Contains the full lesson along with a supporting toolkit, including teachers’ notes.
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.