Systematic Veterinary Virology

INTRODUCTION

• Infectious bursal disease (IBD, Gumboro disease) is an immuno-suppressive disease of domestic poultry caused by a birnavirus. The disease was discovered in 1962 in Gumboro, Delaware, USA. Hence, it is also known as Gumboro disease. 
• Chickens between two and three weeks of age were affected and showed signs of disease and a transient immunosuppression. However, in the 1980s the disease changed character. And the birds infected within the first week of life, developed bursal atrophy leading to a subclinical immunosuppression with increasing incidence of diseases of the skin, gastrointestinal and respiratory systems.
• Later a new strain appeared, causing a more rapid bursal atrophy, immunosuppression, diarrhoea and weight loss. Even vaccinated birds were affected and the natural immunity declined faster than after infection with the old type of virus.
• The mortality in Leghorns reached up to 90% and the morbidity almost 100%. Three different syndromes occur and these are referred to as “classical”, “very virulent” (vvIBD), and “variant” infectious bursal disease. This classification is based on pathogenicity.