*Host adapted and non-host adapted species varying in virulence for different hosts
*Host adapted and non-host adapted species varying in virulence for different hosts
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*Different species cause specific diseases in particular hosts
*Repsiratory, enteric, pleural and reproductive diseases in animals and humans
*Repsiratory, enteric, pleural and reproductive diseases in animals and humans
*Intestinal infections often subclinical and persistent
*Intestinal infections often subclinical and persistent
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*Persistent infections can occur if replication delayed by environmental conditions
*Persistent infections can occur if replication delayed by environmental conditions
*Many infections subclinical due to intracellular existence of ''chlamydia'' preventing inflammatory reactions
*Many infections subclinical due to intracellular existence of ''chlamydia'' preventing inflammatory reactions
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*Chronic infections may fail to induce an immune response, or may repeatedly stimulate the immune system, causing a delayed hypersensitivity reaction and tissue damage
*Prolonged faecal shedding of organisms
*Prolonged faecal shedding of organisms
*Clinical infections occur in non-natural host species
*Clinical infections occur in non-natural host species
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*CLinical signs depend on route of infection and degree of exposure