What is Parainfluenza Virus?
The human parainfluenza virus (HPIV) is a type of virus that has a specific structure, being covered by an envelope and holding a single strand of RNA. This virus belongs to a family called Paramyxoviridae and is further divided into four kinds, called serotypes, numbered one to four. The fourth serotype can be even further divided into HPIV-4A and HPIV-4B. HPIV can cause infections in both the upper and lower parts of the respiratory tract – the system involved with breathing. Mostly children under the age of 5, adults with weakened immune systems, and older adults are affected. It’s quite a common virus causing illness and death, especially in infants, globally.
These respiratory viruses were first identified in the late 1950s in children with an illness called croup, hence they were initially known as “croup-associated viruses”. Although HPIV shares some similarities with the influenza (flu) virus, it is uniquely different and can be easily separated from flu viruses. For instance, it shares a few antigenic sites – parts of the virus that the body’s defensive system recognizes and fights against – with the flu virus. It also doesn’t grow well in embryonated eggs which is a tool often used for studying viral growth.
The fourth serotype, discovered in 1959, was classified as having similar qualities to the previous three known types of parainfluenza virus. A new category of viruses was then established and named “parainfluenza viruses”.
What Causes Parainfluenza Virus?
Parainfluenza viruses are part of the Paramyxoviridae family, and there are four main types, known as HPIV-1, HPIV-2, HPIV-3, and HPIV-4, with some further subtypes of HPIV-4a and HPIV-4b. Different types of parainfluenza viruses belong to different groups, for example, HPIV-1 and HPIV-3 are part of the Respirovirus group, and HPIV-2 and HPIV-4 are part of the Rubulavirus group. Types 1 to 3 parainfluenza viruses are often responsible for lower respiratory infections in people of all ages, especially infants, young children, adults, those with weakened immune systems and older adults.
The parainfluenza viruses vary in shape and size, generally measuring between 150 to 200 micrometers. These viruses include six main components, which are crucial for their function. These parts are the nucleocapsid protein (NP), the phosphoprotein (P), the fusion glycoprotein (F), the matrix protein (M), the hemagglutinin-neuraminidase (HN) glycoprotein, and the RNA polymerase (L).
While all parainfluenza viruses share common structure and behavior, they affect people in different ways. Each type typically infects people at different ages and can cause varying symptoms and illnesses.
Risk Factors and Frequency for Parainfluenza Virus
The human parainfluenza virus, or HPIV, is a common virus that causes respiratory infections, especially in crowded areas. It has some risk factors that make people more susceptible to catching it, such as malnutrition, exposure to environmental smoke or toxins, vitamin A deficiency, and overcrowded conditions.
- HPIV is a leading cause of hospitalizations for children under 5 years of age due to respiratory infections, accounting for up to 17% of such hospitalizations.
- Studies have shown that 60% of children infected with HPIV-3 are around 2 years old, and the rate of HPIV-3 infection increases up to 80% for children around 4 years old.
- The virus often co-exists with other respiratory viruses, leading to more serious, severe, and prolonged illnesses.
The timing and frequency of HPIV outbreaks vary according to the specific type:
- HPIV-1 usually sees a marked increase in cases from September to December in odd-numbered years.
- HPIV-3 infections happen annually, primarily from April to June, with potential for a second spike between November and December in even-numbered years when HPIV-1 cases are low.
- HPIV-2 outbreaks can occur in alternate years to HPIV-1 or cause yearly outbreaks, though they are usually smaller in size.
- HPIV-4 has a less frequent and irregular pattern, similar to that of HPIV-3.
The parainfluenza virus is particularly contagious and can easily spread through direct person-to-person contact or through infected droplets in the air. This makes outbreaks in places like nursing homes and daycare facilities quite common.
Signs and Symptoms of Parainfluenza Virus
The human parainfluenza virus is associated with illnesses affecting both the upper and lower respiratory tracts across all age groups. This can lead to several different conditions, including:
- The common cold
- Croup
- Tracheobronchitis
- Bronchiolitis
- Pneumonia
Parainfluenza can also exacerbate existing health conditions such as asthma, chronic obstructive pulmonary disease, and congestive heart failure. While these infections are usually mild in healthy individuals, they can lead to more serious respiratory illnesses in young children and adults with compromised immune systems.
The specific symptoms caused by parainfluenza can differ depending on the type of virus. HPIV-1 and HPIV-2 often cause croup and cold-like symptoms, while HPIV-3 mainly causes bronchiolitis and pneumonia. HPIV-4 is less well-studied, but is thought to cause similar symptoms to HPIV-3.
Individuals with croup often have a fever, a distinctive hoarse bark-like cough, and wheezing. This is due to inflammation in the throat and upper trachea. Bronchiolitis, which occurs when found in infants and young children, starts with a fever and nasal congestion, and then progresses to a cough, fast breathing, and chest retractions. Symptoms typically last between 8 to 15 days, but usually resolve within 21 days.
Pneumonia, another potential result of parainfluenza infection, is a major cause of hospitalization in the US. Young children with pneumonia often have a fever, cough, and rales (abnormal lung sounds), and may have areas of lung tissue damage or consolidation visible on chest X-rays. Tracheobronchitis, which occurs when the lower and large airways become inflamed, is associated with a cough, wheezing and sometimes a fever or upper respiratory tract infection.
While the parainfluenza viruses usually infect the respiratory tract, they can occasionally spread to other parts of the body, including the neurological system, kidneys, joints, and gastrointestinal tract.
Testing for Parainfluenza Virus
While the Human Parainfluenza Virus 1 (HPIV-1) is often linked to a disease called croup and can usually be identified by typical symptoms of this disease, other types of the virus don’t have such distinctive symptoms. Therefore, lab tests are necessary to diagnose these other types.
If your doctor needs to take a sample for testing, a special type of swab called a flocked swab is usually used instead of a cotton swab, as it can collect more of the virus. They can take samples from various parts of your body including your throat, nose, or lungs, or they could use mucus from your nose or lungs.
When they collect the sample can also affect the test’s results. Early in the infection, samples from your upper airways (like your nose and throat) are usually better. However, if the disease has progressed, mucus or fluid from your lungs may be a more effective sample.
The virus can be active for a long time in some people. For example, HPIV-3 has been found in children up to six weeks after they first showed symptoms. In adults or people with weakened immune systems, HPIV-1, HPIV-2, and HPIV-3 can be active for several months.
There are many ways to test for the virus in a sample. For many years, a method called a viral culture was the best option. This test checks for signs of the virus damaging cells, which can suggest an infection. However, this method is usually not used anymore as it takes a long time to get results.
Another quicker test uses fluorescent antibodies (a type of protein produced by the body in response to an infection) to identify the virus. This method can accurately detect types 1-3 of the virus, but not type 4. Therefore, if symptoms suggest an HPIV infection, this could be a practical test to use.
The most accurate test for diagnosing the virus is a Polymerase Chain Reaction (PCR) test. This test is fast, reliable, and now more widely available as commercial options exist. It has shown to have superior sensitivity and specificity compared to the viral culture and fluorescent antibody tests.
Lastly, a test called the Serologic diagnosis can detect the virus, but it’s primarily used as a research tool and isn’t typically used in day-to-day medical practice.
Treatment Options for Parainfluenza Virus
The treatment for Human Parainfluenza Virus (HPIV) infection involves managing the symptoms in healthy children and adults as currently, there isn’t any proven antiviral medication for this specific viral infection available.
If HPIV infection leads to a condition known as croup, corticosteroids – a type of medicine that reduces inflammation, have been found to be beneficial. These can be taken orally or injected into the muscle, and both methods were shown to be better than inhaling the medication. Alongside this, a medication called epinephrine can be used in a nebulized form. This means it’s turned into a fine mist which can then be inhaled. This treatment can provide relief from symptoms quickly – sometimes within 30 minutes – but the effect usually lasts no more than 2 hours. This treatment can be beneficial and provide some relief while waiting for the anti-inflammatory effects of corticosteroid therapy to take effect.
The worsening of chronic respiratory diseases caused by different viruses, including the HPIVs, might be avoidable with early antiviral treatment. Even though there is no specific antiviral treatment for HPIV in clinical practice currently, new strategies are being researched and developed. For example, one approach could involve removing the sialic acid receptors on cells that the virus uses to latch onto and infect the cell. This is done using a protein called DAS181.
Another method might involve inserting peptides – small proteins, into the cell membrane to prevent the virus from entering the cell. Both these methods are still being studied for their practical use.
The severest impact of HPIV infection is observed in patients with compromised immune systems. For these patients, the focus of treatment remains largely on managing symptoms and providing support.
What else can Parainfluenza Virus be?
Viruses are often the cause of acute respiratory tract infections. An infection known as HPIV can be particularly hard to diagnose because it shares many symptoms with other bacterial and viral infections. A few of the common viruses that may cause symptoms similar to HPIV include:
- Respiratory syncytial virus
- Influenza types A and B
- Human rhinovirus
- Human metapneumovirus
- Adenoviruses
- WU polyomavirus
- Human bocavirus
So, it is important for doctors to consider these causes when trying to diagnose respiratory infections.
What to expect with Parainfluenza Virus
Parainfluenza viruses are one of the leading causes of respiratory infections caused by a virus. They can lead to more serious health issues and possibly death in people with weakened immune systems compared to healthy individuals. So for healthy children and adults, infection with this virus usually has a good recovery rate, and responding to the symptoms is often sufficient.
However, once the virus begins to replicate and cause invasive infections in people with weakened immune systems, the situation can become serious. Thus, it’s crucial to diagnose and treat viral infections promptly in individuals with compromised immunity.
Possible Complications When Diagnosed with Parainfluenza Virus
Infection with the human parainfluenza virus can cause different types of diseases in people with weak immune systems and the elderly. These might range from minor symptoms in the upper respiratory system to serious illnesses in the lower respiratory system. This severe condition might necessitate the use of machines to aid in breathing and could potentially result in death. It’s important to note that human parainfluenza virus type 3 (HPIV-3) often leads to more severe diseases in people with weakened immune systems, while HPIV-1 and HPIV-2 follow suit. However, type 4 of this virus (HPIV-4) is usually not associated with serious illness.
Early life infections with certain types of viruses from the Paramyxoviridae family (especially the respiratory syncytial virus and the human parainfluenza virus) have a strong link with the development of breathing issues such as asthma and COPD in later stages of life.
Implications of HPIV infection:
- Minor to severe illnesses in the upper or lower respiratory system
- May require mechanical ventilation
- Potential risk of death
- HPIV-3 usually leads to more severe illnesses
- HPIV-4 is rarely associated with serious illness
- Early childhood infection may lead to breathing issues like asthma and COPD later in life
Preventing Parainfluenza Virus
The parainfluenza virus is mainly spread from person to person through tiny droplets in the air. Young children can spread a large number of these viruses, which can survive on surfaces like toys for up to 10 hours. To prevent the spread of the virus in healthcare settings, measures like keeping people with the virus away from others are enough, since it’s not usually spread through smaller particles in the air.
However, it’s been found that both healthy people and those with weakened immune systems can carry low levels of the parainfluenza virus for a long time, even if they don’t show any symptoms.
When an outbreak is detected in healthcare settings, especially where patients with weak immune systems are being treated, stronger steps are recommended to control the infection. These steps include limiting visits, avoiding patient-to-patient contact, social distancing, requiring masks for anyone in contact with infected patients, cleaning surfaces regularly, and maintaining good hygiene. If the outbreak is hard to control, it might be necessary to also screen people without symptoms, including patients and healthcare staff.
