Dynamics of anti-MSP3 and Pfs230 antibody responses and multiplicity of infection in asymptomatic children from southern Ghana.

BACKGROUND: During a Plasmodium infection, exposure of human host immune cells to both the asexual and the sexual stages of the parasite elicit immune responses. These responses may be protective and prevent the development of high parasitaemia and its associated clinical symptoms, or block the transmission of malaria to an uninfected person. This study aimed at examining the dynamics of naturally acquired immune responses against the asexual and sexual forms of Plasmodium falciparum as well as assessing differences in the multiplicity of infection (MOI) in asymptomatic Ghanaian children living in two communities with varying malaria transmission intensities. METHODS: School children aged between 6 and 12 years were recruited from Obom, a high malaria prevalence setting and Abura, a low malaria prevalence setting and enrolled in monthly multiple cross sectional surveys between February and May 2015. Filter paper blood blots (DBS) as well as thick and thin blood smears were made from finger-pricked blood at each visit. Plasmodium falciparum parasite prevalence was determined by microscopy and PCR. Serum eluted from the DBS were used to assess anti-Pfs230 (sexual stage) and anti-MSP3 (asexual stage) antibody levels using indirect ELISA and DNA extracted from the DBS used to assess MOI. RESULTS: Malaria parasite point prevalence and MOI throughout the study was higher in Obom than Abura. The trend of parasite prevalence estimated by microscopy was similar to that determined by PCR in Obom but not in Abura. The trend of MSP3 antibody seroprevalence followed that of PCR-estimated parasite prevalence in Obom, while in Abura the trend of Pfs230 antibody seroprevalence followed that of PCR-estimated parasite prevalence. CONCLUSIONS: Microscopy can more accurately predict changes in parasite prevalence in high transmission settings than low transmission settings. In high transmission settings, P. falciparum parasite prevalence can predict antibody seroprevalence to MSP3, whilst in low transmission settings, seroprevalence against Pfs230 may be a useful predictor of parasite prevalence.

Plasmodium falciparum genotype and gametocyte prevalence in children with uncomplicated malaria in coastal Ghana.

BACKGROUND: Plasmodium falciparum gametocytes are vital to sustaining malaria transmission. Parasite densities, multiplicity of infection as well as asexual genotype are features that have been found to influence gametocyte production. Measurements of the prevalence of Plasmodium sp. gametocytes may serve as a tool to monitor the success of malaria eradication efforts. METHODS: Whole blood was collected from 112 children aged between 6 months and 13 years with uncomplicated P. falciparum malaria attending three health facilities in southern Ghana from June to August, 2014 before (day 0) and 4 days after completion of anti-malaria drug treatment (day 7). Malaria parasites were observed by microscopy and polymerase chain reaction (PCR); submicroscopic gametocyte carriage was measured by a Pfs25 (PF3D7_1031000) mRNA real time reverse transcriptase polymerase chain reaction (RT-PCR). Parasite genotyping was performed on gDNA extracted from dried filter paper blood blots by amplification of the polymorphic regions of msp1 (PF3D7_0930300) and msp2 (PF3D7_0206800) using PCR. RESULTS: Microscopy estimated 3.1% (3/96) of the total population to carry gametocytes on day 0, which decreased to 2.1% (2/96) on day 7. In contrast, reverse transcriptase-real time PCR (RT-PCR) analysis of a subset of 35 samples estimated submicroscopic gametocyte carriage to be as high as 77% (27/35) using primers specific for Pfs25 (CT < 35) on day 0 and by day 7 this only declined to 60% (21/35). Genotyping the msp2 gene identified higher levels of MOI than the msp1 gene. CONCLUSIONS: Although below detection by microscopy, gametocyte prevalence at submicroscopic levels are high in this region and emphasize the need for more effective elimination approaches like the development of transmission-blocking vaccines and safer gametocytocidal drugs.

Plasmodium falciparum histidine rich protein-2 diversity and the implications for PfHRP 2: based malaria rapid diagnostic tests in Ghana.

BACKGROUND: Malaria rapid diagnostic tests (RDTs) play a key role in malaria management and control. The PfHRP-2 based RDT is the most widely used RDT for malaria diagnosis in Ghana. Deletion of pfhrp2 in Plasmodium falciparum parasites affect the diagnostic accuracy of PfHRP-2 based RDT kits. Identifying the prevalence and distribution of P. falciparum parasites with deleted pfhrp2 is important for malaria control. AIM: The purpose of this study was to identify and confirm the prevalence of pfhrp2 deletant P. falciparum parasites circulating within different regions of Ghana. METHODS: DNA was extracted from the membrane of spent CareStart™ PfHRP-2 RDT kits and dried filter paper blood blots using Chelex-100. Exon 2 of pfhrp2 and pfhrp3 genes were amplified by polymerase chain reaction (PCR), resolved by agarose gel electrophoresis and visualized under UV light. RESULTS: Microscopic analysis of blood smears from samples that were PfHRP-2 RDT positive revealed a parasite prevalence of 54/114 (47.4 %) and 2/26 (7.7 %) in Accra and Cape Coast, respectively. PCR analysis increased parasite prevalence in the RDT positive samples to 94/114 (82.5 %) and 6/26 (23.1 %) in Accra and Cape Coast respectively. The exon 2 of the pfhrp2 gene was deleted in 18/54 (33.3 %) of the microscopy confirmed and 36.2 % (34/94) of the PCR confirmed RDT positive samples collected in Accra. No RDT sample, confirmed to contain parasites by either PCR or microscopy was negative by pfhrp2 exon 2 PCR in Cape Coast. A survey of an additional 558 DBS revealed that 22.4 % (46/205) and 40 % (44/110) of PCR positive samples in Accra and Cape Coast, respectively, lacked the exon 2 region of pfhrp2 and possibly the entire pfhrp2 gene. CONCLUSIONS: A high number of P. falciparum parasites, which lack pfhrp2 exon 2 gene have been identified in two communities in Ghana. Continuous nationwide monitoring of the prevalence of pfhrp2 deletant parasites would be essential to malaria control. The use of RDT kits that are effective at malaria diagnosis despite deletion of pfhrp2, such as the PfHRP-2/PfLDH combo RDT kit could enhance the diagnosis of clinical malaria in Ghana.