A woman in Taiwan has become the first person in the world with a confirmed case of a new strain of bird flu, adding to a growing body of evidence of the potential threat from animal viruses that mutate to be able to infect people.

Scientists from Taiwan said the infection — with a bird flu strain called H6N1 — appeared to be one isolated human case and probably posed little threat for the moment. But it showed how this virus, like others in the past, had been able to acquire genetic changes allowing it to jump across species.

Another new strain of bird flu, called H7N9, is continuing to infect and kill people in China after it first emerged in humans there earlier this year.

Infectious diseases that pass from animals into humans are known as zoonoses and have kept scientists on the alert for decades. Several major human epidemics, including the worldwide outbreak of Human Immunodeficiency Virus (HIV) that causes AIDS and the 2009-10 H1N1 flu pandemic, began as zoonotic events. Many diseases also make the jump and then just peter out.

“This again underscores that there are so many viruses out there and we just don’t really know which pose the greatest threats to us,” Wendy Barclay, a flu virologist at Imperial College London, told Reuters when asked about the H6N1 case.

She called for more vigilance, surveillance and research into animal diseases with the potential to jump to humans.

In a study in the journal Lancet Respiratory Medicine Nov. 14, scientists said the H6N1 case was found in a 20-year-old woman from central Taiwan who went into hospital in May with flu-like symptoms and shortness of breath.

Initial tests on throat-swab samples taken from the patient indicated an unclassified subtype of a flu virus, the researchers said, and further genetic analysis showed it was a new H6N1 bird flu virus very similar to chicken H6N1 viruses that have been circulating in Taiwan since 1972.

The woman responded to treatment with Roche’s flu medicine Tamiflu and has since fully recovered, they added.

Ho-Sheng Wu, who led the case study from the Centres for Disease Control in Taipei, said the important feature of the genetic analysis was that it showed the virus had a mutation in the haemagglutinin — a binding protein on the virus’s surface — that enables it to get into human cells and cause infection.

Further investigations into the patient found that she worked in a delicatessen, had not been abroad for three months prior to her infection, and had not been in close proximity to poultry or wild birds.

“The source of infection remains unknown,” Ho-Sheng wrote in the study.