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.
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.