Which of the following is NOT a method of transmission for disease by flies?

The correct answer is based on the understanding of how flies can transmit diseases. Flies are known as vectors in the spread of various infectious diseases, and they employ several methods of transmission.

Mechanical transmission occurs when flies carry pathogens on their body parts or in their saliva and transfer them to surfaces or food items. Fecal contamination also plays a significant role as flies often land on feces and then move to human food or surfaces, contaminating them with pathogens. Propagative transmission is when the pathogen develops within the fly itself before being transmitted to a host, which can occur with certain diseases.

In contrast, direct contact with infected hosts is not a method typically associated with disease transmission by flies. Flies do not directly touch or interact with infected individuals in a way that facilitates the transfer of pathogens; instead, their role is primarily as a transmitter of pathogens through contaminated surfaces or food, rather than through direct physical contact.