Predominance of Trypanosoma cruzi lineage I in Mexico

Abstract

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.

FIG. 1.

RAPD patterns obtained with primer OPA-04 for different T. cruzi stocks. Total genomic DNA of each stock was amplified by PCR. Amplification products were analyzed by electrophoresis in 2% agarose gels and were detected by staining with ethidium bromide. MW, molecular weight markers; i, invariant bands; s, singleton bands. Unmarked bands are parsimony bands.

FIG. 2.

Unrooted neighbor-joining tree derived from Jaccard's genetic distances calculated among the 24 different RAPD types. The different genotypes are localized at each terminal branch. Reference stocks are underlined. T. cruzi I is composed of genotypes R01 to R18, and T. cruzi II comprises genotypes R20 to R23. Only significant bootstrap values, obtained by Wagner parsimony analysis, are indicated for the principal nodes.

FIG. 3.

MCA of the 24 different RAPD types scored. The ADE-4 ellipses option computes the means, variances, and covariance of each group of points on both axes and draws a corresponding ellipse. This ellipse theoretically clusters 90% of the points belonging to the different groups chosen. (a) CAR 30 and CANIII-cl1 stocks attributed to T. cruzi I; (b) CAR 30 and CANIII-cl1 stocks attributed to T. cruzi II.