Reducing and Preventing the Spread of Disease

Washing hands with soap, covering the mouth when coughing, disinfecting surfaces and sterilising medical equipment remove pathogens before they can reach a new host. Cooking food thoroughly and keeping it cool stops Salmonella from multiplying, and sewage treatment and clean water prevent cholera.

People with a serious infection, such as TB or Ebola, are kept apart from others so that they cannot pass the pathogen on, and people who may have been exposed are quarantined. Infected farm animals are separated, and their movements are restricted.

A vaccinated person is protected, and if enough people in a population are vaccinated the pathogen cannot spread easily, which also protects the people who cannot be vaccinated. This is called herd immunity. How vaccines work is covered later in the course.

Condoms reduce the spread of HIV and other sexually transmitted infections, and screening donated blood and not sharing needles stop the spread of blood-borne pathogens.

Mosquitoes lay their eggs in standing water, so draining swamps, covering water tanks and clearing containers cuts the number of mosquitoes.

Insecticides can be sprayed in homes and on breeding sites, and biological control, such as fish that eat mosquito larvae, can also be used.

Insecticide-treated bed nets, window screens and repellents stop mosquitoes from biting people, especially at night when the Anopheles mosquito feeds.

Insecticides and natural predators are used to control aphids and other insects that spread plant viruses.

An infected plant is pulled up and burnt or removed, so that it cannot release spores or virus particles to infect others. The crop that remains is protected.

Growing a different crop in a field each year means that a pathogen or a pest that feeds on one type of plant has nothing to feed on the next year, so its numbers fall in the soil.

Plants that have been selectively bred, or genetically engineered, to resist a disease are grown, so that they do not become infected.

Cleaning tools and boots, using disease-free seed, controlling imports of plants and keeping a space between plants all limit the spread.

Fungicides kill fungi on crops, and insecticides control insect vectors such as aphids.

Symptoms such as a rash, a fever, leaf spots, white powder or galls are looked for, sometimes with a microscope. It is quick and cheap, but the symptoms may be missed early on, and different diseases can look alike.

A test contains antibodies that stick to an antigen from the pathogen. If the sample contains the antigen, the test shows a colour change, such as a line on a lateral flow test. It gives a result in minutes, but it is less sensitive than DNA testing.

Techniques such as PCR copy a tiny amount of the pathogen's DNA so that it can be detected and identified. It is very sensitive and accurate, and shows which strain it is, but it needs equipment, trained staff and more time.

Disease in a crop is spotted by inspecting fields for symptoms. Samples can be tested in the laboratory for the pathogen's antigen or DNA, and portable test kits can be used in the field.