A mysterious illness causing an odd "twitching" symptom has stricken several students and a staff member at a Virginia high school.

Testing continues at William Byrd High School in Roanoke County where students and staff have shown strange symptoms of twitching and spasms since September, but a cause has yet to be determined.

About 30 students staged a walkout and protest earlier this week, and the school has said about 300 of the school's 1,200 students have been absent.

School officials say they do not plan to close the school.

Roanoke County school officials and health officials have found no environmental cause for the symptoms, which have affected fewer than 10 students, the Associated Press reported.

"I have seen them in the hallway, and it seems pretty bad," said senior Charlie Wallace, told the Roanoke Times. "It's uncontrollable. Twitching, that's the only way you can describe it."

Students and parents met Monday night with officials from the school system, the Virginia Department of Health and the companies conducting the environmental tests.

Parents asked about the symptoms and urged officials to close the school and offer classes elsewhere. But Superintendent Lorraine Lange said that health experts said that based on the environmental test results, there's no need to close the school.

So far, the illness has sickened several students and a teacher at William Byrd High School and officials can't specify specific symptoms to watch out for.

But one mother said her child is experiencing bouts of sudden twitching and uncontrollable arm spasms, along with headaches and dizziness.

That's no consolation to students and parents, who paced an auditorium at a public meeting Monday night with officials from the school system, the Virginia Department of Health and the companies that conducted environmental tests.

Health experts tested for mold, and the school came up clean. Disturbed by the twitching that accompanies the illness, many students and parents want the school to remain closed.

"They wave. It's convulsing. They can't stop it," said senior Layne Gulli of the symptoms. "You don't know how to avoid it. You don't know if you're next, or if your friend is next, or if it's an epidemic."

"There's rumors it was carbon dioxide from the photography room," said sophomore Joe Bradshaw. "We heard it was lead paint. Nobody knows what it is.

— Associated Press