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InlrodnctionThe development of vaccines for the control of bovine leptospirosis has received a good deal of attention in recent years, and a number of reports on the evaluation of such vaccines are now available in the literature. Most of this work has been carried out with Leptospira pornona, this being a serotype of major importance for bovines. This paper will review that work, and will also deal briefly with strategical aspects of the use of such vaccines. Development and Evaluation of VaccinesYork and Baker (1953) developed the first L. pomona vaccine to be reported. It consisted of inactivated allantoic fluid, from embryonated eggs infected with an egg-adapted bovine strain of that organism (Cornell T262). This strain had been maintained by the authors by serial egg passage following its isolation in 1947. It has since formed the basis of some other vaccines, prepared by growing it in liquid culture media.It has proved itself to be a good antigen, and an excellent strain for cultural purposes. York and Baker's vaccine was found to give very good clinical protection to both calves and guinea pigs, against virulent challenge with infected, defibrinated blood. The authors also gave a method for potency testing the vaccine in guinea pigs.Brown at al. (1954) used strain T262 to prepare a L. pomona vaccine in liquid culture medium. They reported this vaccine as having superior antigenic properties to those which they produced in embryonated eggs. They found it to protect calves and guinea pigs against virulent challenge. Burnstein er al. (1956), in further studies with this vaccine, obtained serological evidence indicating a duration of immunity of not less than 14 months in cattle. These authors also found that guinea pigs and swine were protected by the vaccine. Hoag and Bell (1955) stressed the importance of leptospiruria in relation to the control of this disease, and developed an oily adjuvant vaccine from a soluble antigen. This was pispared by heating cultures of L. pornonu to which acetic acid had been added. The resulting precipitate was finally dissolved at a concentration of 5 times the original pooled culture volume, before mixing with an adjuvant comprised of petrolatum and lanolin. Hoag and Bell found that this vaccine gave complete protection to calves, including the prevention of leptospiruria, against a virulent challenge of infected Mood which produced leptospiruria in all controls. Challenge was carried out two months after the vaccinations. Kenzy et al. (1957) discussed the evaluation of three different L. pomona vaccines, and reported some findings on the pathogenicity of living, egg-propagated L. ponwna in cattle. Thevaccines were found to be comparable immunizing agents in cattle. Calves which were three months of age and over when vaccinated, developed a high level of immunity. In one experiment, 8 of 12 such animals were protected against leptospiruria when challenged 18-20 months after vaccination. When urinary shedding occurred in vaccinates following challenge, it was usually slight a...

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