During a longitudinal study investigating the dynamics of malaria in Ugandan lakeshore communities, a consistently high malaria prevalence was observed in young children despite regular treatment. To explore the short-term performance of artemether-lumefantrine (AL), a pilot investigation into parasite carriage after treatment(s) was conducted in Bukoba village. A total of 163 children (aged 2–7 years) with a positive blood film and rapid antigen test were treated with AL; only 8·7% of these had elevated axillary temperatures. On day 7 and then on day 17, 40 children (26·3%) and 33 (22·3%) were positive by microscopy, respectively. Real-time PCR analysis demonstrated that multi-species Plasmodium infections were common at baseline, with 41·1% of children positive for Plasmodium falciparum/Plasmodium malariae, 9·2% for P. falciparum/ Plasmodium ovale spp. and 8·0% for all three species. Moreover, on day 17, 39·9% of children infected with falciparum malaria at baseline were again positive for the same species, and 9·2% of those infected with P. malariae at baseline were positive for P. malariae. Here, chronic multi-species malaria infections persisted in children after AL treatment(s). Better point-of-care diagnostics for non-falciparum infections are needed, as well as further investigation of AL performance in asymptomatic individuals.

Plasmodium malariae, a protozoan parasite that causes malaria in humans, has a global distribution in tropical and subtropical regions and is commonly found in sympatry with other Plasmodium species of humans. Little is known about the genetics or population structure of P. malariae. In the present study, we describe polymorphic genetic markers for P. malariae and present the first molecular epidemiological data for this parasite. Six microsatellite or minisatellite markers were validated using 76 P. malariae samples from a diverse geographical range. The repeat unit length varied from 2 to17 bp, and up to 10 different alleles per locus were detected. Multiple genotypes of P. malariae were detected in 33 of 70 samples from humans with naturally acquired infection. Heterozygosity was calculated to be between 0·236 and 0·811. Allelic diversity was reduced for samples from South America and, at some loci, in samples from Thailand compared with those from Malawi. The number of unique multilocus genotypes defined using the 6 markers was significantly greater in Malawi than in Thailand, even when data from single genotype infections were used. There was a significant reduction in the multiplicity of infection in symptomatic infections compared with asymptomatic ones, suggesting that clinical episodes are usually caused by the expansion of a single genotype.

The burden and duration of asymptomatic malaria infections were measured in residents of the malaria endemic village of Gonoa, Madang Province, Papua New Guinea. Plasmodium falciparum, P. vivax and P. malariae infections in people aged 4 years to adulthood were compared. Frequent sampling at 3-day intervals for up to 61 days allowed assessment of individual episodes of infection. Statistical assessment of P. falciparum detection revealed a periodicity consistent with synchronous replication of this species over periods up to 27 days. The duration of P. falciparum episodes was longer across all age groups than that of P. vivax and P. malariae. A trend for decreasing duration with age was also noted in data from each species. This was most prominent in P. falciparum infections: median duration in 4-year-olds was > 48 days compared with a median between 9 and 15 days in older children and adults. The results are consistent with the slow acquisition of immunity to antigenically diverse Plasmodium populations and suggest a faster rate of acquisition to P. vivax and P. malariae than to P. falciparum.

Monkey blood samples were collected from 214 monkeys relocated as part of the wildlife rescue organized in French Guiana during the filling of the Petit Saut Dam on the Sinnamary River. These samples were tested for malaria parasites by microscopy of thick blood films and by nested PCR for small subunit rRNA genes (SSUrRNA). Parasitic blood forms similar to Plasmodium brasilianum were detected in 4 monkey species: Alouatta seniculus macconnelli, Saguinus midas midas, Pithecia pithecia and Ateles paniscus paniscus, with the highest prevalence in Alouatta monkeys. PCR was more sensitive than the conventional method for detecting low-grade parasitaemia in positive monkeys. The examination of blood films indicated that 5·6% of the animals carried parasites whereas the nested PCR for ribosomal DNA indicated a prevalence of 11·3%. The P. brasilianum SSUrRNA gene sequence was analysed and aligned with those from P. malariae, P. falciparum and P. vivax. This suggested that P. brasilianum and P. malariae are very closely related. Similar results were obtained from analysis of the sequences in P. malariae and P. brasilianum isolates of a polymorphic gene fragment analogous to the merozoite surface protein-1 (MSP-1) gene of P. falciparum. The P. brasilianum/P. malariae sequences were more similar to those of P. vivax than to those of P. falciparum, at least in the gene region examined. The high degree of DNA homology in the sequences of the SSUrRNA and msp1-like genes is consistent with other characterizations demonstrating a taxonomic relationship between P. brasilianum and P. malariae species. Our results provide further evidence that P. brasilianum and P. malariae are virtually identical and should probably be considered to be a single malaria species. This raises the question as to whether monkeys living in the rainforest are natural reservoirs for both simian and human malaria. These results have implications for the interpretation of the current epidemiological situation in French Guiana.