Recombinant Fiber-2 Protein-Based Indirect ELISA for Antibody Detection of Fowl Adenovirus Serotype 4

Clinical cases of hepatitis-hydropericardium syndrome (HHS) from fowl adenovirus serotype 4 (FAdV-4) have increased in China since 2013. Therefore, the development of a new serologic method for HHS detection is now urgent. Here, the FAdV-4 strain JSJ13 was used to construct a plasmid for prokaryotic expression of the JSJ13 fiber-2 protein. The protein, purified by affinity chromatography, was refolded by gradient dialysis. After coating a 96-well plate with the purified fiber-2 protein (1.5 μg/ml), standard serum and secondary antibodies (1:200 and 1:6000 dilutions, respectively) were used to develop an indirect ELISA (I-ELISA). Nine field-collected serum samples and JSJ13-positive serum were tested by I-ELISA and the results corresponded with those of the serum neutralization test. The I-ELISA was used to test 450 clinical serum samples from different parts of China. Chickens from nonvaccinated flocks had low antibody titers and low virus positivity rates. In contrast, FAdV-4 vaccinated chickens were strongly positive, and the positivity rates of all the flocks exceeded 73.3%. The newly developed I-ELISA with the recombinant JSJ13 fiber-2 protein as the antigen detected antibodies to FAdV-4 accurately and sensitively.