Infectious Bronchitis (IB):

• It is an acute, viral, highly contagious disease of poultry characterized by tracheal rales, coughing and sneezing.
• In laying flocks, there is drop in egg production and poor quality of eggs.
• It is important disease of young chicks, causing high mortality.

Etiology:

• Infectious bronchitis virus (IBV) of genus; Coronavirus, family; Coronaviridae
• ssRNA; measuring 20-200µm
• 20 or more serotypes are present. Best known serotype includes; Massachusetts, Connecticut, Holland, Arkansas-99, JMK and Florida.
• Among these strains, Massachusetts is most common and also produce severe type of disease.

Epidemiology:

• Disease was first reported in USA in 1931.
• It is now distributed worldwide.
• Birds of all age are susceptible. But disease is most severe in young chicks.
• IBV has also been isolated from pheasants causing respiratory signs and decreased egg production.

Transmission:

• Nasal discharge containing virus particle spread by aerosol over 1200 yard was reported.
• Virus may be transmitted through contaminated feed and equipments.
• Clothing, foot wear, etc. of attendants and visitors may also spread the infection.
• Spread is mainly through horizontal way.
• Birds that are infected may remain as carrier.

Pathogenesis:

• Virus gains entry through aerosol or contaminated feed.
• Virus localise in respiratory system followed by viremia
• Virus then gets distributed and reaches reproductive and urinary system and replicates upto 1-8 days post infection.
• Urogenital tract infection results in nephritis with tubular damage and interstitial infiltration of lymphoid cells.

Clinical Findings:

It is seen in several forms:

a. Respiratory form:

• It is most common in birds of all ages.
• Abnormal respiratory sounds, gasping and sneezing
• Watery nasal discharge, accompanied by eye discharge
• Facial swelling
• Mortality may be as high as 30% in kidney form.

b. Reproductive form:

• Damage in functional oviduct.
• Reduced egg production and quality
• Drop in egg production may sometimes be more than 50%.
• Eggs may be smaller than normal, deformed.
• Egg shell shows loss of pigment, shell becomes thinner or may be entirely absent.
• Albumen becomes watery and thin.
• Small hemorrhages may be seen in the albumen or yolk.
• Oviduct fails to develop completely or partially.

c. Kidney form:

• Marked depression, usually with respiratory symptoms and mortality as high as 30%
• Ruffled feathers, wet droppings
• Increased drinking

Postmortem Findings:

• Excess mucus in the respiratory tract.
• Congested lungs and air sac are cloudy and thickened.
• Air sac may contain yellow cheese-like mass (caseous exudate).
• In most severe form, caseous plug may be found in lower trachea or bronchi.
• Reduction in size of oviduct.
• Kidneys are swollen and pale and tubules are distended with urates.
• In some birds, there may be visceral gout; in which urates may coat the internal organs.

Diagnosis:

• Based on clinical findings and PM findings
• Isolation of virus in chick embryo
• Serum neutralization test (SNT), AGPT, CFT, FAT
• ELISA, immunoperoxidase technique, serum agglutination test

Differential Diagnosis:

1. Ranikhet disease:

• Disease is often accompanied by nervous signs along with respiratory form
• Hemorrhage is present in proventriculus and cecal tonsils.
• High mortality of chickens.

2. Avian influenza:

• Severe depression
• Cyanosis of comb/wattle is noted in AI
• Edema of head and neck
• Sudden death

3. Infectious laryngotracheitis (ILT):

• Blood-tinged mucus in trachea
• Diptheritic lesion in trachea/larynx
• Pump handle breathing is observed.

4. CRD:

• More chronic course than IB
• Marked sinus swelling
• Slow spreading, air sacculitis

5. Infectious coryza:

• Characteristic foul-smelling nasal exudate
• Severe facial swelling
• Low mortality

6. Avian Metapneumovirus infection:

• Swelling around eyes and head
• Frothy ocular discharge

7. Colibacillosis:

• Fibrinous pericarditis, perihepatitis, septicemia signs

Treatment:

• There is no specific treatment for IB
• Treatment with antibacterials is recommended to prevent air sacculitis.
• Electrolyte replaces are recommended to compensate for acute loss of sodium and potassium.

Control Measures:

• Strict isolation of chickens growing in poultry farm.
• Disinfection of poultry houses with appropriate disinfectant.
• Ventilation of houses with filtered air under positive pressure.
• Birds of different age group should be raised separately.
• Vaccination of poultry flocks; Live freeze-dried vaccine; 1^st at 21 days, 1 drop in each eye/nostril, booster dose at 6^th week and then 14^th week in drinking water.