Inapparent chlamydial infection in the urogenital tract of guinea-pigs.

Microbiologically inapparent urogenital infection appeared to be induced in male guinea-pigs inoculated intra-urethrally with low doses of the guinea-pig inclusion conjunctivitis strain (GP-IC) of Chlamydia psittaci. This state was indicated by the ability of inoculated animals to donate eye infection to normal animals caged with them. Donors failed to develop overt urogenital infection throughout the period of transmission judged by both absence of infected cells in urethral scrapings and failure to isolate GP-IC in cell culture; however, inoculation of donors with 5-iododeoxyuridine led to transient appearance of infectivity in scrapings. In distinction from overtly infected animals, donors failed to develop serum antibody and remained susceptible to urethral challenge with larger doses of GP-IC. Animals that had recovered from overt urethral infection were resistant to challenge and appeared unable to transmit eye infection.