Download Timeline of a Scientific Story: Malaria

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Timeline of a Scientific Story: Malaria
In this activity, students can try to arrange 11 events in the history of malaria
into chronological order. The first pages are background information for the
teacher, then the following pages can be printed out and cut into cards for
arranging.
The activity is intended to illustrate the way that knowledge based on
observation and growing understanding is part of science over many centuries
and how human interventions are part of that story. The teachers notes also
highlight areas of `How Science Works’ which are illustrated.
Two of the cards – climate change and international travel are deliberately
difficult to place as they are not `events’ but have been and continue to be
major factors over the centuries (the Romans certainly travelled widely!).
About 400 BC:
Hippocrates, a Greek physician and called the `father of modern medicine’
describes the symptoms of malaria and observes that the illness seems to be
related to time of year and closeness of marshy areas.
How Science Works: Hippocrates had made an observation –it took many
centuries for other scientists to develop a hypothesis and then have the ability
to develop theories and explanations.
About 100 BC
Romans find that draining marshes reduces the risk of the illness.
They didn’t need to fully understand the science behind the observation in
order to act to reduce the risk
About 1600
Peruvian Indians use the powdered bark of the Chinchona tree to treat the
symptoms of malaria. It becomes known as Jesuit powder after they bring the
medicine back to Europe. The medicine was available in London in 1649 to
treat the disease which was then known as ‘Agues’.
The Peruvian Indians must have been used to using natural products to treat
illnesses. The active substance in the Chinchona tree bark is quinine which
was later used in other malaria treatments and is now also an ingredient in
tonic water. It might have been the European colonisers that took malaria to
Peru in the first place.
1879
Alphonse Levaran, working in Algeria believed that whatever was causing
malaria would be found in the blood of sufferers. He began work examining
fresh blood. It was known that small black particles called melanins were in the
blood of sufferers but the actual cause of the illness wasn’t understood. In his
work in Algeria and then the marshy areas of Southern Italy, Levaran found
other particles in the blood of sufferers of `marsh fever’ and showed that they
were the parasites that cause the illness and that the melanin particles were
the results of the parasites attacking red blood cells.
How Science Works: Levaran carried out experiments to try to develop an
explanation of the transmission of the disease. His hypothesis was that it
related to the melanin and his work was to try to support this and to explain
how.
1890 – 94
Levaran tried to find the source of the parasites – he examined the air, soil and
water of marshy areas without success and developed the hypothesis that the
parasite has one stage of its lifecycle in mosquitoes and is introduced into
humans by the mosquitoes bite.
Late 1890s
Ronald Ross, a British Army doctor carried out experiments with mosquitoes
biting humans and tried to follow the life cycle of the parasite. He also made
progress by studying avian (bird) malaria. His work, building on Levaran’s, led
to the understanding that mosquitoes were the `vector’ and the parasite the
cause of the illness.
How science works: Ross carried out carefully designed experiments to test his
hypothesis that the parasite’s life cycle included time in the mosquito and time
in the human and that it moved from one to the other through mosquito bites.
1940s onwards
The insecticide DDT is developed and used against mosquitoes as part of a
global malaria eradication programme. This also involves draining stagnant
water, putting paraffin on marshes and using mosquito nets. All these
measures contribute to interrupting the lifecycle of the parasite and to a large
drop in malaria in many areas, particularly around the Mediterranean. Drugs
such as chloroquine are effective in treating those that do contract malaria.
1962
Scientist Rachel Carson publishes `Silent Spring’ – detailing the links between
the use of pesticides (including DDT) and deaths and falling populations of
animals in the area. The persistence of some of these pesticides in the food
chain was leading to unwanted effects like thinner bird egg shells. Although
DDT is banned in 1972 in the USA, the dilemma of putting malaria control
above protection of the wider ecosystem is still causing controversy.
1970s onwards
Controls on DDT, and socio-economic and political factors lead to a reduction in
malaria control and the disease starts to increase again.
Constant factors in the story of malaria:
International travel helps to spread the disease. This has been happening
throughout human history – we tend to think of it as a new phenomenon
as air travel makes frequent visits to malarial zones more practical.
Climate change affects the range of mosquitoes' habitable areas. This
also has happened throughout human history and before. As the Earth’s
climate has warmed and cooled, the malaria carrying species of mosquito
have been able to inhabit increasing and decreasing areas respectively.
Evolution and adaptation. Resistance of the mosquitoes to chemical
control methods and of the parasite to drugs make intervention and
treatment an ever changing challenge.
Continuous development of preventative and treatment drugs.
Economic factors. The areas, particularly in Africa, where malaria is the
most serious problem, often do not have the wealth to invest in control
and treatment.
Sorting Cards
The sheets below can be printed out and cut up – students could sort them
into the order they think things would have happened. This can be used to
look at `how science works’ or an introduction to studies of life cycles or
transmission of illness. The exercise could also be the basis of a short
research project for students to find out about the different parts of the story.
The cards about international travel and climate change are impossible to place
as they have always happened – but can lead to discussion between students
or groups of students.
Hippocrates observes that malaria occurs more at
certain times of year and in areas close to marshes
Romans find that draining marshes reduces the risk
of malaria
Peruvian Indians use the bark of a tree to treat the
symptoms of malaria. It becomes known as Jesuit
powder after they bring the medicine back to
Europe.
The protozoan parasite causing malaria is found
The mosquito is identified as the vector of the illness
DDT is developed and used against mosquitoes
`Silent Spring’ by Rachel Carson alerts people to the
damage that can be done by uncontrolled use of
pesticides
DDT is banned in many countries
A range of prophylactic drugs are developed to
prevent people contracting malaria
The parasite develops resistance to some
prophylactic drugs
International travel spreads the parasite
Climate change affects the size of the area habitable
by mosquitoes.