Chagas' Disease: Diagnosis

on 10.12.08 with 0 comments

In the acute stage the parasite may be found in the blood via a thin blood smear, thick smear or buffy coat. As a concentration technique an anion-exchange minicolumn may be used (Woo’s technique similar to Lanham’s column, but with a different buffer, see African sleeping sickness). Strout’s concentration technique includes the double centrifugation of serum (from 10-20 ml of blood), after which the motile trypanosomes can be detected in the sediment. PCR techniques for T. cruzi exist, but can only be carried out in better equipped laboratories. The serology is positive from the fourth week. To know whether the neonate from a seropositive mother is infected, PCR is performed and IgM antibodies in its blood are determined. A positive serology (IgG) 6 months after birth also indicates infection. In-vitro and in-vivo culture is possible, but usually not available. Biopsies of lymph nodes, heart and muscles sometimes show parasitic pseudocysts (amastigotes in the cells). This is quite an aggressive technique, however, and not very sensitive. Several chronic cases have been described where the parasites were seen on a blood smear, the PCR was positive, but the classical serological tests (ELISA, IFA, HAI) as well as anti-cruzipain antibodies were negative. How frequent this situation is, is not clear at present.

In the latent and chronic phases the serology is positive but only seldom will a positive parasitaemia be found. Parasites may be detected via culture (NNN-medium [Novy-Nicolle-McNeal agar] or inoculation of a test animal) and via xenodiagnosis.

Category: Medicine Notes



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