Effects of levamisole on pathogenesis of Marek's disease

Levamisole was administered to chickens previously inoculated with Merek's disease virus (MDV) or infected by contact, and the influence of the drug on the mortality rate of Merek's disease (MD) was examined. The chickens inoculated with MDV and then administered levamisole (3 mg/bird) began to die earlier than chickens not treated with levamisole. However, the chickens infected with MDV by contact and then treated with the levamisole had delayed deaths. When the capacity of peritoneal exudate cells (PEC) to inhibit MDV plaque formation on chicken kidney cell (CKC) cultures was examined, the inhibitory activity of PEC from chickens inoculated with MDV and treated with levamisole at 4 days or 2 months of age was much weaker than that of PEC from chickens of the same ages that were not treated with levamisole. This effect was also noted when levamisole was added to CKC cultures to examine the inhibitory activity of PEC from MDV-infected chickens not treated with levamisole. These results indicate that the administration of levamisole to MDV-inoculated chickens in doses used in the present experiment suppressed the macrophage restriction on MDV replication and hastened the death of chickens by MD during the early course of infection.