03 July 2026
German researchers at the University of Veterinary Medicine Hannover have successfully developed a scalable bovine mammary gland organoid platform, demonstrating that the udder serves as a highly permissive replication site for diverse mammalian and avian Influenza A strains beyond H5N1.
The research team isolated primary epithelial cells from the udders of slaughtered dairy cattle and successfully cultured three-dimensional bovine mammary gland organoids (MGOs).
The team utilized this tractability to benchmark contemporary bovine HPAIV H5N1 against low-pathogenic avian (LPAIV) and mammalian-adapted strains.
Results:
- Bovine H5N1 rapidly infected the organoids, with viral RNA escalating by four orders of magnitude within 24 hours and peaking at – genome copies per reaction at 48 hours post infection. Mammalian-adapted strains, swine-origin H1N1 and human pandemic H1N1, matched the replication efficiency of the bovine-adapted H5N1 strain perfectly, yielding high infectious particle counts.
The organoids abundantly express both -linked (avian-type) and -linked (human-type) sialic acid cellular receptors. This receptor duality allows multiple viral lineages to attach without needing immediate genetic mutations. Interestingly, low-pathogenic H9N2 showed restricted, abortive replication despite the receptor presentation, emphasizing that internal host factors beyond receptor binding control successful infection.
The realization that human and porcine H1N1 strains multiply just as seamlessly inside bovine mammary tissue as H5N1 indicates that a highly permissive influenza niche exists broadly within the secretory compartment. This raises a major biological concern: if a dairy cow becomes simultaneously coinfected with an avian strain and a mammalian strain, the mammary gland could serve as a functional "mixing vessel" for genetic reassortment. Such a scenario could generate novel hybrid viral strains with enhanced zoonotic transmission capabilities.
The conceptualization of the cow udder as a potential incubator for reassortment among human, porcine, and avian lineages is independently bolstered by co-infection observations reported by Pinto et al. (2025) in separate bovine mammary cell line assays.
Based on this study, the widespread outbreaks across US dairy farms underscore a significant potential threat to public health and expose a profound systemic failure by regulatory authorities, whose management of the crisis has been far from professional or responsible.
Fritsch et al. (2026). Beyond H5N1: Influenza A virus infection in bovine udder organoids. Emerging Microbes & Infections, Advance online publication.
Pinto et al. (2025) The cow udder is a potential mixing vessel for influenza A viruses. bioRxiv. Sep 1:2025-08.
