Malaria is caused by a protozoan called a malarial parasite.
It spreads by the bite of the female Anopheles mosquito which carries the malarial parasite in its salivary glands. When a mosquito bites a healthy person, the malarial parasites get transferred to the blood of a healthy person and cause malaria.
Symptoms include high fever with chills and sweating, weakness etc.
Dengue:
Dengue is a communicable disease caused by the bite of female Aedes mosquitoes carrying the dengue virus.
Symptoms of dengue include high fever, severe headache, pain in muscles and joints as well as a fall in blood platelet count.