Final answer:
Plasmodium vivax is the causative agent of malaria. It is spread by mosquitos and infects red blood cells, causing various symptoms.
Step-by-step explanation:
The causative agent of malaria is Plasmodium vivax. Malaria is caused by protozoa of the genus Plasmodium, which are spread by mosquitos. When an infected mosquito bites a human, the parasites enter the bloodstream and infect red blood cells, leading to symptoms such as fever, joint pain, and fatigue.
The causative agent of malaria is Plasmodium protozoa. There are several species of Plasmodium that can cause malaria, including Plasmodium falciparum, which is known for being the most lethal to humans. These parasites go through part of their life cycle in mosquitoes and are transmitted to humans by the bite of an infected Anopheles mosquito. Once in the human host, these parasites infect and multiply within red blood cells, leading to symptoms like fever, joint pain, and anemia.
Returning to the question, the correct answer is (a) Plasmodium vivax, which is one of the species of Plasmodium that causes malaria. The other options listed (Trypanosoma cruzi, Leishmania donovani, and Giardia lamblia) are the causative agents of other diseases, not malaria.