The delivery of a suspicious powder to the California home of the British actor Eric Idle is being treated as an attempted anthrax attack.

The “certified letter”, which was posted from Thailand, was opened by a member of staff at Idle’s Hollywood Hills home on Monday evening and Los Angeles police, fire and hazardous materials responders were dispatched. It is not thought the employee was harmed.

The house was evacuated but a considerable police presence remains outside the property.

Anthrax is an acute infectious disease caused by a spore-forming bacterium. It commonly affects hoofed animals but can occur in humans exposed to the infection or following a release of spores in biological warfare by terrorists.

Five people died and 17 were infected by anthrax in letters posted to media outlets and to two Democratic US senators in the aftermath of the attack on the World Trade Center in 2001.

Idle, 76, became famous as a member of the Monty Python team, writing and starring in the TV series Monty Python’s Flying Circus as well as in films such as Life of Brian and The Meaning of Life. He went on to act in films such as Nuns on the Run and Splitting Heirs.

His greatest solo success was as writer of the musical Spamalot, adapted from the film Monty Python and the Holy Grail. The original 2005 production received 14 Tony award nominations and won in three categories, including best musical.

On Tuesday, Idle took to Twitter to reassure fans as to his safety and thank them for their concern: