Gametocyte clearance in children, from western Kenya, with uncomplicated Plasmodium falciparum malaria after artemether-lumefantrine or dihydroartemisinin-piperaquine treatment.

BACKGROUND: The efficacy and safety of artemether-lumefantrine (AL) and dihydroartemisinin-piperaquine (DP) against asexual parasites population has been documented. However, the effect of these anti-malarials on sexual parasites is still less clear. Gametocyte clearance following treatment is essential for malaria control and elimination efforts; therefore, the study sought to determine trends in gametocyte clearance after AL or DP treatment in children from a malaria-endemic site in Kenya. METHODS: Children aged between 0.5 and 12 years from Busia, western Kenya with uncomplicated Plasmodium falciparum malaria were assigned randomly to AL or DP treatment. A total of 334 children were enrolled, and dried blood spot samples were collected for up to 6 weeks after treatment during the peak malaria transmission season in 2016 and preserved. Plasmodium falciparum gametocytes were detected by qRT-PCR and gametocyte prevalence, density and mean duration of gametocyte carriage were determined. RESULTS: At baseline, all the 334 children had positive asexual parasites by microscopy, 12% (40/334) had detectable gametocyte by microscopy, and 83.7% (253/302) children had gametocytes by RT-qPCR. Gametocyte prevalence by RT-qPCR decreased from 85.1% (126/148) at day 0 to 7.04% (5/71) at day 42 in AL group and from 82.4% (127/154) at day 0 to 14.5% (11/74) at day 42 in DP group. The average duration of gametocyte carriage as estimated by qRT-PCR was slightly shorter in the AL group (4.5 days) than in the DP group (5.1 days) but not significantly different (p = 0.301). CONCLUSION: The study identifies no significant difference between AL and DP in gametocyte clearance. Gametocytes persisted up to 42 days post treatment in minority of individuals in both treatment arms. A gametocytocidal drug, in combination with artemisinin-based combination therapy, will be useful in blocking malaria transmission more efficiently.

Genetic diversity and population structure of Plasmodium falciparum in Kenyan-Ugandan border areas.

Kenya has, in the last decade, made tremendous progress in the fight against malaria. Nevertheless, continued surveillance of the genetic diversity and population structure of Plasmodium falciparum is required to refine malaria control and to adapt and improve elimination strategies. Twelve neutral microsatellite loci were genotyped in 201 P. falciparum isolates obtained from the Kenyan-Ugandan border (Busia) and from two inland malaria-endemic sites situated in western (Nyando) and coastal (Msambweni) Kenya. Analyses were done to assess the genetic diversity (allelic richness and expected heterozygosity, [He ]), multilocus linkage disequilibrium ( ISA ) and population structure. A similarly high degree of genetic diversity was observed among the three parasite populations surveyed (mean He  = 0.76; P > 0.05). Except in Msambweni, random association of microsatellite loci was observed, indicating high parasite out-breeding. Low to moderate genetic structure (FST  = 0.022-0.076; P < 0.0001) was observed with only 5% variance in allele frequencies observed among the populations. This study shows that the genetic diversity of P. falciparum populations at the Kenyan-Ugandan border is comparable to the parasite populations from inland Kenya. In addition, high genetic diversity, panmixia and weak population structure in this study highlight the fitness of Kenyan P. falciparum populations to successfully withstand malaria control interventions.

Le Kenya a réalisé d'énormes progrès au cours de la dernière décennie dans la lutte contre le paludisme. Néanmoins, une surveillance continue de la diversité génétique et de la structure de la population de P. falciparum est nécessaire pour affiner la lutte contre le paludisme et pour adapter et améliorer les stratégies d'élimination. Douze loci microsatellites neutres ont été génotypés chez 201 isolats de P. falciparum provenant de la frontière entre le Kenya et l'Ouganda (Busia) et de deux sites d'endémie palustre situés dans l'ouest (Nyando) et sur la côte (Msambweni), au Kenya. Des analyses ont été effectuées pour évaluer la diversité génétique (richesse allélique et hétérozygotie attendue, ([He]), déséquilibre de parenté des multiple loci ( ISA ) et structure de la population. Un degré hautement similaire de diversité génétique a été observé parmi les trois populations de parasites étudiées (He = 0,76; P > 0,05). A l'exception de Msambweni, une association aléatoire entre les microsatellites a été observée, indiquant une forte reproduction des parasites. Une structure génétique faible à modérée (FST  = 0,022-0,076; P < 0,0001) a été observée avec seulement 5% de variance dans la fréquence des allèles observée parmi les populations. Cette étude montre que la diversité génétique des populations de P. falciparum à la frontière entre le Kenya et l'Ouganda est comparable à celle des populations de parasites à l'intérieur du Kenya. De plus, la diversité génétique élevée, la panmixia et la structure démographique faible dans cette étude soulignent l'aptitude des populations de P. falciparum du Kenya à résister aux interventions de lutte contre le paludisme.

Plasmodium falciparum histidine-rich protein (PfHRP2 and 3) diversity in Western and Coastal Kenya.

Plasmodium falciparum histidine-rich proteins 2 (PfHRP2) based RDTs are advocated in falciparum malaria-endemic regions, particularly when quality microscopy is not available. However, diversity and any deletion in the pfhrp2 and pfhrp3 genes can affect the performance of PfHRP2-based RDTs. A total of 400 samples collected from uncomplicated malaria cases from Kenya were investigated for the amino acid repeat profiles in exon 2 of pfhrp2 and pfhrp3 genes. In addition, PfHRP2 levels were measured in 96 individuals with uncomplicated malaria. We observed a unique distribution pattern of amino acid repeats both in the PfHRP2 and PfHRP3. 228 PfHRP2 and 124 PfHRP3 different amino acid sequences were identified. Of this, 214 (94%) PfHRP2 and 81 (65%) PfHRP3 amino acid sequences occurred only once. Thirty-nine new PfHRP2 and 20 new PfHRP3 amino acid repeat types were identified. PfHRP2 levels were not correlated with parasitemia or the number of PfHRP2 repeat types. This study shows the variability of PfHRP2, PfHRP3 and PfHRP2 concentration among uncomplicated malaria cases. These findings will be useful to understand the performance of PfHRP2-based RDTs in Kenya.

Unclear association between levels of Plasmodium falciparum lactate dehydrogenase (PfLDH) in saliva of malaria patients and blood parasitaemia: diagnostic implications?

BACKGROUND: The use of saliva in diagnosis of infectious diseases is an attractive alternative to procedures that involve blood drawing. It promises to reduce risks associated with accidental needle pricks and improve patient compliance particularly in malaria survey and drug efficacy studies. Quantification of parasitaemia is useful in establishing severity of disease and in assessing individual patient response to treatment. In current practice, microscopy is the recommended technique, despite its limitations. This study measured the levels of Plasmodium falciparum lactate dehydrogenase (PfLDH) in saliva of malaria patients and investigated the relationship with blood parasitaemia. METHODS: Matched pre-treatment blood and saliva samples were collected from patients at Msambweni District Hospital, Kenya. Parasitaemia was determined and only those confirmed to be Plasmodium falciparum mono-infected were recruited. PfLDH was quantified in saliva using a commercial ELISA kit. A total of 175 samples were collected. Relationship between blood parasitaemia and concentration of PfLDH in saliva was determined using Pearson correlation statistics. F test was used to determine whether there is a significant difference between levels of PfLDH in saliva of patients with moderate to high parasitaemia and those with low parasitaemia. RESULTS: One-hundred and seventy-five patient samples were positive for malaria by microscopy. Of these, 62 (35%) tested positive for PfLDH in saliva, 113 (65%) were false negatives. For those that tested positive, (53) 85% were from patients with moderate to high parasitaemia while 9 (15%) were from patients with low parasitaemia. A correlation co-efficient of 0.18 indicated a weak positive relationship between the concentration of PfLDH in saliva and blood parasitaemia. There was a marginal difference between levels of PfLDH in saliva of patients with moderate to high parasitaemia and those with low parasitaemia [F (1, 59) = 1.83, p = 0.1807]. CONCLUSION: The results indicate that there is a weak correlation between levels of PfLDH in saliva and blood parasitaemia. This is weak association could be as a result of low sensitivity of the assay used as well as presence of inhibitors and proteases in saliva. Further studies should be focused towards reducing the number of false negatives and developing a customised assay that is specific for detection of PfLDH in saliva.