Oregon Announces Another Domestic Cat Infected With H5N1

 
Cats as part of the ecology of H5N1

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Last week the Oregon Department of Agriculture (ODA) announced two more cat deaths due to H5N1 - both linked to the consumption of commercial cat food (see Oregon Dept. of Agriculture Statement On H5N1 In Domestic Cats - WSDA Health Alert on Raw Pet Food). 

There is a small discrepancy between the USDA List infected cats in Oregon and the ODA list. The USDA shows 2 from Linn county, while the ODA only lists one. 

While the ODA has not released any details, a new cat (from a different county; Clackamas) was added to their list dated the 18th of February (see graphic below), making either the 6th or 7th cat from that state.  In all probability, however, both numbers are substantial undercounts. 

Since the emergence of a new, more mammalian-adapted H5N1 virus in 2021, we've seen a number of outbreaks in cats around the world (see reports from Poland & South Korea). In those outbreaks, as well as several recent cases in California and Oregon, the consumption of raw meat and/or milk was the likely exposure.

In other cases cat have been believed infected through predation of wild birds or rodents, or via exposure to contaminated areas outside of the home.  

While the USDA lists 89 domestic cats infected with H5N1, no one knows the real number.  Feral cats are unlikely to be tested for the virus, and we've seen reports of household pets that died, but were never tested. 

Although the CDC continues to rank the risk to general public from avian flu as low, they do provide very specific guidance to pet owners on how to limit their risk of infection from the virus (see What Causes Bird Flu in Pets and Other Animals).

Given the levels of HPAI H5 we are seeing reported in wild birds, livestock, and peridomestic animals, their advice is very much worth heeding. 

Canada: Summary of NACI Statement on Guidance on Human Vaccination Against Avian Influenza in a Non-pandemic Context

 

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Yesterday, in Canada PHAC Announces Plans To Purchase 500,000 doses Of H5N1 Vaccine, we looked at the press release on their intent to purchase a small number of doses of an H5N1 vaccine for humans. 

Canada joins a handful of other countries - including the United States (4.8 million doses), Japan (10 million doses), the UK (5 Million doses) -  in securing a small stockpile of the vaccine.

Vaccination requires two doses - 30 days apart - so these purchases would only serve as a stop-gap measure for a relatively small number of high risk individuals (e.g. laboratory personnel conducting H5 testing, those working with infected animals, healthcare workers, etc.) depending on the size of their stockpile.

Along with yesterday's press release, the NACI (National Advisory Committee on Immunization) published a 38-page document describing how - and when - their stockpile might be used. 

I've reproduced the link and the decision table below, but you'll want to follow the link to read it in its entirety.  You'll find excerpts from the report's summary below that.  

I'll return with a postscript after the break.

Rapid response: Preliminary guidance on human vaccination against avian influenza in a non-pandemic context as of December 2024

Summary of NACI statement of February 19, 2025: Rapid response on preliminary guidance on human vaccination against avian influenza in a non-pandemic context as of December 2024

Download in PDF format
(191 KB, 5 pages)

Organization: Public Health Agency of Canada

Date published: 2025-02-19

          Overview

• On February 19, 2025, the Public Health Agency of Canada (PHAC) released the National Advisory Committee on Immunization's (NACI) Preliminary guidance on human vaccination against avian influenza in a non-pandemic context as of December 2024. This guidance is based on current evidence and NACI expert opinion.
• As of February 14, 2025, 68 human cases of avian influenza A(H5N1) were reported in the US since the start of 2024, primarily among dairy and poultry workers, while Canada reported one human case. Of these human cases, a small number have been severe, including the one case in Canada, and one death has been reported in North America (Louisiana, US). Most human cases can be traced to animal exposures, although some have had an unknown source of exposure.
• The number of human cases of avian influenza A(H5N1) in North America is increasing, primarily among poultry and dairy farm workers. Some Canadians may face increased risk of exposure to H5N1 viruses due to occupational hazards (e.g., poultry and dairy farm workers, laboratory workers); however, the risk to most Canadians remains low at this time.
• This NACI guidance offers a preliminary framework to advise Canadian provinces and territories (PTs) on whether to use human vaccines against avian influenza (HVAI) in a non-pandemic context, centered on the objective to prevent human infection with avian influenza A(H5N1) viruses. Preventing transmission from animals to humans will help to prevent severe disease in humans and could also help limit opportunities for viral adaptations that could facilitate human-to-human transmission.
• In the event that PTs determine it is necessary to start offering HVAI, NACI has identified key populations to consider prioritizing for vaccination including laboratory workers handling live avian influenza A (H5N1) virus and people with ongoing contact with known infected animals or their environments. NACI has also provided product-specific advice to advise PTs on recommended use of HVAI should it be needed (e.g., recommended schedule, guidance on concurrent administration).
• Refer to the full NACI statement for the detailed guidance framework.

What you need to know

• Avian influenza H5N1 outbreaks on both poultry and dairy farms have increased in recent months both globally and in North America, and cases have been reported in humans. Among the human cases of H5N1 in North America, almost all have been reported in people with exposures to dairy cattle or poultry including in non-commercial settings. While the source of exposure is not known for a few North American H5N1 cases, no evidence of human-to-human transmission has been reported to date. Almost all cases in North America have also been mild, with only a few cases of severe disease or death.
• Many countries, including Canada, are boosting surveillance activities, securing access of human vaccines against avian influenza (HVAI), and preparing for the possible use of HVAI to prevent and respond to avian influenza A(H5N1) outbreaks.
• HVAI can be used proactively in a non-pandemic context to protect people who may be at increased risk of being exposed to the virus through animals.
• At this time, based on the available supply and what is known about the epidemiological situation, NACI has provided guidance to assist provinces and territories (PTs) in deciding if, when, and how to use HVAI.
• NACI has not recommended broad deployment of HVAI, but has identified considerations for when HVAI could be used for key populations. NACI has outlined scenarios where it could be appropriate for PTs to consider using an available vaccine supply based on the evolving epidemiology.
• NACI reiterates a strong recommendation for all individuals 6 months of age and older to receive an authorized, age-appropriate seasonal influenza vaccine to reduce the burden of seasonal influenza in Canada. This includes those likely to have significant exposure to avian influenza A viruses (e.g., H5N1) through interactions with birds or mammals. While seasonal influenza vaccines do not protect against avian influenza A(H5N1), they may reduce the severity of seasonal influenza and may potentially reduce the risk of co-infection with both seasonal and avian influenza strains.
• NACI will continue to monitor the evolving evidence and epidemiology of avian influenza A(H5N1) in animals and humans, scientific developments, and evidence on HVAI, and will update guidance as necessary.
• To receive information regarding updates to the CIG and new NACI recommendations, statements and literature reviews, please subscribe to our publications mailing list. 

        (Continue . . . ) 

While a vaccine will be an important tool in any pandemic response, there are no guarantees how effective any H5 vaccine will be, and it will likely be 6 - 12 months into a pandemic before large quantities of any vaccine would be available to the public. 

Until then, NPIs (non-pharmaceutical interventions) - face masks, handwashing, social distancing, etc. - will be our primary tools against any novel respiratory virus. 

And of course, there are no guarantees that HPAI H5 will spark the next pandemic.  It is simply the one that is banging on our door the loudest right now. 

Canada PHAC Announces Plans To Purchase 500,000 doses Of H5N1 Vaccine

 

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As concerns over the evolution and spread of the HPAI H5 virus increase, countries around the world have begun to purchase varying amounts of pre-pandemic H5 vaccines for their populations. Some of these vaccines are based on older strains of the virus, while others are based on more recent strains. 

Whether - or how closely - they will match any emerging pandemic strain is unknown, which is why most countries have elected to purchase only enough for high-risk individuals.  

The United States ordered about 4.8 million doses last summer, enough for about 2.4 million people.  In 2023 Japan announced plans to stockpile about 10 million doses.  While last December the UK announced plans to purchase 5 million doses. 

Today Canada's Public Health Agency announced plans to purchase 500,000 doses of GSK’s human vaccine against avian influenza; ArepanrixTM H5N1 A/American wigeon clade 2.3.4.4b. 

I've reproduced their press release below. I'll have a bit more after the break. 

Government of Canada purchases avian influenza vaccine to protect individuals most at risk

From: Public Health Agency of Canada

News release

February 19, 2025 | Ottawa, ON | Public Health Agency of Canada

The Public Health Agency of Canada (PHAC) and its partners are focused on keeping people and animals in Canada safe and ensuring Canada is ready for any potential health threats. This includes taking proactive measures to protect the health of people in Canada by authorizing and securing the supply of a human vaccine against avian influenza as part of our readiness and potential use, as needed, based on risk conditions. Leveraging an existing agreement, PHAC has secured an initial supply of 500,000 doses of GSK’s human vaccine against avian influenza – ArepanrixTM H5N1 A/American wigeon clade 2.3.4.4b. This vaccine will be used as part of Canada’s contingency planning to protect people who may be at increased risk of being exposed to the virus through animals infected with avian influenza.

While the current risk to the public remains low, individuals with higher-level exposure to infected animals are at increased risk and should take appropriate precautions. Canada reported its first domestically acquired human case of avian influenza A(H5N1) on November 9, 2024, and continued vigilance will help prevent additional human cases. To date, there has been no evidence of sustained person-to-person spread of the virus in any of the cases identified globally. However, avian influenza has the potential to cause serious illness in people.

PHAC will provide vaccines to provinces and territories based on an equitable and risk-based approach, with 60% of available doses going to provinces and territories and 40% kept in a federal stockpile for national preparedness. Provinces and territories will make decisions on the potential use and administration of their respective vaccination programs in the context of local risk conditions, with PHAC supporting program monitoring and evaluation to adjust national efforts as needed.

Canada’s National Advisory Committee on Immunization (NACI) has also released preliminary guidance on the use of human vaccines against avian influenza in a non-pandemic context. Based on the evolving epidemiological situation in Canada and the United States, broad vaccine deployment is not recommended at this time but the guidance provides recommendations for the possible use of this vaccine by provincial and territorial public health authorities in current and potential future scenarios to protect the health of individuals at increased risk of being exposed to the virus.

PHAC continues to work closely with the Canadian Food Inspection Agency, Health Canada, provincial and territorial public health authorities, animal health leaders and experts, industry groups, and international organizations to prepare for and manage the global risks of avian influenza. We remain committed to protecting Canadians by continuously strengthening our preparedness for emerging issues, such as avian influenza, through proactive measures including risk assessments, lab capacity and testing, monitoring and surveillance, science coordination and expert engagement, as well as guidance for professionals and the public.

Quotes

“As we confront the ongoing global health risks posed by avian influenza, our priority remains protecting the health of people in Canada. The proactive steps we are taking, including securing vaccine doses, reflect our commitment to being prepared for any potential public health threats.”

The Honourable Mark Holland
Minister of Health

“By making human vaccines against avian influenza available for potential use in individuals at increased risk of exposure to avian influenza as part of our readiness, we are enhancing our capacity to protect people in Canada and respond rapidly to emerging public health challenges.”

Dr. Theresa Tam
Chief Public Health Officer

Quick facts

• Avian Influenza A(H5N1) may pose a higher risk to individuals who have ongoing contact with infected animals and their environments, including poultry. 

• The Arepanrix H5N1 A/American wigeon clade 2.3.4.4b vaccine is based on established technology for seasonal and pandemic influenza vaccines. Health Canada completed the review of the regulatory submission on February 18, 2025 and authorized the vaccine strain change.

• The National Advisory Committee on Immunization provides expert guidance on vaccine use in Canada. Their guidance on the use of Arepanrix H5N1 A/American wigeon clade 2.3.4.4b vaccine can be found on Canada.ca.

None of these purchases is intended to protect an entire population, as it is expected to take 2 doses - 30 days apart - to convey immunity. With a population of nearly 40 million, Canada would need nearly 80 million doses while the United States would need over 600 million.

Having some quantity of pre-existing vaccine on hand, however, could allow certain high risk individuals (like farmers or HCWs) to be partially protected, while an updated vaccine is being developed.

Today's announcement does not provide a time-table for manufacture or delivery, but it generally takes several months to manufacture, fill and finish.

USDA Adds A New Species (Black Rats) to Their Mammalian Wildlife With HPAI H5 List

 

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Presumably only a small percentage of HPAI H5 infected mammalian wildlife are ever found and tested, but this week the USDA's list has reached a milestone of sorts, surpassing 500 entries. Four of the ten entries added this week are feline (3 house cats, 1 bobcat), while a new species - the Black Rat (n=4) - makes its first appearance.

House cats were only first added to the list in May of 2024, and since then 89 have been added. Other felines (bobcats, mountain lions, tigers, etc.) add more than 5 dozen more to the list. 

Rodents, were first added in June of last year, and now (deer mouse, house mouse, black rat) make up > 20% of the the list (n=108). 

The susceptibility of cats (both wild and domestic) to HPAI H5N1 has been long known (see 2015's HPAI H5: Catch As Cats Can), but the role that rodents may play in its ecology is less well studied.

• Last August, in Pathogens: Susceptibility of Synanthropic Rodents to H5N1 Subtype HPAI Viruses, we looked at a study where researchers challenged several rodent species (house mice, brown rat, black rat) with two (older 2010, 2007) HPAI H5N1 viruses, and found they are both susceptible to the virus and could potentially play a role it its evolution and spread.

• Also in August 2024, in Emer. Microbe & Inf.: HPAI Virus H5N1 clade 2.3.4.4b in Wild Rats in Egypt during 2023, we a surprisingly high percentage of wild rats testing positive for H5 antibodies in Egypt, suggesting that some number may survive the infection. 

The USDA's list is far from exhaustive, since many states have reported zero - or only a few - infections. Reporting is often limited by animals dying in remote and difficult to access places, or by animals that survive the infection. 

It is fair to say that what is reported is just the tip of the pyramid.

Not so very long ago, HPAI H5 was pretty much just an avian virus, with only occasional spillovers to humans and a few cats unlucky enough to be fed a diet of raw chicken. But starting in 2021 we began to see reports of numerous spillovers into a much wider range of mammals (see chart below).

Credit ECDC/EFSA

As the HPAI H5 virus continues to find new mammalian hosts it is likely to become more deeply entrenched in our shared ecology, increasing the risks that it will find new evolutionary pathways that were unavailable to it when it was primarily a disease of birds.

Meaning that even if we somehow manage to control this virus in the henhouse and the dairy, it could still deliver a nasty surprise down the road. 

UK Confirms HPAI H5N5 In 2 Grey Seals

 

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While most of our HPAI concerns center around the H5N1 subtype, we continue to watch other strains (H5N6, H5N5, H5N9, etc.) with considerable interest since history has shown how quickly an obscure subtype can take center stage (see EID Journal: Comparison of 2016–17 and Previous Epizootics of HPAI H5 In Europe).

In China, H5N6 continues to spill over into humans, killing roughly 50% of those hospitalized.  In Europe, and in Canada, we are watching a milder H5N5 virus circulate in wild birds, and occasionally spill over into mammals. 

Both have some degree of pandemic potential, but neither has spread as efficiently as the current HPAI H5N1 threat.  

Today, in a brief notice (see above), the UK has announced the detection of HPAI H5N5 in two grey seals, detected in Norfolk.   Last November, they reported an outbreak in poultry of H5N5 in Yorkshire along with > 2 dozen dead birds infected with H5N5 from around the kingdom (see map below).

While this latest report hasn't appeared on the WOAH WAHIS list, that organization has already published 11 reports on H5N5 in birds and mammals since the first of the year from 6 different countries (Norway, Canada, Iceland, Greenland, Germany & the UK). 

A few recent blogs on this subtype include:

Virus Evolution: Recurring Incursions & Dissemination of Novel Eurasian-origin H5Nx Avian Influenza Viruses in Atlantic Canada

More Reports On HPAI H5N5 In Iceland

Icelandic Food and Veterinary Authority (MAST) : H5N5 Infection In Domestic Cat

We've seen reports of H5N5 in European birds going back to 2016, but it was first detected in dead raccoons on Prince Edward Island about 21 months ago (see CIDRAP Report). Since last May, we've seen increasing reports of its western expansion (see WAHIS: More Reports of HPAI H5N5 in Canada).

Last July, in Cell Reports: Multiple Transatlantic Incursions of HPAI clade 2.3.4.4b A(H5N5) Virus into North America and Spillover to Mammals, researchers reported finding the mammalian adaptive E627K mutation in a number of samples.

They wrote:

Thus, while A(H5N5) viruses are comparably uncommon, their high virulence and mortality potential demand global surveillance and further studies to untangle the molecular markers influencing virulence, transmission, adaptability, and host susceptibility.

While H5N5 is likely to remain a minor player, it is not impossible that we could the threat shift to H5N1 to H5N5, or H5N6, or to some other n-type, in the months or years ahead.  After all, 5 years ago H5N1 was in serious decline, while HPAI H5N8 reigned supreme. 

The H5Nx virus has an large - and growing - array of diverse hosts to inhabit, and no lack of genetic diversity on which to draw. All reasons why we could always see additional shifts in the fluscape in the future.

HK CHP: Mainland China Reports 2 More H9N2 Cases

 

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For the second week running Hong Kong's CHP Avian Influenza Report is announcing 2 more H9N2 infections on the mainland (see last week's blog). Over the past 6 months Mainland China has reported 17 such cases, although the actual number of infections is thought to be much higher. 

A bit unusually, both cases reported this week are older adults (F, 72 & 56).  Most of the cases reported by China have been children or adolescents (14 of the past 17 cases).  While most H9N2 have been mild or moderate, at least 2 deaths have been reported. 

In addition to > 140 confirmed human infections (see FluTrackers list), seroprevalence studies have shown people with exposure to infected poultry often develop H9 antibodies, suggesting mild or asymptomatic infection.

H9N2 is poorly controlled in Chinese poultry, despite the long-term use of vaccines (see J. Virus Erad.: Ineffective Control Of LPAI H9N2 By Inactivated Poultry Vaccines - China), which has led to the creation and spread of numerous of genotypes.

A reminder that livestock vaccines must be well-matched, properly applied, and continually updated (see MPR: Poultry AI Vaccines Are Not A `Cure-all’ & The HPAI Poultry Vaccine Dilemma) if they are to be effective.

Over the past 15 years we've watched as H9N2 has expanded its geographic range - spreading out of Asia into Europe, the Middle East and Africa. While it occasionally spills over into humans, H9N2's biggest threat may come from its unique ability to reassort with other, potentially more dangerous, avian viruses.

 

Its internal genes have often been found inside many HPAI viruses (including H5N1, H5N6, H7N9, and most recently zoonotic H3N8) - (see The Lancet's Poultry carrying H9N2 act as incubators for novel human avian influenza viruses).  

H9N2 is such a versatile virus, it has even been detected in  Egyptian Fruit bats (see Preprint: The Bat-borne Influenza A Virus H9N2 Exhibits a Set of Unexpected Pre-pandemic Features).

Seven years ago, in EID Journal: Two H9N2 Studies Of Note, we looked at two reports which suggested that H9N2 continues to evolve away from current (pre-pandemic and poultry) vaccines and is potentially on a path towards better adaptation to human hosts.

While admittedly not at the very top of our list of pandemic concerns, the CDC has 2 different lineages (A(H9N2) G1 and A(H9N2) Y280) on their short list of influenza viruses with zoonotic potential (see CDC IRAT SCORE), and several candidate vaccines have been developed.