Cambridge International A Level Biology Revision Guide

Chapter 10: Infectious diseases
This programme was also hugely expensive and often
unpopular. People living in areas where malaria was
temporarily eradicated by the programme lost their
immunity and suffered considerably, even dying, when
the disease returned. Some villagers in South-East Asia
lost the roofs of their houses because dieldrin killed a
parasitic wasp that controlled the numbers of thatcheating
caterpillars. Some spray teams were set upon and
killed by angry villagers in New Guinea. The programme
could have been more successful if it had been tackled
more sensitively, with more involvement of local people.
In the 1970s, war and civil unrest destroyed much of the
infrastructure throughout Africa and South-East Asia,
making it impossible for mosquito control teams to
work effectively.
The reasons for the worldwide concern over the spread
of malaria are:
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an increase in drug-resistant forms of Plasmodium
an increase in the proportion of cases caused by
P. falciparum, the form that causes severe, often
fatal malaria
difficulties in developing vaccines against malaria
an increase in the number of epidemics, because of
climatic and environmental changes that favour the
spread of mosquitoes
the migration of people from areas where malaria is
endemic, for economic and political reasons.
Malaria is still one of the world’s biggest threats to health:
40% of the world’s population lives in areas where there
is a risk of malaria. Between 2000 and 2011, control
measures have achieved a decrease in mortality rates
of about 25% across the world, and 33% in the WHO’s
African region.
Control methods now concentrate on working within
the health systems to improve diagnosis, improve the
supply of effective drugs and promote appropriate methods
to prevent transmission. Several recent advances give hope
that malaria may one day be controlled. The introduction
of simple dip stick tests for diagnosing malaria means
that diagnosis can be done quickly without the need
for laboratories. The whole genome of Plasmodium has
been sequenced, and this may lead to the development of
effective vaccines. Several vaccines are being trialled, but
it is not likely that a successful vaccine will be available for
some time. Drugs are used in combination to reduce the
chances of drug resistance arising.
Three factors may lead to improvements in the control
of malaria:
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use of modern techniques in gene sequencing and drug
design
development of vaccines targeted against different
stages of the parasite’s life cycle
a renewed international will to remove the burden
of disease from the poorest parts of the world, allied
to generous donations from wealthy individuals and
foundations.
QUESTIONS
10.6 Describe how malaria is transmitted.
10.7 Describe the biological factors that make malaria a
difficult disease to control.
10.8 Describe the precautions that people can take to
avoid catching malaria.
Acquired immune deficiency
syndrome (AIDS)
Features of AIDS and HIV are listed in Table 10.4. AIDS
is caused by the human immunodeficiency virus (HIV)
(Figure 10.7).
protein
core
protease
RNA
gp 41
gp 120
protein
capsomeres
reverse
transcriptase
outer lipid
membrane
Figure 10.7 Human immunodeficiency virus (HIV). The outer
envelope contains two glycoproteins: gp120 and gp41. The
protein core contains genetic material (RNA) and two enzymes:
a protease and reverse transcriptase. Reverse transcriptase uses
the RNA as a template to produce DNA (page 466) once the virus
is inside a host cell.
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