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Concerns Arise Over Mutating H5N1 Bird Flu Strain in Texas

Recent research from Texas Biomedical Research Institute (Texas Biomed) has unveiled significant mutations in an early strain of bird flu isolated from a human in Texas. This strain exhibits a unique set of alterations that enhance its ability to replicate in human cells and increase the severity of disease it causes in mice, when compared to a strain obtained from dairy cattle. These findings have been reported in the journal Emerging Microbes & Infections.

The study underscores the pressing issue regarding H5N1 bird flu strains currently present in the U.S., notably the rapid mutation rate of the virus when it transitions to new hosts.

H5N1 is typically found in wild birds and often proves fatal for chickens. Notably, in the spring of 2024, the virus began infecting dairy cows for the first time. By early 2025, the outbreak had permeated herds across several states, resulting in dozens of human infections, predominantly affecting farm workers. Most individuals who contracted the virus showed mild symptoms including eye inflammation, and human-to-human transmission has not yet been observed. However, the first U.S. fatality due to H5N1, which followed exposure to infected chickens, was reported in January 2025.

“The ticking clock represents the virus’s evolving ability to more readily infect humans and potentially transmit between people, which poses a significant concern,” stated Dr. Luis Martinez-Sobrido, a Texas Biomed professor who specializes in influenza viruses and has been researching H5N1 since the outbreak began. His team is engaged in developing specialized tools and animal models to evaluate prophylactic vaccines and therapeutic antiviral treatments.

Human vs. Bovine Strains

In their recent study, researchers analyzed H5N1 strains isolated from both a human patient and a Texas dairy cow.

“The human strain has nine mutations that the bovine strain lacks, indicating these changes occurred after the virus infected a human,” Dr. Martinez-Sobrido explained.

Research using mouse models demonstrated that the human H5N1 strain replicated more efficiently than the bovine version, leading to more severe infection and significantly higher levels in brain tissue. Additionally, the researchers assessed several FDA-approved antiviral drugs to evaluate their efficacy against both strains in cell cultures.

“Fortunately, these mutations did not impact the effectiveness of existing FDA-approved antivirals,” noted Dr. Ahmed Mostafa Elsayed, the study’s first author. Dr. Martinez-Sobrido emphasized that antivirals will play a critical role in mitigating a potential pandemic, particularly since the human population lacks preexisting immunity to H5N1, with seasonal flu vaccines providing minimal protection as indicated by a separate study in collaboration with Dr. Aitor Nogales from the Center for Animal Health Research in Spain.

Future Directions and Actionable Steps

Texas Biomed is actively investigating the specific mutations present in the human H5N1 strain to discern which factors contribute to its heightened pathogenicity and virulence. The team aims to unravel the mechanisms that enable H5N1 to infect a diverse array of mammal species; for instance, exploring why it has lethal effects in cats but causes only mild symptoms in cows, and understanding the differences in human infections derived from cows versus those stemming from chickens.

In a separate collaborative effort, Dr. Elsayed and colleagues published a third paper assessing the historical context of H5N1 in dairy cattle in the journal mBio. They are advocating for a One Health approach that simultaneously addresses the health of humans and animals.

“A pivotal goal must be the eradication of bird flu from dairy cows to reduce the risk of mutations and potential transmission to humans and other animal species,” Dr. Elsayed urged. He recommended measures such as thorough disinfection of milking equipment and imposing stricter quarantine protocols as immediate steps to expedite the elimination of the virus in cattle.

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