Spread of infectious diseases

A chain of infection is defined as the way in which a pathogen reaches a patient.

The chain of infection consists of three links:

• the source of infection
• the transmission route and
• the recipient.

The source of infection (pathogen reservoir) can be animals, humans, contaminated food, water and objects. The pathogens spread from the source of infection.

In the direct route of infection, the pathogens enter the body with contaminated food, body fluids and excretions (smear infection) of other infected persons and as droplet infection.

In the case of indirect infection, an infected animal or a contaminated object is interposed.

Thus, different chains of infection are distinguished:

Homogeneous-homonomous chain of infection: When an infectious disease spreads, it is transmitted from person to person. Only the human being is affected. An example of this are all sexually transmitted diseases. Furthermore, many diseases transmitted by droplet infection, but also infectious diseases through contaminated food or drinking water. This also includes nosocomial infections.

Homogeneous-heteronomous chain of infection: When an infectious disease spreads, it is transmitted from animal to human (without the involvement of an insect). Both humans and animals are affected. An infectious disease (e.g. plague or rabies) that is transmitted from a vertebrate to humans is called a zoonosis,

Heterogeneous-homonome chain of infection: The spread of an infectious disease occurs from human to human, whereby an insect or an arachnid that is not itself diseased is involved as a vector. Infectious diseases such as malaria/borreliosis/leishmaniasis/endemicspotted fever are affected by this.

Heterogeneous-heteronomous chain of infection: the spread of an infectious disease occurs from animal to human with the involvement of an insect. Example plague: a sick rat infects the rat flea, which in turn can infect a human as a vector.