Guy Thwaites

Out-of-Africa migration and Neolithic coexpansion of Mycobacterium tuberculosis with modern humans

Tuberculosis caused 20% of all human deaths in the Western world between the seventeenth and nineteenth centuries and remains a cause of high mortality in developing countries. In analogy to other crowd diseases, the origin of human tuberculosis has been associated with the Neolithic Demographic Transition, but recent studies point to a much earlier origin. We analyzed the whole genomes of 259 M. tuberculosis complex (MTBC) strains and used this data set to characterize global diversity and to reconstruct the evolutionary history of this pathogen. Coalescent analyses indicate that MTBC emerged about 70,000 years ago, accompanied migrations of anatomically modern humans out of Africa and expanded as a consequence of increases in human population density during the Neolithic period. This long coevolutionary history is consistent with MTBC displaying characteristics indicative of adaptation to both low and high host densities.

The Influence of Host and Bacterial Genotype on the Development of Disseminated Disease with Mycobacterium tuberculosis

The factors that govern the development of tuberculosis disease are incompletely understood. We hypothesized that some strains of Mycobacterium tuberculosis (M. tuberculosis) are more capable of causing disseminated disease than others and may be associated with polymorphisms in host genes responsible for the innate immune response to infection. We compared the host and bacterial genotype in 187 Vietnamese adults with tuberculous meningitis (TBM) and 237 Vietnamese adults with uncomplicated pulmonary tuberculosis. The host genotype of tuberculosis cases was also compared with the genotype of 392 cord blood controls from the same population. Isolates of M. tuberculosis were genotyped by large sequence polymorphisms. The hosts were defined by polymorphisms in genes encoding Toll-interleukin 1 receptor domain containing adaptor protein (TIRAP) and Toll-like receptor-2 (TLR-2). We found a significant protective association between the Euro-American lineage of M. tuberculosis and pulmonary rather than meningeal tuberculosis (Odds ratio (OR) for causing TBM 0.395, 95% confidence intervals (C.I.) 0.193–0.806, P = 0.009), suggesting these strains are less capable of extra-pulmonary dissemination than others in the study population. We also found that individuals with the C allele of TLR-2 T597C allele were more likely to have tuberculosis caused by the East-Asian/Beijing genotype (OR = 1.57 [95% C.I. 1.15–2.15]) than other individuals. The study provides evidence that M. tuberculosis genotype influences clinical disease phenotype and demonstrates, for the first time, a significant interaction between host and bacterial genotypes and the development of tuberculosis.

Host Genotype-Specific Therapies Can Optimize the Inflammatory Response to Mycobacterial Infections

Susceptibility to tuberculosis is historically ascribed to an inadequate immune response that fails to control infecting mycobacteria. In zebrafish, we find that susceptibility to Mycobacterium marinum can result from either inadequate or excessive acute inflammation. Modulation of the leukotriene A(4) hydrolase (LTA4H) locus, which controls the balance of pro- and anti-inflammatory eicosanoids, reveals two distinct molecular routes to mycobacterial susceptibility converging on dysregulated TNF levels: inadequate inflammation caused by excess lipoxins and hyperinflammation driven by excess leukotriene B(4). We identify therapies that specifically target each of these extremes. In humans, we identify a single nucleotide polymorphism in the LTA4H promoter that regulates its transcriptional activity. In tuberculous meningitis, the polymorphism is associated with inflammatory cell recruitment, patient survival and response to adjunctive anti-inflammatory therapy. Together, our findings suggest that host-directed therapies tailored to patient LTA4H genotypes may counter detrimental effects of either extreme of inflammation.

British Infection Society guidelines for the diagnosis and treatment of tuberculosis of the central nervous system in adults and children

SUMMARY AND KEY RECOMMENDATIONS: The aim of these guidelines is to describe a practical but evidence-based approach to the diagnosis and treatment of central nervous system tuberculosis in children and adults. We have presented guidance on tuberculous meningitis (TBM), intra-cerebral tuberculoma without meningitis, and tuberculosis affecting the spinal cord. Our key recommendations are as follows: 1. TBM is a medical emergency. Treatment delay is strongly associated with death and empirical anti-tuberculosis therapy should be started promptly in all patients in whom the diagnosis of TBM is suspected. Do not wait for microbiological or molecular diagnostic confirmation. 2. The diagnosis of TBM is best made with lumbar puncture and examination of the cerebrospinal fluid (CSF). Suspect TBM if there is a CSF leucocytosis (predominantly lymphocytes), the CSF protein is raised, and the CSF:plasma glucose is <50%. The diagnostic yield of CSF microscopy and culture for Mycobacterium tuberculosis increases with the volume of CSF submitted; repeat the lumbar puncture if the diagnosis remains uncertain. 3. Imaging is essential for the diagnosis of cerebral tuberculoma and tuberculosis involving the spinal cord, although the radiological appearances do not confirm the diagnosis. A tissue diagnosis (by histopathology and mycobacterial culture) should be attempted whenever possible, either by biopsy of the lesion itself, or through diagnostic sampling from extra-neural sites of disease e.g. lung, gastric fluid, lymph nodes, liver, bone marrow. 4. Treatment for all forms of CNS tuberculosis should consist of 4 drugs (isoniazid, rifampicin, pyrazinamide, ethambutol) for 2 months followed by 2 drugs (isoniazid, rifampicin) for at least 10 months. Adjunctive corticosteroids (either dexamethasone or prednisolone) should be given to all patients with TBM, regardless of disease severity. 5. Children with CNS tuberculosis should ideally be managed by a paediatrician with familiarity and expertise in paediatric tuberculosis or otherwise with input from a paediatric infectious diseases unit. The Childrens HIV Association of UK and Ireland (CHIVA) provide further guidance on the management of HIV-infected children (www.chiva.org.uk). 6. All patients with suspected or proven tuberculosis should be offered testing for HIV infection. The principles of CNS tuberculosis diagnosis and treatment are the same for HIV infected and uninfected individuals, although HIV infection broadens the differential diagnosis and anti-retroviral treatment complicates management. Tuberculosis in HIV infected patients should be managed either within specialist units by physicians with expertise in both HIV and tuberculosis, or in a combined approach between HIV and tuberculosis experts. The co-administration of anti-retroviral and anti-tuberculosis drugs should follow guidance issued by the British HIV association (www.bhiva.org).

Tuberculous meningitis: a uniform case definition for use in clinical research

Tuberculous meningitis causes substantial mortality and morbidity in children and adults. More research is urgently needed to better understand the pathogenesis of disease and to improve its clinical management and outcome. A major stumbling block is the absence of standardised diagnostic criteria. The different case definitions used in various studies makes comparison of research findings difficult, prevents the best use of existing data, and limits the management of disease. To address this problem, a 3-day tuberculous meningitis workshop took place in Cape Town, South Africa, and was attended by 41 international participants experienced in the research or management of tuberculous meningitis. During the meeting, diagnostic criteria were assessed and discussed, after which a writing committee was appointed to finalise a consensus case definition for tuberculous meningitis for use in future clinical research. We present the consensus case definition together with the rationale behind the recommendations. This case definition is applicable irrespective of the patients age, HIV infection status, or the resources available in the research setting. Consistent use of the proposed case definition will aid comparison of studies, improve scientific communication, and ultimately improve care.

Diagnosis of adult tuberculous meningitis by use of clinical and laboratory features

BACKGROUND The diagnosis of tuberculous meningitis is difficult. Discrimination of cases from those of bacterial meningitis by clinical features alone is often impossible, and current laboratory methods remain inadequate or inaccessible in developing countries. We aimed to create a simple diagnostic aid for tuberculous meningitis in adults on the basis of clinical and basic laboratory features. METHODS We compared the clinical and laboratory features on admission of 251 adults at an infectious disease hospital in Vietnam who satisfied diagnostic criteria for tuberculous (n=143) or bacterial (n=108) meningitis. Features independently predictive of tuberculous meningitis were modelled by multivariate logistic regression to create a diagnostic rule, and by a classification-tree method. The performance of both diagnostic aids was assessed by resubstitution and prospective test data methods. FINDINGS Five features were predictive of a diagnosis of tuberculous meningitis: age, length of history, white-blood-cell count, total cerebrospinal fluid white-cell count, and cerebrospinal fluid neutrophil proportion. A diagnostic rule developed from these features was 97% sensitive and 91% specific by resubstitution, and 86% sensitive and 79% specific when applied prospectively to a further 42 adults with tuberculous meningitis, and 33 with bacterial meningitis. The corresponding values for the classification tree were 99% and 93% by resubstitution, and 88% and 70% with prospective test data. INTERPRETATION This study suggests that simple clinical and laboratory data can help in the diagnosis of adults with tuberculous meningitis. Although the usefulness of the diagnostic rule will vary depending on the prevalence of tuberculosis and HIV-1 infection, we suggest it be applied to adults with meningitis and a low cerebrospinal fluid glucose, particularly in settings with limited microbiological resources.

Tuberculous meningitis: many questions, too few answers

Tuberculous meningitis (TM) is difficult to diagnose and treat; clinical features are non-specific, conventional bacteriology is widely regarded as insensitive, and assessment of newer diagnostic methods is not complete. Treatment includes four drugs, which were developed more than 30 years ago, and prevents death or disability in less than half of patients. Mycobacterium tuberculosis resistant to these drugs threatens a return to the prechemotherapeutic era in which all patients with TM died. Research findings suggest that adjunctive treatment with corticosteroids improve survival but probably do not prevent severe disability, although how or why is not known. There are many important unanswered questions about the pathophysiology, diagnosis, and treatment of TM. Here we review the available evidence to answer some of these questions, particularly those on the diagnosis and treatment of TM.

Improving the Bacteriological Diagnosis of Tuberculous Meningitis

ABSTRACT We made a bacteriological diagnosis of tuberculous meningitis in 107 of 132 (81%) adults with clinical tuberculous meningitis: acid-fast bacilli were seen in 77 of 132 (58%) and cultured from 94 of 132 (71%). Volume of cerebrospinal fluid, duration of symptoms, cerebrospinal fluid neutrophils, lactate, and glucose were all independently associated with bacteriological confirmation.

A common human TLR1 polymorphism regulates the innate immune response to lipopeptides

Toll‐like receptors (TLR) are critical mediators of the immune response to pathogens and human polymorphisms in this gene family regulate inflammatory pathways and are associated with susceptibility to infection. Lipopeptides are present in a wide variety of microbes and stimulate immune responses through TLR1/2 or TLR2/6 heterodimers. It is not currently known whether polymorphisms in TLR1 regulate the innate immune response. We stimulated human whole blood with triacylated lipopeptide, a ligand for TLR1/2 heterodimers, and found substantial inter‐individual variation in the immune response. We sequenced the coding region of TLR1 and found a non‐synonymous polymorphism, I602S (base pair T1805G), that regulated signalling. In comparison to TLR1_602S, the 602I variant mediated substantially greater basal and lipopeptide‐induced NF‐κB signalling in transfected HEK293 cells. These signalling differences among TLR1 variants were also found with stimulation by extracts of Mycobacterium tuberculosis. Furthermore, individuals with the 602II genotype produced substantially more IL‐6 than those with the 602SS variant in a lipopeptide‐stimulated whole‐blood cytokine assay. Together, these observations demonstrate that variation in the inflammatory response to bacterial lipopeptides is regulated by a common TLR1 transmembrane domain polymorphism that could potentially impact the innate immune response and clinical susceptibility to a wide spectrum of pathogens.

Adjunctive dexamethasone in bacterial meningitis: a meta-analysis of individual patient data

Summary Background Dexamethasone improves outcome for some patients with bacterial meningitis, but not others. We aimed to identify which patients are most likely to benefit from dexamethasone treatment. Methods We did a meta-analysis of individual patient data from the randomised, double-blind, placebo-controlled trials of dexamethasone for bacterial meningitis in patients of all ages for which raw data were available. The pre-determined outcome measures were death at the time of first follow-up, death or severe neurological sequelae at 1 month follow-up, death or any neurological sequelae at first follow-up, and death or severe bilateral hearing loss at first follow-up. Combined odds ratios (ORs) and tests for heterogeneity were calculated using conventional Mantel-Haenszel statistics. We also did exploratory analysis of hearing loss among survivors and other exploratory subgroup analyses by use of logistic regression. Findings Data from 2029 patients from five trials were included in the analysis (833 [41·0%] aged <15 years). HIV infection was confirmed or likely in 580 (28·6%) patients and bacterial meningitis was confirmed in 1639 (80·8%). Dexamethasone was not associated with a significant reduction in death (270 of 1019 [26·5%] on dexamethasone vs 275 of 1010 [27·2%] on placebo; OR 0·97, 95% CI 0·79–1·19), death or severe neurological sequelae or bilateral severe deafness (42·3% vs 44·3%; 0·92, 0·76–1·11), death or any neurological sequelae or any hearing loss (54·2% vs 57·4%; 0·89, 0·74–1·07), or death or severe bilateral hearing loss (36·4% vs 38·9%; 0·89, 0·73–1·69). However, dexamethasone seemed to reduce hearing loss among survivors (24·1% vs 29·5%; 0·77, 0·60–0·99, p=0·04). Dexamethasone had no effect in any of the prespecified subgroups, including specific causative organisms, pre-dexamethasone antibiotic treatment, HIV status, or age. Pooling of the mortality data with those of all other published trials did not significantly change the results. Interpretation Adjunctive dexamethasone in the treatment of acute bacterial meningitis does not seem to significantly reduce death or neurological disability. There were no significant treatment effects in any of the prespecified subgroups. The benefit of adjunctive dexamethasone for all or any subgroup of patients with bacterial meningitis thus remains unproven. Funding Wellcome Trust UK.