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<<   作成日時 : 2010/12/14 20:29   >>

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 鉤虫などの腸内寄生虫に感染した子どもは、アレルギーになりにくいという。
 最近数十年でわれわれの環境が無菌的となり、アレルギーと喘息の世界的な増加に寄与して可能性が、「衛生仮説」として提起されている。人生の早期にウイルスなどの病原体への曝露が免疫系を刺激して、通常の感染と戦うモードに、そして温和な物質に過激に反応する傾向を抑制することに役立つ可能性が考えられている。しかし、衛生仮説に矛盾する研究結果も多い。
 ノッティンガム大のJohanna Feary博士らは、腸内寄生虫感染が一般的な南アメリカ、アフリカ、キューバ、ベトナム、トルコで実施された寄生虫感染と子供のアレルギーリスクの間の関連についての21研究を分析した。約29,000人の多くは子どもを対象にしている。大多数は鉤虫、回虫、鞭虫を含む土地蠕虫科に感染していた。皮膚テストでチリダニ、ゴキブリの蛋白質のようなアレルゲンへの反応が、31%低かった。
 発展途上地域で寄生虫感染を抑制することは重要な目標であり続けるが、そうした感染の根絶がアレルギーの増加をもたらす可能性を提起する。
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Parasites may protect against allergies
http://www.reuters.com/article/idUSTRE6B65X420101207

NEW YORK | Tue Dec 7, 2010 3:18pm EST

NEW YORK (Reuters Health) - Children infected with hookworm or other intestinal parasites may be less likely than uninfected children to have allergies, a new research review finds.

The study, published in the journal Allergy, gives some support to the idea that our increasingly germ-free surroundings may be contributing to a worldwide increase in allergies and asthma in recent decades -- a theory known as "the hygiene hypothesis."

It's thought that exposure to viruses and other pathogens early in life may help nudge the immune system toward a normal infection-fighting mode, and away from a tendency to overreact to benign substances, which is the basis of allergies.

Studies so far, however, have come to conflicting conclusions about the hygiene hypothesis. Some, for example, have linked early attendance at daycare, where kids swap germs freely, to a lower risk of developing allergies and asthma -- which would seem to support the hygiene theory. But others have found no such protective effect.

For this latest analysis, Dr. Johanna Feary and colleagues at the University of Nottingham in the UK analyzed 21 previous studies on the association between parasitic infection and children's allergy risk.

The research, which included almost 29,000 people, most of them children, was conducted in South America, Africa, Cuba, Vietnam and Turkey -- regions where intestinal parasite infections are common. The majority of subjects were infected by the geohelminth family of parasites -- which includes hookworm, roundworm and whipworm.

When Feary's team pooled the results of all the studies, they found that participants with any current parasitic infection were 31 percent less likely than others to display reactions when exposed to common allergens like dust mite or cockroach proteins in a skin test.

Such skin responses indicate that the immune system is reacting to the proteins, though that does not necessarily mean the person has a full-blown allergy that might bring on sneezing, congestion or other symptoms with greater exposure to the substance.

The findings also do not prove that intestinal parasites, themselves, are protective against allergies. Further research on the relationship between the two is still needed, according to Feary and her colleagues.

Since allergies are common in developed countries, and on the rise in developing ones, the researchers note, it is increasingly important to understand how environment might be affecting allergy risk worldwide.

Curbing parasitic infections in the developing world remains an important goal, Feary and her colleagues point out. Nonetheless, they add, these findings raise the question of whether eradicating such infections could have the unintended effect of boosting allergy rates in countries where health services are already overstretched.

SOURCE: link.reuters.com/cyb98q Allergy, online November 18, 2010.

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

1. J. Feary, 2. J. Britton, 3. J. Leonardi-Bee
Article first published online: 18 NOV 2010
DOI: 10.1111/j.1398-9995.2010.02512.x
© 2010 John Wiley & Sons A/S

Keywords: * allergen skin sensitization; * atopy; * helminth; * IgE; * parasite

画像To cite this article: Feary J, Britton J, Leonardi-Bee J. Atopy and current intestinal parasite infection: a systematic review and meta-analysis.
Allergy 2010; DOI: 10.1111/j.1398-9995.2010.02512.x00: 00–00.

Abstract

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.

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