Molecular cloning, characterization and diagnostic performance of the Schistosoma bovis 22.6 antigen

Animal schistosomiasis caused by Schistosoma bovis is a veterinary problem in many areas of the world. It affects a large number of animals and causes important economic losses in livestock production. The 22.6 kDa antigen is a tegumental protein of unknown function, restricted to schistosomes. In S. bovis it has been identified in the tegument and in an excretion-secretion extract, consisting of several, non-glycosylated isoforms that are recognised by the sera of animals infected with S. bovis. The aims of the present work were to clone, sequence, express and characterize at molecular level the S. bovis 22.6 antigen (Sb22.6), as well as to assess the usefulness of the corresponding recombinant protein as a diagnostic antigen in ELISA tests for the detection of free-range cattle farms infested with S. bovis. Immunolocalization studies revealed that Sb22.6 is expressed in the tegument and some internal tissues of the adult worms, but it is not exposed on the surface of the adult worms and schistosomula. The reactivity of the recombinant Sb22.6 (rSb22.6) in ELISA against antibodies in sera from S. bovis experimentally infected hamsters and sera from free-range cattle from a S. bovis endemic area showed that the recombinant protein and the soluble extract of adult worms (SbC) exhibited a similar diagnostic performance. In addition, rSb22.6 did not show cross-reactions with antibodies against Fasciola hepatica, also a frequent trematode parasite in cattle. The rSb22.6 antigen can be readily produced in large amounts and in a highly reproducible fashion, avoiding the types of problem that arise upon using crude extracts such as the SbC. In conclusion, this protein represents a promising epidemiological tool for the surveillance of S. bovis and may help to implement control measures in the areas and farms were the parasite is present.