The tpi Gene as a Tool for Epidemiological Studies of Giardiasis

Giardia duodenalis is a protozoon that causes infection in humans and animals. It can be transmitted by contaminated water, from person to person or by contact with animals; it being the cause one of the most common intestinal infections in our country, so it is a public health concern. The epidemiological study thereof requires the molecular characterization of parasites, using genes with great variability, such as the one that codes triosephosphate isomerase (tpi), and analizing the homology between isolates. The purpose of this work is to establish the identity criterion for epidemiological comparison of Giardia isolates. 2-3 stool samples were collected in alternate days from 26 patients with giardiasis. After DNA extraction, a fragment of the tpi gene and a fragment of the beta-giardin (bg) gene-used for comparison purposes-were amplified by means of PCR techniques. The obtained fragments were sequenced and the sequences analyzed with the BioEdit and DnaSP v.5.0 software. The tpi gene sequences showed a high divergence, with values of diversity. ranging from 0 to 0.21219. The appearance of multiple peaks in the chromatogram points to the presence of various clones in the same sample. The differences between isolates from the same patient where equal or higher than those found for the collection of all samples. The variability of the tpi gene does not allow identity criteria to be established, which are necessary for isolate identification. Mixed intragenotype infections occur very frequently, which suggests the environmental path is the principal path of transmission and/or there is very high genetic variability.