Improved humoral immune response in sheep against epsilon toxoid following co-adjuvantation with gel and water in oil formulation

Enterotoxaemia, a highly fatal and devastating disease of sheep and goats still continues to cause huge economic losses to small ruminant farming all over the world. Although the disease can be prevented by immunization, the present vaccines often fail to confer a high and persisting antibody titre demanding intermittent booster injections. Thus, with an aim to develop better enterotoxaemia vaccine, a novel aluminium hydroxide gel precipitated oil adjuvant epsilon toxoid vaccine (OAV) was formulated. The immunogenicity and protective efficacy of this new vaccine in comparison to presently available epsilon toxoid vaccine (TV) and aluminium hydroxide gel vaccine (AHV) was evaluated in the target species, sheep using indirect ELISA, mice neutralization test (MNT) and standard tube agglutination test (STAT). Among the vaccines tested, OAV generated maximum immune response with persistent high titre of neutralizing antibodies with protection up to 12 months following a single dose whereas; TV and AHV protected only up to 30 days and 3 months, respectively. To our knowledge, this is the first report of a vaccine which offers protection for 12 months against enterotoxaemia in sheep. Thus, the present study delineates an effective and simple approach for the prevention of extremely lethal enterotoxaemia through the use of the newly formulated OAV.