Infectious bursitis in chickens is an acute, contact infectious disease in young chickens. Clinical manifestations are loss of spirit, anorexia, intermittent diarrhea, tremor, and severe weakness, and changes in autopsy are characterized by dehydration, skeletal muscle bleeding, tubular urate deposition, and bursa and bleeding.
The harm of this disease is mainly the virus invading the central immune organ of chickens, a bursa, so that the production of lymphocytes in the chicken's bursa is destroyed, and immunoglobulins are reduced or unable to be produced, resulting in immune dysfunction. As a result, the response of the flock to vaccination is reduced, and the susceptibility to a variety of other diseases is increased, that is, immunosuppression occurs.
The size of the pathogenic virions is 55 to 63 nanometers, and 20 nanometers in diameter virus particle fragmentation products can appear during artificial culture and proliferation. The virus is strongly resistant to physicochemical factors, and it is still viable after heating for 56c for 5 hours and 60c for 90 minutes; it is still infectious to chickens after 3 years of preservation in a 20c environment. Viruses survive longer in nature, and viruses in sick chicken coops can survive for up to 122 days. Viruses have strong resistance to ether, chloroform, phenols, liters of mercury and quaternary amine salts, but are sensitive to chlorine-containing compounds, iodine-containing preparations, and formaldehyde.
Infectious bursitis, which is endemic, is spread to many developed chicken countries and regions around the world, causing considerable economic losses. Since 1979, there have been reports of this disease in Beijing, Shanghai, Shandong, Jiangsu, Heilongjiang, Henan, Jilin, Yunnan and other provinces in China. Since 1988, different types of chicken farms in China have undergone serious epidemics, causing huge economic losses.
The natural host of the infectious bursitis virus is mainly limited to chickens and turkeys. Infectious bursitis virus isolated from chickens can only make chickens infected, experimental infection turkeys do not have disease, but can produce antibodies, the virus isolated from turkeys can only infect turkeys, no effect on chickens. Different breeds of chickens can be sick, of which laihang chickens are more susceptible.
The occurrence of this disease is closely related to the day age, and the sensitivity of chickens of different days of age to this disease is different, which is characterized by the onset of the disease when the bursa is functional, the young chicks are protected by maternal antibodies, and the adult chickens are insensitive due to the contraction of the bursa, or the hidden passage. However, in some cases, acute outbreaks have been reported in flocks aged 14 to 20 weeks. Under natural conditions, the disease may occur at 2 to 11 weeks of age, but it is more common at 3 to 6 weeks of age, of which 4 weeks of age is the most susceptible. Chicks without maternal antibodies can develop disease soon after they emerge from their shells due to wild poisoning.