influenza

virus def

simple, miniscule, infectious, obligate intracellular parasite

host range

limited range of animals which can be infected

influenza A - structure

mainly spherical, enveloped, ssRNA, - sense, segmented genome - 8 segments

flu A - 3 surface proteins

HA - haemagglutinin, NA - neuraminidase, M2 - matrix protein 2

HA function

binds sialic acid receptors, agglutinates RBCs, antigenic - neutralising

NA function

cleaves salic acid to release virus, degrades mucin (protects mucosal surfaces from infection), antigenic - non-neutralising

M2 function

forms proton channel that facilitates uncoating and assembly, stabilises viral budding, antigenic- neutralising

outer lipid envelope

lipid bilayer from host cell's plasma membrane, supported by M1 protein (role in virion assembly)

nucleocapsid structure

each of 8 different ssRNA, nucleoprotein, RNA polymerase

how many serotypes of influenza are there

4

how do serotypes differ

according to internal structure proteins - nucleocapsid and matrix

influenza A infects …

humans, swine, birds. horses, bats, dogs

influenza B infects ..

humans, seals

influenza C infects ..

humans, swine, dog

influenza D infects …

swine, cattle

epidemic def

a rapid spread of infection in a city/state/country over a short period of time

pandemic def

an epidemic that spreads across borders/worldwide, affecting large numbers

how are antigens used for subtyping

2 surface glycoproteins are used for subtyping , viruses are named by specific HA and NA types. 18 HA types and 11 NA types = 198 combination

stages in replication cycle

attachment, uncoating, transcription, replication, assembly, budding

attachment steps

HA binds sialic acid on host cell, virus endocytosed, vesicle membrane transferred to endosome

uncoating steps

acidification of endosome, M2 increases H+ causing uncoating

transcription steps

nucleocapsid goes to nucleus, transcribed mRNA are translated into protein in cytoplasm

replication steps

vRNP (-s) converts to cRNP (+s), through replication it generates vRNP, transported to cytoplasm

assembly

HA/NA transported to cell surface with M1 and genome segments

budding

virus buds off by NA

what determines pathogenicity

HA - exists as a trimer in the virion

sites in HA monomer

receptor binding site - for host specificity, cleavage site - single chain is cut into 2

human viruses usually bind to ..

a2,6 linked galactose

avian viruses usually bind to ..

a2,3 linked galactose

2 reasons why we still have influenza pandemics

antigenic drift, antigenic shift

antigenic drift

minor changes in the antigenic sites of HA/NA, due to: error prone replication & no proofreading, provides a selective advantage

antigenic drift occurs in which flu type

A B C

antigenic shift

major change because of gene reassortment, happens when 2 different flu viruses infect the same host, due to segmented genome and wide host ranges, complete change of HA/NA

antigenic shift occurs in which flu type

A

antiviral examples

amantadine/rimantadine, neuraminidase inhibitors (oseltamivir and zanamavir)

amantadine/rimantadine function

M2 ion channel inhibitors, blocks viral coating, has anticholinergic effect, only in type A

neuraminidase inhibitors use

used for treatment and prophylaxis, in type A and B