One Health: Mapping reported modes of transmission of HPAI A (H5N1) to humans: A scoping review

 

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Over the past 2 decades we've seen dozens of suspected ways that HPAI has transmitted to humans. While most have involved direct contact with an infected bird or animal, some have come from (direct or indirect) environmental exposures, and a few appear to have come from close contact with an infected human.

Due to the risks involved, the CDC has issued PPE guidance for both commercial and backyard raisers of poultry (and dairy workers), but it isn't clear how many are following this advice.

There are reportedly more than 11 million backyard poultry flocks in the United States, and tens of millions more in Europe and Asia. That's a lot of opportunities for spillovers. 

We've seen at least 2 fatalities linked to raising backyard birds in the United States (see H5N5 in Washington State and H5N1 in Louisiana, and there are a number of cases where we simply don't know the exposure. 

Many cases around the globe have been linked either to the slaughter, preparation, or consumption of poultry, as was mentioned in this recent report from the WHO:

Human infection with avian influenza A(H5N6) virus

From 1 to 7 May 2026, one new case of human infection with avian influenza A(H5N6) virus was reported to WHO in the Western Pacific Region. The case is a 55-year-old female from Chongqing Municipality, China, with symptom onset on 16 April 2026. She developed severe pneumonia, was hospitalised on 23 April, and died on 3 May. She had purchased, slaughtered, and consumed poultry. Samples collected from a cutting board tested positive for influenza A (H5). All close contacts tested negative and developed no symptoms.

Yet live bird markets flourish around the world, including here in the United States (see NJ & RI Both Report H5N1 in Live Markets), despite repeated calls for their closure (see Interventions in live poultry markets for the control of avian influenza: A systematic review).

In 2022 we looked at Zoonoses & Public Health: Aerosol Exposure of Live Bird Market Workers to Viable Influenza A/H5N1 and A/H9N2 Viruses, Cambodia, 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)).

These risks go far beyond just human exposure, of course, as live markets also bring together different types of birds which may also silently carry LPAI viruses like H3N2, H9N2, and H6N1, which could reassort with HPAI H5.

While many of these reports are anecdotal, or inconclusive, the reality is more than 1,000 people have been infected with H5N1, and it behooves us to understand the risks if we hope to avoid many more in the future. 

To that end we have a lengthy scoping review on the modes of transmission of the H5 virus to humans, one that includes a small - but significant - number of suspected human-to-human transmissions. 

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

Mapping reported modes of transmission of highly pathogenic avian Influenza A (H5N1) to humans: A scoping review

 Nicole Billias a b c, Victoria D’Alessandro a b, Dimitra V. Pouliopoulou a b, Jessica J. Wong a b h, Erin Miller a, Jessica P. Hopkins d e f, Eleni C. Boutsikari g, Lauren Cipriano h, Tiago da Veiga Pereira i, Jennie Johnstone j, Saverio Stranges k l m n, J. Scott Weese o, Joy C. MacDermid a b c, Kieran L. Quinn d, David Fisman d, Pavlos Bobos a b k 
  
https://doi.org/10.1016/j.onehlt.2026.101492 

         PDF  

Abstract

Background

Highly Pathogenic Avian Influenza A (subtype H5N1) poses a threat to human health, and its pandemic potential emphasizes the need to better understand detailed reported transmission pathways to humans. Existing literature is outdated or lacks detailed, comprehensive analysis of the range of transmission routes and how the virus may enter the human body.

Objective

To comprehensively map all reported H5N1 transmission pathways to humans, as well as viral entry routes.

Methods

CINAHL, Embase, MEDLINE, Scopus, PubMed, grey literature, and reference lists (of included studies) were searched up to October 29th, 2025, with no language restrictions. Observational studies and grey literature reporting H5N1 transmission evidence to humans were included. Two reviewers conducted duplicate screening independently. One reviewer completed data extraction, which was cross-verified for accuracy by a second. Findings were summarized narratively.

Results

120 sources met inclusion criteria (70 studies, 50 grey literature). Reported H5N1 transmission pathways were classified into animal-to-human (111 of 120 sources, 92.5%; including poultry-to-human in 102 sources [85.0%] and cattle-to-human in nine sources [7.5%]), environment-to-human (37 of 120 sources, 30.8%), and human-to-human (14 of 120 sources, 11.7%).

Reported transmission pathways were further classified as direct or indirect contact, synthesized, and linked to suspected routes of human entry, including mucosal entry (eyes, nose, mouth), inhalation of aerosols or droplets, ingestion, and percutaneous exposure. Entry routes are biologically plausible and do not imply relative likelihood or causal attribution.

Conclusions 

There are multiple reported pathways of H5N1 exposure, and a single pathway may involve multiple ways to infect humans. Further research is needed to determine causal mechanisms, identify specific risk factors and measures of association, and strengthen evidence-based prevention strategies.

        (Continue . . .)

Two years ago the WHO published Interim Guidance to Reduce the Risk of Infection in People Exposed to Avian Influenza Viruses, which lists a number of `risk factors', including:

• keep live poultry in their backyards or homes, or who purchase live birds at markets;

• slaughter, de-feather and/or butcher poultry or other animals at home;

• handle and prepare raw poultry for further cooking and consumption;

Given the potential public health threat, it makes sense to try to limit high-risk  exposures - particularly in backyard poultry, live bird markets, and commercial poultry and dairy operations - through better biosecurity and consistent use of PPEs.  

But as we discussed five weeks ago in MMWR: Knowledge, Attitudes, and Practices Regarding Avian Influenza Among Owners of Backyard Flocks, many backyard poultry producers still have limited knowledge of avian flu symptoms and risks, and their biosecurity & PPE  measures often fall short of recommendations.

Commercial poultry operations and dairy farms have been similarly reluctant or slow to fully implement biosecurity and PPE recommendations, and surveillance and reporting remains passive and incomplete.

And as for the public, most remain unconvinced of the seriousness of the  threat (see Two Surveys (UK & U.S.) Illustrating The Public's Lack of Concern Over Avian Flu).

While HPAI H5 many never gain the ability to spread efficiently from human-to-human, we do seem intent on giving it every opportunity to do so. 

Australia Confirms 5th Detection of H5N1 In Migratory Birds

 

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Last Saturday we learned of the 4th confirmed detection of H5N1 in Australian wild birds, and that a 5th test was presumed positive. Today Australian authorities confirmed that fifth case.

June 2026 H5 bird flu detection

As of 2:00pm AEST, 30 June 2026, Australia has five cases of H5 bird flu in wild birds confirmed by CSIRO’s Australian Centre for Disease Preparedness (ACDP).

There are four confirmed in Western Australia (WA) and one in South Australia (SA).

There is no evidence of any mass mortality. There is no evidence of infection in poultry or the wider agriculture industry.

The risk to human health remains low.

Australia is well prepared to respond quickly.

If you notice multiple sick or dead birds or other animals, you should not touch them or get too close. Record your location and report it to the 24-hour Emergency Animal Disease Hotline on 1800 675 888.

More information is available in the update below.

While the 5th detection overall, this is the 4th in Western Australia.  We get more details from the Department of Primary Industries and Regional Development.

Fourth positive H5 bird flu case confirmed in WA
Media release

Western Australia has recorded its fourth confirmed detection of H5 bird flu in a migratory seabird on the State’s South Coast.

Last updated: 30 June 2026

Western Australia has recorded its fourth confirmed detection of H5 bird flu in a migratory seabird on the State’s South Coast.

CSIRO’s Australian Centre for Disease Preparedness today confirmed the H5 bird flu strain in the previously reported suspect giant petrel found at Roses Beach, west of Esperance.

There has now been a total of five confirmed detections of H5 bird flu in Australia, including four in WA and one in South Australia.

All of the detections have involved migratory seabirds that are known to occasionally visit southern Australia.

There is still no evidence of spread or large-scale deaths in local wildlife or any detections in poultry.

The Department of Primary Industries and Regional Development (DPIRD) is leading the response in WA, with a focus on enhanced surveillance and early detection in this investigative phase.

The response is being coordinated across multiple levels of government, involving joint efforts from DPIRD, the Department of Biodiversity, Conservation and Attractions, local governments and other State agencies.

Divisional commands have been established in the South West and South Coast.

Surveillance along the Esperance coast continues and the DPIRD patrol vessel PV Hamelin will be deployed to support monitoring in the area.

This will enable observations of wildlife colonies in priority areas for any signs of ill health, death or unusually low numbers of species that would normally populate the islands in winter.

A community meeting will be held in Esperance early next week for authorities to share an update on the State’s response activities.

Training sessions are also being delivered with DBCA to support local governments, veterinarians and wildlife rehabilitators to safely retrieve sick or dead birds.

DPIRD is encouraging the community to continue to report unwell or deceased birds through to the Emergency Animal Disease Hotline on 1800 675 888.

There has been more than 672 reports from WA to the Emergency Animal Disease (EAD) hotline since Friday 19 June. These reports are being prioritised by DPIRD for further investigation or testing, based on the risk of H5 bird flu.

To date, a total of 25 negative test results have been recorded for coastal regions across the State, including the Esperance area, Mid West, Great Southern, South West, Peel and the Perth metropolitan area.

Anyone who sees sick or dead birds or marine mammals should AVOID and not handle the animals but RECORD and take photos or a video and REPORT to the Emergency Animal Disease Hotline on 1800 675 888.

More information is available on the Australian Government's Bird Flu (Avian influenza) website. 

While confirmed numbers remain low, this report indicates there is a sizable backlog of reports from the EAD hotline that have not been investigated or tested.  

So far, no poultry has been affected, but the bulk of Australia's poultry industry is located in the eastern half of the country, well away from these first detections.  

(Graphic generated using Perplexity)

Only time will tell if this is a short-lived, limited incursion or - as we saw in North America in late 2021 - the prelude to a hostile takeover.

Stay tuned. 

Nipah: WHO DON Report & A Narrative Review On Nipah Pandemic Preparedness

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Five months ago, in the wake of a nosocomial Nipah outbreak among healthcare workers in Bengal State, India - we reviewed the history and growing concerns over this bat borne henipavirus (see A Brief History of the Nipah Virus). 

Nipah, which is carried by fruit bats in Southeast Asia and the Indian Subcontinent (see map above), was first identified in the late 1990s following a large outbreak in Malaysia spread first from bat(s) to pigs - and then from pigs to humans - eventually infecting at least 265 people, killing 105 (see Lessons from the Nipah virus outbreak in Malaysia).

Limited human-to-human transmission has been occasionally documented, as in India in 2018 (see Nipah Transmission In Kerala Outbreak) where we saw apparent robust household and nosocomial transmission of the virus.

While most outbreaks have remained small, in July of 2018, in IJID: Enhancing Preparation For Large Nipah Outbreaks Beyond Bangladesh, we looked at an article that appeared in the International Journal of Infectious Diseases, that discussed the potential of the Nipah virus producing a large urban epidemic, similar to what we saw in West Africa with Ebola in 2014. 

Nipah (and its Australian cousin Hendra) belong to the Paramyxoviridae family of viruses, and over the past 10 years have been increasingly viewed as having some pandemic potential (see OFID: Viral Families with Pandemic Potential).

Late last week the WHO published a DON report on a recent case in Kozhikode district, Kerala State, India. Notably, this patient was symptomatic for roughly 10 days before being hospitalized, resulting in more than 100 close contacts who are now under monitoring. 

First, a brief excerpt from a much longer WHO report. 

Nipah virus disease - India

25 June 2026

Situation at a glance

On 11 June 2026, the Kerala State Health Department confirmed one laboratory confirmed case of Nipah virus (NiV) infection in Kozhikode district, Kerala State, India. The case is an adult male who developed symptoms on 30 May 2026 and was hospitalized on 10 June 2026. He presented with neurological manifestations and at the time of reporting is on ventilatory support in an intensive care unit (ICU).

As of 18 June 2026, a total of 104 contacts had been identified and were under monitoring, including health and care workers, with no reported secondary cases to date. NiV is a zoonotic disease transmitted to humans through infected animals, or through consumption of fruits or fruit products, such as raw date palm juice contaminated with the saliva, urine, or excreta of infected bats, as well as close contact with infected individuals. The current event involves a single confirmed case, with no secondary transmission identified to date. Public health measures are in place, including isolation, contact tracing, and enhanced surveillance. However, as the source of infection has not yet been identified and given the known presence of animal reservoirs, additional cases cannot be excluded.

 (SNIP)

The current event involves a single confirmed case with no evidence of secondary transmission as of 23 June 2026. The case has been isolated, and public health measures, including contact tracing, enhanced surveillance, and strengthened infection prevention and control in healthcare settings, have been rapidly implemented. The event appears to be geographically limited, with no evidence of international spread reported.

However, as the source of infection has not yet been identified and given the presence of known animal reservoirs and ongoing seasonal risk, additional cases, including sporadic zoonotic spillover, cannot be excluded.

This event represents the second notification of NiV infection in India in 2026, following the earlier two epidemiologically linked cases reported in West Bengal state in January 2026. There is an ongoing moderate sub-national risk, driven by recurrent zoonotic spillover, limited clinical specificity during the early stages of disease, and the absence of licensed vaccines or specific therapeutics, with potential for transmission among close contacts and in healthcare settings. At the regional and global levels, the risk remains low, given the absence of cross-border or international spread and the geographically contained nature of the outbreak.

        (Continue . . . )

Coincidentally, on the very same day (June 25th), a narrative review on Nipah, lessons from the COVID pandemic and pandemic preparedness, appeared in the Journal Infectious Diseases.

While this narrative is framed around the Nipah Virus, the authors clearly intend their work to include other high consequence infectious diseases. They write:

Unlike conventional narrative approaches, this framework (Fig. 1) emphasizes the dynamic interaction between past pandemic experiences and future preparedness needs, positioning NiV not as an isolated threat but as a critical test case for global readiness in the era of emerging “Disease X” scenarios. By linking systemic lessons, identified gaps, and targeted interventions, the framework provides a coherent and scalable model for strengthening pandemic preparedness across diverse settings.

Whether it will be Nipah, MERS, H5N1, or some other high consequence infectious disease (HCID) that sparks the next global health crisis is unknown, but we can be pretty confident that another pandemic will emerge; it's just a matter of time. 

And as bad as it was, COVID is not the worst case scenario. 

This is a long-read, so I've only posted the abstract.  Follow the link to read it in its entirety.  I'll have a bit more after the break.

Nipah virus and the lessons of COVID-19: Are we prepared for the next pandemic threat?

 Sharmake Gaiye Bashir a, Ilyas Abdullahi khalif b, Yusuf Abdullahi Hubow b, Ahmed Mohamed Omar b, Narura Omar Mohamed b, Ayan Abdullahi Mohammed b, Hibo hassan Mohamed b, Nour Ahmed Dahir b, Aniso Mohamed Abdi b, Abas Nor Abdi b, Yakub Burhan Abdullahi b c, Mohamed Sharif Abdi b c, Naima Ibrahim Ahmed b c, Yusuf Hared Abdi b c, Ahmed Abdinasir Abdulle ba 

Available online 25 June 2026.

      

https://doi.org/10.1016/j.imj.2026.100269Get rights and content
Under a Creative Commons license
 
Highlights

• Nipah virus represents a high-fatality zoonotic pathogen with credible pandemic potential and limited global preparedness.

• Lessons from COVID-19 reveal persistent gaps in surveillance, diagnostics, governance, and equitable access to countermeasures.

• Integrated One Health surveillance at human–animal–environment interfaces remains weak and under-operationalized.

• Absence of licensed vaccines or specific antivirals leaves health systems vulnerable to rapid Nipah virus escalation.

• Translating COVID-19 innovations into sustained, equitable preparedness is critical to prevent future “Disease X” scenarios.

Abstract

The coronavirus disease 2019 (COVID-19) pandemic has exposed profound and persistent weaknesses in global preparedness, including fragmented surveillance systems, governance failures, inequitable access to countermeasures, and erosion of public trust. Although SARS-CoV-2 has dominated global attention, other high-consequence zoonotic pathogens with pandemic potential have remained comparatively neglected.

Among these, the Nipah virus (NiV) represents a particularly serious threat, characterized by high case-fatality rates, zoonotic spillover from wildlife reservoirs, documented human-to-human transmission, and the absence of licensed vaccines or specific antiviral therapies. This narrative review synthesizes and contextualizes existing evidence on the NiV through the lens of lessons learned during the COVID-19 pandemic.

Drawing on epidemiological data, outbreak experience, and global health policy literature, this review examines the key dimensions of preparedness, including surveillance and diagnostics, laboratory and health-system capacity, vaccine and therapeutic development, emergency governance, ethical decision-making, and the operationalization of One Health approaches, with particular attention to low- and middle-income and fragile settings.

The review highlights that despite scientific advances achieved during COVID-19, preparedness for the NiV remains limited and uneven. Persistent gaps in integrated surveillance at human–animal–environment interfaces, constrained laboratory capacity, insufficient investment in countermeasures, fragmented governance, and enduring global inequities threaten timely detection and containment.

The NiV should therefore be understood not as an isolated regional concern, but as a warning signal for future “Disease X” scenarios, underscoring the urgent need to translate COVID-19 lessons into sustained, equitable, and multisectoral pandemic preparedness.

        (Continue . . . )

As we discussed 18 months ago in The Wrong Pandemic Lessons Learned - governments today seem to be less well prepared to deal with another global health crisis than they were a decade ago (see From Here To Impunity).

Health Agencies like the WHO, PAHO, ECDC issue frequent pleas and reminders to member states to share data, but local economic and political considerations often take precedence.

The all-too-common thread across the hundreds of epidemiological studies we've looked at on this blog is that more robust surveillance, testing, and sharing of data are essential (see here, here, here, here, here, here, and here), yet, progress continues at a glacial pace.

Although this review offers actionable steps that - if taken now - could help mitigate the effects of the next pandemic, it remains a tough sell to financially strapped governments.

But somehow I remain hopeful. If not for the next pandemic, perhaps for the pandemic-after-next.

Preprint: Two epidemics, one genotype, different outcomes: Evolutionary changes of Avian Influenza H5N1, genotype EA-2024-DI

Credit Avian influenza overview March–May 2026

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If anyone has any doubts over the impact of the 2025-2026 avian flu season in Europe, one need only look at the above graphic from this weeks Avian influenza overview March–May 2026, published by the ECDC.

After a fairly robust series of outbreaks between 2020 and 2023, reports declined sharply in 2023-2024. The following year, they picked up speed, and over the past 12 months they have skyrocketed in Europe. 

The reason behind this revival was the introduction of a new genotype (EA-2024-DI) which rapidly supplanted the previously dominant EA‑2021‑AB, which had driven the resurgence of avian flu after a lackluster 2019-2020 season. 

New genotypes come about due to reassortment, the swapping of gene segments by two or more flu viruses infecting the same host.  While birds are the most common host for reassortment, it can occur in any flu susceptible host, including humans. 

In the first couple of years following H5N1's arrival to north America, more than 100 new genotypes were detected. While most reassortants are unable to compete with the fittest of the group, several overachievers emerged, including B3.13 (Bovine HPAI), D1.1 (primary driver in birds), and D1.2 (detected in pigs). 

Last Friday, in Eurosurveillance: Detection of antibodies against avian influenza in European dairy cattle, the Netherlands, January 2026, we looked at the first confirmed spillover of HPAI H5N1 to European cattle, which cited genotype DI.2.1 (a sub-branch under the EA‑2024‑DI umbrella) as the causative agent. 

All of which brings us to a new preprint, published Friday in bioRxiv, which looks at the impact - and continued evolution - of EA-2024-DI in Europe over the past 2 years. They make particular note EA‑2024‑DI.2.1 which has not only driven huge die offs in wild birds, it has increasingly being found in mammalian wildlife and farm mammals. 

This is a lengthy, and data-dense, report, so I've only posted the Abstract and some excerpts from the Discussion. Follow the link to read it in its entirety.  

I'll have a bit more after the break.

Two epidemics, one genotype, different outcomes: evolutionary changes of Avian Influenza H5N1, genotype EA-2024-DI

 Bianca Zecchin,  Isabella Monne,  Marta Dianati,  Alessio Bortolami, View  Enrico Savegnago, Erga Shkodra, Sandra Revilla-Fernándezd, Mieke Steensels, Steven Van Borm, Emiliya Ivanova, Ivana Rončević, Vladimir Savić, Alexander Nagy, Charlotte K. Hjulsager, Casper Thorup, Lars E. Larsen, Imbi Nurmoja, Ari Kauppinen, Niina Tammiranta, Francois-Xavier Briand, Beatrice Grasland, Ann Kathrin Ahrens, Anne Pohlmann, Anne Günther, Timm Harder, Peter Malik, Laura Garza Cuartero, Svetlana Cvetkova, Juris Ķibilds, Žanete Šteingolde, Egidijus Pumputis, Simona Pileviciene, Chantal J. Snoeck, Manon Bourg, Oxana Groza, Beatriz Bellido Martin, Ron Fouchier, Sanne Thewessen, Oanh Vuong, Monika Ballmann, Marc Engelsma,  Cathrine Arnason Bøe, Anna Pikula, Krzysztof Śmietanka, Margarida Dias Duarte, Margarida Henriques Mourão, Iuliana Onita, Dejan Vidanovic, Zuzana Dirbakova, Martin Tinak, Brigita Slavec, María José Ruano, Maite Barrios, Fereshteh Banihashem, Caroline Bröjer, Stina Hedblom, Siamak Zohari, Claudia Bachofen,  Ashley C. Banyard, Holly A. Coombes, Ben Clifton,  Benjamin C. Mollett,  Joe James, Michael J. McMenamy, Robyn McKenna,  Ken Lemon,  Calogero Terregino,  Alice Fusaro

doi: https://doi.org/10.64898/2026.05.25.727580

Preview PDF

Abstract

Since 2020, high pathogenicity avian influenza H5Nx viruses of clade 2.3.4.4b have become enzootic in Europe, causing recurrent epidemic waves characterized by extensive reassortment events. Here, we describe the emergence of a single high-fitness genotype (EA-2024-DI) that has driven two consecutive waves, evolving into distinct sub-lineages. 

While its circulation is ongoing, during the 2025-2026 wave it caused an unprecedented number of cases in wild birds. Using phylodynamic analyses of a large dataset of genomic sequences, we compared the spatial diffusion and host transmission pattern of the EA-2024-DI sub-lineages across the three most recent epidemic waves (2023-2024, 2024-2025 and 2025-2026). 

We show that the genotype has persisted over time and has spread primarily through wild Anseriformes, but with a marked change in the transmission patterns between the different waves and a shift in the epicenter from Eastern to Central Europe, the latter having emerged as an important hub for virus diffusion throughout Europe.

Our results reveal a recent increase in the frequency of viruses from wild and domestic mammals carrying mutations enhancing virus replication in mammalian hosts, highlighting the importance of proactive monitoring of this group of hosts to better understand its role in the virus ecology and evolution.

(SNIP)

Discussion

Since the introduction of the HPAI A(H5) of clade 2.3.4.4b in 2020, European epidemic waves have been characterized by the emergence of new genotypes with an ever-increasing ability to infect a broad range of wild birds4 . From 2020 to 2023, a rapid turnover of genotypes was observed, most of which became extinct after one or two epidemic waves, whilst others continued to circulate persistently at low frequencies in well-defined ecological niches (e.g., genotypes EA-2021-I, EA-2024-DT, EA-2022-BB andEA-2024-DA)4,6,16. 

Since October 2024, for the first time in Europe, a single genotype, EA-2024-DI, has driven two successive epidemic waves, 2024-2025 and 2025-2026, but with a completely different outcome. An unprecedented number of cases in wild birds was recorded during the 2025-2026 epidemic wave, representing a six-fold rise compared to the equivalent period (1 October-31 March) of the 2024-2025 wave (https://eurlaidata.izsvenezie.it/). 

What drove this exceptionally high level of viral circulation in the wild avian population?

This study reveals that, during the 2024-2025 epidemic, two sub-lineages, EA-2024-DI.1 and EA-2024-DI.2 were co-circulating. These variants evolved from the EA-2024-DI genotype that emerged in Europe in late 2023. The current 2025-2026 epidemic, however, has been caused by a newly emerged drift variant of EA-2024-DI.2, namely EA-2024-DI.2.1.

        (Continue . . . )

As we've seen already in Europe, North America, South America, and Antarctica - when HPAI reaches new territories, it gains access to a more genetically diverse pool of LPAI viruses - and that often helps to fuel its evolution; sometimes in unexpected ways. 

A little over 2 years ago, HPAI H5 infection of cattle, sheep, and goats was thought highly unlikely.  Today, we've seen it on at least 2 continents (and likely a 3rd), likely driven in large part by its increasing genetic diversity. 

This past week, HPAI H5N1 reached Australia for the first time, and there it will find access to not only more unique LPAI viruses, it will find a whole new range of warm-blooded hosts.

While it is impossible to know what evolutionary advantages HPAI may find down under, past performance suggests we should be wary. 

But even if HPAI somehow fails to establish a beachhead in Australia, H5 seems to be evolving with very little constraint on the other 6 continents it has already conquered.  

Arguably Europe's EA-2024-DI.2.1, and North America's B3.13 and D1.1 genotypes are the biggest HPAI threats we've seen to date, but they could easily all be eclipsed by something `new and improved'  sometime in the near future. 

Stay tuned. 

Texas: New World Screwworm (NWS) Now Reported in 10 Counties

 

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The spread of the New World Screwworm (NWS) in Texas continues to accelerate with 10 counties now reporting detections in livestock. Thus far, we've not seen any reports in wildlife, although they must certainly exist. 

Currently Edwards county has reported the most detections (n=6), followed closely by Crockett County (n=5).

Given the life cycle of the NWS can be as short as 21 days (see below) we are likely already well into the second generation in Texas, which may account for the doubling of cases reported over the past 7 days.  

Note: The NWS is extremely cold intolerant, and can only successfully overwinter in extreme south Texas and Southern Florida (and then, only during mild winters).

While the return of cold weather in the fall should kill off the NWS population in the United States, we could see 5 or 6 more generations emerge before then, each likely larger than the last. 

At least, until the release of sterile flies begins to have an effect. 

 Reportedly, the USDA is able to disperse between 4 and 8 million sterile screwworm flies per week into the known infested counties of Texas.

New production facilities are being constructed, including a massive sterile fly production facility at Moore Air Base in South Texas, which is expected to produce 100 million sterile flies per week by November 2027 (increasing to 300 million a week by the end of 2028).

If we start seeing a decline in cases later in the summer, it could be an early indication the program is having an impact. Until then, Texas (and potentially other states) have a long hot battle ahead. 

Australia: DAFF Confirms 4th H5N1 Positive Wild Bird

 

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A week ago Australia reported its first 2 detections of HPAI H5N1, both in migratory birds (Brown Skua & Giant Petrel) in Western Australia (see Australia: 2nd H5N1 Infected Bird Confirmed), followed last Wednesday by a 3rd confirmed detection in South Australia - roughly 1,000 miles east - on the Fleurieu Peninsula, very near Adelaide. 

While detections remain sporadic, the overriding message from the Australian government is to avoid close contact with sick birds (or wildlife), record the incident details, and report sightings to the the Emergency Animal Disease Hotline.

Today we've have the following brief confirmation from Australia's DAFF of a 4th positive case - again in Western Australia - which also reports a presumed 5th case, also in WA.

H5 bird flu testing update
 
27 June 2026

Attributable to Australian Chief Veterinary Officer, Dr Beth Cookson:

Testing at CSIRO’s Australian Centre for Disease Preparedness (ACDP) has confirmed H5 high pathogenicity avian influenza (bird flu) in a giant petrel in Western Australia.

This detection marks the fourth wild migratory seabird in Australia to return a positive result for H5 bird flu, with two others confirmed in Western Australia and one in South Australia.

Western Australian has also reported a further suspect positive detection, in a giant petrel found at Roses Beach, west of Esperance, with samples sent for confirmatory testing at CSIRO’s ACDP. At this stage, there have only been detections in vagrant migratory seabirds that occasionally visit southern Australia. There remains no evidence of any mass mortality events and there are no detections in poultry or in our agricultural production system.

The risk to human health remains low.

You can help to determine if H5 bird flu has spread. If you see multiple sick or dead birds or other animals, do not touch them. Avoid contact. Record what you see. Report it to the Emergency Animal Disease Hotline on 1800 675 888 from anywhere in Australia.

For more information visit: birdflu.gov.au