Orthomyxoviridae: family of segmented negative-strand RNA viruses

Structure and genome

Orthomyxoviruses are pleomorphic enveloped particles bearing surface glycoproteins embedded in a lipid bilayer. Their genome is divided into multiple RNA segments, each packaged with nucleoprotein and viral polymerase subunits. This segmented organization allows reassortment when two related viruses co-infect the same cell, a mechanism important for sudden antigenic change and emergence of novel strains. Detailed studies of surface and internal proteins inform host range and immune recognition; see structural analyses at protein structure.

Genera and host range

The family is conventionally divided into several genera, commonly named Influenzavirus A, Influenzavirus B, Influenzavirus C, Thogotovirus and Isavirus. The first three are the classical influenza viruses that circulate in birds, humans and other mammals, and which are responsible for seasonal epidemics and occasional pandemics (influenza). Avian species are central reservoirs for many influenza A lineages; see literature on avian influenza. Isaviruses primarily infect salmon and are relevant to aquaculture (salmon), while thogotoviruses have been detected in both vertebrates and invertebrates, including vectors such as mosquitoes.

Pathogenesis and clinical importance

Clinical presentations range from mild respiratory illness to severe systemic disease depending on virus type, host species and underlying factors. Influenza A displays the greatest diversity and capacity for cross-species transmission, which underpins its pandemic potential. Influenza B and C are largely confined to humans with generally lower epidemic potential, though they remain important for clinical management and vaccine composition.

Transmission, control and surveillance

Transmission routes differ by virus and host: respiratory droplets and direct contact drive spread among humans and many birds; aquatic transmission and husbandry practices affect fish infections. Control measures include vaccination where available, antiviral drugs in clinical use, biosecurity in animal populations, and coordinated surveillance to detect emerging strains. National and international health authorities publish guidance and maintain monitoring systems to inform responses.

Evolution, ecology and research directions

• Reassortment of genome segments accelerates genetic diversity and can produce novel antigenic types.
• Surface glycoproteins determine receptor binding and host specificity, and are primary vaccine targets.
• Cross-species spillover and ecological reservoirs are active research topics linking virology, ecology and public health.
• Ongoing work addresses antiviral resistance, vaccine design, molecular surveillance and the ecology of nonhuman hosts.

For introductory overviews and deeper reviews consult classification resources and specialist literature; relevant entries include etymology and historical summaries at etymology, taxonomic frameworks at virus classification, public-health guidance and surveillance portals at reference sources and dedicated pages on individual genera such as influenzaviruses, influenza, avian influenza, clinical guidance for human infection, veterinary resources for salmon diseases, and vector studies involving mosquitoes and other invertebrates. Further molecular and ecological studies are summarized in specialist reviews and surveillance reports (vertebrate hosts, invertebrate hosts, and structural biology).