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Influenza: A case study
Influenza: A case study

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7 Questions for the course

The following questions allow you to assess your understanding of the content of this course. Each one relates to one or more of the intended learning outcomes of the study.

If you are unable to answer a question, or do not understand the answer given, then reread the relevant section(s) of the course and try the question again.

Question 1

(This question relates to case study learning outcome (LO) 2.)

Why would Robert Koch have been unable to demonstrate that influenza viruses cause the disease influenza, according to his own postulates?

Answer

Koch’s second postulate states that the pathogen can be isolated in pure culture on artificial media. Viruses can only multiply within host cells, so Koch would have been unable to isolate the virus using artificial media. (Much later, eggs and live cells in tissue culture came to be used for growing flu virus, but this was long after Koch’s death, and they do not strictly conform to the original postulate.)

Question 2

(This question relates to LO2.)

List the various structural components of an influenza A virus and note where each of these elements is synthesised within an infected cell.

Answer

Viral RNA is synthesised in the nucleus of the infected cell. The M-protein and other internal proteins are synthesised on ribosomes in the cytoplasm. The capsid is then assembled in the nucleus. The haemagglutinin and neuraminidase are synthesised on ribosomes on the endoplasmic reticulum. The envelope is derived from the host cell’s own plasma membrane.

Question 3

(This question relates to LO2 and LO4.)

It is very uncommon for a strain of influenza that infects other animals to infect people; nevertheless such strains are very important for human disease. Why is this?

Answer

Animal strains of influenza act as a reservoir of genes that may recombine with human influenza viruses to produce new strains that can spread rapidly in humans. Such pandemic strains frequently produce serious diseases with high mortality.

Question 4

(This question relates to LO2 and LO3.)

Which immune defences are able to recognise and destroy virally-infected host cells?

Answer

Cytotoxic T cells and NK cells are able to recognise and destroy virally-infected host cells.

Question 5

(This question relates to LO4 and LO5.)

Why do most people suffer from influenza several times in their lives?

Answer

The virus mutates regularly (antigenic drift); also new strains are occasionally generated by recombination (antigenic shift). Since the immune response is generally specific for a particular strain of virus, new strains are not susceptible to immune defences which have developed against earlier strains.