The development and evaluation of two tissue culture‐grown Marek's disease challenge viruses

Abstract

Standardized challenge viruses are essential for the evaluation of Marek's disease (MD) vaccines with many MD challenge preparations consisting of lymphocytes or whole blood from infected birds. Virus present in these preparations is difficult to quantify by tissue culture assays and, therefore, the infectious bird dose and long-term storage viability cannot be assured. We report on the properties of two low-passage virulent Australian MD viruses, the Woodlands No. 1 strain and strain MPF 57. Both strains were isolated in chicken embryo kidney cultures and adapted to grow in chicken embryo fibroblast cultures for a maximum of 14 passages. Both strains could be readily assayed in tissue culture and produced titres of 10 3 to 10 4 50% tissue culture infectious doses per ml (TCID 50 ). Birds inoculated at three different doses were observed over 10 weeks, and tissues examined for gross and histological lesions, bursarbody weight ratios and the presence of viraemia. Tissue culture-grown preparations of both strains were only slightly less virulent than the original lymphocyte challenge material and produced similar pathological responses and around 80% death or gross lesions. From bursarbody weight ratios strain MPF 57 appeared to be more virulent than the Woodlands No. 1 strain.

Influence of vaccine deposition site on post-vaccinal viraemia and vaccine efficacy in broiler chickens following in ovo vaccination against Marek's disease

“…These were examined for characteristic cytopathic lesions of MDV at day 7 and negative cultures were repassaged for a further 7 days for reconfirmation. The presence of MDV was detected by immunofluorescent antibody (IFA) staining of the cultures using serotype-specific monoclonal antibody as described previously by De Laney et al (1998).…”

“…All vaccine doses were administered in 100 m l diluent, and unvaccinated controls were sham-vaccinated with diluent alone. The challenge virus used was MPF-57, a cell culture adapted and titrated Australian strain of MDV isolated from a flock vaccinated with serotype 2 and 3 vaccine and designated as very virulent (De Laney et al, 1998).…”

Marek's disease in broiler chickens: Effect of route of infection and herpesvirus of turkey-vaccination status on detection of virus from blood or spleen by polymerase chain reaction, and on weights of birds, bursa and spleen

“…In comparison, De Laney et al (1998) challenged SPF leghorn type birds with the same strain of virus at week 5 and found that bursal weight was reduced up to 50% by 10 weeks postchallenge. Witter et al (1980) have shown that maternal antibody can considerably reduce the loss in bursal weight following challenge with virulent MDV.…”

“…All vaccine doses were administered in 100 ml diluent, and unvaccinated controls were shamvaccinated with diluent alone. The challenge virus used was MPF 57, a cell culture-adapted and titrated Australian strain of MDV isolated from a flock vaccinated with serotype 2 and 3 vaccine and designated as very virulent (De Laney et al, 1998).…”

“…Traditionally, clinical MD diagnosis is based on gross and microscopic lesions together with isolation and identification of MDV from the infected tissues (Sharma, 1985). Virus isolation is usually by virus propagation in cell culture and identificatio n/quantification by cytopathic changes (plaque formation) or identificatio n of infected cells by immunostaining (De Laney et al, 1998). Polymerase chain reaction (PCR) has emerged in recent years as an additional diagnostic tool offering the advantages of serotype specificity (Davidson et al, 1995;Walkden-Brown et al, 2001) and the ability to differentiate between vaccinal and field strains of MDV serotype-1 (Silva, 1992;Zhu et al, 1992;Handberg et al, 2001).…”