Orthomyxovirus

Orthomyxovirus is a family of RNA viruses that includes five genera: Influenzavirus A, Influenzavirus B, Influenzavirus C, Isavirus, and Thogotovirus. The most well-known member of this family is the influenza virus, which is the causative agent of influenza in birds and mammals.

Structure and Classification

Orthomyxoviruses are enveloped viruses with a segmented, single-stranded, negative-sense RNA genome. The envelope of the virus is derived from the host cell membrane and contains two major viral proteins, hemagglutinin (H) and neuraminidase (N). These proteins play a crucial role in the virus's ability to infect host cells.

The Orthomyxovirus family is divided into five genera based on differences in their structure and life cycle. Influenzavirus A, B, and C are responsible for the annual influenza epidemics in humans. Isavirus infects salmon, causing infectious salmon anemia, while Thogotovirus is found in ticks and can cause disease in humans and other animals.

Replication

Orthomyxoviruses replicate in the nucleus of the host cell, a unique feature among RNA viruses. The virus enters the host cell by binding to sialic acid residues on the cell surface. Once inside the cell, the viral RNA is transcribed into messenger RNA (mRNA) by the viral RNA-dependent RNA polymerase. The mRNA is then used to produce viral proteins. New virus particles are assembled in the cell nucleus and bud from the cell surface.

Pathogenesis and Immunity

Orthomyxoviruses are primarily respiratory pathogens. They can cause a range of symptoms, from mild respiratory illness to severe pneumonia. The severity of the disease depends on the virulence of the virus and the immune status of the host.

The immune response to orthomyxoviruses is complex and involves both the innate and adaptive immune systems. The body's first line of defense is the innate immune system, which includes physical barriers like the skin and mucous membranes, as well as immune cells that recognize and destroy infected cells. If the virus manages to evade the innate immune response, the adaptive immune system is activated. This involves the production of antibodies that specifically recognize and neutralize the virus, as well as T cells that kill infected cells.

Prevention and Treatment

Vaccination is the most effective way to prevent infection with orthomyxoviruses. Antiviral drugs are available to treat infection, but their use is limited due to the development of drug resistance.