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 patients personal experience of his or her disease. 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 his or her 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.
In developed countries, the diseases that cause the most sickness overall are neuropsychiatric conditions, such as depression and anxiety. The study of disease is called pathology, which includes the study of etiology, or cause. Terminology
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. 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 bodys normal homeostatic processes. 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 ones 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.