Association of hepatitis A virus infection with allergic sensitization in a population with high prevalence of hepatitis A virus exposure

Understanding Asthma and Allergies by the Lens of Biodiversity and Epigenetic Changes

Exposure to different organisms (bacteria, mold, virus, protozoan, helminths, among others) can induce epigenetic changes affecting the modulation of immune responses and consequently increasing the susceptibility to inflammatory diseases. Epigenomic regulatory features are highly affected during embryonic development and are responsible for the expression or repression of different genes associated with cell development and targeting/conducting immune responses. The well-known, "window of opportunity" that includes maternal and post-natal environmental exposures, which include maternal infections, microbiota, diet, drugs, and pollutant exposures are of fundamental importance to immune modulation and these events are almost always accompanied by epigenetic changes. Recently, it has been shown that these alterations could be involved in both risk and protection of allergic diseases through mechanisms, such as DNA methylation and histone modifications, which can enhance Th2 responses and maintain memory Th2 cells or decrease Treg cells differentiation. In addition, epigenetic changes may differ according to the microbial agent involved and may even influence different asthma or allergy phenotypes. In this review, we discuss how exposure to different organisms, including bacteria, viruses, and helminths can lead to epigenetic modulations and how this correlates with allergic diseases considering different genetic backgrounds of several ancestral populations.

Seroprevalence and susceptibility to hepatitis A in the European Union and European Economic Area: a systematic review

Most of the European Union (EU) and European Economic Area (EEA) is considered a region of very low hepatitis A virus (HAV) endemicity; however, geographical differences exist. We did a systematic review with the aim of describing seroprevalence and susceptibility in the general population or special groups in the EU and EEA. We searched databases and public health national institutes websites for HAV seroprevalence records published between Jan 1, 1975, and June 30, 2014, with no language restrictions. An updated search was done on Aug 10, 2016. We defined seroprevalence profiles (very low, low, and intermediate) as the proportion of the population with age-specific anti-HAV antibodies at age 15 and 30 years, and susceptibility profiles (low, moderate, high, and very high) as the proportion of susceptible individuals at age 30 and 50 years. We included 228 studies from 28 of 31 EU and EEA countries. For the period 2000-14, 24 countries had a very low seroprevalence profile, compared with five in 1975-89. The susceptibility among adults ranged between low and very high and had a geographical gradient, with three countries in the low susceptibility category. Since 1975, EU and EEA countries have shown decreasing seropositivity; however, considerable regional variability exists. The main limitations of this study are that the studies retrieved for analysis might not be representative of all EU and EEA publications about HAV and might have poor national representativeness. A large proportion of EU and EEA residents are now susceptible to HAV infection. Our Review supports the need to reconsider specific prevention and control measures, to further decrease HAV circulation while providing protection against the infection in the EU and EEA, and could be used to inform susceptible travellers visiting EU and EEA countries with different HAV endemicity levels.

Molecular biology and inhibitors of hepatitis A virus

Hepatitis A virus (HAV) is a faeco-orally transmitted picornavirus and is one of the main causes of acute hepatitis worldwide. An overview of the molecular biology of HAV is presented with an emphasis on recent findings. Immune evasion strategies and a possible correlation between HAV and atopy are discussed as well. Despite the availability of efficient vaccines, antiviral drugs targeting HAV are required to treat severe cases of fulminant hepatitis, contain outbreaks, and halt the potential spread of vaccine-escape variants. Additionally, such drugs could be used to shorten the period of illness and decrease associated economical costs. Several known inhibitors of HAV with various mechanisms of action will be discussed. Since none of these molecules is readily useable in the clinic and since the availability of an anti-HAV drug would be of clinical importance, increased efforts should be targeted toward discovery and development of such antivirals.

The association between foodborne and orofecal pathogens and allergic sensitisation -- EuroPrevall study

BACKGROUND

An inverse association between markers of exposure to foodborne and orofecal pathogens and allergic sensitization has been reported. However, the findings of epidemiological studies have not been consistent. This study investigated the relationship between antibodies to hepatitis A, Toxoplasma gondii and salmonella and allergic sensitization to food and aeroallergens in children from different geographical areas.

METHODS

Specific IgE and/or skin prick testing against food and aeroallergens were measured in children from 6 to 12 years of age residing in Greece, the Netherlands, China, India and Russia. Seropositivity to the three pathogens was measured, and data on potential confounders were collected using questionnaire.

RESULTS

Data from 800 children (126 from Athens; 248 from Utrecht; 110 from Hong Kong; 119 from urban Tomsk; and 197 from rural Tomsk) could be analysed. The highest percentage of positive serology to salmonella was found in Hong Kong (46.4%), to T. gondii in urban Tomsk (13.4%) and to hepatitis A in Athens (71.2%). Although not significant, T. gondii seropositivity tends to be negatively associated, and hepatitis A seropositivity tends to be positively associated with allergic sensitization.

CONCLUSION

Inconsistent associations were observed between allergic sensitization to food and aeroallergens and markers of exposure to two common foodborne pathogens. The association with T. gondii tends to be negative, consistent with the 'hygiene hypothesis', but the association with hepatitis A tends to be positive. Taken together, there is no clear evidence that past exposure to foodborne and orofecal pathogens protects against allergic sensitization to food or aeroallergens.

The pathophysiology of the hygiene hypothesis

There has been a considerable increase in the diagnosis of allergic diseases over the last decades. Prevalence of allergies in high-income countries and urban areas appears higher than in rural environments. While environmental factors like pollution or nutrition can be important, it is more likely that in the end they have a small association with allergies. Childhood infections and exposure to certain microbial antigens on the other hand seem to present a strong negative correlation with allergies, and therefore the increase of the allergic burden in the Western world has been frequently related to a decline of childhood infections giving birth to the "Hygiene Hypothesis". We address the issue with emphasis on the associated pathophysiology tightrope walking between the skepticism of the critics, which cast doubt on it, and the pilgrims' belief of having discovered allergy's Holy Grail.

Association of Hepatitis A exposure and TIM-1 with childhood allergic asthma

BACKGROUND

Hepatitis A virus (HAV) receptor (TIM-1) polymorphism plays an important role in asthma and autoimmune diseases. Objective. To analyze the association of TIM-1 polymorphism and HAV infection with childhood allergic asthma in Southwest China.

METHODS

TIM-1 exon 4 (157insMTTTVP) and two polymorphism loci, -416G>C and -1454G>A, in the HAV receptor promoter region were studied. Polymerase chain reaction (PCR) was used to test the genotypes of three polymorphism loci among 579 cases of asthma and 524 controls. The HAV infection status was determined in a case-control study with stratified analysis.

RESULTS

HAV exposure associated with childhood allergic asthma in the study population was compared with controls (odds ratio (OR) = 0.181, 95% confidence interval (CI) 0.126-0.260, p < .001). The -416G>C polymorphism was associated with asthma (OR = 1.384, 95% CI 1.148-1.669, p < .001), but the insertion variant 157delMTTTVP of exon 4 and the -1454G>A polymorphism were not.

CONCLUSION

Our results indicated that the -416G>C polymorphism of the TIM-1 gene is associated with childhood allergic asthma, providing a better understanding of the pathogenesis of the allergic asthma among children aged below 15 years in Southwest China.

Chronic virus infections supress atopy but not asthma in a set of children from a large Latin American city: a cross-section study

Background

The prevalence of allergic diseases has increased over recent decades in affluent countries, but remains low in rural populations and some non-affluent countries. An explanation for these trends is that increased exposure to infections may provide protection against the development of allergy. In this work we investigated the association between exposure to viral infections in children living in urban Brazil and the prevalence of atopy and asthma.

Methods

School age children living in poor neighborhoods in the city of Salvador were studied. Data on asthma symptoms and relevant risk factors were obtained by questionnaire. Skin prick tests (SPTs) were performed to seven aeroallergens, and specific IgE was measured to four of these. Viral infections were determined by the presence of specific IgG in serum to Herpes simplex (HSV), Herpes zoster (HZV), Epstein-Barr (EBV), and Hepatitis A (HAV) viruses.

Results

A total of 644 (49.7%) children had at least one allergen-specific IgE> 0.35 kU/L and 489 (37.7%) had specific IgE> 0.70 kU/L. A total of 391 (30.2%) children were skin test positive (SPT+), and 295 (22.8%) children were asthmatic. The seroprevalence of viral infections was 88.9% for EBV, 55.4% for HSV, 45.5% for VZV and 17.5% for HAV. Negative associations were observed between SPT+ and HSV (OR = 0.64, CI = 0.51, 0.82) and EBV (OR = 0.63, CI = 0.44, 0.89) infections, but no associations were seen between viral infections and the presence of allergen-specific IgE or asthma.

Conclusion

These data do not support previous data showing a protective effect of HAV against atopy, but did show inverse associations between SPT+ (but not specific IgE+) and infections with HSV and EBV. These findings suggest that different viral infections may protect against SPT+ in different settings and may indicate an immunoregulatory role of such infections on immediate hypersensitivity responses. The data provide no support for a protective effect of viral infections against asthma in this population.

Clinical aspects of pediatric food allergy and failed oral immune tolerance

Food allergy seems to represent a new spectrum of disease that has elicited significant community concern and extended waiting lists for allergists and gastroenterologists alike. The apparent rise in prevalence of IgE-mediated food allergy (and associated risk of anaphylaxis) has been postulated to result from effects of a "modern lifestyle" but as yet clear environmental risk factors have not yet emerged. Family history seems to contribute to risk suggesting that gene-environment interactions will be important for identifying a subpopulation with increased susceptibility to any identified lifestyle effects. Non-IgE-mediated food allergy (including food-induced enteropathies and colitides, eosinophilic esophagitis, and Crohn's disease) with potentially similar environmental triggers resulting in diverse immune dysregulatory mechanisms. The evidence underpinning the putative rise in food allergy is discussed and potential mechanisms of disease explored. Clinical aspects of various food allergic conditions including non-IgE-mediated food allergy are outlined.

99th Dahlem conference on infection, inflammation and chronic inflammatory disorders: controversial aspects of the 'hygiene hypothesis'

The 'hygiene hypothesis' proposes that the epidemic of allergic and autoimmune diseases is due to changes in the interactions between humans and the microbes of their ecosystem. This theory apparently does not explain (i) why allergic asthma is rising in 'unhygienic' American inner cities; (ii) why allergic diseases are less prevalent among migrants' children living in European big cities; (iii) why infections with airborne viruses do not 'protect' from allergic sensitization; (iv) why the inverse association between some infections (e.g. hepatitis A virus) and allergic diseases has been reproduced in some populations, but not in others; and (v) why probiotics are not effective in the prevention and therapy of allergic diseases. These challenging questions are useful starting points to improve our understanding of the hypothesis, and to identify among the infectious agents those really responsible for a protective influence against atopic and autoimmune diseases.

The effect of infectious burden on the prevalence of atopy and respiratory allergies in Iceland, Estonia, and Sweden

BACKGROUND

Epidemiologic reports on the effect of microbe exposure on the development of atopy and allergic asthma are inconsistent.

OBJECTIVES

The study investigates the association between serologic markers of infections and occurrence of atopy, allergic asthma, and rhinitis among adults in Iceland, Sweden, and Estonia.

METHODS

Individuals (n = 1249; mean age, 42 years) from Iceland, Sweden, and Estonia underwent a structured interview and blood sampling. Specific IgE was measured against 4 allergens, and IgG antibodies were measured against Helicobacter pylori, Toxoplasmosis gondii, hepatitis A virus, herpes simplex virus 1, Chlamydia pneumoniae, EBV, and cytomegalovirus.

RESULTS

Nonatopic subjects more often had positive serology for Helicobacter pylori, herpes simplex virus 1, Chlamydia pneumoniae, and cytomegalovirus. Having a low number (</=3) of IgG antibodies against the various infectious agents was an independent risk factor for atopy (odds ratio [OR], 1.43; 95% CI, 1.06-1.93), allergic asthma (OR, 1.82; 95% CI, 1.12-2.98), and allergic rhinitis (OR, 1.69; 95% CI, 1.21-2.37). The proportion of atopy that can be explained by a lower number (</=3) of infections was 6.7% in Iceland, 9.2% in Estonia, and 16.4% in Sweden, and 6.7%, 48.2%, and 33.4% for allergic asthma, respectively.

CONCLUSION

Our data are consistent with cumulative protective effect of infections against atopy and respiratory allergies irrespective of route of infection.

CLINICAL IMPLICATIONS

The study indicates what microbes or combination of microbes play a role in the complex interplay between hygiene and allergy and may contribute toward the understanding of the allergy epidemic.

Too clean, or not too clean: the hygiene hypothesis and home hygiene

The 'hygiene hypothesis' as originally formulated by Strachan, proposes that a cause of the recent rapid rise in atopic disorders could be a lower incidence of infection in early childhood, transmitted by unhygienic contact with older siblings. Use of the term 'hygiene hypothesis' has led to several interpretations, some of which are not supported by a broader survey of the evidence. The increase in allergic disorders does not correlate with the decrease in infection with pathogenic organisms, nor can it be explained by changes in domestic hygiene. A consensus is beginning to develop round the view that more fundamental changes in lifestyle have led to decreased exposure to certain microbial or other species, such as helminths, that are important for the development of immunoregulatory mechanisms. Although this review concludes that the relationship of the hypothesis to hygiene practice is not proven, it lends strong support to initiatives seeking to improve hygiene practice. It would however be helpful if the hypothesis were renamed, e.g. as the 'microbial exposure' hypothesis, or 'microbial deprivation' hypothesis, as proposed for instance by Bjorksten. Avoiding the term 'hygiene' would help focus attention on determining the true impact of microbes on atopic diseases, while minimizing risks of discouraging good hygiene practice.

Infectious burden as a determinant of atopy-- a comparison between adults in Finnish and Russian Karelia

BACKGROUND

Evidence of the influence of pathogen exposure on the development of atopy and atopic disease is not unequivocal. We investigated the association between markers of infections and occurrence of atopy among adults in eastern Finland and western Russia, two adjacent areas with profound differences in living conditions and lifestyles.

METHODS

Randomly selected adults aged 25-54 years from Finland (n = 790) and from Russia (n = 387) participated in the study. Skin prick tests were performed to 11 common airborne allergens, and at least one positive prick reaction was considered to indicate atopy. Antibodies to different pathogens including hepatitis A virus (HAV), Helicobacter pylori, Toxoplasma gondii, herpes simplex virus (HSV), Chlamydia pneumoniae and the periodontal pathogens Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans were measured.

RESULTS

In Finland 34.3% and in Russia 23.3% of the study population was atopic (p < 0.001). Seroprevalences to all these pathogens were significantly higher among the Russians. In multivariate logistic regression analysis, only H. pylori was inversely associated with atopy in Russia. A further stepwise analysis revealed that H. pylori alone can explain 32% of the difference in atopy between the countries, and T. gondii, A. actinomycetemcomitans, HSV and C. pneumoniae had a slightly additive effect, whereas, unexpectedly, seropositivity to HAV and, to a lesser extent, P. gingivalis had an opposite effect. The net result of the stepwise analysis showed that 44% of the difference in atopy between the countries could be explained by seropositivity to these seven pathogens.

CONCLUSIONS

Seropositivity to select pathogens, particularly to H. pylori, could explain a substantial part of the difference in atopy prevalence between Finland and Russia. Exposure to HAV was not associated with protection against atopy in this adult population.

Toxocara infection seroprevalence and its relationship with atopic features in a general adult population

BACKGROUND

The relationship of helminth infection with atopy is controversial. Toxocariasis is the most common helminth infection in industrialized countries. The study aimed to investigate the association between Toxocara exposure and atopic features.

METHODS

The study is based on a cross-sectional survey of 463 subjects, randomly selected (stratified by decades of age) from a general adult population. Toxocara exposure was defined by the presence of serum Toxocara antibodies. Main outcome measures included total serum IgE levels, skin prick tests (SPT) to a panel of 13 relevant aeroallergens, specific IgE to aeroallergens (Phadiatop test), and respiratory symptoms evaluated by means of a questionnaire.

RESULTS

A total of 134 subjects (weighted proportion 28.6%, 95% CI 26.5-30.7%) showed Toxocara exposure. Pet ownership, rural habitat, farming, and low educational level were associated with Toxocara exposure. Toxocara exposure was associated with both positive SPT (particularly to mites) and positive specific IgE (Phadiatop test) after adjusting for potential confounders. The effect of Toxocara exposure on total serum IgE levels and blood eosinophil count was different in SPT-positive subjects and SPT-negative individuals. In SPT-negative individuals, Toxocara exposure was associated with an increase in both serum IgE levels and eosinophil counts, whereas an opposite trend was observed in SPT-positive individuals. Toxocara exposure was not associated with respiratory symptoms.

CONCLUSIONS

In this adult population, Toxocara exposure is associated with allergic sensitization, particularly to mites. There is evidence of an intriguing interaction between Toxocara exposure and allergic sensitization for both total serum IgE levels and blood eosinophil counts.

Another explanation for the low allergy rate in the rural Alpine foothills

A low allergy rate in coal and wood heated homes has been described in the small villages in the Alpine foothills and subsequently found to be associated with the farming environment. This was interpreted within the framework of the hygiene hypothesis but there are also alternative explanations. Lower air pollution could be one reason, which is, however, unlikely since the differences between the Bavarian countryside and the Munich municipal area were only weak. There could be genetic differences between the urban and rural population by previous isolation or by self-selection. The potential drop-out of allergy genes, however, will also not explain the absent increase of allergies in two generations. More likely, other lifestyle factors are important. Dietary habits are different in farmers and a less frequent vitamin D supplementation of newborns (otherwise expected to be allergy promoting) has been shown recently. The underlying cause for the "non-allergic farm child" remains speculative until the transfer of any farm-associated factor is leading to a similar risk reduction in the general population.