viruii

Virii is a less common plural form of the word virus. In modern scientific writing, the standard plural is viruses, though virii has appeared in older texts and some informal usage. The term reflects the Latin pluralization pattern for -us endings, but the preferred plural in most contemporary contexts is viruses.

Viruses are non-cellular infectious agents that require a host cell to reproduce. They range in size and shape from simple helical to icosahedral forms and, in some cases, complex or filamentous structures. A typical virus particle, or virion, consists of genetic material—DNA or RNA—encapsulated within a protein shell called a capsid; many also possess a lipid envelope derived from host membranes. Viral genomes can be single- or double-stranded and may be linear or circular.

The diversity of viruses is captured by classifications such as the Baltimore system, which groups viruses by genome type and replication strategy. Viral genomes include dsDNA, ssDNA, dsRNA, and ssRNA, with some using reverse transcription to integrate into the host genome. The high mutation rate of RNA viruses and genetic reassortment in segmented genomes contribute to rapid evolution and genetic diversity.

Viruses infect all domains of life, including bacteria (bacteriophages), plants, and animals. Infection outcomes range from benign to pathogenic, producing diseases that can be acute or chronic. Transmission methods vary and include respiratory droplets, bodily fluids, vectors, and contaminated surfaces. Control relies on diagnostics, vaccines, antiviral drugs, and public health measures. From a research perspective, viruses are valuable tools for studying molecular biology, gene expression, and cellular processes, while also requiring careful biosafety considerations due to their infectious nature.