WASHINGTON – Republican Representative Greg Walden announced Tuesday he "likely" had swine flu, in the first known instance of a US lawmaker thought to have contracted the A(H1N1) virus.

"Just diagnosed with likely H1N1. Ugh. Off to seclusion for awhile," Walden, whose home state is Oregon, said on the micro-blogging site Twitter in a message his office confirmed was authentic.

"He's at home and he's resting," spokesman Andrew Whelan told Agence France-Presse by telephone.

Walden was fine when he arrived at work, but "felt worse and worse as the day went on, so he went to the doctor this afternoon and that's when he found out. He is quickly acting on the doctor's recommendations," said Whelan.

Walden received the seasonal flu vaccine a few weeks ago, but did not get the swine flu vaccine, said the spokesman.

The news came after Democratic Representative Melissa Bean reportedly canceled a swine flu prevention event in her home state of Illinois after her 16-year-old daughter and husband were diagnosed with likely cases.