Fig. 1 Life cycle of T. cruzi showing the four major forms of the parasite. Epimasigotes and amastigotes divide by binary fission, whereas both of the trypomastigote forms are nonreplicative. The small rounded nonflagellated amastigotes can grow in almost any mammalian cell type. In the image shown intracellular amastigotes can be identified as small red dots following DNA staining. The large red dot is the host cell nucleus. Amastigotes differentiate into bloodstream trypomastigotes, which are released after host cell lysis. These can reinvade other cells or be taken by an insect vector during a bloodmeal. (View this art in color at www.dekker.com.)
implications because it provides a theoretical basis for the use of drugs targeted directly at T. cruzi as a means of reducing chronic disease severity and/or progression.
A wide range of techniques have been developed for the diagnosis of T. cruzi infection. Unfortunately, these can lack sensitivity and/or specificity and it is often necessary to use more than one approach. For example, the success of microscopic diagnosis is limited by the low level of parasitemia out with the acute phase and serological tests can suffer from cross-reactivity with antigens of Leishmania or the nonpathogenic trypanosome Trypanosoma rangeli. More recently, encouraging results have been achieved with PCR-based approaches that exploit the species specificity of high-copy-number satellite repeat sequences. Only two drugs are currently available for the treatment of Chagas' disease, nifurtimox and benznidazole. They are partially effective against the acute stage but have several drawbacks. Both can produce toxic side effects, require long-term administration under medical supervision, and remain unproven as a treatment for chronic disease. Improved public health measures such as the ''Southern Cone Initiative'' have been successful in reducing infection rates in some countries where transmission is predominantly domestic. However, even if all the routes of parasite transmission could be blocked throughout its entire geographic range, such is the nature of the infection, some individuals will still be suffering from chronic Chagas' disease in 40 years time.
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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.