The Influenza & Parainfluenza viruses. Orthomyxoviridae & Paramyxoviridae. Classification. ORTHOMYXOVIRIDAE. Influenza viruses. Type A. Type B. Type C. Family:. Genus:. Types:. “ myxo ” refers to interaction with mucins (glycoproteins)
“myxo” refers to interaction with mucins (glycoproteins)
Nucleoprotein (7 or 8 RNA segments)
Matrix protein (M)
80 to 120 nm
Each hemagglutinin spike is made up of three entwined molecules while each neuraminidase is comprised of four entwined molecules.
On the surface of the virus are M2 proteins. Inside the lipid envelope, there are eight RNA gene segments called RNPs(RNA molecule+ Nucleoprotein+ Polymerases).
Ball shaped M1 proteins: as cushions for the RNPs inside.
H or HA
responsible for pathogenicity of the virus
allows virus to adhere to endothelial cells in the respiratory tract
main determinant of immunity
N or NA
allows release of newly formed viruses within host
determinant of disease severity
Antibody against the hemagglutininneutralizes the infectivity of the virus and prevents disease. Ab against neuraminidase only reduces disease.
infects many species
causes widespread epidemics
found only in humans
capable of producing severe disease
causes regional epidemics
causes mild disease
humans are natural hosts, but isolates also found in pigs
does not cause epidemics
Many species of animal (eg. Birds, swine, and hourses) have their own influenza A viruses.
These animal viruses are probably the source of the new antigenic types.
Antigenic shift: Major changes based on reassortment of genome pieces. Occurs every 10-11 years
Antigenic drift: Minor changes based on mutation occurs every year.
Epidemics and pandemics occur when the antigenicity of the virus has changed sufficiently that the preexisting immunity of many people is no longer effective.
It is even possible to include RNA strands from birds, swine, and human influenza viruses into one virus if a cell becomes infected with all three types of influenza.
Influenza A viruses 16 HA types
9 NA types
Species affected humans, pigs, horses, birds, marine mammals
In humans 3 HA types (H1, H2, H3)
3 NA types (N1, N2, N8)
In birds all HA types
all NA types
A / Beijing / 32 / 92 (H3N2)
A virus type, here A
Beijing place where the strain was isolated
32 strain number
92 year of first isolation
H3N2 subtypes H3 and N2 virus sub type, here H3N2
After the virus is inhaled, the neuraminidase degrades the protective mucus layer, allowing the virus to gain access to the cells of the upper and lower respiratory tract.
Viremia rarely occurs, but there is necrosis of the superficial layers of respiratory epithelium.
Circulating IgG against the virus occurs after infection, but offers little protection. Secretory IgA in the respiratory tract is protective.
towel while sneezing
(Zanamivir orTamiflu is recommended by C.D.C.)