A sub-microscopic infectious agent that replicates itself only within living host cells is called a:

A sub-microscopic infectious agent that replicates itself only within living host cells is called a:

• A. Virus
• B. Bacteria
• C. Fungus
• D. Protozoa

Answer: (A)

Viruses are sub-microscopic infectious agents that cannot reproduce unless they are inside living host cells. They hijack the cell’s machinery to make copies of themselves, so they’re described as obligate intracellular parasites. Unlike bacteria, fungi, and protozoa, a virus has no cellular structure of its own and cannot carry out metabolism outside a host. This distinction is why the term fits best for a virus. In infection control, this also explains why disinfection and proper sterilization are essential to inactivate viruses, since antibiotics won’t kill them.

Viruses are sub-microscopic infectious agents that cannot reproduce unless they are inside living host cells. They hijack the cell’s machinery to make copies of themselves, so they’re described as obligate intracellular parasites. Unlike bacteria, fungi, and protozoa, a virus has no cellular structure of its own and cannot carry out metabolism outside a host. This distinction is why the term fits best for a virus. In infection control, this also explains why disinfection and proper sterilization are essential to inactivate viruses, since antibiotics won’t kill them.