The standardization of Cl. perfringens antigens and antisera.

The preparation of laboratory standard antitoxins against Cl. perfringens beta and epsilon toxins is described. These antitoxins are suitable for the quantitative determination of the corresponding antigens by means of the flocculation test. The flocculation test was, however, shown to be more suitable for determining the antigenic value of fresh toxoid rather than toxoid stored without neutralization of excess formalin. A maximal immunity response to alum-precipitated epsilon toxoid was obtained in sheep with two injections containing 90 Lf per dose. The interval between these injections may vary from 2 to 6 weeks. The serum-antibody titres after the primary and secondary injections or after a booster dose given before 12 months after the primary injection did not remain above the protective level in most of the sheep injected for longer than about 5 months. When a sound basic immunity is established the degree of protection following on a booster dose given 12 months later is complete for at least 12 months. An alum-precipitated vaccine containing 25 Lf epsilon toxoid per dose is adequate. The decline in the serum-antibody titre during the first year of vaccination could be eliminated by the use of the antigen in water-in-oil emulsion. Lambs from immune dams were protected for at least up to 13 weeks of age. A satisfactory level of circulating antitoxin against Cl. perfringens beta toxin could be produced in ewes by vaccinating them with APT containing 6.25 Lf beta toxoid per dose. The primary and secondary injections could be separated by 2, 3, 4 or 5 weeks without changing the end result. A booster dose given 2 months before parturition was satisfactory.