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Resistance to clinical and renal leptospirosis in dogs injected with antiserum to Leptospira interrogans serotype canicola and Leptospira interrogans serotype icterohaemorrhagiae was demonstrated. The relationship between resistance induced in serum-injected hamsters was also demonstrated, using criteria of leptospiremia, renal infection, leptospiruria, and clinical signs of disease in dogs and death in hamsters.

Resistance to clinical and renal leptospirosis in dogs vaccinated with a bacterin containing Leptospira interrogans serotype canicola and Leptospira interrogans serotype icterohaemorrhagiae was demonstrated. The relationship between resistance induced in vaccinated dogs and that induced in vaccinated hamsters was also demonstrated, using criteria of leptospiremia, renal infection, leptospiruria, and clinical signs of disease in dogs and death in hamsters.

Leptospira interrogans serotype szwajizak was characterized by (1) its growth in polysorbate 80-bovine albumin medium, (2) its virulence and course of infection in laboratory animals, and (3) its immunogenicity. Growth of this organism was continuous and vigorous at 29 C and 37 C in liquid medium for 10 serial subcultures. Some specific lots of agar were superior to other agars if tested for the ability to support the growth of small inoculums. Individual colonies resulted from growth of small inoculums on solid polysorbate medium. Virulence of the organisms did not appear to be altered by 10 serial subcultures in liquid medium incubated at 29 C. The estimated median lethal dose of szwajizak for hamsters by the intraperitoneal route was 2 cells. Virulence, infectivity, and pathogenicity of szwajizak were shown in the hamster and the guinea pig. Protection results indicate the heat-inactivated szwajizak bacterin was a substantially better immunizing agent than the chemically inactivated bacterin. Serotype hardjo bacterins provided hamsters some protection against death if challenge exposed with szwajizak, but afforded no protection against infection.

Immunity to renal leptospirosis was demonstrated in cattle vaccinated with Leptospira interrogans serotype pomona. Vaccinated cattle, challenge inoculated with virulent L interrogans serotype pomona organisms 12 months after vaccination, were resistant to renal infection; similarly inoculated, but nonvaccinated, cattle were susceptible to renal infection. Relationship was demonstrated between immunity induced in vaccinated cattle and that induced in hamsters vaccinated with a dilution of the same bacterin and later inoculated with virulent L interrogans serotype pomona organisms.

Three groups of ewes were vaccinated with formalin inactivated, whole cell, aluminum hydroxide adjuvanted bacterins prepared from capsulated enteropathogenic Escherichia coli (EEC). Lambs born to and suckling these ewes, compared with lambs of nonvaccinated control ewes, were highly resistant to homologous EEC challenge exposure. Lambs of ewes vaccinated with products prepared from K99 antigen-positive, noncapsulated E coli were highly resistant to heterologous EEC challenge exposure. In both cases, lambs of vaccinated ewes had significantly (P less than 0.005) less morbidity and mortality, fewer challenge inoculum-type E coli per rectal swab evaluation, and had superior weight gains over a 4-day period. Immunoglobulin assay of 122 lamb sera (collected 12 hours after birth) failed to reveal any correlation between serum immunoglobulin values and morbidity or mortality. When tested by plate agglutination technique, using whole cell antigens, or by reverse radial immunodiffusion, using purified capsular antigens, colostral whey samples of vaccinated ewes did not have increased capsular antibody titers. The K99 serum antibody values of K99 antigen-vaccinated ewes were markedly higher than were those of ewes vaccinated with other bacterins or of control ewes.