Infectiuos Bursal Disease Gumboro

INFECTIOUS BURSAL DISEASE

Infectious Bursal Disease

Definition History Etiology Types of infections

Subclinical Clinical

Classic VV

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Classic VV

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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

Inside Bursa of Fabricius Virus infects and destroies B lymphocytes.

Classic VV

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Classic VV

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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.

Classic VV

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Classic VV

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Etiology

Classic VV

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Classic VV

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Classic VV

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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, …

Classic VV

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Classic VV

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Classic VV

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Classic VV

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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.

Classic VV

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Classic VV

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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.

Virus characteristics Virus protein structure Spread of virus Epidemiology Treatment and control Evolution of the virus

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Virus Characteristics

Family: Birnaviridae. Genus: Avibirnavirus. Small, non-enveloped double stranded RNA virus. Has a bi-segmented genome.

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

Active disinfectants Chloramin 2% Glutaraldehyde Formaldehyde, only if tempreture is > 20°C

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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.

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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.

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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

16 +hrs

11-13 hrs

Virus characteristics Virus protein structure Spread of virus Epidemiology Strain classification Treatment and control Evolution of the virus

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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.

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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.

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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

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IBD Vaccination

vaccine

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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

vaccine

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IBD Vaccination

vaccine

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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

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

Standard broiler

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

vaccine

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IBD Vaccination

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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.

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.

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

vaccine

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IBD Vaccination

vaccine

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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

vaccine

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IBD Vaccination

vaccine

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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

vaccine

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IBD Vaccination

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Timing of Vaccination

Too soon MDA neutralises vaccine

Late Late protection

Optimal Sooner the better

There is no IBD vaccination schedule that can be routinely recommended.

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

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IBD Vaccination

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Characteristics Of Good Life Vaccine

1. Early protection.2. Minimum immunosuppression.3. Highest antibody titer.4. Cross protection between different strains.5. Easy application.

Infectiuos Bursal Disease Gumboro

Education

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