Highly Pathogenic Avian Influenza H5N1 in Cats (Felis catus): A Systematic Review and Meta-Analysis

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.

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Brazil Confirms First Bird Flu Outbreak in Commercial Poultry; China Halts Imports

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

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Brazil: First outbreak of avian influenza on a commercial farm | Infectious Diseases 2025 | Infectious diseases | Poultrymed

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.

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Assurance Watch: FARM Biosecurity remains a leader against H5N1 | Ag Proud

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.

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Emergence and interstate spread of highly pathogenic avian influenza A(H5N1) in dairy cattle in the United States

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, ...

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Mild disease and limited spread of bovine H5N1 clade 2.3.4.4b in pigs | Infectious Diseases 2025 | Infectious diseases | Poultrymed

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.

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Experts Are Still Seriously Worried About Bird Flu — Here's What You Need to Know

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.

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Cutting-Edge mRNA Vaccine Shows Promise Against H5N1 in Dairy Cattle

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

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Bird Flu Spreads to Dairy Cattle in Mountain West | Farms.com

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.

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Bird flu in cats points to risk of another pandemic

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.

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

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

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Epidemiology and pathobiology of H5Nx highly pathogenic avian influenza in South Korea (2003–2024): a comprehensive review

Access 135+ million publications and connect with 20+ million researchers. Join for free and gain visibility by uploading your research.

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Clade 2.3.4.4b highly pathogenic avian influenza H5N1 viruses: knowns, unknowns, and challenges | Journal of Virology

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).

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Bird flu scare: Death of a tigress lead to closure of zoos in Uttar Pradesh

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

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Bolus found to detect H5N1 up to a week before symptoms appear

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

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Why we should seriously consider vaccinating wild birds to control bird flu

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.

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Avian Influenza in Cats Is Not Getting the Attention it Deserves, UMD…

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

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Prepare for a bird flu pandemic now, virologists urge

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

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A mathematical model of H5N1 influenza transmission in US dairy cattle

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,...

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Viral factors underlying the pandemic potential of influenza viruses | Microbiology and Molecular Biology Reviews

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 ...

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Curious by Nature: Dr. Richard Webby - Understand Bird Flu Risks | Newswise

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.

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Figure 2. Projected risk maps for H5 HPAI clade 2.3.4.4b and associated...

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.

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Spikes of Bird Flu in Cats Could Be a Warning of a Future Pandemic

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.

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Figure 1. Wild bird H5 HPAI clade 2.3.4.4b incident data in Europe....

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.

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Experts urge avian flu monitoring in cats after surge in H5N1 infections

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

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H5N1 adapts alarming to mammals in South America's South Cone

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

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Characterization of the avian influenza viruses distribution in the environment of live poultry market in China, 2019–2023 - Infectious Diseases of Poverty

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.

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Opinion | Scapegoating Wild Birds Won’t Solve Avian Flu: We Need Radical Farming Reform | Common Dreams

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.

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Scientists Explain: 6 Ways Bird Flu Spreads from Wild Birds to Pet Food Supply Chains

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

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New model reveals H5N1 is spreading undetected in US dairy herds

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.

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