Malaria is caused by single celled plasmodium parasites. When a person is bitten by an infected mosquito , the microbe makes its way through the host bloodstream to the liver where it replicates , returns to the blood and infects red blood cells.

But mosquitoes do not have red blood cells , their blood is a somewhat colourless fluid containing the blood cells equivalent called haemocytes so the parasites escape to its saliva from the gut.