infectious bronchitis r134a_00_1 first reported by schalk & hawn in 1931 in north dakota (usa)...
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Infectious Bronchitis
R134A_00_1
First reported by Schalk & Hawn in 1931 in NorthDakota (USA) in young chicks showing respiratorysigns
Distribution: Worldwide
Transmission: Horizontal, direct contact
Incubation period: 18 - 36 hours.
Infectious Bronchitis
Infectious Bronchitis
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Agent: Coronavirus (RAN)
Host: Chickens of all ages
Affects:• respiratory tract• uro-genital tract
* The virus can be isolated from different organs up to ± 50 d.p.i.
Infectious Bronchitis
Infectious Bronchitis
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Young birds:• respiratory signs• sneezing, coughing, nasal discharge. Mortality may reach 30%, especially in combination with secondary infections (E. coli, M. gallisepticum).
Adult birds:• respiratory signs• egg drops• alteration in the internal and external quality of eggs (misshapen and soft eggs, watery albumen).
Infectious Bronchitis
Pathogenesis:
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Why is IB still a problem?
• Highly infectious• Persistent in the birds• Fast dissemination• RNA virus - mutations
- recombinations• Causes different diseases• Many different serotypes
?
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Ciliostasis Test
• Tool to measure the effect of a virus on the tracheal mucosa• The tracheal mucosa represents a mechanic barrier against foreign particles in the respiratory tract (muco-ciliar apparatus)• Consists of motile structures (cilia) and secretory cells (Goblet cells). They trap and eliminate foreign particles (ex. dust and bacteria).
• Tracheal rings of vaccinated and/or challenged birds are prepared and observed under the microscope.
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בעלי פעילות במצב תקין CILIA( ריסים (
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במצב פגועCILIA( ריסים (
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Ciliostasis test
10 tracheal rings 3 x top
4 x middle
3 x bottom
Results 0 = 100% cilia moving
1 = 75% cilia moving
2 = 50% cilia moving
3 = 25% cilia moving
4 = 100% cilia moving
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New serotypes of IBV can emerge as a result of few aminoacid changes in the S1 part of the spike genome of the virus
Antigenic variation
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Model of the structure of the “S”
protein on the surface of the virus
S1
S2
Virion membrane(Cavanagh, 1983)
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Cross protection against IB viruses belonging to other serotypes may be due to the fact that most of the virus genome remains unchanged
From a practical point of view it is thereforemore relevant to think in terms ofprotectotypes rather than serotypes
There are occasions when existing IB vaccines
do not provide adequate protection against
newly emerging serotypes
With the continual emergence of new serotypes of IBV it seems prudent to evaluate the level of cross protection obtained by the use of currently available vaccines.
Cross protection
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Cross protection studies
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4 groups (10 SPF birds)
1 Massachusetts (Ma5) at 1 day
2 4/91 at 14 days
3 Massachusetts (Ma5) at 1 day & 4/91 at 14 days
4 Not vaccinated
Reared in isolators
Experimental design
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Challenged with different field isolates 5 weeks of age by eye drop (0.1 ml)
Challenge dose: log10 3.0 CD50
Ciliostasis test 5 to 7 days p. challenge
in all experiments, groups vaccinated and challenged with homologous virus were included
Challenge
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0
10
20
30
40
Novaccine
VaccineA
VaccineB
Example of results
Maximum index = 40
Vaccine A:
- - No protection
Vaccine B:
- - Good protection
Ciliostasis Index
Infectious Bronchitis
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0
10
20
30
40
Control Ma5 IB 4/91 Bothvaccines
Protection against: Arkansas
Average ciliostasis index
Vaccines used
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0
10
20
30
40
Control Ma5 IB 4/91 Bothvaccines
Protection against: Brazil
Average ciliostasis index
Vaccines used
Infectious Bronchitis
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0
10
20
30
40
Control Ma5 IB 4/91 Bothvaccines
Protection against: Honduras
Average ciliostasis index
Vaccines used
Infectious Bronchitis
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0
10
20
30
40
Control Ma5 IB 4/91 Bothvaccines
Protection against: South Africa (890/80)
Average ciliostasis index
Vaccines used
Infectious Bronchitis
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0
10
20
30
40
Control Ma5 IB 4/91 Bothvaccines
Protection against: Taiwan (A1121)
Average ciliostasis index
Vaccines used
Infectious Bronchitis
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0
10
20
30
40
Control Ma5 IB 4/91 Bothvaccines
Protection against: Holland (D274)
Average ciliostasis index
Vaccines used
Infectious Bronchitis
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0
10
20
30
40
Control Ma5 IB 4/91 Bothvaccines
Protection against: Holland (D1466)
Average ciliostasis index
Vaccines used
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Conclusions
• The increasing prevalence of new serotypes creates difficulties in the design of adequate vaccination programs against IB
• It is undesirable and not always necessary to consider developing new live vaccines for each new serotype
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Conclusions
• The concept of protectotypes is more relevant from a practical point of view
• The use of IB vaccines belonging to different serotypes may broaden the protection against a wide variety of antigenically different IBV’s