Updates about the novel Coronavirus, SARS-CoV-2, and the disease it causes, COVID-19, keep pouring in. Everyone is just trying to understand the infectious agent and what it does to the human body in order to learn how to better approach the disease and prevent complications. Most recently, there have been reports of an unusually low prevalence of asthma in COVID-19 patients, or lower than initially presumed when compared to other comorbidities which raise risks of Coronavirus-related complications. The preliminary findings have sparked interest in the subject of asthma and risks of COVID-19 infection and related complications.
By definition, asthma is a chronic inflammatory condition of the respiratory system. Asthma affects the lower respiratory system, that is, the lungs and lower airways (trachea, bronchi, bronchioles and alveolar ducts, sacs and alveoli). Asthma causes inflammation of the components of the lower respiratory tract and subsequent narrowing of the airways. This results in symptoms such as coughing, wheezing or other unusual breathing sounds, shortness of breath, feeling like you are not getting enough air, laryngospasms, a feeling of chest tightness and, ultimately, closing of the airways.
Asthma causes and triggers include allergens (e.g. pollen, dust, dust mites, pet hair, mold), irritants (e.g. perfume, scented cleaning products, any strong odors), respiratory tract infections and even exercise, stomach acidity from acid reflux disease and stress (e.g. stressful events can act as triggers for asthma). Asthma is generally a major risk factor for complications in respiratory tract infections. Despite this, there is currently no evidence that asthma is a risk factor for complications in COVID-19 which is surprising news to say the least since the novel Coronavirus infection causes lung involvement in both moderate and severe cases which would be expected to impact asthma sufferers in particular.
COVID-19 is reported to be made worse by virtually every chronic condition, most notably high blood pressure and diabetes (source 1, source 2), but also obesity, chronic obstructive pulmonary disease or COPD, cancer (and cancer treatment) and most forms of cardiovascular and cerebrovascular disease. But it would appear that asthma is not one of the conditions that most predispose to complications, as it was previously thought. Not just that, but asthma may even represent a somewhat protective factor in COVID-19, a tentative statement that adds to the shock of our current situation.
At the beginning of the COVID-19 pandemic, we were warned that conditions such as hypertension, diabetes mellitus and asthma and other chronic respiratory conditions would increase risks of the novel Coronavirus infection. No studies were done specifically on COVID-19 and hypertension, diabetes or asthma – the cautionary advice for those with such conditions was inferred from data on more or less similar human pathogens (e.g. influenza viruses, common cold Coronaviruses, SARS Coronavirus). But it made sense at the time that a viral infectious agent such as SARS-CoV-2, which affected the lungs, would also affect those with respiratory issues impacting the lungs such as asthma.
Asthma and COVID-19 risks
Emerging research appears to indicate that having asthma does not increase risks of the novel Coronavirus infection. Moreover, neither asthma nor asthma treatment consisting of inhaled corticosteroids have been proven to cause severe forms of COVID-19. Preliminary reports show asthma (and COPD, chronic obstructive pulmonary diseases) are not prevalent in COVID-19 patients which would suggest that risks for COVID-19 infection in asthma sufferers are either roughly the same as they are for otherwise healthy individuals, or possibly even lower.
The main concern with asthma and respiratory infections in general is that asthma causes inflammation in the lower respiratory tract (lungs and airways) which ultimately restricts normal breathing. A respiratory infection would build on the existing inflammatory foundation and amplify the side effects to the point of severe complications. Another concern is with asthma medication, notably corticosteroids which are known to lower the immune system. A lowered immune system normally creates a predisposition for other infections, including COVID-19. But it would appear that neither asthma nor asthma medication increase risks of infection with the novel Coronavirus, or risks of complications in COVID-19.
Because asthma appears to be an underrepresented comorbidity in COVID-19 patients, it has given rise to the theory that asthma may potentially represent a protective factor with regards to risks of contracting the novel Coronavirus infection or developing severe forms of COVID-19.
- One working theory is immune system involvement, notably the excessive immune system response that occurs naturally in asthma sufferers with an allergic background. That is, an overzealous immune system response takes timely care of the infection, resulting in disease with few to no symptoms.
- Another theory is that asthma medication mediates COVID-19-related inflammation which prevents cytokine storm-type events that ultimately cause tissue and organ damage responsible for severe COVID-19 complications such as lung tissue injury, heart muscle injury etc. Find out more about what COVID-19 does to the body.
Asthma medication and COVID-19
Having asthma does not appear to increase COVID-19 risks, as it was previously thought. But what is the deal with asthma medication and COVID-19? Asthma medication lowers the immune system with the purpose of reducing excessive inflammation. Inflammation is a normal immune system response, but conditions such as asthma cause excessive inflammation.
Excessive inflammation in COVID-19 causes ‘cytokine storm’-type events brought on by immune system cells infiltrating the lungs, heart muscle and other organs and producing excessive inflammation and subsequent damage. This ultimately lead to tissue and organ damage and side effects such as lung tissue damage, heart muscle damage, damage to blood vessels, respiratory failure, cardiovascular events and multiple organ failure.
For the most part, asthmatics are on top of their treatment with corticosteroids, a type of medication that lowers the immune system to prevent excessive inflammatory responses. This helps them control their symptoms and avert asthma attacks. But it also has been theorized to hold benefits for COVID-19 infections by mediating excessive immune system involvement that creates ‘cytokine storm’-type events that build up to tissue and organ damage and severe complications. Which could potentially represent a protective factor against complications seen with other comorbidities.
ACE2 receptors and asthma
ACE2, the angiotensin-converting enzyme 2, has been brought to the attention of the general population quite early in the COVID-19 pandemic as the point of entry into cells of the novel Coronavirus, SARS-CoV-2. Research has revealed the brain and nervous system, intestines and digestive system, heart and cardiovascular system and nose, lungs and respiratory system as the organs and systems most susceptible to infection with the novel Coronavirus, which is in line with the types of complications described in COVID-19 patients. What have all of these in common? Answer: high expression of the angiotensin-converting enzyme 2, or ACE2.
Basically, ACE2 acts as a receptor for the novel Coronavirus. What this means is that a protein in the novel Coronavirus SARS-CoV-2 binds to healthy cells in the human body via the ACE2 receptor. The higher the expression of ACE2 on the surface of cells in various tissues, organs and systems in the human body, the more affected these tissues, organs and systems are by infection with the virus. Hence COVID-19 symptoms such as headaches, loss of smell and taste, brain inflammation (encephalitis), nausea, diarrhea, arrhythmia, high blood pressure, inflammation of and injury to the heart muscle (viral myocarditis), sore throat, dry cough, pneumonia, lung tissue injury, Coronavirus-related lung function impairment and respiratory failure.
But recent reports testing for ACE2 levels in confirmed COVID-19 patients revealed lower levels of ACE2 expression in children with higher allergies and asthma severity, adults with allergies and adults with mild forms of asthma. This is regarded as a potential reason for why asthma sufferers do not have a higher prevalence of infection with the novel Coronavirus infection, or higher risks of complications from COVID-19. However, ample research is needed to confirm these preliminary reports.