Disease: Difference between revisions

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{{short description|Abnormal condition that negatively affects an organism}}

[[File:Mycobacterium tuberculosis.jpg|thumb|upright=1.3|[[Scanning electron micrograph]] of ''[[Mycobacterium tuberculosis]]'', a species of [[pathogenic bacteria]] that cause [[tuberculosis]]]]

A '''disease''' is a particular abnormal condition that negatively affects the [[structure]] or [[function (biology)|function]] of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be '''medical conditions''' that are associated with specific [[signs and symptoms]]. A disease may be caused by external factors such as [[pathogen]]s or by internal dysfunctions. For example, internal dysfunctions of the [[immune system]] can produce a variety of different diseases, including various forms of [[immunodeficiency]], [[hypersensitivity]], [[allergy|allergies]] and [[autoimmune disorders]].

In humans, ''disease'' is often used more broadly to refer to any condition that causes [[pain]], [[Abnormality (behavior)|dysfunction]], [[distress (medicine)|distress]], [[social problems]], or [[death]] to the person affected, or similar problems for those in contact with the person. In this broader sense, it sometimes includes [[injury|injuries]], [[disability|disabilities]], [[#Disorder|disorders]], [[syndrome]]s, [[infection]]s, isolated [[symptom]]s, deviant [[behavior]]s, and atypical [[human variability|variations]] of structure and function, while in other contexts and for other purposes these may be considered distinguishable categories. Diseases can affect people not only physically, but also mentally, as contracting and living with a disease can alter the affected person's perspective on life.

Death due to disease is called [[death by natural causes]]. There are four main types of disease: infectious diseases, [[deficiency disease]]s, [[hereditary diseases]] (including both [[Genetic disorder|genetic diseases]] and [[Non-Mendelian inheritance|non-genetic hereditary diseases]]), and physiological diseases. Diseases can also be classified in other ways, such as [[transmission (medicine)|communicable]] versus [[non-communicable disease|non-communicable]] diseases. The deadliest diseases in humans are [[coronary artery disease]] (blood flow obstruction), followed by [[cerebrovascular disease]] and [[lower respiratory infections]]. In developed countries, the diseases that cause the most sickness overall are [[neuropsychiatric conditions]], such as [[Major depressive disorder|depression]] and [[Anxiety disorder|anxiety]].

The study of disease is called ''[[pathology]]'', which includes the study of [[Etiology (medicine)|''etiology'']], or cause.

In many cases, terms such as ''disease'', ''disorder'', ''morbidity'', ''sickness'' and ''illness'' are used interchangeably; however, there are situations when specific terms are considered preferable.

<!-- This ";" and ":" formatting is called a "definition list". See [[Help:List#List basics]] for more information. Please do not change the formatting unless you know what you are doing. -->

;Disease

:* benefit that outweighs the harm of any interventions taken – removing the precancerous tissue prevents cancer, and thus prevents a potential death from cancer.

;Mental

:[[Mental disorder|Mental illness]] is a broad, generic label for a category of illnesses that may include affective or [[emotion]]al instability, behavioral dysregulation, cognitive dysfunction or impairment. Specific illnesses known as mental illnesses include [[major depressive disorder|major depression]], generalized [[anxiety disorder]]s, [[schizophrenia]], and [[attention deficit hyperactivity disorder]], to name a few. Mental illness can be of biological (e.g., anatomical, chemical, or genetic) or psychological (e.g., trauma or conflict) origin. It can impair the affected person's ability to work or study and can harm interpersonal relationships. The term [[insanity]] is used technically as a legal term.

:An organic disease is one caused by a physical or physiological change to some tissue or organ of the body. The term sometimes excludes infections. It is commonly used in contrast with mental disorders. It includes emotional and behavioral disorders if they are due to changes to the physical structures or functioning of the body, such as after a [[stroke]] or a traumatic brain injury, but not if they are due to [[psychosocial]] issues.

{{redirect|Flareup|the Transformers character|Flareup (Transformers)}}

In an infectious disease, the [[incubation period]] is the time between infection and the appearance of symptoms. The [[latency period]] is the time between infection and the ability of the disease to spread to another person, which may precede, follow, or be simultaneous with the appearance of symptoms. Some viruses also exhibit a dormant phase, called [[viral latency]], in which the virus hides in the body in an inactive state. For example, [[varicella zoster virus]] causes [[chickenpox]] in the [[acute (medicine)|acute phase]]; after recovery from chickenpox, the virus may remain dormant in nerve cells for many years, and later cause [[herpes zoster]] (shingles).

:{{See also|Convalescence|Recuperation (recovery)|label 2=Recuperation}}Recovery can refer to the repairing of physical processes (tissues, organs etc.) and the resumption of healthy functioning after damage causing processes have been cured.

[[File:Poison ivy rash.JPG|175px|thumb|alt=skin rash on the leg|This rash only affects one part of the body, so it is a localized disease]]

;Localized disease

:A [[systemic disease]] is a disease that affects the entire body, such as [[influenza]] or [[hypertension|high blood pressure]].

{{Main|Nosology|Medical classification}}

Diseases may be classified by cause, [[pathogenesis]] ([[mechanism (biology)|mechanism]] by which the disease is caused), or by [[symptom]](s). Alternatively, diseases may be classified according to the [[organ system]] involved, though this is often complicated since many diseases affect more than one organ.

A chief difficulty in nosology is that diseases often cannot be defined and classified clearly, especially when cause or pathogenesis are unknown. Thus diagnostic terms often only reflect a symptom or set of symptoms ([[syndrome]]).

Classical classification of human disease derives from the observational correlation between pathological analysis and clinical syndromes. Today it is preferred to classify them by their cause if it is known.

The most known and used classification of diseases is the [[World Health Organization]]'s [[International Statistical Classification of Diseases and Related Health Problems|ICD]]. This is periodically updated. Currently, the last publication is the [[ICD-11]].

{{See also|Cause (medicine)|Transmission (medicine)}}

Only some diseases such as [[influenza]] are contagious and commonly believed infectious. The [[microorganism]]s that cause these diseases are known as pathogens and include varieties of bacteria, viruses, protozoa, and fungi. [[Infectious disease]]s can be transmitted, e.g. by hand-to-mouth contact with infectious material on surfaces, by bites of [[vector (epidemiology)|insects or other carriers]] of the disease, and from contaminated water or food (often via [[feces|fecal]] contamination), etc. Also, there are [[sexually transmitted disease]]s. 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.

Some diseases, such as most (but [[Infectious cancer|not all]]) forms of [[cancer]], [[heart disease]], and mental disorders, are [[non-infectious disease]]s. Many non-infectious diseases have a partly or completely genetic basis (see [[genetic disorder]]) and may thus be transmitted from one generation to another.

[[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 disease|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]].

When the cause of a disease is poorly understood, societies tend to mythologize the disease or use it as a [[metaphor]] or symbol of whatever that culture considers evil. For example, until the bacterial cause of [[tuberculosis]] was discovered in 1882, experts variously ascribed the disease to [[hereditary disease|heredity]], a [[sedentary lifestyle]], [[depression (mood)|depressed mood]], and overindulgence in sex, rich food, or alcohol, all of which were [[social ills]] at the time.

When a disease is caused by a [[pathogen]]ic organism (e.g., when [[malaria]] is caused by ''[[Plasmodium]]''), one should not confuse the [[pathogen]] (the cause of the disease) with disease itself. For example, [[West Nile virus]] (the pathogen) causes [[West Nile fever]] (the disease). The misuse of basic definitions in [[epidemiology]] is frequent in scientific publications.

[[File:Walking the dog 7th Brigade Park Chermside P1040698.jpg|alt=A child rides a bicycle. An adult and a child walk a dog along a path in a green park..|thumb|Regular physical activity, such as riding a bicycle or walking, reduces the risk of lifestyle diseases.]]<!-- This special list formatting is designed for definitions like these. See [[Help:List]] before changing. -->

;Airborne: An [[airborne disease]] is any disease that is caused by pathogens and transmitted through the air.

;Non-communicable: A [[non-communicable disease]] is a medical condition or disease that is non-transmissible. Non-communicable diseases cannot be spread directly from one person to another. [[Heart disease]] and [[cancer]] are examples of non-communicable diseases in humans.

{{Main|Preventive medicine}}

Many diseases and disorders can be prevented through a variety of means. These include [[sanitation]], proper [[nutrition]], adequate [[exercise]], [[vaccination]]s and other [[self-care]] and [[public health]] measures.

{{Main|Therapy}}

Medical therapies or treatments are efforts to cure or improve a disease or other health problems. In the medical field, therapy is synonymous with the word ''treatment''. Among psychologists, the term may refer specifically to [[psychotherapy]] or "talk therapy". Common treatments include [[medication]]s, [[surgery]], [[medical devices]], and [[self-care]]. Treatments may be provided by an organized [[health care system]], or informally, by the patient or family members.

[[Preventive healthcare]] is a way to avoid an injury, sickness, or disease in the first place. A treatment or cure is applied after a medical problem has already started. A treatment attempts to improve or remove a problem, but treatments may not produce permanent cures, especially in [[chronic diseases]]. [[Cure]]s are a subset of treatments that reverse diseases completely or end medical problems permanently. Many diseases that cannot be completely cured are still treatable. [[Pain management]] (also called pain medicine) is that branch of medicine employing an interdisciplinary approach to the relief of pain and improvement in the quality of life of those living with pain.

Treatment for [[medical emergencies]] must be provided promptly, often through an [[emergency department]] or, in less critical situations, through an [[urgent care]] facility.

{{Main|Epidemiology}}

Epidemiology is the study of the factors that cause or encourage diseases. Some diseases are more common in certain geographic areas, among people with certain genetic or socioeconomic characteristics, or at different times of the year.

Epidemiology is considered a cornerstone methodology of public health research and is highly regarded in [[evidence-based medicine]] for identifying [[risk factor]]s for diseases. In the study of communicable and non-communicable diseases, the work of epidemiologists ranges from [[outbreak]] investigation to study design, data collection, and analysis including the development of statistical models to test hypotheses and the documentation of results for submission to peer-reviewed journals. Epidemiologists also study the interaction of diseases in a population, a condition known as a [[syndemic]]. Epidemiologists rely on a number of other scientific disciplines such as [[biology]] (to better understand disease processes), [[biostatistics]] (the current raw information available), [[Geographic Information Science]] (to store data and map disease patterns) and [[social science]] disciplines (to better understand proximate and distal risk factors). Epidemiology can help identify causes as well as guide prevention efforts.

In studying diseases, epidemiology faces the challenge of defining them. Especially for poorly understood diseases, different groups might use significantly different definitions. Without an agreed-on definition, different researchers may report different numbers of cases and characteristics of the disease.

Some morbidity databases are compiled with data supplied by states and territories health authorities, at national levels or larger scale (such as European Hospital Morbidity Database (HMDB)) which may contain hospital discharge data by detailed diagnosis, age and sex. The European HMDB data was submitted by European countries to the World Health Organization Regional Office for Europe.

[[Disease burden]] is the impact of a health problem in an area measured by financial cost, mortality, morbidity, or other indicators.

There are several measures used to quantify the burden imposed by diseases on people. The [[years of potential life lost]] (YPLL) is a simple estimate of the number of years that a person's life was shortened due to a disease. For example, if a person dies at the age of 65 from a disease, and would probably have lived until age 80 without that disease, then that disease has caused a loss of 15 years of potential life. YPLL measurements do not account for how disabled a person is before dying, so the measurement treats a person who dies suddenly and a person who died at the same age after decades of illness as equivalent. In 2004, the [[World Health Organization]] calculated that 932 million years of potential life were lost to premature death.

The [[quality-adjusted life year]] (QALY) and [[disability-adjusted life year]] (DALY) metrics are similar but take into account whether the person was healthy after diagnosis. In addition to the number of years lost due to premature death, these measurements add part of the years lost to being sick. Unlike YPLL, these measurements show the burden imposed on people who are very sick, but who live a normal lifespan. A disease that has high morbidity, but low mortality, has a high DALY and a low YPLL. In 2004, the World Health Organization calculated that 1.5&nbsp;billion disability-adjusted life years were lost to disease and injury. In the developed world, [[heart disease]] and [[stroke]] cause the most loss of life, but [[neuropsychiatric conditions]] like [[major depressive disorder]] cause the most years lost to being sick.

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[[File:Charles Mellin (attributed) - Portrait of a Gentleman - Google Art Project.jpg|thumb|upright|[[Obesity]] was a status symbol in [[Renaissance]] culture: "The Tuscan General [[Alessandro del Borro]]", attributed to [[Andrea Sacchi]], 1645. It is now generally regarded as a disease.]]

How a society responds to diseases is the subject of [[medical sociology]].

A condition may be considered a disease in some cultures or eras but not in others. For example, [[obesity]] can represent wealth and abundance, and is a status symbol in famine-prone areas and some places hard-hit by [[AIDS wasting|HIV/AIDS]]. [[Epilepsy]] is considered a sign of spiritual gifts among the [[Hmong people]].

Sickness confers the social legitimization of certain benefits, such as illness benefits, work avoidance, and being looked after by others. The person who is sick takes on a social role called the [[sick role]]. A person who responds to a dreaded disease, such as [[cancer survivor|cancer]], in a culturally acceptable fashion may be publicly and privately honored with higher [[social status]]. In return for these benefits, the sick person is obligated to seek treatment and work to become well once more. As a comparison, consider [[pregnancy]], which is not interpreted as a disease or sickness, even if the mother and baby may both benefit from medical care.

Most religions grant exceptions from religious duties to people who are sick. For example, one whose life would be endangered by [[fasting]] on [[Yom Kippur]] or during [[Ramadan]] is exempted from the requirement, or even forbidden from participating. People who are sick are also exempted from social duties. For example, ill health is the only socially acceptable reason for an American to refuse an invitation to the [[White House]].

The identification of a condition as a disease, rather than as simply a variation of human structure or function, can have significant social or economic implications. The controversial recognition of diseases such as [[repetitive stress injury]] (RSI) and [[post-traumatic stress disorder]] (PTSD) has had a number of positive and negative effects on the financial and other responsibilities of governments, corporations, and institutions towards individuals, as well as on the individuals themselves. The social implication of viewing [[senescence|aging]] as a disease could be profound, though this classification is not yet widespread.

[[Leprosy|Lepers]] were people who were historically shunned because they had an infectious disease, and the term "leper" still evokes [[social stigma]]. Fear of disease can still be a widespread social phenomenon, though not all diseases evoke extreme social stigma.

Social standing and economic status affect health. [[Diseases of poverty]] are diseases that are associated with [[poverty]] and low social status; [[diseases of affluence]] are diseases that are associated with high social and economic status. Which diseases are associated with which states vary according to time, place, and technology. Some diseases, such as [[diabetes mellitus]], may be associated with both poverty (poor food choices) and affluence (long lifespans and sedentary lifestyles), through different mechanisms. The term [[lifestyle disease|''lifestyle diseases'']] describes diseases associated with longevity and that are more common among older people. For example, [[cancer]] is far more common in societies in which most members live until they reach the age of 80 than in societies in which most members die before they reach the age of 50.

An [[illness narrative]] is a way of organizing a medical experience into a coherent story that illustrates the sick individual's personal experience.

People use [[metaphor]]s to make sense of their experiences with disease. The metaphors move disease from an objective thing that exists to an [[affective]] experience. The most popular metaphors draw on [[military]] concepts: Disease is an enemy that must be feared, fought, battled, and routed. The patient or the healthcare provider is a [[warrior]], rather than a passive victim or bystander. The agents of communicable diseases are [[Invasion|invaders]]; non-communicable diseases constitute internal [[insurrection]] or [[civil war]]. Because the threat is urgent, perhaps a matter of life and death, unthinkably radical, even oppressive, measures are society's and the patient's moral duty as they courageously mobilize to struggle against destruction. The [[War on Cancer]] is an example of this metaphorical use of language. This language is empowering to some patients, but leaves others feeling like they are failures.

Another class of metaphors describes the experience of illness as a journey: The person travels to or from a place of disease, and changes himself, discovers new information, or increases his experience along the way. He may travel "on the road to recovery" or make changes to "get on the right track" or choose "pathways". Some are explicitly immigration-themed: the patient has been exiled from the home territory of health to the land of the ill, changing identity and relationships in the process. This language is more common among British healthcare professionals than the language of physical aggression.

Some metaphors are disease-specific. [[Slavery]] is a common metaphor for [[addiction]]s: The alcoholic is enslaved by drink, and the smoker is captive to nicotine. Some cancer patients treat the loss of their hair from [[chemotherapy]] as a [[metonymy]] or metaphor for all the losses caused by the disease.

Some diseases are used as metaphors for social ills: "Cancer" is a common description for anything that is endemic and destructive in society, such as poverty, injustice, or racism. AIDS was seen as a divine judgment for moral decadence, and only by purging itself from the "pollution" of the "invader" could society become healthy again. More recently, when AIDS seemed less threatening, this type of emotive language was applied to [[Avian flu outbreak of 2009|avian flu]] and [[type 2 diabetes mellitus]]. Authors in the 19th century [[Tuberculosis in popular culture|commonly used tuberculosis]] as a symbol and a metaphor for [[Transcendence (religion)|transcendence]]. People with the disease were portrayed in literature as having risen above daily life to become ephemeral objects of spiritual or artistic achievement. In the 20th century, after its cause was better understood, the same disease became the emblem of poverty, squalor, and other social problems.

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* [[Cryptogenic disease]], a disease whose cause is currently unknown

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* [https://medlineplus.gov/healthtopics.html Health Topics], [[MedlinePlus]] descriptions of most diseases, with access to current research articles.

* [http://www.bbc.co.uk/programmes/p00548m0 "Man and Disease"], BBC Radio 4 discussion with Anne Hardy, David Bradley & Chris Dye (''In Our Time'', Dec. 15, 2002)

{{Medical terms to describe disease conditions}}

{{Pathology}}

{{二次利用|date=28 December 2022}}

[[Category:Diseases and disorders| ]]