Influenzavirusten

Influenzaviruses are RNA viruses that belong to the family Orthomyxoviridae. They are the causative agents of influenza, commonly known as the flu. There are four main types of influenza viruses: A, B, C, and D. Influenza A and B viruses are responsible for seasonal epidemics in humans. Influenza C viruses cause mild respiratory illness, and influenza D viruses primarily affect cattle but are not known to infect humans.

Influenza viruses are enveloped viruses, meaning they have an outer lipid membrane. Embedded within this membrane are two key glycoproteins: hemagglutinin (HA) and neuraminidase (NA). These proteins play crucial roles in the virus's life cycle, including attachment to host cells and release of new viral particles. The genetic material of influenza viruses is segmented RNA.

Influenza A viruses are further classified into subtypes based on variations in HA and NA. Common subtypes that circulate in humans include H1N1 and H3N2. These viruses have a high mutation rate, particularly in their HA and NA genes. This phenomenon, known as antigenic drift, leads to small changes in the virus over time, which is why seasonal flu vaccines need to be updated annually. Less frequently, major changes in the virus, called antigenic shift, can occur when genetic material from different influenza strains reassort, potentially leading to pandemics.

Transmission of influenza viruses typically occurs through respiratory droplets expelled when an infected person coughs, sneezes, or talks. These droplets can be inhaled by people nearby or land in their eyes, nose, or mouth. Infected individuals can spread the virus one day before symptoms appear and up to five to seven days after becoming sick.