Trypanosomes

Trypanosomes are flagellated, single-celled parasitic protozoa of the genus Trypanosoma, within the family Trypanosomatidae. They are kinetoplastids, meaning they possess a single, elaborate mitochondrion containing a DNA-containing kinetoplast. The genus includes many species that infect vertebrates, including humans, and they are typically transmitted by insect vectors.

Two notable human pathogens are Trypanosoma brucei, which causes African sleeping sickness, and Trypanosoma cruzi, which causes Chagas disease. T. brucei is transmitted by the bite of tsetse flies (Glossina) in sub-Saharan Africa; humans are infected by subspecies T. b. gambiense or T. b. rhodesiense. T. cruzi is transmitted mainly by triatomine bugs (kissing bugs) in the Americas, with additional routes including congenital transmission, blood transfusion, and organ transplantation.

In the mammalian host, trypanosomes inhabit the blood and lymph and exist as slender and stumpy bloodstream forms; in the insect vector they take procyclic forms in the midgut and metacyclic forms in the salivary glands. A hallmark of these parasites is antigenic variation of surface proteins, particularly variant surface glycoproteins, which helps them evade the host immune response.

Clinical features differ by disease type. African sleeping sickness progresses from fever and lymphadenopathy to central nervous system involvement, sleep disturbances, and, if untreated, coma and death. Chagas disease has an acute phase that may be mild or asymptomatic, followed by a chronic phase that can cause cardiomyopathy, megasyndromes of the esophagus or colon, and progressive organ damage.

Diagnosis relies on parasite detection in blood, lymph, or cerebrospinal fluid, supported by serology or molecular methods. Treatments include antiparasitic drugs such as suramin and pentamidine for early African disease, with melarsoprol or eflornithine-based therapies for CNS involvement, and benznidazole or nifurtimox for Chagas disease. Prevention focuses on vector control, protective measures to reduce contact with vectors, and screening of blood donors.