Abstract
Infection of chicks with attenuated Lp and Sp clones of the RF-1 strain of infectious bursal disease virus was shown to exert no immunosuppressive effect, whereas the parent strain RF-1 tc and the original virulent strain Rf-1 wt immunosupressive. One-day-old chicks infected with Lp and Sp clones showed no suppression of immunological response to live Newcastle disease vaccines B1 and TCND, and to bivalent infectious coryza vaccine. On the other hand, infection with Rf-1 tc or RF-1 wt strains was immunosuppressive for these vaccines. The immunosuppressive effect of RF-1 tc and RF-1 wt strains was more pronounced for infectious coryza vaccine and B1 vaccine than for TCND vaccine. The immunosuppressive effect of RF-1 tc and RF-1 wt strains was lower chicks were infected with these strains at the age of 21 days than they were infected at one day of age.
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