A 23-year-old man has 2 days of fever, cough, sore throat, and runny nose. His temperature is 38 C (100.4 F). Lung sounds are clear to auscultation. A nasopharyngeal swab is obtained. Naked viral particles are seen, and purified RNA molecules are extracted from these particles. Once introduced into human cells, the purified RNA molecules induce viral protein synthesis and viral genome replication. Which of the following is the most likely cause of this patient's symptoms?

Question

A 23-year-old man has 2 days of fever, cough, sore throat, and runny nose.  His temperature is 38 C (100.4 F).  Lung sounds are clear to auscultation.  A nasopharyngeal swab is obtained.  Naked viral particles are seen, and purified RNA molecules are extracted from these particles.  Once introduced into human cells, the purified RNA molecules induce viral protein synthesis and viral genome replication.  Which of the following is the most likely cause of this patient's symptoms?

Quizplus · Accepted Answer

For an RNA molecule purified from a virus (ie, without viral capsid or envelope) to be infectious (ie, able to induce viral protein synthesis and genome replication in the host cell) on its own, it must act as mRNA capable of using the host's intracellular machinery for translation. In other words, the purified RNA molecule must be single-stranded (SS) and positive (+) sense, or SS(+). The question describes a naked (ie, nonenveloped) virus with SS(+) RNA. Of the viruses listed, only rhinovirus (a picornavirus) has these features. Generally, only RNA molecules purified from SS(+) viruses are infectious; purified SS negative (-) sense RNA molecules and double-stranded (ds) RNA molecules are not as they require additional enzymes. (Choice A) HIV is a retrovirus that contains SS(+) RNA. However, viral infectivity requires the action of reverse transcriptase for integration into the host genome; purified RNA by itself cannot cause infection. In addition, HIV is enveloped, unlike the particles isolated from this patient. (Choices B and C) Influenza A is an orthomyxovirus that contains SS(-) RNA; similarly, respiratory syncytial virus is a paramyxovirus that contains SS(-) RNA. For these viruses to replicate in a host cell, an RNA-dependent RNA polymerase must also gain entry into the host cell. (Choice E) Rotavirus is a reovirus containing dsRNA. Its purified RNA is therefore incapable of inducing viral protein synthesis in a host cell on its own (ie, it is non-infectious). For this virus to replicate in a host cell, a specific viral RNA polymerase present in the intact virion must also gain entry into the host cell. Educational objective: For a purified RNA molecule to induce viral protein synthesis in a host cell, it must be able to act directly as mRNA using the host's intracellular machinery for translation. Therefore, in general, purified single-stranded positive-sense RNA can be infectious; single-stranded negative sense or double-stranded RNA is not.

A 23-Year-Old Man Has 2 Days of Fever, Cough, Sore