Historical Control of Malaria
Malaria has afflicted people for much of human history. The prevention and treatment of the disease has been investigated in science and medicine for hundreds of years. These studies have continued up to the present day and eradication/elimination of malaria still seems a distant goal. As malaria remains a major public health problem, causing 250 million cases of fever and approximately one million deaths annually, understanding its history is key.
Timeline of Discoveries and Disease Control Methods
DDT - Attempts at Eradication Post-WWII
After the Second World War the international community turned its attention to the health problems of peacetime. Malaria was rampant throughout much of the developing world, and in the 1950s the World Health Organization (WHO) considered a programme for eradicating malaria similar to that used to eradicate smallpox. The auguries were good: chloroquine was highly effective against the Plasmodium parasite in humans, the new insecticide dichloro-diphenyltrichloroethane (DDT) killed the vector (Anopheles) and draining marshes removed the mosquitoes' breeding grounds.
A mathematical model was developed by MacDonald to explain the dynamics of malaria and how malaria could be eradicated. Four strategies were formulated using this model:
- Preparation - Gather epidemiologic and entomologic information to plan attack
- Attack - Massive IRS spraying of every at risk house with DDT until the number of infective carriers was at or near zero
- Consolidation - Active case finding and treatment with chloroquine/quinine
- Maintenance - Continue until global eradication achieved
Initially, spraying houses with DDT was a success: the number of cases of malaria in Sri Lanka, for instance, fell from 3 million in 1946 to only 29 in 1964. Also, Australia, Brunei, Bulgaria, Cuba, Dominica, Grenada, Hungary, Italy, Jamaica, Mauritius, Netherlands, Poland, Portugal, Puerto Rico, Romania, Saint Lucia, Singapore, Spain, Taiwan, Trinidad and Tobago, United States, Virgin Islands and Yugoslavia were able to successfully eradicate malaria. However, complications of this policy soon became apparent when resistance to chloroquine and environmental toxicity of DDT were reported.
In 1962, Silent Spring by American biologist Rachel Carson was published. The book catalogued the environmental impacts of the indiscriminate spraying of DDT in the US and questioned the logic of releasing large amounts of chemicals into the environment without fully understanding their effects on ecology or human health. The book suggested that DDT and other pesticides may cause cancer and that their agricultural use was a threat to wildlife, particularly birds. This resulted in a large public outcry that eventually led to DDT being banned for agricultural use in the US in 1972. DDT was subsequently banned for agricultural use worldwide under the Stockholm Convention, but its limited use in disease vector control continues to this day and remains controversial.
Click here for the Stockholm Convention guidelines on DDT use
Furthermore, draining all the marshes in tropical parts of the world proved impossible, and chloroquine showed signs of decreasing efficacy. Resistance to chloroquine had been acquired by Plasmodium and gradually, during the 1970s, regions of chloroquine resistance spread throughout the world. Today, there are resistance strains of Plasmodium in many areas. Resistance arose probably due to poor compliance, a major problem in bringing complex and expensive drug treatments to countries with little health infrastructure.
Click here for the WHO position on DDT use.
