Introduction

Infections of the respiratory tract can affect individuals of all age groups commonly causing symptoms such as cough, fever, sore throat, and stuffy or runny nose. Such viral infections may have a significant impact on people with long-term breathing issues, such as asthma. The general term parainfluenza is used to describe different types of human parainfluenza viruses (HPIVs) that can cause viral infections in the upper and lower respiratory tracts. The upper respiratory tract refers to the nose, sinuses, throat and larynx (voice box). The lower respiratory tract consists of the trachea (windpipe), bronchi (smaller branches of the windpipe) and the lungs). They frequently affect young children, individuals with a weakened body’s defence system, and the elderly.¹ Asthma, on the other hand, is a chronic condition represented by swelling and constriction of the airways, leading to symptoms such as shortness of breath and wheezing, and in more severe cases can be life-threatening.²

The correlation between parainfluenza and asthma has not yet been explored in depth; though there are cases where asthmatic patients presented exacerbations associated with HPIV infections. According to a specific study on numerous asthmatic patients, viral-induced deteriorations were present in 3.6% of cases. Another smaller study stated a percentage of 60% of a certain type of HPIV infection in asthmatic adults that exhibited exacerbations. Moreover, research has shown that asthmatic children have a greater likelihood of contracting viral infections, with HPIV being detected in 2.8% of the cases.³

While epidemiological data potentially links HPIV with asthma exacerbations, further animal and human studies are necessary in order to unwind the mechanisms of this involvement.

Information on parainfluenza

The human parainfluenza viruses are RNA viruses belonging to the family of Paramyxoviridae. They can be subdivided into four serotypes- HPIV-1 to HPIV-4, each with unique characteristics and each responsible for causing diverse symptoms, affecting individuals from different age groups. Some of the respiratory system illnesses caused by HPIV include the common cold, croup, bronchitis, bronchiolitis, and pneumonia. Younger children and immunosuppressed people may experience more severe cases which may necessitate hospital care, compared to healthy adults. HPIV can also lead to worsening of chronic illnesses, such as asthma, chronic obstructive pulmonary disease, and congestive heart failure.³

Generally, there is not a particular antiviral agent effective against the virus, and treatment of parainfluenza infections focuses on the management of symptoms. In the case of more severe diseases, medications such as corticosteroids may be used. Furthermore, a novel medication is currently under investigation, which exhibits an antiviral action by blocking a specific step on the viral pathway in the respiratory tract. This agent can potentially be used in immunosuppressed patients who are at higher risk of developing more serious complications, particularly associated with the serotype HIPV-3.¹

Information on asthma

Asthma is a chronic respiratory disease that affects the normal function of the respiratory tract. Despite being one of the most common respiratory problems, affecting around 10% of children and 5% of adults, there is still no definite treatment for asthma. Its management depends on the proper use of antiasthmatic agents and adherence to the directions of healthcare professionals. 

Factors responsible for triggering asthma are believed to be tobacco smoke, air pollution, pets, and other allergens. These irritants can cause inflammation in the airways, leading to the secretion of mucus, swelling of the membranes, and constriction in the airway passage. Characteristic symptoms of an asthma attack include cough, wheezing, shortness of breath, and chest tightness, which in some cases can be life-threatening.⁴

Managing asthma is predominately achieved by using bronchodilator inhalers, which rapidly relieve asthma symptoms by opening the airways and improving breathing. Commonly used bronchodilators are β2-agonists, including salbutamol and albuterol. In addition, other medications such as nonsteroidal anti-inflammatory drugs and inhaled corticosteroids are used, offering their anti-inflammatory and anti-allergic activities.⁴

How does parainfluenza affect asthma?

Parainfluenza, like other viruses, cannot only trigger asthma but also more severe asthma attacks, increasing the risk of hospitalisation. Children are keener to develop exacerbations, possibly due to the fact that their immune system is still developing its defence mechanisms against viruses. Notably, the main culprit for these detectable severe cases is the body's response to infections rather than the virulence of the viruses.⁵

Exacerbation of parainfluenza-related asthma

The epidemiological studies conducted on the cases of parainfluenza-induced asthma exacerbations indicated that they are not as frequent as when occurring due to other viruses, such as rhinoviruses. The exact mechanism of this interaction is still unclear, however, the increased susceptibility of asthmatic patients to infectious episodes is considered to be a crucial factor in the progression of more severe forms of symptoms. In patients with asthma, the normal function of the immune system is often compromised, exhibiting defects in interferons (IFN), a family of important signalling proteins which fight viruses. Additionally, a delay in the response to the infection, due to genetic factors, may result in elevated and continuous inflammation of the epithelium and thus might worsen the asthma attacks.⁶ The epithelium of the airways contains cells that form a structural barrier, which acts as a line of defence against viral penetration. In the case of asthma as well as other allergies, this barrier may get damaged, and if a viral infection occurs, it may result in a higher release of inflammatory cytokines and mediators, increasing the possibility of severe symptoms of asthma.⁷

Parainfluenza as a potential risk factor for asthma onset

While parainfluenza seems to worsen asthma, it can also cause asthma in individuals who do not have asthma to begin with. According to specific studies, respiratory infections due to HPIV  have the potential to predispose a child to develop asthma in later life.³

The mechanisms by which parainfluenza may trigger the onset of asthma include various changes in the processes and components of the immune system to a viral infection. Parainfluenza may cause the release of pro-inflammatory cytokines, which can induce allergic inflammation, eosinophilia, and mucous production, contributing to the development of asthma. Specifically, the virus acts by mediating different types of immune mechanisms (including type 2 inflammation), leading to symptoms of asthma. The interaction itself between viruses and immune cells, such as macrophages, T-cells, and mast cells, is also another important factor to be considered for potentially amplifying asthma initiation. Ultimately, the airway microbiota is believed to be influenced by parainfluenza infections. Modifications in the composition of the microbiota, as well as disruptions in the integrity of the epithelial barrier caused by infections, can further aggravate the symptoms of asthma.⁸

Treatment strategies of parainfluenza infection in asthma

The management of HPIV in asthmatic patients primarily involves the use of antiasthmatic drugs, which aim to prevent and treat severe exacerbations. 

1. Antiviral therapy: This kind of treatment may not be specific but the use of novel antiviral agents is suggested to hinder HPIV infections⁸
2. Inhaled corticosteroids: These medications target inflammatory cells within the epithelium of the airways, and aim to slow the production of proinflammatory cells. Their use is an important part of maintenance therapy for keeping asthma regulated⁶
3. Biologic medications: These agents acting against type 2 inflammation, are commonly used and are efficient in reducing the rate of asthma exacerbations. They also have been found effective in ameliorating the response of the organism to viral infections⁶
4. Inhaled IFN-β: Although still under investigation, these agents may potentially be considered helpful in severe asthma deterioration by blocking the pathways and life cycle of the viruses⁶

Summary

In summary, parainfluenza refers to the group of HPIVs responsible for causing upper and lower respiratory tract infections, particularly observed in young children, immunocompromised people, and the elderly. Asthma is a common chronic condition, characterised by “asthma attacks”, involving inflammation of the airways, mucous production, and difficulty in breathing. 

Although not as commonly as other viruses, HPIV may cause aggravations in asthma attacks, with various explanations being proposed for this correlation. The persistent inflammatory state of the airways, the altered immune pathways with increased production of proinflammatory cytokines and decreased release of cells that attack viruses, along with specific genetic factors, are some of the typical characteristics of patients with asthma. These clinical aspects of asthmatic patients may enhance their susceptibility to viral infections, and potentially result in asthma exacerbations. Furthermore, HPIV may be responsible for not only causing severe asthma attacks but also the initiation of asthma in predisposing individuals. The management of asthma exacerbations associated with parainfluenza infections is not yet standardised but can include the use of corticosteroids, antiviral agents, and biological drugs. 

If you have asthma, it is imperative to adhere to your doctor’s suggestions and monitor your symptoms to keep the condition under control. Since specific therapies for more severe symptoms due to parainfluenza are still lacking, it is important to properly diagnose and effectively manage asthma with proper medications beforehand, allowing you to live a normal life.