Viruses Questions and Answers

Answer: B

Because the virus replicates in the recipient, one course often gives immunity that lasts for life. The cost of that advantage is the possibility of reversion to a pathogenic form, which is why such vaccines need extensive testing.

Answer: C

A live vaccine strain has been weakened by laboratory manipulation, and a weakened organism may mutate back toward virulence. Recombinant methods that delete the regions likely to revert are one way of reducing that risk.

Answer: D

A killed preparation cannot replicate in the recipient, so the immune system meets only the antigen supplied. That makes the vaccine safe from causing infection but means high antigen concentrations and repeat doses are usually needed.

Answer: A

Interferon is a protein that puts uninfected cells into a state in which viral replication is resisted, which is why it acts broadly rather than against one agent. Alpha interferon has proved useful clinically in chronic hepatitis B and C.

Answer: B

Correct answer: Three: alpha, beta and gamma

Three classes are recognised. Alpha and beta are the type I interferons, produced by many kinds of cell in direct response to viral infection and acting to put neighbouring cells into an antiviral state. Gamma is type I I, produced by activated T cells and natural killer cells, and it is chiefly immunoregulatory rather than directly antiviral.

Answer: C

An antiviral interrupts one or more steps of the cycle inside the cell, which is a harder target than a bacterium because so much of the machinery being used belongs to the host. Supplying antibody is passive immunisation, a different approach entirely.

Answer: D

Ready-made antibody is transferred rather than being raised by the recipient, so protection begins at once and fades as the antibody is cleared. Human immunoglobulin is used after a recent exposure, where no effective vaccine exists, or where illness prevents a vaccine response.

Answer: A

The parts are made independently inside the cell and only then brought together, which is why the number of particles rises in a burst rather than by doubling. Maturation is the interval in which those assembled particles accumulate.

Answer: B

Budding wraps the nucleocapsid in host membrane already carrying viral glycoproteins, which is how the envelope is acquired. Because the cell need not be destroyed for release, budding is compatible with a persistent infection in a way that lysis is not.

Answer: C

A particle can take a patch of membrane and leave while the cell repairs itself, so release and cell death are separate events. A naked virus more often accumulates until the cell breaks, which is why the two groups differ in the kind of infection they tend to cause.