Friday, November 21, 2025

South Korea MAFRA Orders Strengthened Quarantine Measures After 3 HPAI H5 Subtypes (H5N1, H5N6, H5N9) Detected In Wild Birds

 

#18,955

South Korea has a long history of dealing with HPAI H5 viruses, going back more than two decades, and in 2014 was the first country to feel the impact of an emerging HPAI H5N8 clade 2.3.4.4 virus which - in its opening months - spread to scores of farms across that nation and led to the culling of more than 10 million birds. 

That experience - combined with a recent surge in HPAI H5 around the globe - has led to increased preparations by South Korea, starting with their release of a new pandemic plan over the summer of 2024, and announcing (last September) a 19-day, Nationwide, Mock-Training Exercise to Prepare for Zoonotic Influenza. 

Just as we've seen reported this fall from Europe, Canada, the United States, and Japan - South Korea is seeing an early start to their avian flu season - and has (for the very first time) detected 3 different HPAI H5 subtypes (H5N1, H5N6, & H5N9) in wild birds. 

Today their Department of Agriculture (MAFRA) has issued both a stark warning, and stricter quarantine measures due to HPAI, including harsher penalties (Imprisonment & Fines) for violations. 

This growing diversity of HPAI H5 viruses in wild birds is not a trivial concern, particularly given the events of last week here in the U.S., when the first known human infection with HPAI H5N5 was reported in Washington State.  

 I've posted a machine translation of the South Korean announcement below. (Note: 10 Million won fine = $6766 USD).


The risk of a domestic outbreak of highly pathogenic avian influenza is increasing, prompting strengthened quarantine measures to prevent further outbreaks.

2025.11.21 13:58:00 Avian Influenza Prevention Division, Quarantine Policy Bureau

The Central Disaster and Safety Countermeasures Headquarters for Highly Pathogenic Avian Influenza ( Headquarters: Minister of Agriculture, Food and Rural Affairs Song Mei-ryeong , hereinafter referred to as the Central Disaster and Safety Countermeasures Headquarters ) announced that it will prepare and implement quarantine measures to prevent further outbreaks as the risk level increases due to the increase in the number of migratory birds residing in the country in November and the increase in the occurrence of highly pathogenic avian influenza in domestic poultry farms and wild birds .

1. Situation

Since the first outbreak of highly pathogenic avian influenza at a native chicken farm in Paju , Gyeonggi Province on Friday , September 12 , there have been six cases in domestic poultry farms and 10 cases in wild birds .
* Poultry farm outbreak status ( 6 cases in total , H5N1 type ): 4 cases in Gyeonggi ( 1 in Paju , 2 in Hwaseong , 1 in Pyeongtaek ), 1 case in Chungbuk ( Yeongdong ), 1 case in Gwangju Metropolitan City ( Nam-gu )
* Status of wild bird detection ( total 10 cases : 7 H5N1 types , 1 H5N6 type , 2 H5N9 types ): 1 in North Chungcheong Province , 1 in South Chungcheong Province , 3 in North Jeolla Province, 1 in South Jeolla Province , 1 in South Gyeongsang Province , 1 in Busan , 1 in Gwangju , 1 in Seoul
2. Increased risk

First , in November , 4 cases of highly pathogenic avian influenza were confirmed in poultry farms and 7 cases in wild birds , and according to the results of the Ministry of Climate Change's winter migratory bird habitat survey ( 200 survey sites ) , 1.33 million birds arrived in the country, an increase of 111.4% compared to the previous month ( 630,000 in October ) .

Second , as a result of a detailed examination of environmental samples * ( soil , wild bird feathers, etc. ) from the surrounding migratory bird habitat and river for the epidemiological investigation of the outbreak farm , detection of H5 type avian influenza antigen was confirmed, indicating that the migratory bird habitat , river , and surrounding farms are significantly contaminated .
  • * Detection of H5 avian influenza antigen confirmed in Gyeonggi ( Balancheon in Pyeongtaek and Gwanricheon in Hwaseong , November 14), Jeollabuk-do ( Gyehwa Bird Sanctuary and Cheongdo Pond in Buan , November 12-13 ), and Chungcheongbuk-do ( Hangokje in Yeongdong , November 17-18)
Third , for the first time in Korea, three serotypes ( H5N1, H5N6, H5N9) were confirmed in wild birds .

Accordingly , all poultry farms across the country must strengthen quarantine measures and promptly report any suspicious symptoms to quarantine authorities .

3. Strengthening quarantine measures

As the risk of avian influenza is increasing, the Ministry of Health and Welfare is strengthening quarantine measures as follows to prevent further outbreaks and take preventive measures .

First , all available rental disinfection vehicles (39 → 135 , an increase of 96 vehicles ) will be preemptively deployed simultaneously starting November 20 to conduct concentrated disinfection in high-risk areas such as migratory bird arrival sites and densely populated breeding areas .
* Separately, 540 units of Nonghyup workshops and 360 units of local governments will continue to operate.
Second , 27 cities and counties with high poultry farming density, such as laying hens and ducks, and a history of past outbreaks will be designated as high - risk areas , and special inspections will be conducted jointly by relevant organizations ( Ministry of Agriculture , Food and Rural Affairs , Ministry of the Interior and Safety , Quarantine Agency , and cities and provinces ) from November 24 to December 10 to supplement any deficiencies .

Third , as the results of the epidemiological investigation on the outbreak farm confirmed weak quarantine management during the shipment process of older hens that laid eggs ( old laying hens ) , starting November 24 , intensive management will be conducted on whether prior reporting and quarantine rules are followed when shipping old laying hens to slaughterhouses . 
* Intensive inspection of compliance with administrative orders, such as prior reporting of loading and unloading platforms at poultry farms when slaughtering laying hens and submitting a pledge to comply with quarantine rules.
Fourth , in order to prevent further outbreaks at laying hen farms , we will strengthen inspections to ensure compliance with the administrative order prohibiting egg transport vehicles from entering farms , and if violations are confirmed, we will take strict measures in accordance with relevant regulations .

* Violation of the administrative order prohibiting entry of egg vehicles into poultry farms is subject to imprisonment for up to one year or a fine of up to 10 million won .

4. Requests

The Director of the Quarantine Policy Bureau of the Ministry of Agriculture, Food and Rural Affairs, Lee Dong-sik, requested , “ Since the risk of outbreak of highly pathogenic avian influenza during this winter season is higher than ever before , local governments should thoroughly inspect whether poultry farms are complying with quarantine measures and provide repeated education and publicity so that farmers can be alert and voluntarily comply with quarantine rules such as disinfection . ”

In addition , he emphasized , “ In order to prevent further outbreaks of highly pathogenic avian influenza, it is most important for poultry farms to have the mindset of ‘ I protect my own farm ’ and to follow basic quarantine rules such as disinfection and changing boots , so please thoroughly follow these . ”

Lastly , he requested that “ relevant organizations, local governments, and livestock farms all work together to do their best in quarantine management so that damage from highly pathogenic avian influenza can be minimized . ”

       (Continue . . . )

 

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Thursday, November 20, 2025

ECDC Threat Assessment Brief: Assessing the risk of influenza for the EU/EEA in the context of increasing circulation of A(H3N2) subclade K

 

#18,954

Ten days ago, in Increasing Concerns Over A `Drifted' H3N2 Virus This Flu Season, we looked at early reports of a rapidly growing subclade (K) of seasonal  H3N2, which has sparked early and robust flu outbreaks in Asia, and which appears to be poorly reactive to this year's flu vaccine. 

A week ago, we looked an a UK HSA  Preprint: Early Influenza Virus Characterisation and Vaccine Effectiveness in England in Autumn 2025, A Period Dominated by Influenza A(H3N2) Subclade K, which was formally published today in Eurosurveillance.

While that preliminary study found `. . . reassuring early evidence that a programme using NH-strain enhanced vaccines offers protection against clinical influenza disease . . .', this is based on very limited data, and reliable VE (Vaccine Effectiveness) numbers won't be available for months. 
Today the ECDC published their own risk assessment, which reports that a vigorous and early flu season has already started, and `vaccination should proceed without delay.'

First the press release, followed by excerpts from the Risk Assessment. 


Circulating respiratory viruses, including influenza viruses, SARS-CoV-2 and RSV, all contribute to pressure on healthcare systems during winter in the EU/EEA. In a typical season, influenza causes substantial morbidity in the European population, with up to 50 million symptomatic cases and 15 000 to 70 000 deaths annually.

All age groups are affected, although children have higher rates of illness and are usually the first to become sick and transmit the disease in their households, which can drive transmission in the community. It is estimated that up to 20% of the population contract influenza annually. This results in absence from school and work and a significant impact on healthcare systems. A higher impact is seen in closed settings such as long-term care facilities (LTCFs), where outbreaks of seasonal influenza can have high morbidity and mortality.

ECDC decided to assess the risk of influenza for the EU/EEA in the context of early circulation of seasonal influenza in the region and the recently emerged influenza A(H3N2) subclade K that is circulating globally. This is to raise awareness of potential implications and provide recommendations to public health authorities. However, considerable uncertainty remains around the likely public health impact of this subclade on the influenza season.

Download

TAB Influenza cover.png
Threat Assessment Brief - Assessing the risk of increasing circulation of A(H3N2) subclade K.pdf - EN - [PDF-533.55 KB]
While there is considerable uncertainty in this risk assessment, for now the risk to the general population is considered moderate. Those over 65 - or with comorbidities - are deemed as having greater risk, and reduced community immunity could result in increased pressure on health care providers.
I've posted some excerpts below, but you'll want to follow the link to read the full 10-page report.   I'll have a brief postscript after the break.

Risk assessment
Based on currently available information, ECDC assesses the risk for the general EU/EEA population from an influenza season dominated by A(H3N2) subclade K as moderate. 
ECDC assesses the risk as high for populations at higher risk for severe disease (people over 65 years of age,people with underlying metabolic, pulmonary, cardiovascular, neuromuscular and other chronic diseases,pregnant people or persons who are immunocompromised, and people living in closed settings such as LTCF).
Even if the individual risk of severe illness remains similar to previous years, a larger epidemic driven by lower immunity to infection could result in a higher absolute number of hospitalisations and increased pressure on healthcare services. This assessment may change as more data become available.
Recommendations
• Those eligible for vaccination, especially those at higher risk of severe disease, should get vaccinated without delay.
• Treating affected individuals with influenza antivirals early is essential to reduce the likelihood of complications and disease progression in populations at higher risk of severe disease. Antivirals become even more important in the context of a circulating influenza strain that may be poorly matched to the vaccine.Testing should guide antiviral treatment where possible, but strong clinical suspicion and the local epidemiology should also guide decisions to avoid delays that may reduce effectiveness
• Antiviral prophylaxis should be considered in outbreaks detected in closed settings, such as LTCFs, regardless of vaccination status.
• Hospitals and LTCFs should review their preparedness plans and enhance their infection prevention and control practices to mitigate against pressure to the healthcare system during the influenza season. Staff and visitors should use face masks within hospitals and LTCFs in periods of increased respiratory virus circulation.
• Countries should provide tailored communication to people on how transmission can be reduced and the impact of severe disease. This should be done through clear messages on vaccination, hand hygiene and respiratory etiquette.
• Countries should continue to report epidemiological and virological surveillance findings promptly via EpiPulseto support rapid assessment and response across the EU/EEA
Disease severity and impact
It remains uncertain whether influenza A(H3N2) will dominate throughout the 2025/26 season or whether co-circulation with A(H1N1)pdm09 and/or B/Victoria will occur. The EU/EEA has not experienced dominant circulation of A(H3N2) since the first half of the 2022/23 influenza season (Figure 2). The 2021/22 season was also dominated by A(H3N2) but with low overall levels of activity, following 2020/21 in which circulation of influenza was interrupted due to the COVID-19 pandemic [6].

Reduced recent exposure may lower population-level protection against infection with A(H3N2), particularly among young children who may have had little or no prior exposure to this subtype. However, protection against severe disease is likely to remain more robust due to cross-reactive immunity from previous influenza infections and vaccination, consistent with observations from past seasons and post-pandemic periods.
Even if the individual risk of severe illness remains similar to previous years, a larger epidemic driven by lower immunity to infection could still result in a higher absolute number of hospitalisations and increased pressure on healthcare services. Serological data for the 2025/26 season are not yet available, and these assessments therefore remain uncertain.

        (Continue . . . )


Fortunately, even a poorly matched vaccine is expected to provide some degree of protection - at least against severe infection - and so it is still very much worth getting.  

I got mine a month ago, but the flu shot is just part of my `flu prevention' routine each year.  I'll also continue to wear a face mask in public, and will liberally apply hand sanitizer at every opportunity. 

Admittedly, I'd do that every year. But with a drifted H3N2 virus in the mix - which often hits my age bracket the hardest - I'll be cinching my mask just a little bit tighter in the months ahead. 

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IJID: Short-Term Risks of Influenza and COVID-19 Following Influenza Infection: A Self-Controlled Case Series Study

When Epidemic Viruses Collide

#18,953

Viral interference is the ability of one circulating virus to inhibit or impede the transmission of another - and while frequently observed, it remains only partially understood.
Sixteen years ago, during the 2009 H1N1 pandemic, some countries that reported rampant rhinovirus outbreaks in the fall saw far less H1N1 activity than expected (see 2009 New Scientist article Common cold may hold off swine flu).

In 2020's When Epidemic Viruses Collide, we looked at a report in The Lancet Microbes which suggested active Rhinovirus infection may temporarily block infection with the influenza A virus (see Interference between rhinovirus and influenza A virus: a clinical data analysis and experimental infection study)

A year later we saw a similar interaction reported by researchers from the University of Glasgow (see Study: Human Rhinovirus Infection Blocks SARS-CoV-2 Replication Within the Respiratory Epithelium) who found at least one common Rhinovirus (A16) inhibited infection of (in vitro) human respiratory epithelium cells by the SARS-CoV-2 virus.

While the exact mechanism behind this subduing of competing viruses is an ongoing topic of research, many researchers believe that exposure to one virus activates not only a targeted immune response - but also the body's innate immune response - essentially raising `shields' against other possible viral invaders.
A heightened immune response that may persist for weeks or even months; an idea that has been dubbed the `temporary immunity hypothesis'.
In 2017's PLoS Comp. Bio.: Spring & Early Summer Most Likely Time For A Pandemic, researchers used `viral interference' and/or temporary immunity to help explain why pandemics typically emerge in the spring or early summer; after the end of regular flu season.
During the first two years of COVID, Influenza A all but disappeared; but how much of that was due to viral interference - and how much was due to social distancing and face mask wearing - is difficult to parse out. 
But over the past 3 years, influenza A has made a strong comeback - and while we've seen concerns raised each winter over seeing a `twindemic' - so far, that has not materialized.  
Providing some answers as to why that might be, we have a study from Beijing that found that influenza A infection reduces the risk of influenza reinfection by 57% for up to 8 months but increases the risk of COVID-19 infection by 48% within 6 months post-influenza.

While this points to an increased risk of COVID infection following a bout of influenza (Flu-COVID), they did not study the reverse (and admittedly far more complex) COVID -> Flu scenario. Other notable limitations include:

  • Data was geographically and temporally limited (Beijing, China, mostly from 2023)
  • they did not take into account prior vaccination or infection history
  • and they did not include non-medically attended asymptomatic or mild cases 
Still, the data on increased COVID susceptibility following influenza season is compelling, which may help inform public health planning going forward. 
And those who experience a bout of influenza just might want to consider taking more stringent preventive measures (masking, social distancing, COVID booster) in the months that follow.

I've just posted the abstract and a few excerpts, so follow the link to read the study in its entirety. 

Chao Wang1,2,3 ∙ Yanlin Gao1,2 ∙ Wei Li1,2 ∙ … ∙ Yunping Shi1 ∙ Ying Zhou1 ∙ Gang Li1,2 ligangcn@126.com … Show more

Highlights
  • Surveillance data from Beijing revealed that COVID-19 peaks occurred 2-4 months after influenza epidemics. 
  • Influenza infection reduces the risk of reinfection by 57%, with protection lasting up to 8 months.
  • Influenza infection increases the risk of COVID-19 by 48% within 6 months.
  • COVID-19 testing and preventive measures during and after influenza seasons should be enhanced.

ABSTRACT

Objectives

Given the inconsistent existing evidence on viral interference between influenza and COVID-19, this study aimed to investigate the short-term risks of influenza reinfection and COVID-19 infections following an initial influenza episode, in the context of cocirculating influenza and SARS-CoV-2 viruses.

Methods

Using a seasonally adjusted self-controlled case series (SCCS) design, we analysed surveillance data from Beijing, China, collected between February 2023 and June 2025. The study included individuals infected with influenza who subsequently experienced either influenza reinfection or COVID-19 within 18 months after the initial influenza infection.

Results

The study comprised 17,859 individuals with influenza followed by COVID-19 (flu-COVID) and 34,291 with sequential influenza infections (flu-flu).
Influenza infection was associated with a transient increase in the risk of COVID-19 within 6 months (IRR = 1.48, 95% CI: 1.39–1.59).
In contrast, the risk of influenza reinfection was significantly reduced during the same period (IRR = 0.43, 95% CI: 0.39–0.49). Although risk modulation varied across demographic subgroups, results from subgroup and sensitivity analyses were largely consistent.

Conclusions

Influenza infection may temporarily increase susceptibility to COVID-19 while reducing the risk of influenza reinfection. These findings highlight the importance of targeted surveillance and preventive strategies during influenza peaks to mitigate subsequent COVID-19 burden.

       (SNIP)

Discussion


Our study revealed markedly divergent short-term risks of SARS-CoV-2 and influenza reinfection within six months following an initial influenza infection. Specifically, compared to the period 7–18 months post-infection, the risk of COVID-19 increased by 48%, while the risk of influenza reinfection decreased by 57%. This pattern suggests that adaptive immune memory—developed through prior natural infection or vaccination—can effectively prevent reinfection or attenuate symptom severity and complications[22].
Previous research has indicated that immunity conferred by influenza vaccination typically persists for approximately six months[20–21]. Our results extend this understanding by showing that natural infection may confer protection against influenza reinfection for up to eight months.

        (Continue . . . )

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Wednesday, November 19, 2025

Open the pod bay doors, HAL (Arguing with A.I.)

 

#18,952

As anyone who has suffered through the tortured syntax of this blog has already deduced; I don't use A.I. to write. In fact, I don't use `writing aids' of any kind, except spell check.  

While some of my reluctance to adopt these tools may stem from being of a certain age (I was born into an analog, early-1950's, vacuum tube world),  I've often been an early adopter of technology.  

I bought my first personal computer in 1979 (an Apple II+), and my second (TRS-80) in 1980.  I taught myself to program in a number of languages, and in my post-paramedic career made a decent living as a computer consultant. 

So, over the past year, I've been cautiously dabbling with several (well known) A.I. apps.  

Not to write my blog, but to do background research, or sometimes to get a better understanding of a topic or a paper.  While I've been impressed with some of their  capabilities, I've also learned that the data dredged up from out of the ether isn't always correct, or current. 
Since it often takes me 4, 5, or even 6 hours to read a paper and write a blog - when I find a study that interest me - I will sometimes ask A.I. to generate a brief summary, just to get an idea whether I want to dive deeper. 
Two days ago I found a paper (see Preprint: Vertical Transmission of Bovine H5N1 Influenza Virus during Pregnancy and Lactation in Mice) that - from the title alone - was clearly about vertical transmission in mice.  

At least, it was clear to me.

Interested, I downloaded the PDF and sent a copy to an A.I. client, and asked for a brief summary.  What it returned was a lengthy, and quite detailed, summary which never once mentioned `mice'. 

Instead, it began by stating:

This paper reports that highly pathogenic avian influenza A(H5N1) in cattle can be transmitted vertically (from cow to calf) and may cause fetal infection and loss. It pulls together field, pathology, and virology data from the 2024–25 US bovine H5N1 outbreaks to make that case. Below is a structured summary and then a critique.

Followed by 2 pages of findings that were not in the paper I uploaded. Somewhat  taken aback, I responded:

`Wait, isn't this about vertical transmission in mice?'

To which the A.I. responded (emphasis mine):

You’re absolutely right to question that, and thanks for catching it — this paper is not about experimental vertical transmission in mice.

From the PDF itself:

  • The title begins: “Vertical Transmission of Bovine H5N1 Influenza Virus …”

  • The first pages describe naturally infected dairy cows, abortions, stillbirths, and neonatal calves, plus detection of virus in bovine placentas, fetuses, and reproductive tissues, not mouse models.

So this is a cattle (bovine) study, documenting vertical transmission in cows, not in mice. 

        (which continued with another 2 paragraphs of abject nonsense) 

Incredibly, the A.I. quoted back the first 7 words of the title (conveniently truncating `in mice' ) in order to convince me I was mistaken. By this time, of course, I already knew better.

While I wanted to say `Open the pod bay doors, HAL' - fascinated - I went with a more direct: `I think you are in error. The abstract reads:'
Panzootic spillover of H5N1 virus clade 2.3.4.4b has resulted in expanded host range among placental mammals, with lactation transmission via milk documented. Whether infection during pregnancy leads to in utero or lactational vertical transmission remains unknown.

Pregnant outbred mice were infected with A/bovine/Ohio/B24OSU-472/2024 during the second or third trimester equivalent. Second trimester infection caused in utero transmission, with infectious virus detected in the uterus, placenta, and fetus. . . . 
At which point the A.I. finally gave up trying to gaslight me, saying:
You’re right — I was mistaken. Thanks for pasting the abstract. Sorry for the confusion. Below is a corrected, focused summary and critique based on the abstract text you provided.
Corrected short summary

Study used pregnant outbred mice infected with A/bovine/Ohio/B24OSU-472/2024 (H5N1 clade 2.3.4.4b) during second- or third-trimester equivalents.

               (Continues . . . ) 

Although the remainder of the summary appeared correct, my confidence in what I was seeing was understandably shaken.  As an experiment, I submitted the same PDF to competitor's A.I. app, and it produced a reasonable enough summary. 
While I expect I'll continue to use A.I. for basic research (assuming, I double check everything), IMHO, A.I. generated `serious' content is nowhere near being ready for prime time.  

Sadly, the internet is currently being deluged by A.I. generated clickbait garbage that - ironically - A.I. then mines to train itself.  A feedback loop that I assume can only further degrade its accuracy over time.  

I'm not a `big thinker', so I'll leave it to others to debate what this means for society going forward.  

I simply offer this as a cautionary tale for anyone who thinks that - if an A.I. regurgitates it - it must be true. 

Now, perhaps more than ever, Caveat Lector should be your guide.

Meanwhile, I'll continue to do what I'm doing; in a curmudgeonly, old fashioned way. 

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Tuesday, November 18, 2025

Transboundary & Emerg Inf: Serological Evidence of HPAI (H5N1) in Invasive Wild Pigs in Western Canada

 

#18,951

Although cattle, goats, alpaca, and sheep have only recently proved their susceptibility to HPAI H5 infection, for the past 2 decades the big livestock concern has been H5's potential to infect and adapt to swine. 

While detections in swine have been limited, we've seen scattered evidence that H5N1 can infect pigs, albeit often asymptomatically. A few past reports include:
In May of 2023, in Netherlands: Zoonoses Experts Council (DB-Z) Risk Assessment & Warning of Swine As `Mixing Vessels' For Avian Flu, we looked at growing concerns in Europe that avian H5N1 could increase its pandemic threat by spreading (and evolving) in farmed swine.
Only days later, a report out of Italy confirming an H5N1 spillover event at a `mixed species' farm (poultry & swine), and the subsequent seroconversion of the majority of the pigs tested on that farm (see Study: Seroconversion of a Swine Herd in a Free-Range Rural Multi-Species Farm against HPAI H5N1 2.3.4.4b Clade Virus).
Last November, we saw two pigs infected with a new, recently emerged genotype (D1.2) in Oregon (see USDA Confirms 2nd Pig on Oregon Farm Tested Positive for H5N1).
So far, studies have shown only limited susceptibility of swine to the H5N1 virus (see EID Journal: Low Susceptibility of Pigs against Experimental Infection with HPAI Virus H5N1 Clade 2.3.4.4b), but there are legitimate concerns that over time,  a more `swine-adapted' strain could emerge.
Surveillance and testing of  commercially raised swine around the world is quite limited, and much of what happens with in the wild typically flies under our radar. But today we have a study which finds (limited) serological evidence of HPAI H5 infection in wild pigs in western Canada. 

While the reported seroprevalence (<5%) was low, it may not fully represent the situation on the ground.  
  • First, because this was based on 267 wild pigs opportunistically trapped and euthanized across four Alberta counties between 2021–2024, with only 120 serum samples subjected to serological analysis.
  • Second, the authors explain ` . . . this method likely excludes sick or debilitated individuals, as they may be less likely to approach traps. Notably, no dead wild pigs have been found or sampled.
  • Third, the authors state ` . . . only a limited number of groups were removed during the IAV outbreak period, and sampling was not evenly distributed across the entire range of wild pigs.
Notably, they also report `Although three of the five seropositive wild pigs originated from the same group this does not constitute evidence of within-group transmission; however, it remains an important observation to report.'

First the link, abstract, and some excerpts from the study. I'll have a bit more after the break.

Serological Evidence of Highly Pathogenic Avian Influenza (H5N1) in Invasive Wild Pigs in Western Canada

Oshin Ley Garcia, Tamiru Alkie, Frank van der Meer, Yohannes Berhane, Susan E. Detmer, Ishara Muhammadu Isham … See all authors
First published: 17 November 2025
https://doi.org/10.1155/tbed/2720469
Academic Editor: Nan-hua ChenSections

PDF

Abstract

Influenza A virus (IAV) can infect a wide range of hosts, including wild and domestic pigs. Swine play an important role in influenza evolution and epidemiology due to their ability to get infected with both avian and human influenza viruses, potentially leading to reassorted virus variants. Interactions at the wild-domestic swine interface have been documented on multiple occasions, raising concern about pathogen transmission and the emergence of novel influenza strains. 

This study investigates the occurrence and subtypes of IAV infecting invasive wild pigs in Alberta, Canada. A total of 267 wild pigs were captured between 2021–2024. Exposure to IAV was initially detected by cELISA, with further confirmation of exposure to the H5Nx virus by hemagglutination inhibition (HI) and virus neutralization (VN) assays.
Although no IAV genetic material was detected by qPCR, the seropositive samples by cELISA (4.17%; 5/120) coincided with the 2022–2024 highly pathogenic avian influenza virus (HPAI) H5N1 epizootic in Alberta, which involved outbreaks in wild species and domestic birds.

These findings, combined with the epidemiological context, suggest interspecies transmission of HPAI H5N1 clade 2.3.4.4b to wild pigs. These results highlight the potential role of wild pigs as a new host in Canada and emphasize the need for continued surveillance of IAV in wild pig populations to assess the risk of spillover events at the wildlife, livestock, and human interfaces.

(SNIP)

5. Conclusion

In summary, this study provides evidence of exposure of wild pigs to HPAI H5N1, likely originating from the concurrent epizootic in wild birds, domestic poultry, and other wildlife species, suggesting interspecies transmission of HPAI H5N1 viruses. Although serological evidence of IAV infection was observed at low prevalence in the wild pig population in Alberta, these findings raise important questions about the potential role of wild pigs in the ecology of HPAI H5N1 viruses in Canada and across North America.
In the context of recurring outbreaks of H5N1, the possibility that invasive wild pigs could act as a mixing vessel and contribute to the emergence of new reassortants highlights the need for ongoing genomic surveillance and targeted research.
        (Continue . . . )


While the number of wild pigs in Canada is a matter of some debate, it almost certainly reaches into the tens of thousands, and their population - and range - are growing rapidly (see Wild Pigs Invasive Species Centre).

In the United States, estimates run in 6-9 million range, mostly clustered  across the Southern tier of states (see APHIS Map below).


Three months ago, in Frontiers Vet. Sci (Review): Emerging Threats of HPAI H5N1 Clade 2.3.4.4b in Swine, we looked at study commissioned by the Swine Health Information Center (SHIC), which examined how commercial and wild pigs could potentially serve as `mixing vessels' for the H5N1 virus. 

The authors wrote:
The expanding host range and ongoing evolution of HPAI H5N1 clade 2.3.4.4b highlight the urgent need for comprehensive surveillance, preparedness strategies, and support for scientific investigations.
According to the USDA, as of Sept.1, there were 74.5 million hogs and pigs on U.S. farms, and according to their last published Influenza A Virus in Swine Surveillance report, during Q2 they received 925 samples:   
A total of 259 samples were subtyped, including H1N1 (n=85), H1N2 (n=101), H3N2 (n=61), H3N1 (n=1), and mixed subtype (n=11).
The USDA further notes:
Due to the voluntary nature of this surveillance, the information in this report cannot be used to determine regional and/or national incidence, prevalence, or other epidemiological measures, but it may help identify IAV-S trends. 
The common appeal across the hundreds of epidemiological studies we've looked at on this blog is that more robust surveillance, testing, and sharing of data is essential (see here, here, here, here, here, here, and here), yet, progress remains painfully slow.
Health Agencies like the WHO, PAHO, ECDC, and others issue frequent pleas and reminders to member states to share data, but local economic and political considerations often take precedence. 
The world continues to treat the spread of HPAI primarily as an agricultural threat, rather than a potential public health concern. A policy that may pay benefits in the short run, but could prove quite costly over time.  
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Monday, November 17, 2025

Preprint: Vertical Transmission of Bovine H5N1 Influenza Virus during Pregnancy and Lactation in Mice

 

Updated CDC Case Count (n=71)
Does not include asymptomatic or `probable' cases'

#18,950


We've long known that influenza infection during pregnancy can lead to bad outcomes (see 2008 EID Journal article Pandemic Influenza and Pregnant Women), which we saw strongly manifest even during the relatively mild H1N1 pandemic of 2009.

In 2024's EID Journal: Systematic Review of Avian Influenza Virus Infection and Outcomes during Pregnancy, the authors reported `. . . high mortality rates for mothers (90.0%, 27/30) and their babies (86.7%, 26/30) when women were infected with avian influenza virus during pregnancy.'

As bad as they were, most of these effects have been attributed to the mother's immune response (fever, cytokine production, etc.) to the infection; not the vertical transmission of the virus to the fetus in utero. 

A 2012 CDC study (Effects of influenza on pregnant women and infants) does cite H5N1 as potentially being an exception, due to its ability to cause extrapulmonary infection & viremia. Their conclusion, however:

`Therefore, the limited evidence to date suggests that vertical transmission of influenza viruses can occur but is likely to be very rare.

Whether vertical transmission remains `very rare' with H5N1 (and potentially, other novel strains), is less certain. There is a paucity of detailed information published on (mild or severe) H5N1 infections globally, and long-term follow up reports are even less common. 

All of which brings us to a preprint, published on the bioRxiv server, which uses a murine (mouse) model to investigate the vertical transmission of bovine (B3.13) H5N1 influenza A virus (during pregnancy and lactation) in outbred (genetically diverse) mice.

Essentially, they demonstrate that in (lab inoculated) pregnant mice (2nd Trimester), the bovine B3.13 H5N1 virus crossed the placenta (roughly 2/3rds of the time) and later spread through milk, infecting pups. 

Exposed offspring were typically smaller, reached developmental milestones later, and showed lasting behavioral changes into adolescence. 

Due to its length, and technical nature, I've just reproduced the abstract and a few excerpts. Follow the link to read it in its entirety.  I'll have a brief postscript after the break. 

Vertical Transmission of Bovine H5N1 Influenza Virus during Pregnancy and Lactation in Mice

Brittany A Seibert, Maclaine A Parish, Sattya N Talukdar, Tianle Zhang, Sabal Chaulagain, Jennifer A Liu, Jaiprasath Sachithanandham, Oscar Hernandez, Cosette Schneider, Lynda Coughlan, Andrew Bowman, Richard J. Webby, Jack R Harkema, Andrew Pekosz, Sabra L Klein
doi: https://doi.org/10.1101/2025.07.07.663583
This article is a preprint and has not been certified by peer review [what does this mean?].

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Abstract

Panzootic spillover of H5N1 virus clade 2.3.4.4b has resulted in expanded host range among placental mammals, with lactation transmission via milk documented. Whether infection during pregnancy leads to in utero or lactational vertical transmission remains unknown.

Pregnant outbred mice were infected with A/bovine/Ohio/B24OSU-472/2024 during the second or third trimester equivalent. Second trimester infection caused in utero infection, with infectious virus detected in the uterus, placenta, and fetus.

Birth following third trimester infection resulted in offspring with decreased size and neurodevelopmental delays, with infectious virus detected in the neonatal milk ring and lungs as well as mammary tissues.

Ongoing H5N1 infections present increased risk for human exposure and an H5N1 vertical transmission model in placental mammals is essential for understanding viral spread and evaluating treatments during pregnancy.

        (SNIP)    

Pregnancy represents a distinct physiological and immunological state, which causes more severe outcomes from influenza infections than in non-pregnant individuals. 6,7 The bovine H5N1 IAV outbreak, including reports of fatal infections in cats on affected farms, 9 multiple infections among dairy farm workers, 10,11 and a pediatric H5N1 case, 12,13 emphasizes the public health risk and heightened potential for household exposure among pregnant women.

Recent reports on cattle farms also indicate that H5N1-infected heifers exhibit reproductive complications, including abortions during mid- to late-gestation, and a reduced number of cattle in estrus during periods of high clinical disease. 14,15
While a previous study demonstrated that bovine H5N1 IAV inoculation of post-birth lactating female mice can result in transmission of virus to offspring through milk, 4 it remains unknown whether in utero transmission of bovine 30 H5N1 viruses occurs.

To address this gap, we established a pregnancy mouse model to study the pathogenesis and transmission dynamics of bovine H5N1 IAV from the 2024 outbreak

       (SNIP)

Although the current public health risk of H5N1 remains low, potential exposure and transmission from individuals working with infected cattle or poultry to multiple household pets raises the spillover risk for family members and veterinarians caring for these animals. 

These results provide the groundwork for understanding the vertical transmission of bovine H5N1 viruses in humans and other placental mammals, including cattle, where adverse pregnancy outcomes have recently been reported following H5N1 infection. 14,15 

        (Continue . . . )

Admittedly, this study has some limitations and caveats; including a) mice have anatomical and immunological differences from humans. b) this study only looked at genotype B3.13, and c) and it is unknown how much these findings will actually translate to humans.
Even without vertical transmission, pregnant women and their offspring are at higher risk during any flu outbreak. 
Many pregnant women remain reluctant to get the seasonal flu vaccine, despite numerous studies confirming the safety and benefits of vaccination (and the early use of antivirals) in protecting the lives of pregnant women and their unborn child, including:

Pediatrics: Maternal Flu Vaccination Extends Protection To Infants

Clinical Infectious Diseases: Flu Vaccine May Reduce Incidence of Stillbirth

JID: Benefits Of Early Use of Influenza Antivirals In Pregnancy
Complicating matters further, pregnant women and young children are often the last cohort to be approved to receive a novel flu (or CoV) vaccine, since most early clinical trials exclude them over safety concerns.

For more on the impact of maternal infection with influenza A, you may wish to revisits 2024's:

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