Which of the following is not a protozoan disease?

Ascariasis is not classified as a protozoan disease; instead, it is caused by a helminth, specifically a type of roundworm known as Ascaris lumbricoides. Protozoan diseases are caused by protozoa, which are single-celled organisms.

In contrast, trichomoniasis is caused by the protozoan Trichomonas vaginalis, and malaria is caused by Plasmodium species, both of which fall under the category of protozoan infections. Amoebic dysentery, or amoebiasis, is caused by the protozoan Entamoeba histolytica, further confirming that it is a protozoan disease. Recognizing the type of organism involved is crucial in understanding the nature of these diseases and their appropriate treatments.