Parasitic protists passed by mosquitoes causes this disease

malaria

Explanation:

"Malaria" is a mosquito-borne illness that is caused by a parasitic protist called "Plasmodium protozoa." These parasites are carried by mosquitoes. Once a mosquito bites a human, it creates an opening for the parasites to enter. The parasites then become harmful once they enter the human body. They infect the human's Red Blood Cells (RBCs), which causes several symptoms such as fever, fatigue, headache, cough, nausea, etc.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.