MLT GlobeVirology: Enteric & other viruses – page 3
63 Virology MCQs on Enteric & other viruses with answers and explanations.
A patient with bulbar poliomyelitis deteriorates rapidly. Which complication is the main cause of death?
Poliovirus destroys motor neurons; involvement of the brainstem or cervical cord paralyses breathing muscles, causing respiratory failure. Kidney failure is not a typical complication.
Which statement about human rotaviruses is NOT true?
Human rotaviruses grow poorly in routine cell culture, so antigen detection or PCR is used. They are naked dsRNA viruses and a major cause of infant diarrhoea.
Which description fits astrovirus?
Astroviruses are small, star-shaped, naked +ssRNA viruses that cause mild childhood gastroenteritis.
Parvovirus B19 is one of the smallest human viruses. What kind of genome does it carry?
Parvoviruses are small (~22 nm), naked, icosahedral viruses with linear ssDNA; they replicate in dividing cells such as erythroid progenitors.
The first rotavirus vaccine (RotaShield) was withdrawn in 1999. Which adverse event led to its withdrawal?
RotaShield was linked to intussusception. Current oral rotavirus vaccines carry a much smaller risk and are recommended worldwide.
A child has watery diarrhoea; stool is rotavirus-negative. Which adenovirus types, unlike respiratory adenoviruses, cause almost exclusively gastroenteritis and rank second to rotavirus in infants?
Serotypes 40/41 (species F) are the enteric adenoviruses, a major cause of infant diarrhoea. Types 3, 7 and 14 are respiratory, and type 8 causes keratoconjunctivitis.
Electron microscopy of stool from a toddler with mild diarrhoea shows small non-enveloped particles with a five- or six-pointed star outline. The likely virus is:
Astroviruses have a characteristic star-shaped surface outline on EM and cause mild childhood gastroenteritis. Rotavirus has a wheel-like appearance.
A very small circular single-stranded DNA genome of about 2 kb is typical of which virus?
Circoviruses have circular ssDNA genomes of about 2 kb, among the smallest known. Herpesviruses (~150 kb) and mimivirus (~1.2 Mb) are much larger.
An immunosuppressed patient develops progressive multifocal leukoencephalopathy with demyelination. Which virus is responsible?
PML is caused by reactivated JC polyomavirus infecting oligodendrocytes; CSF PCR supports diagnosis. Measles causes a different late brain disease, SSPE.
Which human virus is large enough to be seen, just barely, with a light microscope after special staining?
Poxviruses (about 300 x 250 nm) are the largest viruses that infect humans. Their inclusions, such as Paschen bodies, were seen by light microscopy. Poliovirus is about 30 nm.
A patient with advanced HIV has progressive weakness and confusion. MRI shows white matter lesions without mass effect. Which CSF test best supports the likely diagnosis?
Progressive multifocal leukoencephalopathy is caused by JC virus infecting oligodendrocytes and is supported by JC virus DNA in CSF. Toxoplasma usually causes ring-enhancing mass lesions.
During a norovirus outbreak on a hospital ward, staff are told to wash hands with soap and water rather than use alcohol hand rub. The main reason is that norovirus:
Non-enveloped viruses lack the lipid envelope that alcohol destroys, so alcohol rubs are less effective; soap and water physically remove the virus. Enveloped viruses are easily inactivated by alcohol.
The urine cytology of a kidney transplant recipient with rising creatinine shows epithelial cells with enlarged nuclei containing glassy inclusions ('decoy cells'). Which test is best next?
Decoy cells suggest BK polyomavirus reactivation; plasma BK viral load helps identify BK nephropathy, which is confirmed by biopsy. Bacterial culture does not detect it.
Which virus uses CD155 (the poliovirus receptor) rather than the chemokine co-receptor CXCR4 to enter cells?
Poliovirus binds CD155. X4-tropic strains of HIV-1, HIV-2 and SIV use CXCR4 as a co-receptor along with CD4.
Unlike orthopoxviruses such as vaccinia, which poxvirus genus (causing orf) is inactivated by ether?
Parapoxviruses (e.g. orf virus) are ether-sensitive, whereas orthopoxviruses are notably ether-resistant despite their lipid-containing envelope.
Many viruses encode proteins that block apoptosis. Which virus instead is known to trigger apoptosis of its host cells as a mechanism of damage?
Rubella virus induces apoptosis in infected cells, contributing to fetal damage. Poxviruses (vaccinia, myxoma) and EBV encode anti-apoptotic proteins to prolong cell survival.
Which virus has a double-stranded DNA genome AND a lipid envelope?
Poxviruses such as Yabapox are enveloped dsDNA viruses. Polyomaviruses (BK, JC) and adenoviruses are dsDNA but naked.
Parvovirus B19 selectively infects erythroid progenitor cells. Which red cell antigen serves as its receptor?
B19 binds P antigen (globoside); rare P-null (p phenotype) individuals are resistant. Duffy antigen is the receptor for Plasmodium vivax.
Rotavirus was long classified in the family Reoviridae. In which family does ICTV now place it?
In 2022 ICTV split Reoviridae; rotaviruses are now in Sedoreoviridae (order Reovirales). Noroviruses are caliciviruses.
How are human papillomavirus types defined and classified?
HPV cannot be grown in routine culture, so types are defined genetically: a new type differs by more than 10% in L1 nucleotide sequence.