This document discusses infectious bursal disease virus (IBDV) which affects poultry. It begins by describing the virus's characteristics, including that it is a small, non-enveloped double stranded RNA virus with a bi-segmented genome. It then covers the virus's protein structure and the roles of the different proteins. The document discusses how the virus spreads horizontally through infected feces or contaminated equipment. It outlines the virus's epidemiology, describing the natural hosts, ages of highest susceptibility, and pathogenesis. The document concludes by covering treatment and control methods like biosecurity and vaccination programs. It also discusses how extreme vaccination pressure, improper cleaning, and other factors have led to the evolution of more virulent virus strains
5. Virus Classification
IBDV strains are classified into two distinct serotypes;
Serotype 1
Pathogenic IBDV affecting poultry
classic, very virulent, variant IBDV strains
Serotype 2
Apathogenic IBDV.
They are
1. Differentiated by virus neutralization test.
2. There is no cross protection between these two serotypes.
6. Cont. …
Very stable
The virus survives for:
122 days in non disinfected house without birds.
52 days in contaminated water or feed.
5 hours at 56°C
The virus resists pH range from 2 to 12
8. Plan of talk
Virus characteristics
Virus protein structure
Spread of virus
Epidemiology
Treatment and control
Evolution of the virus
9. VP4 -VP 5
VP1 (Polymerase)
1. Encapsidation of the virus particle.
2. Speed of virus replication.
VP2 (external capsid)
encodes the major antigenic determinants of
the virus, including epitopes that are
important in virus neutralization.
VP5
likely has a regulatory function and
plays a role in B-lymphocyte lysis.
VP4
Is a minor and non-structural
polypeptide.
VP 3 (internal capsid)
Interacts with both VP1 and VP2 and form
VP1-VP3 complexes which is likely to be an
important step in the morphogenesis of IBDV
particles.
10. Cont. …
RoleProtein
Encapsidation of viral particle
VP1
RNA dependant RNA polymerase
Small amount in virus capsids
Contain antigenic region responsible for :
Serotype specific
Elicit neutralizing antibodies
VP2
Main capside protein
Morphogenesis of the virus
VP3
Other major structural protein not
exposed at the surface
Viral protease (maturation of VP2 trimming
peptides during virus assumbly
VP4
B-lymphocyte lysis.VP5
11. Cont. …
Key points
Neutralizing antibodies are formed against VP2.
Modification of VP2 leads to modification of immunogenic
characteristics of viruses.
Variant strain:
Mutation VP2
No cross neutralisation with classical strains.
12. Plan of talk
Virus characteristics
Virus protein structure
Spread of virus
Epidemiology
Treatment and control
Evolution of the virus
13. Spread of Virus
IBDV is horizontally transmitted but
not vertically.
Infected and vaccinated birds usually
shed virus through faces from day 2
till day 10 post infection or
vaccination.
16. Plan of talk
Virus characteristics
Virus protein structure
Spread of virus
Epidemiology
Treatment and control
Evolution of the virus
17. Epidemiology
Natural host:
Chickens and turkeys are the natural hosts of the virus.
Age:
Highest susceptibility occures from 3 to 6 weeks of age.
Mainly calssic strain
Lowest susceptibility after 9 weeks of age.
Any infection after 9 weeks would be vv strain
Infection before 2 weeks cause immunosuppression
without clinical signs.
Mainly variant strain
20. Plan of talk
Virus characteristics
Virus protein structure
Spread of virus
Epidemiology
Treatment and control
Evolution of the virus
21. Treatment & Control
Fundamental issues
There is no treatment available.
Vaccination in the face of outbreak will not be effective.
Passive immunity protects progeny against disease, breeder
flocks are immunized against IBD with inactivated vaccines to
confer MDA to their progenies.
22. Cont. …
The approach to IBDV control and prevention involves:
1. Biosecurity
2. Vaccination
23. Biosecurity
Important measures to ensure that birds would be competent to
face any disease include:
1. All infected litter and carcasses of infected birds must be
suitably disposed of away from the site or any other
poultry operation.
2. A thorough well planned disinfection regimen must be
implemented.
3. Downtime between successive flocks must be maximized.
(A minimum of 10 days is recommended between
successive broiler flocks.)
24. Vaccination
Vaccines should cover both classic and variant strains.
Suggested vaccination program would include:
Breeders – Use both classic and variant strains.
Live attenuated vaccines, 2- 3 doses depending on the
challenge.
Inactivated vaccines – 2 doses.
Layers
2 or 3 doses of life attenuated vaccines, may be
intermediate or intermediate plus according to
situation.
25. Plan of talk
Virus characteristics
Virus protein structure
Spread of virus
Epidemiology
Treatment and control
Evolution of the virus
26. Evolution Of The Virus
1. Extreme vaccination pressure.
Use of cloned intermediate IBD vaccine that confers very
narrow protection.
Vaccinating breeders with inactivated classic-type virus
only resulting in chicks hatching with maternal antibodies
of limited to the classic type.
2. Short down time between grow-out.
3. Improper cleaning and disinfection.
4. Increased bird population.