Birnavirus Flashcards
Infectious Bursal
Disease / Gumboro
Disease
Species Affected
Mainly Chickens
Pheasants —> IBD
Turkeys —> immunosuppression
Ostriches —> immunosuppression
Infectious Bursal
Disease / Gumboro
Disease
Most susceptible
Young, 3-6 weeks of age
Infectious Bursal
Disease / Gumboro
Disease
Occurrence
Worldwide
Present in every large chicken farm
Infectious Bursal
Disease / Gumboro
Disease
Spread
Highly contagious!
Contaminated environment is the main source of
infection —> feed, drinking water
Mechanical transmission between farms, stables —>
vehicles, people, insects, rodents
Germinative transmission is insignificant but faeces
contaminated egg shells provide horizontal infection
of day-old chickens
Infectious Bursal
Disease / Gumboro
Disease
Pathogenesis
Virulence variants:
• Classical virulent strains:
cvIBDV
• Very virulent strains: vvIBDV PO (the most frequent)/
Conjunctival/Airborne —> GALT —> Vireamia —> Liver –> Bursa Fabricii
• Virus destroys B lymphocytes in the Bursa Fabricii, gut
(GALT), conjunctiva (CALT), and bronchi (BALT), cecal tonsils, Harderian gland etc
• Highest maturation of B
lymphocytes in Bursa is when animals is between 2-8 weeks of age. Therefore highest activity of virus in bursa is when the animal is between 2-8 weeks of age
Virus shedding after one day of infection for about 2 weeks via faeces
Factors influencing severity of disease:
• Age of chicken (< 2 weeks / 2-8 weeks / > 8 weeks)
• Immunity (level of maternal antibodies)
• Breed/type —> layers are more sensitive than meat hybrids
• Virulence of strain:
• cvIBDV: 5-6% (up to 20%)
mortality
• vvIBDV: 30-50% (up to 100%) mortality
• Antigenicity of the virus:
• Wild type virus
• Vaccine virus
• Specificity of yolk immunity
• Immunosuppression due to concomitant infectons:
• Reoviruses, CAV, E.coli, Ornibacterium rhinotracheale
• Mycotoxins
Infectious Bursal
Disease / Gumboro
Disease
Primary Replication
GALT: Gut associated macrophages and lymphatic tissue
Incubation time of 2-3 days
Infectious Bursal
Disease / Gumboro
Disease
Target Organs
Bursa Fabricii —> Premature B lymphocytes and other
bursal cells
Infectious Bursal
Disease / Gumboro
Disease
Clinical Signs
3-6 week old chickens:
• Fever, trembling, depression, debilitation (weakness), dehydration, excicossis
• Watery diarrhoea and swollen, blood stained vent
• Urate crystals on feathers around vent
• Recumbency, ruffled feathers
• Anaemia: pale combs —> later cyanosis
Subclinical disease: Immunosuppression
• Retarded growth
• Weaker feed utilisation
• Ineffective vaccines
• Altered appearance of other infectious diseases
Clinical outcome is influenced by age:
• 0-3 weeks of age: 0-30% mortality, permanent immunosuppression
• 2-8 weeks of age: 5-100% mortality, immunocompetent (normal immune system) after recovery
• Over 8 weeks of age: no clinical signs
• Young age infection —> damage of the Bcell receptor expression —> weak immune responses against mild antigens —> inefficient vaccinations —> vaccination will
not do anything as immune response is so small and will not produce antibodies
• Immunocomplex deposition and necrotising agents cause the signs of acute disease
Infectious Bursal
Disease / Gumboro
Disease
Pathology / Histopathology
Acute phase:
• Enlargement of the Bursa Fabricii
• Bursa Fabricii: Oedema, inflammation, haemorrhages,
caseous exudate
• Haemorrhages in the subcutaneous connective
tissue, muscles, proventriculus and gizzard mucosa
• Nephritis —> pale, yellow, mottled kidneys
• Splenomegaly, sometimes with haemorrhages
• Liver oedema and dystrophy, with necrotic foci
• Bursa lymphatic depletion, reticular cell karyorhexis,
follicular necrosis, inter follicular tissue proliferation,
mononuclear cell infiltration
• Necrotic processes in the bone marrow
• Lymphoid depletion in the thymus cortex and medulla too
Chronic phase:
• Bursa atrophy and early involution
• Complications and signs of coinfecitons
Infectious Bursal
Disease / Gumboro
Disease
Diagnosis
Age, clinical signs, PM lesions (lesions in the Bursa Fabricii) and histopathology (lymphatic depletion and necrosis)
Virus isolation —> embryonate egg CAM, cell cultures
Detection of virus: RT-PCR, IF, IHC
Determination of virulence:
• Experimental infections
• RT-PCR and sequencing
• Monoclonal antibodies
Differentiation between wildtype and vaccine strains:
• RT-PCR and sequencing
Serology: VN, ELISA
Infectious Bursal
Disease / Gumboro
Disease
Treatment
No specific treatment
Hyperimmune yolk SC and Vitamin E may help
Infectious Bursal
Disease / Gumboro
Disease
Prevention and Immunity
Strict hygiene within the first 2 months:
• Disinfection of egg shells
• Decontaminate fomites
• Thorough cleaning and disinfection of all housing, tools, equipment, clothing etc
• All in, all out technology
Immunisation:
• Attenuated live vaccines:
• Mild —> no bursal damage but no
effect in birds with low maternal Ab level
• Intermediate —> Mild bursal damage, efficient in lower maternal Ab level
• Hot —> pathogenic for seronegative
chicks, efficient in higher maternal Ab levels
• Immunocomplex vaccines:
• Live vaccine strain + specific antibodies (Virus Protecting Factors)
• Regulates viral multiplication and protects from maternal antibodies
• Captured by follicular dendritic cells of spleen
• Recombinant, vector vaccines:
• VP2 gene is cloned into turkey herpesvirus (as a vector)
• Efficient in case of high maternal Ab levels
• Continuous stimuli
• Harmless
• Inactivated vaccines:
• Used as booster vaccinations
• High, homogenous, long lasting immunity
• Complete virus or subunit vaccines —
> recombinant VP2 (produced in yeast or plants)
Timing of immunisation:
• Important to vaccinate at the correct time
• Inhibitory effect of maternal antibodies coincide with the sensitive period
• Homogenous maternal antibody level is necessary for the efficient vaccination
• The vvIBDV can break through maternal Ab protection
• Determination of time depending on maternal Ab level in flock
• Usually start at day 16-18 but vaccination of day old chick with inactivated vaccine is possible too
• In ovo vaccination possible
Application of vaccine:
• Live virus: via drinking water, aerosol, conjunctival, sc
• Immunisation of layers in drinking water may result in non-homogenous maternal Ab levels in the chicken
• Identification of the virulence of the present wild type virus is necessary
• Identification of the antigenic subtype of the present wild type virus is necessary
• Usually repeated immunisations
• Combined vaccines also available (+NDV, IBV, EDSV)
• Vaccination programs for different viruses may interfere with each other in young
animals
General characteristics of Birnaviruses
*2 RNA viruses —> dsRNA with an icosahedral capsid and no envelope
*Four structural proteins
*Very high resistance in environment!
• IBDV can survive in 56℃ for 30 minutes, pH 3-9, and up to 4 months in the litter, Sensitive to disinfectants and detergents (at 40℃)
*Four genera: Avibirnavirus (IBDV), Aquabirnavirus (Infectious Pancreatic Necrosis Virus), Blosnavirus (infects fish), Entomobirnavirus (Drosphila X virus)
