Growth retardation and immunosuppression in SPF chickens infected by fowl adenovirus serotype-8b isolated in China

Abstract

One hundred forty 10-day-old SPF chickens were assigned to 4 groups. Fifty birds in group 1 and 20 birds in group 3 were inoculated with 600 µL (105 TCID50) of strain WF2014, 50 birds in group 2 and 20 birds in group 4 were inoculated with 600 µL DMEM/F-12 medium by intramuscular injection into the leg muscles. Birds in groups 3 and 4 were immunized at 17 days old with the Newcastle diseases (NDV) vaccine. At 3, 7, 11, 15 and 19 days dpi, seven birds from each groups 1 and 2 were randomly weighed and necropsied. Organs or tissues with macroscopic pathological changes, small intestines, and immune organs were collected for histopathological observation, measurement of the ratio of the length of the villus to the depth of the crypt (V/C), apoptosis, and determination of viral load. Chicken sera from groups 3 and 4 were collected at 7, 14, and 21 days after immunization, and antibodies against NDV were evaluated. The results showed that hepatitis, pancreatitis, proventriculitis, a decrease in the V/C ratio in the duodenum, and body weight were observed in WF2014 infected chickens. Apoptosis, severe lesions, and high viral load were found in the bursa of Fabricius, spleen and thymus, and the humoral immune response was suppressed in infected chickens. These suggested that FAdV-8b infection implicated growth retardation and immunosuppression in chickens, and this will lay the foundation for a further study of the mechanism of FAdV-8b infection in chickens.