SM Virology & Molecular Diagnostics Flashcards

Which characteristic of non-enveloped viruses makes them more resistant to disinfection compared to enveloped viruses?

Answer: Non-enveloped viruses lack a lipid membrane that is easily disrupted by alcohol and detergents

Enveloped viruses are susceptible to lipid-dissolving agents (alcohol, detergents) that disrupt their membrane; non-enveloped viruses require more potent disinfectants such as chlorine or glutaraldehyde.

Which specimen type is preferred for diagnosis of lower respiratory tract viral infection including influenza and SARS-CoV-2 when bronchoscopy is performed?

Answer: Bronchoalveolar lavage (BAL) fluid

BAL fluid directly samples the lower respiratory tract and provides the highest diagnostic yield for viral pathogens causing pneumonia compared to upper respiratory specimens.

CRISPR-based diagnostic assays (e.g., SHERLOCK, DETECTR) detect nucleic acids by using Cas enzymes that:

Answer: Exhibit collateral cleavage activity upon binding target sequence, releasing detectable signal

CRISPR diagnostics exploit the collateral (trans) cleavage activity of Cas12 or Cas13 enzymes: upon binding the target sequence, they nonspecifically cleave reporter probes, generating a detectable fluorescent or lateral flow signal.

Rabies virus, after inoculation at a peripheral wound, spreads to the CNS via:

Answer: Retrograde axonal transport along peripheral nerve fibers

Rabies virus binds nicotinic acetylcholine receptors at the neuromuscular junction and travels to the CNS by retrograde axonal transport, explaining the incubation period variability based on wound distance from the brain.

Which FDA-cleared rapid antigen test characteristic is most critical when used as a point-of-care test for influenza in a high-prevalence setting?

Answer: Positive predictive value, which increases with higher disease prevalence

In high-prevalence settings, the positive predictive value (PPV) of rapid antigen tests increases substantially, making positive results more reliable and actionable for patient management.

Congenital cytomegalovirus (cCMV) infection is best diagnosed in the neonatal period using:

Answer: CMV PCR from urine or saliva collected within 21 days of birth

Urine and saliva CMV PCR within the first 21 days of life is the gold standard for cCMV diagnosis, as CMV acquired during delivery or postnatally can confound results obtained after this window.