Karunaratne fractured his little finger during a training session here and has been ruled out of further participation in the tournament.
Prasanna has played 22 ODIs for Sri Lanka in which he has scored 181 runs and taken 21 wickets with his wrist spinners. His last appearance for Sri Lanka was earlier this year when he played against New Zealand in Wellington.
Sri Lanka are in Pool A along with co-hosts Australia and New Zealand, Bangladesh, England, and qualifiers Afghanistan and Scotland. They have played four matches, winning three. Their fifth pool stage match is against Australia here on March 8.
The Event Technical Committee of the cricket World Cup comprises Geoff Allardice (ICC General Manager - Cricket, Chairman), Campbell Jamieson (ICC General Manager - Commercial), John Harnden (Chief Executive, CWC 2015 LOC), Gavin Larsen (Cricket Operations Manager, New Zealand), Russel Arnold and Sanjay Manjrekar (independent nominees).