Serological and molecular investigation of fowl adenovirus

Avian adenoviruses (FAdVs) are poultry pathogens associated with various diseases such as Inclusion Body Hepatitis Syndrome (IBH), Hepatitis-Hydropericardium Syndrome (HHS) and Adenoviral Gizzard Erosion Syndrome (AGE). These infections pose a significant threat to the health and productivity of poultry and cause economic losses to the poultry industry. In addition, FAdV has recently been shown to cause atrophy of the Bursa of Fabricius and thymus and to have immunosuppressive properties. FAdV is usually associated with immunosuppressive agents such as Infectious Bursal Disease Virus (IBDV), Chicken Infectious Anaemia Virus (CAV) and Avian Reovirus (ARV). In FAdV-positive birds, the differential diagnosis based on clinical and necropsy findings is difficult. For this reason, the infection is ignored, and studies that associate the infection with other immunosuppressive diseases are rare. FAdV has more than one serotype, and cross-protection between serotypes through vaccination is insufficient. Commercial imported vaccines are available to protect against infection. However, due to the diversity of serotypes, there may be differences between serotypes, even at the country/regional/farm level, and vaccination may not achieve the desired success. In the study, 42 samples were prepared for PCR analysis by pooling selected internal organs from 630 chickens from 42 flocks and screened for FAdV, IBDV, CAV and ARV. Sera were analysed for FAdV by an in-house ELISA. Inactivated and attenuated vaccines were formulated with a field-isolated FAdV, and groups of Swiss albino mice were periodically vaccinated. Two separate in-house ELISAs were developed to investigate the presence of specific FAdV antibodies in the sera of vaccinated mice and the sera collected from the field from 28 flocks. The results were evaluated using bivariate analysis, logistic regression, and One-Way ANOVA. Molecular analysis detected FAdV in only 3 out of 42 houses (7.14%); the house prevalence rate of other pathogens was 66.67% for IBDV (28 houses), 30.65% for ARV (13 houses) and 27.57% for CAV (12 houses). Serological analysis showed that 19 out of 28 houses (67.86%) had antibodies for FAdV. For one FAdV isolate, according to the adaptation study in Vero and HEK-293 cell lines, better adaptation and hıgher agent levels were obtained in the monolayer Vero cell line. Two vaccine candidates were produced with viruses propagated in Vero cell culture. In order to evaluate the attenuation of the passaged virus, a test was performed on Chicken Embryonated Eggs and it was found that the 14th passage was suitable as vaccine antigen. It was also found that the cytopathic effect began to develop in the 13th passage. According to the results of the seropotency test in the mouse model, positivity was detected in 100% of mice with a cut-off value above 0.101 for the inactivated vaccine and in 100% of mice with a cut-off value above 0.098 for the live vaccine. The positivity for FAdV infection in poultry houses in the field was found to be 67.86%. Up-to-date data on the prevalence of immunosuppressive infections associated with FAdV in chicks in Türkiye were obtained. In addition, effective inactivated and attenuated vaccines have been produced by adapting a field-isolated FAdV to the Vero monolayer cell line and a pre-clinical study has been carried out on seropotency groups. According to the results obtained with both vaccines, a promising immune stimulation was demonstrated, indicating the potential for development. The aim of this thesis study is to investigate the prevalence of FAdV with a comprehensive serological and molecular study, as well as virus isolation, adaptation to mammalian cell culture and evaluation of the seropotency of the developed vaccine in a mouse model. Keywords: Cell culture, ELISA, Fowl Adenovirus, Vaccine, PCR