The hygiene hypothesis of atopic disease--an extended version

Probiotics: a complementary approach in the treatment and prevention of pediatric atopic disease

PURPOSE OF REVIEW

The goal of this article is to review recent primary research and developments in the area of probiotics and pediatric atopic disease.

RECENT FINDINGS

Research developments in probiotics summarized in this article include the following: (1) the role of probiotics in primary prevention of atopic disease, (2) the effect of probiotics on cytokines involved in the allergic immune response, (3) the long-term effects of peri-natal probiotic use and (4) the relationship between the gut microflora and atopic dermatitis.

SUMMARY

Probiotics continue to be an area of active investigation as our understanding evolves of the gut microbiota's role in the altered immune response of atopic patients. Physicians should be aware of these developments as probiotics may be an important complementary approach in the treatment and the natural and long-term course of various pediatric diseases. This article summarizes the research conducted over the past 10 years with a primary focus on the literature published since January 2003.

Single versus dual respiratory virus infections in hospitalized infants: impact on clinical course of disease and interferon-gamma response

BACKGROUND

Dual respiratory viral infections are frequently associated with lower respiratory tract illness in infants. This study aimed to determine the impact of a dual respiratory viral infection on specific aspects of the infant's immune response and the clinical course of illness.

METHODS

A prospective study was performed with 772 infants hospitalized from October 2000 through July 2004. Sensitive polymerase chain reaction methodology revealed the presence of a single respiratory virus in 443 (57%) of 772 cases, whereas dual infections were identified in 153 (20%) of cases. From 250 infants with confirmed respiratory viral infection, fresh heparinized blood was analyzed for interferon-gamma (IFN-gamma) responses by flow cytometry. Of these, 191 patients had a single infection with respiratory syncytial virus (RSV), rhinoviruses, adenoviruses or influenza viruses; and 59 patients had a dual infection with RSV and rhinoviruses, RSV and adenoviruses, influenza viruses and rhinoviruses or adenoviruses and rhinoviruses. The clinical features and peripheral lymphocyte IFN-gamma responses were compared among infants with single or dual infections.

RESULTS

It was found that dual infections with non-RSV respiratory viruses induced peripheral blood mononuclear cell IFN-gamma responses that mimic those of single infections, whereas coinfection with RSV was associated with reduced IFN-gamma responses and a more severe clinical course of lower respiratory tract disease.

CONCLUSIONS

The results indicate that the clinical characteristics and the IFN-gamma response differ significantly in single and dual respiratory viral infection, depending on the nature of the simultaneously detected viruses. In dual infections, RSV involvement was associated with a decreased IFN-gamma response in peripheral blood mononuclear cell and an increase in severity of illness.

Probiotics That Modify Disease Risk

Probiotics are defined as live bacterial preparations with clinically documented health effects in humans. Probiotics have specific properties and targets in the human intestinal tract and intestinal microbiota. Each probiotic strain, independent of its genus and species is unique and, thus, the properties and the human health effects of each strain have to be assessed in a case-by-case manner. Understanding the mechanisms by which probiotics influence the normal intestinal microbiota and counteract aberrancies in microbiota would facilitate the use of probiotics for both dietary management and reduction in risk of specific diseases. Development of intestinal microbiota is an important factor affecting the health of the newborn. Recent studies suggest that specific bacterial components, especially the bifidobacteria, have a key impact on development of a healthy balanced infant microbiota. The composition of infant and child intestinal microbiota may become aberrant and thus influence the development of diarrheal, inflammatory, and allergic diseases. Based on this understanding, positive health effects of probiotics have been reported in the management of diarrheal, inflammatory, and allergic diseases in infants. Most recently, a reduction in risk of atopic diseases followed early administration of specific probiotics.

The hygiene hypothesis and asthma

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

The hygiene hypothesis: does it function worldwide?

PURPOSE OF REVIEW

This article intends to be a systematic review of papers published during 2003-2004 quoted in a Medline search for 'hygiene hypothesis'. The worldwide perspective of the article does not refer just to a geographical concept, but tries also to address the question of whether the consensus on the hypothesis is global or whether it applies to all types of allergic or immunologic disease, to any age sample or infectious agent. Furthermore, the article outlines those clinical and experimental studies which, in the authors' opinion, may represent significant contributions to a better understanding of the hygiene hypothesis and may guide further investigations on the subject.

RECENT FINDINGS

The association between a reduced exposure to infectious agents (as a part of a changed lifestyle) and a higher prevalence of atopy seems now to be confirmed by consistent evidence. Mechanisms underlying this association, however, are not yet completely clear (immune deviation or immune regulation).

SUMMARY

Further experimental and clinical studies are needed, with special reference to the time, duration and intensity of exposure to any specific infectious agent which is related to well-defined allergy outcomes. The background information for using microbial products in allergy prevention and treatment is still limited.

Prevalence of allergy-related symptoms in Singaporean children in the second year of life

This study describes the cross-sectional prevalence of symptoms associated with eczema (chronic itchy rash), asthma (wheeze), and allergic rhinitis (rhinoconjunctivitis) in 1026 subjects between 18.5 and 23 months old (median age is 21 months) in Singapore. The first 2 yr cumulative prevalence of chronic itchy rash, wheeze, and rhinoconjunctivitis were 22.1% (n=227), 22.9% (n=235), and 8.4% (n=86) respectively. In total, 42.2% (414 of 979) reported ever having any of these symptoms. Eczema, although prevalent, was diagnosed only in 34.4% (n=78) of children with chronic itchy rash. Children with this eczematous rash were also more prone to wheeze (cOR=2.0, 95% CI: 1.2-3.0) and rhinoconjunctivitis (cOR=2.0, 95% CI: 1.4-2.8). Similarly, subjects who reported rhinoconjunctivitis and chronic itchy rash were 2.4 times (95% CI: 1.6-3.6) and 1.4 times (95% CI: 1.0-2.0) more at risk of wheezing respectively. Family history of allergy was a significant risk factor for chronic itchy rash (aOR=1.8, 95% CI: 1.3-2.4) and wheeze (aOR=1.7, 95% CI: 1.3-2.4). Thus, symptoms related to allergy were already prevalent during the second year of life. Significant proportions of these symptoms are likely to be due to true atopy as strong relationship with familial history and comorbidity with other potential allergic symptoms were observed.