An oligonucleotide mixture based on the 21 base pair repeat sequence of Plasmodium falciparum was covalently coupled to biotin and used as a probe to detect P. falciparum DNA. The limit of detection was 10 ng. This method was further developed as a fingerprint assay for parasite strain typing. After restrictian enzyme digestion, blotting and hybridization, distinct banding patterns were obtained for the strains tested and these were reproducible. In addition, discrete differences were found between PLF-3 S + /S-strains which may implicate genetic reorganization in the switching mechanism which occurs when parasites are passed from an intact to a splenectomized animal.

An understanding of the biology of the cuticle in the larval stages of Ascariodea is of importance since the cuticle molecules not only possess a variety of functions related to survival but also have a potential role as a target for immunoprophylaxis. Thus, we made a preliminary characterization of surface proteins and antigens from 3rd-stage larvae (L3) and lung-stage larvae of Ascaris suum using two biotin-derivatives and two-dimensional polyacrylamide gel electrophoresis (2D–PAGE). The proteins labelled with biotin comprised a total of 37 and 32 spots, with molecular weights (Mr) ranging from 15 to 101kDa and isoelectric points (pI) from 3·8 to 7·6, in L3 and lung-stage larvae, respectively. The profiles revealed that the individual spots bound to one or both biotin derivatives. In addition, stage-common and stage-specific spots were found in L3 and lung-stage larvae. 2D–PAGE/immunoblotting analysis was performed with antisera from rabbits repeatedly inoculated with A. suum L3. Nineteen spots were recognized as surface antigens, with Mr ranging from 32 to 66kDa and pI from 4·9 to 7·6, from L3 and lung-stage larvae after alignment of the immunoblots with the profile of the surface proteins. These spots were found to include stage-common and stage-specific antigens. Identification of surface proteins by biotin labelling combined with 2D–PAGE allows a substantial shortening of sample preparation time for the target proteins, and will be a viable method for protein analysis of surface proteins and antigens of A. suum L3 and lung-stage larvae.