Infectious Bursal Disease Flashcards
causative agent of Infectious Bursal Disease
Birnaviridae
genome of Birnaviridae
dsRNA, 2 genome segments
Birnaviridae resistancy
no envelope
highly resistant
What does Avibirnavirus genus cause
Infectious bursal disease
what is the Infectious bursal disease
acute disease in 3-6 wk old chickens
with inflammation of the Bursa Fabricus and immunosuppresion
What strains of Infectious bursal disease is there?
classical (only found in australia)
new variant
very virulent
Serotypes of Infectious bursal disease
ST1: pathogenic
ST2: non-pathogenic, from turkey but may infect chickens too
serological cross-reaction but NO cross protection
Infectious bursal disease vaccines can be
hot
intermediate
mild
Infectious bursal disease virus hosts
mainly chickens
phaesents, turkey and ostrich
Infectious bursal disease epizootiology
PO
highly contagious
shedding within 1 day
contaminated environment main source of inf (mechanical transmission between farms)
no germinative route but eggshell inf with faeces
Infectious bursal disease pathogenesis
PO
macrophages of the gut & lymphoid tissue
prim. viraemia
liver
bursa of fabricus
sec. viraemia
spreading in body
Main target cells of Infectious bursal disease
premature B lymphocytes & other bursal cells
highest activity of Infectious bursal disease and why
2-8wks old, also highest activity of the bursa of fabricus
effect of infectious bursal disease virus infection at 2-8wks
5-100% mortality, but immuno-competence after recovery
effect of infectious bursal disease virus infection at 0-3wks
0-30% mortality, permanent immunosuppression
effect of infectious bursal disease virus infection above 8wks
no CS
why does an infection at a young age of Infectious bursal disease cause immunosuppression
damage of Bcell receptor expression
weak immune resp against othe Ag
inefficient vaccination
what causes the signs of acute Infectious Bursal disease
immune-complex deposition and necrotizing agents
what influences the severity of Infectious Bursal disease
- age (2-8wks)
- maternal Ab
- breed of chicken (layers)
- virulence of virus strain
- antigenicity of virus (wild type, vaccine, specificity of yolk immunity)
- immunosuppression (mycotoxins)
Infectious Bursal disease CS age
3-6 wks (after 2-3 dys incubation)
Infectious Bursal disease CS
- lethargy
- watery diarrhea
- swollen, bloddy vent, urate crystals on feathers around vent
- anaemia
Subclinical Infectious Bursal disease CS
immunosuppression
Infectious Bursal disease patho of acute phase
- bursa of fabricus
- haemorrhages
- nephritis
- spleen (enlarged)
- liver (necrotic foci, oedema)
- thymus (lymphoid depletion in cortex)
- BM: necrosis
Infectious Bursal disease patho pf chronic phase
- bursa of fabricus (atrophy, early involution)
- signs of coinfection
Infectious Bursal disease diagnosis
RT-PCR + sequencing
Infectious Bursal disease DDx
- newcastle D (any age, resp & CNS)
- Bact. speticiaemia
- Reticuloendotheliosis (older animals, tumors)
- Chicken anaemia (no inflammation of bursa, only atrophy)
- malabsorption syndrome (no inflammation of bursa)
- Coccidiosis (SI & colon lesions)
Infectious Bursal disease prevention
hygiene
disenfection of egg shells
decontamination of fomites
When to vaccinate against Infectious Bursal disease
timing based on level of maternal Ab level of the flock
which Infectious Bursal disease virus strains easily breaks through maternal antibody protection
vvIBDV
Mild (strongly attenuated) IBDV vaccine strains
- no bursal damage
- efficacious only at lower or seronegative chickens
Intermediate (moderatly attenuated) IBDV vaccine strain
- mild bursa damage
- efficacious at lower maternal antibody level
hot (weakly attenuated) IBDV strain
- pathognomic in seronegative chickens
- efficacious at high maternal antibody levels
- (determination of Ab levels is needed)
which virus is used for the IBD vaccine
VP2 coding gene is cloned into turkey herpes virus vector
IBD immune-complex vaccine
live virus + specific Ab
vaccine virus is protected from maternal Ab, multiplication is controlled, immune complex is captured by the spleen follicular dendritic cells
IBD inactivated vaccines
booster vaccines, for layer parents
high, long-lasting immunity
given IM
Live attenuated vaccine of IBD
- drinking water (PO)
- vaccine virus propagates to bursa
- vacc. time is critical
- protection depends on vaccine strain
Recombinant vector vaccines (HVT)
- in ovo or Sc in hatchery
- will not propagate in the bursa
- protection against VP2 of virus
- DIVA
IBD Immune-complex vaccines
- In ovo or SC in hatchery
- can propagate to bursa
- full protection after vaccine take in bursa
- compatible with Marek vaccine used in hatchery
