Occurrence: Worldwide. Very common.
Species affected: Mainly chickens, serotype 2 also occurs in turkeys and ducks.
Age affected: Young birds (2-16 weeks).
Causes: Infectious bursal disease virus is a birnavirus. It is highly stable and resistant to many physical and chemical agents. It is highly contagious and is spread by contaminated faeces, water and feed. It can also be carried by vectors such as darkling beetles and rats.
Effects: Elevated body temperature (111ºF), watery urate diarrhoea, anorexia, depression, ruffled feathers, head tremors, sleepiness and lameness can occur. Morbidity approaches 80% in White Leghorns and 50% in broilers. Hypervirulent strains occur in many parts of the world and can cause up to 100% morbidity and 80% mortality in laying hens. Normal mortality is not more than 40% in laying hens and 20% in less virulent strains in broilers. The virus is immunosuppressive.
Infectious bursal disease (IBD, gumboro, chicken aids virus)
IBD occurs only in young birds (2-16 weeks) and is seen mainly in chickens. It is subclinical in other poultry species. It is a Birnavirus. It is highly stable and resistant to many physical and chemical agents. Almost impossible to eradicate from a farm.
IBDV spreads by contaminated faeces, water and feed. It is a highly contagious and hardy agent. Other vectors can harbor the virus including darkling beetles their lesser meal worm larvae and rats.
Elevated body temperature, (111oF/44ºC), watery urate diarrhoea, anorexia, depression, ruffled feathers, head trembles, sleepiness and lameness can occur.
Morbidity approaches 80% in white leghorns and 50% in broilers.
Hypervirulent strains occur and can cause up to 100% morbidity and 80% mortality in laying hens. Normal mortality is not more than 40% in laying hens and 20% in broilers.
It is immunosuppressive and very common throughout the world.
The bursa is enlarged (2-4 times), haemorrhagic and/or oedematous early (3-5 days) in the course of the infection, which can result in clinical disease.
Other lesions include an increase in kidney urates, a swollen necrotic spleen, and increased mucous in the intestine.
Later in the infection the bursa is atrophic (7 days), ¼-½ normal size. Thymus may also be atrophic. The bursa remains atrophic through the life of the bird, whereas the thymus can regenerate.
Muscle haemorrhage, rickets, dehydration, haemorrhages at the junction of the proventriculus and gizzard may also be seen especially with the hypervirulent strains.
Oedematous involvement of the bursa of Fabricius in young birds is diagnostic.
Vaccination in ovo with recombinant vaccines, or by spray or in the drinking water in the field. Pullets need a combinations of live and killed vaccines to transfer maternal immunity to the progeny, which can prevent subclinical infections in the progeny. Many antigenic subtypes exist.
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