Prevalence of and challenges in diagnosing subclinical Plasmodium falciparum infections in Southern Ghana

Abstract

Background Many national malaria elimination programmes (NMEP) are intensifying campaigns for malaria control and elimination. However, these efforts are constrained by the high prevalence of subclinical infections which may sustain local disease transmission. The detection and treatment of these subclinical and low-density infection is therefore crucial in monitoring progress towards malaria control and elimination. This study sought to determine the prevalence of subclinical infections in three districts in Ghana, the proportion that could be detected by rapid diagnostic test (RDT), and the occurrence of hrp2/hrp3 deletions which may impede diagnosis by HRP2-based RDTs. Methods A community-based, cross-sectional study was conducted in the Nkwanta South, Sekyere South, and Ga South districts in Ghana. A total of 1134 whole blood samples were screened by HRP2-based rapid diagnostic test (RDT), expert microscopy, and varATS qPCR. 304 P. falciparum positive samples were typed for hrp2/hrp3 deletions by digital PCR (dPCR). Results Parasite prevalence was 57.1% by qPCR, 40.9% by RDT, and 8.4% by microscopy. 33.8% (219/647) of infections were sub-patent. Compared to qPCR, the sensitivity of RDT was 65.7%, and the specificity of 91.9% and thus substantially higher than microscopy (sensitivity 14.4%, specificity 99.4%). Parasite prevalence was highest in children aged 5–15 years (68.2%), followed by adults > 15 years (51.2%) and children < 5 years (45.3%). Prevalence also differed across the three districts, ranging from 44.0% (183/416) in Sekyere South, 55.8% (143/253) in Ga South, to 68.8% (321/466) in Nkwanta South. No hrp2 deletions were observed, and one sample (1/304) carried hrp3 deletion. Conclusion The high prevalence of subclinical malaria infections is likely to be a potential reservoir in sustaining malaria transmission. HRP2-based RDTs detected two-thirds of the subclinical infections. Thus, community test and treatment programs using highly sensitive RDTs could be a valuable strategy to reduce the reservoir.