High prevalence of asymptomatic and sub-patent Plasmodium falciparum infections in Urban Bouake, Cote dIvoire, but no hrp2 deletions: Implications for Malaria Control

Asymptomatic Plasmodium falciparum infections are common in endemic settings, yet diagnosing these infections remains challenging because they are often below the limit of detection of conventional light microscopy (LM) or rapid diagnostic tests (RDTs). Deletions of the hrp2/3 gene, encoding the protein detected by the most sensitive class of RDTs, present a further threat. In this study, the prevalence of asymptomatic and sub-patent P. falciparum infections was characterized in the rainy season in the city of Bouake, Central Cote dIvoire. A cross-sectional survey was conducted in nine neighborhoods of Bouake, Cote dIvoire, in 2016. Matched LM, RDTs, and varATS qPCR, were used to determine the prevalence of P. falciparum infections and to compare the performance of the different diagnostic methods. P. falciparum hrp2/3 deletions were typed by digital PCR. Among 2313 individuals, malaria prevalence was 10.8% by microscopy, 13.0% by RDT, 35.1% by qPCR, and 37.3% (863/2313) when all three methods were combined. 96.4% (832/863) of individuals with P. falciparum infections did not report a recent fever. 57.1% (493/863) of infections were sub-patent. The prevalence was highly heterogeneous across the neighborhoods, ranging from 15% to 55.2%, and differed among age groups (<5 years: 17.7%, 5-14 years: 42.7%, [&ge;]15 years: 35.9%). Compared to varATS qPCR, LM and RDT had a low sensitivity of 24.3% and 34.2%, respectively, although both methods were highly specific (>96%). Sub-microscopic malaria infections were more prevalent in [&ge;]15-year-olds (69.9%, 349/499) and in the neighborhood of Dar es Salam (75.9%, 44/58). No hrp2 deletions were observed, and two samples carried hrp3 deletion/wild-type mixed infections. The high prevalence of asymptomatic and sub-patent infections prompts the implementation of strategies targeting these parasite reservoirs to achieve reductions in malaria burden in this high-transmission city of Cote dIvoire.