IL10 Haplotype Associated with Tuberculin Skin Test Response but Not with Pulmonary TB

Evidence from genetic association and twin studies indicates that susceptibility to tuberculosis (TB) is under genetic control. One gene implicated in susceptibility to TB is that encoding interleukin-10 (IL10). In a group of 2010 Ghanaian patients with pulmonary TB and 2346 healthy controls exposed to Mycobacterium tuberculosis, among them 129 individuals lacking a tuberculin skin test (PPD) response, we genotyped four IL10 promoter variants at positions −2849 , −1082 , −819 , and −592 and reconstructed the haplotypes. The IL10 low-producer haplotype −2849A/−1082A/−819C/−592C, compared to the high-producer haplotype −2849G/−1082G/−819C/−592C, occurred less frequent among PPD-negative controls than among cases (OR 2.15, CI 1.3–3.6) and PPD-positive controls (OR 2.09, CI 1.2–3.5). Lower IL-10 plasma levels in homozygous −2849A/−1082A/−819C/−592C carriers, compared to homozygous −2849G/−1082G/−819C/−592C carriers, were confirmed by a IL-10 ELISA (p=0.016). Although we did not observe differences between the TB patients and all controls, our results provide evidence that a group of individuals exposed to M. tuberculosis transmission is genetically distinct from healthy PPD positives and TB cases. In these PPD-negative individuals, higher IL-10 production appears to reflect IL-10-dependent suppression of adaptive immune responses and sustained long-term specific anergy.     

Is home management of fevers a cost‐effective way of reducing under‐five mortality in Africa? The case of a rural Ghanaian District

Objective To assess the cost‐effectiveness of two strategies of home management of under‐five fevers in Ghana – treatment using antimalarials only (artesunate–amodiaquine – AAQ) and combined treatment using antimalarials and antibiotics (artesunate–amodiaquine plus amoxicillin – AAQ + AMX). Methods We assessed the costs and cost‐effectiveness of AAQ and AAQ + AMX compared with a control receiving standard care. Data were collected as part of a cluster randomised controlled trial with a step‐wedged design. Approximately, 12 000 children aged 2–59 months in Dangme West District in southern Ghana were covered. Community health workers delivered the interventions. Costs were analysed from societal perspective, using anaemia cases averted, under‐five deaths averted and disability‐adjusted life years (DALYs) averted as effectiveness measures. Results Total economic costs for the interventions were US$ 204 394.72 (AAQ) and US$ 260 931.49 (AAQ + AMX). Recurrent costs constituted 89% and 90% of the total direct costs of AAQ and AAQ + AMX, respectively. Deaths averted were 79.1 (AAQ) and 79.9 (AAQ + AMX), with DALYs averted being 2264.79 (AAQ) and 2284.57 (AAQ + AMX). The results show that cost per anaemia case averted were US$ 150.18 (AAQ) and US$ 227.49 (AAQ + AMX) and cost per death averted was US$ 2585.58 for AAQ and US$ 3272.20 for AAQ + AMX. Cost per DALY averted were US$ 90.25 (AAQ) and US$ 114.21 (AAQ + AMX). Conclusion Both AAQ and AAQ + AMX approaches were cost‐effective, each averting one DALY at less than the standard US$ 150 threshold recommended by the World Health Organisation. However, AAQ was more cost‐effective. Home management of under‐five fevers in rural settings is cost‐effective in reducing under‐five mortality.     

Pulmonary tuberculosis: virulence of Mycobacterium africanum and relevance in HIV co-infection

Although Mycobacterium africanum is being isolated in a significant proportion of cases of pulmonary tuberculosis in West Africa, its pathogenic potential remains a matter of discussion. Recent reports leave the question of whether M. africanum causes more severe pathology than M. tuberculosis or resembles opportunistic pathogens and might gain importance in the course of the HIV pandemic. Patients with pulmonary tuberculosis associated with M. africanum (n=556) and M. tuberculosis (n=1350) were studied in Ghana, West Africa, and compared regarding self-reported signs and symptoms, chest radiography, HIV status, mycobacterial drug resistance and mycobacterial clustering as determined by spoligotyping and IS6110 fingerprints. The rate of M. africanum infections was similar in HIV-positive (27%) and HIV-negative (30%) patients. M. africanum clustered less than M. tuberculosis (21% vs 79%; OR, 0.38; 95% CI, 0.3-0.5; p<0.001) corresponding to its lower prevalence (29% vs 70%). Clinically and radiographically, no significant differences were found except that M. africanum caused lower-lobe disease less frequently than M. tuberculosis (OR, 0.39; 95% CI, 0.2-0.7; p(c)=0.01), whereby this association applied to HIV-negative patients only. No difference in virulence, as assessed by the severity of radiological presentation, was found when the two M. africanum subtypes West African 1 and West African 2 were compared. In the population studied, M. africanum closely resembled M. tuberculosis in pathology and cannot be considered an opportunistic pathogen.     

CTLA4 Autoimmunity-Associated Genotype Contributes to Severe Pulmonary Tuberculosis in an African Population

The gene of Cytotoxic T Lymphocyte-associated Antigen 4 (CTLA4), a negative regulator of T lymphocytes, contains a single-nucleotide polymorphism (SNP) at position +6230A->G (ct60A->G), which has been found associated with several autoimmune diseases and appears to reduce T-cell inhibitory activity. In Ghana, West Africa, we compared the frequencies of CTLA4 +6230 A/G and 6 haplotype-tagging SNPs in 2010 smear-positive, HIV-negative patients with pulmonary tuberculosis (TB) and 2346 controls matched for age, gender and ethnicity. We found no difference in allele frequencies between cases and controls. However, +6230A and a distinct CTLA4 haplotype and a diplotype comprising the +6230A allele were significantly less frequent among cases with large opacities in chest radiographs compared to those with small ones (P_{corrected [cor]}=0.002, P_cor=0.00045, P=0.0005, respectively). This finding suggests that an increased T-cell activity associated with the CTLA4 +6230G allele contributes to pathology rather than to protection in pulmonary TB.     

Unequal distribution of resistance-conferring mutations among Mycobacterium tuberculosis and Mycobacterium africanum strains from Ghana

Isoniazid (INH) and rifampicin (RMP) resistance in Mycobacterium tuberculosis complex (MTC) isolates are mainly based on mutations in a limited number of genes. However, mutation frequencies vary in different mycobacterial populations. In this work, we analyzed the distribution of resistance-associated mutations in M. tuberculosis and M. africanum strains from Ghana, West Africa. The distribution of mutations in katG, fabG1-inhA, ahpC, and rpoB was determined by DNA sequencing in 217 INH-resistant (INH^r) and 45 multidrug-resistant (MDR) MTC strains isolated in Ghana from 2001 to 2004. A total of 247 out of 262 strains investigated (94.3%) carried a mutation in katG (72.5%), fabG1-inhA (25.1%), or ahpC (6.5%), respectively. M. tuberculosis strains mainly had katG 315 mutations (80.1%), whereas this proportion was significantly lower in M. africanum West-African 1 (WA1) strains (43.1%; p < 0.05). In contrast, WA1 strains showed more mutations in the fabG1-inhA region (39.2%, p < 0.05) compared to M. tuberculosis strains (20.9%). In 44 of 45 MDR strains (97.8%) mutations in the 81-bp core region of the rpoB gene could be verified. Additionally, DNA sequencing revealed that 5 RMP-susceptible strains also showed mutations in the rpoB hotspot region. In conclusion, although principally the same genes were affected in INH^rM. tuberculosis and M. africanum strains, disequilibrium in the distribution of mutations conferring resistance was verified that might influence the efficiency of molecular tests for determination of resistance.     

ALOX5 variants associated with susceptibility to human pulmonary tuberculosis

The 5-lipoxygenase (ALOX5)-derived lipid mediators leukotrienes and lipoxins have regulatory functions in inflammation by modulating activities of immune cells and cytokine production. Recently, it was shown in ALOX5-/- mice that host control of Mycobacterium tuberculosis is regulated by 5-lipoxygenase (5-LO). ALOX5 polymorphisms were genotyped in 1916 sputum-positive patients with pulmonary tuberculosis (TB) from Ghana and in 2269 exposed, apparently healthy controls. Polymorphisms of a variable number of tandem repeats (VNTR) of the ALOX5 promoter and of the exonic non-synonymous variant g.760G>A were analysed by fragment length determination and fluorescence resonance energy transfer, respectively, and DNA sequencing. Mycobacterial lineages of >1400 isolates were differentiated biochemically and genetically. Carriers of one variant (n repeats not equal 5) and one wild-type VNTR allele (n = 5) or of the exonic allele g.760A had a higher risk of TB [P(corrected) = 0.026, odds ratio (OR) 1.19 (95% CI 1.04-1.37) and P(corrected) = 0.026, OR 1.21 (95% CI 1.04-1.41), respectively]. The association of the exonic variant was stronger in infections caused by the mycobacterial lineage M. africanum West-African 2 [P(corrected) = 0.024, OR 1.70; (95% CI 1.2-2.6)]. Determination of haplotypes revealed the strongest associaton with TB for the 'non-5/760A' haplotype compared with the 'non-5/760G' haplotype (P = 0.003, OR 1.50). Our observation of an association of ALOX5 variants with susceptibility to TB contributes evidence of the importance of 5-LO products to the regulation of immune responses to M. tuberculosis.