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.

Different Origins of Newcastle Disease Virus Hemagglutinin-Neuraminidase Protein Modulate the Replication Efficiency and Pathogenicity of the Virus.

To investigate the exact effects of different origins of Newcastle disease virus (NDV) hemagglutinin-neuraminidase (HN) protein to the biological characteristics of the virus, we systematically studied the correlation between the HN protein and NDV virulence by exchanging the HN of velogenic or lentogenic NDV strains with the HN from other strains of different virulence. The results revealed that the rSG10 or rLaSota derivatives bearing the HN gene of other viruses exhibited decreased or increased hemadsorption (HAd), neuraminidase and fusion promotion activities. In vitro and in vivo tests further showed that changes in replication level, tissue tropism and virulence of the chimeric viruses were also consistent with these biological activities. These findings demonstrated that the balance among three biological activities caused variation in replication and pathogenicity of the virus, which was closely related to the origin of the HN protein. Our study highlights the importance of the HN glycoprotein in modulating the virulence of NDV and contributes to a more complete understanding of the virulence of NDV.