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80-412: Diseases , disorders , infections , and pathogens have appeared in fiction as part of a major plot or thematic importance. They may be fictional psychological disorders , magical , from mythological or fantasy settings, have evolved naturally , been genetically modified (most often created as biological weapons ), or be any illness that came forth from the (ab)use of technology . Human with
160-403: A vector (e.g. a mosquito or fly) or an intermediate host (e.g. tapeworm in pigs can be transmitted to humans who ingest improperly cooked pork ). Indirect transmission could involve zoonoses or, more typically, larger pathogens like macroparasites with more complex life cycles . Transmissions can be autochthonous (i.e. between two individuals in the same place) or may involve travel of
240-432: A Markab of being infected with the disease can bring shame, paranoia, fear, and an angry response from the accused, and Markab doctors would frequently certify someone's death from the disease as death by natural causes, so the family could avoid a scandal and the implied accusation that they or their family were unclean or immoral. Disease A disease is a particular abnormal condition that adversely affects
320-439: A bite. Biological vectors are often responsible for serious blood-borne diseases , such as malaria , viral encephalitis , Chagas disease , Lyme disease and African sleeping sickness . Biological vectors are usually, though not exclusively, arthropods , such as mosquitoes , ticks , fleas and lice . Vectors are often required in the life cycle of a pathogen. A common strategy used to control vector-borne infectious diseases
400-436: A contact between an infected host and a noninfected host. Community transmission means that the source of infection for the spread of an illness is unknown or a link in terms of contacts between patients and other people is missing. It refers to the difficulty in grasping the epidemiological link in the community beyond confirmed cases. Local transmission means that the source of the infection has been identified within
480-612: 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 diseases , hereditary diseases (including both genetic and non-genetic hereditary diseases ), and physiological diseases. Diseases can also be classified in other ways, such as communicable versus 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,
560-424: 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 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. Preventive healthcare
640-871: A drinking glass or a cigarette. Infections that are known to be transmissible by kissing or by other direct or indirect oral contact include all of the infections transmissible by droplet contact and (at least) all forms of herpes viruses , namely Cytomegalovirus infections herpes simplex virus (especially HSV-1) and infectious mononucleosis . This is from mother to child (more rarely father to child), often in utero , during childbirth (also referred to as perinatal infection ) or during postnatal physical contact between parents and offspring. In mammals, including humans, it occurs also via breast milk (transmammary transmission). Infectious diseases that can be transmitted in this way include: HIV, hepatitis B and syphilis. Many mutualistic organisms are transmitted vertically. Transmission due to medical procedures , such as touching
720-578: A fit of animalistic hunger, what is then followed by the loss of taste. Next, the infected people experience aggression (causing unrest and chaos worldwide), and lose their hearing. And finally, the hosts experience a sudden episode of euphoria, before losing their vision. Similar to the Black Death and HIV/AIDS among humans, the Drafa plague bears a stigma among the Markab as a disease that the public felt
800-411: A form of non-genetic inheritance or parental effect . It has been argued that most organisms experience some form of vertical transmission of symbionts. Canonical examples of vertically transmitted symbionts include the nutritional symbiont Buchnera in aphids (transovarially transmitted intracellular symbiont) and some components of the human microbiota (transmitted during passage of infants through
880-458: A hospital epidemiology program, for example. Because these traditional methods are slow, time-consuming, and labor-intensive, proxies of transmission have been sought. One proxy in the case of influenza is tracking of influenza-like illness at certain sentinel sites of health care practitioners within a state, for example. Tools have been developed to help track influenza epidemics by finding patterns in certain web search query activity. It
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#1732782582395960-416: 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 people who were historically shunned because they had an infectious disease, and
1040-422: 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 circumstances . Social determinants of health have been recognized by several health organizations such as
1120-567: A pathogen, as in the case of food or water may carrying hepatitis A virus. Alternatively, the vehicle may provide an environment in which the agent grows, multiplies, or produces toxin, such as improperly canned foods provide an environment that supports production of botulinum toxin by Clostridium botulinum . A vector is an organism that does not cause disease itself but that transmits infection by conveying pathogens from one host to another. Vectors may be mechanical or biological. A mechanical vector picks up an infectious agent on
1200-458: 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,
1280-777: A price to a consumer. This is recognized implicitly when vaccines are offered for free or at a cost to the patient less than the purchase price. The mode of transmission is also an important aspect of the biology of beneficial microbial symbionts, such as coral -associated dinoflagellates or human microbiota . Organisms can form symbioses with microbes transmitted from their parents, from the environment or unrelated individuals, or both. Vertical transmission refers to acquisition of symbionts from parents (usually mothers). Vertical transmission can be intracellular (e.g. transovarial), or extracellular (for example through post-embryonic contact between parents and offspring). Both intracellular and extracellular vertical transmission can be considered
1360-432: A vector for blood-borne diseases , such as Hepatitis C (HCV) and HIV . Indirect contact transmission, also known as vehicle-borne transmission, involves transmission through contamination of inanimate objects. Vehicles that may indirectly transmit an infectious agent include food, water, biologic products such as blood , and fomites such as handkerchiefs, bedding, or surgical scalpels. A vehicle may passively carry
1440-432: A wound, the use of contaminated medical equipment, or an injection or transplantation of infected material. Some diseases that can be transmitted iatrogenically include Creutzfeldt–Jakob disease , HIV , and many more. This is the practice of intravenous drug-users by which a needle or syringe is shared by multiple individuals to administer intravenous drugs such as heroin, steroids, and hormones. This can act as
1520-427: Is open defecation which leads to disease transmission via the fecal-oral route. Even in developed countries there are periodic system failures resulting in a sanitary sewer overflow . This is the typical mode of transmission for infectious agents such as cholera , hepatitis A , polio , Rotavirus , Salmonella , and parasites (e.g. Ascaris lumbricoides ). Tracking the transmission of infectious diseases
1600-443: 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. 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
1680-498: 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)
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#17327825823951760-539: Is also responsible for the increased incidence of herpes simplex virus 1 (which is usually responsible for oral infections) in genital infections and the increased incidence of the type 2 virus (more common genitally) in oral infections. While rare in regards to this sexual practice, some infections that can spread via manual sex include HPV , chlamydia, and syphilis. Infections that are transmitted primarily by oral means may be caught through direct oral contact such as kissing , or by indirect contact such as by sharing
1840-419: 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
1920-549: Is at the core of the specialty of epidemiology . To understand the spread of the vast majority of non-notifiable diseases, data either need to be collected in a particular study, or existing data collections can be mined, such as insurance company data or antimicrobial drug sales for example. For diseases transmitted within an institution, such as a hospital, prison, nursing home, boarding school, orphanage, refugee camp, etc., infection control specialists are employed, who will review medical records to analyze transmission as part of
2000-466: Is by way of respiratory droplets, generated by coughing , sneezing , or talking. Respiratory droplet transmission is the usual route for respiratory infections. Transmission can occur when respiratory droplets reach susceptible mucosal surfaces, such as in the eyes, nose or mouth. This can also happen indirectly via contact with contaminated surfaces when hands then touch the face. Before drying, respiratory droplets are large and cannot remain suspended in
2080-407: Is called disease surveillance . Surveillance of infectious diseases in the public realm traditionally has been the responsibility of public health agencies, on an international, national, or local level. Public health staff relies on health care workers and microbiology laboratories to report cases of reportable diseases to them. The analysis of aggregate data can show the spread of a disease and
2160-548: 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 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
2240-889: Is known. The most known and used classification of diseases is the World Health Organization 's ICD . This is periodically updated. Currently, the last publication is the ICD-11 . Diseases can be caused by any number of factors and may be acquired or congenital . Microorganisms , genetics, the environment or a combination of these can contribute to a diseased state. Only some diseases such as influenza are contagious and commonly believed infectious. The microorganisms that cause these diseases are known as pathogens and include varieties of bacteria, viruses, protozoa, and fungi. Infectious diseases can be transmitted, e.g. by hand-to-mouth contact with infectious material on surfaces, by bites of insects or other carriers of
2320-503: Is not the same as infectious; although all contagious diseases are infectious, not all infectious diseases are contagious). These diseases can also be transmitted by sharing a towel (where the towel is rubbed vigorously on both bodies) or items of clothing in close contact with the body (socks, for example) if they are not washed thoroughly between uses. For this reason, contagious diseases often break out in schools, where towels are shared and personal items of clothing accidentally swapped in
2400-613: Is often used more broadly to refer to any condition that causes pain , dysfunction , 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 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 can affect people not only physically but also mentally, as contracting and living with
2480-638: Is primarily considered as an indirect contact route through contaminated food or water. However, it can also operate through direct contact with feces or contaminated body parts, such as through anal sex . It can also operate through droplet or airborne transmission through the toilet plume from contaminated toilets. Main causes of fecal–oral disease transmission include lack of adequate sanitation and poor hygiene practices - which can take various forms. Fecal oral transmission can be via foodstuffs or water that has become contaminated. This can happen when people do not adequately wash their hands after using
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2560-557: 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 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
2640-400: 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
2720-423: Is the passing of a pathogen causing communicable disease from an infected host individual or group to a particular individual or group, regardless of whether the other individual was previously infected. The term strictly refers to the transmission of microorganisms directly from one individual to another by one or more of the following means: Transmission can also be indirect, via another organism , either
2800-415: Is to interrupt the life cycle of a pathogen by killing the vector. In the fecal-oral route, pathogens in fecal particles pass from one person to the mouth of another person. Although it is usually discussed as a route of transmission, it is actually a specification of the entry and exit portals of the pathogen, and can operate across several of the other routes of transmission. Fecal–oral transmission
2880-478: 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 , in a culturally acceptable fashion may be publicly and privately honored with higher social status . In return for these benefits,
2960-451: 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
3040-470: The acute phase ; after recovery from chickenpox, the virus may remain dormant in nerve cells for many years, and later cause herpes zoster (shingles). Diseases may be classified by cause, pathogenesis ( mechanism by which the disease is caused), or by symptoms . 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
3120-462: 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
3200-448: The toilet and before preparing food or tending to patients. The fecal-oral route of transmission can be a public health risk for people in developing countries who live in urban slums without access to adequate sanitation. Here, excreta or untreated sewage can pollute drinking water sources ( groundwater or surface water). The people who drink the polluted water can become infected. Another problem in some developing countries,
3280-411: The "best of both worlds" – they can vertically infect host offspring when host density is low, and horizontally infect diverse additional hosts when a number of additional hosts are available. Mixed-mode transmission make the outcome (degree of harm or benefit) of the relationship more difficult to predict, because the evolutionary success of the symbiont is sometimes but not always tied to the success of
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3360-588: 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
3440-436: The ability of an organism to enter, survive and multiply in the host, while the infectiousness of a disease agent indicates the comparative ease with which the disease agent is transmitted to other hosts. Transmission of pathogens can occur by direct contact, through contaminated food, body fluids or objects, by airborne inhalation or through vector organisms. Transmissibility is the probability of an infection, given
3520-489: The air for long, and are usually dispersed over short distances. The size of the particles for droplet infections are > 5 μm. Organisms spread by droplet transmission include respiratory viruses such as influenza virus , parainfluenza virus , adenoviruses , rhinovirus , respiratory syncytial virus , human metapneumovirus , Bordetella pertussis , pneumococci , streptococcus pyogenes , diphtheria , rubella , and coronaviruses . Spread of respiratory droplets from
3600-457: The annual start of school, bootcamp, the annual Hajj etc. Most recently, data from cell phones have been shown to be able to capture population movements well enough to predict the transmission of certain infectious diseases, like rubella. Pathogens must have a way to be transmitted from one host to another to ensure their species' survival. Infectious agents are generally specialized for a particular method of transmission. Taking an example from
3680-412: The bacterial cause of tuberculosis was discovered in 1882, experts variously ascribed the disease to heredity , a sedentary lifestyle , 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 pathogenic organism (e.g., when malaria is caused by Plasmodium ), one should not confuse the pathogen (the cause of
3760-851: The birth canal and also through breastfeeding). Some beneficial symbionts are acquired horizontally , from the environment or unrelated individuals. This requires that host and symbiont have some method of recognizing each other or each other's products or services. Often, horizontally acquired symbionts are relevant to secondary rather than primary metabolism, for example for use in defense against pathogens, but some primary nutritional symbionts are also horizontally (environmentally) acquired. Additional examples of horizontally transmitted beneficial symbionts include bioluminescent bacteria associated with bobtail squid and nitrogen-fixing bacteria in plants . Many microbial symbionts, including human microbiota , can be transmitted both vertically and horizontally. Mixed-mode transmission can allow symbionts to have
3840-554: The body and remain suspended in the air for long periods of time. They infect others via the upper and lower respiratory tracts." The size of the particles for airborne infections need to be < 5 μm. It includes both dry and wet aerosols and thus requires usually higher levels of isolation since it can stay suspended in the air for longer periods of time. i.e., separate ventilation systems or negative pressure environments are needed to avoid general contamination. e.g., tuberculosis , chickenpox , measles . A common form of transmission
3920-457: 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. In the developed world, heart disease and stroke cause the most loss of life, but neuropsychiatric conditions like major depressive disorder cause
4000-566: 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
4080-566: The changing rooms. Some diseases that are transmissible by direct contact include athlete's foot , impetigo , syphilis, warts , and conjunctivitis . This refers to any infection that can be caught during sexual activity with another person, including vaginal or anal sex , less commonly through oral sex (see below) and rarely through manual sex (see below). Transmission is either directly between surfaces in contact during intercourse (the usual route for bacterial infections and those infections causing sores) or from secretions ( semen or
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#17327825823954160-411: The condition describe "being drained of something" or "having the life sucked out". Mundanes are immune to the disease, as demon pox is assumed to be caused by the interaction of demon poison with the angelic nature of Shadowhunters. The disease starts with a depressive episode, what is then followed by the loss of sense of smell. Then, humans experience a sudden episode of panic and anxiety, as well as
4240-590: 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. Signs and symptoms Syndrome Disease Medical diagnosis Differential diagnosis Prognosis Acute Chronic Cure Eponymous disease Acronym or abbreviation Remission Transmission (medicine) In medicine , public health , and biology , transmission
4320-530: 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. Many diseases and disorders can be prevented through a variety of means. These include sanitation , proper nutrition , adequate exercise , vaccinations and other self-care and public health measures, such as obligatory face mask mandates . Medical therapies or treatments are efforts to cure or improve
4400-510: The disease, and from contaminated water or food (often via fecal contamination), etc. Also, there are sexually transmitted diseases . 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 not all ) forms of cancer , heart disease , and mental disorders, are non-infectious diseases . Many non-infectious diseases have
4480-444: 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. 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. In an infectious disease,
4560-642: 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
4640-702: The fecal-oral route, such as cholera . Differences in incidence of such diseases between different groups can also throw light on the routes of transmission of the disease. For example, if it is noted that polio is more common in cities in underdeveloped countries, without a clean water supply, than in cities with a good plumbing system, we might advance the theory that polio is spread by the fecal-oral route. Two routes are considered to be airborne : Airborne infections and droplet infections. "Airborne transmission refers to infectious agents that are spread via droplet nuclei (residue from evaporated droplets) containing infective microorganisms. These organisms can survive outside
4720-427: The fluid secreted by the excited female) which carry infectious agents that get into the partner's blood stream through tiny tears in the penis , vagina or rectum (this is a more usual route for viruses ). In this second case, anal sex is considerably more hazardous since the penis opens more tears in the rectum than the vagina, as the vagina is more elastic and more accommodating. Some infections transmissible by
4800-412: The long term evolution of a pathogen. Since it takes many generations for a microbe and a new host species to co-evolve, an emerging pathogen may hit its earliest victims especially hard. It is usually in the first wave of a new disease that death rates are highest. If a disease is rapidly fatal, the host may die before the microbe can be passed along to another host. However, this cost may be overwhelmed by
4880-591: The microorganism or the affected hosts. A 2024 World Health Organization report standardized the terminology for the transmission modes of all respiratory pathogens in alignment with particle physics: airborne transmission; inhalation; direct deposition; and contact. But these newly standardized terms have yet to be translated to policy, including infection control policy or the pandemic accords or updated International Health Regulations. An infectious disease agent can be transmitted in two ways: as horizontal disease agent transmission from one individual to another in
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#17327825823954960-644: The month of 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
5040-482: The most years lost to being sick. 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 was associated with prosperity and abundance, and this perception persists in many African regions, especially since the beginning of the HIV/AIDS . Epilepsy is considered a sign of spiritual gifts among
5120-421: The outside of its body and transmits it in a passive manner. An example of a mechanical vector is a housefly , which lands on cow dung, contaminating its appendages with bacteria from the feces, and then lands on food prior to consumption. The pathogen never enters the body of the fly. In contrast, biological vectors harbor pathogens within their bodies and deliver pathogens to new hosts in an active manner, usually
5200-468: 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
5280-421: The reporting location (such as within a country, region or city). The route of transmission is important to epidemiologists because patterns of contact vary between different populations and different groups of populations depending on socio-economic, cultural and other features. For example, low personal and food hygiene due to the lack of a clean water supply may result in increased transmission of diseases by
5360-424: The respiratory route, from an evolutionary perspective viruses or bacteria that cause their host to develop coughing and sneezing symptoms have a great survival advantage, as they are much more likely to be ejected from one host and carried to another. This is also the reason that many microorganisms cause diarrhea . The relationship between virulence and transmission is complex and has important consequences for
5440-457: The same generation (peers in the same age group) by either direct contact (licking, touching, biting), or indirect contact through air – cough or sneeze ( vectors or fomites that allow the transmission of the agent causing the disease without physical contact) or by vertical disease transmission , passing the agent causing the disease from parent to offspring, such as in prenatal or perinatal transmission . The term infectivity describes
5520-439: The sexual route include HIV/AIDS , chlamydia , genital warts , gonorrhea , hepatitis B , syphilis , herpes , and trichomoniasis . Sexually transmitted infections such as HIV and hepatitis B are thought to not normally be transmitted through mouth-to-mouth contact, although it is possible to transmit some STIs between the genitals and the mouth, during oral sex. In the case of HIV, this possibility has been established. It
5600-438: The short-term benefit of higher infectiousness if transmission is linked to virulence, as it is for instance in the case of cholera (the explosive diarrhea aids the bacterium in finding new hosts) or many respiratory infections (sneezing and coughing create infectious aerosols ). Anything that reduces the rate of transmission of an infection carries positive externalities , which are benefits to society that are not reflected in
5680-402: 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
5760-546: The structure or function of all or part of an organism and 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 pathogens 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 , allergies , and autoimmune disorders . In humans, disease
5840-826: 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 diseases describes diseases associated with longevity and that are more common among older people. For example, cancer
5920-454: 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
6000-493: The wearer can be reduced through wearing of a surgical mask . Direct contact occurs through skin-to-skin contact, kissing, and sexual intercourse. Direct contact also refers to contact with soil or vegetation harboring infectious organisms. Additionally, while fecal–oral transmission is primarily considered an indirect contact route, direct contact can also result in transmission through feces. Diseases that can be transmitted by direct contact are called contagious (contagious
6080-430: 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 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
6160-432: Was found that the frequency of influenza-related web searches as a whole rises as the number of people sick with influenza rises. Examining space-time relationships of web queries has been shown to approximate the spread of influenza and dengue . Computer simulations of infectious disease spread have been used. Human aggregation can drive transmission, seasonal variation and outbreaks of infectious diseases, such as
6240-425: Was only caught by those considered sinful, immoral or unclean by Markab standards, and a punishment by their gods for committing such acts. The disease was named after an island on their homeworld where its inhabitants were wiped out by the disease, an island noted in Markab history for its decadence and immorality. The story of the island was eventually used to frighten small Markab children into behaving. Even accusing
6320-409: 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 and type 2 diabetes mellitus . Authors in the 19th century commonly used tuberculosis as a symbol and a metaphor for transcendence . People with
6400-510: 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
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