Science & Technology in Action

6th Edition


Health Service Executive

Jnr Science Cert
Measles is a highly contagious infection. This lesson describes the structure of viruses and the parasitic nature of their functioning. The symptoms of measles and some of the complications that can accompany the disease are described. The role of vaccination in controlling the disease is highlighted.
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Lesson excerpt

Measles is a highly contagious, systemic infection caused by the measles virus. The World Health Organisation (WHO)estimates there were 164,000 measles deaths globally in 2008. About 30% of cases have one or more complications such as ear infections, diarrhoea or pneumonia. Mortality is generally 1 to 2 per thousand but isolated populations with no previous exposure to measles have, in the past, been decimated by the disease. People who recover from the disease remain resistant to it for the rest of their lives.

Living organisms, including bacteria, exhibit characteristics such as growth, respiration and reproduction. Viruses, even in the presence of nutrients do not show these signs of life. They have no energy-producing mechanism such as mitochondria and do not respire. Receptors on their surface bind to specific sites onhost cells, allowing the viral contents to infect the cell. The viralDNA (or RNA in the case of measles) takes over the host cell so that, instead of performing its normal functions, it makes many copies of the original virion. Viruses are, therefore,obligate parasites; outside the host cell they are not alive in the usual sense of the word.

Viruses are much smaller than bacteria and typically range in diameter from 10 to 300 nm (nanometre). Because they are smaller than the wavelength of visible light (400 to 700 nm) they cannot be seen with an optical microscope.electron microscopes have an effective wavelength of 0.1 nm and so can help reveal the structure of a virus.

True or False?

  1. Measles is a bacterial disease. false
  2. Vaccination gives you the disease. false
  3. A vaccine stimulates the immune system to produce antibodies against a disease. true
  4. If 80% of the population are vaccinated, measles, mumps and rubella will be eradicated. false
  5. A virus cannot be seen with an optical microscope. true
  6. Viruses are obligate parasites. true
  7. Ireland has the highest level of measles vaccination in Europe false
  8. The measles vaccine contains an attenuated strain of measles virus. true
  9. Countries with high uptake of measles vaccine have low incidence of the disease. false
  10. If 90% of the population is vaccinated then the disease can be eradicated. false