Two interferon gamma (IFN-gamma) assays, the IFN-gamma enzyme immunoassay (EIA) and the IFN-gamma bioassay and an absorbed ELISA were used to screen 6 cattle herds for Johne's disease. Each herd had a history of Johne's disease but the majority of infected animals did not show clinical signs. The disease status of the cattle, which were removed from the herds, was confirmed by bacteriological culture of faeces or histopathological examination and culture of tissues collected at necropsy. The sensitivities of the IFN-gamma assays and the absorbed ELISA were determined using test results from infected animals. The sensitivity of the IFN-gamma EIA in detecting subclinical (71.8 to 93.3%) and clinical animals (100%) was not significantly different. However, the IFN-gamma bioassay and the absorbed ELISA were more sensitive in detecting cattle with advanced infections (80%) than those that were subclinically affected (16.7 to 33.3%).

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Chlamydia psittaci was cultured from 29 of 35 koalas (Phascolarctos cinereus) with keratoconjunctivitis. The disease progressed from acute to chronic stages over some months, with a known duration of at least 2 years. One recovered carrier was found. Up to 29% of koalas in some populations were clinically affected. A seasonal spread of infection was indicated by the high percentage of acutely affected cases found in summer. There was no evidence of susceptibility being related to age or sex. The sera of all chronically affected koalas had complement fixation test titres against chlamydial group antigen of 80 or above; in acute cases the titre ranged from 0 to 320. Of normal koalas, 84% were serologically negative, 16% had chlamydial antibody. A titre of 80 or more considered in conjunction with ocular disease could be taken as presumptive evidence of a chlamydial etiology. Chlamydial keratoconjunctivitis may be the ocular disease which was associated with the decline of koala numbers between the years 1885 and 1930.

Procedures for the diagnosis of Br. ovis infection in rams were evaluated by examining 10 rams artificially infected by preputial inoculation. Observations were undertaken at weekly intervals for 1 year to follow changes in clinical, bacteriological and serological findings. Clinical lesions were detected in 1 ram 3 weeks after inoculation and in all rams by 8 weeks; lesions were undetectable in 3 rams at the completion of the trial. The presence of inflammatory cells in semen samples was the earliest indication of infection being demonstrated in 2 rams at 2 weeks and in all rams by 8 weeks; subsequently 86% of samples were positive. Br. ovis was detected in semen smears from 3 rams at 4 weeks but only one in all rams (at 27 weeks); overall 52% of semen smears were positive from 4 weeks onwards. Br. ovis was cultured from semen of 5 rams after 4 weeks and from all rams at 5 weeks; therafter 97% of samples were positive. All rams developed significant titres to the CFT between 2 and 9 weeks; therafter the CFT was a reliable indication of infection in 6 rams, highly suggestive in 3 and unreliable in one. By 8-10 weeks all rams developed significant titres to the IHA which were then maintained in all rams for the remainder of the trial.

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