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Infection and Immunity, November 2003, p. 6148-6154, Vol. 71, No. 11
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.11.6148-6154.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Characterization of Chlamydial Genital Infection Resulting from Sexual Transmission from Male to Female Guinea Pigs and Determination of Infectious Dose

Departments of Microbiology and Immunology,¹ Pediatrics, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205²

Received 8 May 2003/ Returned for modification 24 June 2003/ Accepted 28 July 2003

A major problem in the study of chlamydial genital infections in animal models has been the use of varied doses of chlamydiae for infection in different laboratories. It is clearly desirable to use a dose which approximates that of natural sexual infection, but that dose to date has not been determined because of the inability of researchers to quantify chlamydiae in semen. Fortunately, sexual transmission of chlamydiae has been described for the guinea pig model of infection with the chlamydial agent of guinea pig inclusion conjunctivitis (GPIC). In this study, we undertook to determine the approximate infection dose in actual sexual transmission by comparing the kinetics of infection in female guinea pigs acquired via sexual contact to those of genital infections induced artificially with known quantities of chlamydiae. Groups of guinea pigs were infected intravaginally with 10⁴, 10³, 10², and 10¹ inclusion-forming units (IFU) of GPIC, and the kinetics of the infection were determined. Infection with 10² IFU produced infections with lower peak levels than those in animals receiving 10⁴ or 10³ IFU. Seventy percent of animals receiving 10² IFU became infected, while 100 and 79% of animals receiving 10⁴ and 10³ IFU, respectively, became infected. Animals receiving 10² IFU also had a longer incubation period. Of 19 animals that mated with infected males, 63.2% became infected, with an infection course which was not significantly different than that of the 10²-IFU-infected group. The data suggest that female guinea pigs received approximately 10² IFU by sexual transmission. Of interest was the observation that the guinea pigs infected by sexual transmission shed organisms for a significantly shorter time period than that of any group that was artificially infected. This result suggests that there may be factors associated with semen which passively transfer antimicrobial activity to the female or enhance the innate host response in the female. Immunization of females with an inactivated vaccine was also found to elicit a protective immune response against sexual challenge, demonstrating that the model can be used in the evaluation of possible vaccine candidates and/or methodologies. There is currently no other animal model available for any sexually transmitted disease in which the disease or the ability to prevent the disease may be studied in animals infected by the natural means.

Editor: F. C. Fang

This article has been cited by other articles:

• Cunningham, K. A., Beagley, K. W. (2008). Male Genital Tract Chlamydial Infection: Implications for Pathology and Infertility. Biol. Reprod. 79: 180-189 [Abstract] [Full Text]