Prevention & Control of Disease (Cambridge (CIE) AS Biology): Revision Note

Factors for prevention & control of common diseases

Prevention and control of cholera

• Cholera occurs when people do not have access to effective sanitation facilities and access to clean water

• It is difficult to prevent and control cholera in developing countries

  • The fast-growing cities in developing countries may not have the appropriate infrastructure, and may have limited funds for large-scale projects such as the provision of drainage systems, sewage treatment facilities and clean water supplies

  • Humanitarian crises, e.g. displacement of people due to wars or natural disasters, can cause the destruction of sanitation infrastructure and/or the provision of poor sanitation facilities in overcrowded temporary housing

  • In some developing countries the use of raw human sewage to irrigate crops is common

• Prevention of cholera can occur through:

  • Providing adequate sewage treatment infrastructure

  • The provision of clean, piped water that has been chlorinated to kill bacteria

    • This strategy means that cholera is very rare in developed countries

  • Vaccination programmes in areas where cholera is common

• Cholera can be controlled by:

  • Ready access to treatments such as oral rehydration therapy; a solution containing glucose, salts and water

  • Monitoring programmes by the World Health Organisation (WHO)

  • Using antibiotics in severe cases

Prevention and control of malaria

• Malaria spreads in regions where Anopheles mosquitos can breed; this is dependent on a warm climate, and the availability of standing water

• The 3 main methods for reducing malaria are:

  • Reducing the number of Anopheles mosquitoes in an area

    • Spraying living areas with insecticides

    • Spreading oil over the surface of water bodies in which mosquitoes breed

    • Draining marshes and other unnecessary bodies of water

    • Ensuring ponds and irrigation or drainage ditches are stocked with fish that feed on mosquito larvae

    • Unfortunately, mosquitoes lay eggs in even very small puddles and pools of water and therefore it is practically impossible to control all breeding sites using the methods listed above

  • Reducing the chance of being bitten by these mosquitoes

    • People in malarial zones should sleep under bed nets, which can also be soaked periodically in insecticide to increase effectiveness,

    • People should avoid exposing their skin at dusk when mosquitoes are most active

  • Using drugs to prevent Plasmodium infecting humans

    • Drugs, such as chloroquine and mefloquine, are taken before, during and after a visit to a location where malaria is prevalent.

    • The use of these drugs has resulted in drug-resistant strains of Plasmodium

    • The drugs are expensive and can have disagreeable side-effects

• In the 1950s, the World Health Organisation (WHO) coordinated a worldwide eradication programme; whilst malaria was eradicated from some countries, the programme was mainly unsuccessful because:

  • Plasmodium became resistant to the drugs being used to try and control it

  • Anopheles mosquitoes became resistant to DDT and other insecticides being used against them

• To control malaria, governments, the WHO and other institutions are focusing on:

  • Working within health systems to improve diagnosis

  • Improving the supply of effective drugs

  • Using drugs in combination to reduce drug resistance

  • Promoting appropriate methods to prevent transmission, e.g. the use of biological controls to target the larvae and insecticide-treated bednets

• Recent scientific advances regarding the control of malaria are:

  • Simple dipstick tests for diagnosing malaria – this means a diagnosis can be made much faster and does not require a laboratory

  • The entire Plasmodium genome has been sequenced

  • The approval of two effective malaria vaccines which have been decades in development; these can now be rolled out in affected areas

Prevention and control of tuberculosis (TB)

• TB is spread from person to person when droplets released by the coughing or sneezing of an infected person are inhaled by an uninfected person

  • The droplets contain the TB-causing bacterium Mycobacterium tuberculosis

• The spread of TB increases in overcrowded living conditions, so is prevalent among poorer people with inadequate housing conditions

• Contact tracing, and the subsequent testing of those contacts for the bacterium, is an important part of controlling the spread of TB

• Prevention of TB occurs through the use of the BCG vaccine

  • The vaccine protects up to 70-80% of those who receive it, although its effectiveness decreases with age

• The form of TB that can be transmitted between cattle and humans (caused by Mycobacterium bovis) can be prevented by:

  • Routinely testing cattle for TB and destroying those that test positive

  • Pasteurising milk; this kills any TB-causing bacteria present in the milk

  • Ensuring that meat is cooked properly

Prevention and control of HIV/AIDS

• HIV is spread when body fluids are exchanged between an infected and an uninfected individual

• Preventing the spread of HIV is very difficult as the virus has a long latent stage, which results in it being transmitted by people who have the virus but show no symptoms, and so may not know they are infected

  • This occurs because the virus can change its surface proteins, making it difficult for the human immune system to recognise it and for a vaccine to be developed

• To prevent the transmission of HIV the following measures can be implemented:

  • Blood donations can be screened for HIV and heat-treated to kill any viruses

  • HIV-positive mothers and their babies can be treated with drugs

  • Condoms, femidoms and dental dams can be used to decrease the infection risk during sexual intercourse and oral sex by forming a physical barrier between body and fluids

  • Education programmes about how the virus is transmitted can be released into the community to encourage people to have HIV tests and to avoid unprotected sex

  • Intravenous drug users encouraged not to share needles

• Controlling HIV can occur by:

  • Contact tracing (and the subsequent testing of those contacts for the virus)

  • Screening blood donations

  • Public health measures, such as widespread HIV testing of the population and education programmes

  • Needle-exchange schemes have been set up in some places to exchange used needles for new, sterile ones

  • Encouraging individuals to be tested for HIV

  • Using anti-retroviral drugs

• The socio-economic status of a person or country with HIV can determine how it is controlled

  • For example, HIV-positive mothers are advised not to breastfeed in high-income countries, however, in low- and middle-income countries breastfeeding is more affordable, and offers protection against other diseases, e.g. cholera