Cat Dog Diseases Symptoms 140

Disease is a particular abnormal condition, a disorder of a structure or function, that affects part or all of an organism. The study of disease is called pathology which includes the study of cause. Disease is often construed as a medical condition associated with specific symptoms and signs.

It may be caused by external factors such as pathogens, or it may be caused by internal dysfunctions particularly of the immune system such as an immunodeficiency, or a hypersensitivity including allergies and autoimmunity.

When caused by pathogens (i.e. Plasmodium ssp. in malaria), even in the scientific literature, the term disease is often misleadingly used in the place of its causal agent, viz. the pathogen. This language habitat can cause confusion in the communication of the cause-effect principle in epidemiology, and as such it should be strongly discouraged.