Most of us have experienced seasonal allergies caused by common triggers like pollen, grass, mould, etc. An allergic reaction is usually an over-the-top reaction of your body to an otherwise harmless foreign substance. Common symptoms experienced include sneezing, coughing, itchy and runny nose and nasal congestion. But did you know sometimes these allergic reactions can be caused by viral infections too? 

One such viral infection that can trigger allergic reactions among people is the adenovirus infection. Adenovirus is a group of common viruses that can cause mild to severe respiratory infections. It can cause infections ranging from a simple common cold to severe bronchitis or pneumonia. In many patients, certain allergic reactions like worsening asthma symptoms or eczema flare-ups are observed after an adenoviral infection.

If you ever experience any symptoms of an allergic reaction, consulting your family doctor is recommended to get quick relief and avoid any further complications associated with the allergy. This article discusses at length, the potential link between adenovirus and allergies and ways to manage and prevent the same.

Introduction

Adenovirus belongs to a group of large non-enveloped double-stranded DNA viruses and are responsible for causing various different infections. Without much seasonal variation, the adenoviruses cause self-limited respiratory, gastrointestinal (GI), or conjunctival disease throughout the year. They are highly contagious and spread through close personal contact, respiratory droplets, and contaminated surfaces. Preventive measures include good hygiene practices and avoiding close contact with infected individuals.¹ 

Common infections caused by adenovirus

There are a variety of infections caused by different types of adenoviruses. Respiratory infections like the common cold, pneumonia, bronchitis, etc., are the most common and are caused by numerous types like adenovirus type 4 (Ad4), type 7 (Ad7), type 14 (Ad14) and type 21 (Ad21). Many of these types are also responsible for respiratory infection outbreaks in military settings. 

Other infections caused by adenovirus include conjunctivitis, pharyngoconjunctival fever, keratoconjunctivitis, gastroenteritis and acute hemorrhagic cystitis. Ad3 type is the one that causes pharyngoconjunctival fever. Ad40 and Ad41 are commonly associated with gastroenteritis, leading to diarrhoea and vomiting in children, and Ad8 frequently causes epidemic keratoconjunctivitis, a severe eye infection.² 

Allergic reactions

An allergic reaction or allergy can be defined as a body’s immune response to any foreign substance in the environment. It is usually an exaggerated response to an otherwise inert substance called an allergen. It induces the formation of antibodies in the body which then give rise to a plethora of symptoms in patients.³ 

Common triggers and symptoms

Common triggers for an allergic reaction include pollen, dust mites, mould, pet dander, insect stings, certain foods (like peanuts, shellfish, and eggs), and medications (such as penicillin). Symptoms vary but often include sneezing, runny or congested nose, itching, hives, and swelling. Respiratory symptoms like wheezing and shortness of breath can occur, particularly in asthma sufferers. Severe reactions, or anaphylaxis, can cause throat swelling, difficulty breathing, rapid pulse, dizziness, and a drop in blood pressure, requiring immediate medical attention. Managing allergies typically involves avoiding known triggers and using medications like antihistamines or epinephrine for emergencies.³ 

Adenovirus and immune response

Mechanism of adenovirus infection

How does adenovirus enter the body?

Adenovirus enters the body primarily through the respiratory tract and is transmitted via inhalation of infected droplets from coughs or sneezes. Close personal contact with an infected person, or touching an object or surface with adenoviruses on it, then touching your mouth, nose, or eyes before washing your hands can also spread the infection among people. Additionally, adenovirus can spread via the faecal-oral route, particularly in settings with poor hygiene, leading to gastrointestinal infections.⁴ 

Immune system's response to adenovirus

The immune system recognises the adenovirus that has entered the body as a foreign antigen and develops a response to curb its rapid multiplication and clinical manifestations. The immune system senses adenovirus invasion from the moment it enters the bloodstream. 

Firstly, the viral antigen activates the T-cell, via the antigen-presenting cells (APCs). The T-cells then target and destroy infected cells and also stimulate the B-cells to produce specific antibodies. These antibodies neutralise the virus, preventing it from infecting more cells. Additionally, the release of chemicals like cytokines and interferons leads to inflammation.⁵ 

Potential link between adenovirus and allergic reactions

Case Studies and clinical reports

Instances of allergic reactions post-adenovirus infection

Although adenovirus infections usually result in respiratory, gastrointestinal, or eye-related symptoms, there are many instances where allergic reactions have been recorded post-infection. These can manifest as asthma exacerbations, allergic rhinitis, eczema flare-ups, or conjunctivitis.

Asthma exacerbations

Asthma exacerbation is an allergic reaction that involves episodes of worsening asthma symptoms and lung functions. It is usually seen as a manifestation of a trigger like a viral upper respiratory infection.⁶ A study published in 2009 also links severe asthma exacerbations in children requiring hospitalisation with viral infections caused by respiratory viruses like adenovirus. They also linked these underlying interactions between immunoinflammatory pathways related to responses to the virus.⁷ 

Another literature review published in 2018 shows a regional and age-specific prevalence of respiratory viruses with asthma exacerbations. Among the many respiratory viruses that were included in the review, one was adenovirus. The primary outcome proved that adenovirus has a mean prevalence of 3.8% with asthma exacerbations.⁸ 

Allergic rhinitis

Allergic rhinitis, also called seasonal allergies, involves symptoms like sneezing, and nasal congestion along with itchy and watery eyes. Certain people may experience all these symptoms after an adenovirus infection. 

A review published in 2014, shows an evident relationship between allergic rhinitis and viral infections. Viral infection may contribute to the initiation and aggravation of allergic rhinitis.⁹  The study by Alho et al. in 2003 showed that individuals with allergic rhinitis had significantly higher computerised tomography (CT) scores compared with nonallergic individuals during the common cold caused by viruses like adenovirus. The high CT score is associated with both serum IgE antibody levels and nasal eosinophil counts.¹⁰ 

Eczema flare-ups

Eczema, also known as atopic dermatitis, is a condition that causes the skin to become dry, itchy and bumpy. Individuals who are diagnosed with eczema may notice worsening skin conditions following an adenovirus infection. 

A study was conducted among children hospitalised from June 2018 to December 2019 for human adenovirus pneumonia (HAdV). They were divided among atopic with HAdV, non-atopic with HAdV, and atopic without HAdV infection groups. The results showed that the eosinophil count in the atopic group was significantly higher than that in the non-atopic groups.¹¹ This study shows a link between adenovirus infection and atopic diseases like eczema.

Conjunctivitis

Conjunctivitis occurs due to inflammation of a part of the eye called the conjunctiva. There are three main causes of conjunctivitis, namely, viral, allergic, and bacterial. Out of which, viral conjunctivitis is majorly caused due to adenovirus infection. A study conducted in Beijing, China between the years 2011-2013 shows that out of 876 conjunctivitis cases, 39.8% of patients among the age group of 18-40 were HAdV positive.¹² This study shows a link between adenovirus infection and conjunctivitis.

Implications for public health and medicine

Diagnosis and management

Diagnosis of an adenovirus infection involves clinical evaluation of the patients where the physicians assess the symptoms and medical history, focusing on recent infections and possible allergen exposures. Laboratory testing for adenovirus infection is also performed in a clinical setting using antigen detection or polymerase chain reaction (PCR) testing. Adenovirus genotyping is possible and usually done by molecular methods like full, or partial genomic sequencing.⁴ 

Furthermore, allergic reactions can also be managed by certain medications that include antihistamines, corticosteroids, bronchodilators and topical ointments for eczema. Certain immunotherapy options are also available for patients.¹³ 

Vaccination and prevention

Adenovirus vaccines are available primarily for military personnel that target adenovirus types 4 and 7. These vaccines help prevent respiratory illnesses caused by these virus types, potentially reducing the risk of subsequent allergic reactions triggered by these infections. However, currently, there are no widespread vaccines available for the general public.⁴ 

Hence, prevention is the best option to avoid viral infection and the associated risk of developing allergic reactions. Good hygiene practices, regular disinfection of surfaces, staying away from infected individuals and boosting immunity through proper nutrition, regular exercise, and adequate sleep can mitigate the impact of infections and allergic reactions.

FAQs

1. When do adenovirus symptoms peak?

Ans: Adenovirus infections can occur during any time of the year but they tend to peak during winter and early spring.

2. What age group is at risk for adenovirus?

Ans: Adenovirus infections are most common among children of age 6 months to 2 years. Most children have had at least one adenovirus infection by age 10.

3. How long does it take to recover from adenovirus?

Ans: Most children recover from the infection within a few days. Certain conditions like conjunctivitis may take a week or more as well.

Summary

• Adenovirus is a group of viruses that is responsible for causing mild to severe respiratory infections like common cold, bronchitis, croup or pneumonia
• Sometimes, allergic reaction is also experienced by patients post adenovirus infections that include asthma exacerbation, allergic rhinitis, eczema and conjunctivitis
• There are many instances and studies conducted that show ample evidence for adenovirus being the cause of allergic reactions; however, further research is required to completely understand the correlation and the pathogenesis
• Vaccines are available for certain types of adenovirus but only for military personnel, therefore, medications and prevention of the disease itself are the best options for the management of the same.