#17,970
Information on the HPAI H5 infections in cattle in Texas and Kansas remains scant, but late yesterday the WOAH WAHIS dashboard carried the following brief preliminary epidemiological report on the virus.
EPIDEMIOLOGICAL COMMENTS
Highly pathogenic avian influenza (HPAI) H5N1 Eurasian lineage goose/Guangdong clade 2.3.4.4b was confirmed in samples from sick cattle collected from at least one dairy farm in Kansas and at least one dairy farm in Texas.
The initial sequences represent a sporadically detected 4 gene reassortant (B3.13 per GenoFlu) descended from the previously predominant genotype B3.2 first observed in wild birds in November 2023. No markers for mammalian adaptation nor antiviral resistance were observed.
This is an evolving situation - additional work and studies are in process. Federal and state agencies are moving quickly to conduct additional testing for HPAI, as well as viral genome sequencing, so that we can better understand the situation, including characterization of the HPAI strain or strains associated with these detections.
We've discussed often that we aren't dealing with a single H5N1 threat, but rather with an array of similar H5N1 viruses that are continually reassorting and evolving. As a segmented virus with 8 largely interchangeable parts, the flu virus is like a viral LEGO (TM) set which allows for the creation of unique variants called genotypes.
Although this is rapidly changing situation, last fall researchers from several U.S. labs published a `snapshot' of H5N1's diversity in the United States in the months following its arrival in December of 2021, which found that the virus rapidly reassorted with local wild bird avian influenza viruses generating six major (and numerous minor) genotypes.
Sungsu Youk a f, Mia Kim Torchetti b, Kristina Lantz b, Julianna B. Lenoch c, Mary Lea Killian b, Christina Leyson a, Sarah N. Bevins c, Krista Dilione c, Hon S. Ip d, David E. Stallknecht e, Rebecca L. Poulson e, David L. Suarez a, David E. Swayne a, Mary J. Pantin-Jackwood a
Abstract
Highly pathogenic avian influenza viruses (HPAIVs) of the A/goose/Guangdong/1/1996 lineage H5 clade 2.3.4.4b continue to have a devastating effect on domestic and wild birds. Full genome sequence analyses using 1369 H5N1 HPAIVs detected in the United States (U.S.) in wild birds, commercial poultry, and backyard flocks from December 2021 to April 2022, showed three phylogenetically distinct H5N1 virus introductions in the U.S. by wild birds.
Unreassorted Eurasian genotypes A1 and A2 entered the Northeast Atlantic states, whereas a genetically distinct A3 genotype was detected in Alaska. The A1 genotype spread westward via wild bird migration and reassorted with North American wild bird avian influenza viruses. Reassortments of up to five internal genes generated a total of 21 distinct clusters; of these, six genotypes represented 92% of the HPAIVs examined. By phylodynamic analyses, most detections in domestic birds were shown to be point-source transmissions from wild birds, with limited farm-to-farm spread.
While some genotypes fare better than others, new reassortants tend to cluster in different geographic regions. Some may thrive and spread widely, while others may be less biologically `fit', and are unable to compete.
Hopefully we'll get a more detailed analysis of this virus in the days ahead, along with a better idea of its spread in cattle, goats, and potentially other livestock.
