AssessmentsRespiratory syncytial virus
Respiratory syncytial virus
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 16-month-old boy is brought to the emergency department in winter for evaluation of increased work of breathing. According to his parents, the patient developed a runny nose and congestion earlier in the week. However, over the past day, he also began experiencing cough, fever, and shortness of breath. The patient is otherwise healthy, was born full-term, and is up-to-date on all vaccinations. Temperature is 37.6°C (99.7°F), pulse is 140/min, respirations are 24/min, and blood pressure is 90/52 mmHg. On physical examination, the patient is noted to have nasal flaring, subcostal retractions, and bilateral end-expiratory wheezing. Bedside nasal suctioning is performed and leads to symptomatic improvement. Which of the following pathogens is most likely responsible for this patient’s clinical symptoms?
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.
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.
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.