Effects of age at infection with serotype 2 Marek's disease virus on enhancement of avian leukosis virus-induced lymphomas.

Inoculation of susceptible, 15I5 x 7I chickens with serotype 2 Marek's disease virus (MDV) at various ages had no influence on the development of avian leukosis virus (ALV)-induced viraemia or antibody in chickens infected with ALV and turkey herpesvirus (HVT) at hatch. However, the incidence of ALV-induced lymphoma (LL) was significantly higher in chickens infected with ALV and HVT at hatch and inoculated with serotype 2 MDV up to 6 weeks of age than in chickens receiving serotype 2 MDV at 8 to 10 weeks, uninoculated chickens, or chickens inoculated only with HVT. Metastatic LL in the viscera was more frequently observed in chickens inoculated with serotype 2 MDV at hatch and 2 weeks than in chickens inoculated at 6 weeks of age. In another experiment, chickens inoculated with serotype 2 MDV and HVT at hatch and infected with ALV at 2 or 4 weeks of age developed significantly higher incidence of LL than in uninoculated chickens or chickens inoculated only with HVT. The data suggest that enhancement of LL can occur in chickens infected with serotype 2 MDV within 6 weeks after infection with ALV at hatch. The data also suggest that infection of chickens with serotype 2 MDV at hatch may increase the rate of metastasis of LL and may interfere with age resistance to development of LL.