CPB 69700 RESEARCH SEMINAR

DEPARTMENT OF COMPARATIVE PATHOBIOLOGY

Yi-Ning Chen, BVM, MVM

Graduate Student in Molecular Virology

Department of Comparative Pathobiology

Purdue University

“Pathogenicity And Immunogenicity Of High-Passage Embryo-Passaged Turkey Coronavirus”

Thurs., March 26, 2009

VPTH 112

3:30 pm

.

Abstract: Turkey coronavirus (TCoV) causes acute atrophic enteritis in young turkeys, resulting in increased mortality and decreased body weight gain. Serially embryo-passaged infectious bronchitis virus (IBV), chicken coronavirus, has been reported to be non-pathogenic, inducing virus-specific neutralizing antibody. The objective of the present study was to determine the pathogenicity and immunogenicity of high-passage turkey coronavirus (TCoV) serially passaged in turkey embryos. Turkey poults were orally inoculated with TCoV that was serially passaged in embryonated turkey eggs for 344 times (TCoV P344). At 3, 7, 14, 28, 41, and 56 day-post-inoculation (dpi), 5 turkeys from the infected and 4 turkeys from the negative control groups were weighed, bled, and necropsied. Various tissue samples were collected and subjected to the analysis by histopathology and immunological assays. The entire spike (S) protein gene of TCoV P344 was sequenced and compared to that of the original parent TCoV. Enteritis-related clinical signs, gross lesions, and histopathological alterations were not seen in the negative control as well as the infected turkeys. Turkey coronavirus antigen-positive immunefluorescent enterocytes were detected at 3 and 7 dpi, but the number of fluorescent enterocytes and the intensity of fluorescence were decreased at 7dpi. TCoV S protein-based enzyme-linked immunoabsorbent assay (ELISA) titer appeared at 14dpi, gradually increased from 14 to 28dpi, and reached to the highest peak at 56dpi in TCoV P344-infected turkeys. The virus neutralization (VN) titer in serum of TCoV P344-infected turkeys was 1:13, 1:16, and 1:36 at 14, 28, and 56dpi, respectively. The mRNA levels of interferon gamma (IFN-γ) determined by real-time RT-PCR in the spleen cells increased 4-fold in TCoV P344-infected at 7dpi. There were 40 differences in the S gene deduced amino acid sequences between TCoV P344 and the original parent TCoV. The results indicated that embryo-passaged TCoV in high passages has attenuated pathogenicity and can elicit TCoV-specific humoral and cellular immune responses in the infected turkeys.