RESPONSE OF SPECIFIC-PATHOGEN-FREE TURKEYS TO VACCINES DERIVED FROM MARBLE SPLEEN DISEASE VIRUS AND HEMORRHAGIC ENTERITIS VIRUS

Tissue-culture-propagated marble spleen disease virus (MSDV-TC) and two preparations of spleen homogenate (MSDV-SH and MSDV-SH-TC) were compared as anti-hemorrhagic enteritis virus (HEV) vaccines in specific-pathogen-free turkeys. Both types of vaccines spread horizontally among turkeys, induced anti-HEV antibodies, and protected turkeys against challenge with virulent HEV. Antibody development and horizontal spread of virus occurred earlier in turkeys given MSDV-SH or MSDV-SH-TC than in those given MSDV-TC. Virulent HEV was serially passed in MDTC-RP19 cells. The 30th passage virus (HEV-P30) was nonpathogenic for turkeys but was immunogenic. Turkeys exposed to HEV-P30 had viral antigen in the spleen, developed neutralizing antibodies, and resisted virulent HEV. The principal difference between MSDV-TC and HEV-P30 vaccines was that MSDV-TC caused well-defined splenomegaly in turkeys, whereas HEV-P30 protected turkeys without causing spleen enlargement.