Detection of Plasmodium by PCR: application to field studies and routine diagnosis

A nested polymerase chain reaction (PCR) method that uses genus- and specie s-specific primers was evaluated for a field study in Burkina Faso and for routine diagnosis of imported malaria in France. The results were compared to those of microscopical diagnosis. The overall parasite index was 17.5% ( 7 of 40) by PCR assay, compared with 12.5% (5 of 40) by microscopical exami nation of thick smears of field samples. By contrast, the overall parasite index was 35% (14 of 40) by both PCR and thin smear microscopical examinati on of blood from imported cases. The nested PCR assay is a powerful tool fo r epidemiological studies of malaria prevalence in endemic area. It is not however more sensitive than conventional microscopy for routine diagnosis o f imported malaria. The interpretation of our results is as following: very low parasitaemias that are undetectable by microscopy are frequently obser ved in endemic areas, however, symptomatic imported malaria cases are assoc iated with higher patent parasitaemias.