Detection of Plasmodium falciparum: a comparison of six cloned DNA probes

Probes pRepHind, Rep20, p242B1-1, pPF-14, clone 26 and 34 were compared for their applicability to detect P. falciparum in field conditions. Ninety four clinical samples from patients living in the malaria endemic area of Tumaco (Pacific Coast) plus 88 from Villavicencio (Eastern Plains) were tested in "dotblot" hybridization experiments. Probes Rep20, p242B1-1, pRepHind and pPF-14 detected up to 17 pg of purified P. falciparum DNA, while clone 26 and clone 34 detected up to 425 pg DNA. Probes pPF-14, P242B1-1, pRepHind and Rep 20 exhibited comparable detection levels of parasites in infected blood samples. Sensitivity declined from 69-94% in subjects with parasitemias higher than 10.000 par./ul to 15-42% in subjects with parasitemias lower than 100 par./ul. pPF-14 and p24B1-1 showed the highest sensitivity, while clone 26 and 34 presented significantly lower sensitivities. All probes were shown to be highly specific. Detection levels are dependent on specimen treatment. Treatment consisting of serum removal, Triton X-100 lysis, Proteinase K digestion, Phenol and Chloroform extractions followed by Ethanol precipitation yielded 100% sensitivity for specimens with parasite density higher than 1,000 par./l.