Introduction
Asthma is the most common chronic disease of childhood in high-income
countries and is estimated to affect 358 millions
worldwide.1 Asthma is increasing in prevalence in many
low and middle-income countries (LMICs).2 Temporal
trends of increasing asthma prevalence in LMICs are considered to be
related to urbanization and loss of protective exposures associated with
rural residence.3
Recent years have seen increasing urbanization in LMICs, accompanied by
reductions in poverty, improved access to basic services, and
transformation of the living environment.3 Under such
circumstances, the intensity of microbial exposures in early childhood
is likely to have declined, affecting the maturation and regulation of
the immune system and risk of inflammatory diseases including
asthma.4,5
Geohelminths (caused by Ascaris lumbricoides , Trichuris
truchiura , and hookworm) infect over 1 billion humans
worldwide6 and are most prevalent among children
living in conditions of poverty in tropical regions of LMICs.
Geohelminths cause chronic infections that are associated with
modulation of host Th2 inflammatory mechanisms.7 The
tight regulation of Th2 inflammatory responses may modulate inflammation
associated with allergy and asthma. It has been suggested that the lower
prevalence of asthma symptoms observed in rural compared to urban
populations in tropical regions of LMICs3 is explained
by the immune modulatory effects of endemic geohelminth
infections.5
Epidemiological studies of the relationship between geohelminths and
allergic inflammation (measured by atopy) or asthma have shown
conflicting findings in cross-sectional analyses and intervention
studies done largely in schoolchildren.8-14 We
hypothesized that in utero or early childhood exposures to
geohelminths protect against the development of atopy and asthma in
later childhood. To test this hypothesis, we followed an Ecuadorian
cohort from birth to 8 years of age in an area of high endemicity.
Previous analyses from the cohort showed a protective effect of maternal
geohelminths on atopy to mite allergens at 3 years.15At 5 years, we observed that maternal infections increased the risk of
wheeze while childhood infections protected against wheeze and atopy to
perennial aeroallergens, and raised the possibility that childhood
infections might modulate wheeze through non-allergic
mechanisms.16
To understand better the effects of early childhood geohelminth
exposures on wheeze, asthma and atopy, and whether the previously
observed effects persist, we report findings at 8 years including novel
measurements of airways inflammation and reactivity to provide further
insights on effects of geohelminths on non-atopic wheezing illness and
asthma.