Bharti Jayshankar
December 28, 2024: The Centers for Disease Control and Prevention (CDC) has identified mutations in genetic sequences from a patient in Louisiana suffering from a severe H5N1 bird flu infection. These mutations may enhance the virus’s ability to attach to human upper respiratory cells, raising concerns about potential transmissibility.
The Louisiana patient, along with a teenager in British Columbia, Canada, represents the first severe human cases of H5N1 bird flu in North America for 2024. Both cases exhibited mutations in the hemagglutinin (HA) gene, which is crucial for the virus’s binding to host cells.
Mutation insights
The Louisiana patient likely got the infection from a poultry farm. But tests showed that the mutations were not present in samples from infected poultry on the property, suggesting that these changes developed during the patient’s infection. This contrasts with typical bird flu behavior, where viruses do not easily infect humans due to their preference for cell receptors that are rare in human upper airways.
Scott Hensley, a microbiology professor at the University of Pennsylvania, expressed caution regarding the implications of these mutations. He noted that while the findings are concerning, they should not be overstated as they stem from only two severe cases. However, the experts are emphasizing the need to reduce human infections to prevent potential pandemic scenarios.
Current statistics
Since March 2024, there have been at least 65 confirmed human cases of H5N1 in the United States. Approximately 60% of these cases resulted from contact with infected dairy cows, while others involved direct contact with infected poultry.
The circulating H5N1 strain in Louisiana is of genotype D1.1, which is related to other recent human cases but distinct from the B3.13 genotype found in dairy cows.
The flu has infected about 450 dairy farms in 15 states, according to the US Department of Agriculture’s Animal and Plant Health Inspection Service.
Serological study
A recent study on 115 farm workers in Colorado and Michigan revealed that workers exposed to cows infected with H5N1 virus showed seven per cent of them had evidence of prior infection. Of that, only half of the workers remembered having symptoms of the disease.
The serological study conducted from June to August revealed “eight of the 115 samples, were seropositive against HPAI, or highly pathogenic avian influenza,” said Dr Demetre C. Daskalakis, Director of the National Center for Immunization and Respiratory Diseases.
Public health implications
Despite these findings, the CDC maintains that the overall risk to public health remains low. No person-to-person transmission has been detected in either severe case reported. The agency is actively working with state health departments to monitor and analyze further genetic sequences from affected individuals.
The CDC has issued some norms for US farm workers. It advises that workers exposed to bird flu who do not show symptoms and do not wear personal protection equipment should be tested for the virus.
“Simply put, the less room we give this virus to run, the fewer chances it has to cause harm or to change,” said Centers for Disease Prevention and Control (CDC) Principal Deputy Director, Dr Nirav Shah.
The emergence of mutations in H5N1 bird flu viruses underscores the importance of vigilant monitoring and research into avian influenza.
