Identification and characterization of a Giardia lamblia group-specific gene.

Giardia lamblia consist of heterogeneous isolates that can be divided into at least three groups. Differential screening of a cDNA library with isolate-specific antisera identified a gene which is expressed and found only in Group 3 isolates. This gene, GLORF-C4, is 597 bp in length and predicts a deduced protein of 198 amino acids that is characterized by a polyserine motif. Giardia can also be grouped by their ability to express certain variant-specific surface proteins (VSPs), expression of which is restricted among groups. In Southern blots, probes specific to two VSPs were used to characterize isolates. Failure to detect VSP genes correlated with inability to express the same VSP. Analysis of isolates with these new probes complements and confirms the groupings previously suggested using other criteria. These genetic differences should allow differentiation of isolates and permit the application of basic epidemiological techniques to determine the manner of spread and the presence of animal reservoirs.