Introduction

Parainfluenza is a group of viruses causing common respiratory infections such as colds, bronchiolitis, and pneumonia. The subtype of parainfluenza that affects humans is known as the Human Parainfluenza Viruses (HPIV). These viruses affect infants differently from adults, leading to more severe illnesses in children aged 5 or under. Understanding how HPIV affects infants differently compared to other age groups helps parents and caregivers increase awareness of the disease, leading to better quality care. This article provides a detailed overview of the distinct challenges HPIV poses to infants, alongside preventative measures and possible treatments.

HPIV impact on infants

Parainfluenza can affect infants to a greater extent than adults. A meta-analysis found that 61% of the HPIV hospital admissions and 66% of the HPIV-related in-hospital deaths occurred in infants below one year of age.¹ Infants between 3 months and 5 years old are most likely to develop croup, characterized by a barking cough, and children under age 2 are more prone to developing lower respiratory tract infections such as bronchiolitis and pneumonia. The more severe risk of complications can be attributed to infants’ weaker immune systems.²

Pathophysiology and transmission of HPIV

HPIVs are enveloped RNA viruses from the Paramyxoviridae family. There are four types of HPIVs, with HPIV-1 being the most likely to occur in children, leading to both upper and lower respiratory tract illnesses such as cold-like symptoms. HPIV is transmitted via direct contact with droplets containing the infectious virus or through the air when the infected person coughs or sneezes. Common symptoms of parainfluenza include fever, sore throat, runny nose, and cough. Other symptoms include ear pain, decreased appetite, and irritability.

More severe symptoms are croup (an infection of the larynx and trachea), bronchitis (an infection of the main air passage), bronchiolitis (an infection in the smaller air passage in the lung), and pneumonia. These severe symptoms are characterized by hoarseness in the throat, wheezing, and a barking cough.³

Why infants are more vulnerable

Infants lack prior viral exposure and immunity, making them prone to the highest infection rates with HPIV. For adults, both innate and adaptive immune systems work together to combat pathogens. When a pathogen invades, the innate immune system responds immediately, while the adaptive immune system develops antibodies to attack the pathogen upon reinfection. Antibodies originate from the adaptive immune system, which is still developing in infants but fully developed in adults. Therefore, infants are more prone to infection and reinfection compared to other age groups.⁴ 

Moreover, infant airways are smaller in physical dimensions—around 120µm for 2-4 months old compared to 250µm in the average adult respiratory bronchiole. This smaller airway size increases the chance of obstruction during viral infection, leading to inflammation and the severe symptoms of HPIV.⁵ Lastly, infants lack health literacy and the ability to advocate for their health concerns, increasing the risk of hospitalization and poorer patient self-care.^6,7

Symptoms and complications

The symptoms of HPIV in infants can range from mild to severe. In many cases, infants may present with fever, nasal congestion, and a cough. However, due to their underdeveloped immune systems and smaller airways, infants are at a higher risk of complications such as croup that can cause significant respiratory distress. In severe cases, HPIV can lead to bronchiolitis and pneumonia, requiring hospitalization. Parents and caregivers should be vigilant for signs of worsening symptoms, such as increased difficulty breathing, a bluish skin colour (cyanosis), or persistent high fever, which would require immediate medical attention.

Prevention strategies

Since HPIV is transmitted via direct contact and airborne droplets, frequent hand washing and wearing a mask when sick are crucial prevention strategies. Avoiding close contact with other people, staying at home while sick, and regular disinfection of surfaces can also help protect others. Breastfeeding is encouraged as breast milk contains antibodies that can help fight off parainfluenza infection in immunocompromised infants. Ensuring that infants receive all recommended vaccinations can also provide some protection against secondary bacterial infections that may occur as a result of HPIV.⁸

Management and treatment

Unfortunately, there is no specific antiviral treatment for parainfluenza. Management of the disease focuses on alleviating symptoms and supporting the infant’s immune system to fight off the infection. For milder cases, keeping a cool mist humidifier in the infant’s room, ensuring they drink plenty of fluids, and administering ibuprofen or acetaminophen to reduce fever and discomfort are common practices. In more severe cases, hospitalization may be required to provide supplemental oxygen, intravenous fluids, and other supportive care.⁹

Importance of early detection

Early detection and prompt management of HPIV are crucial in preventing severe complications. Parents and caregivers should monitor infants for any signs of respiratory distress and seek medical advice if symptoms worsen. Regular check-ups with a paediatrician can help in early identification and management of HPIV, reducing the risk of severe outcomes.

FAQ’s 

What are the first signs of parainfluenza in infants?

The first signs of parainfluenza in infants include fever, nasal congestion, runny nose, and cough. As the illness progresses, symptoms may include ear pain, decreased appetite, irritability, and in severe cases, difficulty breathing.

How can I tell if my infant's condition is worsening?

Signs that an infant’s condition is worsening include increased difficulty breathing, bluish skin color (cyanosis), persistent high fever, wheezing, and severe coughing. If any of these symptoms are observed, seek immediate medical attention.

Can breastfeeding help protect my infant from parainfluenza?

Yes, breastfeeding can help protect infants from parainfluenza as breast milk contains antibodies that can boost the infant’s immune system and help fight off infections.

Are there any long-term effects of parainfluenza in infants?

Most infants recover fully from parainfluenza without long-term effects. However, in severe cases where the infant develops complications like pneumonia, there can be lasting respiratory issues that require ongoing medical attention.

Summary

Parainfluenza poses significant challenges to infants due to their underdeveloped immune systems and smaller airways. Understanding these challenges is essential for parents and caregivers to provide effective care and prevent severe complications. By implementing preventive measures, such as frequent hand washing, wearing masks, and breastfeeding, and by ensuring early detection and proper management of symptoms, the impact of HPIV on infants can be minimized. Continuous research and awareness are needed to develop better prevention and treatment strategies for this vulnerable population.