CDC HAN #00529: 2026 Hantavirus Outbreak: Testing for Potential Infection

Credit CDC


#19,166

Lest we forget with all that is going on with the Ebola outbreak in central Africa; the world is still on watch for additional cases of the Andes virus stemming from the outbreak aboard the m/v Hondius. 

Yesterday the CDC released a HAN (Health Alert Network) update on this outbreak (see below). While of primary interest to clinicians, I've reproduced it below.

This update also reminds clinicians to consider other hantaviruses (New World & Old World) when confronted with patients with suggestive symptoms and exposure to sylvatic rodents or rodent excreta. 

First the HAN update, then I'll return with a bit more.

2026 Hantavirus Outbreak: Testing for Potential Infection
May 18, 2026

At a glance
Distributed via the CDC Health Alert Network
May 18, 2026
CDCHAN-00529



Summary

The Centers for Disease Control and Prevention (CDC) is issuing this Health Alert Network (HAN) Health Update to inform clinicians and health departments about testing available for patients with suspected hantavirus infection to include Andes virus. CDC first issued a Health Advisory (CDCHAN-00528) about this outbreak on May 8, 2026.

Hantaviruses are a group of viruses that typically spread to people who come in contact with sylvatic rodents. These viruses can cause severe illness or death in humans. Andes virus, a type of hantavirus endemic in South America, is the only type of hantavirus that is known to spread from person to person. Several other New World hantaviruses are endemic to the United States and are not transmissible from person to person. New World hantaviruses can cause hantavirus pulmonary syndrome (HPS), a potentially serious disease that can cause damage to the lungs.

On May 2, 2026, an outbreak of Andes virus on a cruise ship was reported to the World Health Organization (WHO). This outbreak has raised the possibility of cases being imported to the United States. As of May 18, no confirmed cases of Andes virus associated with the outbreak on the cruise ship have been reported in the United States. Therefore, the overall risk to the American public is still considered extremely low at this time. CDC and health departments in several states are monitoring the health of U.S. passengers from the ship and U.S. air travel contacts of symptomatic ship passengers who were subsequently confirmed to have Andes virus infection. This Health Update informs clinicians about testing and consultation that are available for Andes virus and other hantaviruses endemic to the United States, South America, and other nations.

Background

On May 2, 2026, WHO was notified of a cluster of severe acute respiratory illness (SARI) among passengers and crew aboard the M/V Hondius cruise ship in the Atlantic Ocean. On May 6, 2026, WHO confirmed that the cluster was caused by Andes virus, a hantavirus endemic in areas of South America that can cause hantavirus pulmonary syndrome (HPS). Andes virus is the only hantavirus known to spread from person to person. This type of transmission is rare for hantaviruses and is generally associated with prolonged close contact. As of May 15, WHO has reported 10 cases (8 of them laboratory-confirmed), including 3 deaths.

Hantaviruses cause two syndromes. Hantaviruses found in the Western Hemisphere are often referred to as New World hantaviruses and can cause HPS. Several New World hantaviruses that do not spread person to person are endemic in the United States. These include Sin Nombre virus, the virus mostly commonly associated with U.S. HPS cases. In addition to HPS, hantaviruses can cause other clinically significant illness. Hemorrhagic fever with renal syndrome (HFRS) is a group of clinically similar illnesses that affect the kidneys. HFRS is caused by another group of hantaviruses, often referred to as Old World hantaviruses, that are found mostly in Europe and Asia. However, Seoul virus, a type of hantavirus that causes HFRS, is found worldwide, including in the United States. Non-HPS hantavirus infection can also occur, in which patients experience non-specific viral symptoms without cardio-pulmonary symptoms.

Hantavirus infections can occur year-round but are reported more frequently during the spring and summer months when rodent populations increase and people may have greater exposure to rodent-infested environments such as cabins, sheds, campsites, and homes. The most common hantavirus that causes HPS in the United States is spread by the deer mouse. Andes virus is spread primarily by the long-tailed pygmy rice rat (Oligoryzomys longicaudatus).

Recommendations for Clinicians

Consider Andes virus infection in patients who

(1) have symptoms compatible with hantavirus infection,

AND

(2) were aboard the M/V Hondius cruise ship OR had direct contact with someone associated with the M/V Hondius Andes virus outbreak.

Contact your state, tribal, local, or territorial health department immediately to report a suspected Andes virus case and for assistance with diagnostic testing for Andes virus. 

Know that assays designed to specifically detect Andes virus may not detect other New World hantaviruses endemic in the United States.

Consider infection with other New World hantaviruses in patients who

(1) have symptoms compatible with hantavirus pulmonary syndrome (HPS) or non-HPS hantavirus infection,

AND

(2) have a history of known or suspected exposure to sylvatic rodents or rodent excreta (e.g., urine, droppings, or nesting materials).

Consider infection with Old World hantaviruses in patients who

(1) have symptoms consistent with hemorrhagic fever with renal syndrome (HFRS),

AND

(2) have a history of known or suspected exposure to sylvatic rodents or rodent excreta (e.g., urine, droppings, or nesting materials).

Test for non-Andes hantavirus in patients who have symptoms compatible with hantavirus infection and have a history of rodent exposure, but who are not associated with the M/V Hondius Andes virus outbreak.

Consult with CDC's Viral Special Pathogens Branch (VSPB) to discuss hantavirus diagnostic testing by calling the CDC Emergency Operations Center at 770-488-7100 and requesting VSPB's on-call epidemiologist. VSPB cannot accept specimens without prior consultation.

        (Continue . . . )

As we discussed last year, in Two Recent Studies On the Host Range of Hantaviruses In the United States, hantavirus infections are likely under reported in this country.

Credit CDC

Most Hantavirus cases are sporadic, but occasionally we see clusters. Exposure is often linked to cleaning out sheds and garages in the late spring and summer when mouse activity is high. The CDC has a 20-page PDF guide on reducing exposure risks.

For some past blogs on Hantaviruses, you may wish to revisit:

Argentina's Growing Hantavirus Outbreak

MMWR: A Little Bit Of Seoul (Virus)

Hantaviruses: Of Mice And Men

MMWR: Yosemite Hantavirus

CDC Statement on the Use of Public Health Travel Restrictions to Prevent the Introduction of Ebola Disease into the United States

Scheduled airline traffic around the world – Credit Wikipedia

#19,165

While reassuring the public that the current risk to Americans from the Ebola outbreak in the DRC is `low', yesterday the CDC announced enhanced screening of travelers and imposed `Entry restrictions on non-US passport holders'  if they have visited Uganda, DRC, or South Sudan in the past 3 weeks.

This invocation of Title 42, and a de facto `travel ban' for non-US passport holders is noticeably more restrictive than what we saw during the 2014-2015 Ebola outbreak in West Africa (see CDC Statement On Airport Screening Of Arrivals From West Africa).

First the CDC statement, after which I'll return more on the checkered history of interdicting diseases at ports of entry. 

CDC Statement on the Use of Public Health Travel Restrictions to Prevent the Introduction of Ebola Disease into the United States

For Everyone
May 18, 2026

What to know

On May 18, 2026, CDC, DHS, and other appropriate federal agencies implemented enhanced travel screening, entry restrictions, and public health measures to prevent Ebola disease from entering the United States amid ongoing outbreaks in East and Central Africa.

Statement on Title 42 Order

Title 42 Order

Title 42 Order Suspending the Right to Introduce Certain Persons from Countries Where a Quarantinable Communicable Disease Exists

The Centers for Disease Control and Prevention (CDC), and the Department of Homeland Security (DHS), and other appropriate federal agencies, are taking proactive measures to protect the health and safety of the American public in response to ongoing Ebola Virus Disease (EVD) outbreaks.

Under authority granted by Sections 362 and 365 of the Public Health Service (PHS) Act, 42 U.S.C. §§ 265, 268, and their implementing regulations, CDC is implementing targeted public health measures intended to reduce the risk of Ebola disease caused by the Bundibugyo virus (EVD) by preventing its introduction into the United States. These actions are based on current epidemiological evidence, ongoing risk assessments, and the highly serious nature of EVD. This order will be in effect for 30 days, effective immediately.

Effective immediately, CDC will:

• Enhance public health screening and traveler monitoring for individuals arriving from areas affected by Ebola outbreaks in the region.
• Entry restrictions on non-US passport holders if they have been in Uganda, DRC, or South Sudan in the previous 21 days.
• Coordinate with airlines, international partners, and port-of-entry officials to identify and manage travelers who may have been exposed to Ebola virus.
• Enhance port health protection response activities, contact tracing, laboratory testing capacity, and hospital readiness nationwide.
• Continue deployment of CDC personnel to support outbreak containment efforts in affected regions.

At this time, CDC assesses the immediate risk to the general U.S. public as low, but we will continue to evaluate the evolving situation and may adjust public health measures as additional information becomes available.

If you have traveled through the affected countries you are encouraged to monitor CDC travel health notices and seek medical attention immediately if you develop symptoms consistent with Ebola, including fever, weakness, vomiting, diarrhea, or unexplained bleeding, within 21 days of travel to affected areas.

As we discussed in 2014's The New Normal: The Age Of Emerging Disease Threats, the reality of life in this third decade of the 21st century is that disease threats that once were local, can now spread globally in a matter of hours or days.

Between asymptomatic (or presymptomatic) carriage, and long incubation periods, vast oceans and prolonged travel times no longer protect us against infected travelers crossing borders.

Globally, airlines handle over 5 billion passengers and over 40 million flights per year; that's roughly 12 million passengers and 100,000 flights each day. In the U.S. there are roughly 160 airports which handle international flights. 

With incubation periods that can range from a couple of days to several weeks, anyone who is recently exposed could easily change planes and continents several times before ever they ever show signs of illness.

Previous failed attempts to prevent the spread of H1N1 pandemic flu and COVID illustrate just how difficult interdiction really is. 

• In 2010's Japan: Quarantine At Ports Ineffective Against Pandemic Flu, we looked at a study which found for every person identified, and quarantined, by port authorities - researchers estimated 14 others infected by the virus entered undetected.

• In April of 2012, in EID Journal: Airport Screening For Pandemic Flu In New Zealand, we looked at a study that found that the screening methods used at New Zealand’s airport were inadequate to slow the entry of the 2009 pandemic flu into their country, detecting less than 6% of those infected.

• And in late 2020, a CDC MMWR Risk Assessment and Management of COVID-19 Among Travelers Arriving at Designated U.S. Airports, January 17–September 13, 2020, found that `Symptom-based screening programs are ineffective because of the nonspecific clinical presentation of COVID-19 and asymptomatic cases.'

None of this is to say there is no value in trying to detect, and quarantine, potentially infected travelers coming from an outbreak region; only that we need to temper our expectations.

Surveillance can often identify acutely ill individuals when they are likely to be the most contagious so they can be promptly isolated, and it can provide important surveillance information. And it might even help slow the rate of entry of an emerging disease into a region, allowing additional time to mount public health interventions.

But as far as preventing an infectious disease like Ebola, MERS-CoV, or novel Flu from entering this - or any other country - airport screening is unlikely to provide much in the way of long-term protection. 

The best place to try to stop the next pandemic is not at the inbound passenger gate, but in the places around the world where they are most likely to emerge.

But in our increasingly chaotic and insular world, that goal seems less obtainable with every passing day.

UKHSA MERS-CoV Risk Assessment & Updates

 

#19,164

The month of May has already borne witness to a high-profile Andes Hantavirus outbreak aboard the m/v Hondius and a burgeoning Bundibugyo Ebolavirus outbreak in Central Africa, which makes bringing up MERS-CoV this morning almost feel like piling on.  

But, with the 2026 Hajj only a week away, and nearly 2 million religious pilgrims expected to visit holy sites in Saudi Arabia, the low (but non-zero) possibility of seeing one or more MERS-CoV cases returning from the region cannot be ignored.

The UK's latest MERS-CoV Risk assessment reads, in part:

Risk assessment

The number of reported human MERS-CoV cases per year globally, has fallen to the lowest level since 2014. The identification of 2 imported cases of MERS-CoV in France demonstrates that MERS continues to pose a risk to UK public health, particularly in those who have travelled to the Middle East.

In addition to PCR confirmed cases in the Middle East, there is serological evidence of MERS-CoV infection of camel-workers in Nigeria, Kenya and Morocco. There is therefore a very low risk of importation of MERS-CoV from occupationally exposed individuals from those African countries. It is imperative that health professionals remain vigilant for clinical presentations compatible with Middle East respiratory syndrome. Detailed case definitions and guidance on when to suspect MERS is given in the MERS-CoV: diagnosis and management of cases and contacts.

Today, the UKHSA has published (or updated) more than a half dozen additional documents pertaining to MERS-CoV and/or travel to the Middle East. 

UKHSA risk assessment of MERS-CoV Updated: 18 May 2026

MERS-CoV: risk assessment

Guidance on reducing the risk of getting MERS-CoV for UK residents and travellers to the Middle East.Updated: 18 May 2026 

MERS-CoV: minimum data set form for possible cases
Minimum data set form for possible cases of Middle East respiratory syndrome coronavirus (MERS-CoV).

MERS-CoV: diagnostic testing
Information on taking, submitting and processing clinical samples from patients suspected of having Middle East respiratory syndrome coronavirus (MERS-CoV). Updated: 18 May 2026

MERS-CoV: diagnosis and management of cases and contacts
This guidance is for healthcare professionals and health protection teams (HPTs) on identifying and managing cases of Middle East respiratory syndrome (MERS).Updated: 18 May 2026

MERS-CoV: background information
This guidance gives advice on the transmission, diagnosis, treatment and prevention of Middle East respiratory syndrome coronavirus (MERS-CoV) to the public.Updated: 18 May 2026

MERS-CoV: clinical management and guidance
Guidance on investigating Middle East respiratory syndrome coronavirus (MERS-CoV), public health management of suspected UK cases and advice to travellers.Updated: 18 May 2026

MERS-CoV: biological principles for the control of MERS-CoV
This guidance outlines the current knowledge and assumptions about the biology and transmission of Middle East respiratory syndrome coronavirus (MERS-CoV).Updated: 18 May 2026

MERS-CoV: travel from the Middle East advice sheet
Infographic with advice on Middle East respiratory syndrome coronavirus (MERS-CoV) for people travelling to the UK from the Middle East.Updated: 18 May 2026

MERS-CoV: travel from the Middle East advice sheet (HTML version) Updated: 18 May 2026

While the number of reported cases has declined over the past 6 years, we've seen several recent high-profile reports of spillovers, including France MOH: 2 Travelers Returning From Arabian Peninsula Diagnosed with MERS-CoV and WHO: Saudi Arabia Reports 9 New MERS-CoV Cases.

Not surprisingly, over the past year we've also seen a resurgence in MERS-CoV-related studies, including:

The Lancet: The Threat of Another Coronavirus Pandemic

Health Sci Rpts (Narrative Review): Pathogenicity and Potential Role of MERS-CoV in the Emergence of “Disease X”

IJID Editorial: Al-Tawfiq on Global Epidemiology and Public Health Challenges of Middle East Respiratory Syndrome Coronavirus (MERS-CoV)

JEGH: Epidemiological Characteristics of MERS-CoV Human Cases, 2012- 2025

JEGH: Al-Tawfiq & Memish On Recurrent MERS-CoV Transmission in Saudi Arabia

As recently as last March - a WHO-authored commentary, published in Nature - warned that the MERS-CoV continues to circulate in dromedary camels in the Middle East, that it appears to maintain its virulence, and it remains a plausible pandemic threat.

I consider trying to predict the next big global health crisis a mug's game, since so many things could come at us out of left field with little or no warning.  

But recent studies suggest that the frequency, and impact, of pandemics are only expected to increase in the years ahead.

BMJ Global: Historical Trends Demonstrate a Pattern of Increasingly Frequent & Severe Zoonotic Spillover Events

PNAS Research: Intensity and Frequency of Extreme Novel Epidemics

So, while I can't tell you what type of emerging disease will spark the next pandemic - or when - it is all but guaranteed to happen again.  

The only question is; when that day comes, will we be ready?

Canada: PHAC Statement on `Presumed Positive' Hantavirus Case in Vancouver

#19,163

One of the m/v Hondius passengers, recently repatriated to Canada, has developed symptoms and has presumptively tested positive for the Hantavirus. Their spouse is also reportedly mildly symptomatic, and both have been hospitalized (along with a 3rd contact). 

The phrase `presumptive positive' simply means a local laboratory has obtained a positive result, confirmation of these results by the PHAC's National Microbiology Laboratory in Winnipeg will take a couple of days.

While concerning, known cases continue to be reported only among passengers and crew of the m/v Hondius.  Whether additional - `off-ship' infections - will emerge remains to be seen. 

Canada's PHAC released the following statement late Saturday afternoon.

Media update on Andes hantavirus situation

From: Public Health Agency of Canada
Statement

May 16, 2026 | Ottawa, ON

On May 16, 2026, the British Columbia Provincial Health Officer reported that one of the four high risk individuals who was self-isolating and being monitored for symptoms has tested presumptive positive for Andes hantavirus. The person was transported to hospital for assessment and care on May 14 along with their spouse who also has mild symptoms. The couple were passengers on the MV Hondius. Both will remain in isolation in hospital. Out of an abundance of caution, a third individual who was in secure lodging for isolation has been transferred to hospital for assessment and testing.

All infection prevention and control protocols are being followed, including the use of personal protective equipment by healthcare workers and personnel involved in the repatriation. Those involved in the repatriation are not considered at risk given the public health protective measures that were in place, in addition to the length of time between repatriation and the onset of symptoms.

Samples have arrived at the Public Health Agency of Canada’s National Microbiology Laboratory (NML) in Winnipeg for confirmatory testing. Results are expected in the next two days.

The Public Health Agency of Canada, the province of British Columbia, and local public health are working together to ensure all public health measures continue to be followed to protect the health of Canadians.

The overall risk to the general population in Canada from the Andes hantavirus outbreak linked to the MV Hondius cruise ship remains low at this time. But, given the severity of this virus, we are taking a precautionary approach to ensure Canadians are protected.

The Public Health Agency of Canada will continue to actively monitor the situation, provide guidance and support to provincial/territorial public health partners and share updates as needed.

WHO Director Declares DRC Outbreak of Bundibugyo Ebolavirus a PHEIC (Public Health Emergency of International Concern)

#19,162

Overnight, roughly 72 hours after the first reports, the Director of the World Health Organization declared the Bundibugyo virus outbreak in the DRC to constitute a PHEIC. 

This should give us some idea of their level of concern, as previous PHEIC declarations have generally taken weeks or even months.

On Friday we discussed some of the concerning aspects of this latest outbreak, including the fact it has flown under the radar for weeks or months, that the number of cases and deaths is quite high, and that the only vaccine for the ebolavirus is unlikely to be effective against this strain.

While stating that this outbreak  `. . . does not meet the criteria of pandemic emergency, as defined in the IHR.' this declaration does find that neighboring countries to the DRC are at `High Risk ' of seeing imported cases. 

I've posted excerpts from the PHEIC declaration below, follow the link to read the full document. Given the logistics of containment in this part of the world, this is likely to remain a big story for months to come. 

Epidemic of Ebola Disease caused by Bundibugyo virus in the Democratic Republic of the Congo and Uganda determined a public health emergency of international concern
17 May 2026
Statement
Geneva
Reading time: 8 min (2150 words)

Pursuant to paragraph 2 of Article 12 - Determination of a public health emergency of international concern, including a pandemic emergency of the International Health Regulations (2005) (IHR), the Director-General of the World Health Organization (WHO), after having consulted the States Parties where the event is known to be currently occurring, is hereby determining that the Ebola disease caused by Bundibugyo virus in the Democratic Republic of the Congo and Uganda constitutes a public health emergency of international concern (PHEIC), but does not meet the criteria of pandemic emergency, as defined in the IHR.

The Director-General of WHO expresses his gratitude to the leadership of the Democratic Republic of the Congo and Uganda for their commitment to take necessary and vigorous actions to bring the event under control, as well as for their frankness in assessing the risk posed by this event to other States Parties, hence allowing the global community to take necessary preparedness actions.

In his determination the Director-General of WHO has considered, inter alia, information provided by the States Parties – the Democratic Republic of the Congo and Uganda – scientific principles as well as the available scientific evidence and other relevant information; and assessed the risk to human health, the risk of international spread of disease and of the risk of interference with international traffic.

The Director-General of WHO considers that the event meets the criteria of the definition of PHEIC, contained in Article 1 - Definitions of the IHR, for the following reasons: 

1. The event is extraordinary for the following reasons:As of 16 May 2026, eight laboratory-confirmed cases, 246 suspected cases and 80 suspected deaths have been reported in Ituri Province of the Democratic Republic of the Congo across at least three health zones, including Bunia, Rwampara and Mongbwalu.

In addition, two laboratory confirmed cases (including one death) with no apparent link to each other have been reported in Kampala, Uganda, within 24 hours of each other, on 15 and 16 May 2026, among two individuals travelling from the Democratic Republic of the Congo. On 16 May, a laboratory confirmed case has also been reported in Kinshasa, the Democratic Republic of the Congo, among someone returning from Ituri.

Unusual clusters of community deaths with symptoms compatible with Bundibugyo virus disease (BVD) have been reported across several health zones in Ituri, and suspected cases have been reported across Ituri and North Kivu. In addition, at least four deaths among healthcare workers in a clinical context suggestive of viral haemorrhagic fever have been reported from the affected area raising concerns regarding healthcare-associated transmission, gaps in infection prevention and control measures, and the potential for amplification within health facilities.There are significant uncertainties to the true number of infected persons and geographic spread associated with this event at the present time.

In addition, there is limited understanding of the epidemiological links with known or suspected cases.However, the high positivity rate of the initial samples collected (with eight positives among 13 samples collected in various areas), the confirmation of cases in both Kampala and Kinshasa, the increasing trends in syndromic reporting of suspected cases and clusters of deaths across the province of Ituri all point towards a potentially much larger outbreak than what is currently being detected and reported, with significant local and regional risk of spread. Moreover, the ongoing insecurity, humanitarian crisis, high population mobility, the urban or semi-urban nature of the current hotspot and the large network of informal healthcare facilities further compound the risk of spread, as was witnessed during the large Ebola virus disease epidemic in North Kivu and Ituri provinces in 2018-19. However, unlike for Ebola-zaire strains, there are currently no approved Bundibugyo virus-specific therapeutics or vaccines. As such, this event is considered extraordinary.

2. The event constitutes a public health risk to other States Parties through the international spread of disease. International spread has already been documented, with two confirmed cases reported in Kampala, Uganda on 15 and 16 May following travel from the Democratic Republic of the Congo. Both confirmed cases were admitted to intensive care units in Kampala. Neighboring countries sharing land borders with the Democratic Republic of the Congo are considered at high risk for further spread due to population mobility, trade and travel linkages, and ongoing epidemiological uncertainty.

3. The event requires international coordination and cooperation to understand the extent of the outbreak, to coordinate surveillance, prevention and response efforts, to scale up and strengthen operations and ensure ability to implement control measures.

The Director-General of WHO, under the provisions of the IHR, will be convening an Emergency Committee, as soon as possible to advise, inter alia, on the proposed temporary recommendation for States Parties to respond to the event.

(Continue . . . ) 

 

OFID: Central Nervous System Involvement by Novel Clade 2.3.2.1e H5N1 Avian Influenza Virus in a Paediatric Patient

 

#19.161

While seasonal flu can occasionally cause neurological symptoms (see 2018's Neuroinfluenza: A Review Of Recently Published Studies) it is relatively rare, and usually only results in mild, and transient symptoms.

Similarly, avian influenza typically presents as a pulmonary infection, but over the past 2 decades we've seen growing evidence of neurological involvement as well.

A few early reports include: 

• 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.'

HPAI H5Nx's threat largely receded between 2016-2020, but since 2021 has been on the ascendent again, primarily due to highly successful clades like 2.3.4.4b and 2.3.2.1c/e. Along with this renewed vigor we've also seen a rise in reports of neurological manifestations:

CDC EID Journal: Encephalitis and Death in Wild Mammals at An Animal Rehab Center From HPAI H5N8 - UK

Ontario: CWHC Reports HPAI H5 Infection With Severe Neurological Signs In Wild Foxes (Vulpes vulpes) 

In 2022, in Clinical Features of the First Critical Case of Acute Encephalitis Caused by Avian Influenza A (H5N6) Virus, we saw 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. 

The following year, in Cell: The Neuropathogenesis of HPAI H5Nx Viruses in Mammalian Species Including Humans, we looked at an excellent review of recent surge in neurological infections reported in mammals and humans.

Highlights

• Highly pathogenic avian influenza (HPAI) H5Nx viruses can cause neurological complications in many mammalian species, including humans.

• Neurological disease induced by HPAI H5Nx viruses in mammals can manifest without clinical respiratory disease.

• HPAI H5Nx viruses are more neuropathogenic than other influenza A viruses in mammals.

• Severe neurological disease in mammals is related to the neuroinvasive and neurotropic potential of HPAI H5Nx viruses.

• Cranial nerves, especially the olfactory nerve, are important routes of neuroinvasion for HPAI H5Nx viruses.

• HPAI H5Nx viruses have a broad neurotropic potential and can efficiently infect and replicate in various CNS cell types.

• Vaccination and/or antiviral therapy might in part prevent neuroinvasion and neurological disease following HPAI H5Nx virus infection, although comprehensive studies in this area are lacking.

Even the relatively mild `bovine' H5N1 strain (B3.13) has been shown to have neurotropic qualities (see Preprint: Recent Bovine HPAI H5N1 Isolate is Highly Virulent for Mice, Rapidly Causing Acute Pulmonary and Neurologic Disease), at least in mice.

Thirteen months ago (April 2025) we saw 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.

While much of the following report will be primarily of interest to clinicians, we have a detailed follow up on the Vietnamese case. Follow the link to read it in its entirety.

Central Nervous System Involvement by Novel Clade 2.3.2.1e H5N1 Avian Influenza Virus in a Paediatric Patient

Phung Nguyen The Nguyen , Nguyen Thanh Hung , Ngo Ngoc Quang Minh , Nguyen Thi Thu Hong , Nguyen Thi Thanh Huong , Cao Minh Hiep , Le Nguyen Thanh Nhan , Tran Van Dinh , Du Tuan Quy , Tran Thanh Thuc
Open Forum Infectious Diseases, ofag283, https://doi.org/10.1093/ofid/ofag283

Published: 07 May 2026

Novel clade 2.3.2.1e A(H5N1) virus was detected in cerebrospinal fluid but not in respiratory,rectal-swab and blood samples of an eight-year-old boy presenting with meningoencephalitis without respiratory symptoms. Cerebrospinal fluid A(H5N1)-hemagglutinin-specific antibody levels were higher than that of sera. Clinicians should be aware of emerging clade 2.3.2.1eA(H5N1) associated meningoencephalitis.

       (SNIP)

A(H5N1)-associated CNS infection in humans has rarely been reported but typically present as a complication, following respiratory symptoms [3-5]. Notably, our patient presented with meningoencephalitis in the absence of respiratory symptoms. Additionally, unlike the previously reported patients, who had viral RNA detected in both CSF and non-CSF samples [3-5], our patient only had viral RNA detected in serial CSF samples in the absence of viral RNA detected in urine, blood, rectal swab and respiratory samples.

Low respiratory-tract viral loads, transient viral replication in the respiratory tract, and/or delayed sample collection (illness day 6 onward) might explain the negative PCR findings in non-CSF samples, including the endotracheal aspirate sample. 

Notably, HPAI A(H5N1) viruses can infect human respiratory tissues by binding to receptors bearing sialic acids linked to galactose by α2,3-linkages, which are found in the lungs and lower respiratory tract, supported by the chest radiograph findings suggestive of lower left lung pneumonia.

        (SNIP)

In summary, we report on a HPAI A(H5N1) infection in a child presenting with  meningoencephalitis in the absence of respiratory symptoms. Viral RNA was detected in cerebrospinal fluid but not in respiratory, rectal-swab and blood samples.

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.

       (Continue . . . )

Not only can these neurological complications prove quite serious, atypical presentations can significantly delay proper diagnosis, isolation, and treatment. 

A reminder that HPAI H5 isn't your father's influenza. 

And we continue to treat it as such at our considerable peril.