Randomly amplified polymorphic DNA (RAPD) has emerged as an effective genetic marker for analysis of Trypanosoma cruzi population variability. This method has been used to study the genetic variability of Mexican T. cruzi stocks and to relate these results to previous classifications. High clonal diversity was observed among the Mexican populations: 24 RAPD types were scored among 56 stocks analyzed. Only two stocks (3.6%) belonged to the T. cruzi II lineage, while all others belonged to T. cruzi I. The robustness of these clusters was statistically highly significant. Mexican T. cruzi I stocks formed a homogeneous group with reduced genetic distances among its members. Parasites from this group were isolated from both domestic and sylvatic cycles over a broad geographic area in Mexico. The two Mexican stocks classified as T. cruzi II (isolated from sylvatic cycles) were of the same RAPD type, although they were not closely related to the three reference T. cruzi II stocks circulating in domestic cycles in Argentina, Brazil, Bolivia, and Chile. These stocks were also unrelated to the formerly named Zymodeme III.Trypanosoma cruzi, the agent of Chagas' disease, which is widely distributed in Latin America, shows considerable genetic polymorphism (14). Extensive studies carried out by using multilocus enzyme electrophoresis have demonstrated that natural populations of T. cruzi have a clonal structure (21), which has led to subdivision of the taxon into two major lineages, T. cruzi I and T. cruzi II (1,13,18,20). Each lineage is genetically heterogeneous, and despite failure to identify subdivisions within T. cruzi I, five subgroups of T. cruzi II have been proposed as discrete typing units (DTU) on the basis of randomly amplified polymorphic DNA (RAPD) analysis (1, 5). These six DTU have been proposed as a reference framework for genetic variability and for biological characterization studies of T. cruzi stocks.A few studies have attempted to characterize Mexican T. cruzi stocks by genetic methods. Seventeen stocks were analyzed using HindIII restriction fragment length polymorphisms associated with rRNA gene spacers and kinetoplast DNA maxicircle polymorphisms (9,12,22). These studies identified two groups of Mexican stocks, which correlate with geographic origin, although assignment to a T. cruzi lineage was not possible. The same stocks were also analyzed by multilocus enzyme electrophoresis, demonstrating a high degree of heterogeneity that was not related to geographic origin (12). Analysis of minicircle kDNA variability among Mexican stocks showed no correlation between the sequence homologies of the hypervariable region of minicircles and clustering (2), contrasting with results obtained for South American stocks (3, 4).In the present study, 56 Mexican stocks, isolated from diverse hosts and with diverse geographic origins, were analyzed by RAPD. Relevant phylogenetic analyses were used to assess population variability and structure, and to evaluate the taxonomic position of Mexican stocks and their corresp...

Feeding sources of triatomine vectors (Triatoma longipennis) collected in peridomiciles in Mexico were identified by a heteroduplex assay developed with triatomine blood meals. Trypanosoma cruzi parasites were also characterized in the same blood meal samples by multiplex-polymerase chain reaction assay of mini-exon gene inter-genic regions. The main blood meal source was from rats, but the bugs were able to feed on a wide variety of hosts, and human blood meals were identified. Trypanosoma cruzi was the only flagellate species identified in the blood meals. All populations belong to the T. cruzi I lineage, a result that is consistent with the previously assumed predominance of this lineage in Mexico. This combination of blood meal and T. cruzi lineage identification provides a powerful tool for understanding T. cruzi transmission cycles.

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We analyzed triatomine blood feeding patterns to evaluate the role of peridomiciles in Trypanosoma cruzi transmission at the rural village of Tepehuaje de Morelos at Jalisco State, Mexico (1999). A total of 206 bugs were collected in 11 out of 26 households (42.3%). Nymphs predominated in the collections (64.9% of the total). Except for one Triatoma barberi female, a species that belongs to the protracta species complex, all adults were Triatoma longipennis, a species of the phyllosoma complex. Triatomines were exclusively present in peridomestic sites mainly piles of tiles and bricks, and none were found indoors. Overall infection rate was 56.6% and no significant differences (P > 0.05) were observed between nymphs and adults or males and females. Identified blood meals were chicken (29.4%), opossum (20.9%), pig (24.5%), murid (20.9%), dog (3.5%), and armadillo (0.7%). No gut content reacted against anti-human, anti-bovine, anti-rabbit, and anti-cat sera. In contrast to fifth nymphs and adults, 87% of the small nymphs fed on one host, indicating that they are less mobile than other stages. Most fifth nymphs and adults fed on domestic hosts, while small nymphs mainly fed on opossum and murid. Infection blood-meal indexes were around 50% for single meals on opossum and murid, stressing their importance as trypanosome donors. Peridomiciles in Tepehuaje could be regarded as interaction sites among domestic and wild and synanthropic mammals and triatomines, which would facilitate circulation of the same T. cruzi strains between domestic and sylvatic cycles. Stone-made walls and building materials, which hold synanthropic rodents and opossums, should be considered as targets for vector control measures.

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