EID Journal: Experimental Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b Virus Infection in Alpacas, 2026

 

#19,338

In 2024 - just over 2 months after the discovery of HPAI H5N1 in U.S. dairy cattle - the USDA reported that HPAI H5N1 had been Detected In Alpacas from a premises (in Idaho) where HPAI-affected poultry had recently been depopulated. 

Alpacas belong the the family Camelidae, which includes 3 types of camels ( dromedary camels, Bactrian camels, wild Bactrian camels), and 4 lamoids (llama, alpaca, guanaco, and vicuña).

Camelidae - including both camels and alpacas - are known to be susceptible to MERS-CoV (see EID Journal: MERS-CoV Antibodies In Alpacas - Qatar), but less is known about their susceptibility to influenza A viruses.  

In recent years we've seen the mammalian host range of HPAI continue to expand,  with the virus detected in horses, pigs, goats, sheep, mink, dogs, and cats and a growing list of peridomestic animals (see below).

Some animals are clearly more susceptible than others to the virus, and some appear to be dead-end hosts; susceptible to infection but unlikely to contribute to the spread of of the virus. 

In an attempt to determine how vulnerable Alpaca are to the virus, and their ability to carry, and shed the virus, researchers at Germany's FLI (Friedrich-Loeffler-Institut) experimentally infected 6 alpaca with the HPAI H5N1 genotype B3.13 (`bovine') virus.

While they found that H5N1 B3.13 can induce a mild, but productive, upper respiratory infection in alpacas (including nasal shedding of the virus for several days and seroconversion), it still isn't established whether alpacas can efficiently transmit virus to one another. 

That said, there would seem to be enough here to warrant inclusion of camelids in farm biosecurity and surveillance plans. 

Due to its length, I've only posted the highlights. Follow the link to read the report in its entirety. 

Research
Experimental Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b Virus Infection in Alpacas, 2026
 
Jacob Schön , Angele Breithaupt, Nico Joel Halwe, Maxi Hertel, Ann Kathrin Ahrens, Andrea Aebischer, Donata Hoffmann, and Martin Beer
 
Abstract

Highly pathogenic avian influenza (HPAI) A(H5N1) clade 2.3.4.4b virus continues to spread globally and sporadically transmits from avian reservoirs to mammalian hosts. In May 2024, H5N1 infections in young goats and alpacas in the United States were reported. Nevertheless, the overall susceptibility of camelids to clade 2.3.4.4b virus remains unclear. 

We conducted a controlled experimental infection study in 6 alpacas, assessing clinical signs, viral shedding, tissue distribution, and serologic responses after intranasal inoculation with HPAI H5N1 genotype B3.13 virus. 

Observed illness was generally mild; body temperature increased slightly and food intake reduced for up to 3 days postinfection. We detected viral RNA in nasal swab samples and confirmed infectious HPAI H5N1 virus. Immunohistochemistry and RNA in situ hybridization detected virus only in the nasopharyngeal tonsil and nasal conchae at 4 days postinfection.

Our findings suggest alpacas are susceptible to productive H5N1 infection, highlighting implications for livestock surveillance and biosecurity in regions with ongoing circulation.

       (SNIP)

We experimentally confirmed that alpacas can be intranasally infected with a bovine HPAIV H5N1 B3.13 isolate, leading to subsequent nasal shedding of infectious virus. IHC and ISH confirmed H5N1 virus replication in the nasopharyngeal tonsil and the nasal conchae. Productive infection was corroborated by seroconversion at 20 dpi. We detected individual variation of neutralizing antibody levels, but the small number of animals does not enable general conclusions. The infection did not cause fever, but alpacas reduced feed intake. Whether the viral load shed by the alpacas would be sufficient to cause transmission to contact animals remains undetermined. Intermittent viral RNA detection and low viral titer at 3 dpi might reflect technical variability of the sampling procedure rather than reduced shedding.

Our data did not suggest that alpacas replicate H5N1 clade 2.3.4.4b genotype B3.13 virus with exceptionally high efficiency. However, nasal replication occurred, and infectious virus was detectable in nasal swab samples for up to 6 dpi, but sequencing did not indicate accumulation of mutation to that timepoint. Nevertheless, viral adaptation after infection or shedding to naive contact animals or humans cannot be excluded. A follow-up study should include direct-contact animals to assess the biologic relevance of low-level shedding and to clarify the potential role of alpacas in H5N1 transmission. In addition, future studies should include experimental intramammary inoculation of female alpacas to evaluate susceptibility via that route.

In conclusion, H5N1 clade 2.3.4.4b virus will likely continue to drive substantial mortality rates in wild birds and marine mammals across North and South America. Risk for virus spillover into domestic animals, including poultry and potentially camelids, will continue considering their large populations on the continents. The demonstrated capacity of H5N1 clade 2.3.4.4b virus to acquire mammalian-adaptive mutations heightens concern about cross-species transmission and possible establishment in new mammalian hosts, which could intensify wildlife losses, disrupt livestock production, and generate new zoonotic risks. Sustained surveillance, strengthened biosecurity, and rapid response measures will be essential to limit those impacts.

       (Continue . . . )

 

WHO: Bangladesh Reports 4th H5N1 Human Infection for 2026

 


#19,337

In their latest Influenza at the human-animal interface Summary and risk assessment (8 August to 6 September 2026) - published this week - the WHO has announced the 4th H5N1 case in a Bangladeshi child in the past 9 months.

• Last April, we saw a fatal case reported from the Chattogram Division, in a child who fell ill on January 22nd, was hospitalized on January 28th, and who died on February 1st. The H5N1 infection was only determined posthumously, via lab analysis on Feb 7th.

• In early June we learned of a 2nd case, a child from Sylhet Division who was hospitalized on March 28th with a clinical diagnosis of measles with bronchopneumonia. The child was discharged on March 31st, but delayed testing by the IEDCR only revealed a positive H5N1 result on April 20th.

• And last July the WHO reported a 3rd child - also from Sylhet Division - diagnosed with H5 (later confirmed as H5N1). The child (now recovered) fell ill in May, and reportedly had no travel history and no history of exposure to poultry.

In addition to the new H5N1 case in Bangladesh, the WHO also details 3 H9N2 cases in China (previously reported in this blog) and 2 H1N2v Cases from Michigan (reported by CDC here).

Avian influenza viruses in humans

A(H5N1), Bangladesh

On 30 August, Bangladesh, through the national IHR focal point, notified WHO of one laboratory-confirmed human infection with an A(H5) virus in a child from Rangpur division. On 15 August 2026,  the child developed a fever, cough and rhinitis and was admitted to hospital on 17 August. 

On 18 August, a nasopharyngeal swab and throat swab was collected as part of hospital-based influenza surveillance and tested positive for influenza A(H5) by real-time RT-PCR at the icddr,b laboratory on the same day. The sample was subsequently confirmed positive for influenza A(H5N1) at the Molecular and Genomic Laboratory Department of Institute of Epidemiology, Disease Control and Research (IEDCR) and National Influenza Centre (NIC) of Bangladesh. Genetic sequencing is underway. The child remained hospitalized and was improving clinically at the time of reporting.

There was no reported history of travel outside the area of residence. The child had a history of exposure to duck and chickens, including some that were sick, in the household and adjacent households. Poultry meat and oropharyngeal swab specimens collected from several backyard chickens on 26 August tested negative for influenza A(H5).

Close contacts were identified and placed under monitoring and all contacts remained asymptomatic during the observation period, except for two health care workers. Respiratory specimens collected from these two individuals tested negative for influenza A viruses.

This is the 4th laboratory-confirmed human case of avian influenza A(H5) reported in Bangladesh in 2026.

While full genetic sequencing has not been released, the H5N1 virus circulating in India and Bangladesh is typically clade 2.3.2.1a - not 2.3.4.4b which is currently dominant in much of Europe, Asia, and North/South America.

This is the 16th case reported by Bangladesh since 2008 (2 fatal: 1 in 2013 and 1 in 2026), and it reminds us that older clades of the H5 virus continue to circulate, and occasionally spill over into humans. 

While this is just the 10th human H5 case reported to WHO in 2026 (see chart below), the expectation is that many cases go unreported around the globe. 

#Natlprep 2026: Pandemic Planning At Both Ends of the Spectrum

 

Note: This is the 16th day of National Preparedness Month. Follow this year’s campaign on Twitter by searching for the #NatlPrep #BeReady or #PrepMonth hashtags.

This month, as part of NPM26, I’ll be rerunning some updated preparedness essays, along with some new ones.

#19,336

Next week (Sept 25th) the U.N. will host a meeting for world leaders in New York City for the purposes of pandemic planning, which will be broadcast live on UN Web TV.  

As this is a 1 day meeting, and it comes amid headwinds from several directions, it isn't clear exactly what will come from it.

Earlier this month, The Lancet published a comment (excerpts below) on this upcoming meeting, which discussed some of the many challenges it faces.

From commitment to governance: what should the 2026 UN high-level meeting on pandemic preparedness deliver?

Nelson Aghogho Evaborhenea,b Send email to nelsone@ruc.dk ∙ Maureen Lubac,d ∙ Hawi Getnet Degue ∙ Marc Bosonkief ∙ Douglas Muthinji Wanjag ∙ Pimchanok Ratanapisesh ∙ et al.  Article Info

Published September 4, 2026
DOI: 10.1016/j.langlo.2026.104070 External Link Also available on ScienceDirect External Link
Copyright: © 2026 The Author(s). Published by Elsevier Ltd.
 
Download PDF 

In September, 2026, world leaders will convene in New York for the second UN high-level meeting on pandemic prevention, preparedness and response (PPPR).1 The first high-level meeting produced a political declaration that reaffirmed commitments to strengthen pandemic preparedness and advance equity, catalysed the WHO Pandemic Agreement negotiations, and emphasised a whole-of-government and society approach to PPPR.1 Since then, member states have amended the International Health Regulations, adopted the Pandemic Agreement, expanded preparedness financing mechanisms, and proposed reforms to the broader global health architecture.

These developments represent substantial progress. However, the environment in which they must now operate has changed profoundly.

Geopolitical competition has intensified, multiple crises have diverted political attention and financial resources, official development assistance and multilateralism have come under increasing pressure, and the withdrawal of the USA from WHO has accelerated a turn towards nationalism and bilateral approaches to pandemic preparedness,2 adding another layer to an already complex architecture.

Meanwhile, regional institutions have assumed greater responsibilities for PPPR.3 In Africa, for example, the revised statute of Africa Centers for Disease Control and Prevention (CDC) adopted in 2022 expanded the Africa CDC’s mandate and gave it authority to declare a Public Health Emergency of Continental Security, a power Africa CDC exercised during the 2024 mpox outbreak and again during the ongoing Ebola outbreak, alongside WHO’s declaration of a Public Health Emergency of International Concern. Without meaningful coordination, parallel initiatives risk creating overlapping mandates, fragmented financing, and competing expectations relating to surveillance, pathogen sharing, data governance, and equitable access to medical countermeasures.4

Against this backdrop, the credibility of the high-level meeting should not be measured on the basis of yet another ambitious political declaration, but instead, on the basis of whether the meeting delivers a credible governance framework that aligns ongoing reforms, strengthens their coherence, and translates political commitments into sustained preparedness. We outline three priorities.

       (Continue . . . )

The expectation is that these world leaders will adopt a non-binding "political declaration" on preventing and preparing for future pandemics which was drafted over the summer. While long on good intentions, this document lacks much in the way of `teeth' (enforcement mechanisms, dedicated funding, or even a detailed roadmap).

Meanwhile, public health entities and researchers around the world continue to sound the alarm. A few (of many) examples: 

• In April of 2025 the ECDC published ECDC Guidance: Recommendations for Preparedness Planning for Public Health Threats

• In July 2025 Switzerland Unveiled a New Pandemic Plan

• Also in 2025, Canada announced plans to Purchase 500,000 doses Of H5N1 Vaccine and the EU announced plans to purchase up to 27 million doses. 

• Last December the ECDC published Pre-pandemic Guidance: Strategies to Fight Avian and Swine flu in Humans

• And just last month we looked at Referral: Two Related Papers (PNAS & The Lancet) on Preparing for The Next Pandemic

Whether these plans - or the vaccines and antivirals being stockpiled - will be adequate or appropriate for the next global health crisis remains to be seen. As we've seen before, No Pandemic Plan Survives Contact With A Novel Virus.

But having a framework for dealing with a crisis, and running realistic exercises, can be invaluable when the next pandemic strikes.

Most of these pandemic plans are created by - and for - national governments.  What planning may be going on at state/province/or local levels - or for the private sector - is harder to discern. 

But as many people learned to their cost during the last pandemic, it is just as important to be prepared on the individual, family, and neighborhood level.

Sadly, over the past few years much of the public guidance that was once heavily promoted by the CDC and HHS on pandemic preparedness has been expunged from their websites. 

It's as if the first rule of pandemic preparedness in the 2020's is . . . we don't talk about pandemic preparedness.

Buried in the CDC's archives, however, are a number of useful documents, including these from 2017 (download them while they are still available):

• Get Your Household Ready For Pandemic Flu {PDF - 16 pages]
• Get Ready for Pandemic Flu: Educational Settings [PDF – 16 pages]

• Get Ready for Pandemic Flu: Workplace Settings [PDF – 16 pages]  

In addition to the advice offered in these (and other) guidance documents, I'd like to offer 5 things you can do today to prepare for a possibility of seeing another pandemic sometime in the reasonably near future.

1. Get, and become, a `Flu Buddy'

The first item is one we've discussed often (see Yes, We Have No Pandemic . . . But Line Up A Flu Buddy Anyway). I first fleshed out the idea in a 2008 blog called Lifelines In A Pandemic.

A `Flu Buddy’ is simply someone you can call if you get sick, who will then check on you every day (by phone, social media, or in person), make sure you have the food and medicines you need (including fetching prescriptions if appropriate), help care for you if needed, and who can call for medical help if your condition deteriorates.

Those people who care for others, like single parents, also need to consider who will take care of their dependents if they are sick.

2. Avail yourselves of the vaccines that are available now.

While the evidence is limited, there are some studies suggesting that getting the seasonal flu vaccine may give you some small degree of protection against the H5N1 virus. Even if it doesn't, it may reduce your chances of having a dual infection, which could either be more serious, or even lead to a reassortant virus.

COVID remains a threat, and a dual COVID-flu infection can be worse than either one alone, so if you can get one - keeping current with that vaccine makes sense as well.

Since bacterial co-infections are common with influenza, getting the latest appropriate pneumonia vaccines can also a smart move. In 2023, I also updated my Tetanus shot (Tdap), and those over 75 will want to consider the RSV vaccine.

3. Get a Dr. Checkup, Renew Rx Meds, & Handle any Medical Issues

Over the past 3 years I've endured two 21-day scalp and face field treatment (Fluorouracil) following my skin cancer surgery in 2024 (and again in 2026). 

I also got my Rx meds renewed, and have laid in a stock of any OTC meds I might need.

4. Stock up on PPEs or other supplies you might need

I went into COVID with an existing supply of N95 masks and gloves, and I refreshed my stocks in 2022, but if you don't already have all the N95/KN95 or other personal protective gear you would want or need during a pandemic, now is the time buy them.

Once a crisis begins, it is often too late to stock up. And that goes for any preparedness supplies or gear you might desire in an emergency (Hand Sanitizers/OTC meds/etc.)

5. Be prepared to Shelter in Place

If there was one lesson from the opening months of COVID, it is that many of us may elect - or be forced - to stay home, and avoid public places. Supply chains may be compromised, and there may be runs on `necessities' leaving some store shelves bare.

We see this every year before blizzards and hurricanes, and so it makes sense - whenever possible - to keep a stocked pantry, along with the other staples of life.

 
Last winter, in The Gift of Preparedness 2025 we looked a number of items that might make life more bearable during an extended `bug-in' situation.The good news is, much of what you need to do now to prepare for a pandemic would hold you in good stead for any prolonged emergency or disaster. Frankly, there is not much here I wouldn't do to be prepared for hurricanes, blizzards, or earthquakes.

And if we get lucky, and no pandemic (or other emergency) occurs in the near term, I'll count my blessings - and sleep much better at night - knowing I'd done everything I could to be prepared.

And as a wise man once said:

“Everything you say in advance of a pandemic seems alarmist. Anything you’ve done after it starts is inadequate." - Michael Leavitt, Former Secretary of HHS

Taiwan CDC: Both influenza and the COVID-19 epidemic are currently in their peak season, with influenza cases continuing to rise

 

#19,335

A little over 2 weeks ago (Aug 28th), Japan announced the earliest start to their influenza season since the 2009 H1N1 pandemic (see Japan MHLW Reports Unusually Early Start to the Fall Flu Season), while last week Taiwan reported  `. . . emergency room visits reached 11.2%, exceeding the epidemic threshold (11.0%), indicating the start of the epidemic period.'

Four days ago (Sept 11th) South Korea announced the early start to their flu season, and recent reports from China suggest flu is gaining ground in their southern provinces. 

While all of this is unusually early flu activity, Hong Kong - which often sees a biphasic (summer & winter) flu season - continues to report substantial flu (see Update on cluster of Influenza A cases in TWGHs Wong Tai Sin Hospital) as well. 

Today Taiwan's CDC has updated their flu report, and is urging the public to take precautions and to be aware of early warning signs of severe illness. 

        (translation)

Both influenza and the COVID-19 pandemic are currently in their peak season, with influenza cases continuing to rise

The public is urged to implement self-protective measures such as frequent handwashing and wearing masks, and to be aware of the risk signs of severe illness.  

Release Date: 2026-09-15 The Centers for Disease Control (CDC) stated today (September 15th) that both influenza and the COVID-19 pandemic are currently in their epidemic season, and the influenza epidemic continues to rise. The public should strengthen their precautions against influenza and COVID-19, and practice good handwashing, cough etiquette, and wear masks when entering crowded or poorly ventilated places. If symptoms appear, people should wear masks, seek medical attention, and rest at home to reduce the risk of transmission.

The CDC pointed out that the domestic influenza epidemic is rising and in its epidemic season. In the 36th week (September 6th-12th), there were 136,796 outpatient and emergency room visits for influenza-like illnesses, an increase of 16.5% compared to the previous week.

Additionally, last week (September 8th-14th), there were 92 new cases of severe influenza complications (79 H1N1, 5 H3N2, and 8 untyped A cases) and 21 deaths (18 H1N1, 2 H3N2, and 1 untyped A case).

Laboratory monitoring data shows that the influenza virus currently circulating in the community is mainly type A, with type A H1N1 accounting for 82.2%. This flu season (114-115), there have been 1,421 cumulative severe cases (800 H1N1, 503 H3N2, 28 untyped A, 90 B) and 274 deaths (149 H1N1, 104 H3N2, 9 untyped A, 12 B), with most severe cases occurring in people over 65 (65.0%) and those with chronic conditions (82.7%), and 68.3% had not received this season’s flu vaccine.

According to data from the Taiwan Centers for Disease Control (CDC), the COVID-19 epidemic in Taiwan is declining, but it is still in its epidemic period. In week 36 (September 6-12), there were 17,847 outpatient and emergency room visits related to COVID-19, a 13.3% decrease compared to the previous week (August 30-September 5). Last week (September 8-14), there were 53 new locally transmitted severe cases and 18 local deaths. Since October 2025, there have been a cumulative total of 675 locally transmitted cases of COVID-19 complicated by severe illness, of which 124 have died. Severe cases are predominantly among those aged 65 and above (73.3%) and those with a history of chronic diseases (82.8%). 83.6% of these cases have not received the COVID-19 vaccine this season. In the past four weeks, the most prevalent local variants have been NB.1.8.1 and PQ.16.1.1.

The Centers for Disease Control (CDC) reminds the public to pay attention to their health as temperatures gradually cool in autumn. Those who are at high risk of influenza, including themselves and their families, should be especially vigilant. If they experience flu-like symptoms such as fever or cough, they should wear a mask, seek medical attention promptly, or rest at home. If they experience any warning signs (such as shortness of breath, difficulty breathing, cyanosis, bloody sputum, chest pain, altered consciousness, or low blood pressure), they should seek medical attention immediately. A doctor will assess whether they meet the eligibility criteria for publicly funded antiviral influenza medication to ensure timely treatment and reduce the risk of severe complications.

Whether any of this translates to an early flu season for North America or Europe remains to be seen.  The most recent data from the CDC suggests that influenza and RSV activity remains very low, and COVID is only slightly elevated.

 
While it is impossible to predict exactly what kind of winter respiratory season we'll see, past experience suggests it isn't something we should take lightly.  Last year's `moderately severe' flu season is estimated to have caused:

Which is why I'll be rolling up my sleeve again in the next few weeks for both my flu and COVID shots, and I won't hesitate to wear a face mask this winter in crowded indoor public places. 

EID Journal: Characteristics and Superspreading Potential of Andes Virus Person-to-Person Transmission

R0 (pronounced R-nought) or Basic Reproduction Number.

Essentially, the number of new cases in a susceptible population
likely to arise from a single infection. With an R0 below 1.0, a virus
(as an outbreak) begins to sputter and dies out. Above 1.0, and
an outbreak can have `legs’.

Rt represents the actual transmission of a disease in a population
where some people may be immune and control measures are in place

 #19,334

Four months ago the big infectious disease story was an unusual outbreak of Andes Hantavirus (ANDV) aboard a cruise ship out of Argentina, which resulted in 13 identified cases (12 laboratory-confirmed and 1 probable) and 3 fatalities.

The incubation period for ANDV can run up to 6 weeks, with a 42-day monitoring period generally recommended. Some cases can be mild, or even asymptomatic, but the CFR (case fatality rate) can reach 30%-60%.

Although outbreaks of ANDV are fairly rare, and generally limited in size, we've followed several outliers over the years. 

Including, most famously, a 2019 outbreak in Argentina - where, over a period of 3 months - a total of 34 laboratory-confirmed cases of Hanta Pulmonary Syndrome (HPS) - including 11 deaths - were reported in Epuyén, Chubut Province.

The WHO DON report stated:

The index case had environmental exposure prior to symptom onset on 2 November, and subsequently attended a party on 3 November. Six cases who also attended the party experienced the onset of symptoms between 20-27 November 2018.

An additional 17 cases, all of whom were epidemiologically-linked to previously confirmed cases, experienced symptom onset between 7 December 2018 and 3 January 2019 (Figure 1). Potential human-to-human transmission is currently under investigation.

Following the above outbreak, the NEJM published “Super-Spreaders” and Person-to-Person Transmission of Andes Virus in Argentina, which warned: ANDV Epuyén/18−19 strain shows a facility (R>2) for sustaining continuous chains of transmission if no control measures are enforced. 

The idea that 20% of those infected may be responsible for 80% of the forward transmission of a virus has been around for decades, but gained momentum after the 2003 SARS outbreak. 

During that first SARS outbreak, studies found most patients would typically only infect 1 or perhaps 2 additional people, and often none at all. 

But a small percentage of patients proved unusually efficient at spreading the virus, with some responsible for 10 or more secondary infections (see MMWR Severe Acute Respiratory Syndrome --- Singapore, 2003).

A decade later, we'd see the same phenomenon repeated with MERS-CoV (see Superspreaders & The Korean MERS Epidemiological Report) where one Korean MERS patient (#14) is believed to have infected as many as 85 people, while two others (#1 & #16) appear to have infected more than 50 others between them.

 

According to Stein’s excellent 2011 review Super-spreaders in infectious diseases: 

Super-spreading events are shaped by host, pathogen, and environmental factors. Often, more than one factor may be implicated in the same outbreak.

Superspreading events aren’t limited to coronaviruses, as they have been documented with measles, HIV, TB, S. aureus, Ebola, and various STDs . . .among others (cite) 

In January of 2013, in Influenza Transmission, PPEs & `Super Emitters’ we looked at research that found five patients (19 percent) in their study were "super-emitters" who emitted up to 32 times more flu virus than did the rest. Patients who emitted a higher concentration of influenza virus also reported greater severity of illness.  

While the host and the pathogen are important parts to the equation, environment and opportunity also play a pivotal role in exacerbating these superspreader events.

All of which brings us to an EID Journal Dispatch which finds that the 20/80 rule also applies across a larger sampling of ANDV clusters reported over the years, and while the pooled average Rt remains at a reassuring .74, in some outbreaks (including the NEJM report) that number approached or exceeded 1.0. 

I've only reproduced the Abstract and a few excerpts from the dispatch, so you'll want to follow the link to read it in its entirety.  I'll have a brief postscript when you return.

Dispatch
Characteristics and Superspreading Potential of Andes Virus Person-to-Person Transmission

Zihao Guo1 , Kailun Pan1, Yu Zhao, Sheikh Taslim Ali, Kai Wang, Lirong Cao, Zhuang Cui, Shengqiang Liu, Ka Chun Chong, Daihai He, Shi Zhao , and Yuantao Hao2

Abstract

By using historical contact tracing data, we estimated that 23.4% of case-patients caused 80% of Andes virus (ANDV) person-to-person transmission. We demonstrated a low but nonnegligible probability of observing a large-scale ANDV infection outbreak in a rodent-free setting consisting of close contacts, despite the historically self-limited person-to-person transmission of ANDV.

(SNIP)

On May 2, 2026, an ANDV outbreak aboard the MV Hondius cruise ship was reported to the World Health Organization (WHO), with the first case illness onset on April 3 (10). Subsequent epidemiologic investigations proposed a working hypothesis that person-to-person transmission originated from a seed case in a person who probably acquired infection through environmental exposure during travel in Argentina before boarding the ship on April 1 (10). By July 2, a total of 13 ANDV cases had been identified, including 12 laboratory-confirmed and 1 probable case; 3 of those cases were fatal (10). 

According to the initial WHO notification for the outbreak on May 2, public health and control measures, including contact tracing, case isolation, clinical care, and medical evacuation of symptomatic passengers, had been implemented onboard the ship (11). By using historical contact tracing data, we aimed to estimate key epidemiologic characteristics of person-to-person transmission of ANDV, including the serial interval (SI) distribution and transmission heterogeneity, given that those traits strongly shape outbreak size.

(SNIP) 

We identified a total of 88 case-clusters from the included studies, among which 50 (56.8%) were not associated with any secondary person-to-person transmission events. After accounting for variations across lineages or strains, the pooled estimate of Rt was 0.74 (95% credible interval [CrI] 0.28–1.29) and the estimate of k was 0.64 (95% CrI 0.36–1.16). Apart from inherent differences among ANDV lineages or strains, the substantial variation in Rt across lineages or strains could also be attributed to differences in study settings and individual-level heterogeneity in reproduction numbers (5).

We estimated that 23.4% (95% CrI 15.1%–30.3%) of the cases generated 80% of the transmission events, suggesting the person-to-person spread of ANDV exhibited relatively high heterogeneity, although it appeared lower than that observed for other pathogens known for superspreading events, including SARS-CoV, SARS-CoV-2, Middle East respiratory syndrome coronavirus, and Ebola virus (13,14).

(SNIP)

Conclusions

In summary, our results provide insights into the person-to-person transmission potential of ANDV, which exhibited substantial heterogeneity. We found a low but significant chance of observing a relatively large-scale ANDV outbreak in a rodent-free setting consisting of close contacts, which might be eradicated across a few generations of person-to-person transmission. Because no vaccine or antiviral treatment for ANDV infection is currently available, continuous surveillance of person-to-person transmission risk of ANDV is essential for preparedness against future outbreaks.

Dr. Guo is an associate professor in the School of Public Health, Tianjin Medical University, Tianjin, China. His primary research interests include epidemiology and transmission dynamics of emerging infectious diseases.

Simply put, while most ANDV outbreaks are likely to sputter out relatively quickly, there is enough variability in the transmission of the virus that occasional larger outbreaks are possible. 

For more on superspreader events you may wish to revisit:

MMWR Early Release: COVID-19 Superspreading Event In A Church Choir

CDC Update: Rapid Assessment Of COVID Outbreak At 2023 EIS Conference

Ziad Memish: Two MERS-CoV Hospital Super Spreading Studies

The Lancet: Mapping The Korean MERS-CoV Superspreading Event

Australia Reports 1st Sea Lion Death From H5N1

 

YouTube Video ABC News

#19,333

While the last posted update on South Australia's bird flu status appears to be 3 days ago, on Sept 10th, SA's environment minister Emily Bourke announced the death of an endangered Australian sea lion due to H5N1 in the press conference above.

The sea lion recovered from Seal Bay on Kangaroo island - which was being cared for after a shark attack - reportedly died from the virus.

Location Kangaroo Island - Credit Wikipedia

 

Kangaroo Island is home to a number of marine mammals which are known to be susceptible to avian flu (see Preprint: Mass mortality of southern elephant seals during multi-species outbreak of HPAI H5N1 on sub-Antarctic Heard Island), including:

• Australian sea lion.

• Australian fur seal.

• New Zealand fur seal.

• Bottlenose dolphin and common dolphin. 

While Australia's reporting on avian flu has changed; counting events rather than individual H5-positive tests, the numbers continue to rise steadily. 

So far, the virus has not been reported in poultry or other livestock, but the risks to australia's fauna remains high, and only a fraction of the nearly 42,000 hotline reports have been investigated.