Molecular cloning of an immunogenic protein of Baylisascaris procyonis and expression in Escherichia coli for use in developing improved serodiagnostic assays.

Larva migrans caused by Baylisascaris procyonis is an important zoonotic disease. Current serological diagnostic assays for this disease depend on the use of the parasite's larval excretory-secretory (ES) antigens. In order to identify genes encoding ES antigens and to generate recombinant antigens for use in diagnostic assays, construction and immunoscreening of a B. procyonis third-stage larva cDNA expression library was performed and resulted in identification of a partial-length cDNA clone encoding an ES antigen, designated repeat antigen 1 (RAG1). The full-length rag1 cDNA contained a 753-bp open reading frame that encoded a protein of 250 amino acids with 12 tandem repeats of a 12-amino-acid long sequence. The rag1 genomic DNA revealed a single intron of 837 bp that separated the 753-bp coding sequence into two exons delimited by canonical splice sites. No nucleotide or amino acid sequences present in the GenBank databases had significant similarity with those of RAG1. We have cloned, expressed, and purified the recombinant RAG1 (rRAG1) and analyzed its diagnostic potential by enzyme-linked immunosorbent assay. Anti-Baylisascaris species-specific rabbit serum showed strong reactivity to rRAG1, while only minimal to no reactivity was observed with sera against the related ascarids Toxocara canis and Ascaris suum, strongly suggesting the specificity of rRAG1. On the basis of these results, the identified RAG1 appears to be a promising diagnostic antigen for the development of serological assays for specific detection of B. procyonis larva migrans.