Asymptomatic Malaria Cases and Plasmodium Species in Mainland Tanzania and Zanzibar Archipelago (Pemba)

Malaria remains a major public health threat in Sub-Saharan Africa. According to the World Health Organization (WHO) estimates, <i>Plasmodium falciparum</i> species account for nearly 100% of the malaria cases occurring on the African continent. According to the Centers for Disease Control and Prevention (CDC), falciparum malaria predominates, but non-falciparum species are also present in Africa. The aim of the study was to assess the occurrence of asymptomatic malaria cases, as well as to identify <i>Plasmodium</i> species at two different settings with the lowest index of infections in Tanzania (according to the Tanzanian Ministry of Health < 1%), i.e., on the mainland (Arusha Region) and on the Pemba Island (Zanzibar Archipelago). The study was conducted in June 2023 and involved 722 individuals, including 449 residents of mainland Tanzania and 273 residents of the Zanzibar Archipelago. The screening consisted of two phases. In the first one, which was carried out at two different settings, i.e., in the Karatu Lutheran Hospital (Arusha Region, mainland Tanzania) and the Amal Hospital (Pemba, Zanzibar Archipelago), mRDTs (malaria rapid diagnostic tests) were performed, haemoglobin concentrations were measured, and blood samples for further molecular tests were collected onto Whatman micro cards from each of the individuals involved. In the second phase (conducted in Poland, Europe), RT-PCR tests for malaria were performed. The screening found asymptomatic <i>Plasmodium</i> infections in 4.2% of the study subjects from mainland Tanzania and in 4.8% from the Archipelago. The research confirmed cases of <i>P. falciparum</i> malaria but also found single cases of mixed infections with <i>P. falciparum</i> + <i>P. malariae</i> or <i>P. ovale</i>. The results demonstrated that the occurrence of malaria in northern mainland and Zanzibar Archipelago is higher than the official MoH reports present. The study findings are consistent with the reports by CDC, which suggest that non-falciparum species are also present in Sub-Saharan Africa.