Highlights from the Sixth Meeting of the European Society for<i>Chlamydia</i>Research

Historic evidence of infections caused by Chlamydia exists as long as 4000 years ago, and since the first description of the characteristic features of a chlamydial inclusion by Halbersteadter & von Provazek (1907), Chlamydia has been studied extensively. While the genome sequence of several Chlamydia species has provided extensive new knowledge concerning the coding capacity of Chlamydia, effective therapeutic or immunologic means of control or prevention against diseases caused by chlamydial infections are still not available. Hence, millions of samples are tested for the presence of Chlamydia world wide every year, and subjects found positive are treated with antibiotics. However, progress has been made in understanding the pathogenesis and molecular biology of Chlamydia. This was abundantly illustrated at The Sixth Meeting of the European Society for Chlamydia Research held at The Lakeside Lecture Theatres, University of Aarhus, Denmark, July 1–4, 2008. Seventeen papers published in this Chlamydia thematic issue of FEMS Immunology and Medical Microbiology represent the highlights of this conference. Taxonomy in the family Chlamydiaceae has been hotly debated since Everett (1999) proposed the division of the genus Chlamydia into two distinct genera, a proposal later questioned by many in the Chlamydia field (Schachter et al., 2001). At the Aarhus meeting, Richard Stephens presented new evidence based on chlamydial evolutionary biology and sequenced genomes that strongly supports that the genus should not be divided. This is presented in the first article of the thematic issue. The thematic issue also includes a startling, completely new view by Brunham and Rekart of Chlamydia trachomatis disease expression. In 1991, the province of British Columbia, Canada (probably representative of the situation in the western world), initiated a comprehensive STD control program that included diagnostic testing and treatment of positive individuals. Detailed analysis of epidemiological data obtained since then indicates that the rate of C. trachomatis-positive cases per 100 000 individuals fell for the first 6 years; however, since 1998 an increasing number of positive samples is detected each year. Over the same period of time, a constant decrease in diagnosed sequelae (PID, ectopic pregnancy, and tubal infertility) has been observed. Brunham and Rekart explain this paradoxical phenomenon using the arrested immunity hypothesis by which reinfection becomes more likely as herd immunity is reduced. Because protective immunity only develops over time and treatment is normally initiated before this is allowed to happen, the consequence is that while female reproductive health is improved, the number of infected individuals keeps increasing. Only a protective vaccine can reverse this situation. An important aspect of the epidemiology of chlamydial infections is that isolates must be obtained and compared such that infections caused by distinct isolates can be traced. However, owing to the low genetic variability between isolates, a challenge has been in developing methods that allow isolates to be readily and reliably distinguished from one another. In a previous article (Pedersen et al., 2008) and also addressed in this thematic issue, Pedersen and colleagues showed that using both the sequence of the omp1 (ompA) gene and that of three new variable number tandem repeat loci of C. trachomatis, it was possible to discriminate between different isolates, and thus epidemiological associations could be established. A case in point is that of the continued emergence of a mutant of C. trachomatis in the Southern part of Sweden (Ripa & Nilsson, 2007). This mutant has a deletion in the common plasmid encompassing a primer site for two of the most commonly used nucleic acid amplification tests. The spread of this mutant has shown that C. trachomatis can survive, multiply and be sexually transmitted while avoiding detection by the tests used, illustrating that the specificity of such tests also may be a drawback. Interestingly, Pedersen (2008) used their genotyping method to determine that the C. trachomatis new variant does indeed represent a new clonal population. We hope to see you all at the seventh meeting of the European Society for Chlamydia Research to be held in Amsterdam, The Netherlands in 2012.

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