A disease is a pairteecular abnormal, pathological condeetion that affects pairt or aw o an organism. The study o disease is cried pathology which includes the causal study o etiology. Disease is eften construed as a medical condeetion associatit wi speceefic symptoms an signs. It mey be caused bi freemit factors such as pathogens, or it mey be caused bi internal dysfunctions pairticularly o the immune seestem such as an immunodeficiency, or a hypersensitivity includin allergies an autoimmunity.
When caused bi pathogens (i.e. Plasmodium ssp. in malaria), even in the scienteefic leeteratur, the term disease is eften misleadinly uised in the place o its causal augent, viz. the pathogen. This leid habitat can cause confuision in the communication o the cause-effect principle in epidemiology, an as such it shoud be strangly discouraged.
In humans, disease is eften uised mair broadly tae refer tae ony condeetion that causes pyne, dysfunction, distress, social problems, or daith tae the person afflictit, or seemilar problems for thae in contact wi the person. In this broader sense, it whiles includes injuries, disabeelities, disorders, syndromes, infections, isolatit symptoms, deviant behaviours, an atypical variations o structur an function, while in ither contexts an for ither purposes thir mey be conseedered distinguishable categories.
Daith due tae disease is cried daith bi naitural causes. Thare are fower main types o disease: infectious diseases, deficiency diseases, genetic diseases (baith hereditary an non-hereditary), an pheesiological diseases. Diseases can an aa be clessified as communicable an non-communicable. The deidliest diseases in humans are coronary artery disease (bluid flow obstruction), follaed bi cerebrovascular disease an lawer respiratory infections.