Quantitative studies with first-instar triatomines in the xenodiagnosis of Trypanosoma (Schizotrypanum) cruzi in experimentally and naturally infected hosts

Abstract

Over 2,300 first-instar triatomines ( Panstrongylus megistus, Triatoma infestans and Rhodnius prolixus ) were used in quantitative simultaneous xenodiagnosis of Trypanosoma cruzi infections of 29 patients with chronic Chagas's disease, six naturally infected opossums ( Didelphis azarae ), 15 laboratory mice and an experimentally infected Rhesus monkey. This showed that the small bloodmeal size of first-instar triatomines is a disadvantage for xenodiagnosis in hosts with low peripheral parasitaemias but that repeated xenodiagnosis of hosts using large numbers of first-instar bugs can provide useful comparative information relatively quickly and simply. Rectal infections with T. cruzi in P. megistus, Triatoma infestans and R. prolixus were microscopically patent within seven to ten days of a single infective feed in the first instar. There was no significant change in infection rate if examination was delayed for up to four weeks. In the first instar the quantity of blood ingested by the three species during a single feed from various hosts was measured by weighing, either of individual insects or of groups. There were significant interspecific differences when fed on monkey and rabbit but not when fed on opossum. A critical quantity of blood was necessary for each species to ecdyse successfully after a single feed in the first instar: critical weight ranges were 3.0 to 4.3 mg for P. megistus , 2.0 to 3.25 mg for T. infestans and 1.35 to 3.0 mg for R. prolixus. R. prolixus took the largest feeds from opossum and P. megistus from man; feeds of T. infestans from monkey, rabbit and opossum did not differ greatly. Experimental xenodiagnosis of the infected Rhesus monkey showed that for each species there was a direct correlation between bloodmeal size and subsequent infection with Trypanosoma cruzi . An inter-relationship between bloodmeal intake, ecdysis and rate of rectal infection with T. cruzi was demonstrated in all three species.