Policy Backgrounders

Monitoring Possible Public Health Threats: Bird Flu: H5N1 Spreads to Pigs

November 22, 2024

Key Insights

This Policy Backgrounder serves as an update to CED’s Policy Backgrounder: Bird Flu Outbreak: H5N1 Spreads to Cattle, released in May, which discussed the transmission of bird flu to cattle and dairy workers, demonstrating the virus’s ability to transmit between mammalian species. For the first time in this outbreak, the virus has been detected in pigs: on October 30 the USDA announced an ongoing investigation of an Oregon backyard farming operation that had a mix of poultry and livestock, including swine. While the public health risk remains low, the US Centers for Disease Control (CDC) is monitoring the situation carefully and working with states to monitor animal and human exposure.

• The spread of H5N1 to pigs is significant because of pig species’ role as viral “mixing vessels,” as swine can be infected with both bird flu viruses and human flu viruses. This phenomenon, known as reassortment, gave rise to the 2009 H1N1 pandemic.
• H5N1 virus isolated from a Canadian teen in critical condition shows signs of mutation for human adaptation. The Vancouver teen, who was hospitalized with acute respiratory distress syndrome (ARDS), was Canada’s first recorded human case of the virus.    
• H5N1 was also detected in Los Angeles County wastewater on October 28. The virus was also detected last week in other counties throughout the state and is assumed to be the result of discarded contaminated animal products.
• The threat of human-to-human transmission remains low for now but surveillance, including rules on interstate transmission of some cattle, will continue.