Which method of disease transmission involves direct injection of pathogens into the host?

The method of disease transmission that involves direct injection of pathogens into the host is known as biological transmission. This type of transmission typically occurs through vectors, such as mosquitoes or ticks, that carry pathogens from one host to another. In biological transmission, the pathogen often undergoes development within the vector before being transmitted to the next host, allowing it to be injected directly into the bloodstream through the vector's bite. This direct route of entry is crucial for the transmission of many diseases, as it allows the pathogen to bypass external barriers of entry such as skin or mucous membranes.

In contrast, passive transmission involves pathogens being carried without any multiplication or development in a vector, whereas mechanical transmission refers to the mechanical transfer of pathogens on the surfaces of vectors without involving any biological processes. Environmental transmission typically refers to diseases spread through contaminants in the environment rather than direct contact or injection methods.