Characteristics Of T Cruzi

T. cruzi is a member of the family Trypanosomatidae (order: Kinetoplastida), which also includes Trypano-soma brucei, the etiological agent of African sleeping sickness, and Leishmania species, which cause cutaneous/visceral leishmaniasis. Chagas' disease is a zoonosis and the parasite has been detected in more than 150 species of mammals. The opposum Didelphis, which is found throughout South America, plays a central role in the transmission between sylvatic (forest) and domestic habitats, where animals such as dogs, cats, and rodents serve as important reservoirs. T. cruzi is transmitted by blood-feeding reduviid bugs of the subfamily Triatomi-nae. In the insect vector, T. cruzi undergoes differentiation from the noninfectious epimastigote form into the metacyclic trypomastigotes that are capable of initiating an infection in the host (Fig. 1). Trypomastigotes can invade a large number of mammalian cell types including macrophages, muscle cells, and nerve cells. Epimastigotes (Fig. 2) are the stage that is most easily cultured in the laboratory.

mitochondrion kinetoplast glycosome flagellar pocket mitochondrion kinetoplast glycosome flagellar pocket

nucleus endoplasmic reticulum acidocalcisome nucleus endoplasmic reticulum acidocalcisome

Fig. 2 Schematic representation of a T. cruzi epimastigotes. T. cruzi contains a large, single mitochondrion that is dispersed through much of the cell. The mitochondrial genome is organized as a defined structure, the kinetoplast (light blue), which is adjacent to the flagellar pocket and base of the flagellum. The parasite contains other subcellular structures typical of eukaryotes including the endoplasmic reticulum (red) and the nucleus (purple). It also possesses a number of unusual organelles'6-1 such as glycosomes (dark blue) and the acidic calcium storage compartments acidocalcisomes (yellow). (View this art in color at www.dekker.com.)

T. cruzi has a complex population structure that reflects at least 60 million years of divergence. On the basis of a large number of genotypic and phenotypic studies the species has now been divided into two major groups, T. cruzi I and II.[7] Group II parasites also display marked heterogeneity and have been separated further into five subdivisions (II a-e). It has been proposed, and there is some experimental evidence,'8- that T. cruzi II is more frequently associated with the development of chronic pathology, whereas T. cruzi I gives rise to more benign disease. Given the considerable genetic diversity of the parasite this is probably an oversimplification. Until recently, reproduction in T. cruzi was thought to be exclusively asexual with the parasite having a clonal population structure. However, new data from phyloge-netic[9] and laboratory'10- studies have demonstrated that genetic exchange can occur and that it is initiated by parasite cell fusion within infected host cells. Although probably a rare event, the potential for genetic exchange could have major epidemiological consequences including the spread of undesirable phenotypes such as virulence and drug resistance.

Trypanosomatids diverged early from the main eu-karyotic lineage and their study has led to the discovery of many novel genetic and biochemical phenomena. These include mitochondrial RNA editing, unusual secondary modifications to cell surface proteins, sequestration of glycolytic and fatty acid biosynthetic enzymes in organelles called glycosomes (Fig. 2), and an oxidative defense system based on the unique low-molecular weight thiol trypanothione. Parasite-specific features such as these have attracted considerable interest in the context of drug design.'11-

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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