A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, Pathogens such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune diseases. In humans, “disease” is often used more broadly to refer to any condition that causes pain, dysfunction, distress, social problems, 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. Diseases usually affect people not only physically, but also emotionally, as contracting and living with many diseases can alter one’s perspective on life, and their personality. Diseases are caused by a variety of pathogens which have developed ways of infecting our bodies.
The lesson in this section offer students the opportunity to learn about the different types of organisms which cause disease, including viruses, bacteria, fungi and protozoans. Stages of a disease 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, vermicelli 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). 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. A flare-up can refer to either the recurrence of symptoms or an onset of more severe symptoms.
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. 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. Death due to disease is called death by natural causes.
There are four main types of disease: pathogenic disease, deficiency disease, hereditary disease, and physiological disease. Diseases can also be classified as communicable and non-communicable disease. Disease Categories Infectious diseases Infectious diseases, also known as transmissible diseases or communicable diseases comprise clinically evident illness (i. e. , characteristic medical signs and/or symptoms of disease) resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism.
In certain cases, infectious diseases may be asymptomatic for much or even their entire course in a given host. In the latter case, the disease may only be defined as a “disease” (which by definition means an illness) in hosts who secondarily become ill after contact with an asymptomatic carrier. An infection is not synonymous with an infectious disease, as some infections do not cause illness in a host. Infectious pathogens include some viruses, bacteria, fungi, protozoa, multicellular parasites, and aberrant proteins known as prions.
These pathogens are the cause of disease epidemics, in the sense that without the pathogen, no infectious epidemic occurs. The term infectivity describes the ability of an organism to enter, survive and multiply in the host, while the infectiousness of a disease indicates the comparative ease with which the disease is transmitted to other hosts. Transmission of pathogen can occur in various ways including physical contact, contaminated food, body fluids, objects, airborne inhalation, or through vector organisms.
 Infectious diseases are sometimes called “contagious” when they are easily transmitted by contact with an ill person or their secretions (e. g. , influenza). Thus, a contagious disease is a subset of infectious disease that is especially infective or easily transmitted. Other types of infectious/transmissible/communicable diseases with more specialized routes of infection, such as vector transmission or sexual transmission, are usually not regarded as “contagious,” and often do not require medical isolation (sometimes loosely called quarantine) of victims.
However, this specialized connotation of the word “contagious” and “contagious disease” (easy transmissibility) is not always respected in popular use. Parasitic Diseases A parasitic disease is an infectious disease caused or transmitted by a parasite. Many parasites do not cause diseases. Parasitic diseases can affect practically all living organisms, including plants and mammals. The study of parasitic diseases is called parasitology. Some parasites like Toxoplasma gondii and Malaria can cause disease directly, but other organisms can cause disease by the toxins that they produce.
Neuropsychiatric conditions A mental disorder or mental illness is a psychological pattern or anomaly, potentially reflected in behavior, that is generally associated with distress or disability, and which is not considered part of normal development of a person’s culture. Mental disorders are generally defined by a combination of how a person feels acts, thinks or perceives. This may be associated with particular regions or functions of the brain or rest of the nervous system, often in a social context.
The recognition and understanding of mental health conditions have changed over time and across cultures and there are still variations in definition, assessment and classification, although standard guideline criteria are widely used. In many cases, there appears to be a continuum between mental health and mental illness, making diagnosis complex. According to the World Health Organization (WHO), over a third of people in most countries report problems at some time in their life which meet criteria for diagnosis of one or more of the common types of mental disorder.
Cardiovascular disease is a class of diseases that involve the heart or blood vessels (arteries, capillaries and veins). Cardiovascular disease refers to any disease that affects the cardiovascular system, principally cardiac disease, vascular diseases of the brain and kidney, and peripheral arterial disease.
The causes of cardiovascular disease are diverse but atherosclerosis and/or hypertension are the most common. Besides, with aging come a number of physiological and morphological changes that alters cardiovascular function and lead to subsequently increased risk of cardiovascular disease, even in health asymptomatic individuals.
Cardiovascular diseases remain the biggest cause of deaths worldwide, though over the last two decades, cardiovascular mortality rates have declined in many high-income countries. At the same time cardiovascular deaths and disease have increased at an astonishingly fast rate in low- and middle-income countries. Although cardiovascular disease usually affects older adults, the antecedents of cardiovascular disease, notably atherosclerosis begin in early life, making primary prevention efforts necessary from childhood.
There is therefore increased emphasis on preventing atherosclerosis by modifying risk factors, such as healthy eating, exercise, and avoidance of smoking. Premature birth In humans preterm birth (Latin: partus praetemporaneus or partus praematurus) is the birth of a baby of less than 37 weeks gestational age. The cause of preterm birth is in many situations elusive and unknown; many factors appear to be associated with the development of preterm birth, making the reduction of preterm birth a challenging proposition.
Premature birth is defined either as the same as preterm birth or the birth of a baby before the developing organs are mature enough to allow normal postnatal survival. Premature infants are at greater risk for short and long term complications, including disabilities and impediments in growth and mental development. Significant progress has been made in the care of premature infants, but not in reducing the prevalence of preterm birth. Preterm birth is among the top causes of death in infants worldwide.
Cancer, known medically as a malignant neoplasm, is a broad group of various diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the body through the lymphatic system or bloodstream. Not all tumors are cancerous. Benign tumors do not grow uncontrollably, do not invade neighboring tissues, and do not spread throughout the body. There are over 200 different known cancers that afflict humans] Determining what causes cancer is complex.
Many things are known to increase the risk of cancer, including tobacco use, certain infections, radiation, and lack of physical activity, obesity and environmental pollutants. These can directly damage genes or combine with existing genetic faults within cells to cause the disease. Approximately five to ten percent of cancers are entirely hereditary. Cancer can be detected in a number of ways, including the presence of certain signs and symptoms, screening tests or medical imaging. Once a possible cancer is detected it is diagnosed by microscopic examination of a tissue sample.
Cancer is usually treated with chemotherapy, radiation therapy and surgery. The chances of surviving the disease vary greatly by the type and location of the cancer and the extent of disease at the start of treatment. While cancer can affect people of all ages, and a few types of cancer are more common in children, the risk of developing cancer generally increases with age. In 2007, cancer caused about 13% of all human deaths worldwide (7. 9 million). Rates are rising as more people live to an old age and as mass lifestyle changes occur in the developing world.
Drug use and abuse Not all diseases are caused by outside agents. Some of them, we cause ourselves. There are many diseases which follow from drug abuse, alcohol abuse or smoking Treatment or cure Medical therapies or treatments are efforts to cure or improve a disease or other health problem. 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 medications, surgery, medical devices, and self-care.
Treatments may be provided by an organized health care system, or informally, by the patient or family members. A prevention or preventive therapy 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. Cures 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. 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 factors for disease. 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). 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-upon definition, different researchers will find very different numbers of cases and characteristics of the disease. Disease is an important aspect of the interaction between humans and their environment – both inanimate and biological. Human bodies function best when healthy and it is important for students to know what causes disease and what they can do to prevent disease, both for themselves and their families.
Diseases are caused by a variety of pathogens which have developed ways of infecting our bodies. The lesson in this section offer students the opportunity to learn about the different types of organisms which cause disease, including viruses, bacteria, fungi and protozoans.