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We have isolated and characterised a Triatoma infestans cDNA encoding a lysozyme. A 174-bp fragment was amplified by PCR using degenerate oligodeoxyribonucleotide primers derived from the known amino acid sequences of lysozyme from other insects. This PCR fragment was used to screen a cDNA gut library of T. infestans. A clone containing the 3'-end of the lysozyme cDNA (219 bp) was isolated and sequenced. RACE was used to amplify the 5'-end of the lysozyme cDNA. After sequencing the complete lysozyme cDNA, the deduced 417 amino acid sequence showed high identity (40-50%) with other chicken-type lysozymes. The amino acid residues responsible for the catalytic activity and the binding of the substrate were essentially conserved. The expression pattern of the lysozyme gene in bugs at different molting and feeding states showed that this gene was upregulated in the digestive tract directly after the molt and after feeding. Additionally, this lysozyme gene was expressed differently in the different regions of the digestive tract, strongly in the cardia and stomach, the anterior regions of the midgut, and only traces of lysozyme mRNA could be detected in the small intestine, the posterior region of the midgut.

Fifth instars of Triatoma infestans with established Trypanosoma cruzi infections were dissected after different periods of starvation to determine the population density and the percentage of different developmental stages of T. cruzi in the small intestine and rectum of the bugs. After a short starvation period of 20 days, the population density in the small intestine was 20% (about 60,000) of the rectal population. The population in the small intestine was strongly reduced after an additional ten days of starvation, and no flagellates could be found there 60, 90 and 120 days after the last feeding. In the rectum, this reduction went down to 1% of the initial population, but a total elimination never occurred. Usually the remaining population contained more live than dead flagellates. Starvation also resulted in an increase in the rectum in the number and percentage of drop-like forms, intermediates between sphero- and epi- or trypomastigotes, from 1% initially to about 10% after 90 days of starvation. The percentage of spheromastigotes increased from 2% at 20 days after the last feeding to about 20% after an additional 40 and 70 days. Therefore, the spheromastigotes of T. cruzi seem to be induced by stress conditions.

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