Updated CDC Surveillance Numbers on Multi-State Cyclosporiasis Outbreak

CDC Surveillance Updated Jul 10th - 843 Confirmed cases

 #19,244

Ten days ago, in Cyclosporiasis Reports: CDC & Michigan DOH, we looked at early reports of a multi-state outbreak of cyclosporiasis, with the CDC reporting 145 cases acquired in the United States between May 1st and June 15th.

At the same time - and not included in the CDC's count - Michigan was reporting an additional 170 cyclosporiasis infections over the previous 9 days.

While fairly common in developing tropical, or sub-tropical countries, Cyclosporiasis – a parasite infection usually acquired through consuming food or water contaminated with Cyclospora cayetanensis - is relatively rare in the United States.

Although it still likely underrepresents the full burden of this outbreak, the CDC's latest update lists 843 confirmed cases, but acknowledges > 1,500 additional reports are under investigation. 

Surveillance of Cyclosporiasis

For Public Health
July 10, 2026

Key points

• CDC is aware that states are likely to report higher case counts of cyclosporiasis than reflected in CDC data and is working closely with states to update numbers as additional cases are confirmed. Since May 1, 2026, CDC has received reports of 843 confirmed domestic cases of cyclosporiasis and is aware of more than 1,500 cases that require further analysis to confirm the illness as domestically acquired cyclosporiasis. So far this year, multiple states have reported an increase in cases in the last two weeks compared to the same period in 2025.

• State and federal partners are working together to investigate several outbreaks of cyclosporiasis. Investigations to identify source(s) of illness are ongoing.

• Cyclosporiasis is a gastrointestinal disease caused by the microscopic parasite Cyclospora.

• On a regular basis, CDC reports all laboratory-confirmed cases that are received from states. State data may include both probable and confirmed cases, which in turn is likely to reflect a higher case count than the CDC surveillance data because initial case reports have not yet been reported to CDC. CDC does not report probable cases.

Current situation

As of July 9, 2026, 843 cases were reported in people who acquired cyclosporiasis in the United States. Cases were reported by 31 states. These people became sick after eating food in the United States and did not report any travel during the 14 days before they got sick.

Sick people ranged in age from 5 to 88 years, with a median age of 44, and 59% were female. The median illness onset date was June 18, 2026 (range: May 1 – July 5). Of 843 people with information available, 86 were hospitalized. No deaths have been reported.

Multiple jurisdictions have reported an increase of cases in the last two weeks compared to the same period in 2025. We assume a 6-week reporting lag between illness onset and case reporting to CDC; therefore, we anticipate that case counts will continue to rise as data are received.

CDC teams are working diligently to collect, analyze, and provide data at the national level. State health departments may have more timely information about the situation in their jurisdictions.

Local, state, and federal (CDC, FDA) public health authorities are investigating several clusters of cases in more than one state. The numbers reported on this page reflect a total surveillance count of cases across the United States, including clusters of cases currently under traceback investigation by FDA and cases that have not been linked to a common source. Investigations to identify potential sources are ongoing.

In order to help prevent infection, the CDC recommends:

Prevention tips

People can take the following food and vegetable handling recommendations to prevent foodborne illness related to fresh produce:

Wash

• Wash hands with soap and water before and after handling or preparing raw fruits and vegetables.

Prepare

• Wash all fruits and vegetables thoroughly under running water before eating, cutting, or cooking.
• Fruits and vegetables that are labeled "prewashed" do not need to be washed again at home.
• Scrub firm fruits and vegetables, such as melons and cucumbers, with a clean produce brush.
• Cut away any damaged or bruised areas on fruits and vegetables before preparing and eating.

Store

• Refrigerate cut, peeled, or cooked fruits and vegetables as soon as possible (within two hours).

  

Cambodian MOH Announces 5th Human H5N1 Case of 2026

 

#19,243

With thanks for the head's up from @FluTrackers, we have the following announcement from Cambodia's Ministry of Health on their 5th confirmed HPAI H5N1 human infection of 2026 - and 39th in just over 3 years - this time involving a 9-month-old girl from Phnom Penh which was confirmed positive on July 9th.

While most infections in Cambodia have been linked to direct or indirect exposure to infected poultry, there is no mention in today's report a suspected source of infection. The investigation, however, is ongoing. 

The MOH announcement, along with the translation, follow:

(Translation)

Kingdom of Cambodia
Nation Religion King
Ministry of Health

Press Release

On Bird flu case in 9-month-old girl

The Ministry of Health of the Kingdom of Cambodia would like to inform the public that there is 1 case of avian influenza in a 9-month-old girl who was confirmed to be positive for the H5N1 avian influenza virus on 9 July 2026 by the National Institute of Public Health and the Pasteur Institute of Cambodia. The patient is a resident of Prek Ta Kong village, Chak Angre Leu commune, Meanchey district, Phnom Penh. The patient has been placed in isolation at the hospital and is receiving intensive medical care.

The emergency response team of the national and sub-national ministries of health has been collaborating with the teams of the provincial agriculture departments and local authorities at all levels to actively investigate the outbreak of bird flu and respond according to technical methods and protocols, find the source of transmission in both animals and humans, and search for suspected cases and contacts to prevent further transmission in the community, as well as distribute Tamiflu to close contacts and conduct health education campaigns among residents in the affected villages.

The Ministry of Health would like to remind all citizens to always pay attention to and be vigilant about bird flu because H5N1 bird flu continues to threaten the health of our citizens. We would also like to inform you that if you have a fever, cough, runny nose, or difficulty breathing and have a history of contact with sick or dead chickens or ducks within 14 days before the onset of symptoms, do not go to gatherings or crowded places and seek consultation and examination and treatment at the nearest health center or hospital immediately. Avoid delaying this, which puts you at high risk of eventual death.

How it is transmitted: H5N1 bird flu is a type of flu that is usually spread from sick birds to other birds, but it can sometimes be spread from birds to humans through close contact with sick or dead birds. Bird flu in humans is a serious illness that requires prompt hospital treatment. Although it is not easily transmitted from person to person, if it mutates, it can be contagious, just like seasonal flu.

How to prevent:

Do not touch or eat sick or dead chickens and wear gloves and a mask or cover your nose with a scarf before handling chickens for food. Then blanch them in boiling water before plucking their feathers.

1/2

Address: Lot No. 80, Samdech Pen Nut Street (289)
Phone: (+855) 23 885 970

Website: www.moh.gov.kh

Sangkat Boeung Kak 2, Khan Toul Kork, Phnom Penh

Email: info@moh.gov.kh

Telegram: t.me/MOHCambodia

In February of 2023 an older clade of H5N1 (2.3.2.1.x) reemerged in Cambodia's population after a 9 year absence, spilling over into 6 humans in 2023, 10 people in 2024, and 18 people in 2025.

Last October Dr. Erik Karlsson (@eakarlsson.bsky.social‬) from the Institut Pasteur du Cambodge, Phnom Penh, Cambodia, - along with a long list of colleagues - published a brief letter in the NEJM on first 16 cases.

Among them were 4 `clusters' (Father/Daughter, two neighbors, 2 siblings, and 2 cousins living in the same household), 6 fatalities, and 12 cases < 18 years of age.

While human-to-human transmission was considered, the available evidence suggests a `shared' exposure instead, with infected poultry the most likely source of infection.

Most of these recent Cambodian cases have been due to a new reassortment of an older clade of the H5N1 virus (recently renamed 2.3.2.1e) - which appears to be spreading rapidly through both wild birds and local poultry.

Although we usually focus on the more dominant H5 2.3.4.4b clade, these cases remind us that there are other lineages of HPAI H5 still in circulation around the globe (see Viruses: Zoonotic Implications of the Co-Circulation of Clade 2.3.4.4b and 2.3.2.1a H5N1 Avian Influenza Viruses in Nepal in 2023), and each is on their own evolutionary trajectory.

In addition to this very active Cambodia lineage of H5N1, some of the other HPAI H5 contenders we continue to follow include:

South Korea: H5N9 Rising

Viruses: Novel Reassortant H5N2 Highly Pathogenic Avian Influenza Viruses from Backyard Poultry in Mexico

Preprint: Emergence of a Novel Reassorted HPAI A(H5N2) Virus Associated with Severe Pneumonia in a Young Adult

Washington State DOH: H5N5 Avian influenza confirmed in Grays Harbor County resident

Preprint: HPAI A (H5N1) Clade 2.3.2.1a Virus Infection in 2 Domestic Cats, India, 2025

EID Journal: Influenza A(H5N1) Virus Clade 2.3.2.1a in Traveler Returning to Australia from India, 2024

EM&I: Characterization of oseltamivir-resistant A(H5N1) clade 2.3.4.4b, genotype D1.1 variants identified in poultry farms of British Columbia, Canada

Abrupt Shift in H5N1 Genotypes in Wild Birds in US/Canada

Nature https://www.nature.com/articles/s41591-026-04300-1

#19,242

In the fall of 2024 - while we were watching the bovine B3.13 genotype spread in U.S. cattle - a new genotype (D1.1) of H5N1 appeared in Canada and the Pacific Northwest which very quickly became dominant in wild birds and swept eastward across the United States and Canada.

Since then, we've seen roughly 2 dozen confirmed human infections from this D1.1 genotype - several of them severe or fatal (see CDC Statement: First H5 Bird Flu Death Reported in United States) - along with studies suggesting it may better adapted to humans than B3.13 (see J.I.D.: Avian influenza virus A(H5N1) genotype D1.1 is better adapted to human nasal and airway organoids than genotype B3.13).

In early 2025  D1.1 was  detected in dairy cattle in two states (Nevada & Arizona), and later in Wisconsin, further raising concerns over its ability to infect mammals.

When it comes to treating H5N1 infection, Oseltamivir (aka `Tamiflu') remains the overwhelming drug of choice (see below), and makes up > 90% of our stockpiled influenza antiviral armamentarium. 

CDC Influenza Antiviral Medications: Summary for Clinicians - Jan 2026

Previous reports on the incidence of oseltamivir resistance in H5N1 have been fairly reassuring (see 2023's Antiviral Research: Antiviral susceptibility of clade 2.3.4.4b HPAI H5N1 Viruses Isolated From Birds & Mammals in the United States, 2022), but we've seen how quickly that status quo can change. 

Which is why the surprise announcement in February of 2025 that Oseltamivir Resistant H5N1 (Genotype D1.1) had been found On 8 Canadian Poultry Farms in the fall of 2024, raised so many concerns.

In a report from Canada's CFIA and PHAC - the authors described the detection of a (previously) rare H275Y substitution in the neuraminidase (NA) protein of a number of genotype D1.1 isolates, one which is associated with strong resistance to the NA inhibitors oseltamivir and peramivir.

Normally, we only see this mutation appear in a small percentage (1%) of patients receiving antiviral treatment.  Because it is thought to exact a `fitness penalty' on influenza A viruses - limiting forward transmission -  H275Y in the `wild' is fairly rare. 

But over the past few years we've seen evidence of creeping oseltamivir resistance in seasonal H1N1 (FluView Week #20: EOY Review of Increased Detection of Oseltamivir Resistant H1N1 Viruses), along with growing concerns that oseltamivir monotherapy may no longer be the most effective treatment of H5N1.

Emerg Microbes & Inf: Antiviral Activities of Multiple Antivirals Against HPAI H5N1 in Vitro and in Mice

Nature Comms: Baloxavir outperforms oseltamivir, favipiravir, and amantadine in treating lethal influenza A(H5N1) HA clade 2.3.4.4b infection in mice

Nature Comms: Oseltamivir and Baloxavir Monotherapy and Combination Therapy Efficacy Against Clade 2.3.4.4b A(H5N1) Influenza Virus Infection in Ferrets

All of which brings us to a new study, published in Emerging Microbes & Infections, which characterizes the oseltamivir resistant D1.1 viruses detected on 8 Canadian poultry farms in the fall of 2024.  

This is a lengthy, and at times technical, review.  I've posted the abstract and a few excerpts below, but many will want to read the report in its entirety.  I'll have a bit more after the break.

Characterization of oseltamivir-resistant A(H5N1) clade 2.3.4.4b, genotype D1.1 variants identified in poultry farms of British Columbia, Canada

Maxime Cochin , Yacine Abed , Robert Vendramelli , Katrina Dionne , Catherine Bourassa , Geneviève Laroche , show all
Article: 2686474 | Received 16 Feb 2026, Accepted 04 Jun 2026, Published online: 08 Jul 2026
 https://doi.org/10.1080/22221751.2026.2686474

ABSTRACT

Highly pathogenic avian influenza A(H5N1) viruses of clade 2.3.4.4b, genotype D1.1, are responsible for widespread outbreaks in poultry and continue to cause sporadic, sometimes severe, human infections. Herein, we characterized a wild-type (WT) influenza A(H5N1) D1.1 isolate (BC-H5N1-WT) and its H275Y neuraminidase (NA) variant (BC-H5N1-H275Y), both of which emerged on farms in British Columbia, Canada, during the fall 2024 outbreak.

In vitro analysis assessed replication kinetics in MDCK cells, with supernatants collected at different days post-infection (p.i.) and titrated by TCID50 and qRT-PCR. Neuraminidase inhibitor (NAI) susceptibility was determined by NA inhibition assays, whereas susceptibility to baloxavir acid (BXA) was evaluated by plaque reduction assay. In vivo virulence was evaluated in BALB/c mice infected with serial 10-fold dilutions of each virus to monitor weight loss and mortality. Viral titers in lungs, brain, nose, kidney, spleen, and heart were quantified at day 4 p.i. The BC-H5N1-WT virus was susceptible to the four antivirals tested, whereas BC-H5N1-H275Y displayed resistance to oseltamivir and peramivir but remained susceptible to zanamivir and BXA.

The BC-H5N1-WT exhibited significantly higher viral replication titers than BC-H5N1-H275Y at all tested time points and showed larger plaque sizes. In mice, BC-H5N1-WT was more virulent with LD50 values of 1.78 × 103 PFUs compared to 8.71 × 104 PFUs for BC-H5N1-H275Y, and produced higher viral titers in lungs and other organs. Despite the reduced fitness of the resistant H5N1 D1.1 variant, its emergence in the absence of viral selection pressure underscores the need for continued surveillance.

        (SNIP)

In October 2024, several chicken farms in the province of BC, Canada, faced an outbreak of HPAIV. Whole genome sequencing confirmed that the virus was an H5N1 virus of the clade 2.3.4.4b [Citation7]. Phylogenetic analysis of the hemagglutinin (HA) and neuraminidase (NA) genes confirmed that the viruses involved were reassortant H5 viruses of clade 2.3.4.4b with an avian NA of N1 subtype from a North American wild bird lineage [Citation7].

Notably, this NA has a longer stalk compared to the truncated NA stalk of traditional HPAI H5N1 strains [Citation8]. Fully Eurasian 2.3.4.4b H5N1 viruses also possess this untruncated (long-stalk) NA, differing from the short-stalk NA common in most pre-2020 highly pathogenic H5N1 strains.

Interestingly, the NA gene from 8 of the 45 sampled poultry farms harboured the well-described H275Y (N1 numbering) substitution that confers high levels of resistance to oseltamivir (OSV) and peramivir (PER), which are influenza NA inhibitors (NAI).

Of note, there was no evidence of OSV or PER use in the related farms that could explain the presence of such H275Y mutants in these animals. Although old H1N1 viruses with the H275Y substitution were associated with a fitness loss [Citation9–11], more recent seasonal and pandemic H1N1 mutant viruses were more fit than the wild-type (WT) virus due to the presence of permissive NA mutations [Citation12–14].

       (SNIP)

It has been well described that the H275Y NA substitution can be selected under OSV pressure either clinically or in experimental in vitro/in vivo procedures. However, to the best of our knowledge, there was no use of OSV in poultry that could explain the emergence of the H275Y NA substitution in BC farms.

• One possible explanation could be poultry exposure to antivirals in the environment (e.g. via contaminated water near human treatment centers) [Citation40]. 
• Another possibility is cross-species contamination where the mutation would emerge in humans and spills back into poultry but the only human Canadian case with H5N1 infection so far was not infected by this mutant [Citation6].
•  A more probable scenario seems to be that the H275Y substitution has emerged spontaneously as influenza viral replication involves an error-prone RNA-dependent RNA polymerase, with random mutations occurring frequently. Such mutation could potentially favour a more optimal balance between HA and NA in some viruses.

OSV is considered the preferred antiviral for the control of a potential influenza pandemic involving avian influenza viruses such as H5N1. Consequently, stockpiles of this compound have been established in several countries worldwide. This study and other observations suggest that it would be unwise not to consider alternatives in the event of the emergence of the H275Y substitution. 

 

This should include the consideration of other antivirals such as BXM, as well as combinations of antivirals with different mechanisms of action, i.e. ZAN (NAI) and BXM (polymerase inhibitor). Also, our findings confirm the need for extensive surveillance studies for influenza drug resistance not restricted to humans.

        (Continue . . . )
 

While the origin of this cluster of H275Y bearing H5N1 viruses remains unclear, the good news is these viruses (at least, back in 2024) showed diminished virulence (in BALB/c mice).

But as we saw with seasonal H1N1 in 2008, `fitness penalties' can be offset by permissive mutations elsewhere in the NA, which is why we follow reports like this one with interest.  

D1.1 isn't the only genotype of concern, and new genotypes will undoubtedly emerge in the future. Most will be evolutionary failures, but the success of B3.13 and D1.1 remind us there are exceptions. 

Even if widespread oseltamivir resistance doesn't emerge, our antiviral stockpile is limited, and we've previously seen problems getting them to patients during the first critical 48 hours of infection (see Sporadic Tamiflu (Oseltamivir) Shortages Reported In U.S. & Canada). 

Once again, our first line of defense will likely rely heavily on NPIs (non-pharmaceutical interventions), like face masks, hand washing, ventilation, staying home while sick, and avoiding crowds.

Which is why I'm recommending that people seriously consider now (see #Natlprep 2025: Personal Pandemic Preparedness) what they will do if another pandemic virus should embark on a new world tour.

Australia Confirms H5N1 in Local Seabird - Confirmed Detections (N=13)

Greater Crested Tern

Link  CC 4.0 Author mattf1996

#19,241

While long expected (see Australia : Biodiversity Council Webinar on HPAI H5 Avian Flu Threat), just three weeks ago Australia reported their first detection of HPAI H5N1 in a migratory bird (brown skua) in Western Australia.

Since then two other states (South Australia & NSW) have reported detections in migratory birds - with the nation's tally standing at 7 as of Monday, July 6th.

Overnight (here in the U.S.) Reuters has reported two new events of import - the first detection of H5N1 in a local seabird in SA, and testing of a dead seal in NSW -  although the most recent governmental summary report mentions neither of them.

It is also worth noting that some of the granular reporting featured in earlier  announcements (exact locations, dates of recovery, suspected cases under investigation, etc.) have recently been replaced by briefer summaries. 

 First, the latest official update. 

June 2026 H5 bird flu detection

As of 8.30pm AEST, 10 July 2026, Australia has 13 confirmed detections of H5 bird flu in wild birds.

There are seven confirmed in Western Australia (WA), five in South Australia (SA) and one in New South Wales (NSW).

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 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 a bit terse, we get some additional detail - including confirmation of the detection in a local seabird - in the following report from Australia's Chief Veterinary Officer: 

H5 bird flu testing updates 

10 July 2026

Attributable to the Australian Chief Veterinary Officer, Dr Beth Cookson:

Testing at CSIRO’s Australian Centre for Disease Preparedness has confirmed four additional detections of H5 high pathogenicity avian influenza (bird flu).

This includes a detection in a greater crested tern, found near Robe, South Australia. This is the first detection of H5 bird flu in an Australian wild non-migratory seabird.

CSIRO’s ACDP has confirmed two additional positive cases in wild migratory seabirds from South Australia. The petrels were found in Port Vincent, Yorke Peninsula and Emu Bay, Kangaroo Island.

CSIRO’s ACDP has also confirmed another positive result in a previously reported suspect petrel from Mullaloo Beach, Perth in Western Australia. Testing remains underway for a further suspect case from a petrel at Horrocks Beach in the Shire of Northampton.

There have now been 12 confirmed or presumed positive detections of H5 bird flu in 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. 

And lastly we get the following update from Western Australia's Department of Primary Industries and Regional Development, where roughly 100 of  > 1,400 wildlife-related reports have thus far been investigated, producing 7 positive results.

H5 bird flu confirmed on northern WA beaches
Media release

Western Australia has now recorded seven confirmed (or presumed positive) cases of H5 bird flu in individual wild migratory seabirds.

Last updated: 10 July 2026

Western Australia has now recorded seven confirmed (or presumed positive) cases of H5 bird flu in individual wild migratory seabirds.

Testing at CSIRO’s Australian Centre for Disease Preparedness today confirmed the virus in the previously reported suspect positive dead petrel at Mullaloo Beach on the north Perth metropolitan coast.

Another dead petrel previously reported at Horrocks Beach near Northampton was classified as presumed positive with further testing unable to definitively determine H5 bird flu virus through viral sequencing.

It is considered highly likely this bird was infected with H5 bird flu based on the H5 test results, species involved, coastal location and the broader epidemiological picture.

WA is responding to both cases with heightened surveillance in the coastal areas.

Nationally, there have been 13 confirmed or presumed positive results of H5 bird flu in Australia.

This includes 12 wild migratory seabirds, and one confirmed detection announced today in a greater crested tern found near Robe in South Australia. This is the first confirmed detection in an Australian non-migratory seabird.

Importantly, at this time, there is no evidence of any large-scale deaths in wildlife, nor any evidence of infection in poultry or in our agricultural production system

The seven confirmed detections in WA are isolated occurrences and dispersed along a significant length of coastline from east of Esperance to Northampton.

Coastal communities are encouraged to report sick or dead wildlife to the Emergency Animal Disease (EAD) Hotline for assessment.

There has been more than 1400 wildlife-related reports from WA to the hotline since the first confirmed case on 19 June. Of these reports, 228 have been prioritised for further investigation.

To date, a total of 93 negative test results has been recorded across the State.

Each report is carefully reviewed and assessed based on factors such as the species involved, the number of animals affected, the location and the likelihood of disease risk.

Not every report will result in birds being tested or collected, but every report does help inform the understanding of the disease and what is happening in the environment.

People are reminded to avoid handing the animals, record their observations by photo or video and report to the EAD hotline on 1800 675 888.

Based on the previous report of July 6th, the number of wildlife hotline reports has increased by roughly 400 in the past 4 days, while the number of samples tested in WA have risen from 70 to roughly 100. 

Given that 7% of the first 100 tests from WA have come back positive, it is probably safe to say that we are only seeing the tip of the iceberg.

Stay tuned. 

EFSA: An LPAI H9N2 Mystery

#19,240

A little over a week ago the EFSA published their quarterly avian flu review - which in addition to documenting the last 3 months of Europe's extraordinary 2025-2026 avian flu season - announced the surprise finding of an older, Middle-Eastern/African clade of LPAI H9N2 circulating in Hungary's poultry. 

Despite being clearly zoonotic - LPAI H9N2 is considered a `non-reportable' disease in poultry or wild birds by WOAH (see Terrestrial Animal Code). As a result, there are huge gaps in surveillance and reporting around the world. 

At the same time we've seen a growing number of studies - mostly out of Asia - warning of its growing adaptation to mammalian hosts (see EM&I: Enhanced Replication of a Contemporary Avian Influenza A H9N2 Virus in Human Respiratory Organoids).

Our own CDC lists two lineages (A(H9N2) G1 and A(H9N2) Y280) as having at least some pandemic potential, and several candidate vaccines have been developed.

In terms of risk of emergence, the H9N2

Y280 lineage is ranked higher than H5N1

While there is still much to be learned about them, over the past couple of months we've seen 2 new lineages of LPAI H9N2 described in the literature.

EM&I: A new clade of H9N2 avian influenza virus circulating in Laos

Preprint: Outbreak of H9N2 Avian Influenza Viruses in Lesser Rhea in Peru, June-July 2025

Where H9N2 is endemic (Asia, Africa, the Middle East) attempts at controlling the virus with vaccines have been largely unsuccessful (see J. Virus Erad.: Ineffective Control Of LPAI H9N2 By Inactivated Poultry Vaccines - China).

While most human 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)). 

Reports of LPAI H9N2 in European poultry have been rare, but in this latest report the EFSA describes an outbreak in 7 premises in Hungary.

Apart from these HPAI A(H5N1) outbreaks, Hungary reported the detection of A(H9N2) clade G5.5 virus back in April in 7 establishments keeping chickens (broilers), all of which were located in a single geographical area within one settlement. Increased mortality in one establishment initially raised suspicions of HPAI, however, the birds tested negative for HPAI A(H5) and A(H7) viruses. 

Tests for infectious bronchitis virus returned positive and pathological examinations revealed tracheitis, presenting with a clinical picture typical of a co-infection (Belkasmi et al., 2020; Regragui et al., 2025). This prompted testing for A(H9N2) virus.

As this specific clade had originally been restricted to countries outside the EU, such as those in the Middle East (Fusaro et al., 2024), poultry workers were interviewed about their travel history; however, no plausible link could be established. 

The source of introduction therefore remained unknown at the time of reporting. All affected establishments were stamped out, cleaned, and disinfected. After 2-3 weeks following repopulation, the birds will be tested again for A(H9N2) virus. Waterfowl flocks present in the affected county were tested for A(H9) virus prior to movement, but all these tests returned negative. 

The report goes on to describe the LPAI H9N2 virus:

Low pathogenic avian influenza A(H9N2) clade G5.5 (CDC, online-a) was identified in two genetically characterised samples collected from commercial poultry establishments in Hungary in April 2026. This clade is circulating in domestic birds in some countries in Africa, the Middle East and West Asia, and has previously never been detected in birds in the EU/EEA. 

Avian influenza A(H9N2) viruses belonging to clade G5.5 have also been reported in sporadic human cases, including Oman and Senegal in 2019, Ghana in 2024, and Italy in March 2026 in a patient who returned from West Africa (Pariani et al., 2026). 

The viruses that are most closely related to the Hungarian strains are A(H9N2) viruses of the same clade that had been circulating in the Middle East one or two decades ago. The long branches and time separating the Hungarian viruses from their progenitors suggest a significant gap of data, making it impossible to determine their origin.

Similarly to the majority of the A(H9N2) viruses of lineages G and B, they possess the HA-Q226L mutation (H3 numbering), which is associated with preferential binding to human-like α2-6-linked sialic acid (SA α2-6) receptors. 

The only recent reports of Clade G5.5 appear to have come from Oman, Senegal, and Ghana, although we are hindered by a general lack of testing, surveillance and reporting.

How it ended up in Hungary - some 4,000km from these locations - is a genuine mystery.  While migratory birds, imported exotic birds, or even human carriage are possible, there is scant evidence to support any conclusion. 

LPAI H9N2 may not be our biggest pandemic threat, but it is far from benign. The fact that H9 has successfully flown under the radar - only to turn up unexpectedly in central Europe - suggests we may want to consider expanding our testing and reporting systems beyond H5 and H7 viruses.  

Viruses: First Ecuadorian Pediatric Case of Multisystem and Neurological Involvement Associated with Influenza A—H5N1 Virus—Case Report

 

#19,239

In January of 2023 Ecuador reported its first (and as far as we know, only) human infection with H5N1; in a 9-year-old girl with reported contact with backyard poultry. 

The initial report included no details on when she was infected, her symptoms, or her current condition.

 

But the following day PAHO published a report stating : The patient is currently hospitalized in a pediatric intensive care unit, in isolation and with antiviral and supportive treatment.

A week later the WHO published a far more detailed report which stated:

The case is a nine-year-old girl, with no known comorbidities, from Bolívar Province, Ecuador. She developed symptoms of conjunctival pruritus and coryza on 25 December 2022. On 27 December, she was brought to a local health center for medical evaluation and treatment. On 30 December, due to the persistent symptoms including nausea, vomiting and constipation, she was admitted to a general hospital where empirical treatment for meningitis was started with antibiotics and antipyretics. On 3 January 2023, she was transferred to a pediatric hospital in critical condition where she was admitted to the intensive care unit (ICU) with septic shock and was treated with antivirals and mechanical ventilation due to pneumonia.

 Eight months later a report appeared in Travel Medicine which stated:

The patient was a 9-year-old girl without co-morbidities from Bolivar Province, who was admitted to a hospital due to severe flu symptoms in 30 December 2022. She was transferred to the ICU of a paediatric hospital on 3 January 2023 due to complications with septic shock and pneumonia. She received complex support antiviral treatment, including oseltamivir, managing to improve her critical condition; She continued in interdisciplinary management with favorable progress and was finally discharged from the hospital.

I mention these prior reports because today we have a new case report - published in the journal Viruses - which paints a far different picture of this patient's course of illness; one which had much more neurological involvement than previously acknowledged. 

Other than a vague mention that `empirical treatment for meningitis was started' during hospitalization in the WHO report, there was little to suggest this case presented as anything other than severe flu symptoms & pneumonia leading to septic shock. 

 Whereas, today's report states:

The clinical course was characterized by an atypical initial presentation of bilateral periorbital edema and headache, progressing to acute encephalitis, cerebral ischemia, flaccid tetraplegia, central diabetes insipidus, and refractory septic shock. 

They also indicate that respiratory symptoms were minimal upon admission, instead citing `progressive neurological symptoms', which prompted urgent medical evaluation

Those early reports become problematic because clinicians require timely information on the full range of symptoms and/or presentation of novel flu infection, if they are to consider them in their differential.  

First, I've posted some brief excerpts from the case report, but the paper is very much worth reading in its entirety. After the break we'll look back at some other recent reports of severe neurological involvement from H5N1 infection. 

First Ecuadorian Pediatric Case of Multisystem and Neurological Involvement Associated with Influenza A—H5N1 Virus—Case Report
Frances Fuenmayor 1,*, Santiago Chávez 2, María de los Ángeles Costta 1, Mateo Carvajal 3, Denisse Benítez 3,Rommel Guevara 3, Erika Muñoz 3, Paúl Cárdenas 3,Marisol Carrillo 4 … Melanie Orellana 2
Viruses 2026, 18(7), 749;
https://doi.org/10.3390/v18070749

Abstract

Influenza A (H5N1) is a highly pathogenic zoonotic virus with a human fatality rate of approximately 60%. Pediatric cases and associated neurological manifestations remain poorly documented in Latin America. This report describes the first confirmed Ecuadorian pediatric case of H5N1-associated encephalitis and multisystem organ failure in a previously healthy 9-year-old female following direct contact with infected poultry.

The clinical course was characterized by an atypical initial presentation of bilateral periorbital edema and headache, progressing to acute encephalitis, cerebral ischemia, flaccid tetraplegia, central diabetes insipidus, and refractory septic shock.

Diagnostic confirmation was achieved via nasopharyngeal RT-PCR, with additional RT-PCR and sequencing performed on cerebrospinal fluid, which identified conserved influenza A M1/M2 gene fragments, while laboratory markers—including marked elevations in IL-6, ferritin, and CRP—indicated a severe hyperinflammatory state.

Management involved an intensive multidisciplinary approach utilizing oseltamivir, intravenous immunoglobulin, modulated-dose corticosteroids, desmopressin, and mechanical ventilation. Despite a severe clinical course, the patient achieved a favorable recovery, with a Glasgow Coma Scale score of 15/15 at discharge and only partial residual paresis and left hypoacusia as sequelae. This landmark case provides rare evidence of H5N1 neuroinvasion in a pediatric patient and demonstrates that timely detection combined with aggressive immunotherapy and antiviral treatment can improve survival.

Furthermore, it underscores the critical necessity for strengthened regional molecular surveillance and clinical training to recognize atypical presentations of emerging zoonoses in Latin America, especially in cases involving contact with sick poultry.

        (SNIP) 

(SNIP)

This case underscores the severity of multisystemic involvement in influenza A H5N1 in pediatric patients, as well as the importance of a structured follow-up protocol for managing neurological and metabolic sequelae. Our findings highlight the need for active surveillance in children exposed to avian-influenza risk factors and for protocols covering early identification, continuous monitoring, and rehabilitation after resolution of the acute illness. Given the magnitude of these clinical implications, primary prevention through zoonotic control remains a fundamental pillar for reducing the incidence of new cases.

(Continue . . . )

Although the `classic' presentation of H5N1 infection has been severe flu symptoms and fever leading to pneumonia, we've seen a number of atypical presentations over the years.   

Many recent cases - particularly from genotype B3.13 - have been mild, often with conjunctivitis and minor respiratory symptoms.  Some are even asymptomatic.  

But avian H5N1 also has a history of causing severe neurological manifestations both in humans, and in other avian and mammalian hosts.

• A 2009 PNAS study (Highly pathogenic H5N1 influenza virus can enter the central nervous system and induce neuroinflammation and neurodegeneration) found that the H5N1 virus was highly neurotropic in lab mice, and in the words of the authors `could initiate CNS disorders of protein aggregation including Parkinson's and Alzheimer's diseases’.

• Six years later - following the 2014 death of the first imported H5N1 case in Canada - we saw a study (see CJ ID & MM: Case Study Of A Neurotropic H5N1 Infection - Canada), where the authors wrote: `These reports suggest the H5N1 virus is becoming more neurologically virulent and adapting to mammals'.

• In a 2015 Scientific Reports study on the genetics of the H5N1 clade 2.3.2.1c virus - Highly Pathogenic Avian Influenza A(H5N1) Virus Struck Migratory Birds in China in 2015 – the authors described its neurotropic effects, and warned that it could pose a ` . . . significant threat to humans if these viruses develop the ability to bind human-type receptors more effectively.'

Since 2022 we've seen a steady stream of reports of spillover of avian H5N1 into mammalian hosts, with many exhibiting severe (often fatal) neurological manifestations. A few of many recent blogs include:

Cell: The Neuropathogenesis of HPAI H5Nx Viruses in Mammalian Species Including Humans

PLoS Pathogens: Evolution of Highly Pathogenic H5N1 Influenza A Virus in the Central Nervous System of Ferrets

Emerging Microbes & Inf.: Neurotropic HPAI H5N1 Viruses with Mammalian Adaptive Mutations in Free-living Mesocarnivores in Canada

Pathogens: Zoonotic Mutation of Highly Pathogenic Avian Influenza H5N1 Virus Identified in the Brain of Multiple Wild Carnivore Species

While severe neurological involvement from human H5Nx infection remains relatively rare:

In 2022 (see Clinical Features of the First Critical Case of Acute Encephalitis Caused by Avian Influenza A (H5N6) Virus), we reviewed the first known case of neuroinfluenza in an H5N6 patient; a 6-year-old girl who was admitted to a hospital with mild pneumonia - but severe encephalitis - in January of that year.

That was followed 15 months ago (April 2025) by a preliminary report on a neuroinvasive infection in an 8-y.o. girl (see Vietnam: Ho Chi Minh DOH Reports A Rare H5N1 Encephalitis Case In a Child), which reported:

As noted by infectious experts, this is a rare case in which the A/H5N1 avian influenza virus damages the central nervous system and does not attack the respiratory tract.

We followed up on that case last May in OFID: Central Nervous System Involvement by Novel Clade 2.3.2.1e H5N1 Avian Influenza Virus in a Paediatric Patient, where the authors warned:

Testing for IAV and  A(H5N1) virus should be considered in patients presenting with CNS infection with a history of exposure (e.g. dead poultry). Clinicians should be aware of meningoencephalitis associated with A(H5N1) infection in the absence of respiratory symptoms.

A reminder that while it can sometimes be mild, H5N1 isn't your father's influenza.