Transmission of HPAI H5N1 virus to dairy cattle
A recent study published in Nature provides an in-depth analysis of the clinical, pathological, and epidemiological aspects of the unprecedented spillover of the highly pathogenic avian influenza (HPAI) H5N1 virus into dairy cattle herds across multiple states in the U.S.
The study documents the clinical signs observed in infected cows, which include reduced feed intake, altered fecal consistency, respiratory distress, and a significant decrease in milk production, often accompanied by abnormal milk color and consistency. The virus was detected not only in milk but also in various tissues, with a notable tropism for the mammary gland's epithelial cells.
Whole viral genome sequencing from various species on the affected farms revealed a complex pattern of interspecies transmission, indicating the virus's ability to jump species barriers. The study also found evidence of efficient transmission among cattle, with the virus spreading to a different state after the transportation of seemingly healthy cows from an affected farm. This finding highlights the potential for subclinical carriers to spread the virus, a significant concern for disease control efforts. In non-clinical animals, viral RNA was detected in 6 out of 19 nasal swabs and 4 out of 8 urine samples, indicating subclinical infection.
The H5N1 virus has wreaked havoc on both domestic and wild avian populations since its emergence in the U.S. in 2022, leading to the loss of millions of birds. The virus has also shown a propensity to infect mammals, with reported cases in cats, red foxes, bears, seals, and even a polar bear. The current study adds to this list by reporting the first known spillover into ruminants, specifically dairy cattle.
The research identifies a new reassortant genotype of the virus, B3.13, which combines genetic segments from Eurasian wild bird and American bird lineages. Phylogenomic analysis revealed that the virus strains from the affected farms are closely related, suggesting potential transmission routes between farms and interspecies transmissions, including from cattle to cats and raccoons.
The zoonotic potential of the virus is a looming concern, especially as it adapts to new hosts, which could lead to an increased risk of pandemics.
In summary, the article by Caserta et al. provides a comprehensive analysis of the H5N1 virus's spillover into dairy cattle, its transmission dynamics, and the urgent need for control measures to prevent further spread and potential human health risks.
