Can early infection explain the sibling effect in adult atopy?

Abstract

Atopy is strongly and inversely related to family size, a pattern which is plausibly assumed to reflect a protective effect of early infection. The current study tested this hypothesis by case-referent analysis of an adult cohort in the UK.The study established that atopy, defined by prick tests to common aeroallergens, was less common among those from larger families after adjustment for potentially confounding factors. In particular, a higher number of brothers appeared to offer protection. The current authors attempted to explain this distribution by examining contemporary family-doctor records of early childhood infections; and by a number of other indirect indices of early-life "hygiene".The sibling effect was unexplained by evidence of infection with either hepatitis A or Helicobacter pylori, or by counts of infections or antibiotic prescriptions in early life. There was a significant and independent negative association between the number of gastrointestinal infections before the age of 5 yrs and the odds of atopy. Dog ownership and home moving in early life also displayed potentially protective associations.Although the current study replicates the finding that atopy is inversely associated with family size this could not be explained by documentary or serological evidence of early infection. The findings support the suggestion that the "sibling effect" in atopy may not simply reflect protection by early infection. Eur Respir J 2003; 22: 956-961.

Parasitic Helminths as Potential Therapeutic Agents Against Autoimmune Disorders

“…The "sibling effect", that children with more siblings have a lower risk of developing atopic disorders (Strachan, 1989), is the basic finding that the hygiene hypothesis comes from. The sibling effect on atopic disorders has been demonstrated in cohort studies (Benn et al, 2004;Matheson et al, 2009;Cullinan et al, 2003). A similar effect was reported in case of T1D (Cardwell et al, 2008a) and IBD (Koloski et al, 2008).…”

“…Therefore, the geographical distribution and/or chronological transition of some autoimmune diseases cannot be explained by the hygiene hypothesis. For atopic disorders, the sibling effect itself has been confirmed (Benn et al, 2004;Matheson et al, 2009;Cullinan et al, 2003). However, some authors suggest that infections in early life do not explain the observed sibling effect (Benn et al, 2004;Cullinan et al, 2003).…”

“…For atopic disorders, the sibling effect itself has been confirmed (Benn et al, 2004;Matheson et al, 2009;Cullinan et al, 2003). However, some authors suggest that infections in early life do not explain the observed sibling effect (Benn et al, 2004;Cullinan et al, 2003). In a report on the preventive effects of endotoxins against AD (Flohr et al, 2005), apparent infections in early life were shown to increase the risk of AD.…”

Allergies, infections and the hygiene hypothesis – The epidemiological evidence

“…These studies have, however, brought up conflicting evidence. A number of surveys have shown protection of allergy whereas others could not confirm these results (Jarvis et al, 2004;Bodner et al, 2000;Cullinan et al, 2003). Hepatitis A might just be a marker of unhygienic environmental exposures rather than being a true culprit of the association.…”

Parasite immunomodulation in autoimmune disease: focus on multiple sclerosis

“…Epidemiological evidence is strong, particularly with the dichotomous response seen by Fleming and Cook where a threshold infection prevalence of 10% of Trichuris trichiura appeared to suppress MS risk [15]. Strong associations are seen geographically, where the areas with the highest helminth burdens tend to be those with lowest autoimmune and allergic conditions, and in studies correlating allergic symptoms in childhood with exposure to factors such as farms, dogs, cats or overcrowding [16][17][18][19], any or all of which one could argue to be useful as surrogates for potential helminth infection. Similarly, a German study demonstrated a reduced risk of inflammatory bowel disease in subjects who spent greater amounts of time outside as part of their occupation [20].…”