-WATER STAGNATION:- Due to excessive garbage and plastics the water gets stagnated in the pouches of the plastics and other things,which provide base for the breeding of mosquitos!
-THE MIXAGE OF SEWAGE INTO DRINKING WATER:- The water is generally dirty in slums as they are not developed areas of the indian economy , and malarial parasites grow and flourish in these dirty water only dengue parasites grow in clean water. So this provided another foundation for the mosquitos to breed
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brainyest answer!! :P