Browsing by Author "Jones, S."
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Item Detecting asymptomatic carriage of Plasmodium falciparum in southern Ghana: utility of molecular and serological diagnostic tools(Malaria Journal, 2022) Agbana, H.B.; Rogier, R.; Lo, A.; Abukari, Z.; Jones, S.; Gyan, B.; Aidoo, M.; Amoah, L.E.Background: Asymptomatic malaria infections can serve as potential reservoirs for malaria transmission. The density of parasites contained in these infections range from microscopic to submicroscopic densities, making the accurate detection of asymptomatic parasite carriage highly dependent on the sensitivity of the tools used for the diagnosis. This study sought to evaluate the sensitivities of a variety of molecular and serological diagnostic tools at determining the prevalence of asymptomatic Plasmodium falciparum parasite infections in two communities with varying malaria parasite prevalence. Methods: Whole blood was collected from 194 afebrile participants aged between 6 and 70 years old living in a high (Obom) and a low (Asutsuare) malaria transmission setting of Ghana. Thick and thin blood smears, HRP2 based malaria rapid diagnostic test (RDT) and flter paper dried blood spots (DBS) were prepared from each blood sample. Genomic DNA was extracted from the remaining blood and used in Plasmodium specifc photo-induced electron transfer poly merase chain reaction (PET-PCR) and Nested PCR, whilst the HRP2 antigen content of the DBS was estimated using a bead immunoassay. A comparison of malaria parasite prevalence as determined by each method was performed. Results: Parasite prevalence in the high transmission site of Obom was estimated at 71.4%, 61.9%, 60%, 37.8% and 19.1% by Nested PCR, the HRP2 bead assay, PET-PCR, HRP2-RDT and microscopy respectively. Parasite prevalence in the low transmission site of Asutsuare was estimated at 50.1%, 11.2%, 5.6%, 0% and 2.2% by Nested PCR, the HRP2 bead assay, PET-PCR, RDT and microscopy, respectively. The diagnostic performance of Nested PCR, PET-PCR and the HRP2 bead assay was similar in Obom but in Asutsuare, Nested PCR had a signifcantly higher sensitivity than PET-PCR and the HRP2 bead assay, which had similar sensitivity. Conclusions: Nested PCR exhibited the highest sensitivity by identifying the highest prevalence of asymptomatic P. falciparum in both the high and low parasite prevalence settings. However, parasite prevalence estimated by the HRP2 bead assay and PET-PCR had the highest level of inter-rater agreement relative to all the other tools tested and have the advantage of requiring fewer processing steps relative to Nested PCR and producing quantitative results.Item A multi-stage malaria vaccine candidate targeting both transmission and asexual parasite life-cycle stages(Elsevier BV, 2014) Theisen, M.; Roeffen, W.; Singh, S.K.; Andersen, G.; Amoah, L.; van de Vegte-Bolmer, M.; Arens, T.; Jones, S.; Bousema, T.; Adu, B.; Dziegiel, M.H.; Christiansen, M.; Sauerwein, R.Effective control and eventual eradication of malaria drives the imperative need for clinical development of a malaria vaccine. Asexual parasite forms are responsible for clinical disease and death while apathogenic gametocytes are responsible for transmission from man to mosquito. Vaccines that combine antigens from both stages may provide direct protection and indirect benefit by reducing the force of infection. We constructed a chimeric antigen composed of a fragment of the Plasmodium falciparum (Pf) glutamate-rich protein fused in frame to a correctly folded fragment of Pfs48/45. The chimera was produced in Lactococcus lactis and induced robust antibody responses in rodents to the individual components. Specific antibodies showed strong transmission blocking activity against multiple Pf-strains in the standard membrane feeding assay and functional activity against asexual stages in the antibody dependent cellular inhibition assay. The combined data provide a strong rationale for entering the next phase of clinical grade production and testing. © 2014 Elsevier Ltd.Item Naturally acquired antibody responses to recombinant Pfs230 and Pfs48/45 transmission blocking vaccine candidates(Journal of Infection, 2015-07) Jones, S.; Grignard, L.; Nebie, I.; Chilongola, J.; Dodoo, D.; Sauerwein, R.; Theisen, M.; Roeffen, W.; Singh, S.K.; Singh, R.K.; Singh, S.; Kyei-Baafour, E.; Tetteh, K.; Drakeley, C.; Bousema, T.Objectives: Pfs48/45 and Pfs230 are Plasmodium falciparum sexual stage proteins and promising malaria transmission-blocking vaccine candidates. Antibody responses against these proteins may be naturally acquired and target antigens may be under selective pressure. This has consequences for the future evaluation of vaccine immunogenicity and efficacy in populations naturally exposed to malaria. Methods: We determined naturally acquired antibody responses to the recombinant proteins Pfs48/45-10C and Pfs230-230CMB in children from three malaria endemic settings in Ghana, Tanzania and Burkina Faso. We also examined genetic polymorphisms in the P. falciparum gene pfs48/45. Results: Antibody prevalence was 1.1-18.2% for 10C and 6.7-18.9% for 230CMB. In Burkina Faso we observed evidence of an age-dependent acquisition pattern for both 10C (p<0.001) and 230CMB (p=0.031). Membrane feeding assays on a separate dataset demonstrated an association between functional transmission reducing activity and antibody prevalence for both 10C (p=0.017) and 230CMB (p=0.049). 17 single nucleotide polymorphisms were found in pfs48/45 (from 126 samples), with 5 non-synonymous SNPs in the Pfs48/45 10C region. Conclusions: We conclude there are naturally acquired antibody responses to both vaccine candidates which have functional relevance by reducing the transmissibility of infected individuals. We identified genetic polymorphisms, in pfs48/45 which exhibited geographical specificity. © 2015 The British Infection Association.Item Racial Misidentification and Psychopathology Among People of African Descent: Is there a relationship?(2010) Nonterah, C.; Mate-Kole, C.C.; Conway, J.; Jones, S.This study examined racial identity and psychopathology in people of African ancestry. Two hundred and twenty-one (221) participants were recruited comprising Continental Africans, African Americans and African Caribbean people. The results demonstrated a significant correlation between psychopathology and stages of racial identity development. Lower levels of African Self-Consciousness were related to anxiety, hostility and phobic anxiety. African Americans obtained the highest levels of African Self-Consciousness. Further factor analyses of the African Self-Consciousness scale yielded two main factors; Value for Africentric beliefs and Value for Group identification. The findings suggest that racial identity plays an important role in the mental health of people of African ancestry.