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The word is derived from the Greek word αἰτιολογία (aitiología), meaning "giving a reason for" (from αἰτία (aitía) 'cause' and -λογία 'study of'). [1] More completely, etiology is the study of the causes, origins, or reasons behind the way that things are, or the way they function, or it can refer to the causes ...
An etiological agent of disease may require an independent co-factor, and be subject to a promoter (increases expression) to cause disease. An example of all the above, which was recognized late, is that peptic ulcer disease may be induced by stress, requires the presence of acid secretion in the stomach, and has primary etiology in ...
Other exceptions to Koch's postulates include evidence that some pathogens can cause several diseases, such as the varicella-zoster virus causing chickenpox and shingles. Conversely, diseases like meningitis can be caused by a variety of bacterial, viral, fungal, and parasitic pathogens.
The causes listed are relatively immediate medical causes, but the ultimate cause of death might be described differently. For example, tobacco smoking often causes lung disease or cancer, and alcohol use disorder can cause liver failure or a motor vehicle accident.
However, most infections with M. tuberculosis do not cause disease, [169] and 90–95% of infections remain asymptomatic. [87] In 2012, an estimated 8.6 million chronic cases were active. [ 170 ] In 2010, 8.8 million new cases of tuberculosis were diagnosed, and 1.20–1.45 million deaths occurred (most of these occurring in developing countries ).
Primary pathogens cause disease as a result of their presence or activity within the normal, healthy host, and their intrinsic virulence (the severity of the disease they cause) is, in part, a necessary consequence of their need to reproduce and spread. Many of the most common primary pathogens of humans only infect humans, however, many ...
An idiopathic disease is any disease with an unknown cause or mechanism of apparent spontaneous origin. [ 1 ] For some medical conditions, one or more causes are somewhat understood, but in a certain percentage of people with the condition, the cause may not be readily apparent or characterized.
Risk factors for mental illness include psychological trauma, adverse childhood experiences, genetic predisposition, and personality traits. [7] [8] Correlations between mental disorders and substance use are also found to have a two way relationship, in that substance use can lead to the development of mental disorders and having mental disorders can lead to substance use/abuse.