A person in the US state of Texas is recovering from bird flu after being exposed to dairy cattle, officials said Monday amid growing concern over the current global strain of the virus as it spreads to new species.

It is only the second case of a human testing positive for bird flu in the country, and comes after the infection sickened herds that were apparently exposed to wild birds in Texas, Kansas and other states over the past week.

"The patient reported eye redness (consistent with conjunctivitis), as their only symptom, and is recovering," said the Centers for Disease Control and Prevention (CDC). They were told to isolate and are being treated with the antiviral drug used for the flu.

The current outbreak began in 2020 and has led to the deaths of tens of millions of poultry, with wild birds also infected as well as land and marine mammals.

Cows and goats joined the list last week, a surprising development for experts because they were not thought susceptible to this type of influenza.

The infected person was likely a farm worker, Louise Moncla, a pathobiologist at the University of Pennsylvania School of Veterinary Medicine, told AFP.

"If we find continued clusters of infections in cows, then it means we need to start surveilling cows -- and that would be a big change to how we think about these viruses," she added.

"But at this time, there's not an enormous need for concern by the public," she said.

The CDC said that the infection does not change its bird flu human health risk assessment for the US, which it rates as low.

The first US bird flu case in a human occurred in a Colorado prison inmate in 2022 -- however, that was through infected poultry.

- Milk supply safe -

Experts are worried about the increasing number of mammals infected by the current H5N1 strain of Highly Pathogenic Avian Influenza (HPAI) and whether it is actually spreading between them.

"Initial testing has not found changes to the virus that would make it more transmissible to humans," the US Department of Agriculture, the CDC, and the Food and Drug Administration said in a joint statement last week.

The strain appears to have been introduced by wild birds but spread between cows hasn't been ruled out, the statement added.

The Texas health department said the cattle infections do not present a concern for the commercial milk supply, as dairies are required to destroy milk from sick cows. Pasteurization also kills the virus.

The findings marked the first time ever that HPAI has been detected in dairy cattle, according to the American Veterinary Medical Association (AVMA). Earlier in March, Minnesota reported bird flu cases among goats.

- Ongoing outbreak -

The affected cows were primarily older animals that showed decreased lactation and low appetite, "with little to no associated mortality reported," added the AVMA. Dead wild birds were generally found nearby.

A nine-year-old boy died from the virus in Cambodia in February, adding to the three deaths there in 2023 -- though the bird flu spreading in Europe and North America appears to cause milder infections, said Moncla.

Bird flu has killed tens of thousands of marine mammals since spreading in South America, according to the Scientific Committee on Antarctic Research.

British seabird populations are suffering "widespread and extensive declines" according to a recent impact assessment.

The disease has hit European farms hard too, with French authorities raising the risk level to "maximum" in December, and Czech officials reporting in February they had culled 140,000 birds in 2024 alone.