SOKOINE UNIVERSITY OF AGRICULTURE
College of Veterinary Medicine and Biomedical Sciences
BLS 113: Virology CAT 2 Total Marks: 80 Date: 14th June 2024 Time: 1 hour
General instructions: Answer all THREE questions. A zero mark will be given to any rubbed or cancelled answer in the specific question.
1. Select the best answer among the alternative statements given for each question and circle it (60 marks)
i. What is a key driving force for the evolution of viruses?
A) Sexual reproduction B) Mutation and natural selection
C) Binary fission D) Vegetative propagation
ii. What is the primary mechanism by which viruses undergo mutations?
A) Mitosis B) Meiosis C) Recombination D) Transcription
iii. What is the primary mechanism by which influenza viruses undergo antigenic shift?
A) Point mutations in the viral genome
B) Reassortment of gene segments between different virus strains
C) Integration of viral DNA into the host genome
D) Horizontal gene transfer
iv. Which term describes a change in a single nucleotide of the viral genome?
A) Insertion B) Deletion C) Point mutation D) Frame shift mutation
v. What is the term for the gradual accumulation of small genetic changes in a virus population over time?
A) Genetic drift B) Genetic recombination C) Antigenic drift D) Point mutation
vi. How can recombination contribute to virus evolution?
A) By altering the viral target of antiviral drugs B) By promoting host immune response
C) By facilitating the exchange of genetic material between different virus strains
D) By inhibiting viral replication
vii. Which process allows viruses to acquire new genetic material from other viruses or host cells?
A) Horizontal gene transfer B) Genetic reassortment
C) Viral recombination D) All of the above
viii. Which term describes a mutation that changes a viral protein such that it can no longer be recognized by the host’s immune system?
A) Synonymous mutation B) Nonsynonymous mutation
C) Antigenic drift D) Antigenic shift
ix. What is a quasispecies in the context of viral evolution?
A) A group of viruses with identical genetic sequences.
B) A population of viruses with a high degree of genetic diversity.
C) A virus that infects multiple host species.
D) A virus that has undergone antigenic shift.
x. How do viruses with segmented genomes like influenza achieve genetic diversity?
A) Through mutation accumulation only.
B) Through both mutation and reassortment.
C) Through mutation and integration into the host genome.
D) Through lateral gene transfer.
xi. What term describes the process by which two or more different influenza virus strains exchange genetic material, leading to the emergence of a new virus?
A) Antigenic drift B) Antigenic shift C) Recombination D) Point mutation
xii. How does the antigenic shift contribute to the emergence of novel influenza virus strains with pandemic potential?
A) It leads to gradual changes in viral surface proteins.
B) It facilitates recombination between different influenza virus strains.
C) It facilitates reassortment between different influenza virus strains.
D) It results in point mutations in the viral genome.
xiii. Which of the following statements is true about viral evolution?
A) Viruses evolve more slowly than their host organisms.
B) Viral evolution is driven solely by natural selection.
C) High mutation rates in viral genomes contribute to rapid evolution.
D) Viral genomes are too small to undergo significant evolutionary changes.
xiv. What is the consequence of a high mutation rate in RNA viruses compared to DNA viruses?
A) RNA viruses have greater genetic stability. B) RNA viruses evolve more rapidly.
C) RNA viruses have lower diversity. D) RNA viruses are less likely to develop drug resistance.
xv. Which type of selection might lead to the fixation of beneficial mutations in a viral population?
A) Neutral selection B) Purifying selection
C) Positive selection D) Negative selection
xvi. Which factor plays a crucial role in the emergence of new infectious diseases caused by viruses?
A) High host immunity B) Limited host range
C) Evolutionary changes in the virus D) Lack of genetic variation
xvii. Which of the following is a characteristic of persistent viral infections?
A) Rapid onset of symptoms B) Clearance of the virus by the immune system
C) Long-term presence of the virus without causing severe symptoms D) High mortality rate
xviii. How can viruses cause damage to host cells during infection?
A) Inhibition of viral replication B) Stimulation of host cell division
C) Induction of apoptosis D) Activation of the immune response
xix. Which factor is crucial in determining the severity of viral infections?
A) Viral replication rate B) Host age and health status
C) Virion shape D) Presence of an envelope
xx. How do oncogenic viruses contribute to the development of cancer?
A) By promoting normal cell division B) By inducing apoptosis in infected cells
C) By enhancing host immune response D) By disrupting cellular growth control mechanisms
xxi. How does the integration of viral genetic material into the host cell genome contribute to oncogenesis?
A) By inhibiting cellular signaling pathways B) By promoting normal cell division
C) By disrupting cellular growth control mechanisms D) By enhancing host immune response
xxii. What is the primary mechanism by which oncogenic RNA viruses contribute to cancer development?
A) Integration of viral DNA into the host genome B) Induction of apoptosis in infected cells
B) Activation of cellular oncogenes or inactivation of tumor suppressor genes
D) Inhibition of viral replication
xxiii. What is the primary advantage of live attenuated vaccines over inactivated vaccines?
A) They induce a more rapid immune response B) They have a longer shelf life
C) They are safer for immunocompromised individuals D) They require fewer booster doses
xxiv. How do mRNA vaccines work to induce an immune response against viruses?
A) By delivering viral proteins directly into the bloodstream
B) By introducing a small piece of viral genetic material to instruct cells to produce viral proteins
C) By using inactivated viral particles
D) By exposing the immune system to viral surface glycoproteins
xxv. What is the primary target of antiretroviral drugs in the treatment of HIV?
A) Viral entry B) Reverse transcriptase C) Protease D) Integrase
xxvi. What is the primary target of antiviral drugs that inhibit neuraminidase activity?
A) Viral entry B) Reverse transcriptase C) Polymerase D) Release of viral particles
xxvii. Which antiretroviral drug targets the fusion of the human immunodeficiency virus (HIV) with the host cell membrane?
a) Nucleoside reverse transcriptase inhibitors (NRTIs) b) Protease inhibitors c) Entry inhibitors d) Integrase inhibitors
xxviii. Which antiretroviral drug class inhibits the integration of the viral DNA into the host cell genome?
A) Nucleoside reverse transcriptase inhibitors (NRTIs) B) Protease inhibitors
C) Entry inhibitors D) Integrase inhibitors
xxix. How can viral mutations contribute to antiviral drug resistance?
A) By increasing viral replication rate B) By inhibiting host cell division
C) By altering the viral target of the drug D) By promoting host immune response
xxx. How does selective pressure, such as the use of antiviral drugs, contribute to virus evolution? A) It inhibits the virus from evolving
B) It promotes the emergence of drug-resistant virus variants
C) It reduces the mutation rate of the virus D) It increases the host’s susceptibility to the virus
2. Match list A with the correct answer in list B, then write the letter from list B in spaces provided in list A (4 marks)
| LIST A | LIST B |
| i. Block reverse transcriptase enzyme, preventing viral DNA synthesis……………………………………………………
ii. Agents that block the binding of gp120 of HIV to host chemokine receptor 5 (CCR5)………………………………… iii. Mimic sialic acids and therefore, once incorporated they inhibit neuraminidase and interfering with the release of influenza virus from infected host cells………………………………….. iv. Bind directly to reverse transcriptase, disrupting its function…. |
A. Nucleoside Reverse Transcriptase Inhibitors (NRTIs)
B. Enfuvirtide (ENF; Fuzeon) C. Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs) D. Integrase inhibitors E. Maraviroc (MVC; Celsen) F. Oseltamivir and Zanamivir |
3. Antiretroviral drugs are designed to target specific stages in the lifecycle of HIV (Human Immunodeficiency Virus)
i. What are the four main targets where these drugs act to prevent HIV replication? (8 marks)
a) —————————————————————————————————————————–
b) ——————————————————————————————————————————
c) ——————————————————————————————————————————
d) —————————————————————————————————————————–
ii. Provide one group of drugs that target each of the four targets named in (i) above (8 marks)
a) ——————————————————————————————————————————
b) ——————————————————————————————————————————
c) ——————————————————————————————————————————
d) ——————————————————————————————————————————
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