Rendimiento del xenodiagnóstico, según el número de cajas utilizadas en 1.181 personas con infección chagásica crónica diagnosticada mediante la reacción de hemaglutinación indirecta / Yielding of xenodiagnosis, according to the number of boxes utilized, in 1.181 persons with chronic chagasic infection diagnosed by means of indirect hemagglutination reaction

ABSTRACT

A study for evaluation of the yielding of xenodiagnosis (XD) in 1,181 persons with a previous positive indierect hemagglutination test (IHAT) for Trypanosoma cruzi infection was carried out. The infections of these people was detected during epidemiological surveys performed in rural-periurban and urban sections of the endemo-enzootic area of Chagas' disease in Chile, which involves the first seven, out of the thirteen political-administrative regions of the country. The sex distribution was 75.0% females and 25.0% males, varying the ages between 2 and 80 years. According to individual and geographical possibilities each person was submitted to 1-8 XD, which consisted in cylindrical wooden boxes containing seven third instar nymphs, laboratory reared, of Triatoma infestans. The boxes, covered with a pieces of tulle fixed with a rubber band were applied on the skin of the posterior side of the arm of the subject to be examined, holdea with a linen bracelet during 25-30 min. After the insects were fed the boxes were maintained in the laboratory at 27-C and 85% relative environmental humidity. Posteriorly, all the nymphs of each box were examined at 30, 60 and 90 days after application. A drop of abdominal content of each of them, homogenized with a drop of saline, was examined at the microscope looking for T. cruzi. XD resulted positive in 503 (42.6%) people. The positiveness of XD showed a trend of increasing according to the number of boxes used, from 11.4% with one to 51.6% with six. Under a practical point of view, the simultaneous application of four XD boxes seems to be advisable. In relation to the IHAT for Chagas' infection, the percentages of XD positivity increased from 39.8% in those people with lower titers (16-128) to 61.7% in those with higher titers (256-1,000)