Date post: | 20-Jan-2015 |
Category: |
Education |
Upload: | ossama-motawae |
View: | 335 times |
Download: | 7 times |
INFECTIOUS BURSAL DISEASE
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Infectious Bursal Disease
Definition: Acute highly contagious viral infection of young chickens. Its primary target is the lymphoid tissue as with a special
predilection for the bursa of Fabricius.
Bursa Life Cycle
1. First 2 weeks:– Immature B lymphocyte
2. Week 3-6:– Well developed B lymphocyte
3. After 6 weeks: – Bursa regression in short life birds
4. After 12 weeks:– Bursa regression in long life birds
Infectious Bursal Disease
Inside Bursa of Fabricius Virus infects and destroies B lymphocytes.
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
History
1962 First recognized in area of
Gumboro, Delaware.
Until 1987 The strain of virus were of low
virulence causing less than 2% mortality and were satisfactory controlled by vaccination.
History
1986-1987 in Europe (VV) Vaccination failures appeared in
different parts of the world. Acute outbreaks occurred in
broilers at the end of the fattening period (3 weeks and older) caused mortality up to 50% or more , strains of increased virulence were identified.
History
1986-1987 in USA (variant) New isolates showed antigenic
drift where classical IBD vaccines were not satisfactory protective.
These isolates showed immunosuppression without IBD clinical signs.
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Etiology
IBDV
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Types of IBD Infection
Two types of IBD infection:1. Subclinical2. Clinical
Subclinical IBD
•The United States saw an increase amount of downgrades in the
slaughter plant .In the 1980’s
•Birds are suffering from respiratory and other secondary infections i.e. Staphylococcus and E. coli.
Investigations
•The underlying reason for this was found to failure of IBD, ND and IB
vaccinations .Conclusion
Subclinical IBD
The presence of an IBD virus that is different from the classic Type 1 isolate that has been diagnosed for years.
The maternal derived antibodies (MDA) were not protecting the broilers from the infection.
Subclinical IBD
Immunosuppression caused by the virus had increased its susceptibility to all the other health challenges resulting in sub-standard performances and poor economic returns.
Subclinical IBD
What is the variant strain? These are the strains that do not express certain virus
epitopes typical for classical strains. No cross protection between both. Variant strains are able to cause an early IBDV infection with
severe bursal damage (atrophy), resulting in immunosuppression.
Mortality is less than 5%.
Subclinical IBD
How does variant infection appear? Early infection (before 3 weeks)
– Immature bursae containing low quantity of B cells leading to low viral replication.
No clinical signs but severe immunosuppression.– Bad performances, vaccination failures, …
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Clinical IBD
Clinical IBD may be:1. Classic IBD2. vvIBD
Classic IBD
Susceptibility: – 3-6 weeks old are the most susceptible.
Morbidity: – From 10% to 90%
Mortality – Seldom exceed 3%.
Incubation period – About 2 to 4 days.
Classic IBD
Affected birds can start shedding the virus 24 hours post-infection.
Able to break through a moderate level of maternal derived antibody.
Classic IBD
Clinical signs are:1. Severe depression2. Vent picking 3. Presence of urate stains on the vent 4. Diarrhea5. Dehydration 6. Loss of appetite and elevated water consumption.
These signs can vary depending on the age of the birds and the general health status prior to the onset of infection.
Classic IBD
Gross and Microscopic Lesions:1. Ecchymotic hemorrhages in muscles and fascia of the
breast and thighs due to the impairment of the clotting mechanism.
2. Hemorrhages on the mucosa at the junction of the proventriculus and gizzard.
3. Kidneys are enlarged and urates are accumulated in the tubules.
4. Spleen is enlarged.
Classic IBD
The bursa of Fabricius is the main organ affected:1. The size is doubled 4 days post-infection and shows paleness
with straw colored transudate. 2. Sectioning of the bursa would demonstrate hemorrhages in
the follicles as well as exudates. 3. From the 5th day post-infection, the bursa will start receding
in size until it is about 1/3 the size of an unaffected bursa.
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Infectious Bursal Disease
Definition History Etiology Types of infections
Subclinical Clinical
Classic VV
Road Map
Very Virulent IBDV
History At the same time that the US is
dealing with variant IBD viruses, Europe, Africa and Asia start seeing acute cases of IBDV. – Diagnosed in flocks at a later
age. – In farms that are on very
good vaccination, biosecurity and management.
Very Virulent IBDV
Mortality – >20% with bursal lesions.
Able to break through higher levels of antibody than classical strains.
Very Virulent IBDV
Occurrence and Clinical signs: Clinical signs produced are similar to the classic virus but with
higher morbidity and mortality (80% and 30% respectively).
Very Virulent IBDV
Gross and Microscopic Lesions: The gross and microscopic lesions of the hypervirulent IBDV
are similar to the classic virus but the acute phase is more severe and more generalized in the flock.
Hemorrhages are prominent in the pectoral and thigh muscles and in the Bursa of Fabricius.
The bursal lesions are very diagnostic. The thymus, spleen and bone marrow are affected more
severely.
IBDV
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Treatment and control Evolution of the virus
Road Map
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Treatment and control Evolution of the virus
Road Map
Virus Characteristics
Family: Birnaviridae. Genus: Avibirnavirus. Small, non-enveloped double stranded RNA virus. Has a bi-segmented genome.
Virus Characteristics
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
Virus Characteristics
Active disinfectants Chloramin 2% Glutaraldehyde Formaldehyde, only if tempreture is > 20°C
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Treatment and control Evolution of the virus
Road Map
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Treatment and control Evolution of the virus
Road Map
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.
VP5likely 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.
Virus Protein StructureRole Protein
Encapsidation of viral particleVP1RNA dependant RNA polymeraseSmall amount in virus capsids
Contain antigenic region responsible for : Serotype specific Elicit neutralizing antibodies
VP2Main capside protein
Morphogenesis of the virus VP3Other major structural protein not exposed at the surface
Viral protease (maturation of VP2 trimming peptides during virus assumbly VP4
B-lymphocyte lysis. VP5
Virus Protein Structure
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.
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Treatment and control Evolution of the virus
Road Map
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Treatment and control Evolution of the virus
Road Map
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.
Spread of Virus
Horizontal transmission occurs through:1. Infected faeces.2. Contaminated equipment (especially footwear) 3. Other organic material.
Spread of Virus
Lesser mealworm (Alphitobius diaperinus) acts as a vector carrying IBDV from one cycle to the next.
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Treatment and control Evolution of the virus
Road Map
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Treatment and control Evolution of the virus
Road Map
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
Epidemiology
Oral infection
Persistence 52 days in contaminated water or feed.
Excretion Day 2-10 post infection
Pathogenesis
Other OrgansSpleen, thymus
Oral Infection
Duodenum, jejenum & caecumMacrophages & lymphatic cells
LiverKupffer cells
Bursa of FabriciusImmature B-lymphocytes
4-5 hrs
5 hrs
16 +hrs
11-13 hrs
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Strain classification Treatment and control Evolution of the virus
Road Map
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Strain classification Treatment and control Evolution of the virus
Road Map
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 are1. Differentiated by virus neutralization test.2. There is no cross protection between these two serotypes.
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Strain classification Treatment and control Evolution of the virus
Road Map
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Strain classification Treatment and control Evolution of the virus
Road Map
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.
Treatment & Control
The approach to IBDV control and prevention involves:1. Biosecurity2. Vaccination
Treatment & Control
BiosecurityImportant 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.)
Treatment & Control
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.
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Strain classification Treatment and control Evolution of the virus
Road Map
IBDV
Virus characteristics Virus protein structure Spread of virus Epidemiology Strain classification Treatment and control Evolution of the virus
Road Map
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.
IBDVVIRUS PROTEIN 2
VP2Classic Vs Variant strains
IBDV VP2Classic and Variant Strains
Central cup-shaped
Peak APeak B
Peak 1
Variant Strain
Peak 2
Classic Strain
VP2Chicken embryo Vs Tissue culture propagation
IBDV VP2Field Virus
Amino acids 253
Amino acids 284
IBDV VP2Chicken Embryo Propagation
Amino acids 253
Amino acids 284
IBDV VP2Tissue Culture Propagation
Amino acids 253
Amino acids 284
IBD VACCINATION
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
To protect young chick during the first one to two critical weeks post hatch.
Parent Breeder Chickens Are Hyperimmunised Against IBDV.
Live IBD Vaccine (2) 4 - 10 weeks of age
Inactivated IBD vaccine (1) 16 - 18 weeks of age or before onset of production
The resultant high level of IBDV neutralizing antibodies are passively transferred to the day old chick via the yolk sac (MDA).
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
MDAMaternal Derived Antibodies
MDA Decrease
MDA is protective when present at a sufficiently high titre. Due to metabolism and growth, the antibody titre declines to
half (t1/2) at a rate of:• Broilers 3.5 days• Broiler breeders 4.5 days • Layers 5.5 days
2 to 3 weeks post hatch, the susceptibility of a chicken flock to an IBDV infection increases.
MDA & Vaccination
Breeder flocks are immunized against IBD, so they would confer protective antibodies to their progenies.Advantage
Protects chickens from early infection.Disadvantage:
Neutralizes live vaccines.
MDA DecreaseELISA titer
Age
Maternal antibody will normally protect chicks for 1-3 weeks By boosting the immunity in breeder flocks with oil adjuvanted
vaccines, passive immunity may be extended to 4 or 5 weeks
MDA Variation
ELISA titer
Age
Standard broiler
Layer
Organic broiler
MDA Protective Threshold
ELISA titer
AgeProtected Non protected
Protective threshold against classical IBDV
Protective threshold against vvIBDV
MDA Protective Threshold
ELISA titre
AgePossible to use intermediate plus
Possible to use intermediate
Vaccine take intermediate
Vaccine take intermediate plus
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
Types of IBD vaccines
1. Life attenuated vaccines2. HVT Recombinant Vaccine3. Virus-Antibody Complex Vaccines4. Inactivated vaccines
Live Attenuated Vaccines
Live attenuated vaccines They are administered as the primary defense in the young
susceptible chicken. Commercial live vaccines are classified into 3 groups:
a) Intermediate strainsb) Intermediate plus strainsc) Hot strains
HVT Recombinant Vaccine
Composition The concept of recombinant vaccines is to insert genes of
critical immunizing epitopes (VP2) of IBD virus into a vector virus HVT (herpesvirus of turkeys).
While the vector virus replicates, the VP2 also replicates at the same rate resulting immunization against both.
HVT Recombinant Vaccine
Precautions The HVT is usually a slow replicating virus, it induces immune
response after 14 days. Adding a gene to the HVT may slows its replication and
extends the 14 days.
Immune Complex Vaccine
CompositionAntibody specific for the virus
+ Vaccine virus
Both are mixed in an appropriate ratio. The antibodies surround the vaccine virus.
Immune Complex Vaccine
Significance of adding antibodies The presence of antibodies protect vaccine virus from being
neutralized by MDA. Antibodies delay, by several days, the normal course of
vaccine virus replication. This process controls the time of releasing vaccine virus.
Immune Complex Vaccine
Precaution The level of MDA should be adjusted to the vaccine virus
strain.
Inactivated vaccines
They are administered to boost the immunity of parent birds.
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
Live Vaccines
Objective of using life vaccines:Live vaccines are administered to achieve active immunity.
Classification of Live Vaccines
Live vaccines are classified into 3 groups according to their ability to break through levels of MDA.
1. Mild These vaccine strains are highly attenuated. They can break through very low levels of MDA. They are no longer applicable in the commercial
environment.
Classification of Live Vaccines
2. Intermediate They are attenuated IBDV strains. They can break through MDA titres ≤ 6 log2 VN
3. Intermediate Plus/Hot They are less attenuated IBDV strains They can break through MDA titres ≤ 8 log2 VN
When To Use a More Invasive Vaccine?
The main feature of the presence of very virulent IBDV field challenge is increased mortality.
vvIBDV can break through higher levels of MDA than intermediate IBDV vaccines infections can occur before it is possible to immunise the chicks with intermediate vaccines.
When To Use a More Invasive Vaccine?
To be able to compete with such vvIBDV viruses and induce immunity in the face of still high maternal immunity, more invasive IBDV vaccines strains are required.
The main objective is to reduce mortality and the prevalence of vvIBDV in the flocks
Once this aim has been reached return to intermediate vaccines
General Recommendations
In farms with IBD problems or in “hot areas”1. Use a hot or intermediate plus vaccine 3 – 4 cycles;2. Followed by an intermediate vaccine
In “endemic” areas, multiple age farms and farms relying solely on hot vaccines1. Use continuously a hot vaccine.
Whenever possible try to switch back from a hot vaccine to an intermediate
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
Choosing Live Vaccine
Choice of live vaccine depends on:1. Virulence of field infection
Mild and Intermediate vaccine strains can not protect against vvIBDV.
Mild and Intermediate vaccine strains cannot be administered at an early age due to MDA interference.
2. Age of chickens to be vaccinated The earlier the vaccination the higher the level of MDA,
requiring a stronger vaccine.
Choosing of live vaccine
3. Age at which Gumboro outbreak occurs. Early outbreaks require earlier vaccination. Infections before 2 weeks require using vaccine that cover
variant strains. Late infections requires intermediate plus or hot strains.
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
Timing of Vaccination
Too soon MDA neutralises vaccine
Late Late protection
Optimal Sooner the better
121
Timing of Vaccination
There is no IBD vaccination schedule that can be routinely recommended.
Timing of Vaccination
Factors influencing a vaccination schedule include:1. Type of chicken to be vaccinated (broiler or commercial layer).2. Level of MDA
– The higher the start level of MDA the later the age of vaccination.
3. Uniformity of MDA– If the variation in MDA levels is too high (CV>30%) a second
IBD live vaccination is required to effectively immunize the flock.
4. Field pressure.
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
IBD Vaccination
Hyperimmunisation of Breeders Vaccination and Maternal Immunity Types of Vaccines
Live Vaccines Choosing live vaccine Timing of Vaccination Characteristics of good life
vaccine
Road Map
Characteristics Of Good Life Vaccine
1. Early protection.2. Minimum immunosuppression.3. Highest antibody titer.4. Cross protection between different strains.5. Easy application.