Poxviridae and Picronaviridae Questions and Answers

Q: A virus is naked, icosahedral, acid-resistant and spreads by the faecal-oral route. It is most likely

Correct answer: an enterovirusTake the properties in turn: naked and icosahedral makes it a picornavirus; acid resistance excludes the rhinoviruses and the aphthoviruses, both of which are destroyed at low pH; and the faecal-oral route requires a virus that survives the stomach. Only the enteroviruses satisfy all three, and acid stability is precisely what defines the genus.

Q: Viral meningitis and myocarditis are among the diseases caused by

Correct answer: enterovirusesThe enteroviruses cause a range of disease out of proportion to their reputation: aseptic meningitis, of which they are the commonest cause, myocarditis and pericarditis from the coxsackie B group, pleurodynia, hand-foot-and-mouth disease, and paralytic poliomyelitis. Most infections nevertheless remain silent, which is why the viruses circulate so freely.

Q: Why can a rhinovirus not establish infection in the intestine?

Correct answer: It is inactivated by stomach acidRhinoviruses lose infectivity at pH 3, and the fasting stomach is at about that pH, so a swallowed rhinovirus is destroyed before it reaches the intestine. Its low optimum temperature would be an additional handicap, but acid is what actually stops it. This is the single property that divides the respiratory picornaviruses from the enteric ones.

Q: Which property lets an enterovirus reach the intestine alive?

Correct answer: Resistance to pH 3.0 to 5.0Enteroviruses tolerate the acidity of the stomach and the bile that follows it, so they arrive in the intestine intact and can establish infection there. The property is structural - a capsid that does not disassemble at low pH - and it is what makes faecal-oral transmission possible and defines the genus against the acid-labile rhinoviruses.

Q: Which of these best describes the picornavirus replication strategy?

Correct answer: The RNA is translated directly, then copiedA positive-sense RNA genome is a messenger, so on entering the cytoplasm it is translated at once into the polyprotein, and the RNA polymerase released from that polyprotein then copies the genome - first into a negative-sense strand, which serves as the template for many new positive strands. Translation must precede replication, since the polymerase does not arrive in the particle.

Q: A vaccine against hepatitis A is practical largely because the virus has

Correct answer: a single serotypeA vaccine works by raising antibody against the antigens of the strain it contains, so a virus with many serotypes needs a vaccine with many components, or none at all. Hepatitis A has exactly one worldwide, so a single inactivated preparation protects against every isolate, and immunity is durable. That is why an effective hepatitis A vaccine exists and a common cold vaccine does not.

81.

A virus is naked, icosahedral, acid-resistant and spreads by the faecal-oral route. It is most likely

A.an enterovirus
B.a rhinovirus
C.a poxvirus
D.an aphthovirus

Answer: A

Correct answer: an enterovirus

Take the properties in turn: naked and icosahedral makes it a picornavirus; acid resistance excludes the rhinoviruses and the aphthoviruses, both of which are destroyed at low pH; and the faecal-oral route requires a virus that survives the stomach. Only the enteroviruses satisfy all three, and acid stability is precisely what defines the genus.

Discuss in Forum

82.

Viral meningitis and myocarditis are among the diseases caused by

A.aphthoviruses
B.enteroviruses
C.poxviruses
D.rhinoviruses only

Answer: B

Correct answer: enteroviruses

The enteroviruses cause a range of disease out of proportion to their reputation: aseptic meningitis, of which they are the commonest cause, myocarditis and pericarditis from the coxsackie B group, pleurodynia, hand-foot-and-mouth disease, and paralytic poliomyelitis. Most infections nevertheless remain silent, which is why the viruses circulate so freely.

Discuss in Forum

83.

Why can a rhinovirus not establish infection in the intestine?

A.It grows only above 37 degrees
B.It is destroyed by bile salts alone
C.It is inactivated by stomach acid
D.It cannot bind any human receptor

Answer: C

Correct answer: It is inactivated by stomach acid

Rhinoviruses lose infectivity at pH 3, and the fasting stomach is at about that pH, so a swallowed rhinovirus is destroyed before it reaches the intestine. Its low optimum temperature would be an additional handicap, but acid is what actually stops it. This is the single property that divides the respiratory picornaviruses from the enteric ones.

Discuss in Forum

84.

Which property lets an enterovirus reach the intestine alive?

A.A lipid envelope that resists acid
B.An optimum growth temperature of 33 degrees
C.Replication inside the nucleus
D.Resistance to pH 3.0 to 5.0

Answer: D

Correct answer: Resistance to pH 3.0 to 5.0

Enteroviruses tolerate the acidity of the stomach and the bile that follows it, so they arrive in the intestine intact and can establish infection there. The property is structural - a capsid that does not disassemble at low pH - and it is what makes faecal-oral transmission possible and defines the genus against the acid-labile rhinoviruses.

Discuss in Forum

85.

Which statement about the poxvirus outer membrane is correct?

A.Naturally released virions have one that artificially extracted virions lack
B.Artificially extracted virions have one that released virions lack
C.Neither form has any membrane
D.Both forms carry two membranes

Answer: A

Correct answer: Naturally released virions have one that artificially extracted virions lack

A poxvirus leaves the cell by budding and acquires an extra outer membrane on the way, giving the extracellular enveloped virion. A particle released by artificially breaking the cell open is the intracellular mature form and lacks that membrane. Both are infectious, but the extra membrane matters - it carries different proteins, is important for spread within the host, and is why antibody against one form does not fully neutralise the other.

Discuss in Forum

86.

Which of these best describes the picornavirus replication strategy?

A.The genome is translated only after integration
B.The RNA is translated directly, then copied
C.The RNA is copied into DNA
D.The DNA is transcribed in the nucleus

Answer: B

Correct answer: The RNA is translated directly, then copied

A positive-sense RNA genome is a messenger, so on entering the cytoplasm it is translated at once into the polyprotein, and the RNA polymerase released from that polyprotein then copies the genome - first into a negative-sense strand, which serves as the template for many new positive strands. Translation must precede replication, since the polymerase does not arrive in the particle.

Discuss in Forum

87.

A vaccine against hepatitis A is practical largely because the virus has

A.a double-stranded DNA genome
B.an envelope carrying spikes
C.a single serotype
D.115 serotypes

Answer: C

Correct answer: a single serotype

A vaccine works by raising antibody against the antigens of the strain it contains, so a virus with many serotypes needs a vaccine with many components, or none at all. Hepatitis A has exactly one worldwide, so a single inactivated preparation protects against every isolate, and immunity is durable. That is why an effective hepatitis A vaccine exists and a common cold vaccine does not.

Discuss in Forum

88.

Which family would you expect to be inactivated by a lipid solvent?

A.Picornaviridae only
B.Poxviridae only
C.Both equally
D.Neither, since neither depends on a lipid envelope for entry

Answer: D

Correct answer: Neither, since neither depends on a lipid envelope for entry

Picornaviruses are naked, so there is no lipid to dissolve. Poxviruses do have membranes, but the infectious particle does not depend on an intact envelope for entry in the way a herpesvirus or an influenza virus does, and vaccinia is notably ether-resistant - a well-known exception to the rule that lipid solvents inactivate membrane-containing viruses. Neither family is a good test case for solvent sensitivity.

Discuss in Forum

Loading…

Topics

Other Subjects

Tags: Poxviridae and Picronaviridae Questions and Answers || Poxviridae and Picronaviridae MCQ Questions and Answers || Poxviridae and Picronaviridae GK Questions and Answers || Poxviridae and Picronaviridae GK MCQ Questions || Poxviridae and Picronaviridae Multiple Choice Questions and Answers || Poxviridae and Picronaviridae GK || GK on Poxviridae and Picronaviridae || Microbiology Questions and Answers || Microbiology MCQ Questions and Answers || Microbiology GK Questions and Answers || GK on Microbiology

Poxviridae and Picronaviridae Questions and Answers

Topics

Other Subjects

About Us

Stay informed about all important Dates & Notifications