Analysis of malaria parasite RNA from decade-old Giemsa-stained blood smears and dried mosquitoes.

We have analyzed RNA isolated from recently prepared and historically preserved slides containing smears of Plasmodium-infected blood. We found that slides preserved as long as 20 years can yield RNA that is a suitable template for polymerase chain reaction (PCR) amplification. Mosquitoes that have been stored for years under ambient temperature can also be used as an RNA source. The RNA amplification from slide-derived material is shown to be dependent upon the addition of reverse transcriptase and the resultant products are specific to the developmental state of the parasite. Amplification of ribosomal RNA with primers conserved for Plasmodium and hybridization with species-specific probes provide a general, unbiased method for species determination. Messenger RNA transcripts from slides also appear to serve as templates. The procedure may add complementary information to that derived from microscopic examination of Giemsa-stained blood smears including species identification, variant antigen identification and drug resistance status.