HANOI, Vietnam – A new strain of bird flu virus has developed in several cities and provinces in Vietnam, according to news reports.

Outbreaks have occurred in six provinces so far, and more than 180,000 birds have been culled, according to the Bangkok Post. Two people have died from the flu strain, but those deaths occurred before the new strain was identified.

The new strain is suspected of posing a higher risk of human deaths than previous viruses. It appeared in July and was widespread by August. The Ministry of Agricultural and Rural Development in Vietnam said the flu strain is thought to be a mutation of H5N1, the Post said.