Orthomyxovirus

Orthomyxovirus is a family of RNA viruses that cause a range of respiratory illnesses in humans and animals. The most well-known member of this family is influenza virus, responsible for seasonal epidemics and occasional pandemics of the flu. Orthomyxoviruses are characterized by their segmented, single-stranded RNA genome, which is typically divided into seven or eight segments. This segmented genome is a key feature that contributes to their ability to evolve rapidly through reassortment.

The virions are enveloped and roughly spherical, with a diameter of about 80 to 120 nanometers. The envelope contains two major surface glycoproteins: hemagglutinin (HA) and neuraminidase (NA). Hemagglutinin is responsible for binding the virus to host cells, while neuraminidase plays a role in the release of newly formed virions from infected cells. The virus infects the respiratory epithelium, leading to symptoms such as fever, cough, sore throat, and muscle aches.

Orthomyxoviruses are classified into several genera, with influenza A, B, C, and D viruses being the most significant. Influenza A viruses are further categorized into subtypes based on their HA and NA proteins. The segmented nature of their genome allows for genetic reassortment, a process where different strains of the virus can exchange genetic material when co-infecting a single host cell. This reassortment is a major driver of influenza evolution, leading to new strains that can evade pre-existing immunity and cause widespread outbreaks. Transmission occurs primarily through respiratory droplets produced when an infected person coughs, sneezes, or talks.