Microbiology, pathology, pathogenesis and transmission
Microbiology, pathology, pathogenesis and transmission 1. Microbiology, pathology and pathogenesis Human influenza viruses are single-strand RNA viruses that belong to the Orthomyxoviridae family, consisting of the genera influenza A, B, and C viruses. Only influenza A and B viruses cause epidemics in humans. Based on their main antigenic determinants, the haemagglutinin (H or H
Microbiology, pathology, pathogenesis and transmission
1. Microbiology, pathology and pathogenesis
Human influenza viruses are single-strand RNA viruses that belong to the Orthomyxoviridae family, consisting of the genera influenza A, B, and C viruses. Only influenza A and B viruses cause epidemics in humans. Based on their main antigenic determinants, the haemagglutinin (H or HA) and neuraminidase (N or NA) transmembrane glycoproteins, influenza A viruses are further subdivided into 18 H (H1–H18) and 11 N (N1–N11) subtypes, but only 3 hemagglutinin subtypes (H1, H2 and H3) and two neuraminidase subtypes (N1 and N2) have circulated consistently in the human population and are responsible for annual epidemics. HA and NA are critical for virulence, and are major targets for the neutralizing antibodies of acquired immunity to influenza. The 2009 pandemic influenza A(H1N1) virus (hereafter referred to as influenza A(H1N1)pdm09) which appeared for the first time in 2009 causing a global influenza pandemic, is now a seasonal influenza virus that co-circulates with other seasonal viruses (namely influenza A(H3N2) and influenza B viruses).
2. Transmission
Influenza viruses are spread from person-to-person. They can be transmitted by exposure to infectious droplets expelled by coughing or sneezing that are then inhaled, or can contaminate hands or other surfaces. The typical incubation period for influenza is 1-4 days (average 2 days). Most persons ill with influenza shed virus (i.e. may be infectious) from a few days before symptoms begin through 5-7 days after illness onset. However, very young children can be infectious for >10 days after illness onset; adults with severe disease (e.g. viral pneumonia) may also shed virus for >10 days, and severely immunocompromised persons can shed virus for even longer.[20] Children have the highest rates of seasonal influenza infection and illness in this group can amplify viral transmission in the community.
Influenza: NICD recommendations for the diagnosis, management, prevention and public health response, National institute of communicable diseases, 2021