Free Viruses MCQs with Answers

• A. immunity produced by the vaccine lasts only days
• B. influenza virus infects only elderly people
• C. antibiotics destroy the vaccine
• D. the surface antigens of the virus mutate frequently

Explanation: Influenza's RNA genome mutates rapidly and its haemagglutinin and neuraminidase surface proteins keep changing, so last year's antibodies…

• A. contaminated drinking water
• B. the bite of Aedes mosquitoes
• C. coughing and sneezing
• D. eating contaminated food

Explanation: Aedes aegypti and Aedes albopictus mosquitoes carry the dengue virus between people, which is why outbreaks follow the mosquito season and…

• A. lack their own metabolism and the structures that antibiotics target
• B. are too small for drugs to reach
• C. live only in the soil
• D. are destroyed by stomach acid

Explanation: Antibiotics attack bacterial machinery such as cell walls and 70S ribosomes, and viruses possess neither, borrowing the host's instead.

• A. mosquito bites
• B. contaminated milk
• C. airborne droplets
• D. the bite of an infected animal such as a dog

Explanation: The rabies virus travels in the saliva of infected mammals and enters through a bite, then moves along nerves to the brain, causing…

• A. Hepatitis B
• B. Hepatitis C
• C. Hepatitis A
• D. Hepatitis D

Explanation: Hepatitis A, like hepatitis E, spreads by the faecal oral route through polluted food and water and usually resolves on its own.

• A. consist only of short circular RNA with no protein coat
• B. contain DNA genomes
• C. are larger than any virus
• D. infect only animals

Explanation: Viroids are the smallest known infectious agents, naked circles of RNA that cause plant diseases such as potato spindle tuber.

• A. release, assembly, biosynthesis, penetration, attachment
• B. attachment, penetration, biosynthesis, assembly, release
• C. biosynthesis, attachment, release, penetration, assembly
• D. penetration, release, attachment, assembly, biosynthesis

Explanation: The phage first attaches by its tail fibres, injects its DNA, then commandeers the host to make viral parts, assembles complete particles…

• A. DNA ligase
• B. RNA polymerase
• C. reverse transcriptase
• D. restriction endonuclease

Explanation: Reverse transcriptase copies the viral RNA into DNA, which then integrates into the host chromosome.

• A. antibodies on the cell surface
• B. MHC class one molecules
• C. antigen receptors of B lymphocytes
• D. CD4 receptors on helper T lymphocytes

Explanation: The viral glycoprotein gp120 fits the CD4 receptor, which is why helper T cells and macrophages, the CD4 bearing cells, are the targets.

• A. window period
• B. latent phase of AIDS
• C. incubation of tuberculosis
• D. vaccination period

Explanation: During the window period, which may last weeks to a few months, antibody tests can miss the infection even though the person is already…

• A. Blood
• B. Saliva
• C. Semen
• D. Vaginal secretions

Explanation: Blood, semen and vaginal secretions carry enough virus to transmit infection, but saliva contains too little and is even mildly antiviral.

• A. free virus particles circulating in the plasma
• B. virus crystals stored in lymph nodes
• C. viral DNA integrated into the chromosome of the host cell
• D. the inactive form of the virus outside the body

Explanation: Once reverse transcriptase makes the DNA copy, integrase inserts it into the host genome, where it can stay silent for years or direct the…

• A. the virus is too large for the immune system
• B. HIV infects only animals
• C. antibodies can never form against HIV
• D. the virus mutates its envelope proteins very rapidly

Explanation: The envelope glycoproteins change faster than a vaccine can be designed, and the virus hides inside cells as a provirus.

• A. repeating the ELISA only
• B. the Western blot technique
• C. a blood culture on agar
• D. a chest X ray

Explanation: ELISA is sensitive but can give false positives, so Western blot, which separates the viral proteins and shows which antibodies are…

• A. during pregnancy, during delivery and through breastfeeding
• B. only through the genes she passes on
• C. only if the child is vaccinated
• D. never, since HIV requires a needle to spread

Explanation: Mother to child transmission can occur across the placenta, at birth and in breast milk, which is why antiretroviral treatment during…

• A. Sharing needles contaminated with infected blood
• B. Sexual contact with an infected person
• C. Transfusion of infected blood
• D. Sharing a meal with an infected person

Explanation: HIV needs direct access to blood or mucous membranes, so casual contact such as meals, handshakes and sneezing carries no risk.

• A. single drugs are too expensive to manufacture
• B. the drugs increase each other's side effects
• C. HIV develops resistance rapidly to any single drug
• D. they kill the virus directly by oxidation

Explanation: HIV mutates so fast that a population resistant to one drug soon appears, but becoming resistant to three at once is far harder.

• A. Oncoviruses
• B. Lentiviruses
• C. Spumaviruses
• D. Adenoviruses

Explanation: Lentiviruses, meaning slow viruses, cause long incubation, persistent infections, which fits HIV's years long course from infection to…

• A. prevent transmission of the virus through transfusion
• B. increase the storage life of the blood
• C. raise the red cell count of the unit
• D. detect anaemia in the donor

Explanation: One unit of infected blood can transmit HIV directly into the recipient's circulation, so screening donated blood is one of the most…

• A. makes vaccination unnecessary
• B. destroys the host's red blood cells
• C. binds to receptors on host cells and allows the virus to enter
• D. makes the virus resistant to heat

Explanation: gp120 projects from the envelope and locks onto CD4 receptors, the first step of infection, which is why it is also the main target…