Birnaviridae Flashcards
General characteristics
nonenveloped, hexagonal, single shell with icosahedral symmetry
2 segments linear dsRNA (designated as A and B)
replication takes place where
cytoplasm
infectious bursal disease (IBD)
acute, highly contagious infection
young chickens
primary target of IBD
lymphoid tissue
special predilection for bursa of fabricius (cloacal bursa)
Bursa of fabricius development
develops from out pouching of hindgut
B cell development
IBD serotype 1
pathogenic to chickens
3 antigenic subgroups: variant viruses (no mortality)
classic or standard viruses (10-50% mortality)
very virulent viruses (50-100%) mortality
IBD serotype 2
asymptomatic infections in chickens and turkeys
IBD transmission
contact, fecal-oral excreted by infected birds very stable in environment can survive in poultry houses after cleaning and disinfection detected in water and feed after 52 days
IBD pathogenesis
replication in gut associated macrophages and lymphocytes in ceca and small intestine,
go to liver,
go to bloodstream,
target organ is BF at max development (specific source for mature B lymphocytes)
max virus replication and depletion of B cells (necrosis and apoptosis)
can lead to: secondary viremia, localization in other tissues, triggering of INdirect t cell activation and direct macrophage activation leading to cytokine storm-> acute phase-> death, immunosuppression
When is highest susceptibility to IBD
3-6 weeks
Recovered birds or subclinical cases
Immunosuppression
diminished antibody response and increased susceptibility to range of opportunistic infectious agents
destruction of B cells causes
apoptosis, humoral immunosuppression
indirect activation of t cells causes
cell mediated immunosuppression
CS IBD
distress, depression, ruffled feathers, diarrhea, anorexia, dehydration, swollen bursa fabricius with hemorrhages
What you see during acute stage
enlarged edematous bursa
what you see 5 days post infection
bursa returns to normal size, may be hemorrhagic
what you see 8 days post infection
bursa atrophied and up to 1/8 normal size
Immune complex vaccines
live IBD vaccine virus + anti-IBDV antibody
in ovo
live recombinant vaccine that uses viral vector (herpes virus of turkeys) to express VP2 Ag of IBDV
Vaccines available
Live IBD vaccine: from fully or partially attenuated straings, mild, intermediate, or intermediate plus(hot)
Mild vaccine strains- no bursal lesion, can tbe effectively used in chicks with maternal Ab (until 4 wks age)
intermediate and hot- less affected by MDA, some succes at earlier stages
