Bird flu mutating rapidly, scientists sound alarm after first US H5N1 death

Bird flu virus may have turned deadlier in the recent outbreak this year as scientists have discovered a strain in a person in Texas with as many as nine mutations. These changes in the virus can increase its efficiency in causing the disease, replicating in the brain, and increasing its severity as per researchers at the Texas Biomedical Research Institute (Texas Biomed).

This discovery had brought to light a concern that H5N1 strains of bird flu undergo rapid mutations when it infects a new host species. While the virus is commonly present in wild birds and pose risk to chicken, its spread in a wide range of mammals means multiple mutations that makes it more deadly. For the first time, the virus started infecting dairy cows in the spring of 2024. These findings have been published in the journal Emerging Microbes & Infections.

H5N1 is known to cause mild illness and eye inflammation in humans, however the first death in US due to the virus (reported in January 2025) following exposure to infected chickens sparked concerns.

“The clock is ticking for the virus to evolve to more easily infect and potentially transmit from human to human, which would be a concern,” said Texas Biomed Professor Luis Martinez-Sobrido, Ph.D., whose lab specializes in influenza viruses and has been studying H5N1 since the outbreak began last year. The team has developed specialized tools and animal models to test prophylactic vaccines and therapeutic antivirals.

What is concerning in the recent study

The scientists looked at and compared H5N1 strains isolated from a human patient and from dairy cattle in Texas. They found that there were nine mutations in the human strain that were not present in the bovine strain, which suggested that they occurred after human infection.

The researchers in mouse studies discovered that human strain replicated more efficiently causing severe disease, compared to the bovine strain. It was also found to replicate more in the brain tissue.

Good news

Scientists also tested several FDA-approved antiviral medications to check if they were effective against both virus strains.

“Fortunately, the mutations did not affect the susceptibility to FDA-approved antivirals,” said Staff Scientist Ahmed Mostafa Elsayed, Ph.D., first author of the study.

Considering humans have no pre-existing immunity against H5N1 and seasonal flu vaccines provide limited protection, antivirals will be a key line of defence in a scenario of a pandemic.

What scientists are now studying

Texas Biomed is investigating human H5N1 mutations to pinpoint those driving increased virulence. The team aims to understand why H5N1 infects diverse mammals, causes mild disease in cows but is lethal in cats, and why infections from cows are less harmful to humans than those from chickens.

“A key priority will be to eradicate bird flu from dairy cows to minimize the risk of mutations and transmission to people and other species,” Dr. Elsayed said. “Steps that can be taken now include thorough decontamination of milking equipment and more stringent quarantine requirements, which will help eliminate the virus more quickly in cows.”