A disease or medical problem is an abnormal condition of an organism that impairs bodily functions, associated with specific symptoms and signs. It may be caused by external factors, such as invading organisms, or it may be caused by internal dysfunctions, such as autoimmune diseases.
In human beings, "disease" is often used more broadly to refer to any condition that causes extreme pain, dysfunction, distress, social problems, and/or death to the person afflicted, or similar problems for those in contact with the person. In this broader sense, it sometimes includes injuries, disabilities, disorders, syndromes, infections, isolated symptoms, deviant behaviors, and atypical variations of structure and function, while in other contexts and for other purposes these may be considered distinguishable categories.
In many cases, the terms disease, disorder, morbidity and illness are used interchangeably. In some situations, specific terms are considered preferable.
This term broadly refers to any abnormal condition that impairs normal function. Commonly, this 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 parasites, and aberrant proteins known as prions. An infection that does not produce clinically evident impairment of normal functioning is not considered a disease. Non-infectious diseases are all other diseases, including most forms of cancer, heart disease, and genetic disease.
Illness and sickness are generally used as synonyms for disease. However, this term is occasionally used to refer specifically to the patient's personal experience of his or her disease. In this model, it is possible for a person to be diseased without being ill, (to have an objectively definable, but asymptomatic, medical condition), 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 his or her life). Illness is often not due to infection but a collection of evolved responses, sickness behavior, by the body aids the clearing of infection. Such aspects of illness can include lethargy, depression, anorexia, sleepiness, hyperalgesia, and inability to concentrate.
In medicine, a disorder is a functional abnormality or disturbance. Medical disorders can be categorized into mental disorders, physical disorders, genetic disorders, emotional and behavioral disorders, and functional disorders.
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. 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 organic brain syndrome.
A medical condition is a broad term that includes all diseases and disorders, but also includes normal situations, such as pregnancy, that might benefit from medical assistance or have implications for medical treatments.
As it is more value-neutral than terms like disease, it is sometimes preferred by people with these conditions. On the other hand, by emphasizing the medical nature of the condition, this term is sometimes rejected, such as by proponents of the autism rights movement.
Additionally, the term medical condition is used as a synonym for medical state, where it describes a patient's current state, as seen from a medical standpoint. This usage is seen in statements that describe a patient as being "in critical condition", for example.
Morbidity (from Latin morbidus: sick, unhealthy) refers to a diseased state, disability, or poor health due to any cause. The term may be used to 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 is the simultaneous presence of two medical conditions, such as a person with schizophrenia and substance abuse.
In epidemiology and actuarial science, the term morbidity rate can refer to either the incidence rate, or the prevalence of a disease or medical condition. 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.
Transmission of disease
Main article: Transmission (medicine)
Some diseases such as influenza are contagious and infectious. The micro-organisms that cause these diseases are known as pathogens and include varieties of bacteria, viruses, protozoa and fungi. Infectious diseases can be transmitted by as, by hand to mouth contact with infectious material on surfaces, by bites of insects or other carriers of the disease, and from contaminated water or food (often via faecal contamination), etc. In addition, there are sexually transmitted diseases. In some cases, micro-organisms 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 cancer, heart disease and mental disorders are , in most cases, not considered to be caused by infection (see Non infectious disease), although there are important exceptions. Many diseases (including some cancers, heart disease and mental disorders) have a partially or completely genetic basis (see Genetic disorder) and may thus be transmitted from one generation to another.
Social significance of disease
Obesity was a status symbol in renaissance culture: "The Tuscan General Alessandro del Borro", attributed to Charles Mellin, 1645. It is now generally regarded as a disease.
A condition may be considered to be a disease in some cultures or eras but not in others. Conditions such as attention-deficit hyperactivity disorder and obesity are considered to be diseases by developed countries, but which have been regarded differently in other cultures. For example, obesity can also represent wealth and abundance, and is a status symbol in famine-prone areas and some places hard-hit by HIV/AIDS.
Sickness confers the social legitimization of certain benefits, such as illness benefits, work avoidance, and being looked after by others. In return, there is an obligation on the sick person to seek treatment and work to become well once more. As a comparison, consider pregnancy, which is not usually interpreted as a disease or sickness by the individual. On the other hand, it is considered by the medical community as a condition requiring medical care.
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 recognitions as diseases of post-traumatic stress disorder, also known as "Soldier's heart," "shell shock," and "combat fatigue;" repetitive motion injury or repetitive stress injury (RSI); and Gulf War syndrome 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 aging as a disease could be profound, though this classification is not yet widespread. Lepers were a group of afflicted individuals who were historically shunned 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.
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