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

Preconceptional, pregnant, and postnatal exposure to outdoor air pollution and indoor environmental factors: Effects on childhood parasitic infections

BACKGROUND

Parasitic infections (PIs) are common and pose substantial health hazards in children globally, but the fundamental environmental variables exposure during crucial time window(s) are unclear.

OBJECTIVES

To identify key indoor and outdoor environmental factors leading to childhood PIs throughout critical time window(s).

METHODS

A combined cross-sectional and retrospective cohort study was performed on 8689 children residing in Changsha, China. Data was acquired pertaining to the health status and environmental exposure of the children in their homes. Personal exposure to outdoor air pollutants at the residential address during the preconceptional, perinatal, and postnatal periods was computed using data from ten air quality monitoring stations. An analysis of the relationships between childhood PIs and both indoor and outdoor factors was conducted using a multiple logistic regression model.

RESULTS

Childhood PIs were associated with outdoor CO and ozone (O3) exposure during the 10th-12th months prior to pregnancy, with ORs (95 % CI) of 1.68 (1.24-2.27) and 1.60 (1.15-2.22), respectively; childhood PIs were also associated with CO exposure during one year prior to pregnancy and the first trimester in utero [ORs = 1.57 (1.14-2.15) and 1.52 (1.17-1.97)]. Childhood PIs were found to be associated with PM2.5 exposure during pregnancy and the first year, with odds ratios of 1.51 (1.14-2.00) and 1.95 (1.22-3.12) per IQR increase in pollutant exposure, respectively. Exposures to smoke, renovation-related indoor air pollution (IAP), dampness and plant-related indoor allergens in the early life and past year were all associated with childhood PI, with odds ratios (95 % CI) ranging from 1.40 (1.01-1.95) for environmental tobacco smoke (ETS) during pregnancy to 1.63 (1.12-2.37) for mold/damp stains in the past year. In terms of PI risk, the early life and present periods were critical time windows for outdoor and indoor exposures, respectively. Certain individuals were more vulnerable to the PI risk associated with both indoor and outdoor exposures. Antibiotic use during child's lifetime and early years increased and decreased the PI risk of exposure to outdoor and indoor environments, respectively.

CONCLUSIONS

Exposure to outdoor air pollution in early life and indoor environments in the past year were found to be associated with childhood PI.

Concurrent allergy and helminthiasis in underprivileged urban South African adults previously residing in rural areas

This study investigated whether prior exposure to helminths (Ascaris IgE, Ascaris eggs and Trichuris eggs) either in childhood or in adulthood, and residence in rural and resource‐limited urban areas influence allergy outcomes (asthma, rhinitis, IgE atopy and food allergy) in a South African population. Participants historical and present allergies data were collected through questionnaires and clinical record files. Coproscopy and immunoassays (ImmunoCAP^TM Phadiatop, total IgE and allergen‐specific fx3 IgE immunoassays and Ascaris IgE radioallergosorbent [RAST] tests) were used for active helminthiasis and allergy screens respectively. Data were analysed using logistic regression analysis, and models were adjusted for age, gender and locality. High Ascaris IgE was significantly associated with asthma (adjusted odds ratio [aOR] = 2.20, p = .047), IgE atopy (aOR = 18.18, p < .0001) and food allergy (aOR = 14.47, p < .0001). Asthma was significantly less likely among participants with Ascaris eggs (aOR = 0.43, p = .048) and Trichuris eggs (aOR = 0.36, p = .024). The findings of co‐occurrent helminthiasis and allergic disorders in a population that has resided both in rural and peri‐urban informal settlements both oppose and agree with two main notions of the hygiene hypothesis that (i) individuals residing in rural settings with poor sanitation and geohelminth infection are less prone to allergy, and (ii) helminth infections protect against allergy respectively. Further research is warranted.

Helminth infections and allergic diseases: systematic review and meta-analysis of the global literature

INTRODUCTION

There is considerable research interest in the role of helminth infections in the development of allergic diseases. However, findings from previous studies are mixed. Existing systematic reviews of these studies are outdated. We performed a systematic review of the global literature on the association between helminth infections and development and clinical outcomes of allergic diseases.

METHODS

We searched Cochrane Library, MEDLINE, EMBASE, ISI Web of Science, PubMed, Global Index Medicus, Scielo, KoreaMed, Google Scholar, and Lilacs for studies published up to January 2020. We included observational epidemiological studies (cohort, case-control and cross-sectional studies) of children and adults reporting associations between helminth infections and asthma, allergic rhinitis, eczema and atopy. We performed random-effects meta-analysis to summarize the effect estimates.

RESULTS

We included 80 studies with 99,967 participants. In the meta-analyses, we did not observe an overall association between helminth infections and allergic diseases. There was, however, evidence that A. lumbricoides infections was associated with an increased risk of bronchial hyperreactivity in children (RR:1.41, 95%CI: 1.17-1.70; I²=50, p for I²=0.09), and was associated with an increased risk of atopy among helminth-infected adults (RR:1.37, 95%CI: 1.18-1.61; I²=52, p for I²=0.02). We found no study that addressed the association between helminth infection and clinical outcomes of allergic diseases. The overall strength of the underlying evidence was low to moderate.

CONCLUSION

Helminth infections may increase the risk of bronchial hyperreactivity in children and atopy in adults. Well-designed longitudinal cohorts may help clarify potential causal associations between chronic helminth infections and allergic diseases.

Schistosoma mansoni infection is associated with decreased risk of respiratory allergy symptoms and low production of CCL2

OBJECTIVES

We measured the production of cytokines, chemokines and antibodies involved in allergic responses and sCD23 levels during Schistosoma mansoni infection.

METHODS

Individuals (n = 164) were selected using the ISAAC questionnaire and parasitological exams. The subjects were divided as follows: those infected individuals with allergy-related symptoms (A-I), those with allergy-related symptoms only (A-NI); those only infected (NA-I); and those non-infected individuals without allergy-related symptoms (NA-NI). We used supernatants from cell culture (mitogenic stimulation) to measure cytokine and chemokine levels using cytometric bead arrays. Serum levels of anti-Ascaris lumbricoides (Asc) and anti-Blomia tropicalis IgE were measured using ImmunoCAP, and sCD23 was measured using ELISA.

RESULTS

Schistosoma mansoni infection was associated with a lower risk of allergy-related symptoms. In A-I, there were higher levels of TNF-α, IL-10, IL-6, IFN-γ and CXCL8 than in NA-NI group, with TNF-α and IL-6 also at higher levels compared to A-NI group. Levels of IL-6, CXCL8, total and anti-Asc IgE, as well as the numbers of eosinophils, were higher in NA-I than in NA-NI, and the antibodies were also lower in A-NI than in NA-I group. In AI and NA-I, there was less production of CCL2 than in NA-NI. There were no differences in the levels of IL-2, IL-4, IL-17, CCL5, sCD23 and anti-Blomia IgE.

CONCLUSIONS

Patients with allergy-related symptoms and infected (simultaneously) had higher levels of IL-10; due to the infection, there was increased production of IL-6 and CXCL8 and less CCL2. These data may characterize deviation to Th1 or attenuation of the Th2 response in allergy sufferers in areas endemic for schistosomiasis.

What Can Parasites Tell Us About the Pathogenesis and Treatment of Asthma and Allergic Diseases

The same mechanisms that enable host defense against helminths also drive allergic inflammation. This suggests that pathomechanisms of allergic diseases represent evolutionary old responses against helminth parasites and that studying antihelminth immunity may provide insights into pathomechanisms of asthma. However, helminths have developed an intricate array of immunoregulatory mechanisms to modulate type 2 immune mechanisms. This has led to the hypothesis that the lack of helminth infection may contribute to the rise in allergic sensitization in modern societies. Indeed, the anti-inflammatory potential of helminth (worm) parasites and their products in allergy and asthma has been recognized for decades. As helminth infections bring about multiple undesired effects including an increased susceptibility to other infections, intended helminth infection is not a feasible approach to broadly prevent or treat allergic asthma. Thus, the development of new helminth-based biopharmaceutics may represent a safer approach of harnessing type 2–suppressive effects of helminths. However, progress regarding the mechanisms and molecules that are employed by helminths to modulate allergic inflammation has been relatively recent. The scavenging of alarmins and the modulation of lipid mediator pathways and macrophage function by helminth proteins have been identified as important immunoregulatory mechanisms targeting innate immunity in asthma and allergy. In addition, by regulating the activation of dendritic cells and by promoting regulatory T-cell responses, helminth proteins can counterregulate the adaptive T helper 2 cell response that drives allergic inflammation. Despite these insights, important open questions remain to be addressed before helminth molecules can be used for the prevention and treatment of asthma and other allergic diseases.

Is Ascaris lumbricoides a risk factor for development of asthma? A systematic review and meta-analysis

There are numerous epidemiological and experimental evidences to suggest that Ascaris lumbricoides infection is a neglected risk factor for development of asthma. For this purpose, we conducted a systematic review and meta-analysis for better understanding of this relationship. Systematic searching (PubMed, Scopus, Web of Science and Google Scholar) was done, up to September 30, 2019 to identify the relevant studies. We applied random-effects meta-analysis model to generate the overall odds ratio (OR) and 95% confidence intervals (CIs). Heterogeneity was assessed with I2 and τ2 statistic. Finally, 19 studies (totally 25 datasets), including 14 datasets with microscopic methods (1830 asthmatic patients (APs) and 3802 healthy controls (HCs)) and 11 datasets with serological methods (1543 APs and 3507 HCs) met the eligibility criteria. Considering to the serological methods, our results demonstrated that the APs had higher seroprevalence rate of A. lumbricoides (48.3% vs. 35.1%) than HCs, showing a significant association (pooled crude OR, 1.53; 95%CI, 1.07-2.18). Moreover, microscopic methods showed a higher prevalence of A. lumbricoides infection in the APs compared to the HCs (37.2% vs. 30.2%), but no significant association was found between APs and HCs (pooled crude OR, 1.19; 95%CI, 0.92-1.55). After adjustment for confounders, results showed no significant association for both serological (pooled adjusted OR, 1.43; 95%CI, 0.93-2.19) and microscopic (pooled adjusted OR, 1.05; 95%CI, 0.78-1.42) methods. Despite heterogeneous results, accurate and better quality studies are needed to determine the effect of A. lumbricoides infection on induction or exacerbation of asthma.

Exposure to Ascaris lumbricoides infection and risk of childhood asthma in north of Iran

BACKGROUND

Asthma and Ascaris lumbricoides infection are common health issues affecting 250 and 700 million people worldwide, respectively. The relationship between ascariasis and asthma is a matter of substantial interest and research.

METHODS

We performed a case-control study to evaluate whether the exposure to Ascaris infection is associated with asthma in children. We also assessed potential risk factors for Ascaris infection and asthma in study area. We enrolled 145 asthmatic children and 115 healthy controls. The Global Initiative for Asthma guideline was used to evaluate asthma symptoms and severity in study participants. Ascaris infection was assessed by the presence of anti-Ascaris IgG ≥ 11 IU/mL measured by enzyme-linked immunosorbent assay.

RESULTS

We have found a significant relationship between exposure to Ascaris and asthma (odds ratio, 2.92; 95% CI 1.04-8.18; P value = 0.034), and this relationship remained significant after adjustment for covariates (adjusted OR, 3.36; 95% CI 1.04-13%; P value = 0.047). Ascaris infection was more frequent in children with mild sustainable asthma (13.2%; 15/113) than in children with moderate sustainable asthma (6.2%, 2/32), although there was a non-significant difference between these groups (OR, 2.3; 95% CI 0.5-10.1; P value = 0.35). Based on results of a multi-regression analysis, contact with soil (OR, 6.7; 95% CI 1.9-23.5), and drinking unsafe water (OR, 4.2; 95% CI 1.2-14.2) were significant risk factors for Ascaris infection in the study area.

CONCLUSION

Results of this study suggest that A. lumbricoides infection might affect susceptibility to asthma in children. These results could be useful in prevention, early diagnosis and management of childhood asthma.

Asthma and atopy prevalence are not reduced among former tuberculosis patients compared with controls in Lima, Peru

Background

Although there are theoretical reasons for believing that asthma and atopy may be negatively correlated with tuberculosis, epidemiological studies have had conflicting findings.

Objective

To determine if people with confirmed tuberculosis were less likely to be atopic and less likely to have atopic disease including asthma compared to those with no previous tuberculosis.

Methods

Patients in Lima, Peru with a prior history of tuberculosis were identified from clinic records in this cohort study. A representative sample of individuals without a prior tuberculosis diagnosis was recruited from the same community. Allergen skin prick testing was performed to classify atopic status. Allergic rhinitis was identified by history. Asthma was defined by symptoms and spirometry. Eosinophilic airway inflammation was measured using exhaled nitric oxide levels.

Results

We evaluated 177 patients with, and 161 individuals without, previous tuberculosis. There was a lower prevalence of atopy among people with prior tuberculosis on univariate analysis (odds ratio 0.57; 95% confidence interval 0.37–0.88) but, after adjustment for potential confounders, this was no longer statistically significant (aOR 0.64, 95% CI 0.41–1.01). The prevalence of allergic rhinitis (aOR 0.76, 95% CI 0.47 to 1.24 and asthma (aOR 1.18, 95% CI 0.69 to 2.00) did not differ significantly between the two groups. We also found no significant difference in the prevalence of elevated exhaled nitric oxide (aOR 1.30, 95% CI 0.78 to 2.17) or a combined index of atopic disease (aOR 0.86, 95% CI 0.54 to 1.36).

Conclusion

In this urban environment in a middle-income country, prior tuberculosis may be associated with a reduced risk of atopy but does not protect against asthma and atopic disease.

The hygiene hypothesis at a glance: Early exposures, immune mechanism and novel therapies

The hygiene hypothesis was proposed almost three decades ago. Nevertheless, its mechanism still remains with relevant controversies. Some studies defend that early exposures during childhood to microbes and parasites are key determinants to prevent allergies and autoimmune diseases; however, other studies demonstrated that these early exposures can even potentiate the clinical scenario of the diseases. Based on several studies covering the influences of microbiome, parasites, related theories and others, this review focuses on recent advances in the hygiene hypothesis field. In addition, the main immunological mechanisms underlying the hygiene hypothesis are also discussed. We also strongly encourage that researchers do not consider the hygiene hypothesis as a theory based strictly on hygiene habits, but a theory combining diverse influences, as illustrated in this review as the hygiene hypothesis net.

Role in Allergic Diseases of Immunological Cross-Reactivity between Allergens and Homologues of Parasite Proteins

Implied under the rubric of the hygiene hypothesis is that helminth infection can protect against allergic disease. It is well known that helminths induce processes associated with type 2 immune responses, but they also induce important regulatory responses that can modulate these type 2-associated responses-modulation that influences responses to bystander antigens including allergens. Indeed, most epidemiological studies demonstrate a beneficial effect of helminth infection on atopy, but there are also convincing data to demonstrate that helminth infection can precipitate or worsen allergic inflammation/disease. Reasons for these disparate findings are much debated, but there is a school of thought that suggests that helminth-triggered type 2-associated responses, including IgE to cross-reactive aeroallergens, can offset the regulatory effects imposed by the same organisms. The cross-reactivity among helminths and allergenic tropomyosins dominated the antigen/allergen cross-reactivity field, but recent data suggest that cross-reactivity is much more common than previously appreciated. It has been demonstrated that a high degree of molecular similarity exists between allergens and helminth proteins. Thus, an understanding of the mechanisms underlying the response induced by helminth infection and their impact on the induction of allergic disease in the host are critical for designing therapies using iatrogenic infections or parasite products to treat inflammatory diseases and for developing vaccines against helminth parasites.

Human Helminths and Allergic Disease: The Hygiene Hypothesis and Beyond

There is much debate about the interaction between helminths and allergic disease. The "Hygiene Hypothesis," a very popular concept among scientists and the lay public, states that infections, especially during childhood, can protect against allergic diseases. Indeed, helminth infections are known to induce regulatory responses in the host that can help the control of inflammation (including allergic inflammation). However, these infections also induce type-2-associated immune responses including helminth-specific IgE that can cross-react against environmental allergens and mediate IgE-driven effector responses. Thus, it is the delicate balance between the parasites' anti- and pro-allergenic effects that define the helminth/allergy interface.

Modulation of the immune response by infection with Cryptosporidium spp. in children with allergic diseases

It has been demonstrated that the allergic response can be ameliorated by the administration of pathogen derivatives that activate Toll-like receptors and induce a Th1-type immune response (IR). Cryptosporidium is a parasite that promotes an IR via Toll-like receptors and elicits the production of Th1-type cytokines, which limit cryptosporidiosis. The aim of this study was to investigate allergy-related immune markers in children naturally infected with Cryptosporidium. In a cross-sectional study, 49 children with or without clinical diagnosis of allergies, oocysts of Cryptosporidium spp. in the faeces were screened microscopically. We microscopically screened for leucocytes, examined T and B cells for allergy-related activation markers using flow cytometry and evaluated serum for total IgE using chemiluminescence. Children with allergies and Cryptosporidium in the faeces had significantly lower levels of total IgE, B cells, CD19(+) CD23(+) and CD19(+) CD124(+) cells as well as a greater percentage of interferon-gamma (IFN-γ(+) ) and IL-4(+) CD4(+) cells than children with allergies without Cryptosporidium. This is the first description of the modulation of the IR in children with allergic diseases in the setting of natural Cryptosporidium infection. Our findings suggest the involvement of CD4(+) cells producing IL-4 and IFN-γ in the IR to Cryptosporidium in naturally infected children.

Anti-Ascaris immunoglobulin E associated with bronchial hyper-reactivity in 9-year-old rural Bangladeshi children

BACKGROUND

Studies have addressed the immunomodulatory effects of helminths and their protective effects upon asthma. However, anti-Ascaris IgE has been reported to be associated with an increased risk of asthma symptoms. We examined the association between serum levels of anti-Ascaris IgE and bronchial hyper-responsiveness (BHR) in children living in rural Bangladesh.

METHODS

Serum anti-Ascaris IgE level was measured and the BHR test done in 158 children aged 9 years selected randomly from a general population of 1705 in the Matlab Health and Demographic Surveillance Area of the International Centre for Diarrhoeal Disease Research, Bangladesh. We investigated wheezing symptoms using a questionnaire from the International Study of Asthma and Allergies in Childhood. BHR tests were successfully done on 152 children (108 'current wheezers'; 44 'never-wheezers'). We examined the association between anti-Ascaris IgE level and wheezing and BHR using multiple logistic regression analyses.

RESULTS

Of 108 current-wheezers, 59 were BHR-positive; of 44 never-wheezers, 32 were BHR-negative. Mean anti-Ascaris IgE levels were significantly higher (12.51 UA/ml; 95% confidence interval (CI), 9.21-17.00) in children with current wheezing with BHR-positive than in those of never-wheezers with BHR-negative (3.89; 2.65-5.70; t test, p < 0.001). A BHR-positive test was independently associated with anti-Ascaris IgE levels with an odds ratio (OR) = 7.30 [95% CI, 2.28-23.33], p = 0.001 when adjusted for total IgE, anti-Dermatophagoides pteronyssinus IgE, pneumonia history, parental asthma, Trichuris infection, forced expiratory volume in one second, eosinophilic leukocyte count, and sex.

CONCLUSIONS

Anti-Ascaris IgE level is associated with an increased risk of BHR among 9-year-old rural Bangladeshi children.

The Role of Helminth Infection and Environment in the Development of Allergy: A Prospective Study of Newly-Arrived Ethiopian Immigrants in Israel

Helminth infection may be protective against allergy and account for the low prevalence of allergy in developing countries. We studied prospectively the prevalence of allergy in Ethiopian immigrants with heavy helminth infection on arrival in Israel, and again after a year of adjustment to an urban industrialized setting, to explore the roles of helminth infection, changed environment and background immunity on the manifestations of allergy. 126 newly arrived Ethiopian immigrants were studied at baseline and 115 after a year of follow up in Israel. Allergic symptoms, Skin prick tests (SPT), Tuberculin (PPD) skin tests, stool and blood samples were obtained for determining parasites, blood IgE and eosinophil levels, respectively. Anti-helminthic therapy was offered to the entire infected individuals, but only 50/108 (46.3%) took the medication. At baseline, there was a significant negative association between helminth infection and allergy, 4/18 (22.2%) of uninfected participants were allergic compared to 7/108 (6.5%) of helminth-infected participants (p = 0.028), as well as between helminth infection and SPT reactivity, 12/18 (66.6%) of uninfected participants compared to 43/108 (39.8%) of helminth-infected participants (p = 0.033). After one year, a significant general increase in allergy and SPT was observed. While only 11/126 (8.7%) were allergic at baseline, 30/115 (26.1%) became allergic at follow-up (p<0.0001), and while 55/126 (43.7%) were SPT+ at baseline, 79/115 (68.7%) became SPT+ at follow-up (p<0.001). A twofold increase in allergen sensitization was also observed after one year in Israel, particularly for dust mites, grasses and olive tree (p<0.001). These results show that: a) Helminth infection is significantly associated with low allergy and low SPT reactivity; b) One year after immigration to Israel, allergy and SPT reactivity increased significantly in all immigrants; c) Higher increases in positive SPT and allergy were observed after a year in the group that remained infected with helminths, even though they had a lowered helminth load; d) The reasons for the increased allergy one year after immigration needs further investigation but probably reflects the combined influence of the decreased helminth load and novel environmental factors.

The role of intestinal parasitic infections in allergy is of great interest since it has been suggested that they suppress the development of allergy. Urbanization has also been claimed to cause allergy because of air pollution and higher exposure to allergens. The present study took advantage of the special opportunity presented by the recent Ethiopian immigration to Israel in order to study this question. A cohort of newly arrived Ethiopian immigrants to Israel, highly infected with parasites, was studied prospectively for the presence of allergy and response to allergens on arrival and after a year of follow up in Israel. The results showed clearly a significant inverse association between the presence of parasitic infections and allergy on arrival, while after a year of living in Israel, accompanied by a lowered parasitic infection load, a general increase of allergy was observed in all immigrant groups, and not only in those that had parasitic infections on arrival. These results lend support to the suppressive effect of intestinal parasites on allergy, but suggest that additional factors, most probably environmental, also play a role in the generation of allergy.

The IgE response to Ascaris molecular components is associated with clinical indicators of asthma severity

Background

Asthma is a common chronic disease worldwide and Ascaris lumbricoides infection (ascariasis) is frequent in tropical regions. However, the effect of ascariasis on asthma severity has not been sufficiently explored. We sought to evaluate the influence of the IgE immune response to Ascaris extract and purified house dust mites (HDM) and Ascaris allergens on indicators of asthma severity in patients living in the tropics.

Methods

Asthmatic patients from Cartagena, Colombia were recruited. Clinical assessment included questionnaires, physical examination, allergy skin tests, spirometry, parasite stool examination and IgE antibody measurements. Asthma was diagnosed by a physician according to validated criteria. Indicators of severity were occurrence of severe dyspnea episodes, night awakenings events, > 4 emergency room (ER) visits and hospitalizations during the last year. Specific IgE to Der p 2, Ascaris spp., Blomia tropicalis and Dermatophagoides pteronyssinus extracts was determined by ImmunoCap. IgE to tropomyosins (Asc l 3, Blo t 10 and Der p 10), Blo t 5 and Asc s 1 was detected by ELISA. Logistic regression analyses were used to explore the relationships between sensitization and indicators of asthma severity.

Results

After adjustment for HDM sensitization, Ascaris sensitization remained associated with severe dyspnea (aOR: 1.90, 95% CI: 1.08 - 3.34, p = 0.03) and > 4 ER visits (aOR: 2.23, 95% CI: 1.15 - 4.30, p = 0.02). We also found that sensitization to the species specific markers Blo t 5 and Asc s 1, as well as the cross-reactive tropomyosins of D. pteronyssinus and Ascaris were associated with > 4 ER visits. Der p 2 sensitization was associated with bronchodilator responsiveness (aOR: 2.24: 1.25-4.02, p = 0.01). Remarkably, significantly higher IgE levels to HDM species specific allergens were found in Ascaris sensitized patients.

Conclusions

In this tropical population, IgE sensitization to Ascaris and the cross-reactive tropomyosins was frequent and associated with clinical indicators of asthma severity. The significant relationship between sensitization to the nematode-specific marker Asc s 1 and ER attendance supports these findings. Moreover, ascariasis increases the human IgE responses to HDM specific allergens.

Schistosome infection is negatively associated with mite atopy, but not wheeze and asthma in Ghanaian schoolchildren

BACKGROUND

Epidemiological evidence suggests that helminth infection and rural living are inversely associated with allergic disorders.

OBJECTIVE

The aim of the study was to investigate the effect of helminth infections and urban versus rural residence on allergy in schoolchildren from Ghana.

METHODS

In a cross-sectional study of 1385 children from urban-high socio-economic status (SES), urban-low SES and rural schools, associations between body mass index (BMI), allergen-specific IgE (sIgE), parasitic infections and allergy outcomes were analysed. Allergy outcomes were skin prick test (SPT) reactivity, reported current wheeze and asthma.

RESULTS

Helminth infections were found predominantly among rural subjects, and the most common were hookworm (9.9%) and Schistosoma spp (9.5%). Being overweight was highest among urban-high SES (14.6%) compared to urban-low SES (5.5%) and rural children (8.6%). The prevalence of SPT reactivity to any allergen was 18.3%, and this was highest among rural children (21.4%) followed by urban-high SES (20.2%) and urban-low SES (10.5%) children. Overall, SPT reactivity to mite (12%) was most common. Wheeze and asthma were reported by 7.9% and 8.3%, respectively. In multivariate analyses, factors associated with mite SPT were BMI (aOR 2.43, 95% CI 1.28-4.60, P = 0.007), schistosome infection (aOR 0.15, 95% CI 0.05-0.41) and mite sIgE (aOR 7.40, 95% CI 5.62-9.73, P < 0.001) but not area. However, the association between mite IgE and SPT differed by area and was strongest among urban-high SES children (aOR = 15.58, 95% CI 7.05-34.43, P < 0.001). Compared to rural, urban-low SES area was negatively associated with current wheeze (aOR 0.41, 95% CI 0.20-0.83, P = 0.013). Both mite sIgE and mite SPT were significantly associated with current wheeze and asthma.

CONCLUSION AND CLINICAL RELEVANCE

Infection with schistosomes appeared to protect against mite SPT reactivity. This needs to be confirmed in future studies, preferably in a longitudinal design where schistosome infections are treated and allergic reactions reassessed.

Ascaris lumbricoids Infection as a Risk Factor for Asthma and Atopy in Rural Bangladeshi Children

Controversy persists as to whether helminth infections cause or protect against asthma and atopy. The aim of this study was to investigate the effects of helminth infection on asthma and atopy among Bangladeshi children. A total of 912 children aged 4.5 years (mean = 54.4, range = 53.5–60.8 months) participated in a cross-sectional study nested into a randomized controlled trial in Bangladesh. Ever-asthma, ever-wheezing and current wheezing were identified using the International Study of Asthma and Allergies in Childhood questionnaire. Current helminth infection was defined by the presence of helminth eggs in stools, measured by routine microscopic examination. Repeated Ascaris infection was defined by the presence of anti-Ascaris IgE ≥ 0.70 UA/ml in serum measured by the CAP-FEIA method. Atopy was defined by specific IgE to house dust mite (anti-DP IgE) ≥ 0.70 UA/ml measured by the CAP-FEIA method and/or positive skin prick test (≥ 5 mm). Anti-Ascaris IgE was significantly associated with ever asthma (odds ratio (OR) = 1.86, 95% CI: 1.14–3.04, highest vs. lowest quartile; P for trend 0.016). Anti-Ascaris IgE was also significantly associated with positive anti-DP IgE (OR = 9.89, 95% CI: 6.52–15.00, highest vs. lowest; P for trend < 0.001) and positive skin prick test (OR = 1.69, 95% CI: 1.01–2.81, highest vs. lowest, P for trend 0.076). These findings suggest that repeated Ascaris infection is a risk factor for asthma and atopy in rural Bangladeshi children. Further analysis is required to examine the mechanism of developing asthma and atopy in relation to helminth infection.

Global numbers of infection and disease burden of soil transmitted helminth infections in 2010

BACKGROUND

Quantifying the burden of parasitic diseases in relation to other diseases and injuries requires reliable estimates of prevalence for each disease and an analytic framework within which to estimate attributable morbidity and mortality. Here we use data included in the Global Atlas of Helminth Infection to derive new global estimates of numbers infected with intestinal nematodes (soil-transmitted helminths, STH: Ascaris lumbricoides, Trichuris trichiura and the hookworms) and use disability-adjusted life years (DALYs) to estimate disease burden.

METHODS

Prevalence data for 6,091 locations in 118 countries were sourced and used to estimate age-stratified mean prevalence for sub-national administrative units via a combination of model-based geostatistics (for sub-Saharan Africa) and empirical approaches (for all other regions). Geographical variation in infection prevalence within these units was approximated using modelled logit-normal distributions, and numbers of individuals with infection intensities above given thresholds estimated for each species using negative binomial distributions and age-specific worm/egg burden thresholds. Finally, age-stratified prevalence estimates for each level of infection intensity were incorporated into the Global Burden of Disease Study 2010 analytic framework to estimate the global burden of morbidity and mortality associated with each STH infection.

RESULTS

Globally, an estimated 438.9 million people (95% Credible Interval (CI), 406.3 - 480.2 million) were infected with hookworm in 2010, 819.0 million (95% CI, 771.7 - 891.6 million) with A. lumbricoides and 464.6 million (95% CI, 429.6 - 508.0 million) with T. trichiura. Of the 4.98 million years lived with disability (YLDs) attributable to STH, 65% were attributable to hookworm, 22% to A. lumbricoides and the remaining 13% to T. trichiura. The vast majority of STH infections (67%) and YLDs (68%) occurred in Asia. When considering YLDs relative to total populations at risk however, the burden distribution varied more considerably within major global regions than between them.

CONCLUSION

Improvements in the cartography of helminth infection, combined with mathematical modelling approaches, have resulted in the most comprehensive contemporary estimates for the public health burden of STH. These numbers form an important benchmark upon which to evaluate future scale-up of major control efforts.

Effects of geohelminth infection and age on the associations between allergen-specific IgE, skin test reactivity and wheeze: a case-control study

Background

Most childhood asthma in poor populations in Latin America is not associated with aeroallergen sensitization, an observation that could be explained by the attenuation of atopy by chronic helminth infections or effects of age.

Objective

To explore the effects of geohelminth infections and age on atopy, wheeze, and the association between atopy and wheeze.

Methods

A case-control study was done in 376 subjects (149 cases and 227 controls) aged 7–19 years living in rural communities in Ecuador. Wheeze cases, identified from a large cross-sectional survey, had recent wheeze and controls were a random sample of those without wheeze. Atopy was measured by the presence of allergen-specific IgE (asIgE) and skin prick test (SPT) responses to house dust mite and cockroach. Geohelminth infections were measured in stools and anti-Ascaris IgE in plasma.

Results

The fraction of recent wheeze attributable to anti-Ascaris IgE was 45.9%, while those for SPT and asIgE were 10.0% and 10.5% respectively. The association between atopy and wheeze was greater in adolescents than children. Although Anti-Ascaris IgE was strongly associated with wheeze (adj. OR 2.24 (95% CI 1.33–3.78, P = 0.003) and with asIgE (adj. OR 5.34, 95% CI 2.49–11.45, P < 0.001), the association with wheeze was independent of asIgE. There was some evidence that the association between atopy and wheeze was greater in uninfected subjects compared with those with active geohelminth infections.

Conclusions and clinical relevance

Atopy to house dust mite and cockroach explained few wheeze cases in our study population, while the presence of anti-Ascaris IgE was an important risk factor. Our data provided only limited evidence that active geohelminth infections attenuated the association between atopy and wheeze in endemic areas or that age modified this association. The role of allergic sensitization to Ascaris in the development of wheeze, independent of atopy, requires further investigation.

Parasitic infection may be associated with discordant responses to QuantiFERON and tuberculin skin test in apparently healthy children and adolescents in a tuberculosis endemic setting, Ethiopia

Background

M. tuberculosis remains one of the world’s deadliest pathogens in part because of its ability to establish persistent, latent infections, which can later reactivate to cause disease. In regions of the globe where disease is endemic, as much as 50% of the population is thought to be latently infected, complicating diagnosis and tuberculosis control. The tools most commonly used for diagnosis of latent M. tuberculosis infection are the tuberculin skin test and the newer interferon-gamma release assays, both of which rely on an antigen-specific memory response as an indicator of infection. It is clear that the two tests, do not always give concordant results, but the factors leading to this are only partially understood.

Methods

In this study we examined 245 healthy school children aged from 12 to 20 years from Addis Ababa, a tuberculosis-endemic region, characterised them with regard to response in the tuberculin skin test and QuantIFERON™ test and assessed factors that might contribute to discordant responses.

Results

Although concordance between the tests was generally fair (90% concordance), there was a subset of children who had a positive QuantIFERON™ result but a negative tuberculin skin test. After analysis of multiple parameters the data suggest that discordance was most strongly associated with the presence of parasites in the stool.

Conclusions

Parasitic gut infections are frequent in most regions where M. tuberculosis is endemic. This study, while preliminary, suggests that the tuberculin skin test should be interpreted with caution where this may be the case.

New Allergens of Relevance in Tropical Regions: The Impact of Ascaris lumbricoides Infections

One of the many aspects of the relationships between parasite infections and allergic diseases is the possibility that allergens from parasites enhance the T_H2 responses, especially IgE production, in allergic diseases such as asthma. In this review we discuss about the allergenic composition of the nematode Ascaris lumbricoides and their potential impact on allergy sensitization and asthma pathogenesis and prevalence in populations living in the tropics and naturally exposed to both, mite allergens and helminth infections.

Specific IgE Anti-Ascaris in Brazilian Children and Adolescents

From an article published by our group by Medeiros et al, we discuss and review the literature on the role of serum specific anti-ascaris IgE in patients with respiratory allergies living in countries where helminthic infestations are common. Medeiros et al conducted a study using 101 patients aged 12 to 21 years with respiratory allergy. Median IgE level was 660 IU/mL. Serum specific anti-ascaris IgE was positive in 73% (74/101) of the individuals, but parasitological stool examination yielded positive results in only 33.7% (34/101). The correlation coefficient between serum total IgE level and serum specific anti-ascaris IgE was 0.52 (P < 0.001) and this effect occurred regardless of eosinophil count and of the presence of intestinal helminthic infection. In patients with respiratory allergy with very high serum total IgE levels, in whom the past or present history of parasitic infection is a possible explanation, the presence of serum specific anti-ascaris IgE was common and should be better evaluated in allergic patients from Ascaris lumbricoides endemic areas.

Socio-epidemiological Aspects of Respiratory Allergic Diseases in Southern Africa

The prevalence of respiratory allergic diseases has been increasing in Southern Africa both in urban and in rural environments. Various factors may contribute toward this situation, namely, exposure to aeroallergens, such as grass pollens and house dust mites. However, other irritant environmental triggers, such as exposure to tobacco smoke and certain indoor and outdoor fumes, may also play a relevant part. Furthermore, certain parasitic and mycobacterial infections may act as allergic disease risk modifiers, although such an influence should be confirmed. Finally, certain cultural and socioeconomic factors may also influence accessibility to healthcare and adherence to treatment of these diseases.

IgE cross-reactivity between Ascaris lumbricoides and mite allergens: possible influences on allergic sensitization and asthma

Nematode infections such as Ascariasis are important health problems in underdeveloped countries, most of them located in the tropics where environmental conditions also promote the perennial co-exposure to high concentrations of domestic mite allergens. Allergic diseases are common, and most of patients with asthma exhibit a predominant and strong IgE sensitization to mites. It is unknown whether co-exposure to Ascaris lumbricoides and the domestic mites Blomia tropicalis and Dermatophagoides pteronyssinus potentiates Th2 responses and IgE sensitization, thereby modifying the natural history of allergy. Recently, we obtained experimental evidence of a high cross-reactivity between the allergenic extracts of these invertebrates, involving well-known allergens such as tropomyosin and glutathione transferases. There is indirect evidence suggesting that the clinical impact of these findings may be important. In this review, we discuss the potential role of this cross-reactivity on several aspects of allergy in the tropics that have been a focus of a number of investigations, some of them with controversial results.

Atopy and current intestinal parasite infection: a systematic review and meta-analysis

BACKGROUND

The rate of increase in prevalence of allergic disease in some countries implies environmental exposures may be important etiological factors. Our aim was to undertake a systematic review and meta-analysis of epidemiological studies to quantify the association between current intestinal parasite infection and the presence of atopy and to determine whether this relation is species specific.

METHODS

We searched MEDLINE, EMBASE, LILIACS and CAB Abstracts (to March 2009); reviews; and reference lists from publications. No language restrictions were applied. We included studies that measured current parasite infection using direct fecal microscopy and defined atopy as allergen skin sensitization or presence of specific IgE. We estimated pooled odds ratios (OR) and 95% confidence intervals (95% CI) using data extracted from published papers using random-effects model.

RESULTS

Twenty-one studies met our inclusion criteria. Current parasite infection was associated with a reduced risk of allergen skin sensitization OR 0.69 (95% CI 0.60-0.79; P < 0.01). When we restricted our analyses to current geohelminth infection, the size of effect remained similar OR 0.68 (95% CI 0.60-0.76; P < 0.01). In species-specific analysis, a consistent protective effect was found for infection with Ascaris lumbricoides, Tricuris trichuria, hookworm and Schistosomiasis. There were insufficient data to pool results for atopy defined by the presence of specific IgE.

CONCLUSION

Intestinal parasite infection appears to protect against allergic sensitization. Work should continue to identify the mechanisms of this effect and means of harnessing these to reduce the global burden of allergic disease.

The presence of serum anti-Ascaris lumbricoides IgE antibodies and of Trichuris trichiura infection are risk factors for wheezing and/or atopy in preschool-aged Brazilian children

BACKGROUND

The elucidation of factors that trigger the development of transient wheezing in early childhood may be an important step toward understanding the pathogenesis of asthma and other allergic diseases later in life. Transient wheezing has been mainly attributed to viral infections, although sensitisation to aeroallergens and food allergens may occur at an early age. In developing countries, intestinal helminthic infections have also been associated with allergy or atopy-related disorders.

OBJECTIVE

The aim of this study was to explore the association of Trichuris trichiura and Ascaris lumbricoides infections with wheezing and atopy in early childhood.

STUDY DESIGN

A cross-sectional study using a Portuguese-language ISAAC phase I questionnaire, adapted for preschool-aged children, nested in a cohort study of childhood diarrhoea, was conducted on 682 children. Two faecal samples per child were examined for the presence of intestinal helminthic infection. IgE antibodies against three allergenic preparations (Dermatophagoides pteronyssinus, Blomia tropicalis and common child food), as well as against A. lumbricoides antigens, were measured in a sub-sample of these children, whose parents allowed the procedure. Atopy was defined by the presence of levels of serum IgE antibodies ≥0.35 kU/L against at least one of the three tested allergenic preparations.

RESULTS

Active T. trichiura infection but not A. lumbricoides infection was positively associated with wheezing in the total studied children population [adjusted OR = 2.60; CI = 1.54;4.38] and in the atopic children sub-population [adjusted OR = 3.07; CI = 1.00;9.43]. The association with atopy was also positive and statistically significant only in the brute analysis [OR = 2.13; CI = 1.03;4.40]. Anti-A. lumbricoides IgE antibodies, but not current A. lumbricoides infection, were positively associated with wheezing in atopic children [adjusted OR = 2.01; CI = 1.00;4.50] and in non-atopic children [adjusted OR = 3.07; CI = 1.13;8.35] and it was also associated with atopy [adjusted OR = 7.29; CI = 3.90; 13.4]. On the other hands, reports of wheezing were not significantly associated with atopy.

CONCLUSIONS

These data corroborate previous studies showing that wheezing is predominantly associated with infection in early childhood and shows that anti-A. lumbricoides IgE antibodies, but not active Ascaris infections, are associated with wheezing and atopy. Additionally, the data demonstrate that T. trichiura infection may play a role in the pathogenesis of atopic wheezing in early childhood.

Chronic helminth infections protect against allergic diseases by active regulatory processes

Developed countries are suffering from an epidemic rise in immunologic disorders, such as allergy-related diseases and certain autoimmunities. Several studies have demonstrated a negative association between helminth infections and inflammatory diseases (eg, allergy), providing a strong case for the involvement of helminth infections in this respect. However, some studies point in the opposite direction. The discrepancy may be explained by differences in frequency, dose, time, and type of helminth. In this review, new studies are discussed that may support the concept that chronic helminth infections in particular—but not acute infections—are associated with the expression of regulatory networks necessary for downmodulating allergic immune responses to harmless antigens. Furthermore, different components of regulatory networks are highlighted, such as the role of regulatory T and B cells, modulation of dendritic cells, early innate signals from structural cells (eg, epithelial cells), and their individual contributions to protection against allergic diseases. It is of great interest to define and characterize specific helminth molecules that have profound immunomodulatory capacities as targets for therapeutic application in the treatment or prophylaxis of allergic manifestations.

Allergic disorders in Africa and africans: is it primarily a priority?

In Africa, the burden of some diseases has been a problem for centuries. The spectrum of African diseases includes allergies, infections, nutritional deficiencies, and natural disasters. Efforts made by scientists to search for possible means of disease control have been outstanding; however, in some infections, solutions are still out of reach. In disease control programs, it might be worthwhile to pay attention to the most striking diseases than merely follow a holistic approach. This short review tackles the problems of allergy and allergens in Africa as compared with other disease burdens that may suggest the need for a more balanced approach based on priority.

Interactions between helminth parasites and allergy

PURPOSE OF REVIEW

To review the findings of recent human studies of the association between helminth parasite infections and allergy and discuss their potential relevance to public health.

RECENT FINDINGS

Different helminth parasites may have different effects on allergy that may depend on the timing or intensity of the exposure or host genetic factors. Infections with Trichuris trichiura in early life are associated with a reduced prevalence of allergen skin test reactivity later in life and infants of helminth-infected mothers have been reported to have a reduced prevalence of eczema. Hookworm infection has been associated with a reduced prevalence of asthma in Ethiopia. Several studies have reported that anti-Ascaris IgE is an important risk factor for asthma, but this could be explained by an enhanced ability of atopics to produce IgE. Toxocara infections may be associated with an increased risk of wheeze in some populations that may be caused by the host response to the parasite or by parasite-enhanced Th2 responses to aeroallergens.

SUMMARY

Although helminth infections can modulate the host inflammatory response directed against the parasite, a causal association between helminths and atopic diseases remains uncertain.

Reduced helminth burden increases allergen skin sensitization but not clinical allergy: a randomized, double-blind, placebo-controlled trial in Vietnam

BACKGROUND

Observational evidence suggests that infection with helminths protects against allergic disease and allergen skin sensitization. It is postulated that such effects are mediated by helminth-induced cytokine responses, in particular IL-10.

OBJECTIVE

We tested this hypothesis in a rural area of central Vietnam where hookworm infection is endemic.

METHODS

One thousand five hundred and sixty-six schoolchildren aged 6-17 were randomly allocated to receive either anti-helminthic therapy or a placebo at 0, 3, 6, and 9 months. We compared changes in the prevalence of exercise-induced bronchoconstriction, allergen skin sensitization, flexural eczema on skin examination, questionnaire-reported allergic disease (wheeze and rhinitis symptoms), and immunological parameters (hookworm-induced IFN-gamma, IL-5, IL-10) between 0 and 12 months.

RESULTS

One thousand four hundred and eighty-seven children (95% of these randomized) completed the study. The most common helminth infections were hookworm (65%) and Ascaris lumbricoides (7%). There was no effect of the therapy on the primary outcome, exercise-induced bronchoconstriction (within-participant mean percent fall in peak flow from baseline after anti-helminthic treatment 2.25 (SD 7.3) vs. placebo 2.19 (SD 7.8, P=0.9), or on the prevalence of questionnaire-reported wheeze [adjusted odds ratio (OR)=1.16, 95% confidence interval (CI) 0.35-3.82, P=0.8] and rhinitis (adjusted OR=1.39, 0.89-2.15, P=0.1), or flexural dermatitis on skin examination (adjusted OR=1.15, 0.39-3.45, P=0.8). However, anti-helminthic therapy was associated with a significantly higher allergen skin sensitization risk (adjusted OR=1.31, 1.02-1.67, P=0.03). This effect was particularly strong for children infected with A. lumbricoides at baseline (adjusted OR=4.90, 1.48-16.19, P=0.009). Allergen skin sensitization was inversely related to hookworm-specific IL-10 at baseline (adjusted OR=0.76, 0.59-0.99, P=0.04). No cytokine tested, including IL-10, changed significantly after the anti-helminthic therapy compared with the placebo.

CONCLUSION

A significant reduction in worm burden over a 12-month period in helminth-infected children increases the risk of allergen skin sensitization but not of clinical allergic disease. The effect on skin sensitization could not be fully explained by any of the immunological parameters tested.

Association between total immunoglobulin E and antibody responses to naturally acquired Ascaris lumbricoides infection and polymorphisms of immune system-related LIG4, TNFSF13B and IRS2 genes

The 13q33-34 region harbours a susceptibility locus to Ascaris lumbricoides, although the underlying genes are unknown. Immunoglobulin (Ig)E and IgG confer protective immunity and here we sought to investigate in an endemic population whether LIG4, TNFSF13B and IRS2 genes influence IgE and IgG levels against Ascaris and the ABA-1 allergen as a putative resistance marker. Mite-allergic asthmatic patients were analysed for potential relationships between Ascaris predisposition and allergy. One thousand and sixty-four subjects from Cartagena, Colombia, were included. Single nucleotide polymorphisms (SNPs) were genotyped using TaqMan assays. Antibody levels were measured by enzyme-linked immunosorbent assay. Linear and logistic regressions were used to model effects of genotypes on antibody levels. The GG genotype of LIG4 (rs1805388) was associated with higher IgE levels to Ascaris compared with other genotypes. TNFSF13B (rs10508198) was associated positively with IgG levels against Ascaris extract and IgE levels against ABA-1. In asthmatics, IRS2 (rs2289046) was associated with high total IgE levels. Associations held up after correction by population stratification using a set of 52 ancestry markers, age, sex and disease status. There was no association with asthma or mite sensitization. In a tropical population, LIG4 and TNFSF13B polymorphisms are associated with specific IgE and IgG to Ascaris, supporting previous linkage studies implicating the 13q33 region. Our results suggest that genes protecting against parasite infections can be different to those predisposing to asthma and atopy.

Gastrointestinal nematode infection interferes with experimental allergic airway inflammation but not atopic dermatitis

BACKGROUND

Some helminth infections are negatively associated with the prevalence of allergic disorders, arguing for a modulation of allergic reactions by the parasites, depending on the worm species, intensity and phase of infection and the type of disease.

OBJECTIVE

The aim of this study was to analyse the influence of a chronic infection with the gastrointestinal nematode Heligmosomoides polygyrus, in a murine model of allergic airway disease and of atopic dermatitis (AD), respectively.

METHODS

Mice were infected with H. polygyrus and systemically sensitized with the model allergen ovalbumin. Subsequently, the animals were challenged with the allergen either via the airways for induction of airway disease, or via skin patches for induction of dermatitis.

RESULTS

Mice concomitantly infected with H. polygyrus showed diminished eosinophil and lymphocyte recruitment into the lungs and decreased allergen-specific IgE levels when compared with sensitized and airway challenged controls. In addition, animals showed a trend towards reduced airway hyper-reactivity. In contrast, no significant differences in the severity of eczematous skin lesions were observed between infected and control animals in the AD model. Although H. polygyrus infection reduced CD8+ and CD4+ T-cell infiltration into the skin and production of allergen-specific IgE, mast cell recruitment was significantly increased in worm-infected mice in the dermatitis model. The worm infection was associated with significantly elevated numbers of Foxp3+ regulatory T cells (Treg) in peribronchial lymph nodes in H. polygyrus-infected sensitized and airway challenged mice. In contrast, Treg cells were basically absent in eczematous skin and their number was not increased in skin-draining lymph nodes of mice with experimental dermatitis.

CONCLUSION

Infection with the gastrointestinal nematode used in our study leads to significant inhibition of mucosa-associated but not cutaneous allergic reactions, pointing to a site specificity of the immunomodulation exerted by helminths. This finding might be an important aspect for future considerations of helminths for treatment of allergic diseases.

Immune and genetic aspects of asthma, allergy and parasitic worm infections: evolutionary links

There are important parallels in the immunobiology of allergy and asthma, and of the human host's response to parasitic worms. Th-2 immune actions with 'weep and sweep' mucosal biology are common to both - pathological in the first and protective in the second. Common up-regulating genetic variants of Th-2 immunity, notably in IL13 and STAT6, predict increased risk of asthma and allergy, but diminished intensity of infection by Ascaris and Schistosoma. Endemic exposures of humans to parasitic worms may have been one evolutionary force selecting for genetic variants that promote asthma and allergy.

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.

Out of Africa: what can be learned from the studies of allergic disorders in Africa and Africans?

PURPOSE OF REVIEW

Allergic diseases have only recently gained serious attention in Africa. This review discusses recent studies that have focused on allergy among Africans and people of African ancestry.

RECENT FINDINGS

Time trend studies of the prevalence of allergies in Africa show a consistent increase over a period of 7-10 years. Recent studies have reported that the link between IgE, skin reactivity to allergens and allergic symptoms increases with increasing gross national income of the country. Association between helminth infections, and allergies seem contradictory, which may be attributed to differences in the length of infection and species studied. Importantly, researchers have identified an 'urban diet' component, which is associated with increased skin reactivity to allergens. Finally, whereas Africans in rural Africa seem to suffer less from allergies, people of African ancestry in affluent countries have higher prevalence and greater severity of allergic symptoms than natives of these host countries, raising important issues on genetic control of allergic diseases.

SUMMARY

Mechanisms underlying the development of allergy are a complex interaction of genetic susceptibility and environmental exposures. Identification of specific environmental factors, mechanistic pathways and genetic risk factors in sufficiently powered studies will be necessary to better understand and control the allergic march in Africa and elsewhere.

Atopic disorders and parasitic infections

This chapter examines the relationship between atopic disorders and parasitic infections. Atopy is an exaggerated IgE-mediated Type-1 immune response in predisposed individuals. Conflicting information exists in regard to the relationship of parasitic infections and the classic allergic diseases, that is, atopic dermatitis, allergic rhinitis and asthma. Attention is paid to the explanations for these discrepancies in the literature found within both human and animal studies on atopy with particular emphasis on helminthic infections. The factors that cause only a proportion of atopic individuals to develop clinical disease have not been defined although helminths confer protection in many studies examined. Early childhood infections help induce a Th1-biased immunity and prevent the induction of the Th2 system that causes atopy. Acute parasitic infections may increase manifestations of allergy, whereas chronic infections with parasites decrease atopic predisposition. Nonetheless, a causal association between geohelminth infection and atopic disorders has not been established. Some helminthic substances, especially the cytokines, have respiratory and anti-allergic effects, and may therefore become useful as therapeutic modalities for many atopic and allergic disorders.

Cross-reactive IgE antibody responses to tropomyosins from Ascaris lumbricoides and cockroach

BACKGROUND

Evidence indicates that infection with Ascaris lumbricoides may promote development of allergy and asthma.

OBJECTIVE

To study the role of tropomyosin, a pan-allergen in invertebrates, in IgE responses to A lumbricoides.

METHODS

Recombinant A lumbricoides and Periplaneta americana tropomyosins were expressed in Pichia pastoris. Levels of IgE to tropomyosins from A lumbricoides and P americana were determined by chimeric ELISA in sera from 119 children living in a parasite-endemic area and 112 patients with cockroach allergy from the allergy clinics. Presence of tropomyosin in A lumbricoides larvae at L3 stage was evaluated by immunofluorescence using mAb 1A6, directed against mite tropomyosin. Molecular modeling of P americana and A lumbricoides tropomyosins was performed by using the MODELLER program.

RESULTS

A lumbricoides tropomyosin showed 69% to 98% sequence identity to tropomyosins from other invertebrates. The predicted structure of A lumbricoides tropomyosin was similar to that of P americana tropomyosin and showed the characteristic coiled-coil structure. Strong correlation was found for IgE antibodies to tropomyosins from A lumbricoides and P americana in sera from children living in a parasite-endemic area and from patients with cockroach allergy. Larvae of A lumbricoides reacted strongly with mAb 1A6.

CONCLUSION

Tropomyosin induces IgE responses in A lumbricoides-infected children and in patients allergic to cockroach.

High titre of anti-Ascaris immunoglobulin E associated with bronchial asthma symptoms in 5-year-old rural Bangladeshi children

BACKGROUND

Increasing interest has arisen whether helminthic infections protect against asthma and allergy. The prevalence of wheezing among Bangladeshi children is higher in rural areas where helminthic infectious burden is greater, which is contrary to the general assumption.

OBJECTIVE

We therefore examined the association between Ascaris infection, serum level of anti-Ascaris IgE, which should be investigated differently from the infection, and wheezing in 5-year-old children from rural Bangladesh.

METHODS

A total of 219 children who reported wheezing during the previous 12 months and 122 randomly selected age-matched individuals who had never experienced wheezing were tested for serum levels of total and specific Ascaris, Dermatophagoides pteronyssinus, alternaria and cockroach IgEs, and for intestinal helminth infection as well.

RESULTS

Anti-Ascaris IgE levels were significantly and independently associated with current wheezing during the previous 12 months [odds ratio (OR) per log(e) increment is 1.31 (95% confidence interval (CI) 1.08-1.60), P=0.007], a history of at least four episodes of wheezing [OR per log(e) increment is 1.52 (95% CI 1.18-1.96), P=0.001], wheezing with sleep disturbances [OR per log(e) increment is 1.35 (95% CI 1.10-1.64), P=0.011] and wheezing with speech disturbances [OR per log(e) increment is 1.57 (95% CI 1.19-2.08), P=0.001]. These were adjusted for gender, pneumonia history, parental asthma, Trichuris infection, use of dry leaves as fuel and other specific IgE levels. The prevalence of Ascaris infection by the presence of wheezing was not significantly different (76% vs. 72%, respectively).

CONCLUSION

We conclude that a high titre of anti-Ascaris IgE is associated with an increased risk of asthma symptoms among 5-year-old rural Bangladeshi children with a high helminthic infectious load.

Infection by Ascaris lumbricoides and bronchial hyper reactivity: an outstanding association in Venezuelan school children from endemic areas

Asthma and other respiratory diseases have increased in the last years among Venezuelan children from helminthic endemic areas where the infection by Ascaris lumbricoides has been associated to bronchial airway inflammation in parasitized individuals. The aim of this work was to investigate the possible associations between the development of bronchial hyper reactivity and the immune response against A. lumbricoides in urban and rural children. We evaluated 470 school children from rural and urban communities. Pulmonary function tests were performed and >or=20% PC(20) changes were considered as a positive diagnostic of bronchial hyper reactivity. The prevalence and intensity of A. lumbricoides infection was determined by faecal examination. Specific serum IgE levels using a modified ELISA and skin prick tests against A. lumbricoides and the common allergen Dermatophagoides pteronyssinus were done. The number of circulating lymphocyte sub populations was determined by flow cytometry analysis. In rural children, bronchial hyper reactivity was associated with increased specific levels of anti-A. lumbricoides IgE (p<0.0001) and skin test positivity for A. lumbricoides (p<0.0001). The percentage of FEV1 predictive values correlated inversely (p<0.0001) with anti-A. lumbricoides IgE levels. Elevated numbers of circulating CD3+CD4+ and CD20+CD23+ cells were found in rural children with bronchial hyper reactivity compared to their asymptomatic counterparts. They correlated positively with anti-A. lumbricoides IgE levels (p<0.005 and <0.0001, respectively). In contrast, in urban children, bronchial hyper reactivity was associated with elevated anti-D. pteronyssinus IgE levels (p=0. 0089), skin hyper reactivity towards this aero allergen (p=0.003) and to an increase in the number of CD3+CD8+ (p<0.0001). Our results suggest that the IgE response against A. lumbricoides infection may be involved in the development of bronchial hyper reactivity among rural children from endemic areas and also that improved hygienic conditions in the urban environment is associated with increased responses to airborne allergens.

Protective effect of Schistosoma mansoni infection on allergic airway inflammation depends on the intensity and chronicity of infection

BACKGROUND

Population studies have suggested that chronic and intense helminth infections, in contrast to acute and mild helminth infections, might suppress allergic airway inflammation.

OBJECTIVE

We sought to address the question of how the chronicity and intensity of helminth infections affect allergic airway inflammation in a well-defined experimental model.

METHODS

C57/Bl6 mice were infected with Schistosoma mansoni, followed by sensitization and challenge with ovalbumin (OVA), and different stages and intensities of infection were studied. To this end, mice were analyzed at 8, 12, or 16 weeks, representing the acute, intermediate, or chronic phases of infection, respectively.

RESULTS

Lung lavage eosinophilia, peribronchial inflammation, and OVA-induced airway hyperresponsiveness were increased during acute infection but significantly decreased when infection progressed into chronicity. Decreases in lung lavage eosinophilia were parasite density-dependent. Similar levels of OVA-specific IgE were found during all phases of infection, whereas both OVA-specific and parasite-specific T(H)2 cytokine levels were significantly reduced during chronic infection. Inhibition of airway inflammation could be transferred to OVA-sensitized recipient mice by B cells and CD4(+) T cells from spleens of chronically, but not acutely, infected mice. This suppression was IL-10-dependent.

CONCLUSION

During chronic, but not acute, helminth infections, suppressive mechanisms are induced that regulate immune reactions to inhaled allergens. These data confirm human epidemiologic observations in a well-controlled animal model.

CLINICAL IMPLICATIONS

Characterization of chronic helminth infection-induced regulatory mechanisms will help in the development of future therapeutics to treat or prevent allergic disease.

Chronic helminth infections induce immunomodulation: consequences and mechanisms

Worldwide, more than a billion people are infected with helminths. These worm infections generally do not lead to mortality, however, they are chronic in nature and can lead to considerable morbidity. Immunologically these infections are interesting; chronic helminth infections are characterized by skewing towards a T helper 2 type response as well as regulatory responses. The regulatory network is associated with chronic helminth infections and is thought to prevent strong immune responses against parasitic worms, allowing their long-term survival and restricting pathology. This regulatory network is thought to also temper responses to non-helminth antigens, like allergens or self-antigens, possibly leading to lower prevalence of allergies and autoimmune diseases in subjects that are chronically infected with helminths. This raises the interesting idea that helminths may bear molecules that have potential therapeutic action against allergies and possibly other inflammatory diseases. However, on the other side of the coin, this would predict that helminth infected subjects might not respond strongly to third party antigens like vaccines. This is an important issue, since most vaccines that are being developed against diseases such as HIV, tuberculosis or malaria will be introduced in areas where helminth infections are highly prevalent. Moreover, these vaccines are proving difficult to develop and are often weak, thus any confounder that would affect their efficacy needs to be taken into consideration. Helminth derived molecules have been identified that induce T helper 2 and regulatory responses via modulation of dendritic cells and some appear to do so via Toll like receptor (TLR) signaling. New insights into these pathways could be useful to antagonize suppression and hence boost vaccine efficacy or to optimize suppression induced by helminth derived molecules and control inflammatory diseases.

Sensitization to Ascaris lumbricoides and severity of childhood asthma in Costa Rica

BACKGROUND

Little is known about sensitization (defined as a positive IgE) to helminths and disease severity in patients with asthma.

OBJECTIVES

To examine the relationship between sensitization (defined as a positive IgE) to Ascaris lumbricoides and measures of asthma morbidity and severity in a Costa Rican population with low prevalence of parasitic infection but high prevalence of parasitic exposure.

METHODS

Cross-sectional study of 439 children (ages 6 to 14 years) with asthma. Linear regression and logistic regression were used for the multivariate statistical analysis.

RESULTS

After adjustment for parental education and other covariates, sensitization to Ascaris lumbricoides was associated with having at least 1 positive skin test to allergens (odds ratio, 5.15; 95% CI, 2.36-11.21; P < .001), increased total serum IgE and eosinophils in peripheral blood, reductions in FEV(1) and FEV(1)/forced vital capacity, increased airway responsiveness and bronchodilator responsiveness, and hospitalizations for asthma in the previous year (odds ratio, 3.08; 95% CI, 1.23-7.68; P = .02).

CONCLUSION

Sensitization to Ascaris lumbricoides is associated with increased severity and morbidity of asthma among children in Costa Rica. This association is likely mediated by an increased degree of atopy among children with asthma who are sensitized to Ascaris.

CLINICAL IMPLICATIONS

In areas with a low prevalence of helminthiasis such as Costa Rica, Ascaris sensitization may be an important marker of severe atopy and disease morbidity in children with asthma.

Allergic disorders in African countries: linking immunology to accurate phenotype

Identification and characterization of risk and protective factors for allergy is important for developing strategies for prevention or treatment. The prevalence of allergy is clearly higher in affluent countries than in developing countries like, e.g. Africa. Especially in urban areas of developing countries, allergy is however on the increase. In Africa, we have the unique opportunity to investigate risk and protective factors and the influence of urbanization and westernization, i.e. almost to take a look at Europe, Australia or the USA as they were before their allergy epidemics. Moreover, migrants from developing to affluent countries experiencing an increased burden of allergy provide new insights into risk and protective factors. Allergen exposure, diet and infections are the major exogenous influences playing a role as risk and protective factors. Depending on the nature, timing, chronicity and level of exposure, each of them can promote or inhibit allergy. Perhaps with the exception of infections, availability of data from Africa on their role in the development of allergy is limited. Detailed epidemiological studies in rural and urban Africa combined with basic immunological research are needed to unravel mechanisms of increase in allergy and of protection. The maturation of the immune system at young age under influence of exogenous factors results in differences in T-cell-skewing (Th1/Th2/Treg) and humoral responses. It is essential to perform studies from a 'non-Eurocentric' angle (e.g. local allergens, locally validated questionnaires and diagnostic procedures). Such studies will provide the affluent countries with new leads to combat the allergy epidemic and more importantly help prevent it in Africa.

Ascaris, co-infection and allergy: the importance of analysis based on immunological variables rather than egg excretion

The ratio of Ascaris seropositivity to the presence of eggs in the faeces was 2.44 in children residing near Cape Town, South Africa. Similar and larger ratios have previously been described for children and women living in the city. The new finding strengthens the concept that when helminthic infections occur together with non-helminthic diseases, an analysis of the interaction must include the use of disease-related immunological variables and not be based only on egg excretion status. One of the reasons is that many egg-negative people who live where helminthiasis is highly endemic are immunologically activated as a result of transitory non-patent or intermittent patent infection by Ascaris and/or other worms.