USMLE® Step 1 style questions USMLE
A 45-year-old man comes to his primary care physician for evaluation of three days of cough and nasal congestion. The patient has been having green nasal discharge and states, “Doc, I think I need some antibiotics.” In addition, he has been experiencing a scratchy throat and generalized malaise. Past medical history is notable for hypertension, hyperlipidemia, and type II diabetes mellitus. He does not consume alcohol or tobacco products. Temperature is 37.6°C (99.7°F), pulse is 74/min, respirations are 12/min, and blood pressure is 140/77 mmHg. Physical examination reveals mild erythema of the posterior pharynx. A rapid influenza A and B test is performed and returns negative. Which of the following pathogens is the most likely cause of this patient’s clinical presentation?
Content Reviewers:Rishi Desai, MD, MPH
It mainly causes upper respiratory tract infections, and gets its rhino- name, meaning nose, because it commonly causes a runny nose, nasal congestion, and sneezing, as well as a sore throat and cough.
There are over 100 serologic known types and all of them can cause a "common cold” in humans!
Now, rhinovirus belongs to the picornaviridae family of viruses.
They are naked viruses, about 30 nanometers in diameter, and they’re surrounded by an icosahedral capsid, which is a spherical protein shell made up of 20 equilateral triangular faces.
And they’re “naked” because the capsid isn’t covered by a lipid membrane.
They’re also single-stranded, positive-sense ribonucleic acid, or RNA, viruses.
This means that their RNA is actually mRNA, which the host cell ribosomes use to make viral proteins.
Unlike other picornaviruses, rhinoviruses are acid labile.
That means they can be destroyed by stomach acid, so they don’t typically infect the GI tract and don’t spread through a fecal-to-oral route.
On the other hand, rhinoviruses commonly infect the epithelium of the respiratory mucosa, which lines the nasal cavity.
So rhinovirus transmission occurs through contact with infected respiratory secretions, like snot and aerosols, particularly from nose blowing or sneezing.
Touching an infected surface, like a door handle or shaking hands, and then touching an uninfected respiratory mucosa is a main way to transfer an infection - that’s because rhinoviruses can survive up to 2 hours on the skin, and 4 days on surfaces.
Once rhinovirus has been introduced to the respiratory mucosa, it targets cell surface receptors expressed at the surface of nasal epithelial cells.
Rhinoviruses can target a few specific receptors for entry, but one in particular is intercellular adhesion molecule-1, or ICAM-1.
This attachment allows for rhinovirus to be eaten, or endocytosed, into the host cell.
During the endocytosis process, the icosahedral capsid breaks open, allowing the single stranded RNA of Rhinovirus to gain access to the host cell cytoplasm.
In the cytoplasm, the host cell ribosomes take over viral protein production, helping the virus replicate.