Sci Adv: Mammary and Respiratory Infection of Sheep with H5Nx clade 2.3.4.4b Viruses with Milk-mediated Transmission to Lambs

 

#19,154

While we await further news on the offloading of hantavirus exposed passengers from the m/v Hondius, we still have plenty of older and emerging threats to keep our eye on.  Late last week a new study was published in Science Advances by Canadian researchers who investigated the susceptibility of sheep to both HPAI H5N1 and HPAI H5N5. 

Since the first outbreak of HPAI H5N1 was reported in U.S. dairy cattle a little over 2 years ago, surveillance and testing of mammalian livestock has focused almost exclusively on lactating dairy cows.

Yet during this time, we've also seen sporadic HPAI spillovers into goats, alpacas, pigs, and sheep in the UK and the discovery of  H5N1 antibodies in sheep in Norway. Other non-bovine findings include:

Transboundary & Emerg Inf: Serological Evidence of HPAI (H5N1) in Invasive Wild Pigs in Western Canada,

Preprint: Highly Pathogenic Avian Influenza H5 Virus Exposure in Goats and Sheep (in Pakistan).

EID Journal: Evidence of Influenza A(H5N1) Spillover Infections in Horses, Mongolia

Livestock surveillance - even of cattle - remains passive and limited, despite the call from animal health authorities (see WOAH Statement (Oct 22nd): High Pathogenicity Avian Influenza (HPAI) in Cattle) to increase vigilance. 

Although cattle-centric, WOAH does refer to `cattle and other livestock populations' in their messaging, but until now spillovers into sheep, goats, and other non-bovie ruminants have been often dismissed as either rare or dead end infections.

Today's study illustrates that small ruminants are not only susceptible to HPAI H5 infections; there is the potential for `widespread virus transmission within flocks'.  

The authors discuss the need for increased surveillance and the implementation of stricter biosecurity measures, particularly in mixed-species environments.

First the link, abstract, and some excerpts from a much longer study.  Follow the link to read it in its entirety.  I'll have a bit more after the break.  

 

Mammary and respiratory infection of sheep with H5Nx clade 2.3.4.4b viruses with milk-mediated transmission to lambs
Tamiru N. Alkie , Carissa Embury-Hyatt, Anthony V. Signore , Estella Moffat , Darwin Ramos, Sugandha Raj, Tamiko Hisanaga, Ifeoluwa Ayilara , Daniel S. Sullivan, [...] , and Yohannes Berhane 9 authors Authors Info & Affiliations
Science Advances
8 May 2026
Vol 12, Issue 19

Abstract

H5Nx clade 2.3.4.4b viruses are evolving rapidly, expanding host ranges and threatening animal and public health. In the US, genotype B3.13 dominates dairy outbreaks, while D1.1 is linked to fewer cases. In the UK, an asymptomatic ewe infected with genotype DI.2 raised concerns about ruminant susceptibility.

We inoculated lactating and nonlactating sheep with D1.1 (H5N1) and A6 (H5N5) viruses. Intramammary inoculation in lactating sheep caused clinical mastitis, high viral loads in milk, and transmission to suckling lambs, which further spread infection to the uninoculated mammary glands. Both ewes and their lambs seroconverted.

Aerosol exposure of nonlactating sheep led to transient respiratory infection, with low-level viral replication, and seroconversion. In vitro, both viruses replicated in sheep mammary epithelial cells.

These findings establish sheep as a viable ruminant model for H5N1 and H5N5 infection and highlight previously unidentified transmission dynamics, including milk-mediated and lamb-to-ewe spread, relevant for surveillance and biosecurity in ruminant populations.

        (SNIP)

Deep sequencing of milk samples from mammary glands, oral swabs, and lung tissues revealed the emergence of viral variants distinct from the consensus sequence generated from the challenge D1.1 virus.

Notably, the left mammary gland of a D1.1-infected sheep appeared to select for the variant PB2-701N, while the right gland retained mixed residues of PB2-627 (E/K) and PB2-701 (D/N). Sequence analysis suggests that the PB2-D701N mutation arose before transmission to the left gland, as oral swab from one suckling lamb already carried this mutation.

Dairy cows experimentally infected with H5N1 via the intramammary route acquired PB2-E627K mutation (32). While D1.1 viruses from some dairy cases exhibited the mammalian adaptive mutation PB2-D701N, the genotype B3.13 from all dairy cases retained the bovine-specific PB2-M631L mutation (74). Both PB2-E627K and PB2-D701N provide IAVs with significant replication advantages in mammalian hosts and enhanced viral transmission (75, 76).

(SNIP)

The findings from this study have significant implications, even though there are limitations such as small sample sizes and the lack of assessment of transmission from inoculated mammary glands to uninoculated glands from the environment.

However, all experimental studies in dairy cows revealed the restriction of infections and virus replication to infected quarters only. Our experimental approach has demonstrated that small ruminants are susceptible to H5N1 infections. 

The detection of seropositive goats and sheep during periods of heightened H5N1 activity underscores the necessity for more extensive investigations within the small ruminant herds. Once mammary infections with H5N1 have occurred in some lactating ruminants, virus can spread between the udders of lactating ruminants during suckling as some neonates could access milk from cohoused multiple lactating mothers.

This scenario suggests potential for widespread virus transmission within the flocks. We suggest increased surveillance and the implementation of biosecurity measures, especially in mixed-species livestock systems or where large numbers of lactating ruminants and their neonates were cohoused or allowed to graze on communal pastures. 

Moreover, similar to infected dairy cows, milk obtained from infected lactating small ruminants was found to harbor higher levels of infectious viruses. This raises important zoonotic considerations in areas where raw milk consumption is common. Furthermore, the handling of infected small ruminants poses risks to human health, highlighting the need for thorough risk assessments to be carried out.

       (Continue . . . )

Whether sheep, goats, or other small ruminants will ultimately increase the risk of HPAI remains unknowable, but it does give the virus more places where it can hide, thrive, and potentially make genetic improvements. 

Mixed-species farms are particularly worrisome, as they provide novel viruses with access to numerous hosts, and fresh opportunities to reassort or adapt (see Study: Seroconversion of a Swine Herd in a Free-Range Rural Multi-Species Farm against HPAI H5N1 2.3.4.4b Clade Virus).

While the evidence of HPAI H5's growing host range continues to mount, the $64 question remains; can we adapt to the threat faster than the threat is adapting to us?

Stay tuned. 

ECDC: Rapid Scientific Advice on Management of Hantavirus Exposed Passengers

#19,153

The ECDC has released their own set of recommendations for EU countries regarding the management of passengers returning from the m/v Hondius.  It should be noted that this is an advisory document, and not a mandate.

While these types of documents carry considerable weight, each member state can decide how to best manage the situation.

I've provided the the summary, and a link to the full 8-page PDF below.

Rapid Scientific Advice on the management of passengers - In the context of the Andes virus outbreak on the cruise ship MV Hondius

Assessment
9 May 2026

As of 9 May 2026, a total of eight cases of Andes virus infection, including three deaths and one critically ill patient, linked to the M/V Hondius cruise ship have been reported.

Key messages

ECDC has classified all people on board the ship and for the purpose of disembarkation and repatriation to be high-risk contacts.

• Monitoring/quarantine up to six weeks (42 days); Day 0 = 6 May 2026.
• High-risk contacts: self-quarantine, daily symptom monitoring, test if symptomatic.
• Low-risk contacts: passive monitoring; isolate and test if symptoms develop.
• Flights: trace contacts for probable/confirmed cases only (same row ±2 rows on long flights).
• IPC: masking, one to two metres distancing, PPE for healthcare/cleaning
• Strong risk communication and misinformation management.

This document provides advice for public health professionals in the EU/EEA managing individuals potentially exposed to ANDV, including on:Defining contact classification criteria based on level of exposure, including close and prolonged contact with symptomatic people;

• The identification, management and monitoring of contacts, including advice on testing.
• Appropriate infection prevention and control (IPC) measures for managing repatriated passengers and crew, suspected and confirmed cases and their contacts in healthcare and community settings; and
• Risk communication, community engagement and the management of misinformation.

ECDC rapid scientific advice disclosure statement: ECDC issues rapid scientific advice to meet an emergent or urgent public health need or to quickly reply to external requests. To accommodate the accelerated timeline, the process and methods used for the development of rapid scientific advice may be modified from those of standard assessments and recommendations. Potential limitations are described.

Publication file

Rapid Scientific Advice on the management of passengers - In the context of the Andes virus outbreak on the cruise ship MV Hondius

CDC Statement On Quarantine of Returning Passengers From the m/v Hondius

 

 #19,152

Late yesterday the CDC released a brief statement on how passengers from the m/v Hondius - currently enroute to the Canary Islands - will be repatriated and quarantined following potential exposure to the Hantavirus. 

While somewhat lacking in details, it clearly expresses the intent to quarantine returning passengers for an unstated period of time at the National Quarantine Center at the University of Nebraska. 

`Quarantine' refers to the sequestration of healthy-but-exposed individuals, while `isolation' refers only to symptomatic or confirmed infections.  At this point, none of the 17 returning passengers are symptomatic.

If symptoms were to develop, they would be moved to the Nebraska Biocontainment Unit.

Long time readers will recall that we've seen the National Quarantine Center activated before, including 2018's Nebraska Medicine Statement On Patient Being Monitored Following Possible Ebola Exposure. 

While not explicitly stated, this appears to be a federally mandated quarantine, although I'm pretty sure they will `ask nicely' first. Between the CDC's Legal Authorities for Isolation and Quarantine, and various other state and federal statutes, I'm sure they can enforce it if anyone resists. 

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

CDC Provides Update on Hantavirus Outbreak Linked to M/V Hondius Cruise Ship

Statement
For immediate release: May 8, 2026
CDC Media Relations
(404) 639-3286
media@cdc.gov
https://www.cdc.gov/media/

The U.S. government is actively monitoring and responding to a hantavirus outbreak linked to the M/V Hondius cruise ship. At this time, the risk to the American public remains extremely low.

CDC developed health guidance for impacted American passengers, which was delivered by the U.S. Department of State. CDC's premier infectious disease experts are continuing to work closely with international partners to develop consistent monitoring guidance. This guidance will be distributed today, in addition to resources targeted for state and local health departments.

The U.S. government's top priority is the safe repatriation of American passengers. These individuals are planned to be evacuated on a U.S. government medical repatriation flight to Offutt Air Force Base in Omaha, Nebraska, where they will be transported to the National Quarantine Center at the University of Nebraska, Omaha.

The CDC deployed a team of epidemiologists and medical professionals to the Canary Islands, where the M/V Hondius is expected to dock. The team will conduct an exposure risk assessment for each American passenger and provide recommendations for the level of monitoring required. An additional CDC team will deploy to Offutt AFB to support public health assessment of returning passengers.

https://www.cdc.gov/hantavirus/about/index.html

https://www.cdc.gov/hantavirus/about/andesvirus.html

It is less clear how stringently individual states will handle the 6+ passengers who have already returned from the cruise (reportedly to Georgia, Texas, Virginia, Arizona, and California).   

The Texas DSHS released as statement 2 days ago, which stated:

DSHS statement on Texas residents who were on board the MV Hondius

News Release

May 7, 2026

The Centers for Disease Control and Prevention has notified DSHS that two Texas residents were passengers on the MV Hondius, a ship that experienced an outbreak of hantavirus while traveling in the Atlantic Ocean. The passengers left the ship and returned to the United States before the outbreak was identified.

Public health workers in Texas have reached the two individuals, and they report they are not experiencing any symptoms and did not have any contact with a sick person while aboard the ship. They have agreed to monitor themselves for symptoms with daily temperature checks and contact public health officials at any sign of a possible illness.

And yesterday the State of Virginia released:

Hantavirus – Statement from the Virginia Department of Health
Posted on May 7, 2026

Last Updated: May 8, 2026

As of May 7, 2026, please see the Virginia Department of Health’s statement:

• The Virginia Department of Health is monitoring this situation closely and has been in active communication with our federal partners at the Centers for Disease Control and Prevention (CDC).
• To date, one Virginia traveler who was on the MV Hondius disembarked the ship and has returned home. This person is currently in good health and is under public health monitoring. To protect the privacy of this person, no further details will be shared about this individual.
• Our understanding is that fewer than 30 U.S. Citizens were on board the ship. A small number (<5) of other potentially exposed Virginians might be identified in the days ahead.

Exactly what `under public health monitoring' means isn't detailed. Neither state mentions restricting social contacts or activities, but that could change given the CDC's announced plan of action. 

While I'm still reasonably confident that this outbreak can be contained, that assumes everyone takes the threat seriously, and does what is needed to nip this in the bud. 

Regardless of how this outbreak resolves itself, this is a sobering reminder of how quickly the threat board can change.  

CDC HAN #00528: 2026 Multi-country Hantavirus Cluster Linked to Cruise Ship

 
WHO Epi Chart of Probable & Confirmed Cases

#19,151

While it remains to be seen whether the hantavirus outbreak aboard the m/v Hondius has `legs' , overnight the CDC published its first HAN advisory on the outbreak. 

The CDC’s Health Alert Network (HAN) is designed to ensure that communities, agencies, health care professionals, and the general public are able to receive timely information on important public health issues.

Given the extended incubation period, and the co-circulation of other respiratory and gastrointestinal illness this time of year, we are likely to hear of a lot of `suspected' cases in the days and weeks ahead. 

While most will probably turn out to be false alarms, it is imperative that physicians maintain a high index of suspicion when dealing with epidemiologically linked patients.   

While primarily of interest to clinicians, I've reproduced the CDC HAN below. Follow the link for references. 

2026 Multi-country Hantavirus Cluster Linked to Cruise Ship
May 8, 2026

Distributed via the CDC Health Alert Network
May 8, 2026
CDCHAN-00528

Summary

The Centers for Disease Control and Prevention (CDC) is issuing this Health Alert Network (HAN) Health Advisory to inform clinicians and health departments about a new cluster of hantavirus disease cases caused by infection with Andes virus. Hantavirus disease can cause severe illness and can be fatal. Clinicians should be aware of the potential for imported cases, although the risk of broad spread to the United States is considered extremely unlikely at this time. As a precaution, this Health Advisory summarizes CDC's recommendations for U.S. public health departments, clinical laboratories, and healthcare workers about hantavirus disease case identification, testing, and biosafety considerations in clinical laboratories.

Background

On May 2, 2026, the World Health Organization (WHO) was notified of a cluster of severe acute respiratory illness (SARI) among passengers and crew of a cruise ship in the Atlantic Ocean. The cluster included two deaths and one critically ill passenger, whose laboratory tests confirmed hantavirus. On May 6, 2026, WHO confirmed that the type of hantavirus responsible for this outbreak is the Andes virus. As of May 8, 2026, WHO has reported eight cases (six confirmed and two suspected), including three deaths. Investigations are ongoing to assess exposure risk of all Americans passengers on the cruise ship or who may have been exposed to an infected cruise ship passenger on an aircraft.

The cruise ship departed from Ushuaia, Argentina, on April 1, 2026, and traveled across the South Atlantic Ocean, stopping at several remote locations, including Antarctica, South Georgia Island, Tristan da Cunha, Saint Helena, and Ascension Island. It carried 147 people (86 passengers and 61 crew) from 23 different countries. The extent of their contact with wildlife before or during the expedition is unknown.

CDC is working with partners (federal government, state and local and international) on safely repatriating American passengers from the cruise ship to a facility in Nebraska with specialized medical capabilities. On May 7, 2026, CDC sent a team to meet the cruise ship in the Canary Islands, Spain following travel from Cape Verde, South Africa. The team is prepared to assess exposure risk among U.S. passengers and determine appropriate monitoring measures.

CDC is also coordinating with international partners to align public health guidance and has already issued health guidance to affected Americans via the State Department. The risk to the public's health in theUnited States is considered extremely low at this time. As a precaution, CDC is working to increase awareness of the outbreak among travelers, public health agencies, laboratories, and healthcare professionals nationwide.

Hantavirus pulmonary syndrome

Hantaviruses are a group of viruses that can cause severe illness and death. They are most commonly transmitted (spread) to humans through contact with infected rodents (e.g., urine, droppings, saliva). Rarely, infection can occur from rodent bites or scratches. From 1993 through 2023, a total of 890 laboratory-confirmed cases of hantavirus were reported in the United States.

In the Americas, hantaviruses can cause hantavirus pulmonary syndrome (HPS), a severe and potentially deadly disease that affects the lungs. HPS can be life-threatening. Among patients who have severe respiratory symptoms, the case fatality rate has been estimated at approximately 38%.

Andes virus, confirmed as the cause of this hantavirus outbreak, is the only type of hantavirus that has been documented to spread from person-to-person. Although rare, spread between people has typically required close, prolonged contact with a symptomatic person. This could include direct physical contact, prolonged time spent in close or enclosed spaces, and exposure to the infected person's saliva, respiratory secretions, or other body fluids (e.g., kissing, sharing utensils, handling contaminated bedding).

Symptoms of HPS caused by Andes virus usually appear within 4-42 days after exposure. Early symptoms can include fever, fatigue, and muscle aches, especially in large muscle groups like the thighs, hips, back, or shoulders. Early symptoms such as fever, headache, muscle aches, nausea, and fatigue can be easily confused with influenza or other viral illnesses. About half of all HPS patients have experienced headaches, dizziness, chills, and gastrointestinal symptoms, including nausea, vomiting, diarrhea, and abdominal pain. Late symptoms of HPS appear approximately 4-10 days after the initial phase of illness and can include coughing, shortness of breath, and chest tightness Individuals are generally only infectious while symptomatic.

Early diagnosis of HPS can be difficult, especially within the first 72 hours of symptoms, before the virus can be accurately detected in body secretions and excretions. Repeat diagnostic testing is often done 72 hours after symptom onset. CLIA assays for detection of New World hantavirus IgM and IgG antibodies are available at CDC, some state public health laboratories, and Quest Diagnostics.

For questions or concerns about submitting a specimen, please contact your state or local health department or CDC's Emergency Operations Center at 770-488-7100.

No specific treatment is recommended for hantavirus infection; early supportive care is critical even before the diagnosis is confirmed. Patients with suspected HPS can deteriorate rapidly, and delayed care reduces the chance of survival. In severe cases, extra-corporeal membrane oxygenation (ECMO) can significantly improve survival (up to ~80%) if started early. Usually, the critical phase of disease is fairly short, and survivors can recover quickly.

Recommendations for Healthcare Providers

• Be prepared to follow CDC's guidance under Appendix A: Type and Duration of Precautions Recommended for Selected Infections and Conditions | Infection Control | CDC.

• In healthcare settings, for patients with suspected or confirmed Andes virus infection, CDC recommends patient placement in an airborne infection isolation room and the use of a gown, gloves, eye protection, and an N95 or higher-level respirator when entering the patient's room.

• Include HPS in the differential diagnosis for an ill person who has compatible symptoms AND who has reported epidemiological risk factors, including at least one of the following, within the 42 days before symptoms onset:

• Had direct physical contact, or spent time in close or enclosed spaces, with a symptomatic person with confirmed or suspected Andes virus infection or with any objects contaminated by their body fluids.

• Had exposure to an infected person's saliva, respiratory secretions, or other body fluids (e.g., kissing, sharing utensils, handling contaminated bedding).

• Experienced a breach in infection prevention and control precautions that resulted in potential contact with body fluids of a patient with suspected or confirmed Andes virus infection.

• Consider and perform diagnostic testing for more common illnesses as well, such as COVID-19, influenza, and other common causes of gastrointestinal and febrile illnesses in an acutely ill patient with epidemiological risk factors and compatible symptoms.

For More Information

General Resources 

About Hantavirus | CDCAbout Andes Virus | CDCReported Cases of Hantavirus Disease | CDCHantavirus Prevention |CDC

Clinician Resources 

Clinical Overview of Hantavirus | CDCClinician Brief: Hantavirus Pulmonary Syndrome (HPS) | CDCClinician Brief: Hemorrhagic Fever with Renal Syndrome | CDCHantavirus Disease Trainings for Healthcare Providers | CDCAppendix A: Type and Duration of Precautions Recommended for Selected Infections and Conditions | Infection Control | CDC

Health Department Resources 

Hantavirus Case Definition and Reporting | CDC

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
Article PDF
Full Issue PDF

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.