London-based European healthcare MD Fiona Hall said she was recruiting four staff as part of a 'minor restructure' after Mursell's departure.
Mursell, who was unavailable for comment, is understood to have left without a job to go to. He had been at WS for around two years, having formerly worked at Grayling.
Mursell's exit leaves Roy Stairmand as WS UK's sole healthcare director.
Hall, who joined earlier this year from Shire Health London, is recruiting for an associate or account director, account manager, senior account executive and an account executive.
She said WS UK had been working on four fresh pieces of healthcare business this year, such as a contract working alongside other WS offices to promote next month's 15th International Aids Conference, to take place in Bangkok.
The conference, which runs from 11-16 July, is hosted jointly by the International Aids Society and the Thai Ministry of Public Health.
WS Asia-Pacific healthcare director Jill Mortensen is heading the agency's work on the event.