Disease

Concepts

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.^[4]

Disease

The term disease broadly refers to any condition that impairs the normal functioning of the body. For this reason, diseases are associated with the dysfunction of the body's normal homeostatic processes.^[5] Commonly, the term is used to refer specifically to infectious diseases, which are clinically evident diseases that result from the presence of pathogenic microbial agents, including viruses, bacteria, fungi, protozoa, multicellular organisms, and aberrant proteins known as prions. An infection or colonization that does not and will not produce clinically evident impairment of normal functioning, such as the presence of the normal bacteria and yeasts in the gut, or of a passenger virus, is not considered a disease. By contrast, an infection that is asymptomatic during its incubation period, but expected to produce symptoms later, is usually considered a disease. Non-infectious diseases are all other diseases, including most forms of cancer, heart disease, and genetic disease.

Acquired disease

An acquired disease is one that began at some point during one's lifetime, as opposed to disease that was already present at birth, which is congenital disease. Acquired sounds like it could mean "caught via contagion", but it simply means acquired sometime after birth. It also sounds like it could imply secondary disease, but acquired disease can be primary disease.

Acute disease

An acute disease is one of a short-term nature (acute); the term sometimes also connotes a fulminant nature

Chronic condition or chronic disease

A chronic disease is one that persists over time, often for at least six months, but may also include illnesses that are expected to last for the entirety of one's natural life.

Congenital disorder or congenital disease

A congenital disorder is one that is present at birth. It is often a genetic disease or disorder and can be inherited. It can also be the result of a vertically transmitted infection from the mother, such as HIV/AIDS.

Genetic disease

A genetic disorder or disease is caused by one or more genetic mutations. It is often inherited, but some mutations are random and de novo.

Hereditary or inherited disease

A hereditary disease is a type of genetic disease caused by genetic mutations that are hereditary (and can run in families)

Iatrogenic disease

An iatrogenic disease or condition is one that is caused by medical intervention, whether as a side effect of a treatment or as an inadvertent outcome.

Idiopathic disease

An idiopathic disease has an unknown cause or source. As medical science has advanced, many diseases with entirely unknown causes have had some aspects of their sources explained and therefore shed their idiopathic status. For example, when germs were discovered, it became known that they were a cause of infection, but particular germs and diseases had not been linked. In another example, it is known that autoimmunity is the cause of some forms of diabetes mellitus type 1, even though the particular molecular pathways by which it works are not yet understood. It is also common to know certain factors are associated with certain diseases; however, association does not necessarily imply causality. For example, a third factor might be causing both the disease, and the associated phenomenon.

Incurable disease

A disease that cannot be cured. Incurable diseases are not necessarily terminal diseases, and sometimes a disease's symptoms can be treated sufficiently for the disease to have little or no impact on quality of life.

Primary disease

A primary disease is a disease that is due to a root cause of illness, as opposed to secondary disease, which is a sequela, or complication that is caused by the primary disease. For example, a common cold is a primary disease, where rhinitis is a possible secondary disease, or sequela. A doctor must determine what primary disease, a cold or bacterial infection, is causing a patient's secondary rhinitis when deciding whether or not to prescribe antibiotics.

Secondary disease

A secondary disease is a disease that is a sequela or complication of a prior, causal disease, which is referred to as the primary disease or simply the underlying cause (root cause). For example, a bacterial infection can be primary, wherein a healthy person is exposed to bacteria and becomes infected, or it can be secondary to a primary cause, that predisposes the body to infection. For example, a primary viral infection that weakens the immune system could lead to a secondary bacterial infection. Similarly, a primary burn that creates an open wound could provide an entry point for bacteria, and lead to a secondary bacterial infection.

Terminal disease

A terminal disease is one that is expected to have the inevitable result of death. Previously, AIDS was a terminal disease; it is now incurable, but can be managed indefinitely using medications.

Illness

The terms illness and sickness are both generally used as synonyms for disease; however, the term illness is occasionally used to refer specifically to the patient's personal experience of their disease.^[6][7][8][9] In this model, it is possible for a person to have a disease without being ill (to have an objectively definable, but asymptomatic, medical condition, such as a subclinical infection, or to have a clinically apparent physical impairment but not feel sick or distressed by it), and to be ill without being diseased (such as when a person perceives a normal experience as a medical condition, or medicalizes a non-disease situation in their life – for example, a person who feels unwell as a result of embarrassment, and who interprets those feelings as sickness rather than normal emotions). Symptoms of illness are often not directly the result of infection, but a collection of evolved responses – sickness behavior by the body – that helps clear infection and promote recovery. Such aspects of illness can include lethargy, depression, loss of appetite, sleepiness, hyperalgesia, and inability to concentrate.^[10][11][12]

Disorder

A disorder is a functional abnormality or disturbance that may or may not show specific signs and symptoms. Medical disorders can be categorized into mental disorders, physical disorders, genetic disorders, emotional and behavioral disorders, and functional disorders.^[13] The term disorder is often considered more value-neutral and less stigmatizing than the terms disease or illness, and therefore is preferred terminology in some circumstances.^[14] In mental health, the term mental disorder is used as a way of acknowledging the complex interaction of biological, social, and psychological factors in psychiatric conditions; however, the term disorder is also used in many other areas of medicine, primarily to identify physical disorders that are not caused by infectious organisms, such as metabolic disorders.

Medical condition or health condition

A medical condition or health condition is a broad concept that includes all diseases, lesions, disorders, or nonpathologic condition that normally receives medical treatment, such as pregnancy or childbirth. While the term medical condition generally includes mental illnesses, in some contexts the term is used specifically to denote any illness, injury, or disease except for mental illnesses. The Diagnostic and Statistical Manual of Mental Disorders (DSM), the widely used psychiatric manual that defines all mental disorders, uses the term general medical condition to refer to all diseases, illnesses, and injuries except for mental disorders.^[15] This usage is also commonly seen in the psychiatric literature. Some health insurance policies also define a medical condition as any illness, injury, or disease except for psychiatric illnesses.^[16]

As it is more value-neutral than terms like disease, the term medical condition is sometimes preferred by people with health issues that they do not consider deleterious. However, by emphasizing the medical nature of the condition, this term is sometimes rejected, such as by proponents of the autism rights movement.

The term medical condition is also a synonym for medical state, in which case it describes an individual patient's current state from a medical standpoint. This usage appears in statements that describe a patient as being in critical condition, for example.

Morbidity

Morbidity (from Latin morbidus 'sick, unhealthy') is a diseased state, disability, or poor health due to any cause.^[17] The term may refer to the existence of any form of disease, or to the degree that the health condition affects the patient. Among severely ill patients, the level of morbidity is often measured by ICU scoring systems. Comorbidity, or co-existing disease, is the simultaneous presence of two or more medical conditions, such as schizophrenia and substance abuse.

In epidemiology and actuarial science, the term morbidity (also morbidity rate or morbidity frequency) can refer to either the incidence rate, the prevalence of a disease or medical condition, or the percentage of people who experience a given condition within a given timeframe (e.g., 20% of people will get influenza in a year).^[18] This measure of sickness is contrasted with the mortality rate of a condition, which is the proportion of people dying during a given time interval. Morbidity rates are used in actuarial professions, such as health insurance, life insurance, and long-term care insurance, to determine the premiums charged to customers. Morbidity rates help insurers predict the likelihood that an insured will contract or develop any number of specified diseases.

Pathosis or pathology

Pathosis (plural pathoses) is synonymous with disease. The word pathology also has this sense, in which it is commonly used by physicians in the medical literature, although some editors prefer to reserve pathology to its other senses. Sometimes a slight connotative shade causes preference for pathology or pathosis implying "some [as yet poorly analyzed] pathophysiologic process" rather than disease implying "a specific disease entity as defined by diagnostic criteria being already met". This is hard to quantify denotatively, but it explains why cognitive synonymy is not invariable.

Syndrome

A syndrome is the association of several signs and symptoms, or other characteristics that often occur together, regardless of whether the cause is known. Some syndromes such as Down syndrome are known to have only one cause (an extra chromosome at birth). Others such as Parkinsonian syndrome are known to have multiple possible causes. Acute coronary syndrome, for example, is not a single disease itself but is rather the manifestation of any of several diseases including myocardial infarction secondary to coronary artery disease. In yet other syndromes, however, the cause is unknown. A familiar syndrome name often remains in use even after an underlying cause has been found or when there are a number of different possible primary causes. Examples of the first-mentioned type are that Turner syndrome and DiGeorge syndrome are still often called by the "syndrome" name despite that they can also be viewed as disease entities and not solely as sets of signs and symptoms.

Predisease

Predisease is a subclinical or prodromal vanguard of a disease. Prediabetes and prehypertension are common examples. The nosology or epistemology of predisease is contentious, though, because there is seldom a bright line differentiating a legitimate concern for subclinical or premonitory status and the conflict of interest–driven over-medicalization (e.g., by pharmaceutical manufacturers) or de-medicalization (e.g., by medical and disability insurers). Identifying legitimate predisease can result in useful preventive measures, such as motivating the person to get a healthy amount of physical exercise,^[19] but labeling a healthy person with an unfounded notion of predisease can result in overtreatment, such as taking drugs that only help people with severe disease or paying for treatments with a poor benefit–cost ratio.

One review proposed three criteria for predisease:

• a high risk for progression to disease making one "far more likely to develop" it than others are- for example, a pre-cancer will almost certainly turn into cancer over time
• actionability for risk reduction – for example, removal of the precancerous tissue prevents it from turning into a potentially deadly cancer
• benefit that outweighs the harm of any interventions taken – removing the precancerous tissue prevents cancer, and thus prevents a potential death from cancer.^[20]

Types by body system

Mental

Mental illness is a broad, generic label for a category of illnesses that may include affective or emotional instability, behavioral dysregulation, cognitive dysfunction or impairment. Specific illnesses known as mental illnesses include major depression, generalized anxiety disorders, 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 relationship.^{[citation needed]}

Organic

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.

Stages

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 phase; after recovery from chickenpox, the virus may remain dormant in nerve cells for many years, and later cause herpes zoster (shingles).

Acute disease

An acute disease is a short-lived disease, like the common cold.

Chronic disease

A chronic disease is one that lasts for a long time, usually at least six months. During that time, it may be constantly present, or it may go into remission and periodically relapse. A chronic disease may be stable (does not get any worse) or it may be progressive (gets worse over time). Some chronic diseases can be permanently cured. Most chronic diseases can be beneficially treated, even if they cannot be permanently cured.

Clinical disease

One that has clinical consequences; in other words, the stage of the disease that produces the characteristic signs and symptoms of that disease.^[21] AIDS is the clinical disease stage of HIV infection.

Cure

A cure is the end of a medical condition or a treatment that is very likely to end it, while remission refers to the disappearance, possibly temporarily, of symptoms. Complete remission is the best possible outcome for incurable diseases.

Flare-up

See also: Exacerbation

A flare-up can refer to either the recurrence of symptoms or an onset of more severe symptoms.^[22]

Progressive disease

Progressive disease is a disease whose typical natural course is the worsening of the disease until death, serious debility, or organ failure occurs. Slowly progressive diseases are also chronic diseases; many are also degenerative diseases. The opposite of progressive disease is stable disease or static disease: a medical condition that exists, but does not get better or worse.

Refractory disease

A refractory disease is a disease that resists treatment, especially an individual case that resists treatment more than is normal for the specific disease in question.

Subclinical disease

Also called silent disease, silent stage, or asymptomatic disease. This is a stage in some diseases before the symptoms are first noted.^[23]

Terminal phase

If a person will die soon from a disease, regardless of whether that disease typically causes death, then the stage between the earlier disease process and active dying is the terminal phase.

Recovery

See also: Convalescence and 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.

Extent

Localized disease

A localized disease is one that affects only one part of the body, such as athlete's foot or an eye infection.

Disseminated disease

A disseminated disease has spread to other parts; with cancer, this is usually called metastatic disease.

Systemic disease

A systemic disease is a disease that affects the entire body, such as influenza or high blood pressure.

Types of causes

Airborne

An airborne disease is any disease that is caused by pathogens and transmitted through the air.^[30]

Foodborne

Foodborne illness or food poisoning is any illness resulting from the consumption of food contaminated with pathogenic bacteria, toxins, viruses, prions or parasites.^[31]

Infectious

Infectious diseases, also known as transmissible diseases or communicable diseases, comprise clinically evident illness (i.e., characteristic medical signs or symptoms of disease) resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism.^[32] Included in this category are contagious diseases – an infection, such as influenza or the common cold, that commonly spreads from one person to another – and communicable diseases – a disease that can spread from one person to another, but does not necessarily spread through everyday contact.

Lifestyle

A lifestyle disease is any disease that appears to increase in frequency as countries become more industrialized and people live longer, especially if the risk factors include behavioral choices like a sedentary lifestyle or a diet high in unhealthful foods such as refined carbohydrates, trans fats, or alcoholic beverages.^[33]

Non-communicable

A non-communicable disease is a medical condition or disease that is non-transmissible.^[34] Non-communicable diseases cannot be spread directly from one person to another. Heart disease and cancer are examples of non-communicable diseases in humans.^[35]

Burdens of disease

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.^[41]

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 billion disability-adjusted life years were lost to disease and injury.^[41] 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.

Language of disease

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 metaphors 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 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.^[49] This language is empowering to some patients, but leaves others feeling like they are failures.^[50]

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".^[49][50] 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.^[51] This language is more common among British healthcare professionals than the language of physical aggression.^[50]

Some metaphors are disease-specific. Slavery is a common metaphor for addictions: 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.^[49]

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.^[49] More recently, when AIDS seemed less threatening, this type of emotive language was applied to avian flu and type 2 diabetes mellitus.^[52] Authors in the 19th century commonly used tuberculosis as a symbol and a metaphor for 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.^[51]