Browsing by Author "Amoako, N."
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Item Analysis of erythrocyte invasion mechanisms of plasmodium falciparum clinical isolates across 3 malaria-endemic areas in Ghana(Journal of Infectious Diseases, 2015-04) Mensah-Brown, H.E.; Amoako, N.; Abugri, J.; Stewart, L.B.; Agongo, G.; Dickson, E.K.; Ofori, M.F.; Stoute, J.A.; Conway, D.J.; Awandare, G.A.Background.Plasmodium falciparum invades human erythrocytes by using an array of ligands that interact with several receptors, including sialic acid (SA), complement receptor 1 (CR1), and basigin. We hypothesized that in malaria-endemic areas, parasites vary invasion pathways under immune pressure. Therefore, invasion mechanisms of clinical isolates collected from 3 zones of Ghana with different levels of endemicity (from lowest to highest, Accra, Navrongo, and Kintampo) were compared using standardized methods. Methods.Blood samples were collected from children aged 2-14 years in whom malaria was diagnosed, and erythrocyte invasion phenotypes were determined using the enzymes neuraminidase, chymotrypsin, and trypsin, which differentially cleave receptors from the erythrocyte surface. In addition, antibodies against CR1 and basigin were used to determine the contributions of these receptors to invasion. Gene expression levels of P. falciparum invasion ligands were also examined. Results.The parasites generally expressed SA-independent invasion phenotypes across the malaria-endemic areas, with parasites from Kintampo showing the highest invasion rates in neuraminidase-treated erythrocytes. CR1 was a major mediator of SA-independent invasion, while basigin was essential for both SA-dependent and SA-independent invasion mechanisms. Furthermore, expression of the basigin ligand PfRh5 was the best predictor of donor parasitemia. Conclusions.Erythrocyte invasion phenotypes expressed by P. falciparum are influenced by endemicity levels, and the PfRh5-basigin pathway is a potential vaccine target. © The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America.Item Associations between Red Cell Polymorphisms and Plasmodium falciparum Infection in the Middle Belt of Ghana(PLoSONE 9(12): e112868., 2014) Amoako, N.; Asante, K.P.; Adjei, G.; Awandare, G.A.; Bimi, L.Red blood cell (RBC) polymorphisms are common in malaria endemic regions and are known to protect against severe forms of the disease. Therefore, it is important to screen for these polymorphisms in drugs or vaccines efficacy trials. This study was undertaken to evaluate associations between clinical malaria and RBC polymorphisms to assess biological interactions that may be necessary for consideration when designing clinical trials. In a cross-sectional study of 341 febrile children less than five years of age, associations between clinical malaria and common RBC polymorphisms including the sickle cell gene and G6PD deficiency was evaluated between November 2008 and June 2009 in the middle belt of Ghana, Kintampo. G6PD deficiency was determined by quantitative methods whiles haemoglobin variants were determined by haemoglobin titan gel electrophoresis. Blood smears were stained with Giemsa and parasite densities were determined microscopically. The prevalence of clinical malarial among the enrolled children was 31.9%. The frequency of G6PD deficiency was 19.0% and that for the haemoglobin variants were 74.7%, 14.7%, 9.1%, 0.9% respectively for HbAA, HbAC, HbAS and HbSS. In multivariate regression analysis, children with the HbAS genotype had 79% lower risk of malaria infection compared to those with the HbAA genotypes (OR P 0.21, 95% CI: 0.06–0.73, p 5 0.01). HbAC genotype was not significantly associated with malaria infection relative to the HbAA genotype (OR P - 0.70, 95% CI: 0.35–1.42, p - 0.33). G6PD deficient subgroup had a marginally increased risk of malaria infection compared to the G6PD normal subgroup (OR 5 1.76, 95% C ; 0.98–3.16, p - 0.06). These results confirm previous findings showing a protective effect of sickle cell trait on clinical malaria infection. However, G6PD deficiency was associated with a marginal increase in susceptibility to clinical malaria compared to children without G6PD deficiency.Item Comparison of genomic signatures of selection on Plasmodium falciparum between different regions of a country with high malaria endemicity(2015-07-16) Duffy, C.W.; Assefa, S.A.; Abugri, J.; Amoako, N.; Owusu-Agyei, S.; Anyorigiya, T.; MacInnis, B.; Kwiatkowski, D.P.; Conway, D.J.; Awandare, G.A.Abstract Background Genome wide sequence analyses of malaria parasites from widely separated areas of the world have identified contrasting population structures and signatures of selection. To compare relatively closely situated but ecologically contrasting regions within an endemic African country, population samples of Plasmodium falciparum clinical isolates were collected in Ghana from Kintampo in the central forest-savannah area, and Navrongo in a drier savannah area ~350 km to the north with more seasonally-restricted transmission. Parasite DNA was sequenced and paired-end reads mapped to the P. falciparum reference genome. Results High coverage genome wide sequence data for 85 different clinical isolates enabled analysis of 121,712 single nucleotide polymorphisms (SNPs). The local populations had similar proportions of mixed genotype infections, similar SNP allele frequency distributions, and eleven chromosomal regions had elevated integrated haplotype scores (|iHS|) in both. A between-population Rsb metric comparing extended haplotype homozygosity indicated a stronger signal within Kintampo for one of these regions (on chromosome 14) and in Navrongo for two of these regions (on chromosomes 10 and 13). At least one gene in each of these identified regions is a potential target of locally varying selection. The candidates include genes involved in parasite development in mosquitoes, members of variant-expressed multigene families, and a leading vaccine-candidate target of immunity. Conclusions Against a background of very similar population structure and selection signatures in the P. falciparum populations of Ghana, three narrow genomic regions showed evidence indicating local differences in historical timing or intensity of selection. Sampling of closely situated populations across heterogeneous environments has potential to refine the mapping of important loci under temporally or spatially varying selection.Item Comparison of genomic signatures of selection on Plasmodium falciparum between different regions of a country with high malaria endemicity(BMC Genomics, 2015-07) Duffy, C.W.; Assefa, S.A.; Abugri, J.; Amoako, N.; Owusu-Agyei, S.; Anyorigiya, T.; MacInnis, B.; Kwiatkowski, D.P.; Conway, D.J.; Awandare, G.A.Genome wide sequence analyses of malaria parasites from widely separated areas of the world have identified contrasting population structures and signatures of selection. To compare relatively closely situated but ecologically contrasting regions within an endemic African country, population samples of Plasmodium falciparum clinical isolates were collected in Ghana from Kintampo in the central forest-savannah area, and Navrongo in a drier savannah area ~350 km to the north with more seasonally-restricted transmission. Parasite DNA was sequenced and paired-end reads mapped to the P. falciparum reference genome. High coverage genome wide sequence data for 85 different clinical isolates enabled analysis of 121,712 single nucleotide polymorphisms (SNPs). The local populations had similar proportions of mixed genotype infections, similar SNP allele frequency distributions, and eleven chromosomal regions had elevated integrated haplotype scores (|iHS|) in both. A between-population Rsb metric comparing extended haplotype homozygosity indicated a stronger signal within Kintampo for one of these regions (on chromosome 14) and in Navrongo for two of these regions (on chromosomes 10 and 13). At least one gene in each of these identified regions is a potential target of locally varying selection. The candidates include genes involved in parasite development in mosquitoes, members of variant-expressed multigene families, and a leading vaccine-candidate target of immunity. Against a background of very similar population structure and selection signatures in the P. falciparum populations of Ghana, three narrow genomic regions showed evidence indicating local differences in historical timing or intensity of selection. Sampling of closely situated populations across heterogeneous environments has potential to refine the mapping of important loci under temporally or spatially varying selection. (PDF) Comparison of genomic signatures of selection on Plasmodium falciparum between different regions of a country with high malaria endemicity. Available from: https://www.researchgate.net/publication/280080639_Comparison_of_genomic_signatures_of_selection_on_Plasmodium_falciparum_between_different_regions_of_a_country_with_high_malaria_endemicity [accessed Sep 13 2018].Item Detection of Dengue Virus among Children with Suspected Malaria, Accra, Ghana(Emerging Infectious Diseases, 2018-08) Amoako, N.; Duodu, S.; Dennis, F.E.; Bonney, J.H.K.; Asante, K.P.; Ameh, J.; Mosi, L.; Hayashi, T.; Agbosu, E.E.; Pratt, D.; Operario, D.J.; Fields, B.et.al.We report new molecular evidence of locally acquired dengue virus infections in Ghana. We detected dengue viral RNA among children with suspected malaria by using a multipathogen real-time PCR. Subsequent sequence analysis revealed a close relationship with dengue virus serotype 2, which was implicated in a 2016 outbreak in Burkina Faso.Item High-throughput genotyping assays for identification of glycophorin B deletion variants in population studies(2021) Amuzu, D.S.Y.; Rockett, K.A.; Leffler, E.M.; Ansah, F.; Amoako, N.; Morang’a, C.M.; Hubbart, C.; Rowlands, K.; Jeffreys, A.E.; Amenga-Etego, L.N.; Kwiatkowski, D.P.; Awandare, G.A.Glycophorins are the most abundant sialoglycoproteins on the surface of human erythro cyte membranes. Genetic variation in glycophorin region of human chromosome 4 (con taining GYPA, GYPB, and GYPE genes) is of interest because the gene products serve as receptors for pathogens of major public health interest, including Plasmodium sp., Babesia sp., Influenza virus, Vibrio cholerae El Tor Hemolysin, and Escherichia coli. A large structural rearrangement and hybrid glycophorin variant, known as Dantu, which was identified in East African populations, has been linked with a 40% reduction in risk for severe malaria. Apart from Dantu, other large structural variants exist, with the most common being deletion of the whole GYPB gene and its surrounding region, resulting in multiple different deletion forms. In West Africa particularly, these deletions are estimated to account for between 5 and 15% of the variation in different populations, mostly attributed to the forms known as DEL1 and DEL2. Due to the lack of specific variant assays, little is known of the distribution of these variants. Here, we report a modification of a previous GYPB DEL1 assay and the development of a novel GYPB DEL2 assay as high-throughput PCR-RFLP assays, as well as the identification of the crossover/breakpoint for GYPB DEL2. Using 393 samples from three study sites in Ghana as well as samples from HapMap and 1000 G projects for val idation, we show that our assays are sensitive and reliable for genotyping GYPB DEL1 and DEL2. To the best of our knowledge, this is the first report of such high-throughput genotyping assays by PCR-RFLP for identifying specific GYPB deletion types in populations. These assays will enable better identification of GYPB deletions for large genetic association studies and functional experiments to understand the role of this gene cluster region in susceptibility to malaria and other diseases.Item Microbial Etiology of Acute Febrile Illness in Children Presenting to Hospitals in Ghana(University Of Ghana, 2019-07) Amoako, N.Background Acute febrile illness (AFI) is responsible for a significant number of childhood mortality and morbidity and remains a common clinical presentation at most hospitals. Lack of appropriate screening techniques present a challenge in identifying potential pathogens associated with AFI. This study investigated the microbial etiology of AFI among febrile children, evaluated the potential use of inflammatory mediators as biomarkers of fever, and developed a web-based model to predict the infection status of febrile children. Methods 858 children aged 1-15 years with acute uncomplicated fever were clinically screened using point-of-care and advanced diagnostic methods. A panel of laboratory tests comprising malaria microscopy, malaria Rapid Diagnostic Test (RDT), complete blood count, blood and urine cultures and polymerase chain reaction (PCR) were employed to screen samples for parasitic, bacterial, and viral pathogens. Concentrations of serum cytokines and hematological parameters were respectively measured using a Luminexbased magnetic bead assay and a fully automated hematology analyzer. The test of sensitivity and specificity, as well as the area under the curve (AUC) of the receiver operating characteristic (ROC) of cytokines and hematological parameters, were used as measures of diagnostic accuracy to predict fever and in the selection of the suitable data mining technique to model malaria and bacterial infection status of febrile children. Results Etiologies of fever were identified in 43.7% (374/858) of children studied. From blood samples analyzed, 38.6% (331/858) tested positive for the Plasmodium parasite which was the most frequent pathogen detected. From 140 blood and 137 urine cultures performed, 59 organisms were identified. The most common organisms isolated were Staphylococcus aureus (4.7%), Escherichia coli (3.2%), Group D Streptococcus (2.5%), Pseudomonas aeruginosa (1.8%), Non-typhoidal salmonellae (1.4%), Coagulase negative staphylococci (1.4%), Citrobacter freundii (1.1%), Enterobacter clocoae (1.1%), Salmonella Typhi (0.9%), Streptococcus pneumonia (0.7%) and Klebsiella pneumonia (0.4%). Pathogens detected using TaqMan-based PCR from 166 blood samples included: Dengue virus (1.2%), Coxiella burnetti (0.6%), Rickettsia (3.0%), HIV (0.6%) and Plasmodium falciparum (37.9%). Of the enrolled children, 3.2% had Plasmodium-bacteria coinfections: Plasmodium-Staphylococcus aureus (0.9%), Plasmodium-dengue (0.3%), and Plasmodium-Rickettsia (0.6%). From the cytokine analysis, tumor necrosis factor (TNF-α) with sensitivity of 84.4% (95% CI: 75.5-91.0) and specificity of 72.2% (95% CI: 46.5- 90.3) was the best predictor of fever, having AUC for the ROC curve to be 0.7. Lymphocyte (LYM-%) was the best hematological predictor of fever, with sensitivity of 65.2%, specificity of 67.3% and a ROC of 0.78. Naïve Bayes model, which incorporated only clinical symptoms, proved useful for the development of the interactive tool to predict infection status of children with AFI. Conclusion Malaria remains a major contributor of AFI in the study area, despite additional diagnoses of bacterial and viral origin. Dengue virus, Rickettsia felis and Coxiella burnetti were detected among the children but not clinically diagnosed. Febrile illnesses due to comorbid infection are common and call for differential diagnosis of AFI to ensure judicious use of drugs and to avoid evolution of drug resistance. In addition, routine haematological parameters including lymphocyte, and circulating cytokines such as TNF-α are useful and independent prognostic factors for fever. A web-based clinical decision tool has been developed to predict infection status of febrile patients.Item Placental malaria and the risk of malaria in infants in a high malaria transmission area in Ghana: A prospective cohort study(Journal of Infectious Diseases, 2013-08) Asante, K.P.; Owusu-Agyei, S.; Cairns, M.; Dodoo, D.; Boamah, E.A.; Gyasi, R.; Adjei, G.; Gyan, B.; Agyeman-Budu, A.; Dodoo, T.; Mahama, E.; Amoako, N.; Dosoo, D.K.; Koram, K.; Greenwood, B.; Chandramohan, D.Background. Whether the risk of malaria is increased in infants born to mothers who experience malaria during pregnancy is uncertain.Methods. We investigated malaria incidence among an infant cohort born to 355 primigravidae and 1500 multigravidae with or without placental malaria (PM) in a high malaria transmission area of Ghana. PM was assessed using placental histology.Results. The incidence of all episodes of malaria parasitemia or clinical malaria was very similar among 3 groups of infants: those born to multigravidae without PM, multigravidae with PM, and primigravidae with PM. Infants born to primigravidae without PM experienced a lower incidence of malaria parasitemia or clinical malaria than the other 3 groups: adjusted hazard ratio, 0.64 (95% confidence interval [CI],. 48-.86, P <. 01) and 0.60 (95% CI,. 43-.84, P <. 01), respectively. The incidence of malaria parasitemia or clinical malaria was about 2 times higher in most poor infants compared to least poor infants.Conclusions. There was no suggestion that exposure to PM directly increased incidence of malaria among infants of multigravidae. In our study area, absence of placental malaria in primigravidae is a marker of low exposure, and this probably explains the lower incidence of malaria-related outcomes among infants of PM-negative primigravidae. © The Author 2013. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved.