Experimental immunization against respiratory disease due to equid herpesvirus 1 infection (rhinopneumonitis) using formalin-inactivated virus with various adjuvants

The efficacy and safety of four adjuvants, viz, alhydrogel, adjuvant 65, levamisole and killed Corynebacterium parvum were compared with Freund's complete adjuvant (FCA) for immunizing foals and yearlings with formalin inactivated, partially purified equid herpesvirus 1 (EHV-1) antigen.The levels of antibody in serum and nasal secretions and the degree of lymphocyte stimulation (LS) induced by inactivated EHV-1 antigen with FCA were higher than those following infection with a virulent strain. Levamisole and C. parvum failed to augment the antibody response to inactivated EHV-1 antigen or to induce specific lymphocyte stimulation. Adjuvant 65 and alhydrogel, although less effective than FCA, both produced good humoral and LS responses. Alhydrogel proved the most satisfactory adjuvant as FCA produced unacceptable local reactions, and adjuvant 65 was difficult to administer.Neutralizing antibody induced by immunization with inactivated RAC-H virus (subtype 1) showed remarkable strain specificity and failed to cross-react with H45 virus (subtype 2).The duration of virus excretion following intranasal challenge was reduced in immunised animals but clinical responses still occurred in some vaccinated animals when high challenge doses of virus (10^9.4TCD₅₀) were used.