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Repeated or chronic infection increases the likelihood of complications following chlamydial infection [Rietmeijer et al., 2002]. Repeated genital tract infections are common In women each episode of pelvic inflammatory disease roughly doubles the risk of permanent tubal damage [Lehtinen & Paavonen; 1994] irrespective of whether infection was silent or overt [Patton et al., 1989]. In trachoma, recurrent infection is also associated with scarring sequelae [Grayston et al., 1985]. This would explain why, in a classic study, Sikhs migrating to British Columbia from a trachoma-endemic area of the Punjab, showed little evidence of further trachoma transmission or conjunctival scarring sequelae in the improved hygienic environment of Canada [Detels et al., 1966].

As reviewed elsewhere [see: host genotype], host factors are also important. To give but one example here, in the Gambia, individuals with moderate or severe inflammatory trachoma at one village survey were more likely than those with milder disease to have similar inflammatory changes at a previous or subsequent survey [Mabey et al., 1992], presumably largely because of factors related to the host response.

In non-human primate models of infection, repeated ocular inoculations with C. trachomatis were necessary to produce the corneal pannus and conjunctival scarring characteristic of severe trachoma [Grayston et al., 1985; Taylor et al., 1982]. Likewise, in the female macaque monkey, repeated genital tract infection was necessary to produce the pelvic adhesions, tubal scarring and occlusion characteristic of severe pelvic inflammatory disease [Patton et al., 1990]. Thus repeated infection or severe infection at young age are associated with severe responses to C. trachomatis infection.

References

Detels, R., Alexander, E. R. & Dhir, S. P. (1966). Trachoma in Punjabi Indians in British Columbia: a prevalence study with comparisons to India. American Journal of Epidemiology 84, 81 - 91. [Classic paper which established the importance of the force of infection in trachoma sequelae].

Grayston, J. T., Wang, S. P., Yeh, L. J. & Kuo, C. C. (1985). Importance of reinfection in the pathogenesis of trachoma. Reviews of Infectious Disease 7, 717 - 725. [Useful review from one of the most experienced groups in trachoma research]

Lehtinen, M. & Paavonen, J. (1994). Heat shock proteins in the immunopathogenesis of chlamydial pelvic inflammatory disease. Pages 599 - 610. In J. Orfila (ed). Chlamydial infections. Proceedings of the seventh international symposium on human chlamydial infections. Publisher: Editrice Esculapio, Bologna, Italy.

Mabey, D. C., Bailey, R. L., Ward, M. E. & Whittle, H. C. (1992). A longitudinal-study of trachoma in a Gambian village - implications concerning the pathogenesis of chlamydial infection. Epidemiology and Infection 108, 343 - 351.

Patton, D. L., Moore, D. E., Spadoni, L. R. et al., (1989). A comparison of the fallopian tube's response to overt and silent salpingitis. Obstetrics and Gynecology 73, 622 - 630. 

Patton, D. L., Wolner-Hanssen, P., Cosgrove, S. J. & Holmes, K. K. (1990). The effects of Chlamydia trachomatis on the female reproductive tract of the Macaca nemestrina after a single tubal challenge following repeated cervical inoculations. Obstetrics and Gynecology 76, 643 - 650.

Rietmeijer, C. A., van Bemmelen, R., Judson, F. N. & Douglas, J. M. Jr. (2002). Incidence and repeat infection rates of Chlamydia trachomatis among male and female patients in an STD clinic: implications for screening and rescreening. Sexually Transmitted Diseases 29, 65 - 72.

Taylor, H. R., Johnson, S. L., Prendergast, R. A. et al., (1982). An animal model of trachoma II. The importance of repeated infection. Investigative Ophthalmology and Visual Science 23, 507 - 515.

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