• The disease tends to be more of a problem in colonies of cats.
• A UK survey has shown that 30% of swabs from cats with conjunctivitis were positive for C. psittaci. Infection was most common in kittens between 5 weeks and 9 months of age.
• Like the feline respiratory viruses, chlamydial infection is probably transmitted primarily by direct or fomite contact with infectious discharges, and possibly over short distances by aerosol.
• Chlamydiae, like the feline respiratory viruses, are relatively unstable outside their host, being inactivated by a number of lipid solvents and detergents.
• The organism is shed predominantly in conjunctival secretions: shedding from the conjunctivae has been demonstrated for up to 18 months after experimental mental infection. Chlamydiae have also been detected in vaginal and rectal swabs for several months after infection. The clinical and epidemiological significance of this is not known.
• Once the infection is enzootic in a colony, clinical signs may persist in individuals for weeks, and recurrent episodes are common. It has been suggested that some of these recurrent episodes may be induced by stress, such as kittening and lactation, which may facilitate transmission of the organism between mothers and their kittens. However, there is some evidence suckling kittens are usually protected from infection from their dam, presumably by colostrally derived antibodies, for the first 6 weeks of age.
• Thus, natural immunity to the disease appears to be relatively inefficient and incomplete, and infection appears to be perpetuated in a colony situation for some months, if not for years.

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