#18,488
In addition to avian flu viruses, we keep a close watch on swine-origin influenza viruses, since they too have a history of spilling over to humans and causing pandemics. While there are numerous swine-variants around the world, here in the United States the CDC has identified 3 as having some pandemic potential.
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
The CDC currently ranks a Chinese Swine-variant EA H1N1 `G4' as having the highest pandemic potential of any flu virus on their list. But there are others worth noting, including a recently emerged (first detected in 2018) variant in Denmark called H1pdm09N1av.
In early 2021, in Denmark: SSI Reports Detection of A Novel Flu, we saw an unusual report of a Danish citizen infected with a novel swine-variant virus, who had no known contact with pigs.
The patient (who had multiple comorbidities) was in pandemic lockdown at the time of her infection and had very little outside contact, making the source of her infection unknown.Nine months later, in EID Journal: Reassortant Influenza A(H1N1)pdm09 Virus in Elderly Woman, Denmark, January 2021, we learned that the virus was a novel reassorted H1N1v, comprised of the human A(H1N1)pdm09 virus with the NS gene from an EA-like H1N1 swine virus.
In January off 2022 we saw another report (see Denmark SSI Reports Novel Swine Variant Flu Infection In Slaughterhouse Worker), providing bare-bones information on another case, which occurred in late November of 2021.
The Statens Serum Institut (SSI) has recently detected a case of influenza in a citizen of Denmark with a virus variant that probably originates from pigs. The citizen works at a Danish pig slaughterhouse. It was a serious course of illness in an otherwise healthy person. All indications are that this is a single case of infection. It is not estimated that there is a risk of infection between people.
In December of 2022 the CDC's EID Journal published a follow up to this report, where we learned more about the patient's severe (and unusual) course of illness, and the genetic characterization of the virus (see Severe Human Case of Zoonotic Infection with Swine-Origin Influenza A Virus, Denmark, 2021).
Over the past few years the incidence of H1pdm09N1av has grown to 27% in Danish pigs, the internal gene cassette from genotype 2 has shown up in other swine flu viruses. With signs of some aerosol transmission in ferrets, and little apparent immunity in humans, this rising variant is very much worthy of our attention.While these two zoonotic infections involved two different swine-origin viruses, they both shared the NS gene segment of H1N1av origin.
doi: https://doi.org/10.1101/2024.12.11.627926
Abstract
In 2018, a single detection of a novel reassortant swine influenza A virus (swIAV) was made in Denmark. The hemagglutinin (HA) of the virus was from the H1N1 pandemic 2009 (H1N1pdm09) lineage and the neuraminidase (NA) from the H1N1 Eurasian avian-like swine lineage (H1N1av). By 2022, the novel reassortant virus (H1pdm09N1av) constituted 27 % of swIAVs identified through the Danish passive swIAV surveillance program.Sequencing detected two H1pdm09N1av genotypes;
- Genotype 1 contained an internal gene cassette of H1N1pdm09 origin,
- Genotype 2 differed by carrying an NS gene segment of H1N1av origin.
The internal gene cassette of Genotype 2 became increasingly dominant, not only in the H1pdm09N1av population, but also in other Danish enzootic swIAV subtypes. Phylogenetic analysis of the HA genes from H1pdm09N1av viruses revealed a monophyletic source, a higher substitution rate compared to other H1N1pdm09 viruses and genetic differences with human seasonal and other swine adapted H1N1pdm09 viruses.
Correspondingly, H1pdm09N1av viruses were antigenically distinct from human H1N1pdm09 vaccine viruses. Both H1pdm09N1av genotypes transmitted between ferrets by direct contact, but only Genotype 1 was capable of efficient aerosol transmission.
The rapid spread of H1pdm09N1av viruses in Danish swine herds is concerning for swine and human health. Their zoonotic threat is highlighted by the limited pre-existing immunity observed in the human population, aerosol transmission in ferrets and the finding that the internal gene cassette of Genotype 2 was present in the first two zoonotic infections ever detected in Denmark.
(SNIP)
In 2021, the first two zoonotic IAV infections were registered in Denmark, both were caused by reassortant swIAVs. The first case was caused by a swine H1N1pdm09 virus (A/Denmark/1/2021(H1N1v)) (17) and the second was caused by a swine H1pdm09N1av virus (A/Denmark/36/2021(H1N1v)) (18); both had NS gene segments of H1N1av origin.
(SNIP)
Together, our longitudinal data have shown that changes have occurred in the population of swIAV circulating in Danish swine with many viruses having traits associated with zoonotic threat. Continued selective pressures and assortment opportunities will only continue to diversify swIAV with more zoonotic infections likely. Continued monitoring of human diagnostic systems to ensure detection of variant H1 infections and risk assessments must remain a priority
While we've been focused primarily on avian H5 viruses this year, this is a reminder than Nature's laboratory is not only open 24/7, it is fully capable of running numerous GOF (Gain of Function) field experiments concurrently.
We now live in an age (see The Third Epidemiological Transition) where the the number, frequency, and intensity of pandemics are only expected to increase over the next few decades.
BMJ Global: Historical Trends Demonstrate a Pattern of Increasingly Frequent & Severe Zoonotic Spillover EventsWhile we can debate when - or from what - another pandemic is inevitable. All we can really control is how well prepared we are, when the inevitable happens.
PNAS Research: Intensity and Frequency of Extreme Novel Epidemics
