Malaria remains one of the most significant causes of morbidity and mortality throughout the world. Recent studies indicate that drugs used in HIV management can have antimalarial properties. In animal models, prophylactic doses of trimethoprim-sulfamethoxazole (TMPSMX), an antibiotic commonly used as prophylaxis against opportunistic infections in HIVexposed and HIV-infected patients, have been shown to arrest liver stage development of malaria parasites. Indeed, the liver stage of malaria parasites may be important to target since it is during this stage that clinical symptoms are absent and fewer parasites are present. TMP-SMX, used in HIV-exposed and HIV-infected subjects for opportunistic infection prophylaxis, significantly reduces clinical malaria, even in areas of moderate to high transmission intensity and high antifolate drug resistance. It is possible that reduction in liver stage parasite burden contributes to this unexpected effect. Nonetheless, the contribution of this liver-stage parasite killing to the reduction in clinical malaria observed in patients receiving TMP-SMX remains undescribed. Our primary objective aims to answer whether TMP-SMX reduces liver stage malaria infection.

For our exploratory objectives, we are interested in TMP-SMX effects on the development of anti-infection malaria immunity and effects on transmission. In mice, TMP-SMX prophylaxis during repeated malaria exposures has been shown to induce protective, anti-infection immunity against malaria (Charlotte Hobbs, unpublished data), which is distinct from naturally acquired immunity in which, after multiple infections, patients have less severe disease. TMP-SMX impact on the development of malaria-specific immunity, however, requires further investigation. Also, TMP-SMX has been shown to have sporonticidal (mosquito-oocyst killing) activity at levels achieved in patients on TMP-SMX prophylaxis in susceptible strains of P. falciparum, but the effects of TMP-SMX on transmission in the field remain undescribed.

This randomized study plans to enroll 164-220 HIV-uninfected, HIV-exposed (HUE) and 60 HIV-uninfected, HIV-unexposed (HUU) children in Kalisizo Hospital Health Center, Labor and Delivery Unit, Kalisizo, located within Rakai District, Uganda. HUE children will be randomized 1:1 into 2 arms. In the first arm (Standard of Care \[SOC\] arm), 82-110 children will receive TMP-SMX until 6 weeks after cessation of breast-feeding (age 12-18 months). In the second arm (Extended Prophylaxis \[EP\] arm), 82-110 children will receive SOC and remain on TMP-SMX for an additional 6 months after the cessation of breast-feeding. The 60 HUU children will serve as controls to establish baseline infection parameters in the community. Blood will be drawn from all subjects monthly via heel/finger stick to analyze malaria parasitemia. Additionally, venous blood will be drawn every 6 months to analyze cellular and humoral immunity. The duration of this study participation will be a minimum of 2 and up to 3 years.

Assessment of TMP-SMX impact on liver stage malaria infection and the development of protective anti-infection immunity in children will help guide decisions regarding TMP-SMX prophylaxis duration for HIV-exposed children in malaria endemic areas.