An initial series of experiments were carried out with pools of heads and bodies of S. ochraceum s.l. (a major Latin American vector of onchocerciasis). Pools containing varying numbers of heads of bodies were spiked with a single O. volvulus L3, and DNA prepared from the pools using either the conventional method of organic extractions followed by adsorption to a silica matrix, or by oligonucleotide capture of O. volvulus genomic DNA followed by magnetic purification of the captured oligonucleotide-DNA complexes. The conventional method consistently produced a positive signal in pools containing up to 50 heads (Table 1) . Pools containing greater than 50 heads were not positive in the assay. All (Table 1 ). In contrast, positive signals were obtained in all pools containing up to 200 heads or bodies in the assays performed on the oligonucleotide capture purified DNA samples ( Table 1) .