Plasmodium falciparum, the most common malarial parasite in sub-Saharan Africa, accounts for a high number of deaths in children less than five years of age. In malaria-endemic countries with stable transmission, semi-immunity is usually acquired after childhood. For adults, severe malaria is rare. Infected adults have either uncomplicated malaria or asymptomatic parasitemia. During a period of one year, we screened 497 afebrile males to investigate the prevalence of asymptomatic P. falciparum parasitemia in villages near Lambaréné, Gabon by use of three different methods. A total of 52% of the individuals had parasites detected by a subtelomeric variable open reading frame polymerase chain reaction (stevor-PCR), 27% of the rapid diagnostic test results were positive, and 12% of the thick blood smears with low parasitemias had P. falciparum. Most positive cases were only detected by the stevor-PCR. Asymptomatic P. falciparum parasitemia in adults living in a malaria-endemic country is frequent.

In 1913 Albert Schweitzer founded one of the first modern hospitals in Africa dedicated to the health of the local population. The Albert Schweitzer Hospital is located in Lambaréné, a small town in Gabon. In 1981 a research department--the Medical Research Unit--was established with the aim to perform research in the field of infectious diseases ( www.lambarene.org ). The main focus lies on clinical research on malaria and other parasitic diseases. Studies on the molecular biology and immunology of parasitic diseases are fostered since the inauguration of a novel building dedicated for basic science. A training program in clinical research in tropical diseases for African scientists has been set up recently.

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Plasmodium infections in endemic areas are often asymptomatic, can be caused by different species and contribute significantly to transmission. We performed a cross-sectional study in February/March 2016 including 840 individuals ≥ 1 year living in rural Gabon (Ngounié and Moyen-Ogooué). Plasmodium parasitemia was measured by high-sensitive, real-time quantitative PCR. In a randomly chosen subset of P . falciparum infections, gametocyte carriage and prevalence of chloroquine-resistant genotypes were analysed. 618/834 (74%) individuals were positive for Plasmodium 18S-rRNA gene amplification, of these 553 (66.3%) carried P . falciparum , 193 (23%) P . malariae , 74 (8.9%) P . ovale curtisi and 38 (4.6%) P . ovale wallikeri . Non-falciparum infections mostly presented as mixed infections. P . malariae monoinfected individuals were significantly older (median age: 60 years) than coinfected (20 years) or P . falciparum monoinfected individuals (23 years). P . falciparum gametocyte carriage was confirmed in 109/223 (48.9%) individuals, prevalence of chloroquine-resistant genotypes was high (298/336, 89%), including four infections with a new SVMNK genotype. In rural Gabon, Plasmodium infections with all endemic species are frequent, emphasizing that malaria control efforts shall cover asymptomatic infections also including non-falciparum infections when aiming for eradication.