Studies on equine herpesviruses - II. Development of a complement fixation test antigen of cell culture origin for equine Herpes-1 (Rhinopneumonitis) virus and use in a microtitre system

A complement fixation (CF) antigen for equine herpes-1 (rhinopneumonitis) virus (EHV 1) of cell culture origin was studied, and an optimum method of preparation in a minimum volume of serum-free overlay fluid developed. Many chemical and physical treatments including fluorocarbon extraction, tweenether treatment, Carbowax concentration or ultracentrifugation (25,000 g) did not further improve the quality of this antigen. Inactivation (56°C for 30 minutes) of equine serum did not affect the CF antibody titre, but removed low levels of anti-complementary activity. The use of a diluent of low ionic strength (0.1 m) did not increase titres in the EHV 1-equine antibody CF system. This EHV 1 CF antigen of cell culture origin was used in a microtitre system and detected the development of antibodies in all of six young horses in Queensland following natural EHV 1 respiratory infection. Maximum serum titres (1/128) were reached 1-2 weeks after the onset of acute respiratory disease, then CF titres declined steadily but were still detectable after 12 months. Serum titres of 1/16-1/32 or higher indicated EHV 1 infection to have occurred within the previous 3-6 months