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Transmission of Pathogens

Human Biology (Year 12) - Pathogens

Ben Whitten

How are pathogens transmitted?

Communicable diseases are spread by transferring pathogenic organisms form one person to another. This can occur in a variety of ways:

  • Transmission by contact

  • Transfer of body fluids

  • Infection of droplets

  • Ingestion

  • Airborne transmission

  • Transmission by vectors

Transmission by contact:

Involves the spread of the pathogen by actual physical contact. The contact could be direct or indirect (touching an object touched by an infected individual). This type of transmission is common with skin infections and STI's.

Transfer of body fluids:

When blood or other body fluids from an infected individual person comes into contact with the mucus membranes or bloodstream of an uninfected individual. Pathogens may then enter the body, for example, HIV, Hepatitis B and Hepatitis C.

Infection by droplets:

Occurs when tiny droplets of moisture containing pathogenic organisms are emitted by an infected individual (breathing, talking, coughing, sneezing). The droplets may be breathed in by others or may settle of food or utensils and be ingested. Examples include measles, mumps, cold and influenza.


Consuming food or drink infected by pathogens; for example, dysentery, typhoid fever and salmonella.

Airborne transmission:

When the moisture in exhaled droplets evaporations, viruses and some bacteria remain viable and can result in infection when inhaled, for example, COVID-19.

Transmission by vectors:

When pathogens are transferred by other animals such as insects, ticks, or mites. This can be direct or indirect. Many vector-borne diseases are spread by a specific vector, for example, malaria and dengue fever are spread by mosquitos.

How else are pathogens transmitted?

It is important to note that not all pathogens are transmitted from human to human, but also from animal to human; these pathogens are referred to as being zoonotic, and when a pathogen is transmitted from an animal to a human, it is referred to as zoonosis. For example, rabies is caused by a lyssavirus transmitted by bats.

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