Absence of association between delayed type hypersensitivity to tuberculin and atopy in children in The Gambia

Impact of Allergic Disease on the Risk of Mycobacterial Disease

BACKGROUND

The association between allergic diseases and the risk of mycobacterial disease is unclear.

OBJECTIVE

To evaluate the association between allergic diseases and mycobacterial diseases.

METHODS

This was a population-based cohort study of 3,838,680 individuals, without prior mycobacterial disease, who participated in the 2009 National Health Screening Exam. We evaluated the incidence of mycobacterial disease (tuberculosis or nontuberculous mycobacterial infection) in participants with allergic disease (asthma, allergic rhinitis, or atopic dermatitis) and those without allergic disease. We followed the cohort up until the date of mycobacterial disease diagnosis, follow-up loss, death, or December 2018.

RESULTS

During a median follow-up of 8.3 (interquartile range, 8.1-8.6) years, 0.6% of participants developed mycobacterial disease. The incidence of mycobacterial disease was significantly higher in those with allergic diseases than in those without allergic diseases (1.0 vs 0.7/1000 person-years; P < .001), with an adjusted hazard ratio of 1.13 (95% CI, 1.10-1.17). Asthma (adjusted hazard ratio, 1.37; 95% CI, 1.29-1.45) and allergic rhinitis (adjusted hazard ratio, 1.07; 95% CI, 1.04-1.11) increased the hazard of mycobacterial disease, whereas atopic dermatitis did not. The association between allergic diseases and hazard of mycobacterial disease was more prominent in older (age ≥ 65 years, P for interaction = .012) and obese (body mass index ≥ 25 kg/m2, P for interaction < .001) participants.

CONCLUSION

Allergic diseases including asthma and allergic rhinitis were associated with an increased risk of mycobacterial disease, whereas atopic dermatitis was not.

BCG for the prevention and treatment of allergic asthma

Allergic diseases, in particular atopic asthma, have been on the rise in most industrialized countries for several decades now. Allergic asthma is characterized by airway narrowing, bronchial hyperresponsiveness, excessive airway mucus production, eosinophil influx in the lungs and an imbalance of the Th1/Th2 responses, including elevated IgE levels. Most available interventions provide only short-term relief from disease symptoms and do not alter the underlying immune imbalance. A number of studies, mostly in mouse models, have shown that Mycobacterium bovis bacillus Calmette-Guérin (BCG) treatment is capable of preventing or reducing an established allergen-driven inflammatory response, by redirecting pathogenic Th2 towards protective Th1 and/or regulatory T cell responses. Dendritic cells stimulated by BCG appear to be a crucial first step in the immunomodulatory effects of BCG. While the protective and therapeutic effects of BCG against allergy and asthma are well documented in animal models, they are less clear in humans, both in observational studies and in randomized controlled trials. The purpose of this article is to provide an up-to-date overview of the available evidence on the anti-allergy, in particular anti-asthma effects of BCG in mice, rats and humans.

Environment and Host-Genetic Determinants in Early Development of Allergic Asthma: Contribution of Fungi

Asthma is a chronic debilitating airway disease affecting millions of people worldwide. Although largely thought to be a disease of the first world, it is now clear that it is on the rise in many middle- and lower-income countries. The disease is complex, and its etiology is poorly understood, which explains failure of most treatment strategies. We know that in children, asthma is closely linked to poor lung function in the first 3-years of life, when the lung is still undergoing post-natal alveolarization phase. Epidemiological studies also suggest that environmental factors around that age do play a critical part in the establishment of early wheezing which persists until adulthood. Some of the factors that contribute to early development of asthma in children in Western world are clear, however, in low- to middle-income countries this is likely to differ significantly. The contribution of fungal species in the development of allergic diseases is known in adults and in experimental models. However, it is unclear whether early exposure during perinatal or post-natal lung development influences a protective or promotes allergic asthma. Host immune cells and responses will play a crucial part in early development of allergic asthma. How immune cells and their receptors may recognize fungi and promote allergic asthma or protect by tolerance among other immune mechanisms is not fully understood in this early lung development stage. The aim of this review is to discuss what fungal species are present during early exposure as well as their contribution to the development of allergic responses. We also discuss how the host has evolved to promote tolerance to limit hyper-responsiveness to innocuous fungi, and how host evasion by fungi during early development consequentially results in allergic diseases.

The Humoral Immune Response to BCG Vaccination

Bacillus Calmette Guérin (BCG) is the only currently available vaccine against tuberculosis (TB), but it confers incomplete and variable protection against pulmonary TB in humans and bovine TB (bTB) in cattle. Insights into the immune response induced by BCG offer an underexploited opportunity to gain knowledge that may inform the design of a more efficacious vaccine, which is urgently needed to control these major global epidemics. Humoral immunity in TB and bTB has been neglected, but recent studies supporting a role for antibodies in protection against TB has driven a growing interest in determining their relevance to vaccine development. In this manuscript we review what is known about the humoral immune response to BCG vaccination and re-vaccination across species, including evidence for the induction of specific B cells and antibodies; and how these may relate to protection from TB or bTB. We discuss potential explanations for often conflicting findings and consider how factors such as BCG strain, manufacturing methodology and route of administration influence the humoral response. As novel vaccination strategies include BCG prime-boost regimens, the literature regarding off-target immunomodulatory effects of BCG vaccination on non-specific humoral immunity is also reviewed. Overall, reported outcomes to date are inconsistent, but indicate that humoral responses are heterogeneous and may play different roles in different species, populations, or individual hosts. Further study is warranted to determine whether a new TB vaccine could benefit from the targeting of humoral as well as cell-mediated immunity.

Early versus late BCG vaccination in HIV-1-exposed infants in Uganda: study protocol for a randomized controlled trial

Background

Bacillus Calmette-Guérin (BCG) vaccination may have nonspecific effects, i.e., effects on childhood morbidity and mortality that go beyond its effect on the risk of childhood tuberculosis (TB). Though the available scientific literature is mostly from observational studies, and is fraught with controversy, BCG vaccination at birth may protect infants in high-mortality populations against serious infections other than TB. Yet, other studies indicate that giving BCG later in infancy may modify immune responses to non-TB antigens and potentially enhance immunity, potentially also against tuberculosis (TB). It is unclear whether BCG vaccination very early in life offers adequate protection against TB and other infections among HIV-1-exposed children because even those who remain uninfected with HIV-1 show signs of impaired immunocompetence early in infancy. This study will compare BCG vaccination at birth with BCG vaccination at 14 weeks of age in HIV-1-exposed infants.

Methods

This is an individually randomized controlled trial in 2200 HIV-1-exposed infants. The intervention is BCG vaccination within 24 h of birth while the comparator is BCG given at 14 weeks of age. The study co-primary outcomes are severe illness in the first 14 weeks of life, and production of tumor necrosis factor, interleukin (IL)-1β, IL-6 and interferon-γ in response to mycobacterial and nonmycobacterial antigens. The study is being conducted in three health centers in Uganda.

Discussion

A well-timed BCG vaccination could have important nonspecific effects in HIV-1-exposed infants. This trial could inform the development of appropriate timing of BCG vaccination for HIV-1-exposed infants.

Trial registration

ClinicalTrials.gov, identifier: NCT02606526. Registered on 12 November 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-1881-z) contains supplementary material, which is available to authorized users.

Tuberculosis, bacillus Calmette-Guérin vaccination, and allergic disease: findings from the International Study of Asthma and Allergies in Childhood Phase Two

Some have suggested a protective effect of tuberculosis (TB) infection on allergic disease risk, but few studies have examined the association between the two. We therefore investigated whether TB disease and bacillus Calmette-Guérin (BCG) vaccination in early life protect against allergic disease. Information on allergic disease symptoms, past TB disease, and BCG vaccination as well as potential confounding factors was gathered by parental questionnaire from a randomly selected subset of 23,901 8- to 12-yr-old schoolchildren in 20 centers in both developed and developing countries. Children were also physically examined for flexural eczema and underwent skin prick testing. Pooled odds ratio (OR) estimates and corresponding 95% confidence intervals (CIs) across study centers were calculated, using random effects meta-analysis models. There were 245 (1.0%) reported cases of TB disease, and 66.3% (15,857) of all children received the BCG vaccine. Asthma, hay fever, and flexural eczema symptoms in the past year as well as flexural eczema on skin examination were all positively linked to a history of TB (adjusted pooled OR 'wheeze in the past year' = 2.27, 95% CI 1.52-3.41; adjusted pooled OR 'hay fever symptoms in the past year' = 2.23, 1.22-4.09; adjusted pooled OR 'flexural eczema symptoms in the past year' = 3.21, 2.01-5.12; adjusted pooled OR 'flexural eczema on skin examination' = 4.04, 1.71-9.56). Even higher risk estimates were seen for severe asthma and eczema symptoms [adjusted OR = 4.02 (2.17-7.47) and adjusted OR = 6.31 (2.19-18.17), respectively]. There was no significant association between past TB and skin prick test positivity (adjusted pooled OR = 1.32, 0.87-2.02). BCG vaccination during the first year of life was also not associated with any of the allergy outcomes. We found a uniform positive association between TB and all allergic disease outcomes, including eczema on skin examination. As this was a cross-sectional study, it is unclear whether this positive association is attributable to a causal relationship, and further longitudinal studies are required.

The burden of allergic rhinitis and asthma

Asthma and allergic rhinitis are common health problems that cause major illness and disability worldwide. The prevalence of allergic rhinitis is estimated to range from 10% to 20% in the USA and Europe. Multiple factors contribute to the wide range of reported prevalence rates. These include type of prevalence rate reported (current or cumulative), study selection criteria, age of participants, differences in survey methods, varied geographic locations and socioeconomic status, any of which are significant enough to confound direct comparison between studies. There is no standard set of diagnostic criteria for allergic rhinitis. In most studies, the criteria for diagnosis are based on the subject's reporting, solely by questionnaire and rarely confirmed by skin testing. In addition, most studies focus on hay fever, leaving perennial allergic rhinitis underestimated. Sinus imaging is generally not performed and, therefore, rhinosinusitis not differentiated. Some investigators report 'current' prevalence while others report 'cumulative' or 'lifetime' prevalence. Epidemiologic studies have consistently shown that asthma and rhinitis often coexist in the same patients. The prevalence of asthma is <2% in subjects without rhinitis while it varies from 10% to 40% in patients with rhinitis. Furthermore, the majority of patients with asthma experience rhinitis, which is a factor in the risk for asthma. Despite recognition that allergic rhinitis and asthma are global health problems, there are insufficient epidemiologic data and more data are needed with regard to their etiologic risk factors and natural history. This aim of this review is to enable the reader to discuss prevalence, risk factors and prognosis of allergic rhinitis and asthma.

No association between tuberculin skin test and atopy in a bacillus Calmette-Guérin vaccinated birth cohort

Previously, an inverse association was suggested between mycobacterial infection and atopy. We aimed to determine the association between tuberculin skin test (TST) and allergic manifestations in a birth cohort where all infants were vaccinated with bacillus Calmette-Guérin (BCG) at birth. Newborns were enrolled randomly and prospectively followed up for a period of 5 yr. Information on family history and environmental factors was obtained at birth, International Study of Asthma and Allergies in Childhood asthma questionnaire, physical examination, skin prick test to common inhalant and food allergens and TST were performed at 2 and 5 yr of age. Positive TST reactivity was defined as an induration of > or = 10 mm. A total of 399 newborns were enrolled, 293 and 125 were available for a followup visit at 2 and 5 yr of age respectively. The prevalence of ever asthma, rhinitis and allergen sensitization tended to increase while eczema decreased with time. No significant association was found between TST reactivity and ever and current wheeze, doctor diagnosed asthma or atopic sensitization both at 2 and 5 yr of age. This prospectively designed birth cohort study did not confirm the previously suggested inverse correlation between TST reactivity and atopic sensitization or any allergic manifestations in Turkish children vaccinated with BCG at birth.

Point-counterpoint. The triumph of the null hypothesis: epidemiology in an age of change

The recent confusion concerning the relation between hormone replacement therapy and cardiovascular disease has stirred a new wave of debate about the value and future of epidemiology. Opponents of epidemiology suggest an ever-diminishing role in an age of small risks and complex diseases, yet proponents are not in consensus about how to adapt their discipline to the challenges associated with ageing societies and changing disease patterns. While epidemiology is likely to be increasingly called upon to make sense of the risks involved with these changes, wading into this era with a mindset and tools that were derived from epidemiology's 'golden era' of tackling major risk factors, has created more confusion than understanding. Increasingly, we need to downsize epidemiology to what is testable, measurable, and relevant, based on robust methodology and public health rationale. Applying an evolutionary perspective, that views health problems of modernity as a manifestation of the mismatch between our ancient genes and hi-tech lifestyles, can provide guidance for a 21st century research agenda.

Lack of an inverse association between tuberculosis infection and atopy: by T-cell-based immune assay (RD1-ELISpot)

The association between mycobacterial exposure, vaccination with bacillus Calmette-Guerin (BCG) in early life and atopy remains controversial. Distinguishing between environmental mycobacterial exposure, TB infection and BCG-vaccination is not possible with the tuberculin skin test (TST) but new accurate blood-tests for TB infection present an opportunity to differentiate TB infection from environmental mycobacterial exposure and BCG-vaccination. We used a new blood test in parallel with TST to investigate whether Mycobacterium tuberculosis infection and/or BCG vaccination are associated with development of atopy in children with prior household TB contacts. All children who had contact with adult active pulmonary TB during the last 6 months underwent TST, chest radiography, and RD1-ELISpot assay. The presence of a BCG scar was documented, and assessment of atopy was carried out by International Study of Asthma and Allergies in Childhood questionnaire, allergy skin prick testing (SPT) and evaluation of serum total IgE. Among 361 children enrolled 39 (11%) had a positive SPT, 236 (63%) positive TST, and 189 (52%) positive RD1-ELISpot. The frequency of SPT positivity, ever wheezing, allergic rhinitis, doctor-diagnosed asthma, high serum IgE level, and median total serum IgE levels did not differ significantly different by TST or RD1-ELISpot status. On the other hand, presence of BGC scar was associated with lower median total serum IgE level (p = 0.01) and lower frequency of high IgE (p = 0.003). M. tuberculosis infection whether measured by TST or RD1-ELISpot, was not associated with atopy in children with household TB contact. Presence of a BCG vaccination scar was inversely associated with atopy, as measured by serum IgE.

Potential health effects from non-specific stimulation of the immune function in early age: the example of BCG vaccination

There is increasing, but still inconsistent evidence that vaccinations and childhood infections may play a role in the normal maturation of the immune system, and in the development and balance of immune regulatory pathways, both of which might impact health later in life. This review covers the epidemiological evidence regarding the role of Bacillus Calmette-Guérin (BCG) vaccination on the following inflammatory or autoimmune diseases: asthma and allergic diseases, Crohn's disease (CD), insulin-dependent diabetes mellitus (IDDM), and specific cancers. The literature is more comprehensive for asthma and allergic diseases, with 16 studies reporting the absence of an association while seven rather suggest a protective effect of BCG. We found insufficient evidence on CD to conclude at this point. Overall, the evidence for IDDM based on four studies leans towards no association, although some effects were observed in population subsets. Five epidemiological investigations provide evidence on a possible link with cancer incidence or mortality at various sites, with indications of both increased and decreased risks. Given the potential public health implications, it is imperative to acquire a better understanding of how BCG vaccination could influence the development of such chronic health conditions in the population.

Absence of relationships between tuberculin responses and development of adult asthma with rhinitis and atopy

OBJECTIVE

To investigate the relationship between tuberculin skin responses and the development of adult asthma, rhinitis, and atopy.

METHODS

Two hundred fourteen patients with mild-to-moderate asthma accompanied with rhinitis and 220 normal volunteers underwent a medical history, chest radiography, allergen skin-prick testing (SPT), bovine Mycobacterium tuberculosis vaccine (BCG) scar identification, purified protein derivative (PPD) tuberculin skin testing, serum-total and serum-specific IgE measurements, and bronchial provocation (provocative dose of histamine causing a 20% fall in FEV(1) [PD(20)]).

RESULTS

Thirty-one normal volunteers (14.1%) and 168 asthma-rhinitis subjects (78.5%) had one or more positive skin test results (p < 0.0001). Neither the presence of a BCG scar nor a history of BCG vaccination had a significant effect on atopy in either group. The rate of PPD positivity had no statistical difference between atopy and nonatopy in both groups. In multivariate logistic regression analysis, the odds ratio for tuberculin reactivity was not related to the level of serum-total IgE nor to the level of serum-specific IgE to Dermatophagoides pteronyssinus (DP) and Dermatophagoides farinae (DF), skin response to DP and DF, and PD(20). Overall, no significant correlations were found between tuberculin skin reactivity and log serum-total IgE or PD(20).

CONCLUSION

There is no relationship between history of tuberculosis infection, tuberculin responses, and development of adult bronchial asthma, allergic rhinitis, and atopy. Our study suggests that the protection provided by intradermal BCG vaccination in infants to prevent atopic diseases may be limited in early childhood, when a substantial memory of cellular immune modulation still exists.

Does the Atopic Phenotype Prevent Development of Active Tuberculosis Infection?

This study investigated the relationship between the atopic phenotype and the development of active tuberculosis. A total of 82 human immunodeficiency virus-negative males with active pulmonary tuberculosis and 88 healthy controls were enrolled into this prospective study. Serum immunoglobulin E (IgE) levels were measured and skin prick tests performed before initiation of treatment. Skin prick tests were positive in 34.1% of the tuberculosis patients and 39.8% of the controls. Allergic respiratory symptoms were significantly less frequent in skin prick test positive tuberculosis patients (21.4%) compared with skin prick test positive controls (62.9%). Median IgE levels in atopic tuberculosis patients were significantly higher than in atopic controls. The low rate of atopic respiratory complaints seen in the tuberculosis patients, despite having similar allergic skin prick test sensitivities to the controls, could be attributed to a weak T-helper (Th) 2 immune reaction and its effects on Th1–Th2 interaction.

Diagnosis and treatment of asthma in childhood: a PRACTALL consensus report

Asthma is the leading chronic disease among children in most industrialized countries. However, the evidence base on specific aspects of pediatric asthma, including therapeutic strategies, is limited and no recent international guidelines have focused exclusively on pediatric asthma. As a result, the European Academy of Allergy and Clinical Immunology and the American Academy of Allergy, Asthma and Immunology nominated expert teams to find a consensus to serve as a guideline for clinical practice in Europe as well as in North America. This consensus report recommends strategies that include pharmacological treatment, allergen and trigger avoidance and asthma education. The report is part of the PRACTALL initiative, which is endorsed by both academies.

Mycobacterial infection and atopy in childhood: a systematic review

The epidemiological relation between mycobacterial infection and the prevalence of atopic disease in humans is still unclear. This is in contrast to studies in murine models in which a clear suppression of atopic symptoms was observed after exposure to mycobacteria or mycobacterial products. We therefore wanted to provide a systematic overview of the published literature on the relationship between mycobacterial infection and atopic disease and to evaluate the causal relationship in a meta-analysis. The EMBASE and MEDLINE databases were searched systematically for papers published in the English literature (1966-2005) on the relation between mycobacterial infection and atopic disease. Original observational or interventional studies involving the paediatric population were included. Two authors independently reviewed articles for data on mycobacterial exposure and atopic disease outcome. Any differences were resolved by discussion. Of a total of 1201 hits, 23 studies (19 cross-sectionals, three case-controls and one prospective cohort) met the inclusion criteria. Only a minority of studies (40%) observed an association between mycobacterial infection and the prevalence of atopic disease outcome. In the meta-analysis, only studies containing data on mycobacterial exposure and atopic disease outcome variables were included. Only cross-sectional studies, in which the relation between a positive tuberculin skin test and allergic symptoms was studied, observed statistically significant negative correlation (odds ratio 0.63; 95% confidence interval: 0.51-0.79). The results of this review show that the evidence of the relationship of mycobacterial infection and atopic disease is based on observations of cross-sectional studies. In a meta-analysis, calculations showed a high level of heterogeneity (I(2)) within studies with similar design making it difficult to pool effects. This may partly be explained by differences in the type and definition of mycobacterial infection and lack of uniformity in the definition of atopy. The results show that only a minority of studies in the literature shows any evidence of inverse relationship between mycobacterial exposure and atopic disease outcome. The fact that the present epidemiological evidence on the relationship between mycobacterial infection and the development of atopic disease is based mainly on cross-sectional observational studies indicates the need for population-based prospective studies to address this issue. This issue needs to be addressed in view of recent suggestions to developing mycobacterial-based vaccines against atopic disease in the future.

The potential of Mycobacterium to protect against allergy and asthma

The increase in the global incidence of atopic disease and asthma during the past few decades has been ascribed to environmental factors, including the reduction in exposure to serious infections. The hypothetical framework to explain the inverse relationship between infections and atopic disease and asthma has been called the "hygiene hypothesis." Animal and experimental models have identified Mycobacteria as important potential candidates in the hygiene hypothesis by demonstrating that exposure to Mycobacteria or mycobacterial proteins led to subsequent reduction in different atopic manifestations. Although there are epidemiological studies in support, they have not always been consistent. In this review we appraise epidemiologic evidence on the inverse relationship between mycobacterial exposure and atopic disease, explore the immunological mechanisms involved and evidence that this effect may be dose-dependent, and discuss the challenges facing the use of Mycobacteria as vaccine for prevention of atopic disease.

Mycobacteria and allergies

Exposure to mycobacteria was inevitable throughout mammalian evolution. Most mycobacteria are saprophytic environmental organisms that are enormously abundant in soil and untreated water and evoke immune responses in the residents of developing countries. A few species are pathogens. For example Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), infects approximately 1/3 of the world's population. Many individuals also receive vaccination with the Bacille Calmette Guérin (BCG), which is an attenuated form of the organism causing bovine TB. In order to understand the possible role that mycobacteria might have in the increases in allergic disorders over the last decades, it is necessary to dissect out these different mycobacterial influences. Above all it is essential, when analysing tuberculin test results, to distinguish between individuals who have latent TB and those who do not. Only then can probable effects of diverse types of exposure emerge. There is no doubt that in animal models mycobacteria can both prevent and treat allergic responses either by boosting Th1 or by driving allergen-specific regulatory T cells (RegT). Clinical trials in man remain inconclusive.

Th1?Th2 Interaction: Is More Complex than a See-saw?

Infections, such as tuberculosis, measles and diphtheria, may decrease the risk of developing atopic allergic disorders. Patients with pulmonary TB having similar allergic skin prick test sensitivity as healthy controls but unable to show vigorous atopic phenotype in their healthy period might be a sign for Th1-Th2 immune interaction.

Is the prevalence of wheeze in children altered by neonatal BCG vaccination?

BACKGROUND

The prevalence of asthma and atopic disease has increased in recent decades, but precise reasons for this increase are unknown. BCG vaccination is thought to be among a group of vaccines capable of manipulating the immune system toward T(H)1 dominance and therefore reducing the likelihood of atopic disease.

OBJECTIVE

The aim of this study was to determine the influence of neonatal BCG vaccination on the prevalence of wheeze in a large community population of children.

METHOD

In a historical cohort study, a parent-completed questionnaire was used to identify the prevalence of wheeze in BCG-vaccinated and nonvaccinated children in Manchester, England.

RESULTS

There were 2414 participants aged between 6 and 11 years. In a univariate analysis neonatal BCG vaccination was associated with a significantly lower prevalence of wheeze (odds ratio, 0.69; 95% CI, 0.55-0.86), and statistical significance was retained when the analysis was adjusted for potential confounders (odds ratio, 0.68; 95% CI, 0.53-0.87).

CONCLUSION

These results demonstrate an association between asthma symptom prevalence and neonatal BCG vaccination, relating to a possible 27% reduction in prevalence, and are therefore of considerable public health importance.

CLINICAL IMPLICATIONS

The capacity of neonatal BCG vaccination to reduce the prevalence of respiratory symptoms in children warrants further investigation.

Do vaccines modify the prevalence of asthma and allergies?

Epidemiological studies suggest the hypothesis that the increase in asthma and allergies in the industrialized world can be explained by a decline in the number of infectious diseases occurring during childhood. In the context of this 'hygiene hypothesis', is immunization in early life a risk factor for promoting allergic diseases? The majority of studies, especially those conducted with more extensive populations, have not found an increased risk, and although 'not finding an increased risk' is not the same as 'the non-existence of any risk at all', it seems that the evidence is tipped in favor of the absence of risk. Conversely, although some surveys have described a protective effect of vaccination, the majority refuted this result. If there is any effect, it is probably a weak one.

Respiratory atopic disease, Ascaris-immunoglobulin E and tuberculin testing in urban South African children

BACKGROUND

Epidemiological relation of intestinal helminth infection and atopic disease, both associated with a T-helper (Th) 2 immune response, is controversial, as it has been reported that helminth infection may either suppress or pre-dispose to atopic disease. This relation has not been tested in an area with a high burden of Mycobacterium tuberculosis (MTB) infection, a known Th1-stimulating infection.

OBJECTIVE

To study the association of intestinal helminth infection and atopic disease in a community where helminth infection is endemic and MTB infection is high.

METHODS

Three-hundred and fifty-nine randomly selected children aged 6-14 years from a poor urban suburb were tested with allergy questionnaire, skin prick test (SPT) to common aeroallergens, Ascaris-specific IgE (Ascaris-sIgE), fecal examination for pathogenic intestinal helminths and tuberculin skin testing (TST). Histamine bronchoprovocation was tested in the group of children aged 10 years and older.

RESULTS

were corrected for demographic variables, socioeconomic status, parental allergy, environmental tobacco smoke (ETS) exposure in the household, recent anthelminthic treatment and for clustering in the sampling unit. Results Ascaris-sIgE was elevated in 48% of children, Ascaris eggs were found in 15% and TST was positive in 53%. Children with elevated Ascaris-sIgE had significantly increased risk of positive SPT to aeroallergens, particularly house dust mite, atopic asthma (ever and recent), atopic rhinitis (ever and recent) and increased atopy-related bronchial hyper-responsiveness. In children with negative TST (<10 mm), elevated Ascaris-sIgE was associated with significantly increased risk of atopic symptoms (adjusted odds ratio (OR(adj)) 6.5; 95% confidence interval (CI) 1.9-22.4), whereas in those with positive TST (>/=10 mm) this association disappeared (OR(adj) 0.96; 95% CI 0.4-2.8).

CONCLUSIONS

These results suggest that immune response to Ascaris (Ascaris-sIgE) may be a risk factor of atopic disease in populations exposed to mild Ascaris infection and that MTB infection may be protective against this risk, probably by stimulation of anti-inflammatory networks.

Beneficial non-targeted effects of BCG--ethical implications for the coming introduction of new TB vaccines

Non-targeted effect of BCG: Several recent studies suggest that BCG has beneficial non-targeted effects on general child survival in low-income countries. Studies of the effect of BCG on morbidity in humans are scarce; some found a positive effect of BCG and others show no effect. Non-targeted effects of vaccines-possible bias and confounding: The major argument against comparing vaccinated and unvaccinated groups is that there is a beneficial social selection bias for vaccinated children-the "Healthy vaccinee effect". However, controlling for various social and health-related background factors in the survival analyses had no effect on the estimates, making this source of bias less likely. A more powerful argument that the findings are not due to the healthy vaccinee effect is that differential non-targeted effects of other vaccines have been observed; diphteria-tetanus-pertussiss vaccination has marked negative effects on child survival, whereas measles vaccine has a positive effect in several studies. Several studies have shown better survival for children reacting to their BCG vaccination with a BCG scar or tuberculin skin test reaction (TST). It could be argued that the reacting children were immunologically stronger and therefore more likely to survive-the "Healthy reactor effect". However, recent findings show that a BCG scar and a TST reaction depend to a large extent on the vaccination technique. Hence, the BCG responses may reflect a true vaccine effect and not merely the health status of the children. Since HIV-1 has been shown to suppress both TST and BCG scar reaction in response to BCG, it is an obvious contributor to the healthy reactor effect, but excluding deaths of children with HIV-1 infection from analysis did not affect the beneficial effect of having a positive TST. Excluding children exposed to tuberculosis (TB) in the household did not affect the estimates either. Furthermore, there are strong sex-differential effects of BCG in both mortality and morbidity data, BCG being more beneficial for girls. These observations cannot consistently be explained by the healthy vaccinee or healthy reactor effects. Ethical implications: For future TB-vaccine studies, these findings imply that: These recommendations might be considered to delay or to be a too large obstacle for the development and trials of new TB vaccines. However, most of the non-targeted beneficial effects of BCG have been observed in children below 2 years of age, which is not a long follow-up time in a TB-vaccine trial. Furthermore, considering the difficulty in setting the TB diagnose in children and the lack of reliable TB-protection markers, it does not seem unreasonable to argue for monitoring of general morbidity and survival in future TB-vaccine trials.

Bacillus Calmette-Guérin vaccination and infant mortality

When the bacillus Calmette-Guérin (BCG) vaccine was introduced in the 1920s, it was suggested that BCG occasionally had nonspecific beneficial effects on mortality beyond the specific protection against tuberculosis. Considering that BCG has since then become the most used vaccine in the world, surprisingly few studies have been undertaken into the effect of BCG on general mortality and morbidity. Recent studies suggest that BCG has beneficial nontargeted effects on general infant morbidity and mortality in low-income countries, often with the most pronounced effect among girls. These observational findings are supported by early trials in which children were randomized or alternated to BCG vaccination. Furthermore, a BCG scar and a positive tuberculin reaction are related to better survival among BCG-vaccinated children in low-income countries, especially for girls. The findings are not explained by frailty bias, in other words, that healthy children are more likely to receive BCG vaccination. A nonspecific, gender-differential effect of BCG on general infant mortality may have large implications for tuberculosis vaccine research and routine vaccination policy.

Respiratory infections and asthma

Respiratory tract infections caused by both viruses and/or atypical bacteria are involved in the pathogenesis of asthma. In particular, several viruses such as respiratory syncytial virus, rhinovirus and influenza/parainfluenza viruses may favour the expression of the asthmatic phenotype, being also implicated in the induction of disease exacerbations. Within this pathological context, a significant role can also be played by airway bacterial colonizations and infections due to Chlamydiae and Mycoplasms. All these microbial agents probably interfere with complex immunological pathways, thus contributing to induce and exacerbate asthma in genetically predisposed individuals.

Ecological correlation among prevalence of asthma symptoms, rhinoconjunctivitis and atopic eczema with notifications of tuberculosis and measles in the Brazilian population

This study aims to assess the relationship among incidence of tuberculosis and measles, in the general population, within the year of birth and the prevalence of asthma, rhinoconjunctivitis and atopic eczema in teenagers from different Brazilian cities enrolled in the International Study of Asthma and Allergies in Childhood (ISAAC) phases I and III. Positive answers to the questions: 'Have you had wheezing or whistling in the chest in the past 12 months?', 'In the past 12 months, has this nose problem been accompanied by itchy-watery eyes?' and 'Has this itchy rash at any time affected any of the following places: the folds of the elbows, behind the knees, in front of the ankles, under the buttocks, or around the neck, ears or eyes?' identified the teenagers with asthma, rhinoconjunctivitis, and atopic eczema, respectively. The incidence of tuberculosis and measles, in the general population, observed in the year of birth of the enrolled teenagers (1981/82 and 1988/89) were obtained from governmental agencies: National Foundation of Health (FUNASA) and Brazilian Institute of Geography and Statistics (IBGE). They were compared with the prevalence of asthma, rhinoconjunctivitis and atopic eczema reported in both ISAAC phases I and III. Although we observed reduction of the incidence of tuberculosis and measles in the general population in all cities, the prevalence of asthma, rhinoconjunctivitis and atopic eczema remained stable in most of the centers. In Pernambuco and Paraná, there has been a significant increase in the prevalence of rhinoconjunctivitis. These data do not corroborate the findings of an inverse relationship between the prevalence of atopic diseases and the decreasing incidence of tuberculosis and measles.

Childhood atopy and allergic disease and skin test responses to environmental mycobacteria in rural Crete: a cross-sectional survey

BACKGROUND

Through its powerful immunoregulatory effects, infection with atypical mycobacteria may exert a protective effect on the development of childhood allergic disease.

OBJECTIVE

To examine the relationship between childhood atopy or allergic disease and previous infection with four species of atypical mycobacteria.

METHODS

Eight hundred and six children aged 8-18 years and living in rural Crete--most of whom had had previous BCG immunization--underwent skin prick testing with 10 aeroallergens; their parents completed a standardized questionnaire relating to allergic disease. No less than 8 weeks later each child underwent intradermal skin tests with 0.1 mL solutions of four selected mycobacterial reagents (Aviumin C, Gordonin, Chelonin and Ranin I).

RESULTS

Twenty-three percent of children were atopic on skin prick testing; far fewer had symptoms of asthma (5%) or hayfever in conjunction with a positive prick test to pollens (2%). Eighty percent of children had positive skin responses to one or more mycobacterial species. Among all children--and those with a BCG scar--there was no association between atopy or allergic symptoms and mycobacterial skin responses; among the few children without a BCG scar however those with positive mycobacterial responses were less likely to be atopic or to report allergic symptoms; these differences were not statistically significant.

CONCLUSIONS

Our findings, in a population of BCG-immunized children, do not lend support to the suggestion that infection with atypical mycobacteria is protective against childhood allergic disease.

Inverse association between Mycobacterium tuberculosis infection and atopic rhinitis in children

BACKGROUND

The association between Mycobacterium tuberculosis (MTB) infection and atopy remains controversial.

AIM

To investigate the association between MTB infection and atopic rhinitis in children living in a high TB incidence area.

METHODS

In this cross-sectional study 418 children aged 6-14 years from an established epidemiological research-site in a poor urban community were invited to participate. They were assessed for allergic rhinitis (ISAAC questionnaire) and skin responses to tuberculin and eight environmental allergens. The presence of a BCG scar was documented, intestinal parasites and total and Ascaris lumbricoides-specific IgE levels were measured. Atopic rhinitis was defined, using the new World Allergy Organization (WAO) definition, as reported allergic rhinitis and a positive skin prick test (SPT > or =3 mm) to any allergen.

RESULTS

Among the 337 children enrolled 10.4% had allergic rhinitis, 17.5% a positive SPT and 53% a positive tuberculin skin test (TST > or =10 mm). Children with a positive TST were significantly less likely to have recent atopic rhinitis (OR(adjusted) 0.06; 95% CI 0.007-0.5) than those with a negative TST. SPTs were significantly more common in children with negative TST who had recent allergic rhinitis (OR(adj) 34.0; 95% CI 7.6-152.6), but not in children with positive TST and recent allergic rhinitis (OR(adj) 0.6; 95% CI 0.07-5.2).

CONCLUSIONS

MTB infection seems to reduce the prevalence of atopic rhinitis, and influences SPT reactivity in children with allergic rhinitis from a high TB incidence area.

Hope for the hygiene hypothesis: when the dirt hits the fan

The hygiene hypothesis was developed in response to data suggesting that the increase in allergic diseases as well as asthma was secondary to a reduced exposure to infectious stimuli. Indeed, the epidemiologic changes, resulting in an increase in atopic disease, have been impressive and intriguing. Furthermore, although there clearly is a genetic component to atopic diseases, genetics cannot account for a marked increase in the incidence and prevalence of allergic manifestations within a few generations. Thus, environmental factors have been suggested as responsible for the changing prevalence. There are two--not mutually exclusive--possibilities, namely, that substances that promote atopy have been added to the environment or that factors that provided protection from allergic disease were lost from the environment. Both outdoor and indoor pollution, along with a long list of other environmental factors, have been proposed. It is of interest that in many developed countries, certain types of pollution have decreased, whereas the prevalence of atopic disease has increased. In this review, we have explored a detailed analysis of a large number of studies that have focused on this issue and suggest that, although the hygiene hypothesis has merit, the stimuli responsible for the new epidemiology remain enigmatic.

The hygiene hypothesis and asthma

PURPOSE OF REVIEW

Reduced exposure to childhood infections may explain the increased prevalence of allergic diseases in industrialized countries (the hygiene hypothesis). This review will examine recent epidemiologic studies of the hygiene hypothesis and asthma.

RECENT FINDINGS

Recent studies have confirmed previous findings of an inverse association between increased exposure to other children during childhood and either allergen sensitization or hay fever. However, there is conflicting evidence regarding the relation between exposure to other children and asthma. Although it has been hypothesized that vaccinations may influence the development of asthma, recent findings do not support this association. Serologic evidence of exposure to certain gastrointestinal pathogens (eg, hepatitis A virus) has been inversely associated with either allergen sensitization or asthma in some, but not all, recent studies. Although heavy infestation with certain parasites (eg, helminths) is protective against allergen sensitization, there is conflicting evidence regarding the relation between parasitic infection and asthma. The results of recent studies suggest that the relation between endotoxin exposure and asthma is complex and likely influenced by factors related to the exposure itself, the host, and other covariates. Although it has been postulated that antibiotic use in early life is a risk factor for asthma, this hypothesis is not supported by recent findings.

SUMMARY

For every exposure studied with regard to the hygiene hypothesis, there are inconsistent findings in relation to asthma. The hygiene hypothesis is not likely to be the sole explanation for the ongoing asthma epidemic in industrialized nations.

Is the mycobacteria-derived purified protein response in atopic asthmatic children different?

BACKGROUND

The response to mycobacteria-derived purified protein (PPD) is mediated primarily by T-helper-1 response and is expected to be inhibited in atopic diseases. The aim of this study was to investigate whether the PPD response is different in atopic asthmatic children.

METHODS

40 atopic asthmatic children (mean age 8.3 +/- 4.9 years) and 40 healthy age- and sex-matched children who had received bacillus Calmette-Guerin (BCG) vaccination were included in the study. Five PPD units were administered intradermally to all children and were interpreted after 48 h.

RESULTS

There was no correlation between serum total IgE level and PPD induration (p=0.054). The PPD induration was not statistically different between the children who used inhaled corticosteroid and those who did not. Although the PPD positivity (induration > or =5 mm) rate was higher in atopic asthmatic children (50%) than in healthy children (32.5%), the difference was not found to be statistically significant. The PPD induration in atopic asthmatic children (7.41 +/- 5.58 mm) was found to be greater than the one in healthy children (5.21 +/- 3.39) (p < 0.039). The induration in atopic asthmatic children (5.21 +/- 3.77) and healthy children (4.43 +/- 2.32) did not show a difference in children who where vaccinated only once with BCG, but it was found to be statistically significantly greater in atopic asthmatic children (12.50 +/- 5.90) than healthy children (7.08 +/- 4.70) who were vaccinated with BCG twice (p <0.012). The proportion of having a PPD induration of > or =10 mm was found to be higher in atopic asthmatic children than in the healthy ones (32.5 vs. 12.5%) (p <0.032).

CONCLUSION

Our data showed that the PPD response was stronger in BCG-vaccinated atopic asthmatic children than in healthy BCG-vaccinated ones.

Immunotherapy with mycobacteria

PURPOSE OF REVIEW

To summarize and evaluate critically recent progress with mycobacteria as a potential novel disease modifying treatment strategy in asthma.

RECENT FINDINGS

The link between exposure to pathogenic or saprophytic mycobacteria and protection from allergic diseases is still controversial, and recent epidemiological studies, which addressed only exposure to Mycobacterium tuberculosis or bacillus Calmette-Guérin, did not help to clarify this issue. Moreover, the clear efficacy of mycobacterial treatment seen in animal models has not been reproduced in human asthma, and a recent small study testing the hypothesis that heat-killed Mycobacterium vaccae attenuates asthmatic reactions after allergen challenge did not provide convincing results. However, it has been shown that treatment of mice with M. vaccae induces the generation of allergen-specific T regulatory cells capable of suppressing allergen-mediated eosinophilic lung inflammation, suggesting that a general deficiency of T regulatory cell activity might be responsible for the increased prevalence of asthma. This hypothesis is supported by findings that a lack of T regulatory cells, as found in genetic disorders of man and mouse attributable to a mutation of Foxp3, a transcription factor specifically expressed by T regulatory cells, is associated with manifestations of severe atopy and autoimmunity, precisely the spectrum of diseases linked to the hygiene hypothesis.

SUMMARY

Further studies on the relationship between mycobacteria and atopic disorders are needed, but there is reason to believe that the novel findings and molecular mechanisms associated with mycobacterial infections will further strengthen the currently unproved therapeutic value of immunotherapy with mycobacteria.

Risk factors for atopy among school children in a rural area of Latin America

BACKGROUND

Infection with common childhood infectious diseases including geohelminth infections may provide protection against the development of atopy and allergic disease. Few studies have investigated risk factors for atopy among children living in rural areas of Latin America.

OBJECTIVE

To identify risk factors associated with atopy among school-age children in a rural area of Latin America.

METHODS

Analytic cross-sectional study of school-age children conducted in seven rural schools in Pichincha Province in Ecuador. Detailed risk factor information was obtained by questionnaire, stool samples were collected for identification of geohelminth parasites, and Mantoux testing was performed to determine tuberculin sensitization.

RESULTS

A total of 1002 children from seven rural schools were recruited. The prevalence of geohelminth infections was high (70.1% were infected with at least one geohelminth parasite) and the prevalence of allergic sensitization was high (20.0% had evidence of aeroallergen sensitization). Factors associated with significant protection against atopy in multivariate analyses were the presence of overcrowding in the child's home, low socio-economic level, and infection with geohelminth parasites, and the protective effects of the three factors were statistically independent.

CONCLUSION

Low socio-economic level, overcrowding and geohelminth infection, are independently protective against atopy among school-age children living in a rural area of Latin America.

The effect of BCG vaccine at birth on the development of atopy or allergic disease in young children

BACKGROUND

Exposure to infectious diseases may reduce the development of asthma or allergy. In particular, the role of the BCG vaccine in modulating asthma or allergy has been a source of speculation.

OBJECTIVE

To study newborns from 3 international sites to evaluate the prospective effect of BCG vaccine on allergic diseases or atopic development.

METHODS

Infants were enrolled from newborn and well-infant clinics in Thailand, Argentina, and Turkey. The standard BCG vaccine for each country was given at birth. Parents who consented to have their infant included in the protocol completed an allergy family questionnaire. Infants underwent a standard purified protein derivative (PPD) test at 9 to 12 months of age, and the reaction size was measured. At the age of 2 years, the children returned to be studied. Allergy skin tests to common allergens appropriate to location and age were performed, and the parents completed the International Study of Allergy and Asthma in Childhood questionnaire. The PPD reaction size was compared with the presence of atopy and allergy questionnaire responses.

RESULTS

A total of 1,704 infants were studied. Statistical significance was found between a negative PPD response vs any positive PPD response and the risk of having an allergic history at the age of 2 years in Turkey (relative risk, 2.11; 95% confidence interval, 1.25-3.55; P = .005) and Thailand (relative risk, 2.16; 95% confidence interval, 1.18-3.94; P = .02) but not Argentina (relative risk, 1.09; 95% confidence interval, 0.70-1.68; P = .70).

CONCLUSIONS

This study further supports the role of infectious agents in modulating asthma and allergy development.