What disease is caused by a parasitic protozoan and often leads to high fevers?

Malaria is indeed caused by a parasitic protozoan, specifically from the Plasmodium species, which is transmitted to humans through the bite of infected Anopheles mosquitoes. One of the hallmark symptoms of malaria is the occurrence of high fevers that often cycle in patterns, such as every 48 or 72 hours depending on the specific type of Plasmodium causing the infection. This fever, along with other symptoms such as chills and sweating, occurs due to the parasites multiplying in the host's liver and then invading the red blood cells, leading to their destruction and triggering an immune response that results in febrile episodes.

In contrast, measles is a viral infection characterized by a distinct rash and does not involve a protozoan parasite. Meningitis refers to the inflammation of the protective membranes surrounding the brain and spinal cord, which can be viral or bacterial in origin, but is not caused by a protozoan. Lymphoma is a type of cancer that originates in the lymphatic system and is unrelated to parasitic infections. Thus, malaria is the correct answer as it directly fulfills the criteria of being caused by a parasitic protozoan and leading to high fevers.