Infectious diseases

Infectious diseases

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Infections: contagious diseases

The broad term infectious diseases includes many diseases that are generally known in Germany, such as influenza (flu), herpes, measles, mumps and rubella - but also geographically distant infections such as Ebola or dengue fever. All infectious diseases have in common the underlying disease-causing microorganisms (such as bacteria and viruses) and the risk of infection. The symptoms depend fundamentally on the pathogen and state of health of the infected person. The handling of a reporting obligation, the necessary measures to protect against infection and also the treatment bans for naturopaths are regulated for the infectious diseases in the Infection Protection Act (IfSG).

Short summary - infectious diseases

  • What is an infectious disease? An infectious disease is an infectious disease caused by an infection with pathogens (parasitic microorganisms). Not every infection leads to an illness. Depending on the pathogen, not only humans, but also animals and plants are affected.
  • What are common pathogens for infectious diseases? The most common pathogens include bacteria and viruses. Fungi and other organisms such as worms or unicellular organisms can also cause diseases.
  • What are common bacterial and viral diseases? A common virus infection known in this country is influenza (flu). Widespread infectious diseases are also skin, respiratory and gastrointestinal infections that can be triggered by different pathogens. HIV (AIDS), tuberculosis and malaria are among the most common life-threatening infectious diseases worldwide.
  • How does an infection come about? Starting from the respective pathogens and their reservoirs, infection from person to person, from animal to person or by direct absorption of the pathogen (for example via contaminated food, contaminated drinking water or soil particles) is possible.
  • What are typical symptoms of infectious diseases? There is often a general feeling of illness with fever and fatigue. Depending on the pathogen, the course and the severity, pain and very specific symptoms may be added. With local infections, skin reddening and swelling often develop. Symptoms can also be completely absent or atypical course of the disease occur.
  • How are infectious diseases treated? The body's immune system plays a crucial role in fighting disease. Many infectious diseases can also be treated with appropriate medications such as antibiotics, antivirals or antifungals. But there is not a special therapy for all diseases.
  • How can I protect myself from infections? Vaccinations are available for some infectious diseases. General hygiene measures and possibly also avoiding contact with the sick (humans and animals) also prevent infection.

Definition and explanations of terms

Infection is the transmission, penetration and multiplication of pathogens (usually parasitic microorganisms) in the host. This can be the human body or also animals and plants. An infectious disease is the resulting disease and immune response. Many of the infectious diseases can be transmitted from person to person via various infection routes.

But what does it mean when the news about infectious diseases such as swine flu or bird flu talks about high pathogenicity and the risk of a pandemic?

Some terms relevant to infectious diseases are briefly explained for general understanding.

Pathogen: disease and defense

In addition to the microorganisms that colonize our skin and mucous membranes and are responsible for the "healthy" bacterial flora (physiological flora or normal flora), there are also pathogenic germs. These are pathogenic for humans and / or other living things. The pathogens have different contagion skills (Virulence) and different strong abilities to trigger a disease in an organism (Pathogenicity).

However, very few pathogens are pathogenic for humans as hosts (triggering the disease). In addition, a disease does not break out if the host has a sufficiently strong immune system. In addition, other properties determine the response to the microorganism or the possible onset of the disease. These are individual factors such as susceptibility, susceptibility, innate resistance or one immunity (due to previous infection or vaccination). The most important and most common pathogenic agents for humans are bacteria, viruses, fungi, parasites and protozoa (single-celled animals).

Incubation period

In addition to the factors mentioned, which can promote or prevent the onset of a disease after an infection, the incubation period Another criterion that depends on the pathogen and the immune situation of the host. The incubation period is the time between the entry of the pathogen (time of infection) until the onset of the disease or until the first symptoms.

Disease occurrence

A epidemic denotes a defined (spatially and temporally), highly frequent occurrence of an infectious disease, such as a flu epidemic.

The increase is one pandemic, whereby the infection spreads indefinitely across countries and continents in a certain time frame, as is the case for example with AIDS (HIV).

A Endemic on the other hand, refers to an indefinite occurrence of a disease that is restricted to a certain area, such as early summer meningoencephalitis (TBE).

Probability of illness and death

The Lethality is the likelihood of dying from a particular disease. This is calculated from documented numbers of those who are ill and those who have died as a result of the disease - based on a selected time frame.

The mortality on the other hand indicates how many people of a certain total number of individuals (often based on hundreds of thousands of people) die in a certain period of time - regardless of the disease rate of this selected group of people.

The morbidity Regardless of the number of deaths, indicates how many people can theoretically suffer a certain illness in a certain period of time. This means the statistical frequency of illness in a certain population group. While the Prevalence indicates an actual frequency of illness at a particular point in time.

Also the Incidence provides information on the frequency of illnesses; it represents the number of New sick people within a certain period of time.

Sources of infection and how they develop

Infection always starts from an infection source - a habitat (biotope) or a host organism (host) in which the pathogens reside. Depending on the type of pathogen, an infection can be spread from this source of origin via various transmission channels. To do this, a host does not have to be ill at all, but can only act as a disease carrier.

The most important source of infection is humans themselves, but animals or plants can also act as pathogens reservoir serve. Some pathogens can also survive outside their hosts for a long time, for example in the soil and soil. This is known, for example, for the causative agents of tetanus and tuberculosis.

In order for an infection to occur, it is usually not only necessary for the pathogen to reach the host, but also for it to penetrate the body. If a pathogen enters the new host from outside, this is called one exogenous infection. In addition, the endogenous infection an infection that spreads and spreads to different areas of the body or organs.

Different pathogens are differently sensitive to environmental influences and get into and out of the host via different paths (entry points).

Transmission paths from person to person

Human-to-human transmission is often via droplet infection or smear infection (contact infection). In the Droplet infection the pathogens are spread over the smallest amounts of saliva and absorbed through the mucous membranes of the upper airways. A Smear infection transmits the pathogens via direct contact (contact infection). If contaminated hands or objects (to which the smallest amounts of stool, urine, blood or nasal secretions adhere, for example) are touched, the pathogens can then be transported to the mucous membranes (mouth, nose, eyes). The stool-mouth route of infection is termed fecal-oral.

Furthermore, pathogens can also enter the body via the genital mucous membranes and trigger so-called sexually transmitted diseases. Wounds and injuries are also potential entry points for pathogens that penetrate through the skin. Seldom germs get directly into the bloodstream (for example via blood transfusions).

Other transmission routes are possible through the intake of food (food infections such as salmonellosis and listeriosis) and water if certain pathogens are present and are absorbed into the gastrointestinal tract.

For unborn babies there is also the possibility of infection via the placenta (diaplacentar) and during childbirth (perinatal).

Transmission from animals to humans

Infectious diseases that affect animals and humans or that can be mutually transmitted are called zoonoses. Common infection routes from animals to humans are animal bites, such as rabies, and droplet and smear infections from touching an animal or contact with excretions (e.g. toxoplasmosis).

But bites, for example from ticks or mosquitoes, can also transmit pathogens to humans via an animal (intermediate) host. Infectious diseases such as Lyme disease and TBE (tick bite), malaria (Anopheles mosquito) and many more are transmitted in this way.

In addition, dust infections from inhalation of pathogens or infections from animal products such as meat, fish, eggs and raw milk sometimes occur. In addition, processed foods (such as cheese) can transmit the pathogens and trigger food infections.

Noscomial infection

The term nosocominal infection describes an infection that was acquired in connection with a medical measure. This can be done, for example, during a hospital stay or outpatient treatment. Here, above all, hygienic conditions together with the increased risk of infection in germ-contaminated facilities play a role, as well as certain pathogen resistance. Such infections are most common in intensive care units, where people are often at high risk of infection.

Course of an infection

Depending on the pathogenicity of the pathogen and the current immune situation of the host, an infection may manifest itself or an infectious disease arise, or an infection remains without any signs of disease.

Due to the many variables (e.g. different pathogens, individual health status, immunity), infectious diseases can take very different courses. The disease can be very mild and slow, or it can appear very suddenly, with a very high fever and other severe symptoms. Some pathogens have a very high level of pathogenicity, so that in serious cases a disease can also lead to death.

A sudden febrile reaction due to infection is commonly referred to as an acute infectious disease. A chronic course is characterized by a slowly beginning and creeping process with subfebrile temperatures (below 38.5 degrees Celsius) over long periods. A course between acute and chronic is called subacute, in which case the disease begins less suddenly and is less extreme.

If episodes of disease repeat and are interrupted by latency periods (symptom-free periods), these are referred to as recurrent infectious diseases. Frequent episodes of fever are typical. However, a large number of infections do not proceed according to the characteristic symptoms, but asymptomatic, subclinical or shortened. This can make the diagnosis considerably more difficult.

Occurrence of multiple infections: secondary infection and reinfection

If, in addition to an existing infection (primary infection), there is another infection with another pathogen, this is referred to as a secondary infection. If the body is already weakened, the development of other diseases can be promoted. The term superinfection is also used in this context, especially if a bacterial infection develops after an existing virus infection.

Reinfection means renewed infection with the same pathogen, mostly due to a weakening or lack of immunity.

Infectious diseases: symptoms

Depending on where an infection occurs in the body and whether the pathogens spread, very different signs of the disease can arise. These range from general symptoms (general feeling of illness with increased temperature, fever and fatigue) to very specific reactions.

A distinction can be made between local or generalized infection based on the localization of symptoms. In the case of a local infection, the symptoms appear directly at the pathogen's entrance. These are signs of inflammation with reddening of the skin, swelling and also itching or pain. Typical examples are bacterial infections of the skin, but also of the eyes, ears and the upper respiratory tract.

If the pathogens spread from the local entry area in the organism (via the blood and lymph channels), it is a generalized infection (general infection). This occurs especially with viral infections. At this stage, there is often (high) fever or, for example, leukopenia (reduced number of white blood cells) and relative bradycardia (slow heartbeat compared to increased body temperature).

If the pathogens have reached a specific target organ after spreading (organ stage), this is usually accompanied by a high temperature and the symptoms develop on the organ in question.

Diagnosis of infectious diseases

As already described, infectious diseases are often asymptomatic or asymptomatic, or they start with flu-like symptoms, which often complicates or delays diagnosis. The course of the fever (fever curve) is often an important indicator of a possible infectious disease. Specific complaints in the individual body areas and organs allow conclusions to be drawn about the type of infectious disease.

In any case, an exact medical history is necessary when visiting a doctor, which records the symptoms and the course of the disease in as much detail as possible. For local infections, the signs of inflammation should be carefully considered. It can also be important to collect information regarding bites, stings, sexual contact, stays abroad, general immune deficiencies and medical interventions.

The family or social history also plays a major role here, since contact with other sick people poses a great risk of infection. Due to globalization and increased mobility today, the introduction of diseases - which occur more frequently in other (distant) countries - is an increasing danger.

In addition to the medical history and the clinical examination, if an infectious disease is suspected, further measures should be taken to determine the infection and pathogens as precisely as possible. This is the most important basis for successful treatment and the basis for further possible steps, such as those that are necessary for a notifiable illness.

Treatment of infections

Once diagnosed, medicine offers specific antidotes for many infectious diseases, such as antibiotics against bacteria, antivirals against viruses and antifungals against fungi. It is also possible to protect yourself against some pathogens through vaccinations. But this is not the case for all diseases and sometimes it is only a question of the body's immune system, whether the pathogen can be successfully combated or not.

German Infection Protection Act

The Infection Protection Act (IfSG) to protect against and combat infectious diseases came into force in 2001 and replaced several other laws (such as the Federal Disease Control Act and the Act to Combat Venereal Diseases).

Obligation to report, anti-transmission and vaccination

The IfSG regulates the reporting of notifiable diseases and specifies information and ways of data transmission. It also bans sick people from visiting certain workplaces and community facilities (such as kindergarten and school) in order to minimize the risk of further infections.

In order to protect the population from communicable diseases, the IfSG also regulates the basis for vaccinations and draws particular attention to the recommendations of the Standing Vaccination Commission (STIKO) at the Robert Koch Institute.

Regulations for alternative practitioners

The legal obligation to report certain illnesses also applies to naturopaths (IfSG Section 6 Paragraph 1). In addition, paragraph 24, in combination with other paragraphs, regulates the treatment of communicable diseases. Thereafter, there is a ban on the treatment of naturopaths for certain diseases. The general duty of care in naturopathic practice is also an important basis when deciding whether to transfer affected people to (specialist) medical treatment.

Overview: pathogens and infectious diseases

The infectious disease with the highest disease burden in Europe is influenza ("real flu"). Depending on the spatial and temporal frequency, there are various diseases worldwide that are among the most dangerous infectious diseases, such as AIDS (HIV), tuberculosis, malaria or Ebola.

Common, but mostly harmless, infectious diseases include many respiratory and gastrointestinal infections.

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As there are a large number of very different infectious diseases and causative agents, the following tables should provide a quick overview of some diseases (without claiming to be complete). Further information can be found above all on the information pages of the Robert Koch Institute (RKI Infectious Diseases A-Z).

Skin and mucous membrane infections

Infectious diseaseTypical pathogensPathogen type
Abscess, folliculitis, boils, carbunclesStaphylococcus aureusbacteria
CandidatesCandida albicansMushrooms
Dermatomycoses (skin fungus, skin lichen)Trichophyton, Epidermophyton, MicrosporumMushrooms
ErysipelasStreptococcus pyogenesbacteria
Gas fireClostridium perfringensbacteria
Herpes zoster (shingles)Varicella zoster virusViruses
Herpes simplexHerpes simplex virus 1/2Viruses
Impetigo contagiosa (pus lichen)Streptococcus pyogenes, Staphylococcus aureusbacteria
Keratoconjunctivitis epidemicaAdenovirusesViruses
leprosyMycobacterium lepraebacteria
AnthraxBacillus anthracisbacteria
Pediculosis (head lice infestation)Pediculus capitis, P. pubis, P. vestimentorumLice (parasites)
Snot (mainly animal disease)Pseudomonas malleibacteria
Scabies (itch infestation)Sarcoptes scabieiMites
Trachoma (conjunctivitis trachomatosa)Chlamydia trachomatisbacteria
Verrucae (warts)PapillomavirusViruses

Respiratory infections

Infectious diseaseTypical pathogensPathogen type
Atypical pneumonia (pneumonia)Chlamydia, legionella, mycoplasma, influenza / adenovirusesBacteria, viruses
diphtheriaCorynebacterium diptheriaebacteria
Legionnaires' diseaseLegionella pneumoniabacteria
Ornithosis (parrot disease)Chlamydia psitaccibacteria
Q feverCoxiella burnettibacteria
SARS (Severe Acute Respiratory Syndrome)SARS coronavirusViruses
Streptococcal pneumonia (pneumonia)Streptococcus pneumoniaebacteria

Infections of the digestive and metabolic organs

Infectious diseaseTypical pathogensPathogen type
Amebiasis (amoeba infection)Entamoeba histolyticaProtozoa
choleraVibrio choleraebacteria
Echinococcosis (canine, fox tapeworm)Echinococcus granulosus, E. multilocularisTapeworms
Giardiasis (Lamellia Disease)Giardia lambliaProtozoa
Hepatitis A-E (classic hepatitis)Hepatitis virusesViruses
Infectious gastroenteritis, food infection (such as botulism, listeriosis, samonellosis etc.)Salmonella, E. coli, staphylococci, clostridia, campylobacter, helicobacter, listeria, rotavirus, norovirus, yersinia, etc.especially bacteria and viruses
Infectious hepatitisEpstein-Barr, cytomegalovirus, salmonella, toxoplasmasViruses, bacteria, protozoa
CryptosporidiosisCryptosporidium hominis and C. parvumProtozoa
ParatyphoidSalmonella enterica serotype paratyphi A - Cbacteria
Abdominal typhoidSalmonella enterica serotype typhibacteria
Worm infectionsAscaris lumbricoides, Enterobius vermicularis, Oxyuris vermicularis, Taenia saginata, T. solium,worms

Infections of the nervous system

Infectious diseaseTypical pathogensPathogen type
Lyme disease (Lyme disease), neuroborreliosisBorrelia burgdorferibacteria
Creutzfeldt-Jakob disease (and new variant nvCJK)Prionsatypical proteins (prion proteins)
Encephalitis (inflammation of the brain)Measles viruses, mumps viruses, rubella viruses, enteroviruses, herpes simplex, varicella zoster, Ebstein-Barr viruses and others.Viruses (or bacteria, protozoa, worms)
Early summer meningoencephalitis TBE virus (flaviviruses)Viruses
Meningitis, meningococcal infectionE. coli, B streptococci, listeria, Neisseria meningitidis, pneumococci, herpes simplex viruses (type 2), coxsackie viruses and the like. a.Bacteria, viruses, protozoa, fungi, worms
Progressive multifocal leukoencephalopathy (PML)JC virus (Human Polyomavirus)Viruses
tetanusClostridium tetanibacteria
rabiesRhabdoviruses (Lyssaviruses)Viruses

Cross-organ infections

Infectious diseaseTypical pathogensPathogen type
AspergillosisAspergillus (molds)Mushrooms
Avian influenza (bird flu)Avian influenza A virusesViruses
Schistosomiasis (schistosomiasis)Schistosoma haematobium, S. mansoni, S. japonicumworms
BrucellosisBrucella abortus, B. melitensis, B. suisbacteria
Dengue feverDengue virus DENV 1-4 (flaviviruses)Viruses
Ebola feverEbola virusViruses
TyphusRickettsia (Rickettsia prowazekii)bacteria
Yellow feverYellow fever virus (flaviviruses)Viruses
Hanta feverHantavirusViruses
Infectious mononucleosis (glandular fever)Epstein-Barr virusViruses
Influenza (flu)Influenza viruses (Orthomyxoviruses A - C)Viruses
CryptococcosisCryptococcus neoformansMushrooms
Lassa feverLassavirusViruses
ListeriosisListeria (Listeria monocytogenes)bacteria
malariaPlasmoidum falciparum, P. vivax, P. ovale, P. malariaeProtozoa
Marburg feverMarburg virusViruses
pestYersinia pestisbacteria
Puerperal fever (postpartum fever)Streptococci, staphylococci, E. coli, gonococci, candidaBacteria, fungi
Relapse fever (lice and tick relapse fever)Borrelia recurrentis, B. duttoni and othersbacteria
ToxoplasmosisToxoplasma gondiiProtozoa
TrichinelloseTrichinella (T. spiralis)Worms (roundworms)
tuberculosisMycobacterium tuberculosisbacteria
Tularemia (rabbit fever)Francisella tularensisbacteria
Cytomegaly (CMV)Human herpes virus 5Viruses


Infectious diseaseTypical pathogensPathogen type
Three-day feverHuman herpes virus type 6Viruses
Whooping cough (pertussis)Bordetella pertussisbacteria
mumpsRubula virusViruses
Poliomyelitis (polio)Polioviruses (type 1-3)Viruses
Ringed rubellaParvovirus B 19Viruses
Scarlet feverA streptococci (Streptococcus pyogenes)bacteria
Chickenpox (varicella)Varicella zoster virusViruses

Sexually transmitted infections

Infectious diseaseTypical pathogensPathogen type
AIDS (HIV infection)Human immunodeficiency viruses (HIV)Viruses
Gonorrhea (gonorrhea)Neisseria gonorrhoeaebacteria
HPV infectionsHuman papilloma viruses (HPV)Viruses
Lymphogranuloma inguinaleChlamydia trachomatisbacteria
syphilisTreponema pallidumbacteria
Ulcus molleHaemophilus ducreyibacteria

(ay, cs)

Author and source information

This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.

Dr. rer. nat. Corinna Schultheis


  • Robert Koch Institute (ed. :): Website www.rki.de - Infectious Diseases A-Z, access: September 17, 2019, rki.de
  • Federal Center for Health Education (Hrsg.): Information portal www.infektionsschutz.de - infectious diseases, infektionsschutz.de
  • Bavarian State Office for Health and Food Safety (ed.): Website www.lgl.bayern.de - Health - Protection against Infection - Infectious Diseases A to Z, lgl.bayern.de
  • Wolfgang Geissel: The worst infectious diseases, in: Ärzte Zeitung online, April 30th, 2018, aerztezeitung.de
  • Herold, Gerd and co-workers: internal medicine. Self-published by Gerd Herold, 2019
  • Bierbach, Elvira (ed.): Naturopathic practice today, textbook and atlas, 4th edition, Elsevier Urban & Fischer Verlag, 2009
  • Edmond, Ronald T. D. and Rowland, H. A. K .: Color Atlas of Infectious Diseases, 2nd adult edition, Schattauer, 1995

ICD codes for this disease: A00-B99ICD codes are internationally valid encodings for medical diagnoses. You can find yourself e.g. in doctor's letters or on disability certificates.

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