|dc.description.abstract||Three turkey rhinotracheitis virus-like (TRTV-like) isolates were
isolated from chickens with swollen heads. All grew well via the
yolk sac (y/s) , chorioallantoic membrane (CAM), tracheal organ
culture (TOC) , chicken embryo fibroblast (CEF) , and Vero cell
routes. Affected embryos were stunted and severely congested. No
pathological alterations were detected in allantoic sac (a/s)
inoculated embryos. The CEF and Vero cells required
trypsinisation for five consecutive passages before any visible
cytopathic effects (CPE) were observed. Intra-cytoplasmic
eosinophilic inclusions were observed in Vero and CEF monolayers .
Only isolate 652/93 caused 100% ciliostasis in TOC. The other two
isolates were able to cause a maximum of only 70-80% ciliostasis.
The isolates were inactivated by chloroform treatment and
exposure to 56°C for 1 h. Long term storage could be achieved at
-70°C or in liquid nitrogen but not at 4°C or at -20°C. The
isolates did not agglutinate chicken red blood cells and were
found to contain genomes of RNA. They were able to elicit TRTV
antibodies in specific pathogen free (SPF) birds as measured with
the Pathasure enzyme linked immunosorbent assay (ELISA) kit. They
could also be neutralised by TRTV-specific antisera.
Electron microscopy of infective allantoic fluid (A/F) revealed
particles of 100-300 nm in diameter with a helical nucleocapsid
component approximately 15 nm in diameter and a fringe of
approximately 12 nm long spikes. The processes of VLP development
and maturation in TOC's and Vero cells were similar with
accumulations of virus-like nucleoprotein close to the plasma
membrane, forming the nucleocapsid. Virus-specified spikes were
then inserted into the plasma membrane after which the VLP budded
from the plasma membrane, incorporating this membrane with spikes
as its own.
Nine viral polypeptides with molecular weights of 200kDa, 83kDa,
53kDa, 40kDa, 37kDa, 28kDa, 19kDa and 15kDa were detected by SDS-PAGE
in samples of the three isolates. The 83kDa and 53kDa
polypeptides were also detected by western blotting using TRTV specific
antisera. Both, a TRTV and a 652/93 isolate non-radioactive
DNA probe, appeared specific for TRTV and TRTV-like
isolates. The 652/93 probe detected 652/93 virus in SPF chickens
for 19 days post-inoculation.
A vaccine produced in SPF eggs using the attenuated 652/93
isolate, was able to protect vaccinates against virulent virus
in laboratory challenge studies. In field trials, birds
vaccinated at day-old or at day-old and again at 14 days, showed
slightly improved performance compared to non-vaccinated birds.
However, this benefit was not statistically significant. It is
suggested that other environmental and disease factors mask the
benefit provided by the vaccine in field trials.
The three TRTV-like isolates appear to be chicken strains of TRTV
and vaccination with an autogenous vaccine appears to afford some
benefit to vaccinates.||en