lesions and the presence of abundant IAV antigen by immunohistochemistry. Some red foxes that survived clinical infection developed anti-H5N1 antibodies. Phylogenetically, the H5N1 viruses from the mesocarnivore species belonged to clade 2.3.4.4b and had four different genome constellation patterns. The first group of viruses had wholly Eurasian (EA) genome segments. The other three groups were reassortant viruses containing genome segments derived from both North American (NAm) and EA influenza A viruses. Almost 17 percent of the H5N1 viruses had mammalian adaptive mutations (E627 K, E627V and D701N) in the polymerase basic protein 2 (PB2) subunit of the RNA polymerase complex. Other mutations that may favour adaptation to mammalian hosts were also present in other internal gene segments. The detection of these critical mutations in a large number of mammals within short duration after virus introduction inevitably highlights the need for continually monitoring and assessing mammalian-origin H5N1 clade 2.3.4.4b viruses for adaptive mutations, which potentially can facilitate virus replication, horizontal transmission and posing pandemic risks for humans.

Zoonotic Animal Influenza Virus and Potential Mixing Vessel Hosts

Influenza viruses belong to the family Orthomyxoviridae with a negative-sense, single-stranded segmented RNA genome. They infect a wide range of animals, including humans. From 1918 to 2009, there were four influenza pandemics, which caused millions of casualties. Frequent spillover of animal influenza viruses to humans with or without intermediate hosts poses a serious zoonotic and pandemic threat. The current SARS-CoV-2 pandemic overshadowed the high risk raised by animal influenza viruses, but highlighted the role of wildlife as a reservoir for pandemic viruses. In this review, we summarize the occurrence of animal influenza virus in humans and describe potential mixing vessel or intermediate hosts for zoonotic influenza viruses. While several animal influenza viruses possess a high zoonotic risk (e.g., avian and swine influenza viruses), others are of low to negligible zoonotic potential (e.g., equine, canine, bat and bovine influenza viruses). Transmission can occur directly from animals, particularly poultry and swine, to humans or through reassortant viruses in "mixing vessel" hosts. To date, there are less than 3000 confirmed human infections with avian-origin viruses and less than 7000 subclinical infections documented. Likewise, only a few hundreds of confirmed human cases caused by swine influenza viruses have been reported. Pigs are the historic mixing vessel host for the generation of zoonotic influenza viruses due to the expression of both avian-type and human-type receptors. Nevertheless, there are a number of hosts which carry both types of receptors and can act as a potential mixing vessel host. High vigilance is warranted to prevent the next pandemic caused by animal influenza viruses.

Mink infection with influenza A viruses: an ignored intermediate host?

Continuously emergence of human infection with avian influenza A virus poses persistent threat to public health, as illustrated in zoonotic H5N1/6 and H7N9 infections. The recent surge of infection to farmed mink by multiple subtypes of avian influenza A viruses in China highlights the role of mink in the ecology of influenza in this region. Serologic studies suggested that farmed mink in China are frequently infected with prevailing human (H3N2 and H1N1/pdm) and avian (H7N9, H5N6, and H9N2) influenza A viruses. Moreover, genetic analysis from the sequences of influenza viruses from mink showed that several strains acquired mammalian adaptive mutations compared to their avian counterparts. The transmission of SARS-CoV-2 from mink to human alerts us that mink may serve as an intermediate host or reservoir of some emerging pathogens. Considering the high susceptibility to different influenza A viruses, it is possible that mink in endemic regions may play a role as an "mixing vessel" for generating novel pandemic strain. Thus, enhanced surveillance of influenza viruses in mink should be urgently implemented for early warning of potential pandemic.

Comparative Antigenicity and Pathogenicity of Two Distinct Genotypes of Highly Pathogenic Avian Influenza Viruses (H5N8) From Wild Birds in China, 2020-2021

To date, there have been three epidemic waves of H5N8 avian influenza worldwide. The current third epidemic wave began in October 2020 and has expanded to at least 46 countries. Active and passive surveillance were conducted to monitor H5N8 viruses from wild birds in China. Genetic analysis of 10 H5N8 viruses isolated from wild birds identified two different genotypes. Animal challenge experiments indicated that the H5N8 isolates are highly pathogenic in chickens, mildly pathogenic in ducks, while pathogenicity varied in BALB/c mice. Moreover, there were significant differences in antigenicity as compared to Re-11 vaccine strain and vaccinated chickens were not completely protected against challenge with the high dose of H5N8 virus. With the use of the new matched vaccine and increased poultry immune density, surveillance should be intensified to monitor the emergence of mutant strains and potential worldwide spread via wild birds.

Phylogenetic and phenotypic characterization of two novel clade 2.3.2.1 H5N2 subtype avian influenza viruses from chickens in China

The extended co-circulation of H5 subtype highly pathogenic avian influenza (HPAI) viruses and H9N2 low pathogenic avian influenza (LPAI) viruses has inevitably facilitated gene reassortment between the two subtypes in fields. And, novel reassortant H5NX viruses harboring partial or even whole sets of H9N2 internal genes have continuously been detected, such as clade 2.3.4.4 H5N2 or H5N6 reassortants. Here, we report two novel H5N2 subtype HPAI isolates of HF9 and QY5 from chickens in live poultry markets during routine surveillance in 2018. Phylogenetic analysis showed that those two H5N2 strains both possessed the HA genes from clade 2.3.2.1e of H5N1 viruses but all the other seven gene segments consistently from the endemic S genotype of H9N2 subtype viruses. Further analysis revealed that HF9 and QY5 differed only in six sites including K353R, A588T and T661I in PB2, I682V and L704S in PB1 plus G631S in PA at the amino acid level. A chicken regression experiment confirmed that both HF9 and QY5 were lethal infection to all tested chickens via contact transmission. Moreover, those two isolates could immediately replicate in mice lungs without adaptation. However, mortality rate of those two variants were distinct in mice model, HF9 with 100% but QY5 with just 20% at the infection dosage of 10^6.0EID₅₀ per mouse. We suppose that the phenotypic difference may probably be attributed to the amino acid substitutions in the polymerase genes between the two isolates that constitute of a subject of further ongoing research.

Surveillance and control of SARS-CoV-2 in mustelids: An evolutionary perspective

The relevance of mustelids in SARS-CoV-2 transmission has become increasingly evident. Alongside experimental demonstration of airborne transmission among ferrets, the major animal model for human respiratory diseases, transmission of SARS-CoV-2 within- and/or between-commercial mink farms has occurred and continues to occur. The number of mink reared for the luxury fur trade is approximately 60.5 million, across 36 mustelid-farming countries. By July 2021, SARS-CoV-2 outbreaks have been reported in 12 of these countries, at 412 European and 20 North American mink farms. Reverse zoonotic transmission events (from humans to mink) have introduced the virus to farms with subsequent extensive mink-to-mink transmission as well as further zoonotic (mink-to-human) transmission events generating cases among both farm workers and the broader community. Overcrowded housing conditions inherent within intensive mink farms, often combined with poor sanitation and welfare, both guarantee spread of SARS-CoV-2 and facilitate opportunities for viral variants, thereby effectively representing biotic hubs for viral transmission and evolution of virulence. Adequate preventative, surveillance and control measures within the mink industry are imperative both for the control of the current global pandemic and to mitigate against future outbreaks.

Influenza A Viruses and Zoonotic Events-Are We Creating Our Own Reservoirs?

Zoonotic infections of humans with influenza A viruses (IAVs) from animal reservoirs can result in severe disease in individuals and, in rare cases, lead to pandemic outbreaks; this is exemplified by numerous cases of human infection with avian IAVs (AIVs) and the 2009 swine influenza pandemic. In fact, zoonotic transmissions are strongly facilitated by manmade reservoirs that were created through the intensification and industrialization of livestock farming. This can be witnessed by the repeated introduction of IAVs from natural reservoirs of aquatic wild bird metapopulations into swine and poultry, and the accompanied emergence of partially- or fully-adapted human pathogenic viruses. On the other side, human adapted IAV have been (and still are) introduced into livestock by reverse zoonotic transmission. This link to manmade reservoirs was also observed before the 20th century, when horses seemed to have been an important reservoir for IAVs but lost relevance when the populations declined due to increasing industrialization. Therefore, to reduce zoonotic events, it is important to control the spread of IAV within these animal reservoirs, for example with efficient vaccination strategies, but also to critically surveil the different manmade reservoirs to evaluate the emergence of new IAV strains with pandemic potential.

Mink is a highly susceptible host species to circulating human and avian influenza viruses

Pandemic influenza, typically caused by the reassortment of human and avian influenza viruses, can result in severe or fatal infections in humans. Timely identification of potential pandemic viruses must be a priority in influenza virus surveillance. However, the range of host species responsible for the generation of novel pandemic influenza viruses remains unclear. In this study, we conducted serological surveys for avian and human influenza virus infections in farmed mink and determined the susceptibility of mink to prevailing avian and human virus subtypes. The results showed that farmed mink were commonly infected with human (H3N2 and H1N1/pdm) and avian (H7N9, H5N6, and H9N2) influenza A viruses. Correlational analysis indicated that transmission of human influenza viruses occurred from humans to mink, and that feed source was a probable route of avian influenza virus transmission to farmed mink. Animal experiments showed that mink were susceptible and permissive to circulating avian and human influenza viruses, and that human influenza viruses (H3N2 and H1N1/pdm), but not avian viruses, were capable of aerosol transmission among mink. These results indicate that farmed mink could be highly permissive “mixing vessels” for the reassortment of circulating human and avian influenza viruses. Therefore, to reduce the risk of emergence of novel pandemic viruses, feeding mink with raw poultry by-products should not be permitted, and epidemiological surveillance of influenza viruses in mink farms should be urgently implemented.

Zoonotic and Reverse Zoonotic Transmissibility of SARS-CoV-2

The Coronavirus Disease 2019 (COVID-19) is the first known pandemic caused by a coronavirus. Its causative agent, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), appears to be capable of infecting different mammalian species. Recent detections of this virus in pet, zoo, wild, and farm animals have compelled inquiry regarding the zoonotic (animal-to-human) and reverse zoonotic (human-to-animal) transmissibility of SARS-CoV-2 with the potential of COVID-19 pandemic evolving into a panzootic.

It is important to monitor the global spread of disease and to assess the significance of genomic changes to support prevention and control efforts during a pandemic. An understanding of the SARS-CoV-2 epidemiology provides opportunities to prevent the risk of repeated re-infection of humans and requires a robust One Health-based investigation. This review paper describes the known properties and the existing gaps in scientific knowledge about the zoonotic and reverse zoonotic transmissibility of the novel virus SARS-CoV-2 and the COVID-19 disease it causes.

Mink, SARS-CoV-2, and the Human-Animal Interface

Mink are small carnivores of the Mustelidae family. The American mink is the most common and was imported to Europe, Asia, and Latin America for breeding, as its fur is very popular. Denmark, the Netherlands, and China are the biggest producers of mink. Mink farms with a high population density in very small areas and a low level of genetic heterogeneity are places conducive to contagion. The mink’s receptor for SARS-CoV-2 is very similar to that of humans. Experimental models have shown the susceptibility of the ferret, another mustelid, to become infected with SARS-CoV-2 and to transmit it to other ferrets. On April 23, 2020, for the first time, an outbreak of SARS-CoV-2 in a mink farm was reported in the Netherlands. Since then, COVID-19 has reached numerous mink farms in the Netherlands, Denmark, United States, France, Greece, Italy, Spain, Sweden, Poland, Lithuania, and Canada. Not only do mink become infected from each other, but also they are capable of infecting humans, including with virus variants that have mutated in mink. Human infection with variant mink viruses with spike mutations led to the culling in Denmark of all mink in the country. Several animals can be infected with SARS-CoV-2. However, anthropo-zoonotic outbreaks have only been reported in mink farms. The rapid spread of SARS-CoV-2 in mink farms raises questions regarding their potential role at the onset of the pandemic and the impact of mutants on viral fitness, contagiousness, pathogenicity, re-infections with different mutants, immunotherapy, and vaccine efficacy.

Canine and Feline Influenza

Influenza virus infections of carnivores-primarily in dogs and in large and small cats-have been repeatedly observed to be caused by a number of direct spillovers of avian viruses or in infections by human or swine viruses. In addition, there have also been prolonged epizootics of an H3N8 equine influenza virus in dogs starting around 1999, of an H3N2 avian influenza virus in domestic dog populations in Asia and in the United States that started around 2004, and an outbreak of an avian H7N2 influenza virus among cats in an animal shelter in the United States in 2016. The impact of influenza viruses in domesticated companion animals and their zoonotic or panzootic potential poses significant questions for veterinary and human health.

Avian Influenza A Virus Associations in Wild, Terrestrial Mammals: A Review of Potential Synanthropic Vectors to Poultry Facilities

The potential role of wild mammals in the epidemiology of influenza A viruses (IAVs) at the farm-side level has gained increasing consideration over the past two decades. In some instances, select mammals may be more likely to visit riparian areas (both close and distant to farms) as well as poultry farms, as compared to traditional reservoir hosts, such as waterfowl. Of significance, many mammalian species can successfully replicate and shed multiple avian IAVs to high titers without prior virus adaptation and often can shed virus in greater quantities than synanthropic avian species. Within this review, we summarize and discuss the potential risks that synanthropic mammals could pose by trafficking IAVs to poultry operations based on current and historic literature.

Truncation or Deglycosylation of the Neuraminidase Stalk Enhances the Pathogenicity of the H5N1 Subtype Avian Influenza Virus in Mallard Ducks

H5N1 subtype avian influenza virus (AIV) with a deletion of 20 amino acids at residues 49–68 in the stalk region of neuraminidase (NA) became a major epidemic virus. To determine the effect of truncation or deglycosylation of the NA stalk on virulence, we used site-directed mutagenesis to insert 20 amino acids in the short-stalk virus A/mallard/Huadong/S/2005 (SY) to recover the long-stalk virus (rSNA+). A series of short-stalk or deglycosylated-stalk viruses were also constructed basing on the long-stalk virus, and then the characteristics and pathogenicity of the resulting viruses were evaluated. The results showed that most of the short-stalk or deglycosylated-stalk viruses had smaller plaques, and increased thermal and low-pH stability, and a decreased neuraminidase activity when compared with the virus rSNA+. In a mallard ducks challenge study, most of the short-stalk or deglycosylated-stalk viruses showed increased pathological lesions and virus titers in the organ tissues and increased virus shedding in the oropharynx and cloaca when compared with the rSNA+ virus, while most of the short-stalk viruses, especially rSNA-20, showed higher pathogenicity than the deglycosylated-stalk virus. In addition, the short-stalk viruses showed a significantly upregulated expression of the immune-related factors in the lungs of the infected mallard ducks, including IFN-α, Mx1, and IL-8. The results suggested that NA stalk truncation or deglycosylation increases the pathogenicity of H5N1 subtype AIV in mallard ducks, which will provide a pre-warning for prevention and control of H5N1 subtype avian influenza in the waterfowl.

Serological evidence of the infection of H7 virus and the co-infection of H7 and H9 viruses in farmed fur-bearing animals in eastern China

Avian influenza virus (AIV) usually infects wild birds and domestic poultry; however, this virus could be transmitted to mammals and humans. The previous studies reported that the farmed mink could be infected with the H5 AIV and H9 AIV, indicating that the farmed fur-bearing animals may be susceptible to AIV. Here, we report the serological evidence of infection of H7 AIV and co-infection of H7 and H9 AIV in healthy framed fur-bearing animals. We collected serum specimens from healthy farmed fur-bearing animals (farmed mink and farmed fox) and make an investigation of serological surveillance of clade 2.3.2 H5 AIV, clade 7.2 H5 AIV, clade 2.3.4.4 H5 AIV, H7 AIV, and H9 AIV. We did not find the hemagglutination inhibition (HI) antibodies against clade 2.3.2 H5 AIV, clade 7.2 H5 AIV, or clade 2.3.4.4 H5 AIV in the serum specimens of farmed fur-bearing animals. However, we found that both farmed mink and farmed fox possess HI antibodies against H7 AIV or H9 AIV; furthermore, we found that some serum specimens possess both anti-H7 AIV antibodies and anti-H9 AIV HI antibodies, suggesting that one farmed fur-bearing animal can be infected with two different subtype AIVs and may play an important role in the reassortment course of the novel avian influenza viruses. Taken together, our data suggested that the enhanced surveillance of AIV in farmed fur-bearing animals and humans or animals in close contact with them is needed.

Emergence of an Eurasian avian-like swine influenza A (H1N1) virus from mink in China

We evaluated the phenotype and genotype of a fatal influenza/canine distemper virus coinfection found in farmed mink in China. We identified a novel subtype H1N1 influenza virus strain from the lungs of infected mink designated A/Mink/Shandong/1121/2017 (H1N1). The results of phylogenetic analysis of 8 gene fragments of the H1N1 strain showed the virus was a swine origin triple-reassortant H1N1 influenza virus: with the 2009 pandemic H1N1 segments (PB2, PB1, PA, NP and M), Eurasian avian-like H1N1 swine segments (HA and NA) and classical swine (NS) lineages. The EID₅₀/0.2 mL of this strain was 10^-6.2 and pathogenicity tests were 100 % lethal in a mouse model of infection. We found that while not lethal and lacking any overt signs of infection in mink, the virus could proliferate in the upper respiratory tracts and the animals were converted to seropositive for the HA protein.

Semiaquatic mammals might be intermediate hosts to spread avian influenza viruses from avian to human

Avian influenza A viruses (AIVs) can occasionally transmit to mammals and lead to the development of human pandemic. A species of mammal is considered as a mixing vessel in the process of host adaptation. So far, pigs are considered as a plausible intermediate host for the generation of human pandemic strains, and are labelled ‘mixing vessels’. In this study, through the analysis of two professional databases, the Influenza Virus Resource of NCBI and the Global Initiative on Sharing Avian Influenza Data (GISAID), we found that the species of mink (Neovison vison) can be infected by more subtypes of influenza A viruses with considerably higher α-diversity related indices. It suggested that the semiaquatic mammals (riverside mammals), rather than pigs, might be the intermediate host to spread AIVs and serve as a potential mixing vessel for the interspecies transmission among birds, mammals and human. In epidemic areas, minks, possibly some other semiaquatic mammals as well, could be an important sentinel species for influenza surveillance and early warning.

Isolation and characterization of a novel H7N8 avian influenza virus from domestic ducks in Central China in 2017

In 2017, an H7N8 avian influenza virus (AIV) was isolated from a domestic duck from a farm in Central China. Sequences analysis showed that this strain received its genes from H7, H1, H2, H3, H5, and H6 AIVs of domestic poultry and wild birds in Asia. It exhibited low pathogenicity in chickens and mild pathogenicity in mice. These results suggest the importance of continued surveillance of the H7N8 virus to better understand the ecology and evolution of the AIVs in poultry and wild birds and the potential threat to human health.

First Report of Chlamydia abortus in Farmed Fur Animals

Chlamydia (C.) abortus, a globally distributed obligate intracellular bacterium, has attracted increasing interest according to its veterinary importance and zoonotic nature. C. abortus can infect a variety of animals and cause foetal loss in livestock resulting in economic loss. In this study, the samples collected from two farms of foxes (n=20), raccoon dogs (n=15) and minks (n=20), were investigated by Chlamydiaceae- and Chlamydia species-specific real-time PCR. The results showed that all the tested foxes (20/20) and raccoon dogs (15/15) harbored Chlamydia spp., while 5% of minks (1/20) were positive for Chlamydia spp. C. abortus was identified in all positive samples as the dominant Chlamydia species, with C. pecorum DNA coexistence in some of the rectal samples (7/20) taken from foxes. Phylogenetic analysis based on specific gene fragments of 16S rRNA, IGS-23S rRNA, and ompA revealed that all sequences obtained in this study were assigned to the Chlamydiaceae family with high similarity to C. abortus S26/3 and B577 previously identified in ruminants. This is the first report confirming that farmed foxes, raccoon dogs, and minks carry C. abortus. Further studies are needed to fully elucidate the epidemiology and pathogenicity of this pathogen in farmed fur animals as well as the potential risks to public health.

Molecular characterization and new genotypes of Enterocytozoon bieneusi in minks (Neovison vison) in China

Microsporidiosis is an emerging and opportunistic disease, and Enterocytozoon bieneusi is the main cause of this disease in humans. Little information is available on prevalence and genotyping of E. bieneusi in minks. We collected 559 feces samples of minks from Heilongjiang and Jilin provinces in 2017, and studied E. bieneusi prevalence by nested PCR. A total of 23 out of 559 minks (4.1%) were detected as E. bieneusi-positive, and were raised in five of the seven investigated farms. Age was the only risk factor associated with E. bieneusi prevalence in investigated minks through logistic regression analysis. Sequence analysis of the ITS gene revealed that five E. bieneusi ITS genotypes, including Peru11, EbpC, and three novel genotypes (HLJM-1, HLJM-2 and JLM-1) were present, suggesting minks may be a potential source of human microsporidiosis.