Infectious agents and foodborne diseases
Infectious agents are organisms that can be passed to, and between, people in the process of infection transmission. Those that cause diseases are often referred to as pathogens (‘pathogenic' means disease-causing). Many infectious agents (bacteria, viruses, fungi and protozoa) are microorganisms that are too small to be seen except with a microscope; the adult stages of disease-causing parasites (e.g. worms) may be seen with the naked eye, but their eggs and immature stages are microscopic. Microbiology is the science that deals with the study of microorganisms.
Although infections often result in disease, it is possible to be infected with a pathogen and still appear healthy. This is either because the disease has not yet had time to develop, or because the person's immune system is keeping it under control. However, the infectious agent can still be passed on to others, for example by spreading into food handled by the infected person.
The majority of foodborne diseases (those caused by infectious agents transmitted to people in the food we eat) are due to bacteria, but viruses, parasites and toxins can also cause foodborne diseases.