How do pathogens spread

How germs spread

People can “catch” an infection in very different ways. The best known is the droplet infection: Viruses or bacteria are contained in the tiny drops that can get from one person to another when coughing or sneezing, for example. Colds, sore throats and also the virus flu "wander" among other things on this way from person to person.

The so-called smear infection is also of great importance in everyday life: if you cough into your hand during a flu and then touch a handle in the tram, pathogens are left there. If the next person uses the handle, these can be transferred. Viruses can also switch from one person to the next by shaking hands. Conscientious hand hygiene is therefore recommended in the case of flu waves in order to protect yourself and others.

Infectious diseases spreading epidemically are as old as humanity. But the conditions have changed. On the one hand, many infections are now treatable and therefore easier to control. On the other hand, the enormous mobility makes it easier for pathogens to spread. While historical epidemics of the plague or cholera sometimes took years for them to spread from one part of the world to the other, this can happen very quickly today. Because the germs travel with the host organisms on the plane today.

In addition, germs reach people in other ways. Herpes viruses, the bacterial pathogens of syphilis and gonorrhea ("gonorrhea"), the hepatitis B virus and HIV can be transmitted during sexual intercourse. Direct blood contacts are another possible transmission path. After all, food and drinking water are still important sources of infection today, especially in warmer countries. Salmonella, the pathogen causing traveler's diarrhea and the hepatitis A virus, reach humans through contaminated food. Cholera is probably the best-known example of a disease that spreads through drinking water: the British doctor Dr. In 1854, John Snow realized from a city map that a public well was the source of infection in a cholera outbreak in London.

Zoonoses: When an animal brings germs to humans

Some infectious diseases, such as measles, are only transmitted from person to person. Many other infections relevant to humans, however, have their origin in the animal kingdom. Infectious diseases that can only be transmitted from animals to humans are called zoonoses.

German research platform for zoonoses

The aim of the National Research Platform for Zoonoses is to improve the prevention, diagnosis and therapy of zoonotic infectious diseases in the long term. It is funded as part of the research agreement on diseases that can be transmitted from animals to humans (zoonoses) by the Federal Ministry of Food, Agriculture and Consumer Protection (BMELV), the Federal Ministry of Education and Research (BMBF) and the Federal Ministry of Health (BMG).

Zoonoses relevant to humans are often caused by insects. Malaria, for example, is a typical zoonosis: its actual host is the Anopheles mosquito. The increasingly common dengue fever, a life-threatening tropical viral fever, is transmitted by yellow fever mosquitoes and the Asian tiger mosquito. Even in our latitudes, insects are occasionally carriers of diseases. The tick in particular is making a name for itself in connection with early summer meningoencephalitis (TBE), a sometimes life-threatening meningitis, and Lyme borreliosis.

German Center for Infection Research

In the German Center for Infection Research (DZIF) around 500 scientists from 35 institutions across Germany are jointly developing new approaches for the prevention, diagnosis and treatment of infectious diseases. This is done with the aim of integrating new research results quickly and effectively into clinical practice.
The DZIF is one of six centers for health research (DZG) set up by the Federal Ministry of Education and Research to combat the most important common diseases.

The second important vector for zoonoses in humans are birds. Avian flu outbreaks, for example, keep attracting attention. Viruses similar to the human flu virus are transmitted via bird excrement. Psittacosis, a bacterial disease that primarily affects the lungs, is another example. It occasionally occurs in owners of pet birds, especially parrots.

Food of animal origin, e.g. raw milk or raw meat, is another important transmission route. Bacteria such as Salmonella or Campylobacter reach humans through these foods and cause, for example, diarrhea.

Often other mammals are also the source of infections in humans. The swine flu pandemic in 2009 and 2010 is an example of this. The flu then became indigenous to humans and is now spreading from person to person as part of the usual flu cycles. Viral rabies and tropical Japan encephalitis are also (predominantly) mammalian zoonoses.