<P> The most known and used classification of diseases is the World Health Organization's ICD . This is periodically updated . Currently the last publication is the ICD - 10 . </P> <P> Only some diseases such as influenza are contagious and commonly believed infectious . The micro-organisms that cause these diseases are known as pathogens and include varieties of bacteria, viruses, protozoa and fungi . Infectious diseases can be transmitted, e.g. by hand - to - mouth contact with infectious material on surfaces, by bites of insects or other carriers of the disease, and from contaminated water or food (often via fecal contamination), etc . In addition, there are sexually transmitted diseases . In some cases, microorganisms that are not readily spread from person to person play a role, while other diseases can be prevented or ameliorated with appropriate nutrition or other lifestyle changes . </P> <P> Some diseases, such as most (but not all) forms of cancer, heart disease, and mental disorders, are non-infectious diseases . Many non-infectious diseases have a partly or completely genetic basis (see genetic disorder) and may thus be transmitted from one generation to another . </P> <P> Social determinants of health are the social conditions in which people live that determine their health . Illnesses are generally related to social, economic, political, and environmental circumstances . Social determinants of health have been recognized by several health organizations such as the Public Health Agency of Canada and the World Health Organization to greatly influence collective and personal well - being . The World Health Organization's Social Determinants Council also recognizes Social determinants of health in poverty . </P>

What is meant by health illness and disease