* Confirmed cases in Saudi Arabia up by a third in past week
* Health minister was replaced on Monday
* Authorities unsure of reason for sudden surge in cases
By Angus McDowall
RIYADH, April 22 (Reuters) - Saudi Arabia has discovered another 17 cases of Middle East Respiratory Syndrome (MERS), as the total number of confirmed infections of the SARS-like disease has jumped by a third in ...