A comparison of three serological methods to detect chicken and turkey antibodies to avian nephritis virus and the use of virus-specific monoclonal antibodies

The C-terminal end of the capsid protein of Avian Nephritis Virus is antigenic and induces broadly cross-reactive antibodies

Avian nephritis virus (ANV) has been isolated frequently from commercial broilers in many countries. The prevalence and economic impact of ANV however has been difficult to ascertain due to the lack of convenient serological techniques. In this study the full-length and fragments of the ANV capsid protein were expressed in Baculovirus and affinity purified recombinant proteins used for the detection of ANV antibodies in ELISA. The crystal structure of Human Astrovirus (HAstV) was used as a model to determine potential homologous C-terminal antigenic regions in ANV. The rp37 fragment from three ANV strains NSW_3, ANV-1 and ANV-2, and a shorter NSW_3 fragment (rp33) were compared for their ability to detect ANV antibodies in seven reference chicken sera. The ANV-1 rp37 antigen was the most strain specific whereas the NSW_3 rp37 and rp33 antigens detected antibodies in all heterologous sera, including ANV-1 serum. Irrespective of the strain used, the two NSW_3 protein fragments rp37 and rp33 were found to be superior as antigens for ELISA when compared to the full-length capsid protein rp75. An ELISA designed using the NSW_3 rp33 could reliably differentiate between uninfected and infected commercial broiler flocks, as demonstrated by statistically significant differences between the OD values. This study identified an ANV immunogenic region and successfully used recombinant protein expression of this region to detect cross-reactive ANV antibodies. The results of this study facilitate future studies into the epidemiology and importance of ANV infections in commercial poultry.

Avian Astroviruses

Avian astroviruses comprise a diverse group of viruses affecting many avian species and causing enteritis, hepatitis, and nephritis. To date, six different astroviruses have been identified in avian species based on the species of origin and viral genome characteristics: two turkey-origin astroviruses [Turkey Astrovirus type 1 (TAstV-1) and type 2 (TAstV-2)]; two chicken-origin astroviruses [Avian Nephritis Virus (ANV) and Chicken Astrovirus (CAstV)]; and two duck-origin astrovirus [Duck Astrovirus type 1 (DAstV-1) and type 2 (DAstV-2)]. ANV has also been detected in turkeys, ducklings, pigeons, and guinea fowl; and TAstrovirus-2-like viruses have also been found in guinea fowl. Astroviruses are commonly associated with enteric disease syndromes in poultry including runting-stunting syndrome of broilers (RSS), poult enteritis complex or syndrome (PEC or PES), poult enteritis mortality syndrome (PEMS), and enteritis in guinea fowl. The molecular characterization of the different avian astroviruses shows great genetic variability among each type, and this variability influences the ability to detect these viruses by molecular and serological techniques. In this chapter, we review the different aspects related to avian astroviruses, including molecular biology, pathogenesis, diagnosis, and control.

Segmentation expression of capsid protein as an antigen for the detection of avian nephritis virus infection in chicken flocks

Subclinical pathological changes in the kidneys of broiler chickens and suppression of growth caused by the avian nephritis virus (ANV) affect poultry flocks worldwide. A test for detection of virus-specific antibodies in serum would be useful for epidemiological investigations, however the poor propagation in cell cultures has restricted the development of serological tests based on the use of ANV particles as antigens. An enzyme-linked immunosorbent assay (ELISA) was developed for detection of ANV-specific antibodies in chicken serum, using a recombinant protein antigen prepared by segmentation expression of the capsid protein antigen epitope of ANV (HM029238) transfected into Escherichia coli. The expressed fusion protein was detected by Western blotting with ANV-positive serum, and the optimal immunoreactive fusion P1 protein was determined. Using the optimized P1-ELISA, ANV-specific antibodies were detected in commercial chicken flocks aged 10-25 days obtained from the Liaoning Province, China. Out of 960 serum samples, 459 (47.8%) were positive for infection with ANV. These results indicate that the P1-ELISA is helpful for preliminary serological diagnosis of ANV infection, and could be used to for screening in ANV infection and for determining antibodies against ANV.