Temporal dynamics of asymptomatic malaria in a high transmission community in Ghana

Asymptomatic Plasmodium falciparum carriers are cryptic reservoirs that sustain malaria transmission, undermining control efforts. However, its temporal dynamics and drivers remain underexplored. A total of 845 asymptomatic individuals in Simiw were screened for P. falciparum carriage in May, August, and October 2021, as well as February 2022, representing the pre-peak, peak and post peak malaria transmission seasons that fall in either the wet or dry seasons. Meteorological data from March 2021 to March 2022 was obtained. Descriptive and inferential statistical analyses, such as Poisson Generalised Linear and Distributed Lag Nonlinear Models, were conducted in R to investigate the influence of seasonality and meteorological factors on PET-PCR-detected asymptomatic Plasmodium falciparum infections. In Simiw, the prevalence of asymptomatic P. falciparum infections ranged from 6.2% to 14.0% by RDT and 13.4% to 32.0% by PET-PCR during the study period. Asymptomatic malaria cases were highest in February 2022, during the dry season. Younger participants (median age: 14 years) had more infections than adults. Seasonal trend showed the strongest nonlinear relationship (exp({beta}) = 190.38, p = 0.01). Features of the dry season predicted asymptomatic malaria cases, as average maximum temperature (exp({beta}) = 1.30, p < 0.001) was a positive nonlinear predictor, whereas average humidity (exp({beta}) = 0.73, p = 0.02) and precipitation (exp({beta}) = 0.99, p < 0.001) were negative nonlinear predictors. According to regression models, the highest counts of asymptomatic malaria cases occur at a monthly maximum temperature of 32oC, monthly average relative humidity of 91% and monthly precipitation of 20 mm, similar to records in February 2022 in the dry season. Additionally, a precipitation of 150 mm forecasted the highest number of cases two months later (exp({beta}) = 3.20, p < 0.001). In this study, the seasonal trend had a much stronger effect on asymptomatic malaria than meteorological factors, such as rainfall.