What is a protozoan? how is a protozoan parasite different from bacteria and multi-celled parasites such as intestinal worms? how does t. brucei differ from the closely related american trypanosome t. cruzi, the causative agent of chagas disease, and from the p. falciparum parasite that causes malaria? describe notable differences in morphology, life cycle, infectivity, transmission, geographical range, disease presentation, and treatment?

What is a Protozoan?
A protozoan is a microscopic, single-celled organism that is classified under kingdom Protista. Some of the popular protozoans include entaomoeba hystolitica, euglena, and paramecium.  

How is a protozoan parasite different from bacteria and multi-celled parasites such as intestinal worms?

The main difference between a parasitic protozoan, bacteria or intestinal worm is the modes of transmission. Protozoan parasites are mostly transmitted through direct contact with an infected person or by drinking contaminated water. Many types of protozoan parasites that live in the tissue or blood are transmitted by arthropods like mosquitoes. Parasitic helminths are transmitted via contaminated soil. As for bacteria, most of them do not have a vector. They are mostly transmitted directly from one infected person to another.

How does t. brucei differ from American trypanosome t. cruzi (the causative agent of chagas disease) and from p. falciparum parasite that causes malaria? Describe the notable differences in morphology, life cycle, infectivity, transmission, geographical range, disease presentation, and treatment?

Trypanosoma brucei causes sleeping sickness. It is confined to the tropical region of Africa and it is transmitted by the tsetse fly. Its clinical symptoms include fever, edema, progressive paralysis and anemia. The t. brucei comes into forms - the trypomastigote which develops in the vertebrate host and the epimastigote which grows in the vector. The trypomastigote has a long undulating membrane and posterior kinetoplast, while the epimastigote has a short membrane and anterior kinetoplast. The drug used to treat the African Sleeping Sickness is pentamidine. The treatment is only used for the first stage of the illness.  

Trypanosoma cruzi causes the Chagas disease. It is transmitted by the reduviid bug, and it is confined to the Americas. The symptoms of the Chagas disease include inflamed lymph nodes, vomiting, body aches, fatigue and spleen enlargement. For the Trypanosoma cruzi, it is distinguished by its three morphological forms - trypomastigote, epimastigote, and amastigote. The trypomastigote and epimastigote look similar, except for the position of the kinetoplast. The kinetoplast of epimastigotes is found on the anterior portion. The amastigote, on one hand, is present inside the cells. The treatment used for the Chagas disease is benznidazole and nifurtimox.

Lastly, Plasmodium falciparum is a protozoan that causes malaria. Mosquitoes serve as the vector of this deadly protist. The symptoms of malaria include profuse sweating, moderate to severe chills, headache, fever, nausea, and abdominal pain. The parasite begins to develop in the gut of the mosquito. At this stage, the P. falciparum is in its gametocyte form. Once a female and male gametocyte combine together in the gut, sporozoite is formed. This form infests a human liver. Once the sporozoite successfully enters the human body through a mosquito bite, it travels to the liver and reproduces. The new form is referred to as the schizonts. Compared to the previous form, the schizonts are multi-nucleated, and they are filled with thousands of merozoites. When the merozoites reach their peak development, the schizont bursts. The merozoites then target the red blood cells. If a merozoite successfully infects an RBC, it is called a trophozoite. Malaria is treated with quinine sulfate and doxycycline. Alternatively, drugs like clindamycin can be used.