Infectious Bursal Disease (IBD):

Synonym: Gumboro disease, infectious nephrosis, IBD

• It is an acute, highly contagious, viral infection of young chickens.
• It occurs in brooding and growing stage of chickens causing significant morbidity and low mortality rates.
• Disease was first described in 1962 and also called avian nephrosis due to severe kidney damage caused by this disease.

Etiology:

• Birnavirus, ds RNA virus, non-enveloped
• Virus has two main serotypes; serotype 1 and serotype 2
• Serotype 2 donot produce disease.
• Virus is resistant to ether, chloroform and common antibiotics, but can be inactivated by 1% solution of formalin or cresol within 1 hour.

Epidemiology:

• Disease was first described in 1962. Name ‘Gumboro’ was given because it was first recognized in Gumboro district of Delaware, a state in USA.
• Disease has got economic importance because of its heavy mortality within 3 weeks of age or older and due to severe and prolonged immunosuppression.
• Gumboro affects young chickens, usually between 21 and 42 days of age.
• Mortality rate may reach upto 51%.
• Classical IBDV strains causes low mortality rates <10%
• vv IBDV strains can cause high mortality rates >60%.
• Flock morbidity rate is typically 100% and mortality rate can range from 5% to greater than 60%.
• Mortality rate is higher in layer breeds compared to broiler chickens.

Transmission:

• Virus is very stable and difficult to remove from poultry houses.
• Virus is discharged through feces and spread from poultry shed by fomites.
• It is very contagious and transmitted through direct contact.
• Infective shed may remain infective for 122 days even after removal of infected birds.
• Virus may remain alive for around 6 months in dry litter.

Pathogenesis:

• Virus enters poultry through ingestion
• Virus invades macrophages and lymphoid cells in caeca.
• Virus then reaches small intestine to liver.
• From liver, it gets access to blood and distributed to other tissues including bursa.
• Virus then gains access to spleen, Harderian gland and thymus.
• Virus destroys immature lymphocytes in cloacal bursa, thymus and spleen.
• This results in immunosuppression

Clinical Findings:

• Disease is typically seen between 3-6 weeks of age and has short incubation period; 2-3 days.
• Earliest symptoms seen in flock is tendency for some birds to pick their own vents.
• Depression, white watery diarrhea
• Soiled vents, loss of appetite, ruffled feathers
• Unwillingness to move, trembling, closed eyes
• Lying down in exhaustion and finally death.
• Morbidity varies from 10-100% and mortality rate 0-20%, sometimes reaches upto 90-100% mortality.

PM Findings:

• Carcass is usually dehydrated.
• Usually, hemorrhages are present in thigh and breast muscles, sometimes on lining of proventriculus.
• Increased mucus on the intestine.
• Kidneys are swollen and white in appearance due to dilation of tubules with urates.
• Bursa is primary target organ. On 3^rd day following infection, bursa begins to increase in size and weight due to accumulation of fluid. By 4^th day; bursa usually is double its normal weight and size. By 5^th day, bursa return to normal size and starts to decrease in size. From 8^th day, it is about 1/3^rd its normal weight.
• Bursa shows necrotic foci and cheesy mass within lumen. Hemorrhages may also be present.
• Spleen are slightly enlarged and have small grey foci uniformly spread on surface.
• Sometimes, hemorrhage is observed at junction of proventriculus and gizzard.

Diagnosis:

• Based on history, clinical findings, and PM findings
• Serological test; AGID, Immunofluorescence test, VNT, ELISA
• ELISA is most commonly used serological test for evaluation of Gumboro virus antibodies in poultry flock.

Differential Diagnosis:

Disease that should be differentiated from IBD includes:

1. Coccidiosis:

• Detection of oocyst in feces
• No bursal swelling or hemorrhage
• Gradual onset
• Respond to anticoccidial drug

2. Infectious Bronchitis (IB):

• Mainly respiratory tract is involved.
• Sneezing, coughing, drop in egg production and egg shell quality
• There is catarrhal exudate in trachea/bronchi.

3. Inclusion body hepatitis (IBH)/Hydropericardium:

• Enlarged mottled liver with necrosis
• Bursal lesion is absent
• Accumulation of fluid in pericardium

4. Vitamin A deficiency:

• Most commonly observed in rapidly growing chicks and layers
• White pustules/plaques in mouth, esophagus and conjunctiva.
• Cheesy exudates in oropharynx/esophagus.
• Respond to nutritional supplement.

5. Marek’s Disease:

• Tumors are seen in nerves and organs
• It is usually seen in older birds.

6. Newcastle Disease (ND):

• Respiratory and neurological signs are present.
• Hemorrhage are found in proventriculus however not restricted to bursa.

7. Highly Pathogenic Avian Influenza (HPAI):

• Severe respiratory signs
• Multi-organ hemorrhages
• High flock mortality

8. Chicken Infectious Anemia (CIA):

• Aplastic anemia is observed.
• Pale bone marrow, thymus atrophy
• No bursal swelling/hemorrhage

9. Avian Leukosis:

• Neoplastic enlargement of bursa and other organs
• It occurs in older birds greater than 14 weeks of age.
• Slower onset.

Treatment:

• There is no effective treatment.
• Symptomatic treatment against liver and kidney disorder may be attempted.
• Hydration therapy with oral fluid and electrolytes.
• Attempt should be made to stimulate immunity. Drugs like E care, Stressnil, vitamin A, E, C may be tried.

Control Measures:

• Strict hygienic and sanitation measures are to be adopted, i.e. biosecurity and farm disinfection.
• Visitor should be discouraged to enter farm.
• Thorough disinfection of personnel should be made while entering and exiting the farm.
• Depopulation of affected birds should be made.
• All the poultry equipments should be sterilized.
• All the dead birds should be disposed off by burning
• Droppings should be removed and treated with formalin before discarding.
• House should be disinfected or fumigated before introduction of new batch of chicks.
• Lime/washing soda in foot bath and infected premises is to be attempted.
• Vaccination of poultry flock; first at 24-26 days, intermediate strain through intraocular route.
• In layer; first dose at 8-12 days, 1 drop intraocular, booster dose at 24-26 days in DW.