Abstract
BackgroundThe 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.MethodsSchool 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.ResultsA 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.ConclusionThese 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.
Highlights
The prevalence of allergic diseases has increased over recent decades in affluent countries, but remains low in rural populations and some non-affluent countries
The results showed that 44.2% of the children had the bed linen changed more than once a week, 82.8% had a sewage system in their home, 64.9% had mold and moisture in the walls of their houses, and 39.6% lived with dogs and 17.7% with cats
In our study, we found no association between the HSV infection and the presence of aerollaergen-specific IgE or asthma; a significant negative association was observed with Skin prick tests (SPTs) in multivariate analyses, indicating that exposures to this infection may be associated with suppression of immediate hypersensitivity responses
Summary
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. The prevalence of allergic diseases, such as rhinitis, asthma and eczema has increased in affluent countries over recent decades, and may have increased in cities of non-affluent countries such as in Latin America [1] Such temporal trends occurring over a relatively short period of time are unlikely to be explained by Strachan [3] observed that children lower in the birth order had a reduced prevalence of hay fever and interpreted this observation in terms of younger children being more highly exposed to infections in early life through contact with their older siblings. Such infections include hepatitis A [11], Herpes simplex [12] and Epstein-Barr viruses [13], viral lower respiratory tract infections [14], and Mycobacterium tuberculosis infection [15]
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