Three persons including wife of a doctor and two students of WAPDA Cadet College have fallen sick due to dengue virus in Tarbela Dam colony. According to reports, there is serious concern among the WAPDA employees living in the colony and they have demanded of the authorities to immediately start spray against mosquitoes in the colony, educational institutions and other adjoining places. Sources said that dengue virus has reached Tarbela Colony and wife of Dr Ghulam Abbas of WAPDA hospital Tarbela Dam has fallen sick.