Value of first-instar triatomines (Hemiptera; Reduviidae) in comparative xenodiagnosis of Trypanosoma (Schizotrypanum) cruzi.

A direct correlation was shown between bloodmeal intake in xenodiagnosis and subsequent infection rate with Trypanosoma (S.) cruzi, in first-stage nymphs of Panstrongylus megistus Burmeister. The parasitaemia of different hosts, or of the same host at intervals, thus can be compared indirectly by the proportion of first-stage nymphs infected in xenodiagnosis, if uniform distribution and infectivity of bloodstream trypomastigotes is assumed. This indirect comparison of host parasitaemia provides important information not obtainable otherwise, since parasitaemia often is too low for quantitative measurement. Infection rates were compared of first-instar P. megistus in experimental xenodiagnosis of patients and animals. All T. cruzi stocks originated from an endemic area of Brazil (Bahia state). Several batches of nymphs were fed sequentially on some hosts, to assess fluctuations of parasitaemia with time; in others, particularly the patients, xenodiagnosis was carried out only once.