Science & Technology in Action

7th Edition


Health Service Executive

Jnr Science Cert
Influenza (the flu) is a viral disease which mainly affects the epithelial cells of the upper respiratory tract. As a major cause of mortality it receives worldwide attention. This lesson deals with the virus and the steps that are taken by health authority when an outbreak occurs.
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Lesson excerpt

What is Influenza and How are People Infected?
Influenza (Flu) is a viral disease mainly affecting epithelial cells of the upper respiratory tract. It is a major cause of mortality and morbidity amongst the elderly and those with chronic medical conditions that make them more susceptible to infection. The virusdamages mucus-producing and ciliated cells, which are responsible for killing and expelling bacteria from the respiratory tract. Consequently, influenza brings the risk of opportunistic infections requiring antibiotic treatment; however antibiotics have no effect on the influenza virus itself.

Influenza spreads from person to person by airborne droplet infection (coughing/sneezing) or contact with contaminated surfaces. Coughing and sneezing are unavoidable and good hygiene practices reduce the risk of transmission. Detergents applied to surfaces kill the virus. Viruses do not survive for long outside a host.

Epidemic risk is greater in winter. In the Northern Hemisphere, influenza season commences in November and continues through to April whilst in the Southern Hemisphere influenza season runs from May to October. Viruses survive longer in cold conditions when the absolute humidity is low.

How Does Influenza Differ from the Common Cold?
The main difference between influenza and the common cold is that the symptoms of influenza come on rapidly and are typically accompanied by muscle aches, headaches, general tiredness and a fever. The common cold has a more gradual onset and is associated with a runny nose and sneezing. Flu normally runs its course in two to seven days but people may be infectious before symptoms appear and remain so for several days; children are particularly infectious.


True or False?

  1. A pandemic is a worldwide epidemic of a disease. true
  2. There are three main types of influenza virus; these are called Type A, Type B and Type C. true
  3. Workers dealing with immune-deficient persons should not receive the nasal spray live influenza vaccine. true
  4. The AIDS virus has a far greater rate of mutation than the influenza virus. false
  5. It is impossible for antigenic shift to cause the re-emergence of virus strains that have disappeared. true
  6. Natural selection leads to the emergence of virus strains that are resistant to antibodies and anti-viral medicines. true
  7. Birds are always severely affected by the influenza virus. false
  8. Some viruses other than influenza combat immune attack by interfering with complement activity and inhibiting the presentation of antigens. true
  9. A virus that kills its host rapidly is the most likely to spread within a population. false