An infectious biological entity that contains genetic material and can reproduce only by using the machinery of a suitable host cell.
A virus consists of genetic material, either DNA or RNA, enclosed in a protein structure and, in some viruses, surrounded by a lipid envelope. Viruses do not have the cellular machinery needed to reproduce independently, so they enter susceptible host cells and use cellular processes to produce new viral components.
Viruses cause many human diseases, including influenza, COVID-19, measles, and HIV infection. Antibiotics do not treat viral infections because antibiotics target bacteria rather than viruses.
QUICK FACT
Viruses are not simply very small bacteria. They differ fundamentally from bacteria in their structure and method of replication.
COMMONLY CONFUSED WITH
- Bacteria: living single-celled microorganisms with their own cellular machinery; some cause disease and can be treated with antibiotics.
- Virus particle (virion): the complete infectious viral particle outside a host cell.
SEE ALSO
