Which of the following protozoan parasites is primarily transmitted by the bite of Anopheles mosquitoes?

The correct choice is the Plasmodium species, as these protozoan parasites are indeed primarily transmitted through the bite of Anopheles mosquitoes. This transmission occurs when a female Anopheles mosquito feeds on the blood of an infected host, allowing the Plasmodium parasites, in their sporozoite form, to enter the bloodstream. Once inside, the parasites travel to the liver, mature, and then enter the bloodstream again to infect red blood cells, leading to the characteristic symptoms of malaria.

In contrast, Entamoeba histolytica is transmitted through the fecal-oral route, specifically via contaminated water or food. Giardia lamblia follows a similar transmission path, being spread through the ingestion of cysts in contaminated water. Trypanosoma cruzi, which causes Chagas disease, is mainly transmitted by triatomine bugs, not mosquitoes. Each of these parasites has distinct transmission mechanisms, highlighting how Plasmodium species are uniquely associated with Anopheles mosquitoes.