The changes that the malarial parasite undergoes in the mosquito represent which one of the following types of biological transmission?
Cyclopropagative
The correct answer is cyclopropagative. In this form of biological transmission the agent both multiplies and undergoes a cyclical change of form inside the vector. In the female Anopheles, ingested gametocytes of Plasmodium undergo sporogony: gametes fuse to a zygote, which becomes a motile ookinete, penetrates the gut wall as an oocyst, and within it thousands of sporozoites form and reach the salivary glands. Both change of form and multiplication occur, over an extrinsic incubation period of 10–14 days.
Why the others are wrong: Propagative means multiplication only, with no change of form — plague bacilli in the rat flea, or arboviruses in mosquitoes. Developmental and cyclodevelopmental mean developmental or cyclical change without multiplication — classically microfilariae in the mosquito, or guinea-worm larvae in Cyclops. Since Plasmodium clearly multiplies in the mosquito, none of these fits.
Key point: Malaria in mosquito = cyclopropagative; filaria in mosquito = cyclodevelopmental; plague in flea = propagative; housefly spread = mechanical.
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