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HPAI-H5N1 (Influenza A (sensitive to (heat, lipid solvents, nonionic…
HPAI-H5N1
Influenza A
Genus: Influenzavirus A
Family: Orthomyxoviridae
classification
Haemagglutinin (HA) subtype 5
Neuraminidase (NA) subtype 1
Morphology and size
Enveloped, helical nucleocapsid, spherical to poleomorphic virions, 80-120 nm in diameter
Nucleic acid
Linear, segmented, negative-sense,
single-stranded RNA, ~13.6 kb in length
sensitive to
heat
lipid solvents
nonionic detergents
formaldehyde
oxidizing agents
Disadvantages of vaccination
Challenge of replicating the virus
-Length of time taken for virus replicating is long.
-Require millions of embryonated (fertilised) chicken eggs
egg-based method is self-defeating towards virus
-active virus kills the chicken embryo before replication occurs on a sufficient scale
Complication of mutation
Frequency of mutation of virus is too high
-The production of vaccine is always not homologous to it
Administration of DNA vaccine by simple injection appears insufficient to stimulate the required immune response
Need for expensive-sounding techniques: gold nanoparticles are coated with the DNA and, using pressurised gas, are blasted into the skin where they directly penetrate immune cells.
High pathogenicity for poultry
Handling of the wild-type (wt) viruses requires enhanced biosafety level 3 (BSL-3) containment
Influenza A
Samples
oropharyngeal, tracheal or cloacal swab from live birds
feces sample for pediatric
immature feathers
PM : internal organs
trachea, lungs, air sacs, intestine, spleen, kidney, brain, liver, heart
Diagnostic Tests
to identify influenza A
Agar gel immunodiffusion (AGID)
ELISA
RT-PCR
To identify subtype
RT-PCR
haemagglutination and neuraminidase inhibition test
sequence analysis of HA and NA genes
distinguish LPAI and HPAI
genetic tests to identify characteristic patterns in HA
virulence tests
virus isolation in embryonated eggs
Serology for surveillance or to demonstrate freedom from disease
HI
ELISA - cross reactivity is an issue
AGID
DIVA - used when vaccination is part of control program
Real time RT-PCR is the choice of many labs
Advantages
Reverse genetics and cell culture provide larger quantities of vaccine more quickly and at lower cost
The required HA and NA genes are identified and used to genetically engineer viruses which are subsequently replicated by cell culture.