Acid alpha naphthyl acetate esterase reacting lymphocytes in the peripheral blood of chickens challenged with Marek's disease after vaccination with three different vaccines.

The average percentage of acid alpha naphthyl acetate esterase reacting lymphocytes (APARL) was enumerated in the peripheral blood of chickens challenged with Marek's disease after vaccination with either turkey herpesvirus (HVT), inactivated Marek's disease virus (IMDV) or a mixture of the two (bivalent vaccine). A gradual increase in APARL value was noticed in the vaccinated chickens from day 7 to 70 after challenge with a virulent Marek's disease virus. The increase was consistent and significantly higher in bivalent (HVT plus IMDV) than in HVT-vaccinated chickens while the slight increase noticed in IMDV vaccinated-challenged birds was inconsistent.