Molecular Investigation of Sub-Microscopic and Mixed Plasmodium Species Infection in North-Central Nigeria

Objective: To assess the level of sub-microscopic and mixed Plasmodium species infection in children in North-Central Nigeria.Methods: Blood sample was obtained from 960 apparently healthy children aged 2-18 years.Plasmodial parasites were identified by Giemsa-stained light microscopy and by DNA amplification of the 18S rRNA gene.Results: A total of 126 out of 960 samples (13.1%) were positive for plasmodial parasites by microscopy while 284 of the 960 samples (29.6%) were positive by the nested PCR assay.The prevalence of sub-microscopic infection was 16.5% (158/960).The proportion of microscopic asymptomatic infections was found to be significantly higher in younger children than in older children (χ 2 = 16.86;df = 2; P = 0.014), while sub-microscopic infections were more frequent in older children than in younger ones.Mono-infections of Plasmodium falciparum, Plasmodium malariae, and Plasmodium ovale were 96.1%, 1.1%, and 0.7%, respectively while 2.1% of the samples had mixed infections.Conclusions: Our results showed that sub-microscopic infections were more prevalent in the study region and this has consequences for sustaining malaria transmission in the area.The inability of microscopy to correctly identify non-falciparum species and mixed Plasmodium species infection in this study clearly shows the importance of molecular screening tools for active field surveillance.