MMWR: Fatal Human Case of HPAI A(H5N5) in a Backyard Flock Owner — Washington, November 2025

#19,150

As we've discussed often, it takes a certain amount of luck for novel flu infections to be detected, properly treated, and then reported to the CDC.  It seems likely that some number of mild illnesses go unrecognized (see MMWR: Serologic Evidence of Recent Infection with HPAI A(H5) Virus Among Dairy Workers) , and even severe cases can be misdiagnosed. 

We've seen instances where patients were only diagnosed retrospectively; sometimes well after they had been treated and released from the hospital (see 2024 Missouri case).

Standard rapid influenza tests don't distinguish between seasonal and novel flu strains, and sometimes, repeated swabs of the upper airway can fail to `capture' a deep lung infection for RT-PCR testing.  

Such is the case of the fatal H5N5 case, reported last November, from Washington state, according to a detailed MMWR report published yesterday by the CDC   As the graphic at the top of this blog shows, the patient repeatedly tested negative for influenza/COVID during the first 6 days of his hospitalization. 

Not surprisingly, a large number (n=139) of hospital personnel and other close contacts were exposed to this patient before he was moved to an isolation unit. 

While no secondary transmissions were reported, it appears only those contacts reporting flu-like symptoms were tested by RT-PCR (NP swabs), and I could find no mention of follow-up serological testing.  

Given this is the first known human infection with novel H5N5, I would have thought a wider net would have been cast.  But that's just me, I guess. Perhaps there's another study in the pipeline on this. 

In any event, the takeaway here appears to be that when dealing with a respiratory infection with someone with contact with poultry or wild birds, a high index of suspicion is warranted, and taking samples from both the upper and lower respiratory tract is recommended. 

Due to it length, I've just posted the summary, abstract, and a few excerpts.  I'll have a postscript after you return. 

Fatal Human Case of Highly Pathogenic Avian Influenza A(H5N5) in a Backyard Flock Owner — Washington, November 2025

Weekly / May 7, 2026 / 75(17);221–225
 
Lynae Kibiger, MPH1; Hanna N. Oltean, PhD1,2; Lisa Leitz3; Emma Krause3; Debra Barrett3; Anna Halloran, MHPA1; Kyle Yomogida, PhD1; Beth Lipton, DVM1; Keely Paris, MPH1; Jared Keirn, MS1; Minden Buswell, DVM1; Allison Black, PhD1; Pauline Trinh, PhD1; Theresa Murray, MT1; Roberto Bonaccorso1; Leticia Banuelos1; Ethan Dieringer1; Jennifer Lenahan, MPH4; Emily Spence Davizon, MPH4; Ellyn P. Marder, DrPH2,4; Jocelyn Mullins, DVM, PhD4; Meagan Kay, DVM2,4; Eric J. Chow, MD2,4,5,6; Sandra J. Valenciano, MD4; John Lynch, MD5,7; Vanessa Makarewicz, MN7; Chloe Bryson-Cahn, MD5,7; Jennifer Hernandez7; Kyla Haggith7; Valicia Linn7; Alex L. Greninger, MD, PhD8; Stephanie Goya, PhD8; Sierra Gulla9; Jennifer Young, MPH9; Sierra Kerns-Funk, MPH10; Brianna da Silva Bhatia, MD10; Hollianne Bruce, MPH11; Krista Kniss, MPH12; Katie Reinhart, PhD12; Rachel Ohlstein13; Shannon Johnson13; Christina Schofield, MD14; Patrick Smith, DO14; Amber Itle, VMD15; Maura Gibson, DVM16; Brandi Torrevillas17; Azeza Falghoush, PhD17; Thomas B. Waltzek, DVM, PhD17; Kevin Snekvik, DVM, PhD17; Mia Torchetti, DVM, PhD16; Timothy M. Uyeki, MD12; Scott Lindquist, MD1 (VIEW AUTHOR AFFILIATIONS)View suggested citation

Summary

What is already known about this topic?

Since 2022, highly pathogenic avian influenza (HPAI) A(H5) viruses have circulated among wild birds in the United States. Seventy human cases of influenza A(H5), most with mild illness, have been reported in the United States since 2024; 14 human influenza A(H5N1) cases were previously identified in Washington.

What is added by this report?

In November 2025, Washington reported the first human case of HPAI A(H5N5) infection worldwide. A positive laboratory result was obtained from a lower respiratory sample after multiple negative upper respiratory sample results; the patient experienced respiratory failure and died 28 days after symptom onset. The public health investigation identified approximately 135 exposed persons.

What are the implications for public health practice?

Symptom management and testing of exposed persons are critical to monitoring for human-to-human transmission of novel influenza infection. Environmental and animal investigations, including genomic analysis, can identify epidemiologic risk factors.ls
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Abstract

Clade 2.3.4.4b influenza A(H5N1) viruses have circulated across migratory bird flyways in the United States since 2022, including in Washington, where backyard flock detections have been reported annually. In November 2025, a Washington resident died from acute respiratory failure after receiving a positive influenza A(H5) test result at a hospital laboratory. 

Washington Public Health Laboratories confirmed influenza A(H5), and genomic sequencing identified influenza A(H5N5) virus (A6 genotype). Polymerase chain reaction testing detected highly pathogenic avian influenza A(H5) virus clade 2.3.4.4b from an apparently healthy backyard flock of ducks and sediment from a watering basin on the patient’s property. Six of eight gene segments from the environmental sample and one duck sample (partial neuraminidase segment) were highly genetically similar to the patient’s virus sequence.

Although existing wild bird surveillance had not detected influenza A(H5N5) virus (A6) in the U.S. Pacific Flyway, introduction via wild birds into the environment of the backyard flock was likely the source of the patient’s exposure. 

The public health investigation identified approximately 135 exposed persons; symptom monitoring and influenza testing detected no additional cases. The overall risk for avian influenza A remains low among the general U.S. population; however, novel avian influenza A virus infection should be considered in persons with symptoms of influenza and potential exposures.

       (SNIP)

The diagnosis of influenza A(H5N5) virus infection in the patient described in this report was complicated by early and repeated negative influenza test results from upper respiratory swab specimens. Negative influenza results from initial upper respiratory specimens have been described in three similar patients with lower respiratory tract disease hospitalized with avian influenza A(H5N1) infection (4). Thus, avian influenza virus infection should not be ruled out in hospitalized patients based on negative influenza laboratory test results from upper respiratory tract specimens if the patients have lower respiratory tract disease, relevant exposures, and no confirmed etiology for their disease. If avian influenza virus infection is suspected in a patient with severe respiratory disease, both upper and lower respiratory tract specimens should be collected for influenza testing by RT-PCR at a public health laboratory (6).

Early negative influenza results delayed initiation of isolation precautions, reporting to public health authorities, and symptom monitoring. Although isolation precautions were not established consistently until the ninth day of inpatient care, no cases among HCP were identified. Likewise, no cases were detected among family members, despite lengthy exposure to both the symptomatic patient and the property. One household member reported direct contact with the ill and dead ducks but remained asymptomatic. Establishing a tiered risk assessment for HCP exposures based on setting and PPE use allowed staff members to continue working while having their symptoms monitored and limited new HCP exposures. The investigation was complicated by its occurrence during viral respiratory season and symptom development among several persons whose symptoms were being monitored. Human-to-human transmission of avian influenza A viruses has only rarely been reported globally and has not been reported in the United States (3,7).

Timely HPAI risk evaluation is important for persons with influenza symptoms requiring hospitalization to support infection prevention and control, early notification of public health authorities, and robust epidemiologic investigation, including genomic sequencing to identify possible transmission pathways. Ill or dead animals should be reported to animal health authorities for surveillance and potential testing and to reduce human exposure. Public health guidance for evaluating suspected cases of avian influenza should include immediate isolation precautions, prompt initiation of antiviral treatment, repeated influenza testing, and specimen collection from multiple sites (2,6,8). Considering the successive influenza A–negative laboratory results in the Washington patient, sampling from both upper and lower respiratory tracts in hospitalized patients should be considered to increase the likelihood of laboratory detection.

        (Continue . . . )


While the exact exposure to H5N5 remains uncertain, it is likely that unprotected (mask, eye protection, gloves) with wild backyard birds was the source of this fatal infection.  

This is remarkably similar to the fatal case reported earlier in 2025 in Louisiana. 

The CDC has released guidelines (see Backyard Flock Owners: Protect Yourself from Bird Flu) - but it is unknown how many backyard poultry owners have actually read it - or would bother to follow their - at times - stringent recommendations.

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. 

Last October, in UF/IFAS Extension: What Backyard Flock Owners Need to Know about Bird Flu (Influenza H5N1), we looked at two H5N1 related publications; one for backyard poultry owners, and another for consumers of poultry products and milk.

While there's plenty of useful guidance out there, getting people to follow it is another thing entirely. 

UKHSA Hantavirus Update: Cryptic Mention of a Suspected Case on Tristan Da Cunha

 

#19,149

The online signal-to-noise ratio regarding the hantavirus outbreak continues to degrade with several `false alarms' making the rounds yesterday, and the arrival of the highly vocal `plandemic' contingent, who view this outbreak as some sort of vast global conspiracy. 

Finding credible, informative, reports is made even more difficult by the tendency of governments to downplay risks to reassure a nervous public. 

While I still believe this outbreak should be containable - there are a lot of moving parts - many of which we probably aren't aware of.  It now appears at least 30 people left the ship before the outbreak was recognized, and some may have had opportunities to spread the virus.  

All of which brings us to the UK's HSA announcement this morning that they are aware of a `suspected' case on Tristan Da Cunha (stop #5 on the map above); a small volcanic island in the south Atlantic that is home to > 200 Brits. 

Exactly why they suspect this person is infected - or their condition - is not stated. Nor do they say how the person was likely exposed (was this a passenger, a local resident, etc.?). 

If confirmed (and that's still an `if'), this would be a significant turn of events. 

First today's statement, after which I'll have a bit more. 

Statement from the UK Health Security Agency (UKHSA), Department for Health and Social Care (DHSC), and Foreign, Commonwealth and Development Office (FCDO)


The UK government continues to work with international authorities in preparing for the arrival of British nationals to the UK from the MV Hondius cruise ship where an outbreak of Hantavirus was confirmed by the World Health Organization.

Two British nationals have confirmed hantavirus, with an additional suspected case of a British national on Tristan da Cunha. None of the British citizens onboard are currently reporting symptoms but they are being closely monitored.

The ship is expected to dock in Tenerife on Sunday, according to the latest updates from the Spanish Health Ministry. UK government staff will be on the ground ready to support the British nationals disembarking. British Passengers and ship crew not displaying any symptoms of hantavirus will be escorted by UK Government staff to an airport and given free passage back to the UK.

FCDO and UKHSA teams will be on the ground to support these arrangements, bolstered by a Rapid Deployment Team sent from the UK. The FCDO is chartering a dedicated repatriation flight for British ship passengers and crew only. This flight will be free of charge.

UKHSA is working with partners to ensure the flight operates under strict infection control measures. Public health and infectious disease specialists from UKHSA and the NHS will be on board to monitor British Nationals whilst on the flight, to ensure that preventative measures are in place and to provide any care in the unlikely event that any passengers become unwell on the flight.

All British passengers and crew on board the MV Hondius will be asked to isolate for 45 days upon returning to the UK and UKHSA will closely monitor these individuals, with testing as required.

Follow up is already underway for individuals who may have been in contact with cases and have since returned to the UK or are in in UK Overseas Territories. The UK government will ensure those self-isolating are given appropriate support.

UKHSA is aware of seven British Nationals who disembarked the ship at St Helena on 24 April.

Two of those people have returned to the UK independently and are isolating at home in the UK. Neither of these individuals is currently reporting symptoms. They are receiving advice and support from UKHSA and have been advised to self-isolate.

Four of these individuals remain in St Helena. A seventh individual has been traced outside of the UK.

The FCDO is in direct contact with the ship and British nationals on board and has stood up consular teams across multiple countries to support British nationals. UK government is working very closely with international partners in response to this incident, including the cruise ship operator and the governments of UK overseas territories which were visited by the ship. UK government teams are working at pace to get medical support to all affected Overseas Territories. The Ministry of Defence has worked with UKHSA to provide vital diagnostic supplies, including PCR tests, which were delivered to Ascension Island via a military plane on 7 May.

The risk to the general public remains very low.

Professor Robin May, Chief Scientific Officer at UKHSA, said:

This is an evolving situation, and we are working closely with partners to support British Nationals on board the MV Hondius.

The risk to the general population remains very low and the public can be reassured that established infection control measures will be put in place at every step of the journey to ensure the safe repatriation of British passengers on board.

Further information on the repatriation of British nationals will be provided in due course.

While it may turn out due more to an unfortunate series of events than anything else, the world's health agencies became aware of this outbreak weeks after it started, and are playing catch up.

Dozens of potentially infected individuals have scattered around the world, and they have had contact with hundreds - perhaps thousands - of people.

Luckily, most won't have been infected, and based on past Andes virus outbreaks, transmission should be limited. At least that's the assumption right now. 

The UK has signaled its intention to have people to `isolate' (technically quarantine) for 45 days after returning to the UK. Note: I suspect someone, somewhere, has determined that `quarantine' is a scarier word than `isolate', but I digress. 

Right now, it isn't clear whether all other countries will follow suit, or whether they'll get the cooperation they'll need from those exposed.  While unpopular, quarantine has proven its worth many times, including in halting the 2018-2019 outbreak of the Andes Virus in Argentina. 

Hopefully we'll take those lessons seriously. 

MMWR: Serologic Evidence of HPAI A(H5N1) Virus Infection in a Veterinary Professional Exposed to an Infected Domestic Cat

 

USDA list of Domestic Cats with H5N1

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We've a new report in today's MMWR that details the probable feline-to-human transmission of the H5N1 virus - during an outbreak of the virus in domestic cats in California in late 2024 - which was linked to contaminated cat food and/or raw milk. 

While long considered possible, actual evidence of  cat-to-human transmission of avian flu viruses has been pretty sparse.  Two notable exceptions being:

• In 2005, the CDC's EID Journal  Probable Tiger-to-Tiger Transmission of Avian Influenza H5N1, reported that while no humans tested positive by RT-PCR, 2 close human contacts (3.5%) tested positive via serology (microneutralization) for the virus 4 weeks later.

• In 2018 we saw evidence suggesting several employers had been infected by LPAI H7N2 during an outbreak in 2016 (see J Infect Dis: Serological Evidence Of H7N2 Infection Among Animal Shelter Workers, NYC 2016).

Admittedly, testing has been fragmented over the years, with many exposed individuals either tested too late, or not at all. And that is a challenge we find once again with today's report.

In today's example, of the 139 people exposed to infected cats, 30 reported flu-like symptoms, but of those only 18 (60%) submitted to PCR testing with 12 declined or were unavailable.  Another 15 asymptomatic cases were tested (combined n=33), meaning that  < 24% of total number of exposed individuals were tested. 

And the timing of sample collection was not ideal, as the `window' for PCR detection can be short, particularly in mild or asymptomatic infections. The authors wrote:

The median interval between the most recent exposure date and specimen collection was 8 days (range = 1–13 days). Specimens from 19 (58%) persons who received testing were collected >7 days after the last exposure.

As the above chart indicates, all PCR tests were negative for H5N1.  

Serological testing for post-infection antibodies faced similar challenges, with only 25 of the 139 exposed individuals (18%) submitting to serological tests. It isn't clear from my reading how many of those may have come from the symptomatic cohort. 

Again timing may be an issue, since they authors report `. . .  the average interval between exposure and serum collection was 104 days (range = 35–137 days)', which could have been long enough for some antibody titers to wane. 

In this case, one of the 25 samples tested positive for H5N1, that belonging to an asymptomatic veterinarian who had unprotected (no respiratory/eye protection) contact with infected cats during the outbreak. 

I've only reproduced the summary and abstract below. Follow the link to read the report in its entirety.  I'll have a brief postscript when you return. 

Serologic Evidence of Highly Pathogenic Avian Influenza A(H5N1) Virus Infection in a Veterinary Professional Exposed to an Infected Domestic Cat — Los Angeles County, California, December 2024–January 2025

Weekly / May 7, 2026 / 75(17);215–220
 
Aisling Vaughan1; Allison Joyce2; Elizabeth Traub2; Mellissa Jae3; Emily Beeler3; Erick Paiva2; Kristopher Ananian2; Crystal Holiday4; Stacie Jefferson4; Jessica Richardson2; Cortney Munna2; Cynthia Chan3; Tamerin Scott3; Noah Kojima2; Tanya Seneviratne2; Alexandra Mellis4; Sonja J. Olsen4; Nicole Green5; Matt Feaster6; Dawn Terashita2; Sharon Balter2; Min Z. Levine4; Jamie Middleton3,*; Annabelle de St. Maurice2,*  

Summary

What is already known about this topic?

Transmission of influenza A(H5N1) viruses from domestic cats to humans has not been documented.

What is added by this report?

During November 2024–January 2025, a total of 139 persons exposed to 19 A(H5N1)-infected domestic cats that consumed raw animal products were identified in Los Angeles County, California. Among 25 exposed persons who received serologic testing, one asymptomatic veterinary professional had serologic evidence of A(H5N1) infection after occupational exposure to an A(H5N1)-infected cat.

What are the implications for public health practice?

These findings provide evidence of zoonotic transmission of influenza A(H5N1) virus from domestic cats to humans. Pet owners are advised not to feed raw animal products to cats. Veterinary professionals should be aware of infection risks, use appropriate personal protective equipment, and adhere to recommended infection control practices to reduce the risk for zoonotic transmission of influenza A(H5N1).

 
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Abstract

Since 2021, avian influenza A(H5N1) clade 2.3.4.4b viruses have spread widely among wild birds and domesticated poultry in the United States, with sporadic spillover into mammals. During November 2024–January 2025, 19 domestic cats in Los Angeles County, California, became ill after consumption of commercially purchased raw milk, raw meat, or raw pet food; nine cats tested positive for influenza A(H5N1) virus (clade 2.3.4.4b genotype B3.13).

Overall, 139 persons were exposed to the 19 infected cats, and all were monitored for symptoms. Although 30 persons reported influenza-like illness symptoms, none received a positive influenza A(H5) reverse transcription–polymerase chain reaction (RT-PCR) test result. In April 2025, the Los Angeles County Department of Public Health and CDC invited all exposed persons to participate in an influenza A(H5N1) serosurvey to determine whether transmission of influenza A(H5N1) virus occurred, including in those without symptoms.

Sera from 25 (18%) of the 139 exposed persons were tested. Among these, antibodies specific to A(H5N1) clade 2.3.4.4.b (antigenically similar to the clade 2.3.4.4.b influenza A[H5N1] virus isolated from the infected cats) were detected in serum from one veterinary professional, who was asymptomatic. This person did not use respiratory or eye protection during the exposure, did not report influenza-like illness after the exposure, and reported no other known risk factors for A(H5N1) infection.

These findings represent serologic evidence of possible transmission of influenza A(H5N1) clade 2.3.4.4.b virus from a domestic cat to a human, highlighting concerns about potential cat-to-human transmission of influenza A(H5N1) virus and the importance of infection control practices in veterinary settings.

        (SNIP)

Limitations

The findings in this report are subject to at least two limitations.

• First, RT-PCR testing and serologic testing were not performed for all persons; therefore, some infections might have been missed.
• Second, serologic testing was performed 4–5 months after exposure, at which time antibody responses might have waned.

Collection of acute and convalescent serology specimens was not feasible in this investigation; however, this step should be considered during future influenza A(H5N1) virus outbreaks in animals.

        (Continue . . . )


We've seen previous examples where the public, or agricultural workers, have been reluctant to cooperate with public health officials or researchers (see EID Journal: Avian Influenza A(H5N1) Virus among Dairy Cattle, Texas, USA).

Around the time this feline outbreak was occuring, we were seeing the first evidence of asymptomatic infections among dairy workers (see MMWR: Serologic Evidence of Recent Infection with HPAI A(H5) Virus Among Dairy Workers), once again uncovered by retrospective serological testing.

Although better cooperation and participation by the public might have turned up more instances of feline-to-human H5N1 transmission - thanks to these researchers - we now have pretty good evidence that feline-to-human transmission of clade 2.3.4.4b. can occur. 

While this should be enough of a signal to convince people to take the threat of HPAI to their pets more seriously - given the ambivalence and hostility towards science I see online - I'm not particularly hopeful.  

PLos Bio: Surveillance on California dairy farms reveals multiple possible sources of H5N1 influenza virus transmission

 

#19,147

Last August, in Preprint: Surveillance on California Dairy Farms Reveals Multiple Sources of H5N1 Transmission, we looked at the testing of air, wastewater, and milk samples from 5 California farms/milking parlors, which found evidence of extensive environmental (air, water & milking equipment) contamination with H5N1.

Key findings included:

• detection of infectious H5N1 virus in milking parlor air and farm wastewater evidence of airborne transmission from exhaled cow breath

• H5N1 infection without mastitis symptoms, suggesting subclinical milk producing cows may be going undetected

• the detection of an N189D HA mutation (which may affect the receptor binding domain) in at least one air sample 

• and heterogeneous patterns of viral infection across individual udder quarters that call into question the assumed `primary role'  played by milking equipment

This week PLoS Biology has published a revised and extended (now 14 farm) study by these same authors which (again) reports multiple plausible H5N1 transmission routes on dairy farms; including milk contact, aerosols in parlors, and contaminated wastewater.

The published version provides additional evidence for infectious H5N1 detection in both air and wastewater (not just viral RNA detection), along with a much larger sampling size. 

Due to its length, I've only posted the link, abstract, and some excerpts from the conclusion.  Follow the link to read it in its entirety.  I'll have a brief postscript after you return.

RESEARCH ARTICLE
Surveillance on California dairy farms reveals multiple possible sources of H5N1 influenza virus transmission
A. J. Campbell1 , Meredith Shephard1☯, Abigail P. Paulos2☯, Matthew D. Pauly1 , Michelle N. Vu1 , Chloe Stenkamp-Strahm3 , Kaitlyn Bushfield1 , Betsy Hunter-Binns4 , Orlando Sablon2 , Emily E. Bendall5 , William J. Fitzimmons5 , Kayla Brizuela1 , Grace E. Quirk1 , Nirmal Kumar1 , Brian McCluskey3 , Nishit Shetty6 , Linsey C. Marr7 , Jenna J. Guthmiller8 , Jefferson J. S. Santos9 , Scott E. Hensley9 , Edith S. Marshall10, Kevin Abernathy4 , Adam S. Lauring5 , Blaine T. Melody11, Marlene K. Wolfe2 , Jason Lombard3 *, Seema S. Lakdawala

        Abstract

Transmission routes of highly pathogenic H5N1 between cows or to humans remain unclear due to limited data from affected dairy farms. We performed air, farm wastewater, and milk sampling on 14 H5N1-positive dairy farms across two different California regions.

Infectious virus was detected in the air in milking parlors and in wastewater streams, while viral RNA was found in exhaled breath of cows. Sequence analysis of infectious H5N1 virus from air and wastewater samples on one farm revealed viral variants relevant for potential human susceptibility. Longitudinal analysis of milk from the individual quarters of cows revealed a high prevalence of subclinical H5N1-positive cows.

Additionally, a heterogeneous distribution of infected quarters that maintained a consistent pattern over time was observed, inconsistent with shared milking equipment serving as the sole transmission mode. The presence of subclinically infected cows was further supported by detection of antibodies in the milk of animals that exhibited no clinical signs during the H5N1 outbreak on one farm. Our data highlight additional sources and potential modes of H5N1 transmission on dairy farms.

        (SNIP)

Discussion

Elucidating the routes of transmission of H5N1 between cows is critical to defining successful mitigation strategies. In this study, we successfully detected H5N1 in the air and in reclaimed farm wastewater on separate dairy farms on multiple days. This included infectious air samples from three different milking parlors and viral RNA from the exhaled breath of rows of cows on two distinct farms. Additionally, we detected viral RNA in farm wastewater at multiple sites on various farms and infectious virus at two different sites on the same farm.

Together, these results highlight the extensive environmental contamination of H5N1 on affected dairy farms and identify additional sources of viral exposure for cows, peridomestic wildlife, and humans.

Dairy parlors, which are often enclosed spaces and where aerosolization of milk occurs, pose the greatest threat from inhalation of the virus to dairy farm workers compared to the open-air housing pens.

       (SNIP)

Taken together, our data confirm the presence of infectious H5N1 virus in the air and reclaimed farm wastewater sites. In addition, we observed high viral loads and H5 antibodies in the milk of cows, including those without clinical signs, and heterogenous patterns of H5N1 positivity by quarter, suggesting that multiple modes of H5N1 transmission likely exist on farms.

These transmission routes could include contaminated milking equipment from an infected cow, aerosols generated within the milking parlor, and/or contact of teats with contaminated water used to clean housing pens.

Multiple mitigation strategies should therefore be implemented to reduce the risk of H5N1 spread within a herd and to humans. Respiratory and ocular personal protective equipment (PPE) for farm workers to prevent deposition of virus-laden aerosols on these sites, especially in the milking parlor. Disinfection of milking equipment between milking of each cow, such as with consistent use of backflush system, could also reduce spread of H5N1 between cows. Treatment of milk from sick cows to inactivate H5N1 prior to disposal as well as treatment of waste streams prior to their use in fields or on farms should also be considered. Finally, identification of infected cows, regardless of clinical signs, for isolation will help reduce the transmission of H5N1 on farms.

        (Continue . . . )
 

This paper calls for a number of actions to reduce the spread of H5N1 on dairy farms, including:

• Respiratory & ocular personal protective equipment (PPE) for farm workers
• Treating waste milk before disposal
• Treating manure/wastewater/waste streams
• Isolating infected cows, including subclinical cases

While the USDA offers many similar biosecurity recommendations for dairy farms  (see APHIS Biosecurity Document) - most are not mandatory - and are left up to the discretion of the owner/operator.  

Although the number of positive herds being reported has declined, it is unclear how sensitive current testing and surveillance practices truly are. 

UKHSA Update On Hantavirus: 2 Nonsymptomatic Passengers Self-Isolating at Home

 

#19,146

The UK's Health Security Agency has published an update this afternoon on the current status of British nationals aboard the m/v Honidius, which also includes details on two passengers who apparently already left the ship, and - while showing no symptoms - are self-isolating at home. 

Given the large number of people who have been exposed aboard ship - and an unknown number of contacts offship - the use of home self-isolation (with daily phone check ins) would seem a reasonable precaution; at least until we get a better handle on the infectivity of this strain. 

Whether other jurisdictions will adopt similar measures remains to be seen. The 2-8 week incubation period of the Andes Virus - and its early flu-like presentation - is likely to present public health agencies around the globe with a formidable challenge over the weeks ahead.

UKHSA update on the hantavirus cruise ship outbreak

Latest information on cases including British nationals.
From:UK Health Security Agency Published 6 May 2026




The UK Health Security Agency (UKHSA) continues to work with the World Health Organization (WHO), Foreign, Commonwealth and Development Office (FCDO), the Department of Health and Social Care (DHSC), and other international partners to prepare for the arrival of British nationals to the UK from the MV Hondius cruise ship where an outbreak of Hantavirus was confirmed.

Three people, including one British national, with suspected hantavirus have been evacuated from the Hondius in order to receive medical care in the Netherlands in co-ordination between the Cape Verde, UK and Dutch governments. UKHSA are in close contact with medical teams providing their care.

The remaining British nationals can now be repatriated once the ship docks at its next destination if they do not develop symptoms. None of the British citizens onboard are currently reporting symptoms but they are being closely monitored. The FCDO is making arrangements for these individuals to return to the UK, where UKHSA is working with government to support them to isolate with regular testing and contact with healthcare professionals.

UKHSA is aware of two people who have returned to the UK independently having been on board the MV Hondius. Neither of these individuals is currently reporting symptoms. They are receiving advice and support from UKHSA and have been advised to self-isolate. UKHSA are supporting a small number of individuals identified as close contacts of those on the boat. They are being offered support and are also self-isolating. None are reporting any symptoms. The risk to the general public remains very low.

Dr Meera Chand, Deputy Director for Epidemic and Emerging Infections at UKHSA said:

• Our thoughts are with all those affected by the hantavirus outbreak onboard the MV Hondius.

• It’s important to reassure people that the risk to the general public remains very low. We are standing up arrangements to support, isolate and monitor British nationals from the ship on their return to the UK and we are contact tracing anyone who may have been in contact with the ship or the hantavirus cases to limit the risk of onward transmission.

• UKHSA will continue to work closely with government partners to offer all necessary support.

UKHSA is working closely with the FCDO, the Home Office, and Border Force to trace further individuals who may have been on the same flight as a confirmed case, in order to carry out public health risk assessments and ensure appropriate precautionary measures are in place.

Hantavirus is the name given to a group of viruses carried by rodents and transmitted by their droppings and urine. They can cause a range of diseases from mild, flu-like illness to severe respiratory illness. Infections in humans are rare and tend to occur in places where people and rodents coexist - most commonly in rural, agricultural settings, though the viruses can also sometimes be found in cleaning sheds, barns and holiday homes where rodents might have nested.

Most hantaviruses do not spread easily between humans, although person-to-person transmission has been observed in some cases involving particular strains. The World Health Organization is leading the international response to this incident and overseeing direction of the ship, including advising on how to minimise the risk of the disease spreading.

The FCDO is in direct contact with the ship and has stood up consular teams across multiple countries to support British nationals. UK government is working extremely closely with international partners in response to this incident, including the cruise ship operator and the governments of overseas territories which were visited by the ship.

Further information on Hantavirus can be found in the recent blog from UKHSA.

ECDC: Threat Assessment Brief On Hantavirus Cluster on a Cruise Ship

#19,145

With the caveat that it is still early days, we've a Threat Assessment Brief this afternoon from the ECDC on the ongoing outbreak aboard the  m/v Hondius which is currently enroute to the Canary Islands. 

As we've seen often in the past, assumptions and recommendations about exotic or novel disease outbreaks are subject to change as more data is gathered, so stay tuned.  

Due to its length, I've only posted the summary below.  Follow the link to read it in its entirety. 

Hantavirus-associated cluster of illness on a cruise ship: ECDC assessment and recommendations

Assessment
6 May 2026

This is a rapidly evolving incident, and this document contains a preliminary assessment and recommendations. ECDC will provide updates as information becomes available.

As of 6 May 2026, seven cases have been reported in a hantavirus-associated cluster of illness on a cruise ship, including three deaths, one critically ill, two symptomatic and one with unknown status.

Epidemiological situation

ECDC was notified on 2 May 2026 by the Netherlands via the European Union (EU) Early Warning and Response System (EWRS) about a cluster of unknown disease with severe respiratory symptoms on a cruise ship in the South Atlantic, operating under a Dutch flag. There were 149 people on board from 23 different nationalities, including nine EU/EEA Member States: Belgium, France, Germany, Greece, Ireland, the Netherlands, Poland, Portugal, and Spain. At the time, two people had died and one had been medically evacuated to South Africa, where the person remained critically ill. A PCR test result for a sample taken from this person came back positive for hantavirus on 3 May 2026.

As of 6 May, a total of seven people had presented with symptoms that included fever, respiratory symptoms, and gastrointestinal symptoms, with at least four rapidly progressing to pneumonia, acute respiratory distress and shock. Of these seven people, three died, one was medically evacuated to South Africa and admitted to an intensive care unit (ICU), two remained symptomatic on board, requiring medical assistance, and one was diagnosed after disembarking the ship and returning to Switzerland. In total, samples from two patients tested positive for hantavirus by PCR; a sample from one additional patient tested positive for Andes virus (ANDV) by PCR. Further laboratory investigations are ongoing.

Orthohantavirus infections are viral zoonotic diseases transmitted to humans primarily through the inhalation of aerosols contaminated with the urine, faeces or saliva of infected rodents. Human disease can be caused by several orthohantavirus species, including the Andes (ANDV) and Sin Nombre (SNV) viruses in the Americas and Puumala and Dobrava viruses in Europe. The incubation time is usually around two weeks but ranges from seven days up to six weeks.

Clinical manifestation of hantavirus infection is divided in two clinical syndromes: Hantavirus Pulmonary Syndrome (HPS), seen in the Americas; and Haemorrhagic Fever with Renal Syndrome (HFRS) seen in Europe and Asia. Severe cases can rapidly deteriorate and become life-threatening. ANDV is a hantavirus primarily found in South America that causes HPS with a high fatality rate. Human-to-human transmission is rare but has been documented in the case of ANDV. No effective antiviral treatment is available; supportive care is key for a better chance of survival.

ECDC provides this risk assessment for discussion at the level of the Health Security Committee including the involved countries, UK HSA and the WHO.

Risk assessment

Person-to-person transmission of ANDV has only been documented following close and prolonged contact. The current hypothesis is that some passengers were exposed to ANDV while spending time in Argentina before embarking, where ANDV is endemic, and may subsequently have transmitted the virus to other passengers onboard the cruise ship. At this early stage of the investigation with limited available information, we consider everyone on the ship to be close contacts, due to the closed setting and shared social areas and activities, aligned with the precautionary principle.

Measures are already implemented on board to reduce the likelihood of infection for passengers and crew on the cruise ship. The cruise ship company and the relevant port authorities have also been advised on how to prepare for the management of cases and contacts (e.g. isolation of cases, use of appropriate personal protective equipment, testing, etc).

Even if transmission of ANDV were to happen from passengers evacuated from the ship, ANDV does not transmit easily so it is unlikely that it would cause many cases or a widespread outbreak in the community, if infection prevention and control measures are applied.

In addition, the natural reservoir for ANDV is not present in Europe, so introduction to the rodent population and potential rodent-to-human transmission in Europe is not expected.

The risk to the general population in the EU/EEA from ANDV spreading from this cruise ship outbreak is very low.

Recommendations

• Symptomatic people should be managed proactively and medically evacuated as soon as possible.
• Upon disembarking, diagnostic testing should be carried out by serology or PCR in people with symptoms. However, negative test results may not exclude infection and subsequent virus shedding. The EURL-PH-ERZV offers diagnostic services to EU/EEA countries lacking capability to diagnose ANDV infection.
• Passengers and crew should practice usual enhanced precautions (e.g. frequent handwashing, respiratory etiquette, physical distancing) and vigilant symptom monitoring while on the cruise ship.
• Infection Prevention and Control (IPC) guidance for healthcare settings who are caring for symptomatic individuals include standard and droplet precautions, which can be escalated to airborne precautions in the event that aerosol-generating procedures are performed.
• Risk communication should be tailored to the different target groups recognising their different levels of risk, information needs and responsibilities. Communication should clearly state what is known, what is unknown, and what may change as investigations progress with timely updates.
• Disembarking passengers should be provided with clear instructions and recommendations until their diagnosis is confirmed or ruled out.

ECDC actions

• Epidemiological updates.
• Hantavirus infection factsheet published.
• European Union Reference Laboratory (EURL-PH-ERZV) offered assistance to EU/EEA national reference laboratories for the diagnosis of ANDV.
• ECDC is supporting the response operations through the EUHTF remotely and on the cruise ship in coordination with the affected countries.
• Ongoing collaboration with partners and affected countries on common case definitions and protocol for management of cases and contacts.

Hantavirus-associated cluster of illness on a cruise ship: ECDC assessment and recommendations

English (403.61 KB - PDF)