Pathogenicity, antigenicity, and detection of turkey astroviruses

The Pathogenicity of TAstV1987 and TAstV2001 isolates was investigated. Both isolates caused gastroenteritis and growth depression in specific pathogen free (SPF) turkey embryos and poults. TAstV1987 infection resulted in microscopic lesions of infected bursas of embryos and poults. There was no statistically significant difference in bursa weight/body weight ratios (P > 0.05). The TAstV2001 did not cause lesions in the bursas or thymuses of embryos or poults. The antigenic relatedness of TAstV1987 and TAstV2001 were determined by cross-neutralization tests in SPF turkey embryos as we' as by enzyme-linked immunosorbent assay (ELISA). The R value as measured by cross-neutralization tests was 0.56%, indicating the viruses belong to different serogroups; whereas the R value measured by ELISA was 70.7%, suggesting these viruses share common antigen(s).; An antigen capture enzyme-linked immunosorbent assay (AC-ELISA) was developed using polyclonal hyperimmune antisera against TAstV1987 and TAstV2001 isolates, and monoclonal antibody (MAb) for TAstV2001. Monoplex and multiplex reverse transcription/polymerase chain reactions (RT-PCR) were developed as well using non-degenerate primer sets specific to the capsid region, and degenerate primer pairs covering the polymerase area of turkey astrovirus virus genome. One ssRNA internal control (IC) template reagent was produced, and applied to the RT-PCR to reduce the false negative rate of the test. Direct EM was also used. The results showed that the polyclonal AC-ELISA had high sensitivity and wide detection spectrum, and the monoclonal AC-ELISA had very high specificity but lower sensitivity (0.06 mug of viral proteins). The EM results indicated that the positive rate of small round viruses (SRVs), including astroviruses and enteroviruses was 33.4%. The monoplex RT-PCR results using primers set SRV revealed that the positive rate of astroviruses was 45.3%, which is 10.9% higher than that of direct EM even if other SRVs were not excluded. Multiplex RT-PCR with both primer sets of SRV and AFCP and the monoplex RT-PCR with degenerate primers showed good specificity and wide detection spectrum with the positive rate of 59.4%, 25% higher than that of EM. With the internal control, an overall test inhibition rate of 12.5% was estimated for the RT-PCR assay.