Trypanosoma cruzi: Inoculation Schedules and Re‐isolation Methods Select Individual Strains from Doubly Infected Mice, as Demonstrated by Schizodeme and Zymodeme Analyses1

Abstract

Groups of mice received double infections with the Y and F strains of Trypanosoma cruzi, the first inoculum of either strain being followed by a second inoculum of the other strain on day 5, 15, 30-40, or 60-65. Parasites were re-isolated from blood into culture, either directly or with an intermediate passage in gamma-irradiated mice, at intervals between 7 and 35 days after the second inoculation. Strain identification in the re-isolated material was by electrophoresis of kDNA fragments generated by the EcoRI restriction endonuclease and by electrophoresis for glucosephosphate isomerase isozymes. Both strains were identified in 22% of re-isolates originating from the experimental mice and only one of them was present in the remaining re-isolates, strain F being the most frequent. In some instances either Y or F was re-isolated from the same blood source, depending on whether culturing had been preceded or not by passage through a mouse. These results are certainly related to strain differences in the various aspects of host-parasite relationship and, possibly, growth rates in culture. The results demonstrate that: (1) more than one strain of T. cruzi can coexist in the same host; (2) the timing and method of parasite isolation from the vertebrate host act as selective factors, and further passages (in mice or cultures) may completely eliminate one (or more) strain from originally mixed trypanosome population, and (3) kDNA restriction "fingerprints" and isozyme profiles are simple, sensitive, and reliable techniques for strain identification both in single and mixed preparations.

Single and concomitant experimental infectionsby Endotrypanum spp. and Leishmania (Viannia) guyanensis (Kinetoplastida: Trypanosomatidae) in the Neotropical sand fly Lutzomyia longipalpis (Diptera: Psychodidae)

“…On the other hand, the correlation between the massive infection found in the stomodeal valve of females coinfected with L. guyanensis IM4216 and the isoenzymatic char-acterization of isolates suggest that there had been selection in the culture medium. Deane et al (1984) demonstrate that the methods of parasite isolation and further passages in culture may completely eliminate one strain from originally mixed population. So, the electrophoretic profiles of isoenzymes of parasites recovered from females submitted to co-infections, including flagellates from negative females by optical microscopy suggest that the mere correlation of sand fly infection/zymodeme may induce parasitological and epidemiological incorrect considerations and that the natural infections, single or concomitant, of sand flies by Endotrypanum and Leishmania are underestimated.…”

“…Besides, the relation between the infection observed in the sand flies intestine and the biochemical and molecular characterization of parasites can lead to a mistaken interpretation regarding the specific identification of flagellates, due to the fact that the tissue cultivation and/ or host fluid originate, usually, pure isolates. According to some authors, this selection process can happen in an extremely fast way (Deane et al 1984, Spithill et al 1984, Ibrahim et al 1994. Consequently, we could have been led to an incorrect estimative of natural (co)infections of sand flies by Leishmania and Endotrypanum.…”

Reinfections with strains of Trypanosoma cruzi, of different biodemes as a factor of aggravation of myocarditis and myositis in mice

“…The conclusion is that, multiple reinfections in endemic areas could be considered an important factor in the morbidity of Chagas disease and that the rupture of this chain, by vector control has positively influenced the evolution of the disease. Previous experimental studies have demonstrated, either through biological characterization 2 or by schizodeme analysis 12 , the persistence, in the same animal, of two inoculated strains of T. cruzi in the same animal. The present study demonstrates that successive infections by T. cruzi represent a real risk of exacerbation of inflammatory cardiac lesions in chronically infected mice and the aggravation of tissue lesions in mice with multiple infections.…”

Trypanosoma cruzi: genetic structure of populations and relevance of genetic variability to the pathogenesis of chagas disease

“…Together with cloning experiments, kDNA restriction analysis demonstrated for the first time that single strains of T. cruzi could contain two or more distinct clones (Morel et al 1980). The existence of these multiclonal T. cruzi strains was confirmed later by several groups using different techniques (Deane et al 1984, Marques-Araújo & Chiari, 1988, Carneiro et al1990, Macedo et al1992, Oliveira et al 1998, 1999.…”