Can Parainfluenza Cause Encephalitis?

Overview

Parainfluenza viruses are well-known for causing respiratory illnesses, predominantly affecting infants, young children, older adults, and individuals with compromised immune systems. These viruses, commonly associated with symptoms resembling the common cold, have been the subject of medical scrutiny due to their potential to induce severe complications. Among these complications is encephalitis, a condition characterised by inflammation of the brain tissue. While encephalitis is typically caused by viral, bacterial, or autoimmune factors, the question arises: can parainfluenza, a common respiratory virus, lead to such a serious neurological disorder?

While isolated case studies have reported neurological manifestations following human parainfluenza virus (HPIV) infections, evidence linking parainfluenza viruses specifically to encephalitis remains limited. Although HPIVs are known to affect the respiratory tract, causing symptoms ranging from mild cold-like symptoms to more severe respiratory tract infections, the likelihood of parainfluenza-induced encephalitis is exceedingly rare. Despite the absence of conclusive evidence, the exploration of this topic provides valuable insights into parainfluenza infections and encephalitis, and the connection between the two medical conditions.

In this article, we delve into the intricacies of the common parainfluenza infections and the uncommon and fatal encephalitis, exploring the existing evidence and shedding light on the potential link between these two entities.

Parainfluenza Viruses: An Insightful Overview

What is parainfluenza?

Human parainfluenza viruses (HPIVs) are known for causing upper and lower respiratory illnesses. It most commonly affects infants, young children, older adults, and people with weaker immune systems, but anyone can be at risk of getting infected by HPIVs.¹

Symptoms and potential illnesses

The symptoms of HPIVs can be confused with the symptoms of the common cold. The symptoms generally appear 2-6 days after infection and may include:¹

• Coughing
• Fever
• Sore throat
• Sneezing
• Runny nose

Less common symptoms include:

• Decreased appetite
• Ear pain
• Irritability

HPIVs  could also cause more serious illnesses in children. These include:

• Croup: The infection of the vocal cords, windpipe, and sometimes into the bronchial tubes
• Bronchitis: The infection of the main air passages which connect the windpipe to the lungs
• Bronchiolitis: An infection in the smallest air passages of the lungs
• Pneumonia: The inflammation of the lungs

Symptoms of these illnesses include wheezing, a barking cough, hoarseness, or stridor, which is a high-pitched sound produced while breathing.¹

Transmission and Treatment

HPIVs are usually transmitted from person to person through:¹

• The air by contaminated droplets released while coughing or sneezing
• Close contact between people, such as touching, hugging, shaking hands etc.
• Touching surfaces or objects that are infected with HPIVs, and then touching your mouth, nose, or eyes without washing your hands

Although there is currently no vaccine  that offers protection against HPIVs, the spread of the virus can still be prevented. By taking the following actions, the spread of HPIVs can be reduced:

• Avoid close contact with people who are sick or show symptoms of HPIV infections
• Wash your hands regularly with soap and water, or use alcohol-based hand sanitisers 
• Avoid touching your mouth, nose, or eyes with unwashed hands

There is currently no specific treatment available for HPIVs, and most people with HPIV illnesses do heal and recover on their own.¹ However if a patient finds it difficult to deal with the symptoms, they can adopt the following measures:

• Take over-the-counter medication for pain and fever relief, such as ibuprofen
• Drink plenty of liquids
• Take hot showers or use a room humidifier to relieve a sore throat or a cough
• Stay home and rest

Understanding Encephalitis

What is Encephalitis?

Encephalitis is the inflammation of the brain, which is most commonly caused by viral or bacterial infections, or autoimmune responses.² It is an uncommon, but serious condition that can cause various neurological problems and potentially be life-threatening.³

Causes of encephalitis

Encephalitis can have many potential causes. The most common cause of encephalitis is viral infection, but other possible causes  include bacterial, fungal, and parasitic infections, and non-infectious causes such as autoimmune diseases.⁴ The most commonly diagnosed cause of encephalitis is a viral infection caused by the herpes virus,  but it can also result from various other viruses carried by ticks, mosquitoes, or other animals such as the West Nile virus. Although viral infections such as chickenpox, measles, mumps, and rubella can cause encephalitis, the rates of  contracting encephalitis via these infections have been lowered significantly  due to vaccines preventing infection.²

Symptoms and Signs

Acute encephalitis often begins with few symptoms, which worsen over the course of days or weeks. Early flu-like symptoms include:

• A high fever
• A headache
• Aching muscles or joints

Infectious encephalitis will often begin with flu-like symptoms, progressing onto altered mental status and cognitive issues such as impaired thinking, remembering, and reasoning. More severe symptoms include:

• Seizures or fits
• Confusion or disorientation
• Weakness or partial paralysis in legs or arms
• Impairment of speech or hearing
• Changes in personality or behaviour
• Uncontrollable eye movements or eyesight problems
• Loss of consciousness

As symptoms of encephalitis can resemble many other medical problems, it is recommended to always first consult with your healthcare provider for a proper diagnosis.

How is encephalitis diagnosed and treated?

When testing for encephalitis, diagnosis is often done via  brain scans, such as CT scans or MRI scans to differentiate between encephalitis and other medical issues such as strokes or brain tumours. Other tests include lumbar punctures, which involve the removal  of some fluid from around  the spinal cord to check for encephalitis, or an electroencephalogram which picks up electric signals from the brain to detect abnormal brain activity.³

 Although there is no specific treatment available for encephalitis caused by viral infections, anti-viral drugs such as acyclovir or ganciclovir are used to treat the viral infection behind encephalitis.⁴ Alongside that, treatment to relieve symptoms is given to support recovery.

Unravelling the parainfluenza-encephalitis connection

This may leave people concerned, wondering whether a common illness like parainfluenza can cause a serious medical condition like encephalitis. Can parainfluenza cause encephalitis? It is possible, however, it is incredibly rare with only a few recorded cases, that the answer is essentially no and it should not be a concern if you are infected with an HPIV. 

Although encephalitis is known for being caused by viral infections, a study done in 1990 found that three children infected with HPIVs had also gotten encephalitis,⁵ which was diagnosed through electroencephalograms, however not many similar cases have been discovered. Following this, there were very few individual cases of HPIVs causing various medical conditions that affect the brain, which were not encephalitis. There have for example been cases of acute encephalopathy caused by HPIVs, which is a condition characterised by brain dysfunction, in 2012 and 2015,^6,7 and two cases of meningitis,⁸ which is also an inflammation of the brain. 

It should be noted that many of these cases are quite old, with our medical techniques greatly advancing since then, and they do not necessarily relate to encephalitis. Although a few case studies show  that HPIVs have caused medical conditions related to the brain, they are still very rare.

With only one case study existing of HPIVs leading to encephalitis, one can assume there is an extremely low chance of a common viral infection progressing to encephalitis.

Summary

It may feel worrying knowing that common viral infections such as HPIV infections can  result in more serious medical conditions, however, you can rest assured knowing neurological medical conditions, particularly encephalitis, are not something to worry about. 

In conclusion, while encephalitis is a known complication of various viral infections, evidence linking parainfluenza viruses specifically to encephalitis remains scarce. Although isolated case studies have reported neurological complications associated with HPIV infections, including acute encephalopathy and meningitis, occurrences of encephalitis attributed solely to parainfluenza are incredibly rare. 

With advances in medical technology and surveillance, our understanding of viral pathogenesis and neurological complications continues to evolve. While vigilance is warranted, particularly in cases of severe or atypical presentations, the likelihood of parainfluenza-induced encephalitis remains exceedingly low. As we navigate the complexities of infectious diseases, it is essential to rely on evidence-based practices and maintain awareness without succumbing to undue concern.