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HPAI H5N1 (Humoral Immunity vs Cell Mediated Immunity (Intracellular virus…
HPAI H5N1
Characteristics of virus causing HPAI H5N1
Family Orthomyxoviridae
(Genera Influenzavirus A)
6 genera: Influenzavirus A, Influenzavirus B, Influenzavirus C,
Thogotovirus, Isavirus, and Quaranjavirus
pleomorphic, spherical, or filamentous
2 kinds of spikes in Influenza A and B viruses
rod shaped spike -
hemagglutinin (HA)
mushroom shaped -
neuraminidase (NA)
enveloped with large spikes
6-8
segmented genomes
of linear -ve sense, single-stranded RNA,
Influenzavirus A
HPAI H5N1 virus
8 segmented genomes
Mutation
antigenic drift
changes in HA / NA protein structure
immune response against proteins prior to mutation no longer effective
endemic infection
Genetic Reassortment
antigenic shift
gene segments from 2 different virus coinfecting the same host packaged
into a single, novel virion
acquisition of new HA/NA protein
completely evade existing immunity
epidemic / pandemic iinfection
transmision through close contact with infected live/dead birds/H5N1-contaminated environments (no human-human transmission)
particular emphasis on
detection of H5 and H7 viruses in domestic poultry as high-pathogenicity phenotype (HPAI viruses)
common pathogens of horses, swine, humans, and domestic poultry
also causes sporadic or geographically limited infections in mink, seals, whales, and dogs.
80-120 nm
in diameter
Vaccination against HPAI-H5N1 in layers
Advantages
Help to control outbreak by slowing spread between birds, protect valuable genetic line, support steady food supply
Targeted AI vaccination based on movement pattern will decrease viral shedding from infected flock
Reduce the cost of control when effective vaccine delivery can be ensured
Decrease disruptions to the poultry sector
Disadvantages
Administering to large number of bird is difficult. Current vaccine do not fully prevent infection
Make distinguish difficult of vaccinated from infected flocks, trading partners refuse to accept vaccinated flock
Current AI vaccine are not 100% effective in preventing spread of disease between birds. Vaccinated birds could be potentially infected and spread the virus than non-vaccinated flock or the so-called “silent infection"
Lead to a false sense of security that underestimate of clinical signs consistent with HPAI or of milder clinical signs, so failure the immediate detection of HPAI in vaccinated flocks
Vaccination assists in driving antigenic change, so there is development of new antigenic variant strains of virus, thereby reducing the value of existing vaccines
Samples and diagnostic assay
Samples that can be taken:
1)oropharyngeal, tracheal and/or cloacal swabs from live
birds
2) Samples from internal organs such as liver, spleen and lungs are also tested in dead birds
Diagnostic Assay
Virus Isolation CEE
results available in 2-10 days
may or may not exhibit cytopathic effects
second step to specifically identify influenza viruses by immunofluorescence,
haemagglutination – inhibition (HI) or RT-PCR is needed
viruses are available for further characterization
However, isolation of highly pathogenic H5N1 viruses is usually
performed only in specially qualified and equipped laboratories since they are highly pathogenic and can kill the embryo
RT-PCR
Targeted at haemagglutinin and neuraminidase genes that is subtype specific
turn-around time of conventional RT-PCR
assays is 6–8 hours.
Real time RT-PCR methods can shorten this time interval to 3-4 hours while providing increased sensitivity and possibility of quantitation of the
viral target gene
diagnostic method of choice in many laboratories
ELISA
simple and convenient to use
more reliable as flock tests than in individual birds
valuable for surveillance and
demonstrating freedom from infection
but it is not very suitable to use in highly susceptible birds as they will die before developing antibodies
Haemagglutination inhiibition test (HI)
Subtype specific comparing to ELISA and AGID, so might miss some infections
Agar Gel Immunodiffusion test (AGID)
DIVA
To differentiate between vaccinated and infected birds
should be used in
surveillance when vaccination is part of a control program
Humoral Immunity vs Cell Mediated Immunity
Intracellular virus. Most virus infect the cells; not freely move
Memory T cells induced in response to seasonal human influenza can cross-react even with avian influenza H5N1
Clearly complex and involve humoral and cell mediated immune responses as well as innate immune responses
Adoptive transfer experiments have shown that CD8+ T memory cells can crossprotect across different subtypes
Currently available vaccine
Recombinant vaccine for influenza A virus-
produce by inserting gene coding for the influenza A virus haemagglutinin into non-influenza live virus vector
Advantage
Live vaccine induce mucosal, humoral and cellular immunity
Administer to young birds and induce early protection -administer at 1 day of age,provide significant protection 1 week later
Differentiate between infected and vaccinated birds
Disadvantage
High level of maternal body anticipated bc of previous infection/ vaccination
Use of recombinant vaccine restrict to country in which they are licensed and legally available
Conventional vaccine -limited to inactivated influenza A virus vaccine. Live conventional influenza vaccines against any subtype is not recommended
Currently available vaccine
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Currently available vaccine
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