RESUMO
Leprosy is a chronic infection of the skin and peripheral nerves caused by Mycobacterium leprae. Despite recent improvements in disease control, leprosy remains an important cause of infectious disability globally. Large-scale genetic association studies in Chinese, Vietnamese and Indian populations have identified over 30 susceptibility loci for leprosy. There is a significant burden of leprosy in Africa, however it is uncertain whether the findings of published genetic association studies are generalizable to African populations. To address this, we conducted a genome-wide association study (GWAS) of leprosy in Malawian (327 cases, 436 controls) and Malian (247 cases, 368 controls) individuals. In that analysis, we replicated four risk loci previously reported in China, Vietnam and India; MHC Class I and II, LACC1 and SLC29A3. We further identified a novel leprosy susceptibility locus at 10q24 (rs2015583; combined p = 8.81 × 10-9; OR = 0.51 [95% CI 0.40 - 0.64]). Using publicly-available data we characterise regulatory activity at this locus, identifying ACTR1A as a candidate mediator of leprosy risk. This locus shows evidence of recent positive selection and demonstrates pleiotropy with established risk loci for inflammatory bowel disease and childhood-onset asthma. A shared genetic architecture for leprosy and inflammatory bowel disease has been previously described. We expand on this, strengthening the hypothesis that selection pressure driven by leprosy has shaped the evolution of autoimmune and atopic disease in modern populations. More broadly, our data highlights the importance of defining the genetic architecture of disease across genetically diverse populations, and that disease insights derived from GWAS in one population may not translate to all affected populations.
Assuntos
Doenças Inflamatórias Intestinais , Hanseníase , Humanos , Criança , Estudo de Associação Genômica Ampla , Predisposição Genética para Doença , Polimorfismo de Nucleotídeo Único , Malaui , Mali , Hanseníase/genética , Proteínas de Transporte de Nucleosídeos/genéticaRESUMO
BACKGROUND: A large, double-blind, randomised, placebo-controlled trial of repeat BCG found 49% efficacy against leprosy but no protection against tuberculosis after 6-9 years' follow-up in 1995. We report here additional follow-up, which resulted in greatly increased tuberculosis case numbers, and allowed subgroup analysis. METHODS: Nearly 47â000 individuals of all ages living in northern Malawi with a BCG vaccine scar were randomly assigned (1:1) between 1986 and 1989 to receive a second BCG or placebo. The investigators and project staff remained masked to all interventions. Enhanced passive surveillance ensured ascertainment of tuberculosis and leprosy to the end of 2018. Tuberculosis case definitions included rigorous microbiological or histological confirmation. Prespecified subgroup analyses were by tuberculosis type, age at vaccination, time since vaccination, previous tuberculin reactivity, HIV status and Mycobacterium tuberculosis lineage. The original trial is registered with ISRCTN registry, ISRCTN11311670. FINDINGS: In follow-up until Dec 31, 2018, 824 participants had developed tuberculosis, including 786 with pulmonary disease, of whom 383 (63%) of 607 with known HIV status were HIV positive. There was no effect of a second BCG overall (odds ratio [OR] 0·92; 95% CI 0·80-1·05), or for pulmonary (0·93; 0·81-1·07), or lymph node tuberculosis (0·60; 0·31-1·17). The OR was lower for those with known HIV-negative tuberculosis (0·77; 0·59-1·00), for those vaccinated as children (aged <5 years, 0·74; 0·41-1·35; aged 5-14 years, 0·77; 0·60-0·99), and for cases arising at least 20 years after vaccination (0·79; 0·63-1·01). There were no differences by tuberculin status at vaccination, or lineage. There was no evidence of protection against leprosy beyond 10 years after vaccination (although there have been only nine diagnostically certain cases since 1995). INTERPRETATION: There was no evidence that repeat BCG vaccination provides appreciable protection against overall tuberculosis in this rural African population with a high prevalence of HIV. Subgroup effects should not be overinterpreted given the multiple analyses done. However, the evidence for modest protection against HIV-negative tuberculosis, and for a delayed benefit in those vaccinated as children, is consistent with other observations in the literature. FUNDING: LEPRA, Wellcome Trust, Bill & Melinda Gates Foundation.
Assuntos
Vacina BCG , Vacinação , Método Duplo-Cego , Seguimentos , Humanos , Malaui/epidemiologiaRESUMO
We combined two tuberculosis genome-wide association studies from Ghana and The Gambia with subsequent replication in a combined 11,425 individuals. rs4331426, located in a gene-poor region on chromosome 18q11.2, was associated with disease (combined P = 6.8 x 10(-9), odds ratio = 1.19, 95% CI = 1.13-1.27). Our study demonstrates that genome-wide association studies can identify new susceptibility loci for infectious diseases, even in African populations, in which levels of linkage disequilibrium are particularly low.
Assuntos
Cromossomos Humanos Par 18 , Loci Gênicos , Predisposição Genética para Doença , Tuberculose/genética , Estudos de Casos e Controles , Cromossomos Humanos Par 18/genética , Gâmbia , Genética Populacional , Estudo de Associação Genômica Ampla , Gana , Humanos , Desequilíbrio de Ligação , Razão de Chances , Polimorfismo de Nucleotídeo ÚnicoRESUMO
Twenty-seven polymorphisms from 12 genes have been investigated for association with tuberculosis (TB) in up to 514 cases and 913 controls from Karonga district, northern Malawi. Homozygosity for the complement receptor 1 (CR1) Q1022H polymorphism was associated with susceptibility to TB in this population (odds ratio [OR] = 3.12, 95% Confidence interval [CI] = 1.13-8.60, P = 0.028). This association was not observed among human immunodeficiency virus (HIV)-positive TB cases, suggesting either chance association or that HIV status may influence genetic associations with TB susceptibility. Heterozygosity for a newly studied CAAA insertion/deletion polymorphism in the 3'-untranslated region of solute carrier family 11, member 1 (SLC11A1, formerly NRAMP1) was associated with protection against TB in both HIV-positive (OR = 0.70, 95% CI = 0.49-0.99, P = 0.046) and HIV-negative (OR = 0.65, 95% CI = 0.46-0.92, P = 0.014) TB cases, suggesting that the SLC11A1 protein may have a role in innate TB immune responses that influence susceptibility even in immunocompromised individuals. However, associations of other variants of SCLA11A with TB reported from other populations were not replicated in Malawi. Furthermore, associations with vitamin D receptor, interferon-gamma, and mannose-binding lectin observed elsewhere were not observed in this Karonga study. Genetic susceptibility to TB in Africans appears polygenic. The relevant genes and variants may vary significantly between populations, and may be affected by HIV infection status.
Assuntos
Predisposição Genética para Doença/genética , Tuberculose/genética , Frequência do Gene/genética , Genótipo , Infecções por HIV/complicações , Humanos , Malaui , Polimorfismo Genético/genética , Tuberculose/complicaçõesRESUMO
We present a large case-control candidate gene study of leprosy susceptibility. Thirty-eight polymorphic sites from 13 genes were investigated for their role in susceptibility to leprosy by comparing 270 cases with 452 controls in Karonga district, northern Malawi. Homozygotes for a silent T-->C change in codon 352 of the vitamin D receptor gene appeared to be at high risk (odds ratio [OR] = 4.3, 95% confidence interval [CI] = 1.6-11.4, P = 0.004), while homozygotes for the McCoy b blood group defining variant K1590E in exon 29 of the complement receptor 1 (formerly CD35) gene appeared to be protected (OR = 0.3, 95% CI = 0.1-0.8, P = 0.02). Borderline evidence for association with leprosy susceptibility was found for seven polymorphic sites in an additional six genes. Some of these apparent associations may be false-positive results from multiple comparisons, and several associations suggested by studies in other populations were not replicated here. These data provide evidence of inter-population heterogeneity in leprosy susceptibility.
Assuntos
Predisposição Genética para Doença/genética , Hanseníase/genética , Adolescente , Adulto , Idoso , Estudos de Casos e Controles , Genótipo , Humanos , Malaui , Pessoa de Meia-Idade , Polimorfismo Genético/genética , Análise de Sequência de DNARESUMO
OBJECTIVE: To document the changing incidence and patterns of tuberculosis (TB) in rural Africa and the extent to which they are influenced by HIV. METHODS: As part of longstanding epidemiological studies in Karonga District, Malawi, a series of case control studies of TB and HIV were conducted from 1988 onwards. Data from these studies, from a total population survey, and from the Malawi national census have been used to reconstruct the changes in the TB epidemic in the area from 1988 to 2001, examining the role of HIV. RESULTS: The incidence of all confirmed TB, and of new smear-positive TB, in adults increased to peak in the late 1990s but appears to have decreased since. Two-thirds of cases are now HIV positive. The rise in incidence was greatest in the 30-44-year-old age group and was particularly marked for women, leading to a decrease in the male : female ratio for TB incidence from 1.3 to 0.8. The proportion of new smear-positive TB cases attributable to HIV increased from 17% in 1988-1990 to 57% in 2000-2001, but the estimated rate of smear-positive TB in the absence of HIV decreased from 0.78/1000 to 0.45/1000. CONCLUSIONS: Without HIV the incidence of smear-positive TB would have fallen in this population. Instead it has risen and is predominantly affecting young adults and women. There is some evidence that the HIV-associated TB epidemic may have passed its peak.
Assuntos
Infecções Oportunistas Relacionadas com a AIDS/epidemiologia , Tuberculose/epidemiologia , Infecções Oportunistas Relacionadas com a AIDS/complicações , Adolescente , Adulto , Idoso , Estudos de Casos e Controles , Feminino , Humanos , Incidência , Malaui/epidemiologia , Masculino , Pessoa de Meia-Idade , Razão de Chances , Prevalência , Fatores de Risco , Tuberculose/complicaçõesRESUMO
To investigate the role of innate immunity in variable efficacy of Mycobacterium bovis BCG vaccination in Malawi and the United Kingdom, we examined 24-h tumor necrosis factor alpha, interleukin-1beta (IL-1beta), and IL-10 responses to mycobacterial purified protein derivatives (PPDs). The rank order in stimulatory potency for different PPDs was the same for all three cytokines. Before vaccination Malawians made higher pro- and anti-inflammatory responses than did United Kingdom subjects. Fewer than 5% of United Kingdom subjects made IL-10 in response to any PPD, compared to 19 to 57% responders among Malawians. Priming for regulatory IL-10 may contribute to the smaller increase in gamma interferon responses in Malawians compared to United Kingdom subjects following BCG vaccination.
Assuntos
Vacina BCG/administração & dosagem , Imunidade Inata , Interleucina-10/biossíntese , Interleucina-1/biossíntese , Tuberculina/administração & dosagem , Fator de Necrose Tumoral alfa/biossíntese , Adaptação Fisiológica , Adolescente , Adulto , Criança , Humanos , Lipopolissacarídeos/administração & dosagem , Lipopolissacarídeos/isolamento & purificação , Malaui , Tuberculina/isolamento & purificação , Tuberculose/imunologia , Tuberculose/prevenção & controle , Reino UnidoRESUMO
BACKGROUND: Most data on HIV prevalence in Malawi come from antenatal clinic (ANC) surveillance and are, therefore, subject to bias. OBJECTIVES: HIV prevalence and risk factors were measured using population-based data to assess the accuracy of ANC surveillance and changes in prevalence and risk factors for HIV over time. METHODS: HIV prevalence was measured in 1988-1993 and 1998-2001 in community controls from case-control studies of mycobacterial disease in Karonga District, Malawi. ANC surveillance studies in the district began in 1999. RESULTS: Age and area-standardized HIV prevalence in women aged 15-49 years in the community was 3.9% in 1988-1990, 12.5% in 1991-1993 and 13.9% in 1998-2001. For men, HIV prevalence was 3.7%, 9.2% and 11.4% in the same periods. In 1988-1993, HIV positivity was associated with occupations other than farming, with increased schooling and being born outside Karonga District. In 1998-2001, non-farmers were still at higher risk but the other associations were not seen. The age- and area-adjusted HIV prevalence in the ANC in 1999-2001 was 9.2%. The underestimate can be explained largely by marriage and mobility. Reduced fertility in HIV-positive individuals was demonstrated in both ANC and community populations. A previously recommended parity-based adjustment gave an estimated female HIV prevalence of 15.0%. CONCLUSIONS: HIV prevalence has increased and continues to be higher in non-farmers. The increase is particularly marked in those with no education. ANC surveillance underestimated HIV prevalence in the female population in all but the youngest age group. Although there were differences in sociodemographic factors, a parity-based adjustment gave a reasonable estimate of female HIV prevalence.
Assuntos
Infecções por HIV/epidemiologia , Soroprevalência de HIV , Adolescente , Adulto , Intervalo entre Nascimentos , Métodos Epidemiológicos , Feminino , Fertilidade , Humanos , Malaui/epidemiologia , Pessoa de Meia-Idade , Paridade , Fatores de RiscoRESUMO
We have previously shown that young adults living in a rural area of northern Malawi showed greater gamma interferon (IFN-gamma) responses to purified protein derivatives (PPD) prepared from environmental mycobacteria than to PPD from Mycobacterium tuberculosis. In order to define the mycobacterial species to which individuals living in a rural African population have been exposed and sensitized, we tested T-cell recognition of recombinant and purified antigens from M. tuberculosis (38 kDa, MPT64, and ESAT-6), M. bovis (MPB70), M. bovis BCG (Ag85), and M. leprae (65 kDa, 35 kDa, and 18 kDa) in >600 non-M. bovis BCG-vaccinated young adults in the Karonga District of northern Malawi. IFN-gamma was measured by enzyme-linked immunosorbent assay (ELISA) in day 6 supernatants of diluted whole-blood cultures. The recombinant M. leprae 35-kDa and 18-kDa and purified native M. bovis BCG Ag85 antigens induced the highest percentages of responders, though both leprosy and bovine tuberculosis are now rare in this population. The M. tuberculosis antigens ESAT-6 and MPT64 and the M. bovis antigen MPB70 induced the lowest percentages of responders. One of the subjects subsequently developed extrapulmonary tuberculosis; this individual had a 15-mm-diameter reaction to the Mantoux test and responded to M. tuberculosis PPD, Ag85, MPT64, and ESAT-6 but not to any of the leprosy antigens. We conclude that in this rural African population, exposure to M. tuberculosis or M. bovis is much less frequent than exposure to environmental mycobacteria such as M. avium, which have antigens homologous to the M. leprae 35-kDa and 18-kDa antigens. M. tuberculosis ESAT-6 showed the strongest association with the size of the Mantoux skin test induration, suggesting that among the three M. tuberculosis antigens tested it provided the best indication of exposure to, or infection with, M. tuberculosis.
Assuntos
Antígenos de Bactérias/imunologia , Vacina BCG/imunologia , Interferon gama/biossíntese , Mycobacterium/imunologia , Adolescente , Adulto , Criança , Feminino , Humanos , Hanseníase/epidemiologia , Malaui/epidemiologia , Masculino , Mycobacterium/genética , Mycobacterium bovis/imunologia , Mycobacterium leprae/imunologia , Mycobacterium tuberculosis/imunologia , Proteínas Recombinantes de Fusão/imunologia , População Rural , Especificidade da Espécie , Linfócitos T/imunologia , Teste Tuberculínico , Tuberculose/imunologia , VacinaçãoRESUMO
Few studies have investigated the risk factors for tuberculosis (TB) infection in highly endemic countries. We conducted a household study in The Gambia, in which a tuberculin skin test (TST) was performed in members of the households of 315 smear-positive pulmonary TB cases and 305 community control subjects. The risk of being TST positive (10 mm or more) was higher in contacts of cases than in contacts of control subjects. It increased with age, male sex, and duration of stay in the household but was not associated with the presence of a bacille de Calmette-Guérin scar. Within the households of the TB cases, the risk of TST positivity was higher in males and was increased with age, social proximity to the case, and the radiologic extent of the disease in the case's chest X-ray. Adjusting on these, the risk of TST positivity was higher in first-degree relatives compared with more distant relatives and nongenetically related household members, but the effect was not statistically significant. In highly endemic areas, the risk of TB infection in contacts of TB infectious cases is associated with age, sex, intensity of exposure to the case, and severity of disease in the case, but it is possible that genetic factors contribute to the susceptibility to Mycobacterium tuberculosis infection.
Assuntos
Busca de Comunicante , Tuberculose Pulmonar/transmissão , Adolescente , Adulto , Fatores Etários , Vacina BCG/administração & dosagem , Criança , Pré-Escolar , Doenças Endêmicas , Exposição Ambiental , Feminino , Gâmbia , Predisposição Genética para Doença , Humanos , Funções Verossimilhança , Masculino , Pessoa de Meia-Idade , Fatores de Risco , Fatores Sexuais , Meio Social , Fatores de Tempo , Teste Tuberculínico , Tuberculose Pulmonar/classificaçãoRESUMO
OBJECTIVE: Tuberculosis (TB) infection is highly prevalent in developing countries. As infected children represent a large proportion of the pool from which TB cases will arise, knowledge of the factors that influence TB infection in children are of importance to evaluate transmission of infection in the community and adapt TB control activities. There are limited data on the risk of infection in child populations in developing countries. METHODS: We performed a household contact study in The Gambia (West Africa), in which children who were living in contact with individuals who had proven smear-positive pulmonary TB cases were investigated. A questionnaire was addressed to the mother or caregiver of the child to investigate the presence of various risk factors and assess the degree of exposure of the child to the individual with TB within the household. A tuberculin skin test (TST) was performed on each child. TST sizes > or =5 and 10 mm, respectively, were considered positive. RESULTS: Households of 206 TB cases were visited, and 384 children aged <5 years were examined. The median age was 2, and 48% were girls. The distribution of TST responses followed a bimodal pattern, with 135 (35%) children presenting a palpable induration. Random effects logistic regression analysis demonstrated that the risk of positive TST response in the child increased with the geographic proximity of the child to the individual with TB within the household and with the degree of activities shared with the individual with TB. It was also associated with the clinical severity of the disease in the index case. Nutritional status and presence of a bacille Calmette-Guérin (BCG) scar were not independent risk factors for TST positivity in this population. On multivariate analysis, the effect of geographic proximity to the individual with TB, household size, and duration of cough in the index case persisted for TST responses > or =5 mm. CONCLUSIONS: In a highly endemic country with high BCG vaccination coverage in Africa, TB infection in children who were in contact with individual with infectious TB was directly related to the intensity of exposure of the child to the individual with TB. Our data suggest that a positive TST in a child reflects most probably TB infection rather than previous BCG vaccination. Contact tracing can play a major role in the control of TB in developing countries.
Assuntos
Infecções por Mycobacterium/epidemiologia , Infecções por Mycobacterium/transmissão , Tuberculose Pulmonar/epidemiologia , Tuberculose Pulmonar/transmissão , Adulto , Pré-Escolar , Exposição Ambiental/estatística & dados numéricos , Feminino , Gâmbia/epidemiologia , Humanos , Lactente , Recém-Nascido , Masculino , Mycobacterium tuberculosis/isolamento & purificação , Vigilância da População/métodos , Prevalência , Fatores de Risco , Inquéritos e Questionários , Teste Tuberculínico/métodos , Teste Tuberculínico/estatística & dados numéricosRESUMO
We have previously shown that young adults living in a rural area of northern Malawi showed greater gamma interferon (IFN-gamma) responses to purified protein derivatives (PPD) prepared from environmental mycobacteria than to PPD from Mycobacterium tuberculosis. In order to define the mycobacterial species to which individuals living in a rural African population have been exposed and sensitized, we tested T-cell recognition of recombinant and purified antigens from M. tuberculosis (38 kDa, MPT64, and ESAT-6), M. bovis (MPB70), M. bovis BCG (Ag85), and M. leprae (65 kDa, 35 kDa, and 18 kDa) in >600 non-M. bovis BCG-vaccinated young adults in the Karonga District of northern Malawi. IFN-gamma was measured by enzyme-linked immunosorbent assay (ELISA) in day 6 supernatants of diluted whole-blood cultures. The recombinant M. leprae 35-kDa and 18-kDa and purified native M. bovis BCG Ag85 antigens induced the highest percentages of responders, though both leprosy and bovine tuberculosis are now rare in this population. The M. tuberculosis antigens ESAT-6 and MPT64 and the M. bovis antigen MPB70 induced the lowest percentages of responders. One of the subjects subsequently developed extrapulmonary tuberculosis; this individual had a 15-mm-diameter reaction to the Mantoux test and responded to M. tuberculosis PPD, Ag85, MPT64, and ESAT-6 but not to any of the leprosy antigens. We conclude that in this rural African population, exposure to M. tuberculosis or M. bovis is much less frequent than exposure to environmental mycobacteria such as M. avium, which have antigens homologous to the M. leprae 35-kDa and 18-kDa antigens. M. tuberculosis ESAT-6 showed the strongest association with the size of the Mantoux skin test induration, suggesting that among the three M. tuberculosis antigens tested it provided the best indication of exposure to, or infection with, M. tuberculosis.
Assuntos
Feminino , Masculino , Adolescente , Adulto , Criança , Humanos , Antígenos de Bactérias , Especificidade da Espécie , Hanseníase , Interferon gama , Linfócitos T , Malaui , Mycobacterium , Mycobacterium bovis , Mycobacterium leprae , Mycobacterium tuberculosis , Proteínas Recombinantes de Fusão , Teste Tuberculínico , Tuberculose , Vacina BCG , VacinaçãoRESUMO
BACKGROUND: Mortality rates of HIV-infected patients treated for tuberculosis remain high. This study aimed to assess the effect on mortality of immunotherapy with single-dose SRL172 added to standard antituberculosis chemotherapy in such patients. METHODS: The double-blind trial enrolled 1229 patients aged 18-60 years, who had never received antiretroviral treatment and who presented with newly diagnosed, sputum-smear-positive pulmonary tuberculosis to referral centres in Lusaka, Zambia, and Karonga, Malawi. Both HIV-positive and HIV-negative patients were enrolled, to avoid stigmatisation. Participants were randomly assigned a single injection of SRL172 or matching placebo within 2 weeks of starting 8 months of antituberculosis chemotherapy and followed up for at least 12 months. The primary endpoint was time to death in the HIV-infected population. Analyses were based on 760 HIV-positive patients after exclusion of 84 patients with errors in storage of the injection, no bacteriological confirmation, or no HIV result. FINDINGS: Of 760 HIV-infected patients, 374 received SRL172 and 386 received placebo. SRL172 did not cause any serious adverse events. The follow-up rate was 88% at 12 months in both groups. Of the HIV-positive patients, 109 (19.5 per 100 person-years) of 372 assigned SRL172 and 107 (19.3 per 100 person-years) of 386 assigned placebo died. In the Cox's regression analysis, stratified by centre, the hazard ratio of deaths (SRL172/placebo) was 1.03 (95% CI 0.79-1.35). There was no evidence of benefit to the group assigned SRL172. INTERPRETATION: Immunotherapy with single-dose SRL172 as an adjunct to standard antituberculosis treatment in HIV-positive adults with pulmonary tuberculosis had no significant effect on survival or bacteriological outcome, though the treatment was safe and well tolerated.
Assuntos
Infecções Oportunistas Relacionadas com a AIDS/tratamento farmacológico , Adjuvantes Imunológicos/uso terapêutico , Antituberculosos/uso terapêutico , Vacinas Bacterianas/uso terapêutico , Imunoterapia/métodos , Tuberculose Pulmonar/tratamento farmacológico , Infecções Oportunistas Relacionadas com a AIDS/diagnóstico , Infecções Oportunistas Relacionadas com a AIDS/microbiologia , Infecções Oportunistas Relacionadas com a AIDS/mortalidade , Adulto , Método Duplo-Cego , Feminino , Seguimentos , Humanos , Injeções Intradérmicas , Malaui/epidemiologia , Masculino , Placebos , Modelos de Riscos Proporcionais , Escarro/microbiologia , Análise de Sobrevida , Resultado do Tratamento , Tuberculose Pulmonar/diagnóstico , Tuberculose Pulmonar/microbiologia , Tuberculose Pulmonar/mortalidade , Zâmbia/epidemiologiaRESUMO
BACKGROUND: The efficacy of BCG vaccines against pulmonary tuberculosis varies between populations, showing no protection in Malawi but 50-80% protection in the UK. To investigate the mechanism underlying these differences, randomised controlled studies were set up to measure vaccine-induced immune responsiveness to mycobacterial antigens in both populations. METHODS: 483 adolescents and young adults in Malawi and 180 adolescents in the UK were tested for interferon-gamma (IFN-gamma) response to M tuberculosis purified protein derivative (PPD) in a whole blood assay, and for delayed type hypersensitivity (DTH) skin test response to tuberculin PPD, before and 1 year after receiving BCG (Glaxo 1077) vaccination or placebo or no vaccine. FINDINGS: The percentages of the randomised individuals who showed IFN-gamma and DTH responses were higher in Malawi than in the UK pre-vaccination-ie, 61% (331/546) versus 22% (47/213) for IFN-gamma and 46% (236/517) versus 13% (27/211) for DTH. IFN-gamma responses increased more in the UK than in Malawi, with 83% (101/122) and 78% (251/321) respectively of the vaccinated groups responding, with similar distributions in the two populations 1 year post-vaccination. The DTH response increased following vaccination in both locations, but to a greater extent in the UK than Malawi. The IFN-gamma and DTH responses were strongly associated, except among vaccinees in Malawi. INTERPRETATION: The magnitude of the BCG-attributable increase in IFN-gamma responsiveness to M tuberculosis PPD, from before to 1 year post-vaccination, correlates better with the known levels of protection induced by immunisation with BCG than does the absolute value of the IFN-gamma or DTH response after vaccination. It is likely that differential sensitisation due to exposure to environmental mycobacteria is the most important determinant of the observed differences in protection by BCG between populations.