Viraus

Viraus is a subcellular infectious agent that reproduces only inside living cells. It consists of genetic material, DNA or RNA, enclosed in a protective protein shell called a capsid; many viruses also carry a lipid envelope derived from the host cell membrane. Viruses are not considered living organisms by some definitions because they lack independent metabolism.

Genome types include DNA viruses (single- or double-stranded) and RNA viruses (single- or double-stranded, positive or negative sense). The Baltimore classification organizes viruses by how they produce mRNA. Virus particles range from about 20 to 300 nanometers and can have icosahedral, helical, or more complex shapes.

Life cycle: They attach to specific receptors on host cells, enter by endocytosis or fusion, release their genome, replicate using host or viral enzymes, synthesize structural and regulatory proteins, assemble new virions, and exit via lysis or budding. Some viruses reverse-transcribe their RNA into DNA (retroviruses).

Classification and host range: Many families (e.g., Herpesviridae, Retroviridae, Coronaviridae) are distinguished by genome type, replication strategy, morphology, and host range. Viruses infect a wide array of hosts, including humans, animals, plants, and bacteria (bacteriophages).

Impact and public health: Viral infections cause a spectrum of diseases. Vaccines and antiviral medications reduce disease burden. Public health measures such as surveillance, hygiene, vaccination campaigns, and vector control play key roles in preventing transmission.

Detection and research: Diagnostics rely on nucleic acid amplification (PCR), antigen tests, and serology, complemented by culture and imaging in some cases. Virology research investigates virus structure, replication, evolution, host interactions, and vaccine design. The field integrates molecular biology, immunology, and epidemiology.