Overview
During early 2024, H5N1 avian influenza began infecting U.S. cattle. The disease presented atypically in these animals, with diagnosis initially challenged by its divergent clinical signs compared to previous observations of H5N1 in other mammalian species. Specifically, H5N1 in dairy cattle caused severe infection primarily in the udders, while the lungs were largely unaffected.
Research Context
H5N1 avian influenza is a zoonotic pathogen known to infect various mammalian species. Historically, H5N1 infections in mammals have often been characterized by respiratory involvement, with the lungs being a primary site of disease. The emergence of H5N1 in U.S. dairy cattle, however, presented a distinct disease pathology.
Findings
When H5N1 avian influenza first infected U.S. cattle in early 2024, the disease's clinical manifestation differed from its typical presentation in other mammalian species. In cows, the infection primarily targeted the udders, leading to severe disease in this organ. Concurrently, the lungs of infected cattle were largely spared from the severe infection observed in the udders. This unique pattern of infection contributed to difficulties in initial diagnosis.
Why This Matters
The atypical presentation of H5N1 in dairy cattle in early 2024, specifically its focus on udder infection rather than the lungs, was a significant factor in the disease remaining unrecognized for a period. This divergence from expected H5N1 pathology in mammals affected the initial diagnostic process.