USDA Screwworm Update (n=11) - FDA EUA For Drug to Treat Dogs & Cats

 

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The number of confirmed screwworm cases (NWS) continues to mount, and a 5th Texas county (Tom Green) has been added, in the latest update to the USDA's dashboard. 

Thus far, all confirmed detections have been in either livestock (cattle or goats), or in pets. While unknown, there are likely a far larger number of wildlife infections, as the NWS will infect just about any warm-blooded animal (including birds).

The CDC describes its life cycle as:

New World screwworm infestations begin when a female fly lays eggs on open wounds or other parts of the body in live, warm-blooded animals. Most infestations occur in animals, but they also occur in people. The smell of a wound or body opening such as the nose, mouth, eyes, ears, or genitals can attract female flies. Wounds as small as a tick bite may attract a female fly to lay her eggs. One female can lay 200 – 300 eggs at a time and may lay up to 3,000 eggs during her 10- to 30-day lifespan.

Eggs hatch into maggots that burrow into the wound to feed on the living flesh. After feeding for about 7 days, larvae drop to the ground, burrow into the soil, and emerge as adult screwworm flies.

Due to its recent return to U.S. soil, the FDA this week granted an Emergency Use Authorization (EUA) for a generic OTC drug to treat NWS infection in dogs and cats. 

FDA Issues Emergency Use Authorization for Generic Over-the-Counter Drug to Treat New World Screwworm in Dogs and Cats

Most dogs and cats in the U.S. are at low risk of NWS; risk is elevated for pets recently in areas with confirmed cases of NWS

For Immediate Release:June 11, 202

The U.S. Food and Drug Administration today issued an Emergency Use Authorization (EUA) for generic Nitenpyram Tablets (nitenpyram) for the treatment of New World screwworm (NWS) infestations (myiasis) in dogs, puppies, cats, and kittens that weigh at least two pounds and are at least four weeks old. This is the first generic animal drug authorized for use against NWS.

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While this provides a faster, and cheaper way for people to treat their pets, it also makes it easier for cases to go unreported.  Hopefully pet owners will still contact their veterinarian, and have their pet examined, after treatment has been initiated.

As the CDC warns, proper disposal of maggots is imperative in order to interrupt the life cycle of these parasites. 

Hong Kong CHP: Locally Acquired Case of H9 Infection - Notification Letter For Doctors

 

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While Mainland China leads the world in reported H9N2 infections, Hong Kong has only reported 10 since 1999, with just 4 of those locally acquired. The last non-imported HK case I can find (see FluTrackers H9N2 case list) was in early 2020. 

And that makes sense, given the nearly 200-fold difference in population pools, and the fact that H9N2 (and other) avian flu subtypes are poorly controlled in mainland poultry. 

Yesterday Hong Kong's CHP announced the detection of a locally acquired H9 case (likely H9N2) in a child without recent travel, and only limited indirect contact with poultry at a live market.  The epidemiological investigation is ongoing. 

Generally mild, H9N2 is closely monitored because it continues to evolve and accrue mammalian adaptations (see CCDC Weekly: Epidemiological and Genetic Characterization of Three H9N2 Viruses . . .).  Our CDC has designated 2 different lineages (A(H9N2) G1 and A(H9N2) Y280) as having at least some pandemic potential (see CDC IRAT SCORE).

While this is likely a one-off infection, Hong Kong's CHP is treating this seriously, and has published a detailed report (below), and has sent notification letters to local doctors. 

CHP investigates case of influenza A (H9) infection (with photo) 

     The Centre for Health Protection (CHP) of the Department of Health (DH) is today (June 12) investigating a case of human infection with influenza A (H9) in collaboration with relevant departments. The patient is a two-year-old boy. His condition has remained mild and he is currently in stable condition. The CHP will send a letter to all doctors in Hong Kong to update them on the latest developments regarding avian influenza A and to urge them to remain vigilant and report any suspected cases. 

Case information 

     The boy lives in Sha Tin District. He developed a fever and mild diarrhoea on June 9. On the following day (June 10), he was brought to Prince of Wales Hospital and was admitted for treatment. His clinical specimen tested positive for the influenza A (H9) virus by the Public Health Laboratory Services Branch (PHLSB) of the CHP. The subtyping result is pending. His clinical diagnosis was novel influenza. He is currently in stable condition and has been admitted to an isolation ward at Princess Margaret Hospital for treatment.      

     The CHP's preliminary investigation revealed that the patient had no travel history during the incubation period. The case has been classified as a locally acquired case. The patient does not attend school or receive daycare services. He is primarily cared for by his family members and spends most of his time at home or nearby. His household does not keep poultry. According to information provided by his family members, he has neither consumed undercooked poultry nor come into contact with any patients.

In early June, one of his family members took him to Wo Che Market on two occasions. During these visits, the patient stayed at a fresh provision shop in the market that sells live chickens to watch the poultry and touched the surroundings of the fresh provision shop. The CHP conducted an investigation with the Food and Environmental Hygiene Department (FEHD) and collected environmental samples from the shop concerned. The shop staff remained asymptomatic. The patient has six household contacts and they remain asymptomatic so far. The CHP has provided them with preventive medication and put them under medical surveillance.      

     The CHP is continuing to investigate the source of infection of the case and is conducting whole genome sequencing of the virus sample. The CHP will also report the case to the World Health Organization (WHO).      

     Humans are primarily infected with the influenza A virus through direct contact with infected poultry or through indirect contact with environments contaminated by their droppings. The CHP's epidemiological investigation indicated that the patient had visited a location where live poultry was sold. It cannot be ruled out that the patient was infected through indirect contact with a contaminated environment at the wet market. As young children have weaker immune systems and are incapable of maintaining good hand hygiene, the CHP advised parents to avoid taking young children to places where live poultry is sold. Transporting poultry may contaminate the ground and the surrounding environment. As young children are shorter in height and easy to be in contact with the surrounding environment, they are at greater risk of coming into contact with poultry droppings or contaminated areas.      

     In the past ten years, the WHO has received reports of a total of over 160 cases of human infection with influenza A (H9) worldwide. To date, most case of human infection with influenza A (H9) have presented with only mild clinical illness. According to the WHO's risk assessment, the influenza A (H9) virus has not acquired the ability for sustained human-to-human transmissions. 

Government's comprehensive follow-up actions

Novel influenza A infection, including influenza A (H9), is a notifiable infectious disease in Hong Kong. Compared to other highly pathogenic avian influenza strains such as H5N1 and H7N9, influenza A (H9) is a low-pathogenic avian influenza strain that causes milder illness. Excluding the aforementioned case, 10 cases of influenza A (H9N2) have been reported since 1999, including four locally acquired cases and six imported cases. No deaths have been recorded so far. In response to the latest local case, the CHP will issue a letter to all doctors in Hong Kong, reminding them of the latest situation of influenza A (H9), and urging them to remain vigilant and report any suspected cases.

Sporadic cases of human infection with avian influenza occur from time to time internationally. Although the current risk of an outbreak is low, the Hong Kong Special Administrative Region Government has consistently implemented preventive measures, including a disease surveillance system, the implementation of livestock control measures at farms, markets and ports, in order to prevent avian influenza.

The PHLSB of the CHP comprises laboratories with high biosafety standards, capable of conducting, testing for high-risk pathogens, and which also possess sufficient testing and genetic analysis capabilities and facilities. Hong Kong currently has sufficient reserve of antiviral medications.

Preventive measures to be taken by the public

Humans are primarily infected with the avian influenza A virus through contact with infected birds, poultry or other animals (whether alive or dead), or through surfaces or environments contaminated with saliva, mucous and animal faeces (such as wet markets and live poultry markets). The virus has very low transmissibility among humans. People who have close contact with live poultry are more susceptible to contracting avian influenza. The elderly, children and people with chronic illnesses have a higher risk of developing complications such as bronchitis and pneumonia, if infected. Members of the public should remain vigilant and take the following measures to prevent avian influenza: 

• Avoid contact with poultry, birds or their droppings. If contact has been made, thoroughly wash hands with soap and water;
• Poultry and eggs should be thoroughly cooked before eating;
• Perform hand hygiene at all times, especially before touching the mouth, nose or eyes; after contact with animals or their living environments; after touching public installations such as handrails or doorknobs; or when hands are contaminated with respiratory secretions, such as after coughing or sneezing;
• Cover the mouth and nose with tissue paper when sneezing or coughing. Dispose of soiled tissues into a lidded rubbish bin, then wash hands thoroughly;
• When having respiratory symptoms, wear a surgical mask, do not go to work or school, avoid crowded places and seek medical advice promptly;
• Avoid crowded public places or areas with poorly ventilated; high-risk individuals may consider putting on a surgical mask when staying in such places; and
• Travellers returning to Hong Kong from areas affected by avian influenza outbreaks should consult doctors promptly if they have flu-like symptoms, and inform the doctor of the recent travel history and wear a surgical mask to help prevent spreading of the disease.

     ​The public may visit the CHP's webpages for more information: Avian Influenza Webpage, Avian Influenza Report, Avian influenza statistics and affected areas around the world, Facebook page and Youtube channel. 

Ends/Friday, June 12, 2026

Issued at HKT 22:19

The CHP has also sent the following letter to doctors reminding them to remain vigilant, and how to report suspected cases. 

Complicating matters, Hong Kong is known for having a biphasic or `double peaked’ flu season, with most activity reported between February and April, but often seeing a less severe season in mid to late summer (see Seasonality of Influenza A(H3N2) Virus: A Hong Kong Perspective (1997–2006).

And, as the latest HK flu report indicates, they are beginning to see signs of a summer uptick in ILI. 

While this is likely an isolated incident, H9N2 is a legitimate zoonotic threat, and so we'll be watching Hong Kong carefully for any additional reports.  

U.S. Screwworm Detections Increase (n=9) as More States Ramp up Surveillance & Prevention Efforts

 

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Since Monday, the number of New World Screwworm (NWS) cases in the U.S. has more than doubled, with cases reported in 5 different counties (Texas=4, New Mexico=1). Although most have been reported in cattle, the screwworm parasite has also been detected in 2 goats and 1 dog. 

While these numbers are still small, the problem is the massive spread of the parasite in Mexico (see map below), which provides numerous opportunities for it to enter the U.S.

Not surprisingly, a number of southern tier states have raised their threat levels, and/or have strengthened their surveillance and prevention efforts, including:

• Alabama

• Florida 

• Georgia

• Louisiana 

• New Mexico

• Tennessee 

While the NWS has been eradicated before in the United States by releasing sterile NWS flies, the current supply isn't sufficient to combat a multi-state outbreak. The USDA is reportedly able to disperse between 4 and 8 million sterile screwworm flies per week into the known infested counties of Texas. 

New production facilities are being constructed, including a massive sterile fly production facility at Moore Air Base in South Texas, which is expected to produce 100 million sterile flies per week by November 2027 (increasing to 300 million a week by the end of 2028).

Meanwhile, much of the fly production from the COPEG facility in Panama is being used to suppress the spread in Northern Mexico, to try to prevent more incursions into the United States. 

Although there is a good chance of eradicating this pest once again in the United States, it isn't going to happen overnight.  The USDA's own risk analysis from 2025 reads:

In a worst-case scenario, the initial detection of NWS myiasis would not occur until 3 weeks or more after the initial introduction of NWS larvae into a United States location favorable for pupation and ongoing maintenance of the NWS life cycle.

In this scenario, a viable population of NWS flies would already exist in the United States at the time of myiasis detection in an animal or person. Releases of sterile NWS flies would be required for at least 9 to 12 weeks in order to control and eventually eradicate that population. The sterile fly releases would need to begin as soon as possible. During the 2016–2017 NWS outbreak in Florida, samples were not sent to the NVSL for identification until 84 days (4 life cycles) after presumptive positive identification by local veterinarians.

Complicating matters is the timing; with the initial outbreak detected in early June - we've 4 or 5 months of very hot weather ahead - conditions which are highly conducive to the spread of the screwworm.  

While the eradication of the NWS 60 years ago in the U.S. was a tremendous achievement, this is a somber reminder that such victories are often fleeting, and that nature always bats last.  

IJID: Regional Signals Preceding the 2026 Bundibugyo Virus Disease Outbreak

 

#19,198

When the Bundibugyo Ebola virus outbreak in the DRC was announced nearly 4 weeks ago, there were already 246 suspected cases and 65 deaths, which suggested the outbreak had been brewing - unrecognized - for several months.

Which isn't to say it went unnoticed, for in the 3 months prior there were a number of reports from the region of `suspected' hemorrhagic fever cases that were either never confirmed, or followed up on.

Admittedly, outbreaks in the DRC are notoriously difficult to manage, as much of the region is a conflict zone, is plagued by a wide variety of infectious diseases, and has only limited public health capacity.  Also, the Ebola PCR test commonly used in the region was Zaire-specific, and would not have detected the much rarer Bundibugyo virus.  

But gaps in surveillance and reporting extend far beyond Central Africa.

As we've discussed often (see Flying Blind in the Viral Storm), over the past few years we've seen a noticeable decline in surveillance and reporting of infectious diseases around the world.

In 2005 the World Health Organization adopted updated IHR (International Health Regulations) which – among other things - required countries to develop mandated surveillance and testing systems, and to report certain types of disease outbreaks and public health events to WHO.

Member states had until mid- 2012 to meet core surveillance and response requirements, but many nations failed to meet that deadline, which has forced the WHO to grant repeated extensions.  

A report 3 years ago (see Lancet Preprint: National Surveillance for Novel Diseases - A Systematic Analysis of 195 Countries), found many member nations still lack the capability to fully investigate cases.

And of course, some nations - for political or economic reasons - simply choose to ignore the IHR whenever convenient, since there are few tangible penalties for doing so (see From Here To Impunity).

Today we've a fascinating look at early signals - and missed opportunities - in the DRC going back to early March of this year. 

While not a long report, I've only posted the Abstract. Follow the link to read the full report.  

Regional Signals Preceding the 2026 Bundibugyo Virus Disease Outbreak

Nahid Bhadelia1,2 ∙ Isaac Gikandi1 ∙ Britta Lassmann1,2

Highlights

• Bundibugyo virus circulated undetected for months prior to outbreak declaration.
• Four earlier regional hemorrhagic fever clusters flagged by open surveillance are unresolved.
• These clusters warrant urgent reanalysis due to concern for regional spread.

Abstract

Background

 The May 2026 Bundibugyo virus disease (BVD) outbreak in the Democratic Republic of the Congo was declared a Public Health Emergency of International Concern after substantial undetected community transmission. We describe regional surveillance signals detected by the Biothreats Emergence, Analysis, and Communications Network (BEACON), our open access event based surveillance program, in the weeks preceding outbreak declaration.

Methods

We reviewed BEACON reports of VHF-compatible illness clusters detected in the transboundary DRC-Uganda-Burundi-South Sudan region during March–April 2026, prior to the May 15 laboratory confirmation of BDBV.

Results

BEACON detected four temporally proximal VHF-compatible illness signals:

• (1) March 9, North Kivu Province—suspected Ebola case under investigation with unresolved laboratory results;
• (2) March 10, Kasaï Province—fatal hemorrhagic illness with secondary cases and negative Ebola PCR;
• (3) March 30, Burundi—35-case undiagnosed cluster near the DRC border with 5 deaths, negative testing for major filoviruses and >200 pathogens, pending metagenomic sequencing;
• (4) April 22, South Sudan—three suspected VHF cases with negative initial testing. 

All four signals shared a similar diagnostic phenotype: VHF-compatible presentation, mobilization of investigation teams, negative initial testing, and no publicly reported confirmed etiology. None were formally reported to have been resolved.

Conclusions

Our detection of four unresolved VHF signals preceding the confirmed BDBV outbreak highlights gaps in formal follow-up mechanisms for negative cases and fragmented regional diagnostic coordination. In light of confirmed BDBV circulation and Africa CDC's identification of 10 countries at high risk for spread, these preceding signals warrant urgent retrospective investigation and laboratory.

When the World Health Organization (WHO) declared the Bundibugyo disease outbreak in the Democratic Republic of the Congo (DRC) and Uganda a Public Health Emergency of International Concern on May 17, 2026, the epidemiology was already telling us we were late [1,2]. Eight of the first thirteen samples submitted to the Institut National de Recherche Biomédicale (INRB) returned positive for Bundibugyo virus.

By May 23, 746 suspected cases, 83 confirmed cases, 176 suspected deaths, and 9 confirmed deaths have been reported in DRC’s Ituri, North Kivu and South Kivu provinces, with spread to multiple urban centers. Uganda has 5 confirmed cases with direct epidemiological links to DRC [3].

There remains significant uncertainty about the true number of infections and how far the virus has spread. Healthcare worker deaths in clinical contexts consistent with viral hemorrhagic fever (VHF) had been reported in multiple sites. The official investigation was anchored, in retrospect, to the death of a nurse in Bunia on April 24, 2026, and to funeral-related exposures that followed. Recent data shows the outbreak began well before this date.

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Nature: Host factors, inflammatory markers, and clinical outcomes of Naegleria fowleri meningoencephalitis

 

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Nearly every year I end up blogging about a rare, mostly fatal brain infection caused by free living amoebas (Naegleria fowleri) that inhabit warm, fresh water (see A Reminder About Naegleria Season - 2019).

Dubbed the `brain eating amoeba' by the press - this infection is called PAM (Primary amebic meningoencephalitis) - and occurs when the amoeba enters the brain through the nasal passages, usually due to the forceful aspiration of contaminated water into the nose.

Not every PAM case is due to Naegleria, as Balamuthia mandrillaris and Acanthamoeba - and other non-Naegleria amoebic infections - can cause similar pathologies. 

As a thermophilic (heat-loving), free-living amoeba, it is hardly surprising that Naegleria is mainly reported during the summer - and that Florida and Texas lead the nation in cases over the past three decades - although infections have occurred as far north as Minnesota.

Last year the CDC's MMWR carried a report on a fatal 2024 case from Texas, which involved a previously health 71-year old woman who used unsterilized water to perform nasal irrigation.  

This is a common way that people around the world have become infected (see 2011's Neti Pots & Naegleria Fowleri).  The CDC and state health departments have long warned on the dangers of using tap water to perform nasal irrigation, and offer advice on safer alternatives. 

For a more detailed look as PAM risks from nasal irrigation, you may with to revisit EID Journal: (Mis)perception and Use of Unsterile Water in Home Medical Devices.

Other routes of infection include swimming in stagnant, warm fresh water ponds, attending water parks, and even in a child playing with a water hose in their own yard. 

Only 3 or 4 cases are reported in the United States each summer, but in 2017 a research letter written by epidemiologists at the CDC (see EID Journal: Estimation of Undiagnosed Naegleria fowleri (PAM), United States) estimated the yearly number PAM cases in the United States probably averages closer to 16 (8 males, 8 females).

Meaning that 70%-80% likely go unrecognized. 

Every year Pakistan reports a dozen or more infections from this `killer amoeba’, as chlorination of their water supplies is often inadequate, and for many, nasal ablutions are part of their daily ritual.

But in 2025 Kerala, India saw an unprecedented outbreak (see The outbreak of amoebic meningoencephalitis in Kerala: A wake-up call) `with with reports indicating a total of 129 cases and 26 deaths as of October 18, 20251.'

Even more remarkable than the sharp rise in cases was the unusually low fatality rate - which normally exceeds 90% - even with treatment. 

Since it was published 2 weeks after the Hantavirus outbreak aboard the m/v Hondius and 4 days after the announcement of a large Bundibugyo virus outbreak in Africa, the following study - published in Nature - probably didn't garner as much attention as it should.

In short, this study looked at a cohort of roughly 200 PAM patients from Kerala, India treated between January and November 2025 using a standardized amphotericin B/miltefosine protocol. 

Roughly of 1/3rd of cases were unresolved at the time of the cut off, and were not included in the analysis - but of the 134 who were -  61 died,  while 73 recovered, giving a case fatality rate of 45.5%. 

Given this remarkable success rate, and the increasing risk of PAM due to climate change, the following report should be of particular interest to clinicians.

Host factors, inflammatory markers, and clinical outcomes of Naegleria fowleri meningoencephalitis

Vijeesh Kadukkatti, Brijil K. Mathew & Peter Mac Asaga
Communications Medicine volume 6, Article number: 290 (2026) 

Abstract

Background

Primary amoebic meningoencephalitis (PAM) caused by Naegleria fowleri carries historical case fatality rates (CFR) exceeding 97%. The 2025 Kerala outbreak, the largest documented globally, provided an unprecedented opportunity to identify host factors and inflammatory correlates influencing survival under standardised management.

Methods

We conducted a prospective observational study of 200 laboratory-confirmed PAM cases across six districts of Kerala, India (January–November 2025). All patients received protocolised amphotericin B ± miltefosine. Demographic, clinical, and laboratory data were collected, including inflammatory biomarkers (IL-6, TNF-α, IL-1β, neutrophil-to-lymphocyte ratio), pathogen burden (qPCR), and treatment timing. Multivariable logistic regression identified mortality predictors; bootstrap resampling and E-value sensitivity analyses assessed robustness.

Results

Here we show that among 200 patients (median age 41 years; 50% male), 134 with resolved outcomes yield a CFR of 45·5% (95% CI 37·3–54·5%; 61 deaths, 73 recoveries). Diabetes mellitus is the only statistically significant predictor of mortality in the adjusted model (adjusted OR 2·59; 95% CI 1·01–6·66; p = 0·048), though the proximity of the lower confidence bound to unity warrants cautious interpretation. This association remains consistent across sensitivity analyses (bootstrap 95% CI 1·06–8·74; E-value 4·62). Asthma demonstrates a protective association in univariable analysis (OR 0·37; p = 0·021), though this finding remains hypothesis-generating. Early treatment (≤2 days) shows a trend toward improved survival (p = 0·084). Inflammatory biomarkers show no association with outcome, though CSF pathogen burden correlates significantly with admission neurological severity.

Conclusions

Under standardised treatment, diabetes mellitus emerges as a key host determinant of PAM mortality. The dissociation between inflammatory markers and outcomes suggests neurological fate may be determined early in infection, with immediate clinical implications as climate change expands the geographic range of N. fowleri.

Plain language summary

Naegleria fowleri is an amoeba found in warm freshwater that can cause a rare but usually fatal brain infection. Historically, more than 97% of people who develop this infection die. In 2025, a large outbreak occurred in Kerala, India, affecting 200 people. We studied these patients to understand what factors influenced survival. The death rate was 45.5%, much lower than expected, likely because all patients received the same standard drug treatment. People with diabetes were roughly twice as likely to die as those without. Surprisingly, common markers of inflammation did not help predict who would survive. As climate change warms freshwater sources worldwide, understanding what determines survival from this infection becomes increasingly important.

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Preprint: The canine respiratory epithelium is a permissive ecosystem for influenza interspecies transmission and emergence

 

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Until 2004, dogs were considered relatively immune to influenza, but that changed abruptly when an equine H3N8 virus spilled over to dogs at a Florida racetrack, and began its world tour.

Three years later, an avian H3N2 virus spilled over to dogs in South Korea, and spread across Asia, eventually arriving in the United States in 2015.

In 2010, in Morens & Taubenberger on Influenza’s History, we looked a a fascinating 11-page historical review of Influenza outbreaks amongst a variety of hosts (human, avian, equine, porcine, canine, etc.) going back more than 3,000 years by Jeffrey K. Taubenberger and David Morens.

They cited a number of pandemics where anecdotal accounts mentioned dogs falling ill, either before - or concurrent to - when human cases emerged.

Since then we've looked at a lot of studies on dogs and flu, including: 

• In late 2012, in China: Avian-Origin Canine H3N2 Prevalence In Farmed Dogs, we looked at a study that found a newly emergent avian origin H3N2 virus prevalent in pet and farmed dog populations in southern China.

• In 2015, in Korea Finds More Dogs With H5N8 Antibodies, we saw evidence of HPAI infection in dogs. 

• Also in 2014, in Study: Dogs As Potential `Mixing Vessels’ For Influenza - we looked at the ability of different influenza strains (canine, equine and human) to infect, and replicate in, canine tracheal tissues. 

• In 2015, researchers reported finding Influenza A(H6N1) In Dogs, Taiwan

• Again in 2015, in Virology J: Human-like H3N2 Influenza Viruses In Dogs - Guangxi, China, we looked at the discovery two H3N2 CIVs possessing high homology with human/swine influenza viruses.

• In 2023 we looked at a lengthy (57-page) preprint called Increased Public Health Threat of Avian-origin H3N2 Influenza Virus During Evolution in Dogs from researchers in China who warned on the continued evolution of canine H3N2, which appears to be moving towards becoming a more `humanized' virus.

• More recently (2025) we looked at A Brief History of Influenza A in Canines & Canadian Report On A Recent Fatal H5N1 Dog Infection.

While dogs are more apt to have less severe flu illness than cats - making infections easier to miss - there is little doubt they are susceptible.  Unknown, however, is whether they are mostly a dead-end host, or if they are capable to transmitting the virus to others. 

Today we've got a preprint from researchers in the UK which attempts to better understand the risks. Using canine lung explants, they find that dogs are a plausible host for influenza reassortment, as they contain both human-type (α2,6) and avian-type (α2,3) receptor cells.

The caveats being that this is an ex vivo study, and is subject to a number of limitations (see below), and there is currently no evidence that novel influenza viruses are spreading efficiently among canines. 

But the only constant with influenza viruses is that they change, making today's status tenuous at best.  Due to its length, I've only posted some excerpts. Follow the link to read the report in its entirety.  

The canine respiratory epithelium is a permissive ecosystem for influenza interspecies transmission and emergence
Hanting Chen, Jack Hassard, Jiayun Yang, Callum Magill, Toby Carter, Jean-Remy Sadeyen, Aimi Ito, Clio Duerr,  Hannah Rose Montgomery, Savitha Raveendran, Kieran Dee,  Maximillian N J Woodall, Grace B Tyson, Maria M Afonso, Verena Schultz,  Claire Mary Smith,  Margaret J Hosie, Stuart Haslam, Munir J Iqbal,  Pablo R Murcia

doi: https://doi.org/10.64898/2026.06.04.730051
This article is a preprint and has not been certified by peer review 

Preview PDF

Abstract

The outcome of virus spillover ranges from dead-end infections to pandemics and is underpinned by host-pathogen interactions as well as evolutionary and epidemiological processes. The emergence of novel influenza A viruses (IAVs) has been associated with reassortment events involving multiple species, highlighting the importance of reservoir and intermediate hosts in viral emergence.

Highly pathogenic H5N1 IAVs of the 2.3.4.4b genotype have caused a panzootic affecting a broad range of mammals. The role of dogs -arguably the most popular companion animal and a natural host of IAVs- in the ecology of IAVs under this new zooepidemiological scenario is unknown. To address this, we characterised the glycome of the dog respiratory epithelium, infected canine tracheal explants with multiple IAVs (including canine H3N2 and H3N8, equine H3N8, avian H3N8 and H5N1, swine H1N1, human H1N1 and H3N2, and bovine H5N1 viruses), and determined their cellular tropism.

We show that the respiratory tract of dogs presents abundant sialylated glycans known to act as IAV receptors. Further, most IAVs (including 2.3.4.4b viruses) infected and replicated in dog tracheas, targeting mainly ciliated cells. Serological testing showed evidence of influenza spillover infections in dogs from the UK.

Overall, our results show that the canine respiratory tract can provide a suitable environment for the generation of new IAVs. Given the multi-host contact networks of dogs in nature, they could act as recipients, bridging hosts, and/or mixing vessels for multiple IAV lineages, playing a central role in the ecology of influenza emergence.

(SNIP) 

Our results suggest that dogs could act as a bridging species for the emergence of novel IAVs, including the H5N1 2.3.4.4b genotype. Serological studies in North America and Europe show that hunting dogs are routinely exposed to H5N1 IAVs 53,54. 

Vaccination of high-risk dog subpopulations could reduce the risk ofinter species infections (avian-to-dog and dog-to-human) and should be considered as preventative measures. 

This study has various limitations. Tracheal explants represent a significant portion of the airways, but this experimental system does not include the upper respiratory tract, the bronchial tree, nor the pulmonary parenchyma, which are likely to exhibit different virus/host interactions due to the presence of different cell types.

Further, explants lack systemic responses that are normally mounted during viral infections. Despite these limitations, our results are consistent with observations reported in field studies 59,60 and experimental in vivo infections 26,27

In sum, influenza spillover and emergence require a succession of processes that occur at different scales8. As the canine respiratory tract is a suitable ecosystem for IAV infection and reassortment and dogs routinely interact with multiple species that support endemic IAVs, dogs could facilitate the flow of virus between sympatric species. Targeted approaches to reduce the risk of IAV infections in dogs should be part of preparedness efforts to control influenza cross-species switching. 

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