The immuno-epidemiology of helminth and plasmodium falciparum co-infection in individuals in the middle belt of Ghana

ABSTRACT Helminths infections affect over 2 billion people in the world. These infections are known to be associated with poverty, poor sanitation and lack of adequate clean drinking water. Malaria parasite infection on the other hand affect about 3 billion people worldwide with varying transmission patterns. In endemic areas, about 60–97% of the cases are attributable to Plasmodium falciparum (Pf) infection which is responsible for 13–28% of deaths in children under 5 years of age. Helminths are known Th2 inducers. Mainly IL-4 cytokine and characterized with high-level tissue eosinophilia, and production of IgE. Malaria parasite infection is traditionally associated with Th1 effector cells with the build-up of IFN-γ cytokines. Helminths have a complex life cycle which involve larvae penetrating the skin and further undergo a heart-lung migration before establishing to become an adult worm in a suitable place within the host. The host immune response to such infection involves both Th1 and Th2 arms of the immune system. A similar presentation is seen in the pre-erythrocytic and erythrocytic life cycles of the malaria parasite. Helminthic infections are also common in malaria endemic areas and their influence on the course of infection and the epidemiology of malaria has not been adequately investigated. This study was set up to investigate the immunoepidemiology of helminths and malaria parasites co-infections in the middle-belt of Ghana in sub-Saharan Africa. Informed consents were sought from 1836 participants, randomly selected in an observational cross-sectional study from September 2015 to August 2016. Biological samples (stool, urine and blood) were collected to screen for parasites at baseline. Those found with infections were followed-up post-treatment. Peripheral Blood Mononuclear Cells (PBMCs) were cultured and flow cytometry was used to analyse for cell phenotypes with surface markers (CD3, CD4, CD8, CD11c TCR-γδ, HLA-DR) and intracellular markers (Foxp3, IL-4 cytokine and IFN-γ cytokine). Again, from culture supernatant and plasma, using BD Cytometric Bead Array (CBA) Human Thl/Th2/Th17 kit and flow cytometry, concentrations of IL-2, IL-4, IL-6, IL-10, TNF, IFN-γ and IL-17A cytokines were estimated. Plasma from participants were also used to estimate concentrations of IgG, IgG1, IgM, IgE antibodies to helminth and malaria parasite crude antigens using ELISA. Data analysis was carried out using Stata statistical software version 13, GraphPad Prism 6 and R Statistical Software where necessary. Ethical approvals were obtained and required quality assurance processes were respected as approved. Of the total 1569 participants with complete recruitment requirements to produce all needed samples at baseline, a prevalence of 19.3% crude helminth and 28.1% crude malaria parasite were reported over the study period. The prevalence of helminth and malaria parasite co-infection was 11.0%. The study documented 55.4% of hookworm infected participants with heavy infection, 83.3% of A. lumbricoides was light infection and 44.4% of T. trichiura with heavy infection. Helminth infection had significant association with climate (OR=1.72, p=0.030), inappropriate footwear use (OR=1.64, p=0.044), farming (OR=1.43, p=0.048), inadequate hand washing (OR=0.68, p=0.048) and traditional religion (OR=3.02, p=0.007). The presence of malaria parasite infection increased the risk of contracting helminth infection (OR=1.94, p<0.001). The prevalence of malaria infections was significantly different when one considers the rainy and dry seasons. Prevalence of 15.8% anaemia was recorded and malaria parasite (p=0.001) significantly reduced haemoglobin compared to helminth infection and with malaria co-infection. With helminth, leukocytosis and eosinophilia were found to be associated significantly. Generally, populations of CD8+ (p=0.028), CD8+/IFN-γ+ (p=0.047) and CD8+/HLA-DR+ (p=0.005), gamma delta T cells (CD3+/TCR-γδ+) (p=0.005) were different among the infection groups. Upon stimulation of Peripheral Blood Mononuclear Cells (PBMCs), among malaria infected individuals, CD4+ regulatory cells producing IFN-γ+ (CD4+/Foxp3+/IFN-γ+, p=0.016), IFN-γ+ and IL-4+ production by activated CD4+ cells (CD4+/HLA-DR+/IFN-γ+ (p=0.020), CD4+/HLA-DR+/IL-4+ (p=0.032)) were significantly higher. Activated CD4+ (CD4+/HLA-DR+) cells, IL-6 (p=0.017) and IL-4 (p=0.021) were significantly higher among hookworm and malaria co-infected individuals. For antibodies, IgG1 to crude malaria parasite antigens were higher in hookworm infected than even malaria infected individuals. Low prevalence of helminth and malaria as well as their co-infections were respectively recorded in the study. Children less than school-age had helminths infections. Hookworm infections were found to boost immune response to malaria parasite antigens whereas malaria tend to suppress the necessary response needed against hookworm. The study suggests that hookworm and malaria parasite co-infection maintain the Th2 effector cell activation in-vitro using malaria parasite antigens. In hookworm and malaria endemic regions, there is the need for careful evaluation of anthelminthic use particularly in Mass Drug Administration (MDA).

Source: KNUST