The dengue infection primarily spreads through the bite of a virus-infected aedes aegypti mosquito. When the mosquito bites you, the virus enters your body and starts to spread. The drop in platelets is caused by a condition referred to as ‘thrombocytopenia’, which happens either via direct bone marrow suppression or by means of an autoimmune reaction and antibodies pushed into place. Thus, while the dengue virus in itself doesn’t destroy the platelets, it can unleash complications which harm platelet function and count.
Remember, the basic dengue spreads is by entering the bloodstream, attaching itself to the platelets and leading to replication. When this happens, the ‘infected’ platelets tend to cause damage to the healthy platelets as well, and are further aggravated by the body’s immune defence attacking them, mistaking them to be foreign bodies. When the bone marrow function is suppressed as well, it can also lead to a staggering drop in the counts, and cause problems.