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Abstract Educational farms provide students with hands-on experience in agricultural and animal practices . However, the close contact between humans and farm animals creates a significant interface for zoonotic disease transmission , yet research on infectious diseases in such settings remains limited. This study investigates the ongoing spillovers of human-origin influenza A virus (IAV) into swine at an educational farm in central Chile , describing IAV prevalence, outbreak dynamics, and the genomic characterization of detected strains. The Menesianos educational farm, located in Melipilla, central Chile, houses approximately 40 swine alongside other domestic animals , such as horses and cows . As part of an active IAV surveillance project, monthly nasal swab samples were collected from pigs between June 2019 and September 2023 for IAV detection via RT-qPCR targeting the M gene, with positive samples subsequently sequenced. During the study period, monthly IAV prevalence ranged from ...

ABSTRACT The highly pathogenic avian influenza virus A(H5N1) clade 2.3.4.4b has caused a human outbreak in North America since March 2024. Here, we conducted a serosurveillance study to determine the risk of A(H5N1) clade 2.3.4.4b (2024 cattle H5N1) to general population. In the initial screening of 180 serum specimens encompassing all age groups, 2.2% (4/180) had detectable neutralizing antibody (nAb) titers against reverse genetics-derived 2024 cattle H5N1, with all collected from older adults aged ≥60 years old. Further screening showed that 4.2% (19/450) of adults aged ≥60 years old had detectable nAb titers against the 2024 cattle H5N1 . 80% (4/5) serum specimens with nAb titer of ≥40 had detectable HI titer, and there was a positive correlation between nAb titer and HA binding (r = 0.3325, 95% confidence interval 0.2477 to 0.4123; P < 0.0001). The nAb titer against seasonal H1N1 virus was 4.2-fold higher for ≥60 years old individuals with detectable H5N1 nAb titer than those ≥...

Abstract Influenza A virus poses significant public health challenges , causing seasonal outbreaks and pandemics. Its rapid evolution motivates continuous monitoring of circulating influenza genomes to inform vaccine and antiviral development. Wastewater-based surveillance offers an unbiased, cost-effective approach for genomic surveillance. We developed a novel tiling amplicon primer panel that covers diversity of influenza A virus, targeting segments of the surface proteins HA, NA, and M of subtypes H1N1 and H3N2. Using this panel, we sequenced nucleic acid extracts from 59 Swiss wastewater samples collected at four locations during the 2022/2023 and 2023/2024 winter seasons. We found that wastewater-based abundance estimates of the dominant H1N1 clades correlated with clinical-based estimates in the 2023/2024 season. Furthermore, wastewater-based sequencing revealed mutations in vaccine and drug target sites , consistent with clinical data. Overall, we demonstrate the effectiveness ...

Highlights •  Impact of genetic evolution in influenza A(H1N1)pdm09 on subtyping assay performance. •  Influenza A subtyping assays are susceptible to primer- or probe-binding mismatches. •  Subclades 6B.1 A.5a.2a.1 and 6B.1 A.5a.2a harbour mutations that caused subtyping failures in some specimens. •  Sequencing confirmed all specimens were H1N1pdm09, within recognized subclades. Abstract Background During the 2023–2024 and early 2024–2025 influenza seasons , several influenza A-positive specimens in our laboratory failed subtyping for H1 , H1pdm09, and H3 using the Allplex Respiratory Panel 1 (Allplex RP1) (Seegene Inc.). This study aimed to identify the cause of these subtyping failures. Materials and Methods Between August 2023 and December 2024 , 23 nasopharyngeal specimens tested positive for influenza A but were unsubtypeable for H1, H1pdm09, and H3. Confirmatory testing by the manufacturer included target-specific PCR for the M and HA genes, followed by seque...

Abstract Influenza A(H1N1)pdm09 virus carrying an I38N substitution was detected in an untreated teenager in Japan . The I38N mutant virus exhibited reduced susceptibility to baloxavir but remained susceptible to neuraminidase inhibitors and showed reduced growth capability . Monitoring antiviral drug susceptibility of influenza viruses is necessary to aid public health planning and clinical recommendations. Source: US Centers for Disease Control and Prevention,  https://wwwnc.cdc.gov/eid/article/31/5/24-1123_article ____

Abstract The unprecedented 2.3.4.4b A(H5N1) outbreak in dairy cattle, poultry, and spillover to humans in the United States (US) poses a major public health threat . Population immunity is a critical component of influenza pandemic risk assessment. We conducted a comprehensive assessment of the population immunity to 2.3.4.4b A(H5N1) viruses and analyzed 1794 sera from 723 people (0.5-88 yrs) in multiple US geographic regions during 2021-2024. Low pre-existing neutralizing and hemagglutinin (HA) head binding antibodies and substantial cross reactive binding antibodies to N1 neuraminidase (NA) of 2.3.4.4b A(H5N1) were detected in US population. Antibodies to group 1 HA stalk were also prevalent with an age-related pattern. A( H1N1 )pdm09 infection and influenza vaccination did not induce neutralizing antibodies but induced significant rise of NA inhibition (NAI) antibodies to N1 of 2.3.4.4b A(H5N1), and group 1 HA stalk antibodies. Understanding population susceptibility to novel influe...

ABSTRACT Unexpected outbreaks caused by the H5N1 highly pathogenic avian influenza virus (HPAIV) in dairy cows in the United States (US) have raised significant veterinary and public health concerns . When and how the H5N1 HPAIV was introduced into dairy cows and the broader epidemiology of influenza A virus (IAV) infections in cattle in the US remain unclear. Herein, we performed a retrospective study to screen more than 1,700 cattle serum samples collected from different bovine breeds in the US from January 2023 to May 2024 using an enzyme-linked immunosorbent assay (ELISA) targeting the nucleoprotein (NP) to detect IAV infections, and the positive samples were further tested by hemagglutination inhibition (HI) assay . Results showed that 586 of 1,724 samples (33.99%) from 15 US states were seropositive by the NP ELISA assay , including 78 samples collected in 2024 and 508 samples collected in 2023 . Moreover, the HI assay revealed that 45 of these ELISA-positive samples were positiv...

Abstract In the past two decades, two pandemic respiratory viruses (H1N1 and SARS-CoV-2) have emerged via spillover from animal reservoirs . In an effort to avert future pandemics, surveillance studies aimed at identifying zoonotic viruses at high risk of spilling over into humans act to monitor the `viral chatter' at the animal-human interface . These studies are hampered, however, by the diversity of zoonotic viruses and the limited tools available to assess pandemic risk. Methods currently in use include the characterization of candidate viruses using in vitro laboratory assays and experimental transmission studies in animal models . However, transmission experiments yield relatively low-resolution outputs that are not immediately translatable to projections of viral dynamics at the level of a host population. To address this gap, we present an analytical framework to extend the use of measurements from experimental transmission studies to generate more quantitative risk assessm...

Abstract Objective :  To analyze the epidemiological, etiological and genetic characteristics of influenza virus in Shandong Province during 2023-2024.  Methods :  The surveillance data of influenza-like illness (ILI) in sentinel hospitals in Shandong from 2023 to 2024 were collected and analyzed. The isolated influenza strains with hemagglutination titers ≥8 were selected for antigenicity analysis , drug susceptibility test, gene sequencing and evolutionary analysis .  Results :  From 2023 to 2024, the positive rate of influenza virus in Shandong was 8.51% (23 663/277 995), the highest positive rate was in the age group of 5-14 years (15.78%, 6 073/38 478), and the highest positive rate was in the 49th week (35.86%, 2 264/6 313). Both antigenicity analysis and evolutionary analysis showed that the A(H1N1)pdm09 subtype and B(Victoria) strain had good matching effect and close evolutionary distance with the 2023-2024 surveillance year vaccine strain. The A(H3N2) ...

{Excerpts} Recent updates Laboratory CDC completed serology testing on blood specimens from close contacts of a child with mild illness in San Francisco who was confirmed to be positive for avian influenza A(H5N1) virus, though, there were no known animal exposures associated with that case.  -- Serology testing was conducted to look for antibodies to influenza A(H5N1) virus in this child, which would indicate recent infection.  -- The child's blood was tested and found to have antibodies to avian influenza A(H5N1) virus.  -- None of the close contacts of the case in San Francisco who were tested had antibodies to avian influenza A(H5N1) virus, which supports the conclusion that none of these close contacts were infected , and that no person-to-person spread occurred among these close contacts.  -- These findings are reassuring. To date, human-to-human transmission of influenza A(H5) virus has not been identified in the United States. CDC has sequenced the virus from...

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 (106 infectious units) and monitoring transmission to contact animals sharing the same airspace . However, humans can be infected with a broad range of influenza virus doses. Therefore, we evaluated the relationship between virus 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 H3N2 pandemic 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 respiratory contacts that became infected, we calculated the transmissible dose 50% (TD50): the donor inoculation dose that resulted in transmission to ...

Abstract Reports of human infections with an influenza A(H5N1) clade 2.3.4.4b virus associated with outbreaks in dairy cows in the United States underscore the need to assess the potential cross-protection conferred by existing influenza immunity . We serologically evaluated ferrets previously infected with an influenza A(H1N1)pdm09 virus for cross-reactive antibodies and then challenged 3 months later with either highly pathogenic H5N1 clade 2.3.4.4b or low pathogenicity H7N9 virus . Our results showed that prior influenza A(H1N1)pdm09 virus infection more effectively reduced the replication and transmission of the H5N1 virus than did the H7N9 virus, a finding supported by the presence of group 1 hemagglutinin stalk and N1 neuraminidase antibodies in preimmune ferrets. Our findings suggest that prior influenza A(H1N1)pdm09 virus infection may confer some level of protection against influenza A(H5N1) clade 2.3.4.4.b virus. Source: US Centers for Disease Control and Prevention,  htt...

Abstract The emergence of highly pathogenic avian influenza A(H5N1) virus in dairy cattle herds across the United States in 2024 caused several human infections . Understanding the risk for spillover infections into humans is crucial for protecting public health. We investigated whether immunity from influenza A(H1N1)pdm09 (pH1N1) virus would provide protection from death and severe clinical disease among ferrets intranasally infected with H5N1 virus from dairy cows from the 2024 outbreak. We observed differential tissue tropism among pH1N1-immune ferrets. pH1N1-immune ferrets also had little H5N1 viral dissemination to organs outside the respiratory tract and much less H5N1 virus in nasal secretions and the respiratory tract than naive ferrets. In addition, ferrets with pH1N1 immunity produced antibodies that cross-reacted with H5N1 neuraminidase protein. Taken together, our results suggest that humans with immunity to human seasonal influenza viruses may experience milder disease fro...

Abstract In 2018, a single detection of a novel reassortant swine influenza A virus (swIAV) was made in Denmark . The hemagglutinin (HA) of the virus was from the H1N1 pandemic 2009 (H1N1pdm09) lineage and the neuraminidase (NA) from the H1N1 Eurasian avian-like swine lineage (H1N1av). By 2022, the novel reassortant virus (H1pdm09N1av) constituted 27% of swIAVs identified through the Danish passive swIAV surveillance program . Sequencing detected two H1pdm09N1av genotypes; Genotype 1 contained an entire internal gene cassette of H1N1pdm09 origin, Genotype 2 differed by carrying an NS gene segment of H1N1av origin . The internal gene cassette of Genotype 2 became increasingly dominant, not only in the H1pdm09N1av population, but also in other Danish enzootic swIAV subtypes. Phylogenetic analysis of the HA genes from H1pdm09N1av viruses revealed a monophyletic source , a higher substitution rate compared to other H1N1pdm09 viruses and genetic differences with human seasonal and other swi...

Abstract Influenza A viruses (IAV) are likely candidates for pandemics . This report summarizes the results of the Swiss national program for surveillance of influenza viruses in pigs and transmissions to humans between 2010 and 2022. Challenges and optimization options in the program are discussed. Nasal swabs or lung tissue samples from pigs with influenza-like signs (e.g. fever, cough) were screened by real-time RT-PCR for swine influenza virus (SIV) genomes, including that of the 2009 pandemic strain A(H1N1)pdm09; positive samples were subtyped for H1, N1, H3 and N2 by RT-PCR and Sanger sequencing. In parallel, humans with influenza-like symptoms and recent contact to diseased pigs were asked to self-sample themselves with a nasal swab. Human swabs were tested for IAV and positive swabs further subtyped to identify potential cross-species transmission between swine and humans. In the pigs, SIV was detected in 375 of 674 farm visits . H1N1 is the only subtype detected in Swiss pigs ...

Abstract Pigs serve as a mixing vessel for influenza viruses and can independently promote the emergence of pandemic strains in humans. During our surveillance of pig populations from 2021 to 2023 in China , 11 H1 subtype swine influenza viruses (SIVs) were isolated. All viruses were reassortants , possessing internal genes of identical origins ( PB2, PB1, PA, NP, M : pdm09/H1N1 origin, NS : North American triple reassortant origin). The H1N1 isolates were all the dominant G4 EA H1N1 viruses in China. Two H1N2 isolates carried early human pdm09/H1N1 HA genes, suggesting a possible pig-to-human transmission route. Mutations that dictate host range specificity were identified in all isolates, a phenomenon which may enhance the affinity to human receptors. These H1 subtype viruses effectively replicated both in vivo and in vitro without prior adaptation and exhibited different pathogenicity and growth characteristics. Some of the H1 viruses were even found to cause lethal infections in mi...

Abstract Influenza A virus (IAV) continuously threatens animal and public health globally , with swine serving as a crucial reservoir for viral reassortment and evolution . In Chile , H1N2 and H3N2 subtypes were introduced in the swine population before the H1N1 2009 pandemic, and the H1N1 was introduced from the H1N1pdm09 by successive reverse zoonotic events . Here, we report two novel introductions of IAV H3N2 human-origin in Chilean swine during 2023. Our study reveals a closer relationship between recent human seasonal H3N2 and novel swine strains. Interestingly, one strain maintains all the genes from the original human virus , but the other strain is already a reassortment of human H3N2 and an H1N2 previously observed on the farm. Observing global IAV sequences, a similar pattern was identified in the USA confirming the reverse zoonotic potential of current seasonal human H3N2 strains. These results highlight the importance of ongoing surveillance and reinforcing biosecurity in ...

Abstract Zoonotic infections (swine-human) caused by influenza A viruses (IAVs) have been reported and linked to close contact between these species . Here, we describe eight human IAV variant infections ( 6 mild and 2 severe cases , including 1 death ) detected in Paraná, Brazil , during 2020–2023. Genomes recovered were closely related to Brazilian swIAVs of three major lineages (1 A.3.3.2/ pdm09, 1B/human-like, and H3.1990.5), including three H1N1v, two H1N2v, two H3N2v and one H1v. Five H1v were closely related to pdm09 lineage , one H1v ( H1N2v ) grouped within 1B.2.3 clade, and the two H3v grouped within a clade composed exclusively of Brazilian H3 swIAV (clade H3.1990.5.1). Internal gene segments were closely related to H1N1pdm09 isolated from pigs . IAV variant rarely result in sustained transmission between people, however the potential to develop such ability is of concern and must not be underestimated. This study brings into focus the need for continuous influenza surveilla...

 {Summary} Swine influenza virus (SIV) is a highly contagious pathogen that poses significant economic challenges to the swine industry and carries zoonotic potential , underscoring the need for vigilant surveillance. In this study, we performed a comprehensive genetic and molecular analysis of H3N2 SIV isolates obtained from 372 swine samples collected in Shandong Province, China . Phylogenetic analysis revealed two distinct genotypes . The surface genes of both genotypes clustered with the human-like H3N2 lineage , while the internal genes of one genotype clustered with the 2009 pandemic H1N1 (pdm/09) lineage . In the second genotype, the NS gene clustered with the classical swine (CS) H1N1 lineage , while the remaining internal genes clustered with pdm/09, suggesting stable integration of pdm/09 gene segments into H3N2 SIV. Homology analysis showed over 96% genetic similarity between the isolates and reference strains from China and Brazil , suggesting potential transmission thr...

{Excerpts} 27 December 2024 Situation at a glance This is an update to the Disease Outbreak News on Undiagnosed disease in the Democratic Republic of the Congo published on 8 December 2024 (now named acute respiratory infections complicated by malaria).  It includes updated epidemiological investigation information and preliminary laboratory results.  On 29 November, an alert was raised by local health zone authorities of Panzi health zone in Kwango province after an increase in deaths , particularly among children under five years of age , following febrile illness .  Enhanced epidemiological surveillance was rapidly implemented, which in the absence of a clear diagnosis was based on the detection of syndromic cases of febrile illnesses with cough, body weakness, with one of a number of other symptoms compatible with acute respiratory and febrile illnesses.  This resulted in a rapid increase in the number of cases meeting the definition, with a total of 891 cases re...