Establishment of a variant type of turkey herpesvirus which releases cell-free virus into the culture medium in large quantities

Abstract

A variant turkey herpesvirus (HVT/VT) which releases 10(5.0) plaque-forming units per 0.1 ml of cell-free virus into the culture medium was established from the prototype HVT FC 126 strain (HVT/WT). Many enveloped and naked virions of HVT/VT but only naked virions of HVT/WT were found in the culture medium. By the HindIII restriction cleavage patterns, the HVT/VT DNAs were almost identical to those of HVT/WT. The HVT/VT was replication-defective in chickens.

Further characterisation of a variant type of turkey herpesvirus which releases large quantities of cell‐free viruses into culture medium

“…The cell-associated virus (trypsinised cells) and cell-free (cell-extracts) extracts prepared from HVT/WT-infected chicken embryo fibroblasts (CEF) were used as inocula. A variant type of HVT, which is referred to as HVT/VT, was established from HVT/WT as described previously (Yachida et al, 1986). The cell-free virus in the culture medium from HVT/VTinfected CEF on the 96th passage was used as the inoculum of HVT/VT in the present study.…”

“…The cell-free virus in the culture medium from HVT/VTinfected CEF on the 96th passage was used as the inoculum of HVT/VT in the present study. Preparation of the inocula was described previously (Yachida et al, 1986). Preparation of the primary CEF cultures from embryonated eggs, and the culture media (MEM) used for growth and maintenance of the cultures, except for those described in the text, have been reported elsewhere (Kirisawa and Mikami, 1983;Onuma etal, 1974).…”

“…Multiple passage of MDV or HVT in cultured cells causes changes in cultural (Nazerian, 1970;Witter and Offenbecker, 1979), antigenic (Ross et al, 1975;Witter and Offenbecker, 1979) or pathogenic (Churchill et al, 1969;Nazerian, 1970;Konobe et al, 1979;Schat et al, 1985) properties. Yachida et al (1986) established a variant type of HVT which releases cell-free viruses into the culture medium in large quantities after the 53rd serial in vitro passage of the FC 126 strain. The variant lacked the ability to infect chickens, but no obvious differences were found between it and the parental virus in genomic characteristics by the Hindlll restriction cleavage patterns.…”

Genomic Difference of Herpesvirus of Turkeys at Low and High Passage Levels in Culture of O1 and FC126 Strains

“…The homologous DNA regions found by low-stringency hybridization were located at the corresponding positions on the restriction enzyme maps of MDV1 and HVT DNAs, indicating the collinear relationship between these two virus genomes (9). The genome structure of both MDVl and HVT consists of a long unique region (UL) and a short unique region (Us) bounded by inverted repeats (1).Serial passages of HVT over 70 times in cultured cells resulted in a loss of their ability to protect chickens from MD (13,18,19). The nonprotective variants of HVT did not replicate in vivo in chickens, but replicated well in cultured cells.…”

“…The O1 strain at less than the 25th passage and the FC126 strain at less than the 22nd passage, named O1-LP and FC-LP, respectively, had the ability to protect chickens against MD ; however, the virus variants at higher passage levels , that is, over the 6Oth passage for the O1 strain (O1-HP) and over the 97th passage for FC126 (FC-HP) did not replicate in vivo in chickens (13,19).…”