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.