Sex-based differences in clearance of chronic Plasmodium falciparum infection.

Multiple studies have reported a male bias in incidence and/or prevalence of malaria infection in males compared to females. To test the hypothesis that sex-based differences in host-parasite interactions affect the epidemiology of malaria, we intensively followed Plasmodium falciparum infections in a cohort in a malaria endemic area of eastern Uganda and estimated both force of infection (FOI) and rate of clearance using amplicon deep-sequencing. We found no evidence of differences in behavioral risk factors, incidence of malaria, or FOI by sex. In contrast, females cleared asymptomatic infections at a faster rate than males (hazard ratio [HR]=1.82, 95% CI 1.20 to 2.75 by clone and HR = 2.07, 95% CI 1.24 to 3.47 by infection event) in multivariate models adjusted for age, timing of infection onset, and parasite density. These findings implicate biological sex-based differences as an important factor in the host response to this globally important pathogen.

Malaria Transmission, Infection, and Disease following Sustained Indoor Residual Spraying of Insecticide in Tororo, Uganda.

Tororo, a district in Uganda with historically high malaria transmission intensity, has recently scaled up control interventions, including universal long-lasting insecticidal net distribution in 2013 and 2017, and sustained indoor residual spraying (IRS) of insecticide since December 2014. We describe the burden of malaria in Tororo 5 years following the initiation of IRS. We followed a cohort of 531 participants from 80 randomly selected households in Nagongera subcounty, Tororo district, from October 2017 to October 2019. Mosquitoes were collected every 2 weeks using CDC light traps in all rooms where participants slept, symptomatic malaria was identified by passive surveillance, and microscopic and submicroscopic parasitemia were measured every 4 weeks using active surveillance. Over the 2 years of follow-up, 15,780 female anopheline mosquitos were collected, the majority (98.0%) of which were Anopheles arabiensis. The daily human biting rate was 2.07, and the annual entomological inoculation rate was 0.43 infective bites/person/year. Only 38 episodes of malaria were diagnosed (incidence 0.04 episodes/person/year), and there were no cases of severe malaria or malarial deaths. The prevalence of microscopic parasitemia was 1.9%, and the combined prevalence of microscopic and submicroscopic parasitemia was 10.4%, each highest in children aged 5-15 years (3.3% and 14.0%, respectively). After 5 years of intensive vector control measures in Tororo, the burden of malaria was reduced to very low transmission levels. However, a significant proportion of the population remained parasitemic, primarily school-aged children with submicroscopic parasitemia, providing a potential reservoir for malaria transmission.

Quantification of anti-parasite and anti-disease immunity to malaria as a function of age and exposure.

Fundamental gaps remain in our understanding of how immunity to malaria develops. We used detailed clinical and entomological data from parallel cohort studies conducted across the malaria transmission spectrum in Uganda to quantify the development of immunity against symptomatic P. falciparum as a function of age and transmission intensity. We focus on: anti-parasite immunity (i.e. ability to control parasite densities) and anti-disease immunity (i.e. ability to tolerate higher parasite densities without fever). Our findings suggest a strong effect of age on both types of immunity, not explained by cumulative-exposure. They also show an independent effect of exposure, where children living in moderate/high transmission settings develop immunity faster as transmission increases. Surprisingly, children in the lowest transmission setting appear to develop immunity more efficiently than those living in moderate transmission settings. Anti-parasite and anti-disease immunity develop in parallel, reducing the probability of experiencing symptomatic malaria upon each subsequent P. falciparum infection.

Antiplasmodial and cytotoxicity evaluation of 3-functionalized 2-azetidinone derivatives.

3-Azido-, 3-amino- and 3-(1,2,3-triazol-1-yl)-ß-lactams were synthesized and evaluated for their antiplasmodial activity against four strains of Plasmodium falciparum and KB cells for their cytotoxicity profiles. The presence of a cyclohexyl substituent at N-1 and a phenyl group on the triazole ring markedly improved the activity profiles of triazole-tethered ß-lactam exhibiting IC(50) values of 1.13, 1.21 and 1.00 µM against 3D7, K1 and W2 strains respectively.

A new library of C-16 modified artemisinin analogs and evaluation of their anti-parasitic activities.

A library of C-16 modified artemisinin analogs was prepared and their antimalarial as well as antileishmanial activities were evaluated. Synthesis of these compounds involved the conversion of artemisinin to its phenol derivatives 7 and 12, and subsequent parallel derivatization by introducing new chemical groups through ester, carbamate, sulfate, phosphate and isourea linkages. Comparison of in vitro antimalarial activities showed that C9-beta artemisinin analogs (8a-f) are more potent than the corresponding C9-alpha diastereomers (9a-f); however, their antileishmanial activities were in the same range. Many of the 10-deoxoartemisinin analogs studied here showed promising antiparasitic activities. For example, compounds 13a-e are approximately three times more active against drug resistant W2 strain of P. falciparum, compared to artemisinin (IC(50), approximately 0.2 - 0.6 nM; cf. artemisinin = 1.6 nM). Further, a number of compounds in this series were notably leishmanicidal, with activities comparable to or better than pentamidine (e.g., 13g and 13j). Detailed in vivo studies involving these active compounds are underway to identify lead candidates for further development.