Trypanosomiasis Life Cycle

Trypanosomiasis is an illness caused by a protozoan hemoflagellate. There are two forms of Trypanosomiasis. The first is Sleeping Sickness, in both the east and west African varieties. The second is Chagas Disease. Each of these diseases is caused by a specific trypanosome.

Sleeping Sickness

• Sleeping Sickness is caused by two distinct protozoans. T. b. gambiense causes west African Sleeping Sickness, and T. b. rhodesiense causes east African Sleeping Sickness. In this disease, the parasites enter into the central nervous system causing headaches, abnormal behavior, loss of consciousness and coma. All stages of African Trypanosomiasis occur in extracellular fluids.

Sleeping Sickness - Human Stages

• An infected Tsetse fly will bite a mammalian host. During the bite, the parasites, in the form of metacyclic trypomastigotes, are injected into the skin tissue. The parasites enter the lymphatic system, eventually passing into the bloodstream. They then transform into bloodstream trypomastigotes and are carried to other parts of the body. They enter into other blood fluids such as lymph and spinal fluid and continue the replication process by binary vision.

Sleeping Sickness - Transmission to Vector

• Tsetse flies will acquire the disease when they bite an infected host. The blood they consume contains the parasites, which will transform into procyclic trypomastigotes in the fly's midgut where they will multiply by binary fission. Eventually, they will leave the midgut and transform into epimastigotes. The epimastigotes will then migrate to the fly's salivary glands. At that point, they will continue reproducing through binary fission. The Tsetse fly will then bite a host and infect it, starting the life cycle again.

Chagas Disease

• Chagas Disease is caused by protozoan T. b. cruzi. This disease is transmitted to humans by blood-sucking triatomine bugs. Chagas Disease occurs in the Americas from the southern part of United States to southern Argentina. While the acute phase of the disease may be asymptomatic, fever, anorexia, myocarditis and enlargement of the lymph glands, liver and spleen may occur. Chronic infections may adversely affect the heart and digestive tract and can be fatal.

Chagas Disease - Human stages

• An infected triatomine bug, also known as a kissing bug, will bite a mammalian host. While feeding, the bug releases infected feces around the bite wound. Trypomastigotes within the feces will enter into the wound or through contact with the mucous membranes. These will invade cells around the inoculation site and change into intracellular amastigotes. The amastigotes will multiply by binary fission within the cells of the infected tissues. They will eventually change into trypomastigotes. The trypomastigotes will then burst out of the infected cells and migrate to the bloodstream. Trypomastigotes that cause Chagas Disease do not reproduce within the bloodstream, unlike those that cause Sleeping Sickness. Instead, they infect other tissues, where they become amastigotes again. This is a continuous infective process.

Chagas Disease - Transmission to Vector

• Kissing bugs acquire the parasites when they bite and feed on the blood of an infected host. The trypomastigotes within the blood will multiply in the bug's midgut, then differentiate into infective metacyclic trypomastigotes in the insect's hindgut. The infected insect will bite another host, passing on the metacyclic trypomastigotes, starting the life cycle again.

Diagnosis and treatment

• For Sleeping Sickness, examination of lymph, blood, bone marrow, cerebrospinal fluid and other bodily fluids for trypomastigotes is required for diagnosis. Once a positive diagnosis has been confirmed, treatment should begin immediately. The drug for west African Sleeping Sickness is Pentamidine Isethionate. East African sleeping sickness is treated with suramin. To treat the late stage of the disease with central nervous system involvement, doctors use Melarsoprol.

  For Chagas Disease, examination of blood for trypomastigotes is required for diagnosis. Once a positive diagnosis has been confirmed, treatment should begin immediately with benznidazole or nifurtimox.