#Surveillance on #California dairy #farms reveals multiple possible sources of #H5N1 #influenza virus #transmission

 

Abstract

Transmission routes of highly pathogenic H5N1 between cows or to humans remain unclear due to limited data from affected dairy farms. We performed air, farm wastewater, and milk sampling on 14 H5N1-positive dairy farms across two different California regions. Infectious virus was detected in the air in milking parlors and in wastewater streams, while viral RNA was found in exhaled breath of cows. Sequence analysis of infectious H5N1 virus from air and wastewater samples on one farm revealed viral variants relevant for potential human susceptibility. Longitudinal analysis of milk from the individual quarters of cows revealed a high prevalence of subclinical H5N1-positive cows. Additionally, a heterogeneous distribution of infected quarters that maintained a consistent pattern over time was observed, inconsistent with shared milking equipment serving as the sole transmission mode. The presence of subclinically infected cows was further supported by detection of antibodies in the milk of animals that exhibited no clinical signs during the H5N1 outbreak on one farm. Our data highlight additional sources and potential modes of H5N1 transmission on dairy farms.

Source: 

Link: https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3003761

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Respirable #Aerosol #Production and Reduction of Avian #Influenza #Transmission #Risk during #Chicken Processing, #Bangladesh

 

Abstract

In Bangladesh, influenza A(H5N1) viruses are endemic in poultry. Processing infected chickens can aerosolize viruses, increasing the risk for human infections. We evaluated particulate matter (PM2.5) mass concentration during slaughtering and defeathering methods used in live bird markets in Bangladesh to identify solutions to reduce aerosol exposure. We slaughtered 675 chickens using cones and barrels with 3 lid types and defeathered 45 chickens using a defeathering machine with 5 lid types. We interviewed 3 slaughterers to understand method preference. For slaughtering, barrels with a solid or star-cut lid reduced PM2.5 mass concentrations by 65%–73% compared with uncovered barrels. For defeathering, machines fully covered by a solid lid or lid with a hole and pivot door reduced PM2.5 mass concentrations by 50% compared with machines with no lid. Slaughterers preferred barrels covered with solid lids and defeathering machines covered with solid or hinged lids. Those methods might reduce aerosol exposure during poultry processing.

Source: 

Link: https://wwwnc.cdc.gov/eid/article/32/4/25-1878_article

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#Genetic and #biological characterization of a #duck-origin clade 2.3.4.4b #H5N6 avian #influenza virus reveals partial #mammalian #adaptation

 

Highlights

• Duck-origin H5N6 virus A/Duck/Jiangsu/628/2022 shares high homology with the human strain A/Yangzhou/125/2022.

• The 628 strain shows mammalian adaptation markers: HA mutations enhance human receptors affinity and NA mutations reduce sensitivity to neuraminidase inhibitors.

• Limited airborne transmission but detectable droplet-mediated spread suggests increased mammalian transmission risk.

Abstract

Clade 2.3.4.4b H5Nx highly pathogenic avian influenza viruses (HPAIVs) have caused extensive outbreaks in poultry worldwide. H5 HPAIVs have caused sporadic but severe human infections in China, representing a persistent zoonotic threat. Here, we identified a duck-origin H5N6 HPAIV (A/Duck/Jiangsu/628/2022) through routine surveillance and assessed its biological characteristics and mammalian pathogenesis. Phylogenetic analysis revealed > 98% nucleotide identity between strain 628 and the concurrent human H5N6 strain A/Yangzhou/125/2022. Molecular characterization identified multiple mammalian adaptation markers: hemagglutinin substitutions (S137A, T160A, T192I) associated with enhanced human receptor binding; neuraminidase mutations (I117T, D198N) linked to reduced neuraminidase inhibitor susceptibility; and polymerase complex changes (PB1-D622G, PA-K142Q) conferring increased mammalian cell replication. In vitro studies demonstrated that 628 virus replicated more efficiently in mammalian than in avian cells and exhibited dual receptor-binding specificity. Mouse pathogenicity assays revealed moderate virulence with progressive lung pathology. Critically, transmission experiments confirmed both direct contact and airborne transmission capabilities of 628 in guinea pigs. These findings demonstrate that circulating H5N6 viruses have acquired partial mammalian adaptation while retaining avian fitness, significantly elevating pandemic potential. Enhanced surveillance of wild bird populations, poultry farms, and live poultry markets is urgently needed to develop effective prevention and control strategies.

Source: 

Link: https://www.sciencedirect.com/science/article/abs/pii/S037811352600146X?via%3Dihub

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#Immunity to #hemagglutinin and #neuraminidase results in additive reductions in #airborne #transmission of #influenza #H1N1 virus in #ferrets

 

Abstract

Currently, there is limited knowledge on the impact of immunity to hemagglutinin (HA) and/or neuraminidase (NA) on the transmission of influenza viruses. Therefore, using intramuscular vaccination, intranasal vaccination, or infection with reassortant viruses, we induced immunity to each antigen alone or both antigens combined in ferrets. We then assessed transmission of the 2009 pandemic H1N1 virus from these ferrets to naïve respiratory contacts. For all strategies used to induce immunity, combined immunity to HA and NA resulted in the largest reductions in transmission. Moreover, immunity to HA and NA conferred additive rather than synergistic reductions in transmission. No escape variants emerged in our transmission studies, and logistical regression showed that the probability of transmission was less than 50% when viral titers in donors were reduced to 101.5 and 102 median tissue culture infectious dose per ml on days 1 and 3 postinfection, respectively. These studies define the relationship between immunity to HA and NA on transmission and identify a threshold titer indicative of decreased transmission in ferrets.

Source: 

Link: https://www.science.org/doi/10.1126/sciadv.aea8719

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Increased contact #transmission of contemporary #Human #H5N1 compared to #Bovine and Mountain #Lion H5N1 in a hamster #model

 

Abstract

The ongoing outbreak of highly pathogenic avian influenza virus (HPAIV) subtype H5N1 in the U.S. poses a significant public health threat. To date, 70 human cases have been confirmed in the United States, including two severe cases and one fatality. While suitable animal models are crucial for predicting the potential pandemic risk of newly emerging pathogens in humans, studies investigating contemporary HPAIV H5N1 transmission dynamics remain limited. Here, we investigate the pathogenicity and transmission efficiency of recent clade 2.3.4.4b H5N1 viruses isolated from a bovine, mountain lion, and a human case using Syrian hamsters. Intranasal inoculation results in productive virus replication in the respiratory tract and shedding for all three isolates. Transmission studies demonstrate limited efficiency via direct contact and airborne routes for all isolates. Although overall transmission is inefficient, the human H5N1 isolate demonstrates relatively greater contact transmissibility than the bovine and mountain lion isolates. Taken together, our findings demonstrate that the Syrian hamster model complements existing animal models for influenza A virus research and expands the resources available for investigating the pathogenicity, transmissibility, and efficacy of countermeasures against HPAIV H5N1.

Source: 

Link: https://www.nature.com/articles/s41467-026-68900-8

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Defining the transmissible dose 50% for two #pandemic #influenza viruses in #ferrets

 

ABSTRACT

Ferrets are widely used to model airborne transmission of influenza viruses in humans. Airborne transmission is evaluated by infecting donor ferrets with a high virus dose and monitoring transmission to contact animals sharing the same airspace. Humans can be infected with a broad range of influenza virus doses. Therefore, we evaluated the relationship between inoculation dose and transmission for two pandemic influenza viruses in ferrets. Donor ferrets were inoculated with 100 to 106 tissue culture infectious dose 50 (TCID50) of the 2009 pandemic H1N1 or 1968 pandemic H3N2 virus and were then paired with respiratory contacts. Using the proportion of donors that became infected across virus doses, we calculated the infectious dose 50 (ID50). Subsequently, by comparing the proportion of contacts that became infected, we calculated the transmissible dose 50% (TD50): the donor inoculation dose that resulted in transmission to 50% of contacts. For the 2009 pandemic H1N1 virus, the ID50 and TD50 were equivalent at <1 TCID50. However, for the 1968 pandemic H3N2 virus, the ID50 and TD50 were 100.5 and 104.08 TCID50 (95% CI: 102.34–105.82), respectively. The increased TD50 for the H3N2 virus was associated with significant reductions in peak viral titers and viral shedding in donors over decreasing virus inoculation doses. Collectively, these studies define a new measure of transmission that permits comparisons of transmissibility between viral strains and subtypes in ferrets. We show that the 1968 pandemic H3N2 virus has a higher TD50 and reduced transmissibility in ferrets relative to the 2009 pandemic H1N1 virus.

Source: 

Link: https://journals.asm.org/doi/full/10.1128/jvi.01635-25?af=R

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Advancing #H5N1 #influenza #risk #assessment in #ferrets through comparative evaluation of airborne virus shedding patterns

 

Abstract

Recent A(H5N1) zoonotic cases linked to poultry and cattle in North America highlight the urgent need to assess the pandemic potential of emerging strains. Using male ferrets, we evaluate two B3.13 and two D1.1 genotype A(H5N1) viruses isolated from humans and observe fatal disease and varying capacities for direct contact transmission. To enhance pandemic risk assessment, we conduct aerosol sampling using cyclone BC251 and water condensation capture-based SPOT samplers and perform comparative analyses to include additional A(H5N1), A(H9N2), A(H7N9), and A(H1N1)pdm09 strains with known transmissibility profiles. Although none of the A(H5N1) strains transmit via the air, B3.13 viruses are detected at significantly higher levels compared to D1.1 strains. Here we show strong correlations between viral loads in nasal washes, airborne virus shedding, and transmissibility in ferrets, highlighting the value of these metrics for identifying zoonotic influenza viruses that may be adapting toward increased transmission potential.

Source: 

Link: https://www.nature.com/articles/s41467-026-68931-1

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