orthomyxoviridae

Orthomyxoviridae is a family of enveloped, segmented, negative-sense RNA viruses that cause influenza-like illnesses in humans and a variety of animals. The family is important in public health and animal health due to seasonal disease and occasional pandemics, particularly from influenza A.

Taxonomy and genera within Orthomyxoviridae include four groups corresponding to Influenzavirus A, B, C, and D. Influenza A and B are major human pathogens responsible for most seasonal flu outbreaks; influenza C generally causes milder disease; influenza D has been identified primarily in cattle and swine with uncertain relevance to humans.

Genome and structure are characteristic of orthomyxoviruses. The virion is enveloped and has a helical nucleocapsid with a segmented, negative-sense RNA genome. The genome organization differs among genera: influenza A and B possess eight RNA segments, while influenza C and D have seven. Surface glycoproteins vary by genus: influenza A and B display hemagglutinin (HA) and neuraminidase (NA); influenza C and D use a single surface glycoprotein called hemagglutinin-esterase-fusion (HEF). The viral replication cycle occurs in the host cell nucleus, a feature that influences transcription and RNA processing. The polymerase complex performs cap-snatching from host pre-mRNAs to prime viral mRNA synthesis.

Disease and transmission are generally respiratory. Humans acquire influenza primarily through respiratory droplets and contact with contaminated surfaces. Animals, notably birds and swine, serve as reservoirs and mixing vessels for influenza A; cross-species transmission and reassortment of genome segments underpin many outbreaks and occasional pandemics.

History and research focus on Orthomyxoviridae emphasize surveillance, vaccine development, antiviral therapies, and understanding the mechanisms of viral evolution and host adaptation.