Malaria diagnosis by the polymerase chain reaction: a field study in south-eastern Venezuela

A polymerase chain reaction (PCR) method that amplifies genus- and species-specific sequences present within the small subunit of ribosomal ribonucleic acid (ssRNA) genes of the human malaria parasites was used for the diagnosis of malaria in south-eastern Venezuela. One hundred blood samples were submitted to deoxyribonucleic acid extraction, PCR amplification and electrophoretic analysis of the PCR products, and the results were compared to those of routine microscopical diagnosis. The sensitivity of PCR for detection of Plasmodium vivax and P. falciparum malaria was 99% and 100%, respectively. However, 6 patients (6%) harboured parasites undetected by microscopy. The PCR assay detected a high proportion of mixed infections: 29% (17/59) of the infections microscopically diagnosed as P. vivax were shown to be mixed infections of P. vivax and P. falciparum. Forty per cent (7/17) of the individuals with a missed P. falciparum infection had received chloroquine in the previous 30 d. These results suggest that, in places where transmission of both P. vivax and P. falciparum occurs, PCR detection of malaria parasites can be a very useful complement to microscopical diagnosis in order to ascertain the true incidence of each species and for the follow-up of patients after specific treatment.