Plasmodium falciparum: Stage-Specific Ribosomal RNA as a Potential Target for Monitoring Parasite Development in Anopheles stephensi

The transcriptional switch of Plasmodium falciparum ribosomal RNA A gene to the C gene was demonstrated during the developmental transition from the vertebrate blood stage to the invertebrate sporozoite stage. Expression of the sporozoite specific C gene in infected mosquitoes was not detected until Day 10 postinfectious blood meal, the time of mature oocyst formation on the midgut. As a potential target for monitoring malaria parasite development in mosquitoes, oligonucleotide probes based on sequences of small subunit ribosomal RNA were evaluated for specificity and sensitivity by filter blot hybridization against different species and stages of malaria parasites. Probes PfC02 and PfA02 were selected as the most sensitive for sporozoite and blood stage parasites, respectively. Filter blot hybridization using probe PfC02 resulted in sensitivity comparable with microscopic dissection in single mosquitoes, detecting mosquitoes with an average of 1.2 oocysts per gut or as few as 800 salivary gland sporozoites.