What type of microorganisms are unable to multiply outside living tissues and can cause diseases?

Viruses are unique microorganisms characterized by their inability to multiply or survive without a host cell. They are composed of genetic material (either DNA or RNA) surrounded by a protein coat and require a living host to replicate. Once inside a host cell, viruses hijack the cellular machinery to produce new viral particles, leading to infection and disease within the host.

This distinction is crucial because while bacteria, fungi, and protozoa can often be found living independently in various environments (such as soil or water) and can reproduce on their own, viruses must rely exclusively on living tissues for their propagation. Understanding this difference is key in fields like microbiology and pathology, as it influences how we approach disease prevention and treatment.