Life Under the Microscope: Trypanosoma brucei

First discovered by Sir David Bruce in 1894 and appropriately named after him, Trypanosoma brucei is the causative agent of African trypanosomiasis, also known as “sleeping sickness”. It is prevalent in tropical and subtropical regions of Africa. Trypanosoma brucei consists of a group of three organisms: T. brucei gambiense, T. brucei rhodesiense, and T. brucei brucei. While all of these organisms cause trypanosomiasis, T. brucei brucei only infects animals and is not pathogenic in humans. All of these organisms within the disease share the same vector, the tsetse fly.


Tsetse fly, the vector of African trypanosomiasis

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Life Under the Microscope: Babesia microti

First reported by Victor Babes in 1888, Babesia microti is an intracellular parasite that infects red blood cells. The infection caused by this organism is known as babesiosis. Originally, Babes had thought the infection was due to the bacterium Haematococcus bovis, however, Theobald Smith and Fred Kilborne correctly identified the parasite as the causative agent in 1893. It was also first believed that this parasite only infected cattle, but again, they were proven wrong after observing a case within a splenectomised patient.

For infections occurring within the United States, the vector of the disease is the Ixodes species tick, which is also the vector of Borrelia burgdorferi , the bacteria that causes Lyme disease. For this reason, coinfections of babesiosis and Lyme disease are common.


Ixodes scapularis, vector of babesiosis infections

The B. microti life cycle is separated into two stages: the asexual and sexual stages. Within the asexual stage, the tick infects the white-footed mouse, Peromyscus leucopus, with sporozoites (the infective agent of the parasite). These sporozoites enter the mouse’s red blood cells and begin reproducing. Some sporozoites enter the sexual stage and mature into gametes. When another tick infects the mouse, these gametes are transmitted and can produce more sporozoites. Whenever humans come in contact with these infected ticks, the sporozoites infect the blood and enter the asexual stage. Inside a human’s red blood cells, the parasite takes on its cyclical form and trophozoite rings are seen on the Giemsa-stained blood smear, similar to the appearance of the malaria parasite, Plasmodium falciparum. However, in babesiosis, these trophozoites can pair up into a tetrad structure to form a “Maltese-cross”.


Babesia microti in tetrad formation (arrow) along with trophozoites

Infections commonly occur within the months of May to September. Most infections are without symptoms; however immunocompromised patients (such as the very young, elderly, and splenectomised patients) can exhibit symptoms ranging from mild to severe after one to eight weeks of exposure. Mild infections can mirror viral infections, whereas severe infections often lead to death. Other symptoms associated with the hemolytic effects of the parasite include malaise, fever, chills, sweating, and myalgia. Hemolytic anemia is present in severe cases with jaundice, hemoglobinuria, and shortness of breath. Severe complications that can occur include respiratory, liver or renal failure, as well as disseminated intravascular coagulation. Quinine sulfate and clindamycin is used in the treatment of babesiosis.