Infectious bronchitis
Infectious
bronchitis is an acute, highly contagious upper-respiratory tract disease of
chickens caused by gamma coronavirus. The primary target organ is the
respiratory tract, but also affects reproductive organs and kidney
(particularly in broilers).
OIE
listed diseases
ETIOLOGY:
Infectious bronchitis
virus (gamma coronavirus) : SS RNA +ve
Subfamily: Coronavirinae
Family: Coronaviridae
HOST
Domestic fowl / chickens (of all ages)
Rarely isolated from other species
TRANSMISSION
Air-borne route
Direct chicken to-chicken contact
Indirectly through mechanical spread
Contaminated
poultry equipment or egg packing materials, manure used as fertilizer, farm
visits, etc.
PATHOGENESIS
Depend on the age of the bird, host immune status, and virulence of
the virus. As age increases, chickens become more resistant
⇓
Virus enter in to body → respiratory tract → virus replication →
⇓
Go in other organs like kidney, and reproductive organs (oviduct, testes)
& alimentary tract
⇓
virus replication
⇓
Virus replication in respiratory tract produced bronchitis and
pneumonia → if secondary bacterial infection→ more morality
⇓
Virus replication in kidney produced necrosis of tubular cells→ gout
⇓
Virus replication in oviduct produced atrophy of epithelium Chicks,
less than 2- weeks of age may suffer damage to the oviduct, resulting in
permanent impairment to their egg-laying capacity.
CLINICAL SIGNS
Incubation period: 18 -36 hours
Respiratory signs
o Seen in birds of all ages with variable
severity
o Depression, ruffled feathers, and huddling
near heat sources
o Tracheal rales, gasping, sneezing, watery nasal discharge, sometimes accompanied by lacrimation, and facial swelling
Renal signs
o Broiler chickens (3–6 weeks of age) infected with a nephropathogenic virus (Gray IBV strain)may appear to recover from the respiratory phase and then show signs of depression, ruffled feathers, wet droppings, increased water intake, and mortality
Reproductive signs (in layers)
o Egg production may drop by up to 50%
o Eggs are often misshapen, soft-shelled, and
contain watery albumen (watery white)
Birds that recover from the infection
may never return to pre-infection egg laying levels.
o Blind or false layer
Macroscopic
Pathology
o The trachea, nasal passages, and
sinuses may be oedematous and typically have serous, catarrhal, or caseous
exudate
o Mucoid plugs of pus in the primary or secondary bronchi, frequently causing asphyxia
o The lungs may show evidence of pneumonia
o The air sac membranes may be cloudy and caseous yellow exudate may be present
o Nephropathogenic infections produce swollen and pale kidneys with the tubules and ureters often distended with urates
o Urolithiasis may be seen
o Egg yolk peritonitis :- Fluid yolk
material may be found in the coelomic (abdominal)cavity
o
Cystic oviduct
Microscopic
Pathology
o
Trachea & Bronchi: Inflammatory and degenerative changes
o
Air sac: Oedema, epithelial desquamation, fibrinous exudate
o Kidney: Interstitial nephritis, Degenerative changes, Urolithiasis , urates in ureter
o Oviduct: Epithelial damage, dilatation of tubular glands, infiltration of inflammatory cells, proliferation of lymphoid follicles
DIAGNOSIS
Based on
clinical signs
Gross and
microscopic lesions
Serological test
includes
o
Virus neutralisation (VN)
o
Immunodiffusion (ID)
o
Hemagglutination inhibition (HI)
o
Immunofluorescence (IF)
o
ELISA
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