Avian Influenza A(H5N1) Isolated from Dairy Farm Worker, Michigan

Abstract

Influenza A(H5N1) viruses have been detected in US dairy cow herds since 2024. We assessed the pathogenesis, transmission, and airborne release of A/Michigan/90/2024, an H5N1 isolate from a dairy farm worker in Michigan, in the ferret model. Results show this virus caused airborne transmission with moderate pathogenicity, including limited extrapulmonary spread, without lethality.

Keywords: H5N1; Influenza; Michigan; United States; clade 2.3.4.4b; ferret; highly pathogenic avian influenza; respiratory infections; zoonoses.

Figure

Transmission and measurement of airborne avian influenza A(H5N1) virus isolated from dairy farm worker, Michigan. A, B) For DCT and RDT testing, ferrets (n = 12) were intranasally inoculated with 10⁶ PFU A/Michigan/90/2024 virus, isolated from the dairy worker, in 1 mL phosphate-buffered saline and were cohoused with naive ferrets in a DCT model (A) or in adjacent cages with perforated sidewalls permitting airborne virus spread but restricting contact in an RDT model (B). Each bar represents a single animal. C, D) For aerosol transmission testing, ferrets (n = 3) were inoculated intranasally with 10⁶ PFU of MI90 virus and tested daily (C). Orange dots represent viral titers from NW in log₁₀ PFU/mL; limit of detection 10 PFU/mL. Gray bars show average viral M gene RNA load. Error bars indicate SD. Limit of detection was 2.9 log₁₀ RNA copies/mL. D) Aerosol samples were collected daily for 5 dpi by using a BC251 cyclone-based sampler (kindly provided by Dr. William Lindsley, National Institute for Occupational Safety and Health) and the SPOT water condensation sampler (Aerosol Devices, https://aerosoldevices.com), as described previously (8). Orange dots represent log₁₀ PFU/mL per hour. Gray bars show average viral M gene RNA. Error bars indicate SD. Limit of detection was 2.5 log₁₀ RNA copies/h. Ferrets were used for tissue collection on day 5. DCT, direct contact transmission; dpi, days postinoculation; NW, nasal washes; RDT, respiratory droplet transmission.