Allergic Diseases are one of the three most common reasons why patients visit their family physician. Respiratory diseases represent more than 25% of all visits to general practitioners and about 80% of patients with recurrent presentations are found to be allergic. Allergy is a Greek word (allos=other and ergos = reaction) and allergen is a protein. Allergy prevalence is higher in children in comparison to adults. Allergy can affect any organ system. Common types of presentations include conjunctivitis(eyes), rhinitis (nose), urticaria and angioedema or atopic dermatitis (skin), asthma (lungs) and anaphylaxis (multiorgan).
Allergies are becoming more complex. Most of the patients with allergies have involvement of multiple organs, ie. multiple allergic diseases in the same patient. Children with allergies will do badly at schools or have asthma attack or anaphylaxis which could be life threatening. Allergic diseases affect quality of life in day to day basis.
Allergic patients have genetic risk factors which increase their risk of sensitization against different allergens. In other words, sensitization to different allergens is a prelude to the development of clinical allergies in different age groups. Early sensitization to inhalant allergens predicts development of wheezing and asthma until adolescence.
The development of sensitization needs a multifactorial interplay of various host factors such as genetic predisposition, immunologica pathways skewed toward the Th2 phenotype, and a gut microbiome with predominant Firmicutes and less of Xylanibacter and Prevotella of the Bacteroids species, and environmental factors including diet, early life exposures related to the hygiene hypothesis, allergen characteristics and load, and parasitic infestations.
Genetics of Sensitizations
It was discovered in the early 20th century that allergies and asthma were heritable. Hopp estimated that around 50% of the risk of developing allergies was genetic and other half due to environmental exposures.
Diet And Sensitizations
Evidences show that diet plays a major role is allergic sensitization. Some studies who evaluated supplemented Vit D3 in maternal diet showed decreased risk of sensitization to children up to 5 years of age. Similarly increased diet rich of pre and probiotics in children’s diet is found to decrease development of allergies in later life. Westernized, fast food culture has replaced traditional eastern diet in our part of world which could also justify the increasing prevalence of allergic diseases.
Gut microbiome and Sensitization
90% of the cells in the human body are not human but part of the microbiome, ie bacterial cells in the skin , oral cavity and the gut. There is strong evidence that diet influences the gut microbiome. With the changing diet habits the microbiome of intestines in children is changing accordingly. But to our disappointments changing microbiome is leading to shift of Th balance towards Th2, increasing risk of allergic diseases.
Bacterial infection, parasitic infestation and Sensitization
Few studies have shown that prior infection with helminthes, tuberculosis, Hepatitis A, Toxoplasma etc lowers the risk of development of allergic diseases. It favors the hygiene hypothesis. The hygiene hypothesis proposed that a reduced stimulation of the immune system by microbial infections and parasitic infestations due to better sanitation, use of antibiotics, and various lifestyle factors including a change in the diet, use of antiseptics and decreasing number of siblings has contributed to increase in sensitization.
Pet ownership and sensitization to pets
There are conflicting evidences regarding early introduction to pets and decreased sensitization to pets. Some of shown protective effect of early introduction to pets, while other have predicted an allergic response in children who are already at risk.
Cigarette smoking and Sensitization
Cigarette smoke and diesel particle exposure are known to be responsible of development of allergies. It not only limits the airways structurally but immunologically it decreases the number of Th cells and indirectly influencing increased risk of allergic sensitization.
Lifestyle factors including stress , ETS exposure is believed to cause epigenetic changes which increases allergic sensitization
More awareness are required to prevent, timely diagnose and provided evidence based treatment to children suffering from allergies in Nepal.