Chronic Chagas disease: PCR-xenodiagnosis without previous microscopic observation is a useful tool to detect viable Trypanosoma cruzi

We evaluate the elimination of the microscopic stage of conventional xenodiagnosis (XD) to optimize the parasitological diagnosis of Trypanosoma cruzi in chronic Chagas disease. To this purpose we applied under informed consent two XD cages to 150 Chilean chronic chagasic patients. The fecal samples (FS) of the triatomines at 30, 60 and 90 days post feeding were divided into two parts: in one a microscopic search for mobile trypomastigote and/or epimastigote forms was performed. In the other part, DNA extraction-purification for PCR directed to the conserved region of kDNA minicircles of trypanosomes (PCR-XD), without previous microscopic observation was done. An XD was considered positive when at least one mobile T. cruzi parasite in any one of three periods of incubation was observed, whereas PCR-XD was considered positive when the 330 bp band specific for T. cruzi was detected. 25 of 26 cases with positive conventional XD were PCR-XD positive (concordance 96.2%), whereas 85 of 124 cases with negative conventional XD were positive by PCR-XD (68.5%). Human chromosome 12 detected by Real-time PCR used as exogenous internal control of PCR-XD reaction allowed to discounting of PCR inhibition and false negative in 40 cases with negative PCR-XD. Conclusion: PCR-XD performed without previous microscopic observation is a useful tool for detection of viable parasites with higher efficiency then conventional XD.

Correlação entre a positividade do xenodiagnóstico artificial e a quantidade de sangue e triatomíneos utilizados no exame, em pacientes chagásicos cronicos / Correlation among the positivity of the artificial xenodiagnosis and the amount of blood and triatomines used in the exam, in chronic chagasic patients

The aim of this study was to verify whether the amount of blood and number of triotomines used could improve the artificial xenodiagnosis performed in 200 chronic phase infected individuals. Ten or 40ml of peripheral blood was collected in heparinized (20.4 IU) vacuum tubes, and fed to 60 and 360 triatomines, respectively. Dipetalogaster maximus (1st instar, about 15 days after eclosion), as well as 3rd instar Triatoma infestans and Triatoma vitticeps and the 4th instar of Rhodnius neglectus were used. The faecal examinations were performed 30 and 60 days after xenodiagnosis procedure. The positivity with 10ml of blood was 19 and with 40ml, 44, from which it was concluded that a correlation existed between the amount of blood and the number of triatomines used (p < 0.01). The positivity of the xenodiagnosis ranged from 9.7 to 100, higher in young and adults up to 34 years old, but independent in relation to the sex of the chronic chagasic individuals studied.