Respiratory syncytial virus

Bronchiol refers to the small airways of the lungs, and itis means inflammation, so bronchiolitis describes inflammation of the small airways in the lungs.

It’s most often caused by infection from the respiratory syncytial virus, or RSV.

It mostly affects young children, and actually causes illness in nearly every child at some point in their life.

Respiratory syncytial virus is a virus that causes the cells lining the respiratory tract to merge; they form a large multinucleated “cell” called a syncytia.

Respiratory syncytial virus is part of the Pneumoviridae family.

It’s transmitted when an infected person sneezes or coughs, which spreads thousands of droplets containing the virus into the surrounding area up to about two meters, or six feet, away.

These droplets can then land in the mouths or noses of people nearby, or be inhaled into their lungs.

The virus can also survive on surfaces for a few hours, so it’s possible to get the virus by touching an infected surface, like a contaminated doorknob, and then touch your own eyes, nose, or mouth.

Upon entering the body, the virus encounters the epithelial cells lining the nasopharynx, which is the part of your throat nearest your nose.

It creates some local damage, and then works its way down the respiratory tree; it’s kind of like a secret agent rappelling down a rope of mucus.

The virus travels down past the trachea and main bronchi to eventually reach the bronchioles, its primary target.

Respiratory syncytial virus is an enveloped virus with a linear negative-sense strand of RNA.

This means that once the virus enters its RNA into a respiratory epithelial cell, that strand has to be converted into a complementary sense strand in order to be translated.

The cell is forced to use its energy and organelles to make viral proteins; it basically turns into a virus factory.

The new viruses invade neighboring cells, creating multinucleated syncytia out of some cells while destroying others.

The cellular destruction attracts nearby immune cells, which are like natural killer cells whose job is to kill the virus-infected cells.

Immune cells release various chemokines that create an inflammatory reaction; this reaction causes epithelial cells to secrete more mucus, and makes the blood vessels in the walls of the airways more leaky.

More immune cells and fluid enter the damaged areas, creating inflammation and swelling.

The extra fluid thickens the walls of the airway, and narrows it.

Children typically have narrower airways than adults to begin with, so this additional narrowing of the airways affects them the most.

This largely explains why children disproportionately suffer from bronchiolitis.

In addition, dead cells and mucus slide into the airway, forming mucus plugs that can trap air behind the plug.