#18,601
Yesterday, in Nevada's HPAI H5 Genotype Question (And Why It Matters), we looked at Monday's release from the state of Nevada on 4 newly infected dairy herds, with the curious added detail that "Preliminary results show this detection to be consistent with a strain that has also been detected in wild birds in all North American flyways."
This appeared to be a departure from the norm, as all previous cattle-related infections had been identified as stemming from the B3.13 `bovine' strain.
While there has been a lot of speculation the past 48 hours, about an hour ago (noon EST), the USDA changed the heading on their Livestock with H5N1 page (see above), to remove the statement: `The genetic sequence for all cattle cases and the alpaca case is influenza A, H5, clade 2.3.4.4b, genotype B3.13'.
Shortly after that, the USDA released the following statement. I'll have a postscript after the break.
APHIS Confirms D1.1 Genotype in Dairy Cattle in Nevada
On January 31, 2025, the USDA Animal and Plant Health Inspection Service (APHIS) National Veterinary Services Laboratories (NVSL) confirmed by whole genome sequence the first detection of highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b, genotype D1.1 in dairy cattle. This confirmation was a result of State tracing and investigation, following an initial detection on silo testing under the USDA’s National Milk Testing Strategy (NMTS) in Nevada.
USDA APHIS continues to work with the Nevada Department of Agriculture by conducting additional on-farm investigation, testing, and gathering additional epidemiological information to better understand this detection and limit further disease spread.
This is the first detection of this virus genotype in dairy cattle (all previous detections in dairy cattle have been HPAI H5N1 clade 2.3.4.4b, genotype B3.13). Genotype D1.1 represents the predominant genotype in the North American flyways this past fall and winter and has been identified in wild birds, mammals, and spillovers into domestic poultry.
The detection does not change USDA’s HPAI eradication strategy and is a testament to the strength of our National Milk Testing Strategy (NTMS). In the interest of sharing information of import to the scientific community, APHIS will publish a technical brief on the findings on our website and post the sequence data on GenBank in the coming week.
aphis.usda.gov
While this is a brief statement, the implications of a second genotype infecting dairy cows are potentially quite significant.
- Countries that have banked on the idea that only the North American B3.13 strain could jump to cattle will now have to re-evaluate that risk.
- Although the number of human infections with both genotypes has been limited, at least two of the D1.1 cases experienced serious illness.
- And if two genotypes can make this leap, presumably others can as well.
I'm sure we'll get more information in the days ahead, hopefully including a read out of any mammalian adaptations.
Stay tuned.
