What to Know About Human Parainfluenza Viruses

Medically Reviewed by Dany Paul Baby, MD on August 25, 2022
Written by Sarah Vallie
5 min read

If you’re a parent or work in the field of childcare, you probably know that children are little germ factories. Illness can spread through a daycare or preschool like wildfire, no matter how many precautions you think you’ve taken. 

One common category of illness that young children develop because it spreads so easily is human parainfluenza viruses.

Human parainfluenza viruses, or HPIVs, are a category of viruses that cause respiratory infections. They are most common in children. There are four different types of human parainfluenza viruses: HPIV-1, HPIV-2, HPIV-3, and HPIV-4. They can each cause respiratory infections and illnesses.

Croup. Croup is a condition known for its barking cough. Coughing and breathing difficulties are caused by swelling around the voice box, windpipe, and bronchial tubes as a result of an infection in the upper airway. Croup is caused by HPIV-1, whereas HPIV-2 accompanies croup less often.

Upper respiratory infections. Upper respiratory infections are infections within your sinuses and throat. These can include conditions like a common cold, sore throat, sinus infection, epiglottitis, and laryngitis. 

Epiglottitis refers to inflammation and swelling of the epiglottis, the thin flap that prevents food and drinks from going down your windpipe. Laryngitis is inflammation of the voice box, or larynx.

Lower respiratory infection. Lower respiratory infections occur in the lower respiratory tract, including the lungs. Common lower respiratory infections include influenza, bronchiolitis, and pneumonia. Bronchiolitis is an infection of the bronchioles, the small passages that air flows through to get to and from the lungs. Pneumonia is inflammation in the air sacs of the lungs caused by infection. 

Respiratory infections can be caused by all types of human parainfluenza viruses. HPIV-1 is most often associated with croup, while HPIV-3 is most often associated with lower respiratory infections like bronchiolitis, pneumonia, and bronchitis.

Human parainfluenza viruses are very contagious. They’re passed when you come into contact with infectious secretions, such as fluids in runny noses and sneezes. Sneezes are the most common way parainfluenza viruses are transmitted. 

Most children will have developed a parainfluenza virus by the time they turn five. Some infections are more common in certain age groups and/or genders:

  • Boys are usually more affected by bronchiolitis, croup, and pneumonia than girls are.
  • Bronchiolitis is most common in winter and spring.
  • Bronchiolitis most often occurs in the age range of 2 to 6 months.
  • Children under the age of two are most likely to develop bronchiolitis and pneumonia.
  • Croup is more often seen in fall and winter.
  • Children aged three months to five years old most commonly get croup, with two-year-olds being the most commonly affected.
  • Pneumonia is most common in winter and spring. Pneumonia transmission increases in crowded areas.
  • 10 to 15% of respiratory infections in children result in pneumonia.

Human parainfluenza viruses can stay infectious in airborne particles for over an hour. They may remain infectious on solid surfaces for several hours. You’re most infectious during the early stages of a human parainfluenza virus infection.

Symptoms of human parainfluenza virus will depend on what type of infection it is and what conditions it causes. Common symptoms of parainfluenza virus include:

  • Labored breathing
  • A rough or barking cough
  • Hoarseness 
  • Wheezing
  • Runny nose
  • Fever
  • Vomiting
  • Diarrhea
  • Loss of appetite
  • Redness in eyes

Certain conditions caused by human parainfluenza viruses may have additional symptoms. Epiglottitis may be accompanied by a very sore throat and difficulty swallowing. With laryngitis, you may become hoarse or lose your voice. Sinus infections often include congestion, fatigue, headaches, and postnasal drip, when you can feel mucus dripping into the back of your throat. Lower respiratory infections may cause chest pain and tightness within the chest. 

Before diagnosing your child with a human parainfluenza virus, your child’s doctor will start by giving your child a physical exam. This will allow them to observe your child’s symptoms. That, along with their knowledge of local HPIV outbreaks, will likely get them closer to diagnosing your child.

If your doctor wants extra diagnostic reassurance or is concerned about problems, they may require additional testing. This may include a:

  • Nasal swab
  • Blood test
  • Chest x-ray

Most human parainfluenza viruses are mild and can be treated at home. Because HPIVs are caused by viruses and not bacteria, antibiotics don’t work. In a typical case of human parainfluenza virus, treatment involves reducing the severity of symptoms until the virus passes. 

Common methods of relieving symptoms include:

  • Ensuring the patient gets plenty of fluids
  • Ibuprofen (Advil) or acetaminophen (Tylenol) to lower fever and reduce discomfort
  • Methods to keep the child calm so their breathing is less labored
  • Using a cool-mist humidifier to loosen the airway

Depending on the age of the child and the symptoms they are presenting, your doctor may recommend cough or cold medicine. In severe cases of croup, your doctor may prescribe a corticosteroid. Corticosteroids are anti-inflammatory drugs. As the cough and breathing difficulties of croup are caused by swelling in the upper airway, the hope is that corticosteroids can reduce this swelling and as a result reduce coughing and breathing problems.

Though most cases are mild, there are some situations in which you should bring your child to the hospital. These include situations in which your child’s symptoms are not getting better or cases where new symptoms develop.

If your child has croup, seek medical attention right away if they:

  • Are struggling to breath
  • Make a noisy, high-pitched sound when inhaling and exhaling
  • Make high-pitched sounds when not upset
  • Breathe at a faster rate than normal
  • Begin drooling or struggling to swallow
  • Seem anxious and agitated
  • Seem listless or fatigued
  • Develop blue or grayish skin around the mouth, nose, and/or fingernails

If your child has pneumonia, there are other common reasons for hospitalization:

  • The child is younger than two months old.
  • They are struggling to breathe.
  • Their oxygen levels are low.
  • They are lethargic.
  • They seem dehydrated.

With most children catching a HPIV before age five, it may seem that preventing parainfluenza viruses is impossible. While it can be difficult to avoid, though, especially if your child is in daycare or school, there are a few things you can do to help protect your child:

  • Keep them away from other children who have symptoms of parainfluenza viruses.
  • Practice good hygiene, including regular and thorough hand washing.
  • Don’t allow your child to share cups or utensils with sick children.

There is currently no vaccine to fight human parainfluenza viruses. Vaccines against HPIV-1 and HPIV-3 are in development, though, so there may be hope on the horizon.