EID Journal Dispatch: Seroprevalence of Influenza A(H5N1) Virus in Domestic Cats at Epicenter of Dairy Cattle Outbreaks, California, USA, 2024–2026

 

Seropositive cats around HPAI Infected Dairy Farm

#19,268

We've known for more than 2 decades that cats - both large and small - are susceptible to HPAI H5 infection (see 2004 CIDRAP Report) and have seen scattered reports over the years (see 2015's HPAI H5: Catch As Cats Can).

Until relatively recently, those reports were fairly rare, and mainly came from zoo animals fed on a diet of raw chicken. But since the emergence of a new, more transmissible clade 2.3.4.4b H5N1 virus in 2021, the number of companion animals (and other mammals) reported to be infected has risen sharply.

While undoubtedly underreported, more than 20% of all of the mammalian wildlife detections reported in the United States  (180 of 813 USDA reports) over the past 4 years have been among felines. 

Many have been reported in and around dairy and poultry farms (see EID Journal: HPAI A(H5N1) Clade 2.3.4.4b Virus Infection in Domestic Dairy Cattle and Cats, United States, 2024).

While many cats infected with HPAI sicken and die, others - based on seroprevalence studies (see Eurosurveillance: (HPAI) H5 virus Exposure in Domestic & Rural Stray Cats, the Netherlands, October 2020 to June 2023) - are likely only mildly affected and survive.

Previously, we've seen evidence of cattle-to-bird-to-cat transmission of avian flu, large outbreaks in animal shelters suggesting cat-to-cat transmission (H7N2), and limited evidence of cat-to-human transmission (see here and here). 

All of which brings us to a new dispatch, published yesterday in the EID Journal, which reports a 25% seropositivity rate among (n=12) cats sampled within 2 km of infected dairy farms, while no cats were seropositive further away (n=61).

While this is just one small, geographically limited, study the authors state: "Proximity to dairy farms in counties experiencing outbreaks may be a risk factor for H5N1 spillover to indoor and outdoor domestic cats."

I've only posted the highlights, follow the link to read the report in its entirety.

Volume 32, Number 9—September 2026
Dispatch
Seroprevalence of Influenza A(H5N1) Virus in Domestic Cats at Epicenter of Dairy Cattle Outbreaks, California, USA, 2024–2026
 
Ian G. Bemis, Ismaila Shittu, Jacob F. Gomez, Esther A. Fadaka, Sofia Perez, Gregory C. Gray, and Kristen K. Coleman 

Abstract

We conducted a serologic study of domestic cats near the epicenter of the dairy cattle outbreaks of influenza A(H5N1) in California, USA. Three of the 12 cats sampled within 2 km of farms had neutralizing antibodies against H5N1 virus. Proximity to dairy farms was a statistically significant risk factor for seropositivity.

(SNIP)

 Although several US dairy industry–related outbreaks of H5N1 among cats have been reported, the resulting seroprevalence of H5N1 virus among domestic cats near affected dairy farms is unknown. Therefore, we performed a serosurvey of domestic cats at the epicenter of the 2024–2025 dairy cattle outbreaks in California’s Central Valley.

(SNIP)

During December 2024–March 2026, we collected 73 serum samples from indoor and outdoor cats (Figure 1) within 9.7 km (6 miles) of >1 dairy farms (mean 4.7 km [2.9 miles]). Among the 73 cats, 3 tested positive for both influenza A virus nucleoprotein antibodies and neutralizing antibodies against H5 clade 2.3.4.4b. One indoor-only and 1 outdoor feral cat had neutralizing antibody titers of 1:160, and 1 indoor-only cat had a titer of 1:640, indicating strong positivity and 100% agreement between the ELISA and microneutralization assay. All negative samples had titers of <1:20.
 
Three (25%) of the 12 cats sampled within 2 km (1.24 miles) of dairy farms were seropositive for H5N1 virus (Figure 2), yielding an overall seropositivity rate of 4.1% for all surveyed cats. Seropositive cats had a mean distance to the nearest dairy farm of 1.34 km (0.8 miles), compared with 4.83 km (3 miles) for seronegative cats (p = 0.014) (Figure 3). Average age of surveyed cats was ≈1.6 years (range ≈3 months–4.9 years); 60% were female and 40% male. Age and sex were not significantly different for seropositive and seronegative cats. Of the 73 cats surveyed, 68 (93%) were in rural areas and 5 (7%) in urban areas. All seropositive cats were in rural areas. No indoor cats were fed raw meat or dairy.

       (SNIP)

Conclusions

Avian influenza A(H5N1) clade 2.3.4.4b is an emerging threat to domestic cats and public health. We report a 25% seropositivity rate for the virus among domestic cats within 2 km (1.2 miles) of dairy farms in the epicenter of the H5N1 cattle outbreaks in California during 2024–2026. Proximity to dairy farms in counties experiencing outbreaks may be a risk factor for H5N1 spillover to indoor and outdoor domestic cats. Our research provides insight into potential H5N1 virus sources and transmission routes among domestic cats in the United States, for which data are scarce. Our results may help refine public health guidance on the prevention of avian influenza in cats and set the stage for future studies.

Although only 3 seropositive cats were identified in our study, their closer proximity to dairy farms compared with seronegative cats is an important epidemiologic finding. 

        (SNIP) 

Our study highlights a critical gap in companion animal surveillance and might be helpful to health agencies as they seek approaches to mitigating this emerging infectious disease threat. Proximity to dairy farms was a risk factor for H5N1 spillover to cats in our study. However, cattle-to-cat transmission of H5N1 virus is a relatively new phenomenon, and most cat infections reported in the literature over the past 20 years have been from bird-to-cat transmission (1). To assess the in situ risk for human-adapted reassortant influenza viruses emerging in cats, future work is needed to characterize the seroprevalence of human influenza viruses in cats and avian influenza viruses in cats near outbreaks in poultry and wild birds. Cat surveillance studies also could provide insight into nearby H5N1 outbreaks that have yet to be discovered, fully investigated, or contained.

        (Continue. . . )
 

Australia Confirms `Some Local Spread' of H5N1 - CSIRO Testing An Additional 11 Samples From SA

 

" I can advise that today the consultative committee on animal diseases, emergency animal diseases met and has agreed based on testing and sequencing by the CSRO lab that some local transmission has occurred between a number of greater crested terns that are resident in South Australia.

While there remains no evidence of any mass mortalities at this point in time, we do expect with this local transmission that there will be further detections in Australian wildlife." -  From Transcript of remarks by Agriculture Minister Julie Collins

#19,267

Overnight South Australia updated their avian flu web portal, announcing that another 11 presumed positive samples have been sent to CSIRO for confirmation and genetic testing.  

Current situation

South Australia’s first confirmed detection of H5 bird flu was in a wild migratory bird (southern giant petrel) on Wednesday, 24 June at Knights Beach at Port Elliot on the Fleurieu Peninsula.

Further confirmed detections include a giant petrel (8 July at Hardwicke Bay, Yorke Peninsula); a southern giant petrel (10 July at Emu Bay, Kangaroo Island); a northern giant petrel (10 July at Port Vincent, Yorke Peninsula); three greater crested terns (10 July at Robe, Limestone Coast; 26 July at Semaphore, metro Adelaide; and 26 July at Robe, Limestone Coast); and seven greater crested terns (28 July at Cape Jaffa, Port MacDonnell and Southend, Lower South East).

A further 11 suspected H5 bird flu detections are undergoing further confirmatory testing at the Australian Centre for Disease Preparedness in Victoria.

The strain of virus is consistent with the strain detected in the Southern Indian Ocean Sub-Antarctic Territories, including Heard Island.

This strain has not been detected in poultry and has not become established in any part of Australia.

Up-to-date national information is available at birdflu.gov.au .

This comes just 1 day after CSIRO confirmed 7 new cases in local seabirds from the state's southeast Limestone Coast.  The results of those tests also strongly suggest local transmission of the virus has occurred among native birds. 

Although disappointing, none of this is particularly surprising. 

The history with HPAI H5 - particularly since the emergence and subsequent evolution of the 2.3.4.4x clade - has been that it travels well in migratory birds, and that when it reaches new territories, it often finds suitable native hosts.

While the situation in Australia continues to evolve, so far there are no reports of spillovers into poultry. 

On Monday I shared an X/Twitter post by Professor Raina Macintyre showing the recent H5N1 detections overlaid on a map of Australia's poultry production regions.

Yesterday, the above mentioned data was published in a preprint on bioRxiv.

HPAI H5N1 risk in Australia: a model for the prediction of poultry outbreaks
Pan Zhang, Samsung Lim, Ashley Quigley, C Raina MacIntyre
doi: https://doi.org/10.64898/2026.07.27.740638
This article is a preprint and has not been certified by peer review  

Preview PDF

Abstract

The panzootic highly pathogenic avian influenza (HPAI) H5N1 virus has now been detected on the Australian mainland, with incursions from the sub-Antarctic region posing an increasing threat to domestic wildlife and poultry populations. Our study aimed to predict the risk of HPAI H5N1 poultry outbreaks across Australia at the local government area (LGA) level using a range of influential risk factors.

We first used a Maximum Entropy (MaxEnt) model to estimate the environmental suitability for HPAI H5N1 occurrence across Australia. The resulting suitability layer was then integrated with five additional predictor layers, including abundance data for two Southern Ocean wild birds, one of which has introduced HPAI H5N1 into Australia; abundance data for 28 native Australian wild birds; native bird flyways across Australia; Australian chicken density; and poultry farm density. The six layers were aggregated and averaged to generate an HPAI H5N1 risk map for poultry outbreaks across Australian LGAs.

Although most incursions have occurred in Western Australia (WA) and South Australia (SA), we identified New South Wales (NSW) and Victoria (VIC) as having the highest predicted risk of HPAI H5N1 poultry outbreaks. Additional high-risk areas were identified in WA, SA, and Tasmania (TAS).

In contrast, the Northern Territory (NT) and large parts of Queensland (QLD), WA, and SA were predicted to be at low risk. These findings provide a spatially explicit framework to support targeted surveillance, preparedness, and biosecurity measures aimed at mitigating the impact of future HPAI H5N1 outbreaks in Australian poultry.

The Australian government has provided a number of resources for both commercial and backyard poultry producers to help improve their biosecurity: 

Biosecurity manuals

• National Farm Biosecurity Manual - Poultry Production
• National Water Biosecurity Manual - Poultry Production
• Chickens – Farm Biosecurity

Watch

• Learn how to protect your backyard poultry and pet birds

HK CHP Reports 3 H9N2 Cases On Mainland

 

#19,266

Although it received brief mention (see below) in the July 17th WPRO avian flu update, Hong Kong's CHP acknowledged 3 recent H9N2 cases in their weekly avian flu report today.  

As usual, details are scant, but we get a little more from the following WHO WPRO report:

Human infection with avian influenza A(H9N2) virus

From 10 to 16 July 2026, three new cases of human infection with avian influenza A(H9N2) virus were reported to WHO in the Western Pacific Region. All three cases were from China. 

The first case is a 4-year-old male from Guangxi Province, with symptom onset on 26 June 2026. The second case is a 4-year-old male from Jiangsu Province, with symptom onset on 22 June 2026. The third case is a 44-year-old male from Guangdong Province, with symptom onset on 26 June 2026. 

All three cases had exposure to live poultry. The first and second cases had mild symptoms and now recovered; the third case had underlying comorbidities and is curently receiving treatment in the intensive care unit.

Since 2015, a total of 173 cases of human infection with avian influenza A(H9N2), including two deaths(both with underlying conditions), have been reported to WHO in the Western Pacific Region. Of these,170 were reported from China, two were from Cambodia, and one was from Viet Nam.

While most human H9N2 cases have been reported out of China (see below), this year Europe saw its first (imported) human infection with H9N2 in Italy (see WHO DON: Avian Influenza A(H9N2) - Italy (Ex Senegal)).

It is assumed that most cases go unreported, since human infections tend to be mild or moderate (but occasionally severe), and very rarely are non-hospitalized patients tested for novel flu. 

Although there is currently no evidence of sustained or efficient human-to-human transmission of H9N2, the virus remains poorly controlled in poultry, and appears on a path towards greater mammalian adaptation.

While trying to predict the source of the next influenza pandemic is a mug's game, H9N2 shows up twice the top 10 zoonotic influenza A viruses the CDC has pegged as having at least some pandemic potential, with the Y280 lineage having a higher emergence score than H5N1.

Given that we've already seen 2 modern influenza pandemics (1957 & 1968) caused by avian viruses spilling over from birds to humans in China, H9N2's continued evolution and spread is very much worthy of our attention. 

New Zealand to Require Biosecurity Plans From Poultry Sector as Australia's H5N1 Count Rises to 27

#19,265

No unexpectedly, the results overnight from Australia's National Lab CSIRO have confirmed the 7 suspected bird flu detections reported yesterday in Southern Australia, doubling their total to 14. 

H5 bird flu updates
 
28 July 2026

Attributable to Australian Chief Veterinary Officer, Dr Beth Cookson:

Testing at CSIRO’s Australian Centre for Disease Preparedness (ACDP) has confirmed H5 bird flu in 7 greater crested terns found in South Australia.

Of these, 1 was found at Cape Jaffa, 5 at Southend and 1 at Port MacDonnell.

There have now been 27 confirmed or presumed positive detections of H5 bird flu in Australia.

All of these have been wild seabirds found in coastal locations. Further laboratory analysis will be undertaken to help determine if there is evidence of local transmission.

There remains no evidence of any mass mortality events and there are no detections in poultry or in our agricultural production system.

Notably, these are native seabirds (greater crested terns), which raises concerns over the local transmission of the virus. Additional genetic testing is underway to try to determine transmission dynamics. 

Meanwhile, the tally in New Zealand remains at 2, but officials fully expect that number to increase.  Two weeks ago, New Zealand's Associate Biosecurity Minister Andrew Hoggard made it clear that - unlike a lot of other countries - the government would not be compensating poultry farmers for losses. 

Farmers told: If bird flu infects your chickens, they will die, and don’t expect compensation

Overnight New Zealand announced plans to require poultry farmers (flocks > 100) to create and submit biosecurity plans - including the management of any outbreaks - to the government by the end of the year.

28 July 2026
Poultry sector gets stronger biosecurity backing to fight bird flu
Hon Andrew Hoggard
Biosecurity

The Government is introducing new biosecurity regulations to help poultry farmers manage H5 bird flu, protect livelihoods, and secure domestic food supply, Biosecurity Minister Andrew Hoggard says.

“Now that H5 bird flu is here, it will almost certainly establish in wild birds.

“Cabinet has approved regulations to ensure the sector has the practices, infrastructure, reporting, and compliance tools needed to manage that risk.”

Poultry operators with more than 100 birds will be required to develop, register, and implement a farm biosecurity plan for avian disease, setting out how they will prevent and manage H5 bird flu.

“Biosecurity measures are currently voluntary in the poultry sector. While there is strong industry co-operation, farmers doing the right thing can still be put at risk by those who are not.”

“Biosecurity New Zealand and industry have been working together on a long-term approach to managing H5 bird flu. There is a good understanding of what good on-farm biosecurity looks like and plenty of information available to poultry farmers through the industry’s bird flu website”

“MPI is available, especially for smaller operators, through it’s On Farm Support team to help with the development of biosecurity plans and enhanced preparedness, including response plans.”

The regulations will focus on outcomes and the risks operators must manage, while giving them flexibility in how they do it.

Operators will need to keep records, undergo audits, and show clear plans for humane culling, disposal, cleaning, and disinfection if their operation is affected.

“When H5 bird flu becomes widespread in wild birds, poultry operators will face a constant infection risk. These regulations will lift on-farm readiness and give farmers the best possible chance to protect their businesses.”

Mr Hoggard says regulating the sector under the Biosecurity Act 1993 will also help protect food supply, trade, wild and captive birds, other animals, and people.

MPI consulted on the proposed regulations late last year and received 36 submissions, with feedback broadly supportive.

The regulations will now be drafted and shared with the industry bodies before coming into force by the end of 2026.

 
While full details haven't been fleshed out, last August the MPI and the poultry industry signed an agreement on biosecurity, whereby the costs would be shared by both parties. 

“This agreement formally recognises industry bodies as decision-makers, alongside the Government, guaranteeing PIANZ and EPF a seat at the table if any of these diseases are detected in New Zealand.”

The agreement covers Newcastle disease, infectious bursal disease virus and all strains of high pathogenicity avian influenza (HPAI), including the HPAI strain H5N1 clade 2.3.4.4b.

“Importantly, the agreement also sets out cost-sharing arrangements between taxpayers and the industry. This recognises the benefits to both parties of being well prepared, reporting early, and responding rapidly,” says Mr Hoggard.

“By sharing the costs of preparation and response, we ensure there are strong incentives on farmers to take preventative measures while also encouraging them to report suspected disease as soon as possible.”

Under the agreement, industry will contribute 45 per cent of readiness costs for all poultry diseases and 45 per cent of response costs, with the exception of HPAI – for which industry will meet 40 per cent of the response costs.

Readiness costs can include the cost of developing plans for response operational activities, running exercises for testing plans, and applied research to improve response operations. Response costs can include diagnostics, communications and activities to control a disease.

For backyard flock owners (with < 100 birds), the MPI offers the the following advice:

Bird flu and protecting your birds and other pets

While New Zealand has been planning for this grim eventuality for years, even countries with decades of experience dealing with H5N1 continue to find biosecurity a challenge.

For more, you may wish to revisit:

Front. Vet. Sci: Biosecurity deficiencies in HPAI-affected poultry farms in Korea, 2020/2021–2024/2025 seasons

South Australia Reports 7 More `Suspect' H5N1 Detections In Native Shore Birds

 

Video Link 

#19,264

Once again Southern Australia is reporting a number (n=7) of `presumed positive' H5N1 tests in local seabirds, all found in greater crested terns recovered on the state's southeast Limestone Coast (5 at Southend Jetty near Beachport, plus 1 at Cape Jaffa and 1 at Port MacDonnell).

Some of the birds were sick, while others were dead. This comes on the heels of yesterday's announcement of  South Australia Confirms 6th & 7th Seabird Infection - National Ttl = 20,

Samples from all 7 birds have been sent to the National laboratory CSIRO for confirmation and WGS (Whole Gene Sequencing). If confirmed, this would bring the nation's total to 27. 

Authorities continue to stress that, so far, there have been no detections in poultry, or indications of any large-scale deaths in wildlife.  This recent change, however - from detections in migratory seabirds to local species - raises new concerns over how the virus may be spreading. 

Add in the close proximity of these recent reports to denser poultry production regions, and spillovers into the agricultural section become a genuine concern. 

A few hours ago Professor Raina MacIntyre posted the following on X, showing the recent H5N1 detections overlaid on a map of poultry production regions.

You can visit the interactive map at EPIWATCH. 

While past performance isn't always a guarantee of future results, the unfortunate history with HPAI H5N1 - particularly over the past 5 years - has been once it reaches new territories, it tends to establish itself fairly quickly in local wildlife. 

We should expect an update from CSIRO in the next couple of days. 

Stay tuned. 

South Australia Confirms 6th & 7th Seabird Infection - National Ttl = 20

 

#19,263

As mentioned yesterday, Australia's National Lab CSIRO was testing samples from 2 suspected H5N1 infected seabirds from South Australia. Not unexpectedly, both have now been confirmed, bringing the nation's total to 20 detections. 

While most of these H5N1 infections have been found in migratory seabirds, 3 of the 7 from South Australia have been in local seabirds (greater crested terns).

Two brief updates.  First from https://www.birdflu.sa.gov.au/ 

Current situation

South Australia’s first confirmed detection of H5 bird flu was in a wild migratory bird (southern giant petrel) on Wednesday, 24 June at Knights Beach at Port Elliot on the Fleurieu Peninsula.

Further confirmed detections include a giant petrel (8 July at Hardwicke Bay, Yorke Peninsula); a southern giant petrel (10 July at Emu Bay, Kangaroo Island); a northern giant petrel (10 July at Port Vincent, Yorke Peninsula); and three greater crested terns (10 July at Robe, Limestone Coast; 26 July at Semaphore, metro Adelaide; and 26 July at Robe, Limestone Coast).

The strain of virus is consistent with the strain detected in the Southern Indian Ocean Sub-Antarctic Territories, including Heard Island.

This strain has not been detected in poultry and has not become established in any part of Australia.

Up-to-date national information is available at birdflu.gov.au.

 

Second, from national birdflu.gov.au website.

Detection of H5 bird flu

As of 1.00 pm AEST, 26 July 2026, Australia has 20 confirmed detections of H5 bird flu in wild seabirds.

• 10 in Western Australia (WA)
• 7 in South Australia (SA)
• 2 in New South Wales (NSW)
• 1 in Queensland (QLD).

This is the serious H5 bird flu strain that has been circulating globally.

There have been no detections in poultry or the wider agriculture industry. There is no evidence of any large scale deaths.

The Consultative Committee for Emergency Animal Disease (CCEAD) has reviewed its previous advice and continues to support heightened biosecurity measures in poultry for up to a further two weeks while risk-based guidance is finalised. This includes options for states and territories to utilise non-mandatory measures, including voluntary housing of free-range poultry where practical and consistent with animal welfare requirements.

State and territory governments are responsible for surveillance and response activities on the ground. They are actively working with industry to provide guidance on implementation of enhanced biosecurity measures, as appropriate. Find out more about bird flu in your state or territory.

National coordination is being led by the Department of Agriculture, Fisheries and Forestry (DAFF).

The risk to human health remains low.

Australia is well prepared to respond quickly.

Preprint: A lethal human H5N5 influenza virus isolate exhibits low pandemic risk traits

 

Credit: Multiple transatlantic incursions of HPAI

clade 2.3.4.4b A(H5N5) virus into North America

and spillover to mammals 

#19,262

We've been following HPAI H5N5's spread in birds and small mammals - first in Europe, then in Canada and the United States - for several years, but last November we saw the first (and fatal) documented infection of a human with HPAI H5N5 in a elderly backyard keeper of poultry in Washington State. 

Like H5N1, H5N5 isn't a single virus, but rather represents a growing array of genetically distinct genotypes which share related H5 and N5 surface proteins

The virus detected in the Washington State patient is similar to - but not an exact match - to the H5N5 viruses that have infected cats in Iceland, raccoons in Canada,  and Polar Bears on Svalbard Island. 

Last March, Viral Creep: H5N5 Update, we looked at its evolution as it has spread across the United States;  shifting from almost exclusively EA H5N5 prior to last fall, to largely EA/AM H5N5 since November. 

Based on USDA Data - Graph created with Gemini

The USDA defines these two strains as:

EA = Eurasian; AM = North American; the EA H5 (2.3.4.4) viruses are highly pathogenic to poultry.

EA/AM: reassortant of H5 goose/Guangdong and North American wild bird lineage

I mention this distinction because today's preprint focuses exclusively on the Washington State case's isolate, which they describe as having  `. . . a clade 2.3.4.4b hemagglutinin and internal gene segments cluster with currently circulating Eurasian lineage clade 6 (EA6) strains'.

Since late 2025 most U.S. H5N5 isolates have been classified as EA/AM, indicating reassortment with local (North American) LPAI viruses.

Whether this makes any practical difference in their pandemic risk is unknown, but the findings of this - or any other study - may not hold true across the full, and continually expanding range of H5N5 viruses.  

Indeed, the authors cite another study from 2024 (the above mentioned Cell Reports by Erdelyan et al.) which reported A(H5N5) viruses demonstrated rapid 100% mortality and some transmission in ferrets.

But more reassuringly - at least in the case of the isolate retrieved from the Washington State patient - that virus displayed relatively low pandemic risk traits:

• It replicated relatively poorly (compared to seasonal H1N1) in upper respiratory cell cultures, 
• It has a more avian-like pH inactivation point (about 5.5)  compared to human-adapted flu strains
• And - unlike in the Erdelyan et al. study- infected ferrets did not infect healthy co-housed ferrets.

While reassuring, the old adage applies.  When you've seen one novel flu virus, you've only seen one novel flu virus. 

Due to its length, I've only posted the abstract and some excerpts. Follow the link to read it in its entirety. 

A lethal human H5N5 influenza virus isolate exhibits low pandemic risk traits
Michelle N. Vu, Grace E. Quirk, Alexis E. Smathers, Kaitlyn Busfield-Thomason, Alaina L. Dorazio, Katelyn R. Domke, G. M. Humber, John Sembrat, Anita K. McElroy, Valerie Le Sage,  Seema S. Lakdawala
doi: https://doi.org/10.64898/2026.07.20.739507
This article is a preprint and has not been certified by peer review  
 
Preview PDF

Abstract

In fall of 2025, a fatal infection of highly pathogenic avian influenza (HPAI) virus H5N5 occurred. To define the risk of this emerging virus to humans, we performed a comprehensive analysis based on our established triage. Serological analysis revealed that humans across all birth years had no detectable neutralizing antibodies to this H5N5 isolate.

Further characterization revealed a lack of phenotypic signatures associated with epidemiologically successful influenza viruses in humans, including reduced replication in human airway cells and an avian-like pH of inactivation.

Additionally, assessment of H5N5 in ferrets revealed a lack of direct contact transmission and moderate disease severity. H5N5 infection in ferrets with prior immunity against the 2009 H1N1 pandemic strain resulted in fewer clinical signs and reduced viral shedding. Together our data suggest that the current H5N5 HPAI lineage poses a low pandemic risk.

Importance 

HPAI H5N5 viruses have caused widespread infection and death in avian species, and characterizing their pandemic risk traits is critical to understanding the threat posed to humans. In this work we analyzed an isolate that resulted in a human fatality in 2025.

We found that this strain lacks many key features of influenza viruses with epidemiological success in humans including reduced growth in human lung cultures, a pH of inactivation less than 5.0, and lack of transmission to cohoused recipient ferrets. Prior immunity with seasonal H1N1 strain also reduced the viral load and disease burden of the virus.

Taken together, these data suggest that currently circulating H5N5 poses a low risk to humans but highlights the importance of phenotypic characterizations for future risk assessments as the virus evolves in wild birds.

(SNIP)

Discussion

The H5N5 (A/Washington/2148/2025) virus that caused a lethal human infection in 2025 was characterized for its pandemic potential with in vitro characterization of H5N5 revealing no neutralizing antibodies across a panel of human sera, indicating widespread susceptibility in the population.

However, in vivo assessment indicated that prior H1N1pdm09 immunity reduced viral burden and disease signs during H5N5 infection, suggesting that there is some protection in the human population from prior IAV infection. This observation is of particular interest given evidence that cross-reactive NA immunity to N1 from human seasonal H1N1 strains was protective against H5N1 infections (19–21), suggesting that there is likely another mechanism of action since the NA proteins are distinct subtypes.

In contrast to our data, characterization of two closely related (>99% nucleotide identity) H5N5 strains by Erdelyan et al. demonstrated high mortality in ferrets after infection (6). These two representative strains were isolated from a bird (crow) and a mammal (raccoon) and displayed a preference for binding avian influenza virus receptor, 3’SLN-linked sialic acid (6). Sequence comparison of the crow and racoon strains as well as the lethal human H5N5 isolate characterized herein indicates that there are no differences at canonical mammalian adaptive sites (Supplemental Table 1). The raccoon strain had modest transmission to two of three cohoused recipient ferrets, with one displaying clinical disease and another one only seroconverting, whereas we did not observe transmission to our cohoused recipients (Figure 2B).

Differences between the study outcomes could be due to the dose of the crow and racoon inoculums, which was 10x higher, differences in virus strains, and the duration of the cohoused exposure. A limitation of our study includes the assessment of only one H5N5 isolate, but there are currently no other human H5N5 isolate to compare to. Further characterization of circulating H5N5 strains is warranted to identify potential strains of higher pandemic potential.

H5N5 continues to circulate in wild bird populations in the US and Europe (22, 23) and thus will continue to evolve and adapt to new hosts. Ongoing surveillance and characterization studies are therefore warranted given its prevalence. Our in vitro studies provide guidance for targeted risk assessment studies in the future. We observed that H5N5 was stable in the environment at mid-range humidity levels and had NA activity similar to the H1N1pdm09 strain. However, H5N5 pH of inactivation was higher than 5.0, and this virus had poor replication capacity in HBE cultures.

Rather than full characterizations of evolving H5N5 strains, future studies could focus on pH of inactivation and HBE growth. Emerging isolates with higher replication fitness in HBE cultures and pH of inactivation ≤5.0 will be of higher risk and could then be tested for ferret transmission.

Australia: CSIRO Confirms Qld's H5N1 - SA Reports 2 `Suspected' Local Birds

 
Confirmed Positive H5N1 in Birds (n=18)

#19,261

While there was never much doubt, we now have confirmation from Australia's National Lab CSIRO that the seabird recovered from Moreton Island  (25 miles N.E. of Brisbane) has tested positive for H5N1.

H5 bird flu confirmed in a wild seabird found at Moreton Island

A dead petrel found by Queensland Parks and Wildlife Service (QPWS) rangers at Moreton Island (Mulgulpin) has been confirmed positive for H5 high pathogenicity avian influenza (H5 bird flu) in laboratory tests by the CSIRO Australian Centre for Disease Preparedness.

The positive test is the first confirmed detection of H5 bird flu in Queensland.

There remain no detections in poultry, nor evidence of large-scale deaths in any animals in Queensland.

The risk to human health remains low.

The community is being urged to continue to report sick or dead wild birds.

Queensland has been preparing for H5 bird flu and has strong response arrangements in place. Australia also has national arrangements to respond to emergency animal disease incidents.

Australia’s first case of H5 bird flu was reported on 20 June 2026 in Western Australia, with further detections in wild seabirds in WA, SA and NSW.

Department of Primary Industries Chief Veterinary Officer Dr Allison Crook said the confirmed positive detection was expected, and the Queensland Government was well prepared to respond.

“We have known that a H5 bird flu detection in Queensland was a matter of when, not if,” Dr Crook said.

“This confirmed positive result has not impacted our poultry sector or native wildlife.

“We have further escalated our surveillance program throughout the state, and are delivering heightened H5 bird flu awareness and engagement activities to ensure industries and communities know what to do.

“There have been more than 1,000 reports from Queensland to the hotline since the first reported case on 20 June 2026, and I thank the public for their support.

“I encourage the community and industry to continue to be vigilant,” Dr Crook said.

“If you find sick or dead wild birds or wildlife, avoid contact, keep children and pets away, record what you see, and report immediately to the Emergency Animal Disease Hotline on 1800 675 888.”

Meanwhile Australia's ABC News is reporting that South Australia has recovered 2 deceased local birds (greater crested terns), and has sent samples to CSIRO for confirmation.  While not explicitly stated in the article, this generally indicates a local test has returned a positive result.

Two additional H5 bird flu cases suspected in SA, including first on a metro beach

While I haven't found any official press releases, ABC News quotes SA Environment Minister Emily Bourke as saying one of these birds was recovered just 4 km from where Australia's first local infected seabird was detected earlier this month.

They quote the SA Environmental Minister as saying:

 "Unfortunately, we are finding that these two cases are in our local [bird] species, so we need to send these tests off now to Geelong for them to have confirmation at that centralised location that they are, or are not, the H5 high strand of this disease." 

Until now, all but one detection of H5N1 in Australian seabirds have been in migratory species.  Additional spread in local birds, while not unexpected, increases the chances of H5 establishing a permanent beachhead.

Results from CSIRO are expected early next week.

 

Preprint: Within- and between-host dynamics of highly pathogenic avian influenza in domestic birds from Pennsylvania farms and live bird markets

Graphic Generated By Gemini using USDA Data
 

#19,260

Last month 3 east coast states (RI, NJ, PA) reported outbreaks of H5N1 in Live Bird Markets (LBMs), raising the tally to 14 markets across 5 states (New York, Pennsylvania, Florida, Rhode Island, and New Jersey) reporting outbreaks in 2026.

Going back 4 years we find 78 reports across 7 states (New York, Pennsylvania, Florida, Rhode Island, New Jersey, Virginia, and California). 

As mentioned 3 weeks ago in USDA Reports Another H5N1 Outbreak at a Live Bird Market (Pennsylvania) - despite 3 June outbreaks in LBMs - the USDA had reported  zero outbreaks in commercial poultry in the region in the previous 90 days. 

Last month, in One Health: Mapping reported modes of transmission of HPAI A (H5N1) to humans: A scoping review, we looked at how live bird markets have traditionally played a large role in the spread (and evolution) of avian flu viruses.  

Exposure to live birds from LBMs has often been cited as a major risk factor for human infection with avian flu - particularly in Asia -  and we've seen cases whose likely exposures were cited as simply living near, or walking past an LBM (see J. Infection: Aerosolized H5N6 At A Chinese LBM (Live Bird Market)).

All of which brings us to a new preprint, published this week, which examines how HPAI H5N1 spread and evolved inside poultry farms and live bird markets in Pennsylvania between 2023 and 2025.

Due to its length, I've only posted some excerpts. Follow the link to read it in its entirety.  I'll have more after the break.

Within- and between-host dynamics of highly pathogenic avian influenza in domestic birds from Pennsylvania farms and live bird markets

Anna S Jaeger, Elena Cruz-Adames, Stephen D Shank, Irina Chupikova, Katie Kumta, Eman Anis, Louise H Moncla
doi: https://doi.org/10.64898/2026.07.17.739193
This article is a preprint and has not been certified by peer review

Preview PDF

Abstract

Since late 2021, highly pathogenic avian influenza viruses (HPAI) of the H5 subtype clade 2.3.4.4b have spread across the Americas, devastating wildlife, agricultural animals, and resulting in dozens of human spillovers. National surveillance strategies generally provide only a single representative sequence per poultry outbreak, precluding fine-scale geographic transmission inference or studies of within-outbreak evolution. 

We produced high-quality deep sequence data from 46 infected Galliformes and Anseriformes sampled from commercial farm and live bird market (LBM) outbreaks in Pennsylvania from 2023-2025. We found that H5N1 viruses were introduced into Pennsylvania at least 68 independent times. 

We recover independent origins of live bird market outbreaks within the same county 3 weeks apart, and transmission between Pennsylvania LBM and New York commercial birds, suggesting high transmission risk within the Northeast live bird market distribution system. 

Analyses of within-farm variant populations show frequent variant sharing between samples from the same outbreak, suggesting that variants are propagated among epidemiologically linked infections. We identified 9 known adaptive mutations in these samples, including one instance of PB2 D701N in a LBM chicken sample, suggesting that while rare, concerning mammalian adaptive mutations can be present within these domestic outbreaks. 

Our data suggest that domestic bird outbreaks support high circulating diversity and wide transmission bottlenecks, increasing the risk of minority variants arising and propagating between infections. These data can help inform targeted biosecurity measures and better quantify the risk of viral adaptation during agricultural outbreaks.

       (SNIP)

We identified approximately 17 independent introductions into Pennsylvania that resulted in domestic infections. Most strikingly, we identify multiple distinct introductions into live bird markets in Pennsylvania among samples collected less than three weeks apart. Upon further phylogenetic analysis of transmission between Pennsylvania and New York, we present compelling evidence of transmission between live bird market settings and distributors in these states, as well as New Jersey. Live bird markets and their distribution systems are a high risk environment for transmission of HPAI given their diverse sources, mixed species, and historical lack of regulations and compliance to biosecurity measures [46,47]. 

More recently, particularly since the influx of HPAI in4 North America, stronger regulations and biosecurity measures have been implemented at the state level for live bird market systems, in particular by the Live Bird Marketing System Biosecurity Assurance Program [48]. 

Our finding of LBM transmission involving domestic birds from multiple states, along with ongoing detections in the LBMS suggest that additional interventions, improvements, or regulation may be needed.

(SNIP)

Taken together, we show here the first of its kind data from natural infections in domestic birds utilizing phylogenetic and within-host methods to quantify diversity, evolution, and transmission across domestic outbreaks. The multiple independent introductions into the state throughout the epizootic show that Pennsylvania is likely a representative model state for understanding finer-scale transmission dynamics of H5N1. 

Our results present evidence that high levels of diversity is being shared within domestic outbreaks, and particularly that continued surveillance and increased regulation of live bird market systems is important for controlling interstate spread particularly within the Northeastern United States. Future study and surveillance where samples are collected from individual domestic infections will allow for true quantification of transmission bottlenecks to further inform biosecurity and control measures in domestic settings. 

        (Continue . . . )

 

In 2016's Interventions in live poultry markets for the control of avian influenza: A systematic review Vittoria Offeddu , Benjamin J. Cowling, and J.S. Malik Peiris laid out the risks of avian influenza from live bird markets, reviewed some of the possible interventions, and concluded:

 

Highlights

• Avian influenza viruses (AIVs) can infect humans. Bird-to-human transmission is particularly intense in live poultry markets.
• Periodic rest days, overnight depopulation or sale bans of certain species significantly reduce AIV-circulation in the markets.
• Market closure would lastingly reduce the risk of animal and human infection.

While there have been numerous attempts to phase out LBMs (see 2009's China Announced Plans To Shut Down Live Poultry Markets In Many Cities), most have encountered stiff public resistance. 

Larger, more modern cities like Hong Kong have gone to great lengths to regulate and restrict live bird markets, and last year, Shanghai Banned Live Poultry Sales until at least 2027.

Currently the CDC considers the risk of human infection (at least, for the general public) from our current clade 2.3.4.4b strain of H5N1 to be low. LBMs are treated as a `manageable' risk; where rest days, mandatory testing, enhanced cleaning, and occasional short‑term shutdowns are employed rather than permanent closures.

But HPAI H5 is always evolving, as the recent introductions of the B3.13 and D1.1 H5N1 genotypes attest.  How long the risk from LBMs will remain manageable is anyone's guess. 

In the meantime, the author's of today's report suggest that - in view of the ongoing detection of avian flu in LBMs - `. . . additional interventions, improvements, or regulation may be needed'.

Queensland Reports `Presumed Positive' H5N1 Test in Migratory Seabird

 

#19,259

After going a week without any new reports of H5N1 in Australia or New Zealand, overnight Queensland's Department of Agriculture announced that samples from a deceased petrel found on Moreton Island (25 miles N.E. of Brisbane) have (preliminarily) tested positive for H5N1.

Initial testing was by the Queensland Government’s Biosecurity Sciences Laboratory (BSL). Samples have been forwarded to CSIRO’s Australian Centre for Disease Preparedness for confirmatory testing.

Typically, even when CSIRO has been unable to fully sequence a sample, Australia has been treating local test results as `likely positive'.  Two announcements from Queensland's government follows:

Queensland detects first case of H5 bird flu


The Department of Primary Industries is responding to a suspect positive case of H5 high pathogenicity avian influenza (H5 bird flu) in Queensland.

This is Queensland’s first suspect positive case of H5 bird flu in a wild seabird.

Samples from a deceased petrel found on Moreton Island have tested positive for H5 bird flu during initial testing at the Queensland Government’s Biosecurity Sciences Laboratory (BSL).

Samples have been sent to CSIRO’s Australian Centre for Disease Preparedness for confirmatory testing.

Australia’s first case of H5 bird flu was reported on 20 June in Western Australia, with further detections in wild seabirds in WA, SA and NSW.

There remain no detections in poultry, nor evidence of large-scale deaths in any animals in Queensland.

The community is being urged to continue to report sick or dead wild birds.

Department of Primary Industries Chief Veterinary Officer Allison Crook said the suspect positive detection was expected and Queensland is well prepared for the next steps.

“We have known that a H5 bird flu detection in Queensland was a matter of when, not if,” Dr Crook said.

“The Queensland Government is well prepared to respond. This suspect positive result has not impacted our poultry sector or domestic wildlife,” she said.

“We are continuing our enhanced passive surveillance program throughout the state and would encourage the community and industry to continue to be vigilant,” Dr Crook said.

“If you find sick or dead wild birds or wildlife, avoid contact, keep children and pets away, record what you see, and report immediately to the Emergency Animal Disease Hotline on 1800 675 888.”

Suspect positive case of H5 bird flu

Biosecurity Queensland has detected suspect positive H5 bird flu in a deceased wild migratory seabird found on Moreton Island (Mulgulpin).

This result is not unexpected following the recent detections of H5 bird flu in Western Australia, South Australia and New South Wales.
On this page

What we are doing
What you need to do
Actions for bird and livestock owners
Signs of bird flu in birds
More information

What we are doing

We are:

• continuing to carry out surveillance
• testing birds and animals
• working with industry, government agencies and response partners
• supporting strong biosecurity practices to help reduce the risk of spread
• keeping Queenslanders informed as the situation develops.

Queensland has been preparing for H5 bird flu and has strong response arrangements in place. Australia also has national arrangements to respond to animal disease incidents.

What you need to do

If you see sick or dead wild birds or wildlife:

• Avoid contact with sick or dead birds, wildlife and their environment. Do not touch or collect them.
• Record what you see, if it is safe. Record the number of dead or sick birds or animals, the species, location, date and time. Take a photo if you can.
• Report sick or dead birds or wildlife to the Emergency Animal Disease Hotline on 1800 675 888.

Your report will be reviewed, and we will contact you if more information is needed. Not all reports will require follow-up, sampling, or further action.

Actions for bird and livestock owners

If you own, care for or work with poultry, review your biosecurity practices now. A strong biosecurity plan helps protect your birds and your property.

Bird and livestock owners should report unusual signs of disease or sudden deaths immediately to the Emergency Animal Disease Hotline on 1800 675 888.

Poultry owners should:

• keep poultry away from wild birds
• keep feed and water where wild birds cannot access it
• keep sheds, yards, aviaries and equipment clean
• limit visitors to areas where birds are kept
• ask essential visitors if they have recently been on other properties with poultry
• wash hands before and after handling birds and eggs
• change into clean footwear before entering poultry areas
• keep good records of bird movements or sales
• report unusual signs of disease or increased deaths in birds.
• Signs of bird flu in birds

Signs can include:

• sudden death
• lack of coordination, tremors or swimming in circles
• twisted necks or other unusual posture
• inability to stand or fly
• diarrhoea
• difficulty breathing, coughing or sneezing
• swelling around the head, neck and eyes
• cloudiness or change in colour of the eyes.

More information

Stay up to date with the H5 bird flu current situation in Queensland.
Visit birdflu.gov.au for more information.

Probably Nothing . . . But It feels a Bit Like Deja Flu

 
Credit China Daily - March 2006

#19,258

Readers with extremely long memories will remember the great shuttlecock shortage of 2006, which was blamed - at least partially - on China's reported culling of roughly 200 million birds between 2003-2006 due to HPAI H5N1. 

This was back when China actually acknowledged avian flu outbreaks in their poultry or wild birds, something which rarely happens today.  The most recent FAO avian flu activity map (since Oct 1st 2025) shows almost no HPAI H5 in Mainland China. 

Of course, South Korea and Japan both saw major avian flu outbreaks, and in South Korea they are still dealing with a serious egg shortage due to the culling of 11 million birds last winter. 

While it seems reasonable to assume that China (and Russia) both saw some poultry losses from avian flu last winter, you wouldn't know it from their official reports. 

All of which brings us to a Yonhap News report overnight which reads almost beat-for-beat like the 2006 article posted above.  So much so, I had to double check to make sure it wasn't a phantom news report from the past.

Badminton Shuttlecock Prices in Japan Soar... Shortage of Chinese Duck and Goose Feathers

Posted July 23, 2026, 15:30

They report a `stagnant demand for duck meat', which they attribute to `changing Chinese diary habits', which has resulted in a growing shortage of duck and goose feathers, and is forcing a move towards using `synthetic shuttlecocks'. 

While this article provides few details, it does state: 

`However, as avian influenza (AI) has recently been rampant, disease control costs have increased due to concerns about infection, worsening the management of poultry farms and leading to a shortage of feathers, a raw material.' 

Perhaps the most important caveat is, although this article mentions avian influenza as a potential factor, that doesn't necessarily mean HPAI H5.  China continues to battle multiple avian viruses, including LPAI H9N2, H3Nx, H6Nx, and H10Nx viruses. Some recent blogs include:

Virulence: Surveillance and biological characterization of H3 subtype avian influenza viruses in Eastern China

J. Inf.: Zoonotic Threat of Novel H6N2 Avian Influenza Virus with Internal Genes Exclusively Derived from H9N2, China, 2025

Vet. Microbiology: The novel H10N3 Avian Influenza Virus Acquired Airborne Transmission Among Chickens: An Increasing Threat to Public Health

Admittedly, this reported shortage of duck feathers is a weak signal at best, but the paucity of official reports from China makes it worth our notice, since we've seen other similarly vague news items prove to be significant in the past.

In 2008 a report by Helen Branswell (then of the Canadian Press) described an early signal of the first SARS-CoV outbreak in 2002. She reported:

Surging vinegar sales in China grabbed the attention of the folks who regularly scour the globe for what might be budding disease outbreaks, like those who work for the Canadian-led Global Public Health Intelligence Network. 

"We were getting lots of rumours, like a lot of sales of vinegar," explains Dick Thompson, who was the spokesperson for the World Health Organization's communicable diseases section at the time.

“Vinegar in southern China is used as a disinfectant. And so if there’s a run on vinegar, there’d be a suspicion that there was some kind of infectious disease or a widespread belief that there is an infectious disease outbreak. So at these meetings we’d been hearing this kind of drip, drip, drip come in about that.”

While our visibility of avian flu in China is limited, it is worth noting that last November - in China MOA Announces New Guidelines to Expedite Animal Vaccine Strain Approvals - we saw a rare acknowledgement that their agricultural vaccines program (including avian flu) was in need of an overhaul. 

Whether today's report turns out to be significant remains to be seen. Like I said, it is probably nothing. 

But, it does seem curious enough to warrant a mention.