Evaluation of chicken anaemia virus mutants as potential vaccine strains in 1-day-old chickens.

The aim of the work reported here was to study the potential of chicken anaemia virus (CAV) mutants as CAV vaccine strains. Seventy 1-day-old chickens were divided into seven groups of 10 birds, and at 1 day old birds were inoculated subcutaneously with RPMI medium, with mutants S77N, Q131P, D186G or R/K/K150/151/152G/A/A, or with wild-type CAV. At day 14 post inoculation (p.i.) one-half of the birds in each group were killed to assess the effect of mutants on their thymuses. At day 21 p.i., birds were inoculated subcutaneously with wild-type CAV. At day 35 p.i., the remaining birds in each group were killed to assess the protective effect of vaccination with the mutants. The thymus weight to body weight ratios were determined and the thymic cortical thickness measured using immunofluorescent staining with an anti-CD8 monoclonal antibody. There was no significant decrease in the thymic cortical thickness at day 14 p.i. in birds inoculated with mutants E186G or R/K/K150/151/152G/A/A. At 14 days after challenge with wild-type CAV, birds inoculated with these mutants and with mutant Q131P had significantly increased thymic cortical thickness compared with unvaccinated unchallenged birds. A serum neutralization assay, based on viral detection using a quantitative polymerase chain reaction assay, was used to determine the neutralizing antibody titres in blood samples collected at day 35 p.i. Mutant E186G induced the highest post-challenge neutralizing antibody titres, followed by mutants Q131P, S77N and R/K/K150/151/152G/A/A. These studies have shown that mutant E186G is an appropriate candidate mutant CAV vaccine strain.