Hannah J. Cochran

Introduction: In the USA, zoonotic influenza A virus (IAV) transmission occurs frequently in youth who exhibit swine at agricultural competitions, presenting an ongoing pandemic risk. However, active surveillance in this high‐risk human population is lacking. Methods: To address this gap, we enrolled 711 youth participants at nine swine exhibitions during 2019–2021 and collected 700 nasal swabs and 400 serum samples. We assessed the neutralizing antibody titers of enrollees against eight influenza A H1 and H3 variant candidate vaccine viruses (CVVs) recommended by the World Health Organization. Results: We found that the highest neutralizing titers are not necessarily associated with the specific viruses which are most prevalent in exhibition swine during the same time period. The geometric mean titers of the cohort were low against the Cluster IV‐A (clade 3.1990.4.a) CVV, which we determined to be the most prevalent HA lineage circulating in exhibition swine during 2020–2021 based on simultaneous IAV surveillance in swine ( n = 430 genome sequences). Conclusions: The relatively low neutralizing antibody levels in this high‐risk population with intense exposure to livestock indicates that sustained outreach and monitoring is needed. Continued monitoring of IAVs in both swine and humans can inform viral risk assessments and provide considerations for candidate vaccine virus selection.

Since 2024, highly pathogenic influenza A(H5N1) viruses have spread extensively among U.S. dairy cattle, where they replicate efficiently in the mammary gland and are shed at high titers in milk. To directly assess susceptibility of commercial swine populations to bovine-derived H5N1 virus, lactating sows with prior influenza virus vaccination histories representative of U.S. commercial swine production systems were inoculated via the intramammary route and co-housed with their 1-week-old piglets to evaluate disease outcomes, viral replication, and potential for vertical transmission. Intramammary inoculation of lactating sows resulted in sustained viral RNA shedding in milk, while piglets exhibited sporadic oral viral RNA positivity that mirrored viral kinetics in milk. Lesions in mammary tissue and viral antigen staining, as well as development of neutralizing antibody responses and changes in milk color and consistency, further confirmed infection in the sows. Despite these molecular findings, none of the animals developed overt clinical disease, and respiratory involvement was not noted during the study period. Collectively, we demonstrate that intramammary exposure results in productive influenza A(H5N1) virus infection in lactating sows despite their vaccination histories, indicating the potential threat of viral spillover into commercial swine populations. The clinically inapparent nature of infection presents a risk of subclinical spread and underscores the importance of expanding viral surveillance to swine.

Highly pathogenic avian influenza A(H5N1) virus exhibits a strong tropism for the bovine mammary gland, challenging our understanding of influenza A virus host range and tissue specificity. We performed experimental studies with an influenza A(H5N1) B3.13 genotype virus in female lactating dairy cattle to define the infectious dose, routes of exposure, and factors linked to morbidity and mortality. Here, we demonstrate that intramammary inoculation with as few as 10 TCID₅₀ establishes a robust infection and shedding of high-titer virus in milk. Despite this low infectious dose, H5N1 does not readily transmit via contaminated milking equipment and close contact with infected animals. High-dose intramammary exposure results in severe disease and mortality, while respiratory and oral exposures are less likely to establish productive infection and associated morbidity. This study challenges current hypotheses of H5N1 transmission on dairy farms, raising important questions about potential agent, host, or environmental cofactors contributing to viral spread.

Ongoing transmission of influenza A virus (H5N1) in U.S. dairy cattle threatens both animal and human health, underscoring the need to understand the durability of host immunity against reinfection with evolving genotypes. We challenged naive and convalescent cows, infected one year prior with H5N1 genotype B3.13, with either homologous B3.13 or heterologous D1.1 genotype virus. Homologous rechallenge resulted in complete clinical protection with no infectious viral shedding. Conversely, heterologous rechallenge led to transient clinical disease and limited infectious viral shedding. Convalescent cows experienced significantly milder disease than naive cows, which developed severe illness with high viral shedding and required early euthanasia, regardless of the strain. These findings indicate that naturally acquired immunity offers strong protection against severe illness but may allow silent transmission of divergent strains. Therefore, natural herd immunity alone is unlikely to eliminate the virus; controlling H5N1 in cattle will likely require vaccination strategies that address viral evolution.

The discovery that highly pathogenic avian influenza A(H5N1) virus exhibits a strong tropism for the bovine mammary gland1–4 represents a major shift in our understanding of influenza A virus host range and tissue specificity. We conducted a comprehensive series of experimental studies with influenza A(H5N1) B3.13 genotype in lactating dairy cattle to address several key questions related to the viral dose required to establish infection, routes of exposure that lead to transmission, and factors contributing to the morbidity and mortality observed on farms. We demonstrate that intramammary exposure to as few as 10 TCID50 is sufficient to establish robust infection, shedding of high viral titers in milk, and clinical mastitis. Despite evidence of such a low infectious dose, we were unable to recapitulate transmission to sentinel cows via contaminated milking equipment and close contact with infected animals under experimental conditions. High-dose intramammary exposure to influenza A(H5N1) drives severe clinical outcomes and mortality observed in dairy cows on-farm, while respiratory and oral exposure are less likely to establish productive infection and associated morbidity. This study challenges current hypotheses of influenza A(H5N1) transmission on dairy farms5,6, raising important questions about potential agent, host, or environmental cofactors that contribute to the spread of the virus.

Cull cows represent a significant percentage of revenue received from the U.S. beef industry; however, cull cows are heavily price discounted at time of slaughter. This experiment’s objective is to evaluate different feeding strategies and their effects on body condition score, subcutaneous fat color, and carcass yield and quality traits in cull cows. The central hypothesis is feeding a high energy diet, with low levels of vitamin A, for 56 d will improve animal performance, carcass yield, and quality traits in addition to capturing the point (rate) of the conversion of yellow to white subcutaneous fat. In the present experiment 98 Angus crossbreed cows were utilized. Cows were fed either low vitamin A diet (LVA) consisting of whole shelled corn, soybean hulls, soybean meal, and a mineral-vitamin supplement or high vitamin A (HVA) diet, formulated using whole shelled corn, fescue hay, dry distiller grains with soluble, and a mineral-vitamin supplement for 56 d. During the 56 d feeding period, body weights and condition scores, and subcutaneous adipose samples were collected every 14 d. On d 56, cattle were slaughtered; 48 h postmortem carcass characteristics and objective color scores (subcutaneous adipose tissue) were recorded and a sample of the longissimus dorsi lumborum was collected. Subcutaneous adipose tissue samples were utilized to record subjective color scores and then ground to be analyzed for β-carotene concentration. The longissimus dorsi lumborum samples (2.54 cm slices) were removed for warner-bratzler shear force (WBSF) and pH testing. Data was analyzed using MIXED procedure of SAS. Feeding cull cows LVA resulted in differences in subcutaneous carcass fat color (P = 0.01) as well as b* values (P < 0.01) on d 56 compared with HVA. Subjective fat color scores were not different (P > 0.10) on d 0 or 14 but were different (P ≤ 0.05) on d 28, 42, and 56. Additionally, 9-cis-β-carotene concentration on d 56 were different (P = 0.05) between treatments. A trend was noticed for all-trans-β-carotene concentration (P = 0.10) on d 56 as well. Cull cow body weights were greater (P ≤ 0.04) when fed the LVA diet starting on d 14, 28, and 42; and a trend was noticed on d 56 (P = 0.09). Overall, cows fed the LVA treatment for 56 d exhibited decreased adipose yellowness and β-carotene concentrations as well as increased live weights.

African swine fever is a high-consequence foreign animal disease endemic to sub-Saharan Africa and the island of Sardinia. The U.S. is the world’s third largest pork producer, and ASF introduction would severely disrupt the pork supply chain, emphasizing the need to protect market access for U.S. proteins. However, niche producers raising swine intended for exhibition may not follow stringent biosecurity protocols, and livestock show circuits may promote untracked animal movement across the country, potentially exacerbating virus’ spread in the event of ASF incursion into the U.S. Youth membership in state or national swine organizations offers a route for outreach and educational activities to enhance foreign animal disease preparedness, and adult presence at swine exhibitions allows a wide variety of programming for all ages to better serve all levels of understanding.