Researchers have uncovered nine mutations in a strain of bird flu found in a person from Texas. The negative aspect of this discovery is that this particular strain is better at causing illness and reproducing in the brain. However, there is some reassurance: the antivirals that have received approval remain effective against it.
A notable strain of bird flu isolated from a human in Texas carries a distinct set of mutations that allow for easier replication in human cells and result in more severe disease in mice, as reported by researchers at Texas Biomedical Research Institute (Texas Biomed) in Emerging Microbes & Infections.
This finding raises significant concerns regarding the H5N1 strains of bird flu currently present in the U.S., particularly the speed at which the virus mutates upon entering a new host.
H5N1, which is naturally found in wild birds and is deadly to chickens, has extended its reach to various mammals and has begun infecting dairy cows for the first time as of spring 2024. By early 2025, this outbreak had affected herds across several states in the U.S. and infected many people, mostly those working on farms. Up to this point, many of the infected individuals experienced mild symptoms and eye inflammation, with the virus not appearing to spread between individuals. The first death from H5N1 in the U.S. was recorded in January 2025, following contact with infected chickens.
“There is an urgency for the virus to evolve further to infect humans more easily and possibly transmit from person to person, which is a concerning prospect,” stated Texas Biomed Professor Luis Martinez-Sobrido, Ph.D., an expert in influenza viruses who has been researching H5N1 since the outbreak began last year. His team has created specialized tools and animal models to assess preventive vaccines and therapeutic antivirals.
Human versus bovine
The recent study focused on comparing H5N1 strains sourced from a human patient and from dairy cattle in Texas.
“The human strain exhibited nine mutations that were absent in the bovine strain, indicating they arose after the human infection,” noted Dr. Martinez-Sobrido.
In experiments with mice, it was observed that the human strain replicated more effectively, led to more severe illness, and was present in much greater amounts in brain tissue compared to the bovine strain. The researchers also evaluated several FDA-approved antiviral medications to determine their effectiveness against both virus strains in cell culture.
“Fortunately, the mutations did not alter the effectiveness of the FDA-approved antivirals,” explained Staff Scientist Ahmed Mostafa Elsayed, Ph.D., the primary author of the study.
Dr. Martinez-Sobrido emphasized that antivirals will be crucial for defense if a pandemic occurs before vaccines are available, particularly since humans lack preexisting immunity to H5N1 and seasonal flu vaccines seem to provide minimal protection, as highlighted in a collaborative study led with Aitor Nogales, Ph.D., at the Center for Animal Health Research in Spain.
Future actions and recommendations
Currently, Texas Biomed is investigating each human H5N1 mutation to identify which ones enhance pathogenicity and virulence. The team aims to understand what enables H5N1 to infect various mammal species, why it causes mild illness in cows yet is fatal for cats, and why infections originating from cows are less harmful to humans than those from chickens.
In another study, Dr. Elsayed and his team reviewed H5N1’s history in dairy cattle for the journal mBio, advocating for a One Health approach to safeguard both animal and human health.
“A crucial goal will be to eradicate bird flu from dairy cows to reduce the risk of mutations and transmission to humans and other species,” stated Dr. Elsayed. “Immediate actions that can be taken include thorough cleaning of milking equipment and stricter quarantine protocols, which will help to swiftly eliminate the virus in cows.”
