Controlling endemic diseaseEdexcel A-Level Biology B: Revision notes

A disease is endemic when it is always present in a region. Malaria is endemic in much of sub-Saharan Africa and parts of Asia and South America, where it causes illness and many deaths, especially in young children.

Malaria is transmitted by the female Anopheles mosquito (the vector), so control methods either reduce the mosquito population, prevent mosquito bites or treat and prevent infection in people. Each has social, economic and ethical implications, and the scientific community has a role in checking that they work.

• Insecticide-treated bed nets stop mosquitoes biting at night and kill those that land on them.
• Spraying the inside walls of homes with insecticide such as DDT kills mosquitoes that rest there.
• Removing or treating breeding sites, such as draining pools or adding larvicides, reduces mosquito numbers.
• Antimalarial drugs treat infection and can protect people at risk.
• A vaccine can give protection by making memory cells against Plasmodium.
• Genetically modified mosquitoes could reduce the population or stop them carrying the parasite.

Social implications concern how a method affects people and communities.

• Nets work only if families use them correctly every night, so education and cooperation are needed. Some people use nets for other purposes, such as fishing.
• Drugs must be taken for the full course, otherwise treatment fails and resistance develops.
• Draining wetlands or spraying homes may disturb communities or be refused.
• New methods such as genetically modified mosquitoes need public acceptance and informed agreement from the communities affected.

Economic implications concern money and productivity.

• Methods cost money to buy, distribute and replace. DDT is cheap, while new vaccines or genetically modified mosquitoes are costly to develop.
• Poorer countries often cannot pay, so funding may come from richer countries and charities.
• Fewer cases mean fewer working and school days are lost, lower health service costs and more tourism, so control can pay for itself.
• Drug and insecticide resistance can make a method fail and raise costs later.

Ethical implications concern what is right or fair.

• DDT saves lives but persists in the environment and builds up in food chains, harming wildlife.
• Draining marshes destroys habitats for other species.
• Genetically modified mosquitoes cannot easily be recalled once released, and their effect on food webs is uncertain.
• Fair access: limited budgets mean choosing whom to protect first, and poorer people should not be left without protection.
• In clinical trials, people in control groups must be treated fairly, for example by receiving the intervention afterwards.

The scientific community checks that control methods work and are safe.

• Methods are tested in controlled trials with large samples and a control group.
• Results are published and peer reviewed, so independent experts check them.
• Other scientists repeat the studies in different places, as results vary with local mosquitoes and conditions.
• Organisations such as the World Health Organization gather the evidence and advise governments.
• Scientists monitor long-term effects, such as resistance, so methods are re-validated.

Science gives the evidence, but decisions about money and ethics also depend on society.