b) You are preparing an essay on ‘The application of DNA
research to the development of vaccines’. Read the text and
underline the relevant sections.
NEW LIGHT ON THE PLAGUE
The plague, which first struck Europe in the sixth century,
was one of the great disasters of history. In the fourteenth
century it became the Black Death, when it may have
killed one-third of the entire population. The microbe that
causes the disease lives on rats, and is passed on to
humans by the bite of a flea. It still survives today, though
outbreaks are less deadly: the World Health Organization
receives reports of 3,000 cases annually. Scientists
believe that the microbe was originally a stomach
infection, but evolved into a more lethal disease about
1,500 years ago.
Now the genetic code of the plague bacterium has been
‘read’ by scientists; a total of 465 million ‘letters’ of DNA.
They believe that this will help in the development of
vaccines for the plague, one of which has begun clinical
trials. In parts of Africa drug-resistant strains of the
disease have evolved, which gives added importance
to the work, as does the threat that the plague might be
used as an agent of bacteriological warfare.