Browsing by Author "Amoah, Linda Eva"

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    Comparison of leucocyte profiles between healthy children and those with asymptomatic and symptomatic Plasmodium falciparum infections
    (Malaria Journal, 2020-10-09) Prah, Diana Ahu; Amoah, Linda Eva; . Gibbins, Matthew P
    Background: The immune mechanisms that determine whether a Plasmodium falciparum infection would be symptomatic or asymptomatic are not fully understood. Several studies have been carried out to characterize the associations between disease outcomes and leucocyte numbers. However, the majority of these studies have been conducted in adults with acute uncomplicated malaria, despite children being the most vulnerable group. Methods: Peripheral blood leucocyte subpopulations were characterized in children with acute uncomplicated (symptomatic; n=25) or asymptomatic (n=67) P. falciparum malaria, as well as malaria-free (uninfected) children (n=16) from Obom, a sub-district of Accra, Ghana. Leucocyte subpopulations were enumerated by flow cytometry and correlated with two measures of parasite load: (a) plasma levels of P. falciparum histidine-rich protein 2 (PfHRP2) as a proxy for parasite biomass and (b) peripheral blood parasite densities determined by microscopy. Results: In children with symptomatic P. falciparum infections, the proportions and absolute cell counts of total (CD3+) T cells, CD4+T cells, CD8+T cells, CD19+B cells and CD11c+dendritic cells (DCs) were significantly lower as compared to asymptomatic P. falciparum-infected and uninfected children. Notably, CD15+neutrophil proportions and cell counts were significantly increased in symptomatic children. There was no significant difference in the proportions and absolute counts of CD14+monocytes amongst the three study groups. As expected, measures of parasite load were significantly higher in symptomatic cases. Remarkably, PfHRP2 levels and parasite densities negatively correlated with both the proportions and absolute numbers of peripheral leucocyte subsets: CD3+T, CD4+T, CD8+T, CD19+B, CD56+NK, γδ+T and CD11c+cells. In contrast, both PfHRP2 levels and parasite densities positively correlated with the proportions and absolute numbers of CD15+cells. Conclusions: Symptomatic P. falciparum infection is correlated with an increase in the levels of peripheral blood neutrophils, indicating a role for this cell type in disease pathogenesis. Parasite load is a key determinant of peripheral cell numbers during malaria infections
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    Insecticide resistance in indoor and outdoor-resting Anopheles gambiae in Northern Ghana
    (Malaria Journal, 2020-08-31) Prah, Diana Ahu; Amoah, Linda Eva; Gibbins, Matthew P.
    Background: Selection pressure from continued exposure to insecticides drives development of insecticide resistance and changes in resting behaviour of malaria vectors. There is need to understand how resistance drives changes in resting behaviour within vector species. The association between insecticide resistance and resting behaviour of Anopheles gambiae sensu lato (s.l.) in Northern Ghana was examined. Methods: F1 progenies from adult mosquitoes collected indoors and outdoors were exposed to DDT, deltamethrin, malathion and bendiocarb using WHO insecticide susceptibility tests. Insecticide resistance markers including voltage-gated sodium channel (Vgsc)-1014F, Vgsc-1014S, Vgsc-1575Y, glutathione-S-transferase epsilon 2 (GSTe2)-114T and acetylcholinesterase (Ace1)-119S, as well as blood meal sources were investigated using PCR methods. Activities of metabolic enzymes, acetylcholine esterase (AChE), non-specifc β-esterases, glutathione-S-transferase (GST) and monooxygenases were measured from unexposed F1 progenies using microplate assays. Results: Susceptibility of Anopheles coluzzii to deltamethrin 24 h post-exposure was significantly higher in indoor (mortality=5%) than outdoor (mortality=2.5%) populations (P=0.02). Mosquitoes were fully susceptible to malathion (mortality: indoor=98%, outdoor=100%). Susceptibility to DDT was significantly higher in outdoor (mortality=9%) than indoor (mortality=0%) mosquitoes (P=0.006). Mosquitoes were also found with suspected resistance to bendiocarb but mortality was not statistically different (mortality: indoor=90%, outdoor=95%. P=0.30). Frequencies of all resistance alleles were higher in F1 outdoor (0.11–0.85) than indoor (0.04–0.65) mosquito populations, while Vgsc-1014F in F0 An. gambiae sensu stricto (s.s) was significantly associated with outdoor-resting behaviour (P=0.01). Activities of non-specific β-esterase enzymes were significantly higher in outdoor than indoor mosquitoes (Mean enzyme activity: Outdoor=: 1.70/mg protein; Indoor=1.35/mg protein. P<0.0001). AChE activity was also more elevated in outdoor (0.62/mg protein) than indoor (0.57/mg protein) mosquitoes but this was not significant (P=0.08). Human blood index (HBI) was predominantly detected in indoor (18%) than outdoor mosquito populations (3%). Conclusions: The overall results did not establish that there was a significant preference of resistant malaria vectors to solely rest indoors or outdoors, but varied depending on the resistant alleles present. Phenotypic resistance was higher in indoor than outdoor-resting mosquitoes, but genotypic and metabolic resistance levels were higher in outdoor than the indoor populations. Continued monitoring of changes in resting behaviour within An. gambiae s.l. populations is recommended.