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INFECTIOUS BURSAL DISEASE(Gumboro, IBD)Dr. Salah M. Hassan, MSc, PhDCollege of Veterinary MedicineUniversity of Mosul

Definition

An acute, very contagious, viral disease of young chickens characterized by destruction of lymphocytes in the BF and, to a lesser extent, in other organs

Definition

Affected chickens have reduced antibody response to vaccination, strong postvaccinal reactions and increased susceptibility to concurrent or secondary disease (i.e. immunosuppression). A 10 disease with morbidity/mortality may also occur.

Incidence

Recognized in all poultry producing areas of the world. One of the most important diseases in concentrated broiler producing areas (often not recognized--subclinical form).

Etiology

Caused by a birnavirus Viruses exhibit different degrees of pathogenicity, variants are recognized Resistant to disinfectants and environmental factors Can persist for months in contaminated houses

Etiology

Once a house is contaminated with IBD virus, the disease tends to recur. IBD virus has some sensitivity to phenolic, formaldehyde, and iodine disinfectants

Occurrence

During embryonic development and through ~10 weeks of age, the BF programs B-lymphocytes which become antibody producing cells in different sites in the immune system

Occurrence

If IBD virus damages the BF in young chickens, a long-term immunosuppression results (decreased number of antibody producing cells). Affected chickens are more susceptible to disease.

Transmission

Virus is shed in feces Feed, water, litter become contaminated Infection is by ingestion of virus Lesser meal worm (Alphitobius diaperinus) carry the virus Early transmitted (mechanically) between farms

Forms of IBD

IBD follows one of two courses depending on age at which chickens are infected (subclinical versus clinical)

Subclinical Form

Chickens less than 3 weeks of age: No clinical signs, but permanent and severe immunosuppression More economically important form Majority of field infections are subclinical



Clinical Form
Chickens 3-6+ weeks of age: Sudden onset, rapid increase in mortality Clinical signs include ruffled feathers, diarrhea, vent pecking, dehydration, trembling, depression, transient immunosuppression

Lesions

Standard IBD Viruses: Initially the BF is swollen (inflamed) Appears edematous and hyperemic, possibly hemorrhagic After 5 days, the BF diminishes in size rapidly (atrophies)

Lesions

Lymphoid necrosis and depletion also occur in secondary lymphoid organs (spleen, HG, cecal tonsils, etc) The secondary lymphoid organs are less severely affected These organs may recover

Lesions

Hemorrhages may be present in thigh and pectoral muscles Kidneys may be swollen

Lesions (microscopic)

Within 36 hours post infection- lymphocyte necrosis By 48 hours- few lymphocytes present; edema, hyperemia, and inflammatory cells evident (accounting for enlarged BF 5 days post infection)

Lesions (microscopic)

By 8-12 days post infection, BF is shrunken to less than one-quarter of its original size Lymphoid follicles are cystic, depleted of lymphocytes Epithelium lining BF is irregular, in-folded Fibroplasia is present in interfollicular c.t.

Lesions (microscopic)

Severe cases - all follicles affected simultaneously Less severe cases - scattered follicles affected, spread to other follicles

Diagnosis

History, clinical signs, lesions Microscopic lesions in BF Serologic testing Virus isolation Challenge studies

Prevention and Control

Immunization of breeders: Provides maternal antibodies Protects chicks Prevents subclinical IBD

Prevention and Control

Breeder vaccination (problem areas); 2 or 3 live primer vaccines (monitor) 1 or 2 inactivated vaccines (monitor) Revaccinate (inactivated) at 38-42 weeks of age if titers are low/poorly uniform Ensure antigenic diversity in program

Prevention and Control

Broilers Decrease exposure by clean-up, disinfection, traffic control (biosecurity) Provide high, uniform levels of maternal antibodies - prevents subclinical IBD Vaccinate broilers - prevents clinical IBD



Prevention and Control
Broilers: Timing of vaccination depends on levels of maternal antibodies High levels of maternal antibody neutralize the vaccine virus Vaccination is ineffective if field virus exposure is high!

Prevention and Control

Complicated by recognition of “variant” and highly virulent strains of IBD virusVariants induce BF damage in chickens even with adequate maternal antibody titersVariants do not cause obvious clinical disease, but induce immunosuppression

Prevention and Control

Variants cause rapid bursal atrophy without inflammation and edema Variants are not from a different serotype, are antigenically different enough to cause problems Consider vaccinating breeders with inactivated vaccines containing standard and variant strains of IBD virus