A live attenuated turkey rhinotracheitis virus vaccine. 1. Stability of the attenuated strain

Abstract

Compared with the severe clinical disease caused by two virulent strains of turkey rhinotracheitis virus (TRTV), an attenuated strain has been shown to cause only slight respiratory infection in 7-day-old TRT-free turkey poults, yet still to be capable of stimulating TRT antibodies and of protecting the poults against challenge with virulent TRTV 21 days later. The stability of the attenuation during 12 turkey-turkey passages of the strain has been demonstrated; the poult passaged and prepassaged strains causing only mild respiratory signs even when bacteria, known to be associated with severe outbreaks of TRT in the field, were included in the inoculum.

Further studies on the development of a live attenuated vaccine against turkey rhinotracheitis

“…It was surprising to find that although the Vero-attenuated virus could be isolated in TOC, it could not be reisolated in Vero cells. The failure to back-passage the virus is interesting in light of the findings recorded by Cook et al (1989a) who were able to backpassage an attenuated TRT virus 12 times from poult to poult using pooled swabbings. The TRT virus used in their trial was attenuated by passaging alternatively in eggs and tracheal organ cultures (Cook & Ellis, 1990) and after attenuation was apparently clinically more virulent in poults than our Vero-attenuated strain.…”

Interaction between live avian pneumovirus and Newcastle disease virus vaccines in specific pathogen free chickens

“…Our findings further support the contention that humoral antibody levels may not correlate well with protection against APV. Previous studies have also emphasized the importance of local or cellular immune responses in resistance to and clearance of APV infection (Cook et al ., 1989;Jones et al ., 1992). …”

“…Live vaccines are used in chickens for protection against NDV (Meulemans, 1988;Gallili & Ben-Nathan, 1998;Alexander & Jones, 2001;Cserep, 2001) and APV (Cook et al ., 1989;Williams et al ., 1991;Alexander & Jones, 2001). In some instances, other live vaccines are given concurrently with NDV vaccines (Gallili & Ben-Nathan, 1998).…”

Experimental and field evaluation of a live vaccine against avian pneumovirus

“…Attenuation of virulent APV by repeated passages in eggs and/or Vero cells has been reported (Buys et al, 1989;Cook et al, 1989aCook et al, ,b, 1996Cook & Ellis, 1990;Williams et al, 1991a). We have also attenuated a US isolate of APV (APV/MN/turkey/ 1-a/97) by continuously passaging it in Vero cells.…”