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.