How is direct transmission of pathogens primarily defined?

Direct transmission of pathogens is primarily defined as the spread of infectious agents from an infected individual to a susceptible one through immediate contact. This type of transmission is often characterized by the transfer of pathogens through blood or body fluids, which can include saliva, semen, vaginal secretions, and other bodily fluids. This mechanism allows for pathogens like viruses and bacteria to enter the body directly, leading to infection.

In contrast, the other options describe forms of transmission that involve intermediary steps or indirect routes. For instance, the consumption of contaminated food or water involves a more complex process where pathogens must survive in the environment before infecting a new host. Airborne particles signify a form of aerosol transmission, which relies on the pathogens being suspended in the air, and insect bites involve vectors that carry pathogens from one host to another rather than direct contact. Thus, the definition of direct transmission aligns closely with contact involving blood or body fluids, establishing it as the primary form of transmission in this context.