Use of Different Immunoresponse Assays for Evaluation of Live Attenuated Sheep Pox Vaccine in Comparison with Challenge Test
Sheep pox (SP) is one of the priorities, high-impact animal diseases in many developing countries, where live attenuated vaccines are routinely used against sheep pox virus (SPV). Sheep pox virus is a member of the family Poxviridae, genus Capri poxvirus. In this study, live attenuated Sheep pox vaccines were evaluated for humoral and cellular immunity using virus neutralization index (NI), ELISA and lymphocyte proliferation assay (XTT) beside routinely titration of life attenuated virus content of vaccine in Vero cell line which gives mean satisfactory TCID50/dose (3.34) for used vaccine batches, in addition to clinical examination of vaccinated sheep and also application of challenge test. Sixty susceptible lambs were divided into (10) groups and vaccinated with field and safety doses of (10) different batches of live attenuated vaccine intradermal (I/D) in tail fold while three lambs kept as control. The results showed that lymphocyte proliferation began to increase till reach to its peak (1.312) at 10th day post vaccination then decrease after that with re-increasing after challenge , serological assays results revealed that protective serum antibody titer started at 10th day post vaccination with mean titer (1.6 and 1.99), mean absorbance (1.56 and 2.02) and at three weeks the mean titer (2.35 and 2.61) , mean absorbance (2.43 and 2.51) for NI and ELISA respectively, also all vaccinated lambs showed satisfactory levels of protection against the virulent SPV through challenge test as SID50 more than (2.5) for all batches of vaccine. The results demonstrated that vaccine titration in Vero cell line and evaluation of humoral, cellular immuneresponses using different assays for vaccinated lambs were possible to be an accurate parameter for evaluation of life attenuated sheep pox vaccine equivalent the protective results obtained against a virulent SPV in challenge test.
