In humans and animals the spread of disease can be reduced in several ways. Good hygiene, such as washing hands and cooking food properly, removes pathogens. Infected people can be kept apart from others. Vaccination makes a person immune to a pathogen, and vaccinating most of a population gives herd immunity. Vectors can be controlled with insecticides and mosquito nets. Condoms reduce the spread of HIV. Antibiotics treat bacterial infections but do not work against viruses.
In plants, infected plants can be destroyed so that the pathogen cannot reach healthy ones. Farmers can also use fungicides, rotate their crops, control insect vectors, and move or import plants only after checks.
Diseases must be detected before they can be controlled. A test can look for an antigen, a molecule on the pathogen, or for the pathogen's DNA. In plants a disease can also be identified by visual identification of symptoms, such as spots or patches on leaves. A positive DNA test shows that the pathogen is present.