Rainsford, 26, has taken 45 wickets from 39 one-day internationals, was the third Zimbabwe player to be ruled out of the Feb 19-April 2 World Cup after he hurt his right ankle ligaments.
Zimbabwe had earlier replaced Tinotenda Mawoyo and Sean Ervine due to injuries.
Panyangara, 25, has taken 26 wickets in 23 ODIs but has yet to play a World Cup match.
Australia’s Nathan Hauritz and Michael Hussey, India’s Praveen Kumar, England’s Eoin Morgan and Sohail Tanvir of Pakistan were also replaced. Reuters