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Randomized clinical trials are the most reliable approaches to evaluating the effects of new treatments and vaccines. During the 2014-2015 West African Ebola epidemic, many argued that such trials were neither ethical nor feasible in an environment of limited health infrastructure and severe disease with a high fatality rate. Consensus among the numerous organizations providing help to the affected areas was never achieved, resulting in fragmented collaboration, delayed study initiation, and ultimately failure to provide definitive evidence on the efficacy of treatments and vaccines. Randomized trials were in fact approved by local ethics boards and initiated, demonstrating that randomized trials, even in such difficult circumstances, are feasible. Improved planning and collaboration among research and humanitarian organizations, and affected communities, in the interepidemic periods are needed to ensure that questions regarding the efficacy of vaccines and treatments can be definitively answered during future public health emergencies.

Background: There is considerable variability in the outcome of Mycobacterium tuberculosis infection. We hypothesized that Mycobacterium africanum was less likely than M. tuberculosis to transmit and progress to tuberculosis disease., Methods: In a cohort study of patients with tuberculosis and their household contacts in The Gambia, we categorized 1808 HIV-negative tuberculosis contacts according to exposure to M. tuberculosis or M. africanum. Positive skin test results indicated transmission, and development of tuberculosis during 2 years of follow-up indicated progression to disease., Results: Transmission rates were similar, but rates of progression to disease were significantly lower in contacts exposed to M. africanum than in those exposed to M. tuberculosis (1.0% vs. 2.9%; hazard ratio [HR], 3.1 [95% confidence interval {CI}, 1.1-8.7]). Within M. tuberculosis sensu stricto, contacts exposed to a Beijing family strain were most likely to progress to disease (5.6%; HR relative to M. africanum, 6.7 [95% CI, 2.0-22])., Conclusions: M. africanum and M. tuberculosis transmit equally well to household contacts, but contacts exposed to M. africanum are less likely to progress to tuberculosis disease than those exposed to M. tuberculosis. The variable rate of progression by lineage suggests that tuberculosis variability matters in clinical settings and should be accounted for in studies evaluating tuberculosis vaccines and treatment regimens for latent tuberculosis infection.

Commercial tests measuring IFN-gamma responses to ESAT-6 and CFP-10 are available for diagnosing Mycobacterium tuberculosis infection. Measures that minimize cost and complexity will facilitate their application in less-developed countries. We investigated whether overlapping peptides representing both ESAT-6 and CFP-10 are required to detect M. tuberculosis infection in a high TB-burden country, and whether they can be combined in a single pool. ESAT-6 and CFP-10 peptides were compared in IFN-gamma enzyme-linked immunospot (ELISPOT) in 183 HIV-negative smear-positive TB cases and 1673 HIV-negative household contacts. Separate peptide pools for each antigen were compared with a combined pool in 498 contacts. Forty per cent of responsive contacts recognized both antigens, 51% only ESAT-6 and 10% only CFP-10, whereas 56% of responsive cases recognized both antigens, 30% only ESAT-6 and 13% only CFP-10. Accordingly, CFP-10 response rates were higher for TB cases (odds ratio 2.409, P<0.001). Low purified protein derivative response rates indicated that responses to CFP-10 only were non-specific in contacts. Agreement between peptides in separate versus combined pools was good (kappa=0.758, r=0.840). Therefore a combined ESAT-6/CFP-10 peptide pool provided maximum sensitivity and efficiency, but CFP-10 was mainly required to detect active disease.

Contact investigation is a key component of tuberculosis (TB) control in developed, but not developing, countries. We aimed to measure the prevalence of TB among household contacts of sputum-smear-positive TB cases in The Gambia and to assess the sensitivity of an enzyme-linked immunospot (ELISPOT) assay in this regard. Household contacts of adult smear-positive TB patients were assessed by questionnaire, purified protein derivative (PPD) skin test, ELISPOT assay, physical examination, chest X-ray and sputum/gastric aspirate. Thirty-three TB cases were identified from 2174 of 2381 contacts of 317 adult smear-positive pulmonary TB patients, giving a prevalence of 1518/100000. The cases identified tended to have milder disease than those passively detected. The sensitivity of ESAT-6/CFP-10 ELISPOT test as a screening test for TB disease was estimated as 71%. Fifty-six per cent of contacts with a PPD skin test result >or=10mm induration had detectable responses to ESAT-6/CFP-10 by ELISPOT; 11% with a negative PPD skin test (<10mm) had a positive ESAT-6/CFP-10 response. Active screening for TB among contacts of TB patients may have a role in TB control in The Gambia. These individuals are a high-risk group, and the disease identified is less advanced than that found through passive case detection. An ELISPOT assay was relatively insensitive as a screening test for TB.

Background: Mycobacterium africanum, a member of the M. tuberculosis complex that is infrequently found outside of western Africa, is the cause of up to half of the tuberculosis cases there., Methods: We genotyped mycobacterial isolates obtained from a study of patients with tuberculosis and their household contacts and compared T cell responses and tuberculin skin test results by infecting genotype., Results: The T cell response to early secreted antigenic target, 6 kDa (ESAT-6), was attenuated in patients with tuberculosis (odds ratio [OR], 0.41 [95% confidence interval {CI}, 0.19-0.89]; P = .024) and household contacts (OR, 0.56 [95% CI, 0.38-0.83]; P = .004) infected with M. africanum, compared with the response in those infected with M. tuberculosis. In these same groups, responses to culture filtrate protein, 10 kDa (CFP-10), were nonsignificantly attenuated (P = .22 and P = .16, respectively), as were tuberculin skin test results (P = .30 and P = .46, respectively). Sequencing of region of difference 1 of M. africanum revealed that Rv3879c is a pseudogene in M. africanum; however, this finding does not provide an obvious mechanism for the attenuated ESAT-6 response., Conclusions: This is the first evidence, to our knowledge, that strain differences affect interferon- gamma -based T cell responses. Our findings highlight the need to test new diagnostic candidates against different strains of mycobacteria. Integrating additional immunologic and genomic comparisons of M. tuberculosis and M. africanum into further studies may provide fundamental insights into the interactions between humans and mycobacteria.

The in vitro IFN-gamma response to tuberculin was recently proposed as a correlate of vaccine-induced immunity to tuberculosis. IFN-gamma also plays a central role in the tuberculin skin test (TST), commonly used as a marker of mycobacterial infection. However, the use of TST as a marker of immunity to tuberculosis is limited for reasons ascribed mainly to interference by environmental mycobacteria. We prospectively investigated the relationship between the TST and cytokine responses to BCG in early infancy, a cohort with relatively low exposure to environmental mycobacteria. Neonatal BCG vaccination induced positive TST responses and predominant IFN-gamma responses to tuberculin in most newborns. However, the production of IFN-gamma, IL-5 and IL-13 was similar in TST responders and non-responders, and there was no significant correlation between the size of TST response and cytokine production. These results indicate that the IFN-gamma assay provides different information than TST in BCG-vaccinated newborns and could be a better marker of vaccine-induced immunity.

Background: Currently, reliable efficacy markers for assessment of new interventions against tuberculosis (TB) are limited to disease and death. More precise measurement of the human immune response to Mycobacterium tuberculosis infection may be important. A qualitative enzyme-linked immunospot assay (ELISPOT) result for early secretory antigenic target 6 (ESAT-6) and culture filtrate protein 10 (CFP-10) offers improved specificity over the purified protein derivative (PPD) skin test reaction in the detection of M. tuberculosis infection. We evaluated the quantitative ELISPOT and PPD skin test responses to recent M. tuberculosis exposure., Methods: We studied quantitative PPD skin test and PPD ELISPOT results in 1052 healthy household contacts of index patients with cases of sputum smear-positive and culture-positive TB in The Gambia, according to a positive or negative ex vivo interferon gamma ELISPOT response to M. tuberculosis-specific antigens (ESAT-6/CFP-10). We then studied the quantitative PPD skin test and PPD ELISPOT results in patient contacts who had positive ESAT-6/CFP-10 results against a natural exposure gradient according to sleeping proximity to a patient with TB., Results: The number of positive results was significantly greater for both PPD skin test and PPD ELISPOT in ESAT-6/CFP-10-positive subjects, compared with others (P<.0001). However, when quantitative PPD skin test and PPD ELISPOT results were compared in ESAT-6/CFP-10-positive subjects, only the ELISPOT count was sensitive to the exposure gradient, increasing significantly according to exposure (P=.009)., Conclusions: The quantitative ELISPOT response to PPD in specific-antigen-positive contacts of patients with TB reflects the infectious load of M. tuberculosis as a result of recent exposure. This finding offers new possibilities for assessment of the efficacy of new interventions, and adjustment should be made for it when relating the early immune response to progression to disease.

Vitamin D receptor (VDR) gene polymorphisms have been implicated in susceptibility to tuberculosis (TB), but reports have been inconsistent. We genotyped the VDR single-nucleotide polymorphisms (SNPs) FokI, BsmI, ApaI, and TaqI in 1139 case patients and control subjects and 382 families from The Gambia, Guinea, and Guinea-Bissau. The transmission-disequilibrium test on family data showed a significant global association of TB with SNP combinations FokI-BsmI-ApaI-TaqI and FokI-ApaI that were driven by the increased transmission to affected offspring of the FokI F and ApaI A alleles in combination. The ApaI A allele was also transmitted to affected offspring significantly more often than expected. Case-control analysis showed no statistically significant association between TB and VDR variants. BsmI, ApaI, and TaqI showed strong linkage disequilibrium. The significance of the family-based associations found between TB and FokI-BsmI-ApaI-TaqI and the FA haplotype supports a role for VDR haplotypes, rather than individual genotypes, in susceptibility to TB.

The purified protein derivative (PPD) skin test for Mycobacterium tuberculosis infection lacks specificity. We assessed 2 more specific M. tuberculosis antigens (ESAT-6 and CFP-10) by enzyme-linked immunospot assay (ELISPOT) compared with PPD by ELISPOT and skin test in The Gambia. Of 735 household contacts of 130 sputum smear-positive tuberculosis cases, 476 (65%) tested positive by PPD ELISPOT, 300 (41%) tested positive by PPD skin test, and 218 (30%) tested positive by ESAT-6/CFP-10 ELISPOT. Only 15 (2%) had positive ESAT-6/CFP-10 results and negative PPD results by ELISPOT. With increasing M. tuberculosis exposure, the percentage of subjects who were PPD skin test positive/ESAT-6/CFP-10 ELISPOT negative increased (P<.001), whereas the percentage of subjects who were PPD skin test negative/PPD ELISPOT positive decreased (P=.011). Eighteen (31%) ESAT-6/CFP-10 ELISPOT-positive subjects in the lowest exposure category had negative PPD skin test results. ESAT-6/CFP-10 ELISPOT probably offers increased specificity in the diagnosis of M. tuberculosis infection in this tropical setting of endemicity, at the cost of some sensitivity.

The present study is an investigation of the safety and immunogenicity of DNA and modified vaccinia virus Ankara (MVA) candidate vaccines, each encoding the malaria DNA sequence multiple epitope-thrombospondin related adhesion protein (ME-TRAP), against Plasmodium falciparum. DNA ME-TRAP and MVA ME-TRAP are safe and immunogenic for effector and memory T cell induction. MVA ME-TRAP, with or without prior DNA ME-TRAP immunization, was more immunogenic and more cross-reactive in malaria-exposed individuals than in malaria-naive individuals, a finding suggesting that recombinant MVA vaccines are particularly promising for the development of a malaria vaccine for exposed populations. Both CD4(+) and CD8(+) T cells were induced by these vaccines.

A double-blind, community-randomized, placebo-controlled trial was conducted in a rural area of The Gambia between June and December 1999 to test whether a reduction in the infectious reservoir can reduce malaria transmission. Overall 14,017 (85%) individuals living in the study area were treated with either placebo or sulfadoxine-pyrimethamine (SP) combined with a single dose of artesunate (AS). Following the mass drug administration (MDA) 1375 children aged 6 months to 10 years were kept under surveillance for clinical malaria in 18 villages throughout the 1999 malaria transmission season. During a 20-week surveillance period 637 episodes of malaria were detected. The mean incidence rate was 2.5/100 child-weeks in the placebo villages, and 2.3/100 child-weeks in villages that received SP + AS. The mean rate ratio, adjusted for individual and village-level covariates, was 0.91 (95% CI 0.68-1.22, P = 0.49). During the first 2 months of surveillance, the malaria incidence was lower in treated villages. After 2 months the incidence was slightly higher in the MDA group but this was not statistically significant. Overall, no benefit of the MDA could be detected. The reason for the absence of an impact on malaria transmission is probably the very high basic reproductive number of malaria, and the persistence of mature gametocytes, which are not affected by AS treatment.

Host genetic factors are major determinants of susceptibility to tuberculosis, and an understanding of the molecular basis of this observation has major implications for the development of novel therapies and vaccines. Slc11a1 (formerly Nramp1), the first murine infection susceptibility locus identified, regulates early innate responses to intracellular pathogens. Variation in the human homologue SLC11A1 is associated with and linked to tuberculosis in genetically different populations. In a case-control study of 329 tuberculosis case patients and 324 control subjects, the association between allele 2 of a functional SLC11A1 polymorphism and tuberculosis has been reproduced. This variant is associated with higher lipopolysaccharide-induced production of the macrophage-deactivating cytokine interleukin-10. Furthermore, monocytes from persons who develop tuberculosis innately produce more interleukin-10 than do monocytes from healthy control subjects. These data therefore confirm the importance of SLC11A1 in tuberculosis susceptibility in humans and suggest that SLC11A1 influences tuberculosis susceptibility by regulation of interleukin-10.

Adenosine triphosphate (ATP) ligation of P2X(7) receptors expressed on human macrophages that are infected with mycobacteria induces cell death and subsequent loss of intracellular bacterial viability. Marked heterogeneity observed in cell donor ATP responsiveness suggests that this antimycobacterial mechanism may be genetically regulated. Five single-nucleotide polymorphisms (SNPs) previously identified in a putative 1.8-kb promoter region upstream of P2RX7 exon 1 were screened for associations with clinical tuberculosis. The frequencies of these promoter SNPs and a polymorphism in P2RX7 exon 13 at position 1513 were compared among >300 Gambian patients with tuberculosis and >160 ethnically matched control subjects by sequence-specific oligonucleotide hybridization and ligation detection reaction analysis. A significant protective association against tuberculosis was found for 1 promoter SNP, at nucleotide position -762 (odds ratio [OR] for variant C allele, 0.70; 95% confidence interval [CI], 0.54-0.89; P=.003; OR for CC genotype, 0.545; 95% CI, 0.318-0.934; P=.027). This association supports a role for ATP/P2X(7)-mediated host regulation of Mycobacterium tuberculosis infection.