Analysis of H5N1 Outbreak in Dairy Cattle
A recent preprint study led by the US Department of Agriculture (USDA) National Veterinary Services Laboratory (NVSL) sheds light on the H5N1 virus outbreak in dairy cattle across multiple states. According to the research team, the virus likely circulated among the animals for four months before its confirmation in late March. The study reveals concerning gaps in data and surveillance, raising concerns about undetected transmission chains.
Genetic Sequencing and Epidemiological Insights
The study, published on the bioRxiv preprint server, provides the first comprehensive report intertwining genetic sequencing findings with epidemiological investigations. It suggests that asymptomatic cattle movement between states is a key driver of transmission. Furthermore, the emergence of variants with mutations capable of interspecies transmission is already observed.
Reassortment Event and Transmission Pathways
Phylogenetic analysis indicates a reassortment event in late 2023 between the current highly pathogenic 2.3.4.4b clade in wild birds and a low-pathogenic wild bird strain, resulting in the B3.13 genotype now found in dairy cows. The NP gene acquired during reassortment may have facilitated the virus’s spread in cattle, potentially enhancing transmission in pigs.
Potential Transmission Routes and Surveillance Gaps
The analysis suggests multiple introductions of the B3.13 genotype from cattle to various hosts, including poultry, raccoons, domestic cats, and wild birds. However, gaps in data and surveillance may obscure the full extent of transmission pathways. The study warns of the virus potentially becoming endemic in cattle, highlighting the risk of interspecies transmission if mammalian adaptations become dominant.
Expert Responses
Experts commend the USDA group for sharing critical data, emphasizing the need for transparency and data access for an effective response. Dr. Angela Rasmussen underscores the importance of understanding transmission dynamics through detailed sample analysis. Dr. Michael Osterholm praises the USDA’s findings, noting their significance in understanding the spillover event.
Safety of Meat Supply and Emergency Measures
The USDA’s announcement of negative H5N1 tests on retail ground beef provides assurance of the safety of the meat supply. Meanwhile, Michigan and Colorado have implemented emergency measures to control the virus’s spread. Michigan mandates biosecurity steps on dairy and poultry farms, while Colorado enforces mandatory testing of lactating cattle moving interstate.
In summary, the study underscores the importance of robust surveillance and response measures to mitigate the impact of H5N1 outbreaks on both animal and human health.
