Viral infection

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A virus infection is the infection (contagion) of a life form - e.g. B. humans, animals, plants - with viruses . These penetrate their organism and multiply there. A viral infection can result in an infectious disease that is characterized by certain symptoms , but can also be symptom-free. A creeping, slow virus infection is technically referred to as a " slow virus infection ".

Viruses can only multiply within host cells . Each type of virus prefers a more or less wide range of organisms, ie certain cells , organs or living beings . The infected cell can be recognized as such by the immune system of an organism and eliminated (eliminated) by its immune system.

In the course of evolution , those viruses that are best adapted to their reservoir host prevail. Damage to the reservoir host up to and including death is not an advantageous effect for a virus, since it depends on this host for its own reproduction. The diseases caused by this virus in the reservoir host are ultimately only side effects of the infection . In humans there are both harmless and untreated or treated extremely dangerous viral infections.

The rhinoviruses and viruses that cause colds and warts or herpes simplex , for example, are widespread and successful worldwide . Infections from viruses that have not yet adapted to humans as hosts, such as the Marburg virus and Ebola virus, are particularly dangerous . Some viruses, such as the HIV virus and the viruses that cause rabies , reproduce successfully by leaving their hosts seemingly undisturbed for a sufficient period of time while the viruses can already be transmitted.

Preventive vaccinations are currently only possible against a limited number of viral infections . Only viral infections in humans are discussed below.

Droplet infection

About droplet infection z. B. the childhood diseases with skin symptoms measles , mumps , rubella , rubella , three-day fever or chickenpox . Here z. For example, measles is caused by a runny nose , cough and small white spots on the inside of the cheeks . The typical red spots appear on the skin about two weeks later . The causative agent of chickenpox, the varicella zoster virus , belongs to the herpes viruses and persists for life in sensitive nerve cells after the disease has ended . In older age, with cellular immunodeficiency, the virus can reactivate as shingles .

The possibility of virus transmission through aerosol mist , droplet infection, when working on medical test equipment is also being discussed .

Contact infection or smear infection

Infection via contact infection or smear infection by means of faecally contaminated food and other objects, infected animals or people is very common . The viruses then penetrate the body through the smallest injuries on the skin or through the mucous membrane of the mouth, nose, eyes , respiratory tract or the stomach and intestines . That is why many viruses initially cause symptoms in the nasopharynx or diarrhea ( local infection ).

Intestinal viruses are mostly non-enveloped viruses because they are more environmentally stable. Enveloped viruses are usually only transmitted via droplet infection or direct contact. After an incubation period of days to weeks (usually around two weeks), more specific disease symptoms can then appear in other organs of the body ( generalized infection ), depending on the virus .

Ebola fever and hepatitis B are also transmitted through skin contact with blood, contact infection or smear infection, because viruses can penetrate through tiny, invisible wounds in the skin ( micro-lesions ).

The poliovirus, transmitted by contact infection or smear infection, lives in the intestine, but hardly causes any complaints there if it does not spread further - otherwise it can lead to polio . The pathogens of acute hepatitis (A and E) also belong to the intestinal viruses; only when the liver is affected do they lead to the symptoms of jaundice .

Rabies is often transmitted via an animal bite and is to be regarded as a contact infection, as infection via micro-injuries to the skin (e.g. hand) is also possible when an infected living or dead animal is touched. This type of virus is no longer transmitted very frequently due to international vaccination measures. Without preventive vaccination or vaccination immediately after an infection, the infection still leads to a fatal disease despite modern antivirals .

Infection through the exchange of body fluids

Some viruses are only transmitted through the exchange of body fluids through direct contact with blood or mucous membranes ( blood transfusion , needle prick , sexual intercourse ). HIV and chronic hepatitis (B and C) are important here. See also hemophilia ( hemophilia ).

Rubella, measles, rubella, and the cytomegalovirus are also transmitted to the unborn child. During the birth process , HIV, hepatitis B and herpes simplex can be transmitted.

Infection via blood-sucking insects

From a global perspective, infection via blood-sucking insects is a very important transmission route. If you look closely, this path of infection belongs to the Infection by Exchanging Body Fluids department , but it is always considered separately. The group of all viruses transmitted by blood-sucking insects is summarized outside of the usual taxonomy under the designation arboviruses (English arthropod borne viruses).

As vectors, blood-sucking insects can transmit various viruses in two different ways.

  • 1. Epidemiologically significant and immediately noticeable is the specific route of biological transmission

A single, specific virus species survives after ingestion of only one specific insect species in an infected person within the insect body in the active state, can possibly also multiply and / or change and infects this new insect the next time the same insect is eaten in a not yet infected person Victim . Basically, in this way, blood-sucking insects can only transmit their specific viruses.

The TBE and RSSE virus, the Louping Ill virus , Powassan virus , Kyasanur forest virus , Omsk hemorrhagic fever virus and the Colorado tick virus are transmitted by tick bites. Viruses transmitted by mosquito bites in Europe are the sand fly virus and the Sindbis fever virus . In North America, the common little house mosquito = Culex pipiens has been identified as a biological vector of the West Nile virus . In the tropics, however , mosquitos are known to be biological carriers of various viruses and the diseases they cause in humans (and animals).

  • 2. unspecific mechanical transmission

As with all vectors, a mechanical transmission of all possible viruses is also possible here through the external and internal contamination of the proboscis ( the proboscis, proboscis ) of blood-sucking insects if the insect is disturbed while an infected person is eating and immediately appears another uninfected person continues to suckle. According to the current state of knowledge, it is to be expected that this possibility of transmission can occasionally occur, if at all, only in populations with a very high virus distribution. This transmission path corresponds to that of infection by needle stick injuries or injection cannulas used several times in a row without sterilization in between , but on a different scale. In theory, the transmission of a single virus can cause infection in this way. In practice, however, a minimum sufficient amount of virus is required for infection. Whether this minimum amount z. B. can be achieved in a contamination of the mosquito bugs alone is questionable.

The nocturnal, blood-sucking butterfly and moth species Calyptra eustrigata , Captra minuticornis , Calyptra orthograpta and Calyptra labilis of the family Noctuidae and order Lepidoptera from South-East Asia have sufficient proportions for mechanical transmission of various viruses . With its proboscis , which has been transformed into a proboscis , these moths penetrate up to 7 mm into the skin of mammals, including humans, and then suck the blood for a maximum of 1 hour. In the event of defensive movements, they are always ready to leave their victim before they have reached satiety , so that they can continue to eat as soon as a new one is received. Other butterfly species such as Lobocraspis griseifulva , Arcyophora spp. and Filodes fulvidorsalis of the families Pyralidae , Noctuidae and Geometridae from Africa, Brazil and South-East Asia ingest tear fluid in mammals and humans. With their suction problems, which are rough on the outside, they rub the eyeball to cause an increase in tear production and can also cause slight injuries to the eyeball. All of these types of butterflies are clearly recognized as mechanical disease carriers. Even the possibility of HIV transmission is being discussed.

Furthermore, as early as 1965 (by Luedke et al.), A purely mechanical transmission of the Blue Tonge virus by arthropods such as z. B. detected by the sheep louse fly ( Melophagus ovinus ).

It is not only in Africa that brakes are responsible for the mechanical transmission of anthrax , Weil's disease and tularemia to humans. Since in particular, horseflies ( Tabanus sudeticus ) and stable flies (Stomoxys) arriving at the lentiviruses belonging EIA virus can be transmitted in a mechanical way, there is a theoretical possibility that through this large blood-sucking insects which also at the same genus belonging HI-virus in this Paths can be transmitted. The suction pipe of this insect species is large enough, each of these type of virus in a sufficient amount of an infection in an injection s cannula to store temporarily the inside and outside. However, no such cases of transmission have been reported with the HI virus.

Local viral infections

Most of the virus infections mentioned so far with their more or less specific symptoms z. As to the skin, the liver or the nervous system are generalized infections . In contrast, some viruses only cause local infections in the respiratory or digestive tract , less often in the meninges or eyes. Here the symptoms of the different viruses and bacteria are then similar. The doctor must differentiate between them in order to avoid unnecessary antibiotics .

Infections of the upper respiratory tract are mostly viral, typical are coughs and runny nose caused by rhinoviruses , RSV or parainfluenza viruses . The real influenza (flu) is characterized by a sore throat and dry cough without a runny nose, as well as fever with headaches and aching limbs . No special therapy is necessary. A tonsillitis , on the other hand, can be caused by bacteria or by Coxsackie virus A or Epstein-Barr virus . Viral infections are not purulent . A lung infection by RSV or parainfluenza viruses is interstitial, d. H. diffusely distributed between the cells and difficult to see on x-rays (in contrast to alveolar pneumonia caused by bacteria). The cough has no sputum and is accompanied by an infection of the upper respiratory tract, i.e. runny nose, cough, headache and fever. A meningitis runs mild in viruses in the cerebrospinal fluid there is no pus . Meningitis is usually caused by pathogens that are also found in the respiratory tract, because from there they enter the bloodstream via lesions .

Intestinal infections caused by viruses ( human rotaviruses , human adenoviruses ) or, more rarely, bacteria usually do not require any special diagnostics or drug therapy. If you have diarrhea , it is important to consume plenty of water and salt .

The herpes simplex virus is transmitted through saliva or through sexual intercourse and causes typical blisters on the lips ( herpes labialis mostly of type 1) or on the mucous membrane in the urogenital area ( herpes genitalis , mostly type 2). The Herpes Simplex disappears after successful immune system and the virus persists in sensory nerve cells, similar to the varicella zoster virus .

Viruses can also cause conjunctivitis or corneal inflammation in the eye.

Viruses do not cause blood poisoning and do not produce toxins .

Dangerous viral infections

As a rule of thumb , viral infections are almost always more common and therefore almost always more harmless than other infections. Most people are latently infected with herpes simplex viruses, varicella zoster viruses , cytomegaloviruses, and Epstein-Barr viruses . However, some seemingly harmless childhood diseases can damage organs if they have not been vaccinated beforehand. An unborn child is particularly at risk from such infections.

Exceptions are the viruses that have not been adapted to humans as the main host (reservoir host) and that have been transmitted to humans, such as. B. rabies , HIV, Ebola fever , Marburg fever or SARS . Such pathogens are extremely dangerous. The diseases caused by them have a high death rate ( lethality ).

Some viruses are critical in the development of certain types of cancer if they cause a latent infection over a long period of time . Papilloma viruses can be detected in almost all cervical carcinomas ; Epstein-Barr virus is associated with the endemic Burkitt lymphoma and nasopharynx carcinoma .

Even with immunosuppression (. Eg for AIDS in chemotherapy or after organ transplantation ) viruses can be dangerous, might otherwise have no symptoms in cells persist . In order to avoid the risk of virus transmission during an organ transplant, the following virus tests are carried out on all organ donors in Germany: HIV, hepatitis B and C, cytomegalovirus and Epstein-Barr virus. In addition, the blood of each organ donor is examined for toxoplasmosis and syphilis. If other infections are suspected or if there is a history of infectious diseases, additional tests can also be carried out in specialized laboratories to protect organ recipients from communicable diseases.

For such severe cases, antivirals are available for therapy. In contrast to antibiotics against bacteria, however, they often have an insufficient effect and are poorly tolerated. Therefore, against native virus, if they are not entirely harmless, routine for a specific immunization schedule prophylactically vaccinated. Other vaccinations are only indicated before traveling to endemic areas , e.g. B. Yellow fever in Africa and South America.

Virus diagnostics

For exclusion diagnosis one can PCT test (procalcitonin) serve a significant increase shows for viruses only a modest increase (100-1000), while in bacteria (<10,000).

If a specific diagnosis is necessary, immunological and molecular biological test procedures are used to detect antigens or antibodies after the diagnostic gap . In general, specific antibodies against the virus are detected, but these do not appear until a few days after infection. IgM antibodies indicate a fresh infection, IgG antibodies can indicate a chronic infection or an existing immunity . Hemagglutinin can be detected in measles, mumps, rubella, influenza and adenoviruses . In the case of the Epstein-Barr virus, diagnostic use is made of the fact that the patient forms antibodies that also cross-react against sheep erythrocytes (clumping in the Paul-Bunnell reaction ). The DNA or RNA of a virus can also be detected using PCR or RT-PCR . Many viruses can, depending on the tropism, also be propagated in a cell culture , where the virus can be assessed based on the lysis of the cells. The transmission electron microscopy is mainly used for rapid diagnosis.

Viral infections by route of infection

Droplet infection:

Smear infection / contact infection (by touching contaminated objects, infected animals and people):

Infection via blood-sucking insects: (sting or bite)

Infection through the exchange of body fluids during sexual intercourse , blood transfusion or needlestick injuries (all pathogens circulating in the blood can potentially also be transmitted through this):

Infection through the exchange of body fluids in the womb with particular risks for the unborn child ( prenatal ):

Infection through the exchange of body fluids during the birth process ( perinatal ):


  • Wolfgang Preiser, Annemarie Berger, Hans Wilhelm Doerr: Therapy of viral diseases. Significant progress also in non-retroviral diseases . In: Deutsches Ärzteblatt . (Cologne) 2000, Volume 97, No. 50, pp. A3433-A3439.
  • Pschyrembel Clinical Dictionary. 266th, updated edition. De Gruyter, Berlin 2014, ISBN 978-3-11-033997-0 .

Web links

Wiktionary: virus infection  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. Vu-Wien: General Virology; Epidemiology ( Memento from March 28, 2010 in the Internet Archive )
  2. Vu-Wien: General Virology; Transmission ( Memento from June 18, 2009 in the Internet Archive )
  3. ^ H. Bänziger: Skin-piercing blood-sucking moths I: ecological and ethological studies on Calpe eustrigata (Lepid., Noctuidae). In: Acta tropica. 1975, Vol. 32, No. 2, pp. 125-144, PMID 240258 .
  4. ^ H. Bänziger: Skin-piercing blood-sucking moths II: Studies on a further 3 adult Calyptra [Calpe] sp. (Lepid., Noctuidae). In: Acta tropica. March 1979, Vol. 36, No. 1, pp. 23-37, PMID 35931 .
  5. ^ Sylvia Koslowsky: Bluetongue Disease in Germany? Risk assessment using a geographic information system (GIS). Dissertation, Free University of Berlin - Department of Veterinary Medicine, Berlin 2002, (PDF).
  6. Steven W. Luger: Lyme Disease Transmitted by a Biting Fly. In: The New England Journal of Medicine . June 14, 1990, Volume 322, No. 24, p. 1752 (Correspondence), doi: 10.1056 / NEJM199006143222415 .
  7. Equine infectious anemia / transmission. ( Memento from June 10, 2007 in the Internet Archive )