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Review
. 2025 Mar 12;16(3):e0294424.
doi: 10.1128/mbio.02944-24. Epub 2025 Feb 11.

mGem: Transmission and exposure risks of dairy cow H5N1 influenza virus

A J Campbell  1 , Kayla Brizuela  1 , Seema S Lakdawala  1
Affiliations
Review

mGem: Transmission and exposure risks of dairy cow H5N1 influenza virus

A J Campbell et al. mBio. .

Abstract

In March 2024, highly pathogenic H5N1 was detected in dairy cows; as of 12 December 2024, it had spread to over 800 herds in 16 states. The ongoing outbreak is a public health crisis affecting both humans and animals, as interspecies transmission has emerged as a common characteristic of this virus. As of 12 December 2024, >30 humans have been infected in the United States related to dairy cow exposure. In this mGem, we discuss transmission modalities between cows within herds, the spread of the virus between dairy farms, and exposure risks for humans. We also highlight major gaps in knowledge constituting barriers to our ability to effectively control the spread of H5N1 in dairy cows and reduce the risks to humans.

Keywords: H5N1; dairy cow; influenza; transmission.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig 1
Fig 1
Spatiotemporal overview of the HPAI H5N1 outbreak in the United States. (A) Timeline of cow H5N1 outbreak events in the United States from late 2023 until 31 October 2024. Confirmations of virus positivity in new states on the right, black; confirmed human cases on the left, red; federal orders, blue. Events on the timeline were curated from the following references (9, 10, 13, 15–36). (B) Heatmap of U.S. states with H5N1 positive herds over the total course of the outbreak until 31 October 2024. State abbreviations and date of the first positive confirmation listed. CA, WI, ID, TX, and NY are the top five dairy producers in the United States and are demarcated by a cow icon. Images created using BioRender.
Fig 2
Fig 2
Risks of H5N1 transmission related to milking parlors and milk waste stream. (A) Schematic of a typical large-scale milking parlor; caution symbols indicate described transmission risks either between cows (numbers 1 and 2) or to dairy farm workers (numbers 3–5). PPE, personal protective equipment. (B) Waste stream for contaminated or unsaleable milk, which could infect other animals if not inactivated after collection. Images created using BioRender.
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    Campbell AJ, Shephard M, Paulos AP, Pauly M, Vu M, Stenkamp-Strahm C, Bushfield K, Hunter-Binns B, Sablon O, Bendall EE, Fitzimmons WJ, Brizuela K, Quirk G, Kumar N, McCluskey B, Shetty N, Marr LC, Guthmiller JJ, Abernathy K, Lauring AS, Melody BT, Wolfe M, Lombard J, Lakdawala SS. Campbell AJ, et al. bioRxiv [Preprint]. 2025 Aug 2:2025.07.31.666798. doi: 10.1101/2025.07.31.666798. bioRxiv. 2025. PMID: 40766457 Free PMC article. Preprint.

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