Which statement is correct regarding infectious agents?

Infectious agents encompass a range of microorganisms, including bacteria, viruses, fungi, and parasites, which can spread through various routes such as airborne particles and water. The correct statement highlights that these agents can be transmitted through the air, where tiny droplets can carry pathogens, or through water sources that may become contaminated. This transmission mode is critical in understanding how infections spread in communities and healthcare settings.

The other options propose misconceptions: not all infectious agents require vectors for transmission; while vectors like mosquitoes may play a role in some diseases, many pathogens can spread directly from person to person or through contaminated surfaces. The idea that infectious agents cannot survive outside a host is inaccurate, as many microorganisms can exist in the environment for extended periods, depending on their type. Finally, the notion that infectious agents are always visible to the naked eye is misleading, as most pathogens are microscopic and cannot be seen without magnification. Understanding these aspects is vital for effective infection control and prevention strategies.