The invariant surface glycoprotein (ISG-75) gene of Trypanosoma evansi buffalo isolate from Karnataka state in India was sequenced and analyzed to elucidate its relationship with other isolates/species. The sequenced ISG-75 gene was also explored to device a polymerase chain reaction (PCR) strategy for the diagnosis of trypanosomiasis in carrier animals. The six cloned ISG gene sequences revealed the open reading frame (ORF) of 1572 and 1527 nucleotide (nt) encoding a polypeptide of 523 and 508 amino acids (aa) respectively and belongs ISG-75 gene family. Sequence analysis revealed 91-100% and 65-99% similarity at nt and aa levels, respectively with other isolates/species and belongs to the RoTat 1.2 strain. The diagnostic PCR based on ISG-75 sequence amplifies a 407 bp product specifically from the different T. evansi isolates and could detect 0.04 pg and 1.2 ng of DNA from purified trypanosomes and T. evansi infected rat blood samples respectively. Subsequently the PCR detected 0.02 and 0.27 trypanosomes ml(-1) respectively, from purified trypanosomes and T. evansi (buffalo isolate) infected rat blood. By the developed PCR assay trypanosomal nucleic acid was detected in experimental rats and buffalo on 24 h post infection (p.i.) and 3rd day post infection (d.p.i.), respectively. The developed ISG-75 gene based PCR assay could be useful in detection of carrier status of trypanosomiasis in animals.
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