MALARIA DIAGNOSIS BY THE POLYMERASE-CHAIN-REACTION - A FIELD-STUDY INSOUTHEASTERN VENEZUELA

A polymerase chain reaction (PCR) method that amplifies genus- and spe cies-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 th e results were compared to those of routine microscopical diagnosis. T he sensitivity of PCR for detection of Plasmodium vivax and P. falcipa rum malaria was 99% and 100%, respectively. However, 6 patients (6%) h arboured parasites undetected by microscopy. The PCR assay detected a high proportion of mixed infections: 29% (17/59) of the infections mic roscopically diagnosed as P. vivax were shown to be mixed infections o f 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 transmissi on 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 f ollow-up of patients after specific treatment.