EFFECTS OF MALARIA ON IMMUNE RESPONSE AGAINST TUBERCULOSIS AMONG CHILDREN IN UASIN GISHU COUNTY, KENYA

Abstract

Among tuberculosis (TB) high incidence regions, Sub-Saharan Africa is particularly affected with approximately 1.6 million new cases every year and 1 million people die from malaria every year (most are children 2 - 5 years old). The efficacy of Bacille Calmette Guerin (BCG) is low and incidence of TB is high in those areas where malaria is endemic. Besides this dramatic situation, the effect of malaria on immunity to TB and data on the diversity of Mycobacterium tuberculosis complex (MTBC) strains causing this epidemic in this area are only sparsely available. The population of MTBC strains circulating and their drug susceptibility trends from malaria and TB co-infected children in Uasin Gishu County was analysed.The effect of malariaon haematological indices, BCG (before and after) vaccination, CD4+ T/CD8+ T cells and cytokine response to M. tuberculosis in malaria and TB co-infected patients and in patients with TB alone were also investigated. ZN staining was done for AFB bacilli and sputum specimens cultured in liquid (BACTEC™ MGIT 960) and solid media (LJ), and drug susceptibility tests performed for first-line drugs including (Isoniazid, Rifampicin, Streptomycin and Ethambutol) using both Genotype®MTBDRPlus andBACTEC™ MGIT 960. MTBC genotyping was carried out by Hain lifescience Line probes, while microscopy was done on Giemsa stained blood slides to examine for malaria parasites.Among the strains analyzed, the results showed that 20 (5.2%) were resistant to Isoniazid, 4 (1.4%) to rifampicin, and 2 (0.5%) were multidrug resistant (at least resistant to Isoniazid and Rifampicin). The population diversity of circulating MTBC strains was high with four different species: M. tuberculosis (91.4%), M. africanum (6.5%), M. bovis BCG(1.8%) and M. bovis (0.3%). Th1 (IL-12p40), Th2 (IL-4 and IL-5), pro-inflammatory (IL-6 and IL-8) and anti-inflammatory (TGF-β and IL-10) cytokines were measured by ELISA in 72 hour old peripheral blood mononuclear cell (PBMC) culture supernatants from 320 co-infected and 64TB patients while Th1 (IFN-γ) was measured by ELISpot. In response to PPD antigen stimulation, significantly increased levels of IL-6, IL-8, IL-10 and TGF-β and decreased IFN-γ and IL-12p40 were seen in malaria and TB co-infected patients compared to those with TB alone. In conclusion, strain classification revealed that the majority of MTBC strains circulating in this region belonged to M. tuberculosis. Resistance rates amongst these patients were at an alarming level. The population of MTBC strains circulating amongst the study patients shows an intriguing diversity raising the question of possible consequences for TB epidemic and for the introduction of new diagnostic tests or treatment strategies in malaria endemic regions. The study showed that malarial infection differentially modulates the various cytokine immune responses to M. tuberculosis antigens, which may influence the cellular and humoral immune responses to M. tuberculosis infection in a susceptible host. The study recommended a search for better diagnostic tools with respect to M. africanum and M. bovis. It also recommended for a better screening tools with respect to mycobaterial infection in malaria endemic region since TST is a delayed hypersensitivity reaction which is T-cell dependent and it was shown that malarial infections caused a depression in T-cell function which might depress the host’s response to tuberculin antigen leading to a false-negative result.