Tuesday, July 14, 2020

ECDC Risk Assessment: Eurasian avian-like A(H1N1) swine influenza viruses


Although it's been on our radar since late 2015 (see  PNAS: The Pandemic Potential Of Eurasian Avian-like H1N1 (EAH1N1) Swine Influenza), a recent study - published late last month (see PNAS: Eurasian Avian-like H1N1 Swine Influenza Virus With Pandemic Potential In China) - has raised new concerns over an evolving swine flu threat.

Specifically, this new study found the virus replicated well in human epithelial cells, can spread via respiratory droplets among ferrets, and  a seroprevalence study of swine workers found 10% (35/338) showed antibodies to this emerging strain. 
While EA H1N1 has been cited as a top contender for sparking a future pandemic, it is far from the only swine flu virus we are watching. The CDC's IRAT (Influenza Risk Assessment Tool) lists 3 North American swine viruses as having pandemic potential (2 added in 2019).

H1N2 variant [A/California/62/2018]  Jul   2019  5.8  5.7 Moderate
H3N2 variant [A/Ohio/13/2017]          Jul   2019  6.6  5.8 Moderate
H3N2 variant [A/Indiana/08/2011]      Dec 2012   6.0  4.5 Moderate

And there are still others (see last week's WHO: Influenza A(H1N2) variant virus – Brazil) that have shown an ability to jump species around the globe.  In truth, global surveillance is so limited, there are probably many more than we know. 

And as we've discussed many times before (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?) - most swine influenza viruses are either H1, H2, or H3 - giving them a distinct advantage, as those are the only influenza subtypes known to have sparked a human pandemic in the last 130 years. 

Nine days ago, in The CDC's Responds to the PNAS EA H1N1 `G4' Swine Flu Study, we looked at the steps the CDC was taking in light of the latest research on EA H1N1.  Those steps included:
    • Coordinating with public health partners in China, including requesting a virus sample
    • Assessing the risk of the virus causing a pandemic using CDC’s Influenza Risk Assessment Tool (IRAT)
    • Evaluating whether an existing candidate vaccine virus (CVV) against a closely related flu virus (called “G5”) would protect against this virus,
    • If needed, creating a new CVV specific to G4 viruses, and
    • Studying whether existing flu antiviral drugs offer protection against this group of viruses.

Today we have a risk assessment authored by the ECDC on this emerging swine flu virus.

Risk assessment
13 Jul 2020
The 2009 pandemic was the latest of several pandemics caused by a swine-origin influenza virus. Swine influenza is not a mandatory notifiable disease according to the World Organisation for Animal Health (OIE) criteria for disease notification.

A recently published study conducted between 2011 and 2018 in China, and based on surveillance data in pigs, identified an emerging genotype 4 (G4) reassortant Eurasian avian-like (EA) A(H1N1) swine influenza virus that contains internal genes from the human A(H1N1)pdm09 and North American triple-reassortant (TR) lineage-derived internal genes. 
This virus demonstrated the ability to replicate in human epithelial cells and can spread through respiratory droplets between ferrets. Antisera against seasonal human A(H1N1)pdm09 virus showed poor reactivity with G4 viruses. In the same study, a subsequent serosurvey found that 10% (35/338) of swine farm workers were positive for this G4 EA A(H1N1) virus, with a higher proportion in people between 18 and 35 years of age (21%; 9/44).

These findings raise concern about the pandemic potential of these viruses, which are already able to replicate successfully in human tissue and tran
smit through droplets between ferrets, being a model for human-to-human transmission.

The reality is that H1, H2, and H3 swine flu viruses are not considered reportable animal diseases to the OIE - and like many others (H9N2, H6N1, H3N1, H10N8) - while they pose some  risk of human infection, are poorly tracked. 

It's only when surveillance (which ranges from limited to non-existent) around the world picks up a human infection, or a research study is published, do we take notice.  

Our track record of predicting which virus will spark the next pandemic is dismal, which is why we track so many threats.  And still - as with COVID-19  and the 2009 H1N1 pandemic - we often get hit by something from out of left field. 

The full ECDC risk assessment is well worth reading - even if it can't quantify that risk - but below you'll find a snippet on the risks of this virus mutating and spreading among humans:

The emergence of new viruses, as experienced with SARS-CoV-2, or with the emergence of the highly pathogenic avian influenza virus A(H7N9) mutation, new genetic variants, and their epidemiological characteristics in humans and other animals are still unpredictable. The factors that drive the processes are not fully understood as also individual host factors play a strong role.
Surveillance and data collection for diseases with mild clinical signs or which are asymptomatic in domestic animals are limited. This is similarly true for mild diseases in humans and a small cluster of human-to-human transmission associated with mild symptoms might be challenging to be detected through the regular sentinel surveillance systems.

However, human cases with swine influenza variant virus infection are detected sporadically through routine surveillance as has been described recently in Brazil, with the report of a human cases of A(H1N2) variant virus. The 22-year-old female slaughterhouse worker presented with influenza-like illness (ILI) on 12 April 2020 and the A(H1N2) variant virus was identified through routine surveillance and sharing of the isolate with the national influenza centre.
This underlines the importance to test patients with ILI also for influenza, and in case the virus is untypable, to share with specialised laboratories for further characterisation [41]. A retro- and prospectiveinvestigation at the site identified another possible case with similar ILI symptoms during the same time period.

For some previous blogs on swine influenza in China, you wish to revisit: