An infectious disease , infectious disease or infection disease (including infection or infectious disease ) is a by pathogens ( bacteria , fungi or viruses ) caused disease in humans, animals or plants. However, it is not to be equated with an infection , since not every infection inevitably leads to an illness.
Infectious diseases show a broad spectrum of time courses and symptoms . These are often specific to the pathogen. They can develop extremely acutely in a few days or develop slowly over weeks, months and sometimes years. There are localized - i.e. restricted to specific areas of the body - and generalized infectious diseases. Some run almost unnoticed (inapparent) in a person who is not immunocompromised or only express themselves in slight, unspecific disturbances of the general condition, or up to extreme exhaustion (prostration). Other diseases develop a highly dramatic clinical picture. The body reacts to these mostly severe, septic infectious diseases with a reaction pattern known as systemic inflammatory response syndrome , which includes fever , accelerated pulse, increased breathing rate, thirst and the need for rest. Fatal outcomes are mostly based on circulatory failure.
The ability of the immune system to eliminate the pathogen is decisive for the course and prognosis of an infectious disease . Medicine has specific antidotes ready for many pathogen-related diseases ( antibiotics against bacteria, antimycotics against fungi and antivirals against viruses). A preventive vaccination is available against some pathogens . But even today some infectious diseases cannot be definitely cured.
With the basic mechanisms of infections and infectious diseases (such as incubation , portability , epidemiology and immunity ), the deal Infectious Diseases , the infection biology and immunology . Infectious diseases are treated by clinical infectious diseases .
Externally visible injuries have been recognized and treated since the Neolithic Age. In the case of internal illnesses or epidemics without an apparent cause, people looked for supernatural sources and viewed them as the work of angry gods. The attempts at healing therefore concentrated on incantations, prayers and offerings.
Using paleopathology , bone changes caused by the infectious diseases tuberculosis (in Egyptian mummies ) and leprosy (in medieval relics) could be determined. Smallpox scars could be diagnosed on the mummy of Ramses II (13th century BC) .
Hippocrates of Kos (460–377 BC) is considered to be the founder of the doctrine of miasms , the poisonous fumes from the soil, which are carried away with the air and thus contribute to the spread of diseases. Together with the miasm theory, the knowledge of contagion also grew . The transfer of an inanimate substance from a sick to a healthy person should cause the disease to break out.
The idea of living pathogens first appeared in the 1st century BC. Chr. On. Marcus Terentius Varro (born 116 BC) said that the air of the swamps is perishable because it is made pregnant by tiny animals that penetrate into the nose, into the whole body. Direct detection was only possible with the invention of the microscope . Antoni van Leeuwenhoek (1632–1723) found that the pupae of the fleas are attacked by tiny mites. The Jesuit Athanasius Kircher (1601–1680) published the discovery of masses of the smallest worms that he had found in the air, in water, in the ground, in milk, cheese, rotten parts of plants and in the blood and pus of plague sufferers. However, the importance of microorganisms as a cause of disease remained hidden. This role was first recognized in the 19th century with a "food disease" caused by the Bacterium prodigiosum ( Serratia marcescens ).
Towards the end of the 18th century the dispute between the two medical schools was in a high phase. On the one hand there were the contagionists , who were of the opinion that diseases could be transmitted by small living pathogens, on the other hand there were the supporters of miasmatology , who continued to regard impurities or poisons that rose from the soil as the cause of epidemics. Through the research of Robert Koch and Louis Pasteur , the contagionists were able to end this argument with the confirmation of their assumptions. Pasteur discovered the bacteriological causes of fermentation and putrefaction . In addition, he was able to refute common ideas about spontaneous generation experimentally.
In the developed world infectious diseases have greatly diminished. The main reason for this is a change in health awareness , hygiene , serial vaccinations and a repertoire of potent antidotes. Nevertheless, they are still the most common cause of death worldwide. While smallpox was eradicated in the 1970s and polio is expected to be eliminated in the next few years, infectious diseases such as AIDS and tuberculosis are on the rise worldwide.
The following infectious disease pathogens have been recognized since 1972:
- 1972 Small round structured viruses (SRSVs) now: caliciviruses , ( diarrhea )
- 1973 Human Rotavirus - Diarrhea (Worldwide)
- 1975 astroviruses - diarrhea
- 1975 Parvovirus B19 - Erythema infectiosum; aplastic crisis in chronic hemolytic anemia
- 1976 Cryptosporidium parvum - acute enterocolitis
- 1977 Ebola Virus - Ebola Hemorrhagic Fever
- 1977 Legionella pneumophila - Legionellosis
- 1977 Hantaan virus - hemorrhagic fever with renal syndrome
- 1977 Campylobacter spp. - diarrhea
- 1980 Human T-lymphotropic virus 1 (HTLV-1) - adult T-cell leukemia / lymphoma; Tropical spastic paraparesis
- 1982 Human T-lymphotropic virus 2 (HTLV-2) - neurological diseases?
- 1982 Borrelia burgdorferi - Lyme disease
- 1983 Human Immunodeficiency Virus Type I (HIV-1) - Acquired Immunodeficiency Syndrome ( AIDS )
- 1983 Escherichia coli O157 ( EHEC ) - diarrhea; hemorrhagic colitis; Hemolytic uremic syndrome
- 1983 Helicobacter pylori gastritis; gastric ulcers; increased risk of gastric cancer
- 1988 Human Herpesvirus 6 (HHV-6) - three-day fever (= Exanthema subitum, Roseola infantum)
- 1989 Ehrlichia spp. - Human monocytic Ehrlichiosis
- 1989 Hepatitis C Virus (HCV) - Hepatitis C
- 1989 Guanarito Virus - Venezuelan Hemorrhagic Fever
- 1990 Human Herpes Virus 7 - Exanthema subitum; Pityriasis rosea
- 1990 Hepatitis E Virus (HEV) - Hepatitis E
- 1992 Vibrio cholerae O139: H7 - new variant associated with epidemic cholera
- 1992 Bartonella henselae - cat scratch disease ; Bacillary angiomatosis
- 1993 Sin Nombre Virus - Hantavirus Lung Syndrome ("Four corners disease")
- 1993 so-called hepatitis G virus (HGV) now GB virus C - no disease value
- 1994 Sabia Virus - Brazilian Hemorrhagic Fever
- 1994 Human Herpes Virus 8 (HHV-8) - Kaposi's sarcoma ; primary lymphoma of the body cavities; Castleman's disease
- 1994 Hendra Virus , (formerly Equines Morbillivirus ) - Pneumonia ; Encephalitis
- 1996 Prion Protein - Transmissible Spongiform Encephalopathies (TSE)
- 1997 Influenza A virus (H5N1) - new avian variant (Hong Kong)
- 1997 so-called Transfusion-transmitted virus (TTV) now: Torqeno-Teno-Virus - no disease
- 1998 Nipah virus - encephalitis
- 2003 SARS-Associated Corona Virus (SARS-CoV) - Severe Acute Respiratory Syndrome (SARS)
- 2020 SARS-CoV-2 - COVID-19
Infectious Disease Triggers
- By far the most common are unicellular, seedless bacteria from a wide variety of groups. Bacteriology deals with them . Examples of bacterial diseases are typical pneumonia , meningitis , Lyme disease , tuberculosis , typhoid , typhus , brucellosis , cholera , plague , Q fever and many others.
- Single-celled cells with a nucleus are called protozoa and are recorded in parasitology . The diseases they cause include malaria , toxoplasmosis and tropical sleeping sickness .
- Pathogenic fungi are the subject of clinical mycology , they can occur as unicellular yeasts or as multicellular yeasts . Aspergillosis and candidiasis are examples of fungal diseases .
- Parasitology is also concerned with the more highly developed, disease-causing tissue animals such as worms (for example in trichinella ) or arthropods .
- A few unicellular algae can also cause infections. The most important of these are the protothecae , the causative agents of protothecosis .
- Viruses are a special case because they only have some characteristics of living beings, so they are classified differently. Virology deals with them . Viral diseases are the classic childhood diseases as well as runny nose , flu , viral pneumonia , hepatitis B and AIDS .
- Finally, there are also pathogens that have no genetic information in the form of DNA or RNA : the prion diseases formerly known as slow virus infections are caused by degenerate proteins, so-called prions . Prion diseases include Creutzfeldt-Jakob disease and the cattle disease BSE, which may be transmitted to humans .
The danger of an infectious disease depends on the so-called virulence of the pathogen. Whether and to what extent an infection also leads to an infectious disease depends, along with many other factors, on the number of pathogens ingested (minimum infectious dose ).
Possibilities of infection and routes of transmission
A basic distinction is made between primary infections , i.e. initial infections in which the organism has the first contact with a pathogen, and secondary infections : here the already infected body is also infected with another germ. So there is then a double infection . Such an additional infection can pose considerable problems for the immune system and also make special demands on therapy and medication . If a viral infection forms the basis for another, now bacterial, infection of the same organ system, this is also known as superinfection in medicine and bacteriology . In the narrower sense, in virology , superinfection is understood to mean a renewed infection with the same pathogen with a still existing primary infection and incomplete immunity.
Differentiation according to the course of the infection
Differentiation according to the origin of the pathogen
An endogenous infection is an infection with a weakened immune system by the body's own, normally completely harmless flora in the form of an ingress of pathogens e.g. B. on the skin or from the stomach, intestines and lungs into your own body (like a wound infection by your own E. coli bacteria ). These pathogens are facultatively pathogenic (i.e. they only cause symptoms under such conditions). Exogenous infection is infection caused by infectious agents in the environment. A special case of exogenous infection is nosocomial infection that was acquired in a hospital, in a doctor's office or other medical facility with a comparable spectrum of germs. Such infections are characterized by the fact that the typical bacterial pathogens from the medical practice or hospital area - such as pseudomonads for example - often show a high level of resistance to common antibiotics . In order to stop the increase in resistance, many hospitals have now been obliged to implement preventive measures based on scientific knowledge. As iatrogenic infection is the medical unintentionally introducing pathogens in carrying out interventions, whether by a doctor or other healthcare professionals, called infection caused the staff themselves or the patient.
Four major routes of infection are distinguished in exogenous infection: droplet infection via aerosols in the air, contact or smear infections (e.g. faecal-oral), parenteral infections through sexual intercourse, blood reserves or contaminated injection cannulas and finally through so-called vectors (carriers, e.g. blood-sucking insects ) common infections.
Direct infections happen from person to person without intermediate steps, indirect infections require a carrier between the hosts, this can be the mentioned insects, drinking water, food or shared objects. Zoonoses are infectious diseases that also or even mainly occur in animals and are transmitted from them directly (contact) or indirectly (e.g. via cow's milk) to humans.
Differentiation according to the pathogen's entry point
An enteral infection is an infection in which the pathogens have entered the organism via the intestine as a gateway. The entire digestive tract (mouth, throat, esophagus, stomach and the entire intestine) is viewed as the inside of a tunnel that is not itself part of the body. The exact place at which the infectious agents penetrate the actual interior of the body is considered to be the gateway.
- fecal-oral infection
- Pathogens from the intestine or feces enter the organism through the mouth, e.g. B. from contaminated drinking water.
In the original sense, this type of infection is an infection in which the pathogens have not entered the organism via the intestine. In medical usage, parenteral is used synonymously with "directly into the blood". The following further infection routes are defined here:
- percutaneous infection
- The pathogens enter the organism through the skin.
- permucous infection
- The pathogens enter the organism through the mucous membranes.
- Inhalation infection
- The pathogens enter the organism via the respiratory tract.
- urogenital infection
- The pathogens enter the organism via the urinary tract.
- genital infection
- The pathogens enter the organism via the genital organs.
- intrauterine infection
- The pathogens enter the body of the unborn child during pregnancy.
Differentiation according to the extent of the infection
In the case of a local infection , the pathogens remain where they first infected the body (entry point). They only cause symptoms at this point, without spreading further in the organism. A generalized infection is understood to be an infectious disease in which the pathogens first multiply at a portal of entry (e.g. in the intestine) and then reach their actual manifestation organs via the blood. These are often the liver (with swelling of the liver), spleen (with splenomegaly ), lymphatic organs, the skin or the nervous system. The pathogens can then no longer be detected at the entry point. In a focal infection ( oven infection ) occurs after a localized disease transmission caused by bacteria, especially by Streptococci a (secondary) condition subsequent to. The pathogens get from the source of the local infection in the body with a delay due to septic metastasis or spurts from this source via the bloodstream to more distant body regions or organs and cause inflammatory or allergic disease processes there. A systemic infection is an infection in which the pathogens spread through the bloodstream over an entire organ system (for example the central nervous system , for example in meningitis, poliomyelitis, encephalitis, rabies, botulism, tetanus and listeriosis) or the entire organism.
Differentiation according to other systematic aspects
Vertical infection is infection from a host to its offspring. A distinction is made between prenatal and intrauterine transmissions before birth, perinatal infections during birth and postnatal infections immediately after birth. A horizontal infection, as opposed to vertical infection, is the transmission to other members of the population.
Virus infections and bacterial infections are by far the most common , but fungal infections , infections by protozoa and worm infections also occur in millions worldwide. Prion diseases are much rarer in humans. Some diseases are only endemic in certain regions ; tropical diseases usually only occur in warmer climates. With them, the distribution of the transmitting vector is often decisive. Infectious diseases such as the flu (influenza) increase seasonally. Major epidemics occur at intervals of years or decades . A large-scale study from 2019 found that women with children had an almost 2/3 reduced chance of dying from an infection compared to childless women. Men with children showed a similar, if somewhat lower, reduction in the probability of death.
Estimation of the frequency of fatal infections according to WHO
|Respiratory diseases||3.9 million||3.0 million|
|AIDS||2.8 million||1.0 million||0.8 million|
|Diarrheal diseases||1.8 million||1.4 Million|
|tuberculosis||1.6 million||1.3 million||1.2 million|
|malaria||1.3 million||0.4 million||0.4 million|
These are rough estimates that need to be scrutinized in their definition. One rarely dies from acute hepatitis. The consequences of chronic hepatitis C ( liver cirrhosis , liver cancer ) are, however, a very common cause of death in Asia .
Typical symptoms of an infectious disease are inflammation , i.e. redness (also exanthema ), swelling, possibly with itching or pain and local or general warming ( fever ). In addition, there are organ-specific defenses or functional disorders such as breathing disorders. Respiratory infections with cough , hoarseness (in the case of larynx ), runny nose , difficulty swallowing in the case of tonsillitis , and possibly sputum with pneumonia are common . Headaches caused by vasomotors can also occur as a frequent partial symptom of the disorder of the general condition (prostration). The second most common are intestinal infections with diarrhea , possibly cramps and pain, they can spread to the liver and cause jaundice . Other examples would be infections of the skin or urinary tract . Also caries is an infectious disease.
The symptoms of an infectious disease are related on the one hand to the harmful effects of the pathogen, but on the other hand also to the reaction of the immune system . Correspondingly, infections in people with a weak immune system are often dangerously inconspicuous and difficult to diagnose because there is no fever, malaise and inflammation parameters in the blood .
Typical emergencies are meningitis , severe sepsis (e.g. Waterhouse-Friderichsen syndrome ), and inflammation of the kidneys in babies . Heart valve inflammation or myocarditis is slow, but also dangerous . Pneumonia or any other infection can be life-threatening, especially with a weakened immune system ( immunosuppression , AIDS , old age).
An important prerequisite for combating an infectious disease is an accurate diagnosis ; H. recognizing the pathogen and its properties. Knowledge of the changes in the blood count that regularly occur in infectious diseases is helpful for diagnosis and prognosis. In cases where the course of the disease is threatening, however, an exact diagnosis of a serious infectious disease cannot be awaited. Instead, antibiotics or antimycotics are used to start a therapy that removes all probable pathogens, such as B. initially bacteria and fungi should hit (calculated therapy). However, if all signs point to viruses as pathogens, the immediate use of antivirals may be necessary.
Many bacteria and also fungi can be grown on blood agar or similar culture media. They can also be viewed under a light microscope after they have been stained (e.g. Gram stain ) . In the case of viruses or intracellular bacteria, a cell culture or an electron microscope would be necessary. More modern methods that are carried out in laboratories are often more practical for clinical use . In molecular biological methods one shows genetic information of the pathogen z. B. by means of the polymerase chain reaction . In immunological methods, antibodies are detected which the immune system forms against specific surface structures, so-called antigens , or, conversely, antibodies are used to detect antigens of the pathogen. There are also other characteristic components of certain pathogens that can be detected (e.g. hemagglutinin ). Animal experiments are now only required in exceptional cases, e.g. B. in tetanus . Tuberculosis is also diagnosed through skin tests ( Tine test , Mendel-Mantoux test ).
Prevention and therapy
Hygiene and vaccinations have been instrumental in reducing infectious diseases. In the medical field measures are routinely the basic hygiene , for example, hand disinfection , barrier measures such as full-face protection , surface disinfection, and waste disposal, and the use of keimarmem or sterile material is provided. The Commission for Hospital Hygiene and Infection Prevention (KRINKO) stipulates in its recommendation "Infection prevention in the care and treatment of patients with communicable diseases" (as of September 2015) which hygiene measures are to be used for the various infectious diseases in order to avoid their spread . These are also fundamental to the treatment and care of COVID-19 patients. Hospital hygienists, hygiene specialists and waste officers work closely together to ensure that infection prevention and occupational safety in clinics are effective.
On the other hand, more attention is paid to the resilience of the organism and its immune system today . The susceptibility to infection can be reduced through a healthy diet , adequate sleep, regular exercise, timely medical treatment and avoidance of stress (see cortisol ).
The outpatient and clinical care of patients with infectious diseases takes place within the framework of general practitioner or specialist treatment. In the case of infections with pathogens that are at risk of transmission in the inpatient area, the patients are accommodated and treated in isolation rooms or wards . In the case of highly contagious infections, placement in a special isolation ward may be indicated. Such quarantine measures can be ordered by the authorities as part of security measures.
One of the oldest infectiological departments is the medical clinic with a focus on infectiology and pneumology at the Charité in Berlin : the clinic was founded in 1891 by Robert Koch . The only German chair for clinical infectious diseases and the largest German special isolation ward for highly contagious diseases are located here. In 1900 the Bernhard Nocht Institute and the associated clinic in Hamburg were founded specifically for the treatment of tropical diseases.
If necessary and possible, infectious diseases are combated with antibiotics , antivirals , antimycotics or antihelminthics . Serious foci of infection sometimes have to be surgically cleaned up. In evidence-based medicine , the effect of herbal remedies is considered to be limited and insufficient in serious disease processes.
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- §30 Infection
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