Introduction: Highly pathogenic avian influenza (HPAI) H5N1, a zoonotic virus primarily affecting birds, has shown increasing cross-species transmission, including to domestic animals such as cats. Recent reports of cat infections, often associated with contact with infected birds or the consumption of raw milk from H5N1-positive cattle, raise concerns about their role in viral adaptation and zoonotic transmission. Objective: To assess the global prevalence and characteristics of H5N1 infections in cats (Felis catus) through a systematic review and meta-analysis. Methods: Following PRISMA guidelines, we conducted a systematic search across PubMed, Scopus, and Web of Science up to 1 March 2025. Observational studies reporting the prevalence or seroprevalence of H5N1 in cats (Felis catus) were included. Data extraction and quality assessment were performed independently by four reviewers. Meta-analyses were conducted using a random-effects model, and heterogeneity was assessed via I2 statistics. Results: Twenty-one studies met the inclusion criteria, of which eight were included in the meta-analysis (n = 3586 cats). The pooled global prevalence of Felis catus infections due to H5N1 influenza was 0.7% (95%CI: 0.3–1.1%), with high heterogeneity (I2 = 86.5%). The prevalence varied by the diagnostic method, region, cat type, and time. Domestic cats and those in Africa had higher infection rates (20.0% and 32.0%, respectively). Case reports (n = 35) revealed a high mortality (74%), predominantly from clade 2.3.4.4b, with neurological and respiratory manifestations. Conclusions: Although the overall prevalence is low, H5N1 infection in cats is increasing, particularly in clade 2.3.4.4b. Their close contact with humans and other animals highlights the need for enhanced surveillance, diagnostics, and One Health strategies to mitigate zoonotic risks.

Brazil’s Ministry of Agriculture and Livestock on Friday confirmed the country’s first outbreak of bird flu in a commercial poultry facility.

Home>Infectious diseases>Infectious Diseases 2025>Brazil: First outbreak of avian influenza on a commercial farm Brazil has confirmed its first outbreak of highly pathogenic avian influenza (HPAI) H5N1 on a commercial poultry farm. The incident occurred in Montenegro, located in the southern state of Rio Grande do Sul. As the world's largest exporter of poultry, Brazil's poultry industry holds significant importance on the global stage. While previous HPAI detections in wild birds did not impact the country's trade status, this outbreak on a commercial farm could lead to trade restrictions, depending on international responses. Brazil reported its first HPAI H5N1 case in wild birds in May 2023, with subsequent detections in backyard poultry.Until now, no cases had been reported in commercial poultry operations.

When the first confirmed case of the H5N1 virus was diagnosed in a Texas herd in March 2024, the industry came together to counteract the spreading virus. The FARM Program's biosecurity program area quickly became a leader in the effort, using the latest science and best on-farm practices to help mitigate the bird flu’s spread.

Highly pathogenic avian influenza (HPAI) viruses cross species barriers and have the potential to cause pandemics. In North America, HPAI A(H5N1) viruses related to the goose/Guangdong 2.3.4.4b hemagglutinin phylogenetic clade have infected wild birds, ...

Home>Infectious diseases>Infectious Diseases 2025>Mild disease and limited spread of bovine H5N1 clade 2.3.4.4b in pigs Highly pathogenic avian influenza virus (HPAIV) H5N1 clade 2.3.4.4b has recently emerged as a significant concern for animal and human health due to its ability to infect multiple mammalian species and its ongoing circulation in wild birds, cattle, and poultry. Since early 2024, this clade has been detected in dairy cows in the United States and has caused sporadic human infections. Given the pivotal role of pigs as “mixing vessels” capable of fostering reassortment and mammalian adaptation of avian influenza viruses (Pigs’ dual susceptibility to avian and human influenza A viruses stems from their respiratory epithelium expressing both α2,3-linked (avian-type) and α2,6-linked (human-type) sialic acid receptors. Consequently, pigs may serve as “mixing vessels” for influenza virus reassortment), the susceptibility and transmission dynamics of this virus in swine warrant critical investigation. A preprint study published in Research Square investigated the susceptibility of Sinclair nanopigs to infection with a bovine-derived clade 2.3.4.4b HPAIV H5N1 isolate. Pigs were experimentally inoculated via intranasal, intratracheal, and oral routes to mimic natural exposure. The results demonstrated productive infection, with pigs developing subclinical or mild clinical signs and subsequently seroconverting. Virus replication was primarily localized to respiratory tissues - especially the upper respiratory tract -with viral shedding detectable in nasal and oral swabs by PCR and infectious-virus assays. Importantly, limited transmission to naïve contact cage mates was documented in some instances, marking a departure from previous studies in which contact transmission was negligible. This limited transmission occurred despite self-limiting viral replication and a brief shedding period. These findings emphasize that, although infection in pigs with this bovine-derived HPAIV H5N1 strain is generally mild or subclinical, swine can nonetheless serve as potential hosts for viral spread and reassortment. Natural spillover infections during H5N1 outbreaks have been documented in multiple regions: China (Zhejiang, 2015): A novel H5N1 strain (clade 2.3.2) was isolated from a slaughterhouse pig during routine influenza surveillance; genetic analysis confirmed avian origin with no swine-adapted segments, indicating direct bird-to-pig transmission (1). Nigeria (2015 outbreak): Among 129 healthy slaughterhouse pigs sampled at a live-animal market, 43 (33 %) harbored influenza A RNA in tracheal swabs, and 22 were confirmed as H5N1 clade 2.3.2.1c by RT-qPCR and sequencing; all positive pigs remained asymptomatic (2). Italy (2021 outbreak): On a free-range, multi-species farm, pig nasal swabs tested negative by RT-PCR, yet most pigs seroconverted to H5N1 clade 2.3.4.4b, as shown by hemagglutination-inhibition and microneutralization assays, despite absence of clinical signs (3). Field evidence from Asia, Africa, and Europe thus demonstrates that pigs in direct contact with infected poultry can experience subclinical and transient H5N1 infection, typically characterized by low viral loads detectable only via sensitive PCR or virus isolation, with seroconversion serving as the primary indicator of exposure. 1. Wu H, Yang F, Lu R, Xu L, Liu F, Peng X, Wu N. Isolation and molecular characterization of an H5N1 swine influenza virus in China in 2015. Archives of Virology. 2018 Mar;163:701-5. 2. Meseko C, Globig A, Ijomanta J, Joannis T, Nwosuh C, Shamaki D, Harder T, Hoffman D, Pohlmann A, Beer M, Mettenleiter T. Evidence of exposure of domestic pigs to Highly Pathogenic Avian Influenza H5N1 in Nigeria. Scientific Reports. 2018 Apr 12;8(1):5900. 3. Rosone F, Bonfante F, Sala MG, Maniero S, Cersini A, Ricci I, Garofalo L, Caciolo D, Denisi A, Napolitan A, Parente M. Seroconversion of a swine herd in a free-range rural multi-species farm against HPAI H5N1 2.3. 4.4 b clade virus. Microorganisms. 2023 Apr 28;11(5):1162.

The FDA and CDC have ended key bird flu surveillance programs, including milk testing and outbreak updates. Experts say this leaves the U.S. blind to a virus that still carries pandemic potential. Without robust monitoring, we may not see the next threat until it’s too late.

The recent spread of highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b into U.S. dairy cattle herds has raised alarms among public health

H5N1 Virus Confirmed in Cattle Across Western States Bird flu has recently spread to dairy cattle in the Mountain West, raising concerns among federal animal health officials. While the virus known as H5N1 has long impacted poultry flocks, its appearance in cows marks a troubling development, though it is not currently considered a threat to public health. Recent outbreaks have affected poultry in several states, including Colorado, Montana, New Mexico, and Wyoming. Meanwhile, the virus has been confirmed in cattle in Arizona and Idaho. Additionally, a February case involving 20 non-poultry birds in Nevada was documented by the Centers for Disease Control and Prevention (CDC). While highly lethal to poultry often killing entire flocks within days cattle appear more resilient, according to the CDC. Human infection cases are rare but do occur, typically in people with direct exposure to infected animals. “The cases that we’ve seen so far have been people working with sick chickens or working with infected cattle and have large occupational exposures,” said Brian Labus, associate professor at the University of Nevada, Las Vegas. “So far we have seen 70 cases in the United States and one person has died. But we haven’t seen it spread person to person.” A federal testing requirement was introduced last spring, mandating that cattle be screened before transport. Officials say this policy has helped limit the virus’s spread. The CDC is continuing to monitor H5N1 in humans using its existing flu surveillance systems. Labus added that “processes such as milk pasteurization and proper cooking” help prevent transmission through dairy and meat products.

It's spring, the birds are migrating and bird flu (H5N1) is rapidly evolving into the possibility of a human pandemic. Researchers from the University of Maryland School of Public Health have published a comprehensive review documenting research on bird flu in cats and calling for urgent surveillance of cats to help avoid human-to-human transmission.

Scientific Reports - Genetic diversity of A(H5N1) avian influenza viruses isolated from birds and seals in Russia in 2023

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Influenza A viruses (IAVs) are important zoonotic pathogens, posing a credible concern to animals and humans. The viral genome is negative-sense, single-stranded, and consists of eight segments. IAVs are classified into 19 hemagglutinin (HA) subtypes and 11 neuraminidase (NA) subtypes (1). H17N10 and H18N11 have only been identified in bats, while H1–H16, H19, and N1–N9 can infect a wide range of avian and mammalian hosts, including humans (2, 3). Wild birds are the natural reservoirs for IAV, where they are referred to as avian influenza viruses (AIVs). All 16 HA subtypes and 9 NA subtypes have been identified in wild birds (4).

LUCKNOW: The death of a tigress in Gorakhpur zoo led to the closure of Lucknow, Kanpur and Gorakhpur zoos along with Etawah Lion Safari for a week on Tuesday ev

Research reveals the impact of early detection via smaXtec bolus on health, productivity and economic effects of H5N1 in U.S. dairy herds.

Facing high egg prices, the Trump administration is considering vaccinating poultry against bird flu, but H5N1 is already out of barn. It’s infected nearly 500 species of wild birds and mammals, ranging from foxes to zoo tigers. It’s time to consider another means of stopping its spread: vaccinating wildlife.

20-Year Review Underscores Need for Better Surveillance to Protect Cats, Humans

Leading virologists from 40 countries warn of critical gaps in pandemic preparedness and outline a plan for readying the world.

Nature Communications - Influenza A H5N1 is an increasing concern in cattle herds in the United States. Here, the authors use mathematical modelling to estimate the size of the current epidemic,...

SUMMARYOver the past 25 years, there has been an increasing number of mammalian (including human) infections caused by avian influenza A viruses that resulted in mild to severe illnesses. These viruses typically did not spread between mammals through ...

Dr. Richard Webby, a virologist at St. Jude Children’s Research Hospital, is sounding the alarm on the growing risk posed by avian influenza, specifically the H5N1 strain now infecting dairy cattle in the U.S.

Download scientific diagram | Projected risk maps for H5 HPAI clade 2.3.4.4b and associated uncertainty intervals. Projected probability of H5 HPAI clade 2.3.4.4b presence by aggregated bird behavioural season (NB = Nonbreeding season, PrM = Pre-breeding migration, B = Breeding season, PoM = Post-breeding migration) during period A (10/8/2016 to 9/8/2021, spanning H5N8 and H5N6 events) and period B (10/8/2021 to 29/2/2024, ongoing H5N1 outbreak) from selected final models with cross-seasonal covariates. Central columns are posterior means from BART ensemble, left and right columns represent 95% credible intervals. from publication: Ecology and environment predict spatially stratified risk of H5 highly pathogenic avian influenza clade 2.3.4.4b in wild birds across Europe | Highly pathogenic avian influenza (HPAI) represents a threat to animal and human health, with the ongoing H5N1 outbreak within the H5 2.3.4.4b clade being the largest on record. However, it remains unclear what factors have contributed to its intercontinental spread. We use... | Avian Influenza, birds and Europe | ResearchGate, the professional network for scientists.

Cats infected with bird flu are falling under the radar when it comes to tracking and managing the virus, and this must change rapidly, scientists warn in a new paper.

Download scientific diagram | Wild bird H5 HPAI clade 2.3.4.4b incident data in Europe. Spatiotemporal distribution of incidents of H5 highly pathogenic avian influenza clade 2.3.4.4b reported in wild birds, harmonised from EMPRES-i and WAHIS databases. A) and B) Geolocated incident reports over time periods A from publication: Ecology and environment predict spatially stratified risk of H5 highly pathogenic avian influenza clade 2.3.4.4b in wild birds across Europe | Highly pathogenic avian influenza (HPAI) represents a threat to animal and human health, with the ongoing H5N1 outbreak within the H5 2.3.4.4b clade being the largest on record. However, it remains unclear what factors have contributed to its intercontinental spread. We use... | Avian Influenza, birds and Europe | ResearchGate, the professional network for scientists.

University of Maryland researchers call for increased surveillance as a global review links rising cat infections to emerging H5N1 strains.

The H5N1 virus has shown increasing signs of adaptation to mammalian hosts in the Southern Cone of South America.

Background The prevalence and transmission of avian influenza viruses (AIVs) in the live poultry market (LPM) is a serious public health concern. This study was to investigate the prevalence of different subtypes of avian influenza viruses in environment of LPM, and to analyze the differences and seasonality of the nucleic acid positive rate (NAPR) of A type, H5, H7, and H9 subtypes in feces, sewage, drinking water, breeding cages, and chopping boards. Methods Feces, breeding cages swabs, drinking water, sewage and chopping boards swabs were collected from live poultry market during 2019–2023 from southern and northern China. Real-time PCR was used to screen for virus subtypes. Viruses were isolated, and deep sequencing was performed to obtain whole-genome sequences. Chi-square test was used for statistical analysis of categorical variable, GraphPad Prism software were used to construct graphs. Results A total of 64,599 environmental samples were collected from live poultry markets in the southern China and northern China between 2019 and 2023. The average NAPR of the A type was significantly higher in the samples collected from the southern China than in those collected from the northern China (P  0.05). The NAPR of H5, H7, and H9 subtypes carried by the five types of environmental samples in the southern China were significantly different (P  0.05), and a higher NAPR was detected in chopping boards (10.84%), breeding cages (0.28%), and drinking water (40.97%) respectively. The average NAPR of the H9 and H5 subtypes displayed seasonality, reaching a peak in January and February in the southern China, while the peak of the H9 subtype was from October to February in the northern China. A total of 19 subtypes were identified. The H5 subtype significantly decreased, the H7 subtype was almost undetectable, and other subtypes, such as the H3 subtype, increased. Conclusions The highly pathogenic H5 subtype has significantly decreased in the live poultry market in China since 2022. However, the proportion of some subtypes, such as the H3 subtype, with low pathogenicity to poultry, has increased, while the H9 subtype remains at a high level. It must be noted that these low pathogenic avian influenza viruses often have no obvious symptoms, can circulate asymptomatically in infected poultry, and are highly pathogenic to humans. Our findings provide insights into the control and prevention of avian influenza viruses and the risk of pandemics associated with avian influenza viruses in the live poultry market.

As we reflect on the wonder of migratory birds, and the spotlight focuses on how our cities and communities can be made more bird-friendly, we must also consider how our food system is posing a threat to their very existence.

1. Direct Contact Between Wild Birds and Domestic Poultry One of the primary ways bird flu spreads from wild birds […]

Researchers developed a nationwide model to simulate the spread of H5N1 in US dairy cattle, revealing significant under-reporting and predicting continued outbreaks into 2025. Targeted farm-level biosecurity and surveillance are urgently needed to contain the epidemic.

spanbBackground/b: Pandemic influenza may cause substantial morbidity and mortality, especially in older adults and those with immunosuppressive conditions. bMethods/b: In this phase 3, stratified, randomized, controlled, observer-blind, multicenter trial, we evaluated the safety, tolerability,/span …

FFAR and Genvax invest $278,163 into a rapid research grant to develop a vaccine to prevent H5N1 in cows.

In this NEJM Outbreaks Update, Editor-in-Chief Eric Rubin and Deputy Editor Lindsey Baden are joined by Indiana Commissioner of Public Health Lindsay Weaver to discuss the current state of avian in...

Home>Infectious diseases>Infectious Diseases 2025>Epidemiological parameters of human H5N1: Rapid review medRxiv preprint | April 17, 2025 A new study published in medRxiv reviewed and analyzed estimates for key epidemiological parameters of human H5N1 infection, including the reproduction number (R₀), serial interval, incubation period, latent and infectious periods, and severity metrics such as the case fatality risk (CFR) and infection fatality risk (IFR). The study also employed modelling to estimate the R₀ for the 2024–2025 U.S. dairy herd outbreak and calculated the serial interval using historical H5N1 transmission data from Indonesia. Low human-to-human transmission: Estimated R₀ values for H5N1 remain consistently low (e.g., 0.04–0.05 in the U.S. outbreak), well below the threshold required for sustained human transmission. Longer incubation and serial intervals: H5N1 displays a median incubation period of approximately 4 days and a serial interval of approximately 6.8 days—both longer than those typically observed for human influenza (approximately 2–3 days). High historical case fatality risk, but lower in the current U.S. outbreak: While historical CFRs reached up to 53%, the ongoing U.S. outbreak has shown a CFR of 1.43%, with most cases presenting mild ocular symptoms (e.g., conjunctivitis). Occupational exposure risk: Serological evidence indicates a heightened risk of infection among poultry cullers and dairy workers exposed to infected animals, although definitions for seropositivity vary across studies. Comparison to H7N7 (Netherlands, 2003): The current outbreak shares key features with the 2003 H7N7 outbreak, including a low CFR, a predominance of conjunctivitis, and a low R₀, suggesting a similar clinical and epidemiological profile. H5N1 currently exhibits limited transmissibility in humans, with reproduction numbers well below 1, indicating low epidemic potential in its current form. The virus shows a longer incubation and serial interval compared to seasonal and pandemic influenza viruses, which may support more effective contact tracing should human-to-human transmission increase. The severity profile in the ongoing U.S. outbreak appears milder than in previous outbreaks, largely characterized by ocular symptoms and a low CFR. Continuous surveillance is crucial, particularly in high-risk occupational groups and mammalian hosts, due to the potential for viral adaptation or reassortment that could enhance transmissibility. The epidemiological characteristics of the current H5N1 outbreak closely resemble those of the 2003 H7N7 outbreak, underscoring the importance of monitoring similar symptomatology and transmission patterns.

There are currently 59 herds quarantined in 4 Idaho counties.

From egg prices to pet food recalls – and now, confirmation that another strain of bird flu has infected a large commercial flock of broiler chickens on a Mississippi farm – headlines are capturing escalating concern over H5N1's spread. According to recent findings by a team of bioinformati...

A recent review published in Vaccines by László Kovács and colleagues provides a comprehensive analysis of vaccine trials targeting the highly pathogenic

The H5N1 avian flu can cause coughing, body aches, fatigue, pneumonia and other symptoms in humans, and experts from the Global Virus Network are urging leaders to step up with knowledge gained during the COVID pandemic.

The ongoing panzootic of H5N1 high pathogenicity avian influenza virus (HPAIV) has caused the deaths of over half a billion wild birds and poultry, and has led to spillover events in both wild and domestic mammals, alongside sporadic human infections. A key driver of this panzootic is the apparent high viral fitness across diverse avian species, which facilitates an increased interface between wild and domestic species. Columbiformes (pigeons and doves) are commonly found on poultry premises and are highly connected to humans in urban settlements, yet relatively little is known about their potential role in contemporary HPAIV disease ecology. Here we investigated the epidemiological role of pigeons (Columba livia) by determining their susceptibility using decreasing doses of clade 2.3.4.4b H5N1 HPAIV (genotype AB). We investigated infection outcomes and transmission potential between pigeons and to chickens for each dose. Following direct inoculation, pigeons did not develop clinical signs, and only those inoculated with the highest dose shed viral RNA or seroconverted to H5N1-AB, revealing a MID50 of 10^5 EID50. Even in the high dose group, only low-level shedding and environmental contamination was observed, and low-level viral RNA were present in the tissues of directly inoculated pigeons, with no distinct pathological lesions. Pigeons did not transmit the virus to naive pigeons or chickens placed in direct contact. Overall, these findings suggest that pigeons have a low susceptibility to clade 2.3.4.4b H5N1 HPAIV and are less likely to significantly contribute to disease ecology, incursions into poultry, or pose a significant zoonotic threat. ### Competing Interest Statement The authors have declared no competing interest. Department for Environment Food and Rural AffairsDepartment for Environment Food and Rural Affairs, https://ror.org/00tnppw48, SE2227, SV3400 Biotechnology and Biological Sciences Research CouncilBiotechnology and Biological Sciences Research Council, https://ror.org/00cwqg982, BB/Y007271/1 European UnionEuropean Union, , 101084171 (Kappa-Flu)

The Global Virus Network published a comprehensive analysis of the H5N1 bird flu outbreak, calling on world governments to address the threat by enhancing surveillance, implementing biosecurity measures and preparing for potential human-to-human transmission.

Virologists from 40 countries say year-long US outbreak raises risk that virus will spread between humans

Easy replication in cattle mammary glands means H5N1 bird flu is under no evolutionary pressure to adapt to spread easily in humans.

NIV shares H5N1 genome data with GISAID after criticism, collected from a two-year-old girl in Andhra Pradesh.

Last week’s 60 Minutes segment on H5N1 focused on some shortcomings in the US agricultural sector as they grapple with H5N1 influenza infections among poultry, cattle, and some dairy workers. The segment focused on legit gaps like poor USDA oversight, limited worker protection, and the spread of the virus through dairy herds. The veterinary experts featured in the piece rightly presented arguments about the need for better biosecurity and surveillance in the ag sector. Bird flu poses growing risk to people as pathogen spreads, scientists warn | 60 Minutes – CBS News But let’s be honest… H5N1 isn’t something we’re going to “contain.” It’s global. It’s in migratory birds, domestic poultry, and now cattle — not just in the U.S., but around the world. Mitigation is the only practical path forward at the farm and ranch level. The real threat to humans is Kennedy’s rapid disassembly of our public health system. He’s intentionally unraveling our capacity to respond if (or when) H5N1 adapts for sustained human-to-human transmission and becomes more virulent. Local and state health departments — the frontline of any pandemic response (think surveillance, antiviral distribution and vaccine delivery and administration) is being cut dramatically by Kennedy. The U.S. has walked away from the WHO. Trust in public health institutions is at historic lows largely because of Kennedy and Trump’s behavior and decision-making. Those who should be reinforcing evidence-based public health practice (Secretary Kennedy) are instead waging a war on science, vaccine development, and the very concept of public health. NIH researchers who once focused on rapid vaccine development (and zoonotic spillover) are being defunded, fired and driven out. Entire teams are gone, and his plan is to cut even further into NIH’s mission next year. If H5N1 reassorts and sparks a human pandemic, we’ll be ‘responding’ with an eviscerated system. And it won’t just be about late vaccine timelines or scarce antivirals (or public health’s ability to distribute and administer them) — it’ll be about the absence of the workforce and infrastructure to mount a response at all. After just 4 months of this administration, we’re already in worse shape now than we were for H1N1 in 2009. What we’ve already lost and continue to lose isn’t just funding or programs, its institutional knowledge, technical capacity, and our public health and research workforce and institutions. If things don’t change, three and a half years from now we’ll be responding to pandemics with stone knives & bearskins.

Robust infectious disease surveillance, including rapid subtyping of influenza A, is essential for early detection, containment, and public health reporting of novel viral threats.

The H5 Avian Influenza A virus infection has emerged as a global concern, particularly in the ASEAN region. This viral infection poses a significant threat to the poultry industry, public health, and regional economies. This region's reliance on poultry production and the zoonotic potential of H5 su …

The Foundation for Food & Agriculture Research (FFAR) and Genvax Technologies are investing $278,163 into a Rapid Outcomes from Agricultural Research (ROAR) grant to develop an H5N1 vaccine for dairy cows.

Latest lab tests reveal Zentek's avian flu treatment matches monoclonal antibody effectiveness. Moving to crucial in vivo testing phase. Get exclusive details.

The mRNA vaccine targets all major clades of the H5 avian flu subtype.

The spread of highly pathogenic avian influenza (HPAI) in U.S. dairy cattle can be traced to a single spillover event from a wild bird, researchers report, raising concern over growing pandemic risks as the virus evolves and leaps between species. HPAI viruses pose serious threats to animal health, agriculture, and potentially human health due to...