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A vaccine against chlamydial ovine abortion was prepared according to an original method and experimentally applied to more than 500,000 animals in large breeding units. The vaccine induced a considerable seroconversion (as demonstrated by complement fixation tests) and reduced by 3--5 times the damage due to chlamydioses. Vaccination of primiparous ewes, followed by 2--3 annual revaccinations, gave good results, conferring resistance on the vaccinated animals.

Serological investigations were performed in order to establish the antigenic relationships between three Chlamydia strains: T44(subgroup A), T13 and Q18 (subgroup B). By using monospecific mouse immune sera a certain degree of antigenical relationships was made evident and the strains could be typed by microagglutination and microimmlnofluorescence reactions. Similar results were obtained by seroneutralization with hyperimmune sera prepared in the rooster. Complement fixation proved to be a group-specific reaction unable to reveal significant differences between the strains studied, not even with monospecific mouse sera. The antigenic relationships established between strains T44 (trachoma) and T13 (psittacosis) suggest the existence features common to subgroup A and B Chlamudia strains. The importance of typing Chlamudia strains with a view to specific prophylaxis is emphasized.

The authors establish the optimal conditions (protein concentration, temperature) for the coupling of purified mycoplasma antigen to sheep red blood cells, in order to obtain an antigenic complex stable for at least 1 year. This comples allows specific determination by passive hemagglutination--a simple and rapid technique--of anti-mycoplasma antibodies in the sera of men or animals suspected of mycoplasma infections. Under the stated experimental conditions, antibody titers equal to or higher than 1/128 indicate an infection with M. pneumoniae.