Scientists warn that bird flu is evolving faster than expected

Texas Biomed researchers have identified nine mutations in a strain of avian flu found in a person in Texas. Bad news: This strain has an increased ability to cause disease and is more efficient at replicating in the brain. Good news: currently approved antiviral treatments remain effective against this strain.

Researchers at the Texas Biomedical Research Institute (Texas Biomed) have identified a strain of avian influenza isolated from a human in Texas that carries a distinctive set of mutations, making it better able to replicate in human cells and causing serious illness in mice. This strain was compared to that found in dairy cattle, and the results are detailed in Emerging microbes and infections.

This finding highlights a major concern regarding the H5N1 strains of avian flu currently circulating in the United States:

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H5N1, naturally occurring in wild birds and deadly to chickens, has recently spread to a wide range of mammals and, for the first time in spring 2024, began infecting dairy cows.

By early 2025, the epidemic had spread through herds in several states in the United States and infected dozens of people, mainly farmworkers. So far, most infected people have mild illness and eye inflammation, and the virus does not spread between people. The first death from H5N1 in the United States was reported in January 2025 following exposure to infected chickens.

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

Human versus cattle

In a recent study, they compared H5N1 strains isolated from a human patient and dairy cattle in Texas.

“There are nine mutations in the human strain that were not present in the bovine strain, suggesting that they occurred after human infection,” Dr. Martinez-Sobrido said.

In studies on mice, they found that, compared to the bovine strain, the human strain replicated more efficiently, caused more severe disease, and was found in much higher quantities in brain tissue. They also tested several FDA-approved antiviral drugs to see if they were effective against the two virus strains in the cells.

“Fortunately, the mutations did not affect sensitivity to FDA-approved antiviral drugs,” said scientist Ahmed Mostafa Elsayed, Ph.D., first author of the study.

Antivirals will be a key line of defense in a pandemic before vaccines are widely available, Dr. Martinez-Sobrido said. This is especially true since humans have no pre-existing immunity to H5N1 and seasonal flu vaccines appear to offer very limited protection, according to a separate study conducted in collaboration with Aitor Nogales, Ph.D., at the Animal Health Research Center in Spain.

Next steps and recommendations

Texas Biomed is currently exploring human H5N1 virus mutations individually to determine which are responsible for increased pathogenicity and virulence. The team wants to understand what allows H5N1 to infect such a wide range of mammal species; why H5N1 causes mild illness in cows but is fatal in cats; and why infections from cows are less harmful to humans than infections from chickens.

In a third article, Dr. Elsayed and colleagues analyzed the history of H5N1 in dairy cattle for the journal mBio and called for a One Health approach to protect both animals and humans.

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

References:

“Replication kinetics, pathogenicity and virus-induced cellular responses of influenza A(H5N1) isolates of bovine origin from Texas, United States” by Ahmed Mostafa, Ramya S. Barre, Anna Allué-Guardia, Ruby A. Escobedo , Vinay Shivanna, Hussin Rothan, Esteban M. Castro, Yao Ma, Anastasija Cupic, Nathaniel Jackson, Mahmoud Bayoumi, Jordi B. Torrelles, Chengjin Ye, Adolfo García-Sastre and Luis Martinez-Sobrido, January 8, 2025, Emerging microbes and infections.
DOI: 10.1080/22221751.2024.2447614

“Avian influenza A (H5N1) virus in dairy cattle: origin, evolution and interspecies transmission” by Ahmed Mostafa, Mahmoud M. Naguib, Aitor Nogales, Ramya S. Barre, James P. Stewart, Adolfo García-Sastre and Luis Martinez-Sobrido, November 13, 2024, mBio.
DOI: 10.1128/mbio.02542-24

“Are we serologically prepared for an avian flu pandemic and could seasonal flu vaccines help us? by Iván Sanz-Muñoz, Javier Sánchez-Martínez, Carla Rodríguez-Crespo, Corina S. Concha-Santos, Marta Hernández, Silvia Rojo-Rello, Marta Domínguez-Gil, Ahmed Mostafa, Luis Martinez-Sobrido, Jose M. Eiros and Aitor Nogales, December 31, 2024, mBio.
DOI: 10.1128/mbio.03721-24