Roundworm Exposure  'Overlooked' Risk Factor for Asthma and Poor Respiratory Health

Pavankumar Kamat

January 13, 2022

A study in  Journal of Allergy and Clinical Immunology  suggests that young European men exposed to roundworm (Ascaris lumbricoides) have an increased likelihood of developing asthma and significant lung impairment.

The global prevalence of Ascaris infections is estimated to be more than 10%, with high seroprevalence and infection rates in developing countries. However, data regarding its prevalence in Europe remains scarce.

Lead author Dr William Horsnell, from the University of Birmingham and the University of Cape Town, said: "Parasitic worm infections are typically thought to only be a problem in low- and middle-income countries, but they may potentially be much more important in Europe – they could be an overlooked risk factor for asthma and poor respiratory health."

Study Design and Results

Researchers at the Universities of Birmingham, Bergen, and Cape Town explored the associations of Ascaris exposure with lung function, asthma, and DNA methylation in 671 adults (age 18-47 years; 46% women) from Norway, Estonia, and Denmark who participated in the RHINESSA study. Participants were considered seropositive if they had serum Ascaris IgG antibodies above the 90th percentile.

Ascaris IgG seropositivity in men was linked to lower FEV1 (-247 mL; 95% CI -460 to -34), the effect size being more than that of current smoking (-151 mL; 95% CI -501 to 199). Seropositive men demonstrated 5% lower predicted FEV1 and 4% lower FEV1/FVC ratio than their seronegative counterparts; women failed to show this pattern.

Men with Ascaris IgG seropositivity had an increased risk of developing asthma (adjusted OR [aOR] 5.84; 95% CI 1.67 to 20.37), wheezing (aOR 3.78; 95% CI 1.85 to 7.74), and experiencing three or more asthma symptoms during the past year (aOR 3.59; 95% CI 2.01 to 6.47) compared with seronegative men. Conversely, women had a lower risk of asthma, wheezing, or three or more asthma symptoms in a year. These associations for men and women remained unchanged after adjusting for house dust mite sensitivity.

Role of DNA Methylation Changes

Genome-wide analyses revealed 23 differentially-methylated sites in men and 3 in women associated with Ascaris seropositivity. These sites were related to lung pathology, including airway muscle contraction, asthma pathogenesis, and immune regulation.

Dr Horsnell said: "Exposure is possibly much more common than expected and may result in serious lung damage that could lead to long-term breathing problems – particularly for young men who are exposed to Ascaris."

Co-author, Dr Nils Oskar Jõgi, University of Bergen, added: "Such infections warrant the development of new diagnostical awareness. We hope this discovery will boost efforts to understand how parasitic worm infection influences the development of serious respiratory conditions in both developed and developing countries."

The authors call for further research to better understand the influence of helminths on long-term lung health.

The RHINESSA study was funded by the Research Council of Norway, the European Research Council Starting Grant, the European Union’s Horizon 2020 research and innovation program, the Bergen Medical Research Foundation, and the Western Norwegian Regional Health Authorities. The study centres also received additional local funding. The authors report no conflicts of interest.

Jõgi NO, Kitaba N, Storaas T, Schlünssen V, Triebner K, Holloway JW, Horsnell WGC, Svanes C, Bertelsen RJ. Ascaris exposure and its association with lung function, asthma, and DNA methylation in Northern Europe. J Allergy Clin Immunol. 2021 Dec 14 [Epub ahead of print]. doi: 10.1016/j.jaci.2021.11.013. PMID: 34996616 Full text



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