MLT GlobeVirology: Respiratory viruses – page 2
37 Virology MCQs on Respiratory viruses with answers and explanations.
Years after an early-childhood infection, a child develops progressive behavioural decline, myoclonus and very high CSF antibody titres. Subacute sclerosing panencephalitis follows which virus?
SSPE is a rare, fatal, persistent measles infection of the brain affecting grey and white matter, with high measles antibody in CSF. It is prevented by measles vaccination.
After acute pharyngitis, which of these viruses can persist silently in tonsils and adenoids for long periods?
Adenoviruses establish latent or persistent infection in lymphoid tissue such as tonsils and adenoids. Influenza, measles and coxsackie B cause acute infections.
Influenza virions (Orthomyxoviridae) are pleomorphic. What is their usual diameter?
Spherical influenza virions are roughly 80-120 nm across, though filamentous forms occur. Parvoviruses are ~20 nm, poxviruses ~250-300 nm.
For best recovery in cell culture, rhinoviruses are incubated at about 33 °C. Why?
Rhinoviruses are adapted to the cooler nasal passages (33-35 °C), which confines them largely to the upper respiratory tract and explains optimal culture temperature.
Seasonal influenza epidemics recur yearly. Which influenza types cause them?
Antigenic drift in both A and B causes annual epidemics, which is why vaccines include A and B strains. Only influenza A undergoes shift and causes pandemics; C gives mild illness.
Children at a summer camp develop fever, sore throat and conjunctivitis after using the same swimming pool. Which virus is the classic cause?
Pharyngoconjunctival fever, often linked to swimming pools, is caused by adenoviruses (commonly type 3), spread in poorly chlorinated water.
Surface peplomers would be seen on which virus?
Peplomers are glycoprotein spikes on the envelope, so only enveloped viruses such as influenza have them. The others are non-enveloped.
Influenza pandemics are mainly caused by antigenic shift, which results from:
Influenza A has a segmented genome, so two strains infecting one host can swap segments and create a new HA or NA subtype. Point mutations cause antigenic drift and seasonal epidemics.
A rapid influenza antigen test is negative in a patient with typical symptoms during flu season. What is the best interpretation?
Rapid antigen tests have high specificity but limited sensitivity. A negative result in a likely case should be confirmed by a molecular test.
A cell culture inoculated with a nasopharyngeal specimen from an infant with bronchiolitis shows large multinucleated cells (syncytia) in HEp-2 cells. The most likely virus is:
RSV causes cell fusion and syncytia in continuous cell lines such as HEp-2. Adenovirus produces rounded, grape-like clusters instead.
In a hemadsorption test, guinea pig red cells stick to a monkey kidney cell monolayer infected with influenza or parainfluenza virus because:
Infected cells insert viral hemagglutinin into their membranes, and it binds sialic acid on red cells. No antibody is needed for hemadsorption.
An unvaccinated child has fever, cough, conjunctivitis, a spreading maculopapular rash and small white spots on the buccal mucosa. Which test best confirms the diagnosis?
Koplik spots with the classic prodrome suggest measles, confirmed by measles IgM and/or RT-PCR of respiratory or urine specimens. Rubella avidity helps date rubella infection, not measles.
A student has painful swelling of the parotid glands. Which specimen is best for RT-PCR confirmation of the likely virus?
Mumps virus is shed in saliva, so a buccal swab near Stensen's duct after gland massage gives the best yield, ideally within a few days of swelling.
Oseltamivir is used to treat influenza. It works by inhibiting the viral:
Neuraminidase inhibitors stop the release of new virions from infected cells.
Mumps virus is classified in which genus under current ICTV taxonomy?
Mumps virus (mumps orthorubulavirus) is in genus Orthorubulavirus, family Paramyxoviridae. Measles is a morbillivirus; RSV an orthopneumovirus.
Human respiratory syncytial virus belongs to which genus and family?
Since 2016 RSV is in family Pneumoviridae, genus Orthopneumovirus; it was formerly a Paramyxoviridae pneumovirus. Human metapneumovirus is the other human pneumovirid.
Parainfluenza viruses produce little CPE in culture. Which test on the infected monolayer is classically used to detect them?
Infected cells express haemagglutinin on their surface, so added guinea pig erythrocytes stick to them (haemadsorption), revealing parainfluenza or influenza virus.