ETIDIOH - NEW

Summary Background Clade 2.3.4.4b highly pathogenic avian influenza A(H5N1) (HPAI H5N1) viruses have spread prolifically in dairy cattle in the US , resulting in dozens of human infections , some without well-established links to animal contacts. Many wild mammals have also been affected, including peridomestic house mice. Methods Here, we evaluated susceptibility, tissue tropism, and shedding in female PWK/PhJ and BALB/cJ mice , two laboratory strains derived from house mice that differ in expression of the antiviral restriction factor Mx1. PWK/PhJ mice, which were selected for their natural expression of Mx1, better reflect the antiviral capacity of most wild house mice, whereas BALB/cJ mice lack functional Mx1. Findings We found that, regardless of Mx1 expression status, mice are susceptible to infection by dairy cattle HPAI H5N1 viruses , that infection leads to systemic spread to non-respiratory sites, and that infected animals shed virus into the environment via urine. Shed virus...

LETTER Highly pathogenic avian influenza (HPAI) viruses of genotype B3.13 were first reported in dairy cattle in March 2024 and, by 4 March 2025, had infected at least 989 cattle herds in 17 states in the US ( https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/hpai-confirmed-cases-livestock ; accessed on March 24, 2025). Importantly, spillover infections of poultry and mammalian species , including cats and humans , have occurred ( https://www.cdc.gov/bird-flu/situation-summary/index.html ; accessed on 4 March 2025). Texas reported several infected herds in the spring (1) and early summer of 2024 but saw fewer outbreaks during the second half of 2024, with reported outbreaks in July and December (2). Since September 2024, almost all reported outbreaks of genotype B3.13 viruses in dairy cattle have occurred in California . Here, we characterized self-submitted samples from a farm in Texas that experienced an outbreak in December 2024. This farm ha...

Summary The recent emergence of highly pathogenic H5N1 avian influenza virus infections in dairy cows and humans in the U.S. has raised alarms regarding the potential for a pandemic . Over 995 dairy cow herds and at least 70 humans have been affected, including cases of severe disease and the first reported H5N1-related death in the U.S . Sporadic human infections with no known contact with infected animals highlight the possibility of viral adaptation for efficient human-to-human transmission. Concurrently, the virus continues to circulate in wild birds, backyard flocks, and hunted migratory species , further amplifying the risk to humans and domestic animals. This article provides an overview of the current outbreak status , emphasizes the importance of robust surveillance systems to detect emerging strains with pandemic potential, and highlights risks to the U.S. dairy and poultry industries. Recommendations for risk mitigation include enhanced biosecurity measures, improved surveil...

Abstract Since Spring 2024, new genotypes of highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b have been identified in the United States (US). These HPAI H5N1 genotypes have caused unprecedented multi-state outbreaks in poultry and dairy farms , and human infections . Here, we discuss the current situation of this outbreak and emphasizes the need for pre-pandemic preparedness to control HPAI H5N1 in both poultry and dairy farms in the US. Source: npj Viruses,  https://www.nature.com/articles/s44298-025-00138-5 ____

Abstract H5N1 influenza outbreaks have been reported on more than 1,070 dairy farms across 17 states in the US . Damage to the mammary gland and high levels of virus in milk were common features of the infected cattle, but it is unclear how the virus initially invades the mammary glands, and no control strategy is currently available. Here, we found that cattle oral tissues support H5N1 virus binding and replication , and virus replicating in the mouth of cattle transmitted to the mammary glands of dairy cattle during sucking . We also found that an H5 inactivated vaccine or a hemagglutinin-based DNA vaccine induced sterilizing immunity in cows against challenges with different H5N1 viruses. Our study provides insights into H5N1 virus transmission and control in cattle. Source: National Science Review,  https://academic.oup.com/nsr/advance-article/doi/10.1093/nsr/nwaf262/8180392?searchresult=1 ____

Abstract The emergence of highly pathogenic avian influenza (HPAI) A(H5N1), clade 2.3.4.4b, genotype B3.13 in U.S. dairy cattle marks a significant shift in the virus' host range and epidemiological profile. Infected cattle typically exhibit mild clinical signs, such as reduced milk production, mastitis and fever, with morbidity generally below 20% and mortality averaging 2%. Transmission within farms is primarily driven by contaminated milk and milking procedures , while farm‐to‐farm spread is mainly linked to cattle movement and shared equipment . The virus demonstrates high replication in mammary glands , with infected cows shedding large quantities of virus in milk for up to 3 weeks, even in the absence of clinical signs. Shedding through other routes appears limited. Infected cattle develop virus‐specific antibodies within 7–10 days , offering short‐term protection, though the duration and robustness of immunity remain unclear. Between March 2024 and May 2025, the virus was co...

Simple Summary The present commentary deals with the pandemic risk brought about by the highly pathogenic avian influenza (HPAI) A(H5N1) virus . Such a pandemic alarm is justified, among others, by the progressively and rapidly expanding range of virus-susceptible hosts , including humans alongside a significant number of domestic and wild avian and mammalian species , several of which appear to be geographically and phylogenetically distant from each other. Despite its well-established zoonotic potential , no clear-cut evidence of a sustained and efficient HPAI A(H5N1) virus interhuman transmission has thus far been reported. Should this happen in a more or less near future, it could pave the way for a new pandemic. Based upon the above, a “ One Health, One Earth, One Ocean ”-focused, holistic approach would be the necessary prerequisite to deal in an appropriate way with the HPAI A(H5N1) virus-associated zoonotic and pandemic risk. Abstract The focus of this commentary is represented...

Abstract Highly pathogenic avian influenza virus (HPAIV) of H5 and H7 subtypes has emerged as one of the most important zoonotic pathogens in the 21st century with significant economic consequences . The recent outbreak of H5N1 avian influenza (AI) in dairy cattle highlighted the importance of early detection in managing and mitigating HPAIV outbreaks. A successful high-speed diagnostic response requires rapid site and specimen access, minimal time for test protocols, and prompt communication of the diagnostic results to government officials. A new diagnostic paradigm that consists of miniaturized extractor and qPCR instruments (EZextractor and EZcycler MiniQ), designed for mobile, on-site testing has been compared with a platform of benchtop instruments (QIAGEN RNeasy and QuantStudio 5) for detecting inactivated H5 avian influenza virus (AIV) spiked in raw milk samples. Two sets of experiments were performed: 1) 15 raw milk samples , obtained from 15 different farms, diluted with phos...

Abstract Highly pathogenic avian influenza (HPAI) viruses with H5 hemagglutinin (HA) genes (clade 2.3.4.4b) are causing an ongoing panzootic in wild birds . Circulation of these viruses is associated with spillover infections in multiple species of mammals , including a large, unprecedented outbreak in American dairy cattle . Before widespread on-farm testing, there was an unmet need for genomic surveillance. Infected cattle can shed high amounts of HPAI H5N1 viruses in milk , allowing detection in pasteurized retail dairy samples. Over a 2-month sampling period in one Midwestern city , we obtained dairy products processed in 20 different states. Here we demonstrate that a tiled-amplicon sequencing approach produced over 90% genome coverage at greater than 20x depth from 5 of 13 viral RNA positive samples, with higher viral copies corresponding to better sequencing success. The sequences clustered phylogenetically within the rest of the cattle outbreak sequences reported. A combination...

Abstract Highly pathogenic avian influenza virus (HPAIV) of H5 and H7 subtypes has emerged as one of the most important zoonotic pathogens in the 21st century with significant economic consequences. The recent outbreak of H5N1 avian influenza (AI) in dairy cattle highlighted the importance of early detection in managing and mitigating HPAIV outbreaks. A successful high-speed diagnostic response requires rapid site and specimen access, minimal time for test protocols, and prompt communication of the diagnostic results to government officials. A new diagnostic paradigm that consists of miniaturized extractor and qPCR instruments (EZextractor and EZcycler MiniQ), designed for mobile, on-site testing has been compared with a platform of benchtop instruments (QIAGEN RNeasy and QuantStudio 5) for detecting inactivated H5 avian influenza virus (AIV) spiked in raw milk samples. Two sets of experiments were performed: 1) 15 raw milk samples, obtained from 15 different farms, diluted with phosph...

Abstract The 2024 outbreak of highly pathogenic avian influenza virus (HPAIV) H5N1 in U.S. dairy cattle presented an unprecedented scenario where the virus infected bovine mammary glands and was detected in milk , raising serious concerns for public health and the dairy industry. Unlike previously described subclinical influenza A virus (IAV) infections in cattle, H5N1 infection induced severe clinical symptoms , including respiratory distress, mastitis, and abnormal milk production . To understand the host immune responses and changes, particularly in the mammary gland, we performed single-cell RNA sequencing analysis on bovine milk somatic cells (bMSCs) in vitro exposed to an H5N1 isolate from an infected dairy farm. We identified ten distinct cell clusters and observed a shift toward type-2 immune responses , characterized by T cells expressing IL13 and GATA3 , and three different subtypes of epithelial cells based on the expression of genes associated with milk production. Our stud...

Abstract We confirmed influenza A virus (IAV) by PCR in serum from 18 cows on 3 affected dairy farms in California, USA . Our findings indicate the presence of viremia and might help explain IAV transmission dynamics and shedding patterns in cows. An understanding of those dynamics could enable development of IAV mitigation strategies. Source: US Centers for Disease Control and Prevention,  https://wwwnc.cdc.gov/eid/article/31/7/25-0134_article ____

Abstract In late 2023, H5N1 high pathogenicity avian influenza (HPAIV) started circulating in dairy cattle in the USA . High viral titres were detected in milk from infected cows , raising concerns about onwards human infections . Although pasteurisation was shown to effectively inactivate influenza viruses in milk, unpasteurised milk still poses a risk of infection, both from occupational exposure in dairies and from the consumption of raw milk. We therefore assessed how long influenza viruses could remain infectious for in milk without heat inactivation. We examined the stability of a panel of influenza viruses in milk , including a contemporary H5N1 HPAIV and a variety of other influenza A and D viruses. We incubated viruses in cows' milk under laboratory conditions : at room temperature to simulate exposure in dairies and at 4°C to simulate exposure to refrigerated raw milk. Following an isolated report of H5N1 viral RNA being detected in milk from a sheep in the UK , we also c...

Abstract Since the first emergence of highly pathogenic avian influenza (HPAI) H5N1 viruses in dairy cattle , the virus has continued to spread, reaching at least 17 states and at least 950 dairy herds in the United States. Subsequently, spillovers of the virus from dairy cattle to humans have been reported. Pigs are an important reservoir in influenza ecology because they serve as a mixing vessel in which novel reassortant viruses with pandemic potential can be generated. Here, we show that oro-respiratory infection of pigs resulted in productive replication of a bovine-derived HPAI H5N1 B3.13 virus . Infectious virus was mainly identified in the lower respiratory tract of principal infected pigs, and sero-conversion was observed in most of the principal pigs at later time points, suggesting limited replication of the bovine-derived HPAI H5N1 B3.13 virus in pigs. In one animal, we detected the emergence of a mutation in hemagglutinin (HA) previously associated with increased affinity ...

ABSTRACT The recent emergence of the H5N1 influenza virus in dairy cattle has raised significant public health concerns . Using a previously established pseudovirus-based neutralization assay , we evaluated the impact of emerging hemagglutinin (HA) mutations on the efficacy of current candidate vaccine viruses (CVVs). Neutralization analysis revealed that the cow-derived H5N1 virus showed up to a 2.2-fold reduction in sensitivity compared to the CVV homologous neutralization titers. Among the 1,453 HA sequences analyzed from cow-derived H5N1 viruses, we identified four major mutations (E2K, D104G, V147M, and S336N) that emerged after the initial isolation, with 134 isolates (9.22%) harboring all four mutations . These multi-mutation variants exhibited up to a 3.3-fold reduction compared with the CVV homologous neutralization titers. Single-mutation analysis demonstrated that the D104G mutation , present in 47.8% of sequences, markedly contributed to antibody escape . Our findings highl...

Abstract Highly pathogenic avian influenza (HPAI) A(H5N1) virus emerged in lactating dairy cattle in March 2024, causing mastitis-related disease and infections in other farm animals and workers . Recent work identified α2,6 and α2,3-linked sialic acids (SA), which serve as influenza virus receptors, in the lactating bovine mammary gland ; however, their distribution across stages of mammary growth and development remains unknown. We compared the distribution of tissue sialylation in mammary glands of prepubertal dairy calves , pregnant dairy heifers , and lactating cows . Mammary glands at all physiological stages expressed both α2,6 SA, the preferred receptor linkage for human influenza viruses, and α2,3 SA, the preferred receptor linkage for avian influenza viruses. Importantly, mammary glands of pregnant dairy heifers exhibited the highest overall expression of α2,3 SA, observed in both tissue and alveolar lumens. Our results suggest that pregnant dairy heifers, like lactating dair...

Abstract In February 2024, H5N1 highly pathogenic avian influenza viruses (HPAIVs) of clade 2.3.4.4b were first reported in dairy cows in the USA. Subsequent multiple outbreaks on dairy farms and sporadic human infections have raised substantial public health concerns . In the same year, four H5N1 HPAIVs of clade 2.3.4.4b were isolated from ducks and geese in live poultry markets (LPMs) spanning seven provinces in China . Evolutionary analysis demonstrated that these viruses had undergone two genetic reassortments with H5 influenza viruses from wild birds in different countries. Except for 565/H5N1, the other three viruses exhibited over 99% genetic homology with avian-origin H5N1 HPAIVs from South Korea and Japan . Notably, 571/H5N1 demonstrated high replication efficiency in bovine-derived cells , particularly in bovine mammary epithelial (MAC-T) cells, and caused 16.7% (1/6) mortality in mice at a dose of 10⁵ EID₅₀/50 μL, indicating its zoonotic potential . Given the potential cross...

ABSTRACT Since 2020, the clade 2.3.4.4b highly pathogenic avian influenza (HPAI) H5N1 viruses have caused unprecedented outbreaks in wild birds and domestic poultry globally , resulting in significant ecological damage and economic losses due to the disease and enforced stamp-out control. In addition to the avian hosts, the H5N1 viruses have expanded their host range to infect many mammalian species , potentially increasing the zoonotic risk . Here, we review the current knowns and unknowns of clade 2.3.4.4b HPAI H5N1 viruses, and we highlight common challenges in prevention. By integrating our knowledge of viral evolution and ecology, we aim to identify discrepancies and knowledge gaps for a more comprehensive understanding of the virus. Ultimately, this review will serve as a theoretical foundation for researchers involved in related avian influenza virus studies, aiding in improved control and prevention of H5N1 viruses. Source: Journal of Virology,  https://journals.asm.org/doi...

Abstract Background .  Influenza A virus (IAV) is a major cause of morbidity and mortality globally , causing seasonal influenza in humans and infecting birds and some mammals. In 2024, IAV H5N1 highly pathogenic avian influenza (HPAI) in the United States moved into cattle. While the outbreak is currently of low risk to the general public, there is an urgent need to monitor the disease and prevent spread.  Methods .  We conducted a nationwide study evaluating the relationship between H5 hemagglutinin gene RNA concentrations in wastewater and reported outbreaks of IAV H5N1 in animals and humans . We utilized an H5-specific droplet digital RT-PCR test to quantify H5 RNA in wastewater in 40 states across the United States, and 1) examined the temporal association between outbreaks and wastewater detections and 2) utilized linear mixed models (LMM) to determine the relationship between measurements in wastewater and outbreak-related factors in the local area.  Results ....

Abstract Influenza A(H5N1) viruses have been detected in US dairy cow herds since 2024 . We assessed the pathogenesis, transmission, and airborne release of A/Michigan/90/2024, an H5N1 isolate from a dairy farm worker in Michigan , in the ferret model. Results show this virus caused airborne transmission with moderate pathogenicity , including limited extrapulmonary spread , without lethality. Highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b viruses have displayed unprecedented global spread among wild birds leading to numerous spillover infections in mammalian species. Of note, outbreaks in dairy cattle and gallinaceous birds have resulted in human infections in the United States during 2024–2025 (1). Increased frequency of H5N1 viruses crossing species barriers has caused concern that the avian influenza viruses are adapting to mammals . A critical component of influenza pandemic preparedness is early identification of emerging novel influenza viruses that cause disease and t...