TRYPANOSOMIASIS

Trypanosoma is a genus of kinetoplastids (class Kinetoplastida), a monophyletic group of unicellular parasitic flagellate protozoa. The name is derived from the Greek trypano (borer) and soma (body) because of their corkscrew-like motion. All trypanosomes are heteroxenous (requiring more than one obligatory host to complete life cycle) and most are transmitted via a vector. The majority of species are transmitted by blood-feeding invertebrates, but there are different mechanisms among the varying species. Then in the invertebrate host they are generally found in the intestine and normally occupy the bloodstream or an intracellular environment in the mammalian host.  Trypanosomes infect a variety of hosts and cause various diseases, including the fatal human diseases sleeping sickness, caused by Trypanosoma brucei, and Chagas disease, caused by Trypanosoma cruzi.  The mitochondrial genome of the Trypanosoma, as well as of other kinetoplastids, known as the kinetoplast, is made up of a highly complex series of catenated circles and minicircles and requires a cohort of proteins for organisation during cell division.

BIOLOGY

CAUSAL AGENTS

The protozoan parasite, Trypanosoma cruzi, causes Chagas disease, a zoonotic disease that can be transmitted to humans by blood-sucking triatomine bugs.  To see drawings of some common species of triatomine bugs found in the United States.

LIFE CYCLE

An infected triatomine insect vector (or “kissing” bug) takes a blood meal and releases trypomastigotes in its feces near the site of the bite wound.  Trypomastigotes enter the host through the wound or through intact mucosal membranes, such as the conjunctiva .  Common triatomine vector species for trypanosomiasis belong to the genera Triatoma, Rhodnius, and Panstrongylus.  Inside the host, the trypomastigotes invade cells near the site of inoculation, where they differentiate into intracellular amastigotes .  The amastigotes multiply by binary fission  and differentiate into trypomastigotes, and then are released into the circulation as bloodstream trypomastigotes .  Trypomastigotes infect cells from a variety of tissues and transform into intracellular amastigotes in new infection sites.  Clinical manifestations can result from this infective cycle.  The bloodstream trypomastigotes do not replicate (different from the African trypanosomes).  Replication resumes only when the parasites enter another cell or are ingested by another vector.  The “kissing” bug becomes infected by feeding on human or animal blood that contains circulating parasites .  The ingested trypomastigotes transform into epimastigotes in the vector’s midgut .  The parasites multiply and differentiate in the midgut  and differentiate into infective metacyclic trypomastigotes in the hindgut . Trypanosoma cruzi can also be transmitted through blood transfusions, organ transplantation, transplacentally, and in laboratory accidents.

GEOGRAPHIC DISTRIBUTION

The Americas from the southern United States to southern Argentina.  Mostly in poor, rural areas of Mexico, Central America, and South America.  Chronic Chagas disease is a major health problem in many Latin American countries. 

CLINICAL FEATURES

The acute phase is usually asymptomatic, but can present with manifestations that include fever, anorexia, lymphadenopathy, mild hepatosplenomegaly, and myocarditis.  Romaña's sign (unilateral palpebral and periocular swelling) may appear as a result of conjunctival contamination with the vector's feces.  A nodular lesion or furuncle, usually called chagoma, can appear at the site of inoculation.  Most acute cases resolve over a period of a few weeks or months into an asymptomatic chronic form of the disease.  The symptomatic chronic form may not occur for years or even decades after initial infection.  Its manifestations include cardiomyopathy (the most serious manifestation); pathologies of the digestive tract such as megaesophagus and megacolon; and weight loss.  Chronic Chagas disease and its complications can be fatal.

LABORATORY DIAGNOSIS

Demonstration of the causal agent is the diagnostic procedure in acute Chagas disease.  It almost always yields positive results, and can be achieved by: Microscopic examination: a) of fresh anticoagulated blood, or its buffy coat, for motile parasites; and b) of thin and thick blood smears stained with Giemsa, for visualization of parasites. Isolation of the agent: a) inoculation in culture with specialized media (e.g. NNN, LIT); b) inoculation into mice; and c) xenodiagnosis, where uninfected triatomine bugs are fed on the patient's blood, and their gut contents examined for parasites 4 weeks later. 

For more information view the source:Center for Disease Control

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