#18,406
The revelation - just over a year ago - that goats and dairy cattle were susceptible to HPAI H5 infection wasn't the first such `Aha!' moment with unexpected influenza hosts. A little over 20 years ago, most researchers believed cats and dogs weren't susceptible to influenza A viruses.
That is, until spillovers occurred in both species (equine H3N8 in dogs and avian H5N1 in cats) in 2003-2004 (see A Dog & Cat Flu Review). A few years later (2007), an Avian H3N2 virus spilled over into dogs in Korea, and has since spread globally, arriving in the United States in 2015.
In 2017 the CDC added Canine H3N2 to their IRAT List of zoonotic influenza viruses with pandemic potential, albeit with relatively low (3.7) Emergence and Impact Scores.
H3N2: [A/canine/Illinois/12191/2015]
The H3N2 canine influenza virus is an avian flu virus that adapted to infect dogs. This virus is different from human seasonal H3N2 viruses. Canine influenza A H3N2 virus was first detected in dogs in South Korea in 2007 and has since been reported in China and Thailand. It was first detected in dogs in the United States in April 2015. H3N2 canine influenza has reportedly infected some cats as well as dogs. There have been no reports of human cases.
But Canine H3N2 continues to evolve (along with both Canine H3N8 and a recently discovered Canine H3N6 virus). Of the three, however, canine H3N2 appears to be making the most progress (see here, here, and here).
Just over a month ago, we looked at Frontiers Vet. Sci: Genetic Characterization of an H3N2 Canine Influenza Virus Strain in China in 2023—Acquisition of Novel Human-like Amino Acid Substitutions, which warned of additional evolutionary changes:
CIV-CC23 has acquired 3 novel human-like amino acid substitutions compared to the preceding H3N2 CIV strains. This findings suggest that H3N2 CIV evolves over time, and if it accumulates a sufficient number of human-like amino acid substitutions, it may acquire the ability to efficiently propagate in humans.
Chinese scientists over the past decade have visibly increased their scrutiny of novel H3 viruses, as they are commonly observed in wild birds and poultry, and are increasingly spilling over into mammals (see EID Journal: Evolution of Avian Influenza Virus (H3) with Spillover into Humans, China).
All of which brings us to a new study from researchers at the Guangdong Provincial Pet Engineering Technology Research Center, which used serial passaging experiments (in murine lungs), to generate a more pathogenic and mammalian adapted virus.We've looked at serial passage experiments many times. The concept (see graphic below) is simple.
This is the laboratory approximation of what can happen when a novel virus is introduced to a high density population of (often farmed) animals (e.g. mink, swine, poultry, etc.).
In today's study, researchers report significant mutations appeared in the Canine H3N2 virus after only 18 passages through laboratory mice, including the emergence of PB2-627K, which is associated in enhanced replication and pathogenicity in mammals.
First the link, Abstract, and some excerpts from the study. Follow the link to read it in its entirety. I'll have a bit more after the break.
Authors: Xiangyu Xiao , Xinrui Wang, Fengpei Xu, Yanting Liang, Yi Luo, Shoujun Li , Pei Zhou
https://doi.org/10.1128/jvi.01984-24
ABSTRACT
As companion animals, dogs are susceptible to various subtypes of influenza A virus (IAV), with the H3N2 and H3N8 subtypes of canine influenza virus (CIV) stably circulating among canines. Compared to the H3N8 CIV, the H3N2 CIV is more widely prevalent in canine populations and demonstrates increased adaptability to mammals, potentially facilitating cross-species transmission. Therefore, a comprehensive elucidation of the mechanisms underlying H3N2 CIV adaptation to mammals is imperative.
In this study, we serially passaged the GD14-WT strain in murine lungs, successfully establishing a lethal H3N2 CIV infection model. From this model, we isolated the lethal strain GD14-MA and identified the key lethal mutations PA(S184N) and PB2(E627K).
Moreover, the GD14-ma[PA(S184N)+PB2(E627K)] strain exhibited markedly enhanced pathogenicity in dogs. Viral titers in lung tissues from infected dogs and mice showed that GD14-ma[PA(S184N)+PB2(E627K)] does not increase its pathogenicity to mice and dogs by upregulating viral titers compared to the GD14-WT strain.
Notably, sequence alignments across all H3N2 IAVs showed an increasing prevalence of the PA (S184N) and PB2 (E627K) mutations from avian to human hosts. Finally, single-cell RNA sequencing of infected mouse lung tissues showed that GD14-ma[PA(S184N)+PB2(E627K)] effectively evaded host antiviral responses, inducing a robust inflammatory reaction. Considering the recognized role of the PB2 (E627K) mutation in the mammalian adaptation of IAVs, our findings underscore the importance of ongoing surveillance for the PA (S184N) mutation in H3N2 IAVs.
IMPORTANCE
Since the 21st century, zoonotic viruses have frequently crossed species barriers, posing significant global public health challenges. Dogs are susceptible to various influenza A viruses (IAVs), particularly the H3N2 canine influenza virus (CIV), which has stably circulated and evolved to enhance its adaptability to mammals, including an increased affinity for the human-like SAα2,6-Gal receptor, posing a potential public health threat. Here, we simulated H3N2 CIV adaptation in mice, revealed that the synergistic PA(S184N) and PB2(E627K) mutations augment H3N2 CIV pathogenicity in dogs and mice, and elucidated the underlying mechanisms at the single-cell level. Our study provides molecular evidence for adapting the H3N2 CIV to mammals and underscores the importance of vigilant monitoring of genetic variations in H3N2 CIV.
(SNIP)
DISCUSSIONIn this study, we successfully established a lethal mouse model for H3N2 CIV and isolated a lethal mouse strain, designated as GD14-MA. Employing reverse genetics, we identified the PA (S184N) and PB2 (E627K) mutations as critical factors contributing to lethality in mice. Pathogenicity studies in dogs revealed that the GD14-ma[PA(S184N)+PB2(E627K)] strain exhibited significantly enhanced virulence compared to the GD14-WT strain. Single-cell RNA sequencing of infected mouse lung tissues showed that GD14-ma[PA(S184N)+PB2(E627K)] effectively evaded host antiviral responses, inducing a robust inflammatory reaction.
In April of 2020, China's MOA reclassified dogs as `companion animals' rather than `livestock', although it is estimated that somewhere between 10 and 20 million dogs are farmed/abducted in China each year for fur and/or meat.
But even in countries where such practices uncommon, animal shelters have proven excellent venues for extended chains of infection (e.g. Canine parvovirus, feline panleukopenia, canine and feline viral respiratory pathogens, etc. )
The avian H7N2 outbreak in cats across several NYC animals shelters over Christmas of 2016 spread to hundreds of felines, and spilled over into several workers (see J Infect Dis: Serological Evidence Of H7N2 Infection Among Animal Shelter Workers, NYC 2016).
Admittedly, the emergence of a human-adapted H3N2 virus is probably a long-shot. But the more opportunities we give it, the greater the chances of it eventually getting lucky.
And since it isn't just canine H3N2 - but rather a large (and growing) array of novel flu viruses all with varying degrees of zoonotic potential (e.g. H5N1, H5N5, H5N6, H9N2, H10Nx, etc.) - the smart money is on preparing now for what could be a very bumpy road ahead.
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