First phenotypic and genotypic description of Fasciola hepatica infecting highland cattle in the state of Mexico, Mexico.

Fascioliasis is a plantborne and zoonotic parasitic disease caused by fasciolid liver flukes. Fasciola hepatica is the only fasciolid species described in the Americas. Human fascioliasis endemic areas are mainly located in high altitude areas of the Americas. Given the necessity to characterize F. hepatica populations involved, the phenotypic and genotypic features of fasciolid adults infecting cattle in the highland area of Toluca, State of Mexico, Mexico, were analyzed and compared to fasciolid materials from the Northern Bolivian Altiplano, representing the altiplanic transmission pattern in a hyperendemic scenario. A computer image analysis system (CIAS) was applied on the basis of standardized measurements. The aforementioned F. hepatica highland populations were compared to standard lowland natural populations of European origin (Spain and France) and F. gigantica of African origin (Burkina Faso). Liver-fluke size was studied by principal component analysis (PCA). Two phenotypic patterns could be distinguished in the F. hepatica material analyzed from the Americas: the valley pattern (Toluca, Mexico) and the altiplanic pattern (Northern Altiplano, Bolivia). PCA showed that the Altiplano population presented a large body size range with a pronouncedly lower minimum size. Mahalanobis distances demonstrated that American populations are very close to European populations. Genetic haplotyping was performed using the ribosomal DNA intergenic region, including ITS-1, 5.8S and ITS-2. The intergenic region was 951 bp-long, providing 2 combined haplotypes due to one mutation appearing in the ITS-2 sequence. Molecular results showed that Fh-1A and Fh-2A, the most frequent haplotypes of F. hepatica from southern Europe, are present in Mexican cattle. Nuclear rDNA biomarkers correlated with adult fluke phenotypic characteristics. Results showed that the Mexican population analyzed and European standard populations presented a phenotypic and genotypic homogeneity, suggesting an introduction with livestock transported during the early colonization period. Results are moreover analyzed in terms of altitude and permanent/seasonal transmission characteristics.