Determinants of trachoma endemicity using Chlamydia trachomatis ompA DNA sequencing

Whole-genome sequencing of ocular Chlamydia trachomatis isolates from Gadarif State, Sudan

BACKGROUND

Trachoma, caused by ocular Chlamydia trachomatis, is the leading infectious cause of blindness worldwide. Sudan first reported trachoma in the 1930s and has since been consistently endemic. Ocular C. trachomatis previously isolated from trachoma patients in Sudan in 1963 was antigenically identical to an isolate from Saudi Arabia (A/SA1). No contemporary ocular C. trachomatis whole genome sequences have been reported from Sudan.

METHODS

This study sequenced twenty ocular C. trachomatis isolates to improve understanding of pathogen diversity in North-East Africa and examine for genomic variation specific to Sudan, possibly related to the persistence of trachoma in surveyed communities. High quality, whole genome sequences were obtained from 12/20 isolates.

RESULTS

All isolates were serovar A and had tarP and trpA sequences typical of classical, ocular C. trachomatis isolates. The Sudanese isolates formed a closely related subclade within the T2-trachoma clade of C. trachomatis phylogeny distinct from geographically disparate ocular isolates, with little intra-population diversity. We found 333 SNPs that were conserved in Sudanese ocular isolates but rare compared to other ocular C. trachomatis populations, which were focused in two genomic loci (CTA0172-CTA0173 and CTA0482).

CONCLUSIONS

Limited intra-population diversity and geographical clustering of ocular C. trachomatis suggests minimal transmission between and slow diversification within trachoma-endemic communities. However, diversity may have been higher pre-treatment in these communities. Over-representation of Sudan-specific SNPs in three genes suggests they may have an impact on C. trachomatis growth and transmission in this population.

Impact of a single round of mass drug administration with azithromycin on active trachoma and ocular Chlamydia trachomatis prevalence and circulating strains in The Gambia and Senegal

BACKGROUND

Mass drug administration (MDA) with azithromycin is a cornerstone of the trachoma elimination strategy. Although the global prevalence of active trachoma has declined considerably, prevalence persists or even increases in some communities and districts. To increase understanding of MDA impact, we investigated the prevalence of active trachoma and ocular C. trachomatis prevalence, organism load, and circulating strains at baseline and one-year post-MDA in The Gambia and Senegal.

METHODS

Pre- and one-year post-MDA, children aged 0-9 years were examined for clinical signs of trachoma in six Gambian and 12 Senegalese villages. Ocular swabs from each child's right conjunctiva were tested for evidence of ocular C. trachomatis infection and organism load (ompA copy number), and ompA and multi-locus sequence typing (MLST) was performed.

RESULTS

A total of 1171 children were examined at baseline and follow-up in The Gambia. Active trachoma prevalence decreased from 23.9% to 17.7%, whereas ocular C. trachomatis prevalence increased from 3.0% to 3.8%. In Senegal, 1613 and 1771 children were examined at baseline and follow-up, respectively. Active trachoma prevalence decreased from 14.9% to 8.0%, whereas ocular C. trachomatis prevalence increased from 1.8% to 3.6%. Higher organism load was associated with having active trachoma and severe inflammation. Sequence typing demonstrated that all Senegalese samples were genovar A, whereas Gambian samples were a mix of genovars A and B. MLST provided evidence of clustering at village and household levels and demonstrated differences of strain variant frequencies in Senegal, indicative of an "outbreak". MLST, including partial ompA typing, provided greater discriminatory power than complete ompA typing.

CONCLUSIONS

We found that one round of MDA led to an overall decline in active trachoma prevalence but no impact on ocular C. trachomatis infection, with heterogeneity observed between villages studied. This could not be explained by MDA coverage or number of different circulating strains pre- and post-MDA. The poor correlation between active trachoma and infection prevalence supports the need for further work on alternative indicators to clinical signs for diagnosing ocular C. trachomatis infection. MLST typing has potential molecular epidemiology utility, including better understanding of transmission dynamics, although relationship to whole-genome sequence variability requires further exploration.

Diversity of Chlamydia trachomatis in Trachoma-Hyperendemic Communities Treated With Azithromycin

Prior studies have theorized that low chlamydial genetic diversity following mass azithromycin treatments for trachoma may create a population bottleneck that prevents the return of infection, but little empirical evidence exists to support this hypothesis. In this study, a single mass azithromycin distribution was administered to 21 communities in the Gurage Zone of Ethiopia in 2003. All children aged 1-5 years had conjunctival swabs performed before treatment and 2 and 6 months after treatment. All swabs positive for Chlamydia trachomatis at 2 months underwent typing of the gene encoding the major outer membrane protein (ompA) of C. trachomatis, as did the same number of swabs per community from the pretreatment and 6-month visits. Diversity of ompA types, expressed as the reciprocal of Simpson's index, was calculated for each community. In total, 15 ompA types belonging to the A and B genovars were identified. The mean diversity was 2.11 (95% confidence interval: 1.79, 2.43) before treatment and 2.16 (95% confidence interval: 1.76, 2.55) 2 months after treatment (P = 0.78, paired t test). Diversity of ompA was not associated with the prevalence of ocular chlamydia (P = 0.76) and did not predict subsequent changes in the prevalence of ocular chlamydia (P = 0.32). This study found no evidence to support the theory that ompA diversity is associated with transmission of ocular chlamydia.

Genome-wide profiling of humoral immunity and pathogen genes under selection identifies immune evasion tactics of Chlamydia trachomatis during ocular infection

The frequency and duration of Chlamydia trachomatis (Ct) ocular infections decrease with age, suggesting development of partial immunity. However, there is a lack of clear correlates of immunity to Ct infection in humans. We screened sera from a cohort of Gambian children followed for six-months against a Ct-proteome microarray. At genome sequence level, we detected signatures of selection from a population of ocular Ct isolates from Guinea-Bissau. Together these approaches allowed us to highlight the focus of humoral responses and hypothesise new modes of pathogen immune evasion. Children who were susceptible to frequent and/or prolonged Ct infection had a less focussed antibody response, including preferential recognition of forty-two antigens. There was evidence of positive and purifying selection across the genome, but little balancing selection. In contrast, most antigens that were associated with susceptibility were under neutral selection. These data suggest an evasion strategy in which Ct presents a large panel of irrelevant antigens to the immune system to block or misdirect protective responses. Development of a focused immune response, possibly induced through vaccination, may be an effective strategy to promote protection to Ct infection.

Molecular characteristics of the ompA gene of serotype B Chlamydia trachomatis in Qinghai Tibetan primary school students

To study the molecular characteristics of Chlamydia trachomatis, the major outer membrane protein gene (ompA) of C. trachomatis from primary school students with trachoma residing in the Qinghai Tibetan area was sequenced and compared with the same serotype in GenBank. In Jianshetang Primary School and Galeng Central Primary School in the Galeng Tibetan Township of Qinghai Haidong Sala Autonomous County, scraped samples were collected from the upper tarsal conjunctiva and lower conjunctival sac of both eyes of 45 students with trachoma, stored at 4°C, and transported to Beijing Tongren Hospital by air within 24 h. The samples were screened for C. trachomatis by real-time PCR. The ompA gene from the C. trachomatis-positive samples was amplified by nested PCR. The serotype was confirmed by National Center for Biotechnology Information (NCBI) BLAST search and homology analysis. The entire ompA gene sequence was compared with the corresponding gene sequences of serotype B strains available in GenBank. Of the 45 students aged 6-13 years with trachoma, 26 C. trachomatis-positive students were identified by the initial real-time PCR screening (average age, (9.09±1.63) years; sex ratio, 1.0), accounting for 57.78% (26/45). The cycle threshold values for real-time PCR were 16.79-37.77. Half (13/26) of C. trachomatis-positive students had a bacterial copy number of >10(5). The compliance rate of the ompA gene sequences with the C. trachomatis serotype B strains in GenBank was up to 99%. Two novel genetic mutations were found when the ompA gene was compared with those of the 11 serotype B strains in GenBank. The two non-synonymous mutations were located at (i) position 271 in the second constant domain, an adenine (A) to guanine (G) substitution (ACT→GCT), changing the amino acid at position 91 from threonine to alanine (Thr→Ala) in all 26 strains; and (ii) position 887 in the fourth variable domain, a cytosine (C) to thymine (T) substitution (GCA→GTA), changing the amino acid at residue 296 from alanine to valine (Ala→Val) in four of the 26 strains. Six mutations were identified relative to ATCC VR-573. The strains could be divided into two gene clusters according to the mutation at nucleotide position 887: CQZ-1 (China Qinghai Tibetan-1) and CQZ-2 (China Qinghai Tibetan-2). We thus detected two novel serotype B mutant strains of C. trachomatis among study subjects with trachoma.

Evolution, phylogeny, and molecular epidemiology of Chlamydia

The Chlamydiaceae are a family of obligate intracellular bacteria characterized by a unique biphasic developmental cycle. It encompasses the single genus Chlamydia, which involves nine species that affect a wide range of vertebral hosts, causing infections with serious impact on human health (mainly due to Chlamydia trachomatis infections) and on farming and veterinary industries. It is believed that Chlamydiales originated ∼700mya, whereas C. trachomatis likely split from the other Chlamydiaceae during the last 6mya. This corresponds to the emergence of modern human lineages, with the first descriptions of chlamydial infections as ancient as four millennia. Chlamydiaceae have undergone a massive genome reduction, on behalf of the deletional bias "use it or lose it", stabilizing at 1-1.2Mb and keeping a striking genome synteny. Their phylogeny reveals species segregation according to biological properties, with huge differences in terms of host range, tissue tropism, and disease outcomes. Genome differences rely on the occurrence of mutations in the >700 orthologous genes, as well as on events of recombination, gene loss, inversion, and paralogous expansion, affecting both a hypervariable region named the plasticity zone, and genes essentially encoding polymorphic and transmembrane head membrane proteins, type III secretion effectors and some metabolic pathways. Procedures for molecular typing are still not consensual but have allowed the knowledge of molecular epidemiology patterns for some species as well as the identification of outbreaks and emergence of successful clones for C. trachomatis. This manuscript intends to provide a comprehensive review on the evolution, phylogeny, and molecular epidemiology of Chlamydia.

Antibody signature of spontaneous clearance of Chlamydia trachomatis ocular infection and partial resistance against re-challenge in a nonhuman primate trachoma model

Background

Chlamydia trachomatis is the etiological agent of trachoma the world's leading cause of infectious blindness. Here, we investigate whether protracted clearance of a primary infection in nonhuman primates is attributable to antigenic variation or related to the maturation of the anti-chlamydial humoral immune response specific to chlamydial antigens.

Methodology/Principal Findings

Genomic sequencing of organisms isolated throughout the protracted primary infection revealed that antigenic variation was not related to the inability of monkeys to efficiently resolve their infection. To explore the maturation of the humoral immune response as a possible reason for delayed clearance, sera were analyzed by radioimmunoprecipitation using intrinsically radio-labeled antigens prepared under non-denaturing conditions. Antibody recognition was restricted to the antigenically variable major outer membrane protein (MOMP) and a few antigenically conserved antigens. Recognition of MOMP occurred early post-infection and correlated with reduction in infectious ocular burdens but not with infection eradication. In contrast, antibody recognition of conserved antigens, identified as PmpD, Hsp60, CPAF and Pgp3, appeared late and correlated with infection eradication. Partial immunity to re-challenge was associated with a discernible antibody recall response against all antigens. Antibody recognition of PmpD and CPAF was destroyed by heat treatment while MOMP and Pgp3 were partially affected, indicating that antibody specific to conformational epitopes on these proteins may be important to protective immunity.

Conclusions/Significance

Our findings suggest that delayed clearance of chlamydial infection in NHP is not the result of antigenic variation but rather a consequence of the gradual maturation of the C. trachomatis antigen-specific humoral immune response. However, we cannot conclude that antibodies specific for these proteins play the primary role in host protective immunity as they could be surrogate markers of T cell immunity. Collectively, our results argue that an efficacious subunit trachoma vaccine might require a combination of these antigens delivered in their native conformation.

Chlamydia trachomatis is the etiological agent of trachoma the world's leading cause of infectious blindness. In this study, we investigated whether delayed clearance of a primary infection in nonhuman primates was attributable to antigenic variation or related to gradual changes in the humoral immune response specific to chlamydial antigens. We found that antigenic variation was not related to the inability of monkeys to efficiently resolve their infection. However, exploring changes in the immune response as a possible reason for delayed clearance revealed that antibody recognition was restricted to the antigenically variable major surface protein and a few conserved polypeptides. Antibody recognition of the major antigenically variable surface protein correlated with the initial reduction in infectious burdens while recognition of conserved chlamydial antigens occurred late and correlated with infection eradication. These findings suggest that delayed clearance of chlamydial infection is not the result of antigenic variation but a consequence of a gradually evolving humoral immune response specific to different chlamydial antigens. Antibody recognition was at least partially directed against conformational epitopes, indicating that an efficacious subunit trachoma vaccine might require a combination of antigens delivered in their native conformation.

Phylogenetic analysis of Chlamydia trachomatis Tarp and correlation with clinical phenotype

Chlamydia trachomatis is the leading cause of infectious blindness worldwide and is the most commonly reported pathogen causing sexually transmitted infections. Tarp (translocated actin recruiting phosphoprotein), a type III secreted effector that mediates actin nucleation, is central to C. trachomatis infection. The phylogenetic analysis of tarP from reference strains as well as ocular, genital, and lymphogranuloma venereum (LGV) clinical isolates demonstrated an evolutionary relationship with disease phenotype, with LGV and ocular isolates branched into clades that were separate from the urogenital isolates. The sequence analysis of Tarp indicated a high degree of variability and identified trends within clinical groupings. Tarps from LGV strains contained the highest number of tyrosine-rich repeat regions (up to nine) and the fewest (two) predicted actin binding domains. The converse was noted for Tarp proteins from ocular isolates that contained up to four actin binding domains and as few as one tyrosine-rich repeat region. The results suggest that Tarp is among the few known genes to play a role in C. trachomatis adaptations to specific niches within the host.

High-risk sexual behaviours and genital chlamydial infections in high school students in Southern Taiwan

Summary

The objective of this study was to determine the prevalence of high-risk sexual behaviours and sexually transmitted infections (STIs) and associated risk factors in Taiwanese high school students. Students in grades 10 and 11 (mean age: 15.9 ± 0.9; range: 13–20 years) at two schools were recruited. An anonymous online real-time computer-assisted self-interviewing questionnaire was designed to assess demographic factors and sexual behaviours. Urine specimens were tested for genital chlamydial and gonococcal infections. The same survey and screening was conducted one year later on the same group of students. Overall, 670 individual students (993 visits) were enrolled with 323 students in both surveys. Twenty-seven percent had had sexual intercourse, and more than three quarters (79%) of them had engaged in high-risk sexual behaviours. Having friends using drugs increased the odds of practicing high-risk sexual behaviours (odds ratio [OR] 1.99, 95% CI: 1.13 to 3.50). Among 182 sexually active students, 8.8% had chlamydial (female: 12.5%; male: 5.3%) and 1.1% had gonococcal infections. Having sex with someone met on the Internet was the most significant risk factor for acquiring chlamydia (OR 8.14, 95% CI: 2.82 to 23.51). In conclusion, this adolescent population reported high prevalence of high-risk sexual behaviours and had a high prevalence of chlamydia supportive of a potential epidemic of STIs and HIV.

Evolutionary dynamics of ompA, the gene encoding the Chlamydia trachomatis key antigen

Chlamydia trachomatis is the trachoma agent and causes most bacterial sexually transmitted infections worldwide. Its major outer membrane protein (MOMP) is a well-known porin and adhesin and is the dominant antigen. So far, investigation of MOMP variability has been focused mainly on molecular epidemiological surveys. In contrast, we aimed to evaluate the impact of the host pressure on this key antigen by analyzing its evolutionary dynamics in 795 isolates from urogenital infections, taking into account the MOMP secondary structure and the sizes/positions of antigenic regions. One-third of the specimens showed a mutational drift from the corresponding genotype, where approximately 42% of the mutations had never been described. Amino acid alterations were sixfold more frequent within B-cell epitopes than in the remaining protein (P = 0.027), and some mutations were also found within or close to T-cell antigenic clusters. Interestingly, the two most ecologically successful genotypes, E and F, showed a mutation rate 60.3-fold lower than that of the other genotypes (P < 10(-8)), suggesting that their efficacy may be the result of a better fitness in dealing with the host immune system rather than of specific virulence factors. Furthermore, the variability exhibited by some genetic variants involved residues that are known to play a critical role during the membrane mechanical movements, contributing to a more stable and flexible porin conformation, which suggests some plasticity to deal with environmental pressure. Globally, these MOMP mutational trends yielded no mosaic structures or important phylogenetic changes, but instead yielded point mutations on specific protein domains, which may enhance pathogen's infectivity, persistence, and transmission.

Co-evolution of genomes and plasmids within Chlamydia trachomatis and the emergence in Sweden of a new variant strain

Background

Chlamydia trachomatis is the most common cause of sexually transmitted infections globally and the leading cause of preventable blindness in the developing world. There are two biovariants of C. trachomatis: 'trachoma', causing ocular and genital tract infections, and the invasive 'lymphogranuloma venereum' strains. Recently, a new variant of the genital tract C. trachomatis emerged in Sweden. This variant escaped routine diagnostic tests because it carries a plasmid with a deletion. Failure to detect this strain has meant it has spread rapidly across the country provoking a worldwide alert. In addition to being a key diagnostic target, the plasmid has been linked to chlamydial virulence. Analysis of chlamydial plasmids and their cognate chromosomes was undertaken to provide insights into the evolutionary relationship between chromosome and plasmid. This is essential knowledge if the plasmid is to be continued to be relied on as a key diagnostic marker, and for an understanding of the evolution of Chlamydia trachomatis.

Results

The genomes of two new C. trachomatis strains were sequenced, together with plasmids from six C. trachomatis isolates, including the new variant strain from Sweden. The plasmid from the new Swedish variant has a 377 bp deletion in the first predicted coding sequence, abolishing the site used for PCR detection, resulting in negative diagnosis. In addition, the variant plasmid has a 44 bp duplication downstream of the deletion. The region containing the second predicted coding sequence is the most highly conserved region of the plasmids investigated. Phylogenetic analysis of the plasmids and chromosomes are fully congruent. Moreover this analysis also shows that ocular and genital strains diverged from a common C. trachomatis progenitor.

Conclusion

The evolutionary pathways of the chlamydial genome and plasmid imply that inheritance of the plasmid is tightly linked with its cognate chromosome. These data suggest that the plasmid is not a highly mobile genetic element and does not transfer readily between isolates. Comparative analysis of the plasmid sequences has revealed the most conserved regions that should be used to design future plasmid based nucleic acid amplification tests, to avoid diagnostic failures.

Chlamydia trachomatis ompA variants in trachoma: what do they tell us?

Background

Trachoma, caused by Chlamydia trachomatis (Ct), is the leading infectious cause of blindness. Sequence-based analysis of the multiple strains typically present in endemic communities may be informative for epidemiology, transmission, response to treatment, and understanding the host response.

Methods

Conjunctival and nasal samples from a Gambian community were evaluated before and 2 months after mass azithromycin treatment. Samples were tested for Ct by Amplicor, with infection load determined by quantitative PCR (qPCR). ompA sequences were determined and their diversity analysed using frequency-based tests of neutrality.

Results

Ninety-five of 1,319 (7.2%) individuals from 14 villages were infected with Ct at baseline. Two genovars (A and B) and 10 distinct ompA genotypes were detected. Two genovar A variants (A1 and A2) accounted for most infections. There was an excess of rare ompA mutations, not sustained in the population. Post-treatment, 76 (5.7%) individuals had Ct infection with only three ompA genotypes present. In 12 of 14 villages, infection had cleared, while in two it increased, probably due to mass migration. Infection qPCR loads associated with infection were significantly greater for A1 than for A2. Seven individuals had concurrent ocular and nasal infection, with divergent genotypes in five.

Conclusions

The number of strains was substantially reduced after mass treatment. One common strain was associated with higher infection loads. Discordant genotypes in concurrent infection may indicate distinct infections at ocular and nasal sites. Population genetic analysis suggests the fleeting appearance of rare multiple ompA variants represents purifying selection rather than escape variants from immune pressure. Genotyping systems accessing extra-ompA variation may be more informative.

Trachoma is an important cause of blindness resulting from transmission of the bacterium Chlamydia trachomatis. One way to understand better how this infection is transmitted and how the human immune system controls it is to study the strains of bacteria associated with infection. Comparing strains before and after treatment might help us learn if someone has a new infection or the same one as before. Identifying differences between disease-causing strains should help us understand how infection leads to disease and how the human host defences work. We chose to study variation in the chlamydial gene ompA because it determines the protein MOMP, one of the leading candidates for inclusion in a vaccine to prevent trachoma. If immunity to MOMP is important in natural trachoma infections, we would expect to find evidence of this in the way the strains varied. We did not find this, but instead found that two common strains seemed to cause different types of disease. Although their MOMPs were very slightly different, this did not really explain the differences. We conclude that methods of typing strains going beyond the ompA gene will be needed to help us understand the interaction between Chlamydia and its human host.

Multiple Chlamydiaceae species in trachoma: implications for disease pathogenesis and control

BACKGROUND

Chlamydia trachomatis is a unique obligate intracellular bacterium that remains the leading cause of sexually transmitted bacterial diseases and preventable blindness worldwide. Chronic ocular infections are referred to as trachoma, and predominate in developing countries. Since 2001, the World Health Organization has promoted control strategies including antibiotics, improved hygiene, and environmental measures with limited success. Consequently, a vaccine is urgently needed. Integral to vaccine design is an understanding of the interactions of the pathogen and host immune response. Various animal models of trachoma show that urogenital C. trachomatis strains and other species of the family Chlamydiaceae produce severe conjunctival inflammation and scarring similar to that of the ocular C. trachomatis strains. However, we do not know the extent of organisms that may be involved in human trachoma. Furthermore, C. trachomatis heat shock protein 60 (Hsp60) has been implicated in inflammation and conjunctival scarring but the role of other Chlamydiaceae Hsp60 in disease pathogenesis has not been examined. In this study, we set out to identify whether other Chlamydiaceae species are present in trachoma, and determine their association with severity of clinical disease and with mucosal and systemic immune responses to Chlamydiaceae species-specific Hsp60 to further investigate the immunopathogenesis of this blinding disease.

METHODS AND FINDINGS

We randomly selected nine of 49 households in a trachoma-endemic region of Nepal. Trachoma was graded, and real-time, quantitative (k)PCR was used to detect genomic DNA and cDNA (from RNA) for Chlamydiaceae ompA and 16S rRNA genes, respectively, from conjunctival swabs. IgG antibody responses to recombinant (r) Chlamydiaceae species-specific Hsp60 were determined for tears and sera. Surprisingly, all three species-C. trachomatis, Chlamydophila psittaci, and Chlamydophila pneumoniae-were detected in eight (89%) study households; one household had no members infected with C. pneumoniae. Of 80 (63%; n = 127) infected individuals, 28 (35%) had infection with C. psittaci, or C. pneumoniae, or both; single and dual infections with C. psittaci and C. pneumoniae were significantly associated with severe conjunctival inflammation (OR 4.25 [95% confidence interval (CI), 2.9-11.3], p = 0.009] as were single infections with C. trachomatis (OR 5.7 [95% CI, 3.8-10.1], p = 0.002). Of the 80 infected individuals, 75 (93.8%) were also positive for 16S rRNA by kPCR for the same organism identified by ompA. Individuals with tear IgG immunoreactivity to Chlamydiaceae rHsp60 were eight times more likely than individuals without tear immunoreactivity to be infected (95% CI 6.4-15.1; p = 0.003), 6.2 times more likely to have severe inflammation (95% CI 4.4-12.6; p = 0.001), and 5.7 times more likely to have scarring (95% CI 3.9-11.1; p = 0.019) while individuals with serum IgG immunoreactivity were 4.1 times more likely to be infected (95% CI 3.1-10.1; p = 0.014).

CONCLUSIONS

We provide substantial evidence for the involvement of C. psittaci and C. pneumoniae, in addition to C. trachomatis, in trachoma. The distribution of Chlamydiaceae species by household and age suggests that these infections are widespread and not just sporadic occurrences. Infection with multiple species may explain the failure to detect chlamydiae among active trachoma cases, when only C. trachomatis is assayed for, and the failure of clinically active cases to resolve their disease following what would be considered effective C. trachomatis treatment. The evidence for viable (RNA-positive) organisms of all three species in single and coinfections, the significant association of these infections with severe inflammation, and the significant association of tear and serum IgG responses to Chlamydiaceae Hsp60 with inflammation and scarring, support the role of all three species in disease pathogenesis. Thus, while our findings should be confirmed in other trachoma-endemic countries, our data suggest that a reevaluation of treatment regimens and vaccine design may be required. Understanding the full impact of Chlamydiaceae species on the epidemiology, immunopathology, and disease outcome of trachoma presents a new challenge for Chlamydiaceae research.

Genotyping of Chlamydia trachomatis from endocervical specimens in Brazil

BACKGROUND

There is no data concerning genotyping of Chlamydia trachomatis from Brazilian samples.

GOAL

To characterize the genotype of C. trachomatis detected in women assisted at a STD public clinic and establish the prevalence of this infection in that population.

STUDY DESIGN

Endocervical samples of a group of 100 women were tested for chlamydial infection with PCR directed to C. trachomatis cryptic plasmid. Genotyping of positive samples were done after omp1 amplification and sequencing.

RESULTS

The overall prevalence of C. trachomatis infection was 19%, with the highest prevalence in women between 15 and 25 years old (68.4%). Four genotypes were found associated with endocervical infections: D, E, F, and K. Sequence analysis revealed a coinfection of genotypes D and E in 1 woman.

CONCLUSIONS

To our knowledge this is the first study to characterize Brazilian C. trachomatis endocervical samples and Brazilian C. trachomatis genotype coinfection. Our results also emphasize the importance of routine diagnosis of C. trachomatis for the control of this STD.

Trachoma: new assault on an ancient disease

Trachoma is the leading infectious cause of blindness worldwide. The World Health Organization (WHO) estimated that approximately 5.9 million persons are blind or have severe vision-loss as a result of trachoma, and another 10 million are at high risk. Trachoma preferentially affects the most deprived communities, and within these communities, women and children bear the brunt of the burden. In recent years, there has been a renewed focus on research and heightened enthusiasm for strengthening trachoma control programs in afflicted countries. WHO has convened an alliance of member countries, non-governmental organizations, and other partners for the Global Elimination of Blinding Trachoma by the year 2020, and endorsed the multi-faceted SAFE strategy for trachoma control. SAFE-Surgery, Antibiotics, Face-washing, and Environmental improvement-has incorporated sound research on elements likely to reduce trachoma, and trachomatis blindness, in endemic communities. This review summarizes current knowledge about trachoma and its causative agent, Chlamydia trachomatis, the epidemiology and risk factors for trachoma as a prelude to reviewing the SAFE strategy. While ongoing research to support the knowledge base for SAFE must continue to be a priority, the full implementation of SAFE is the best hope for countries to reduce the global burden of blindness from this preventable cause.

Modeling the economic net benefit of a potential vaccination program against ocular infection with Chlamydia trachomatis

Trachoma is an ocular infection caused by Chlamydia trachomatis that carries a huge public health burden as a leading cause of preventable blindness globally. We developed a model of the economic benefits of a potential vaccine. Factors that impact the efficacy of a vaccination program (such as the sensitivity and specificity of algorithms to identify high-risk individuals), and personal and environmental risk factors for trachoma affect the maximum vaccination and screening costs at which a vaccination program can achieve a positive net benefit. This model is useful for planning vaccine programs in areas with varying trachoma risk factors and endemicity.

Polymorphisms in Chlamydia trachomatis tryptophan synthase genes differentiate between genital and ocular isolates

We previously reported that laboratory reference strains of Chlamydia trachomatis differing in infection organotropism correlated with inactivating mutations in the pathogen's tryptophan synthase (trpBA) genes. Here, we have applied functional genomics to extend this work and find that the paradigm established for reference serovars also applies to clinical isolates - specifically, all ocular trachoma isolates tested have inactivating mutations in the synthase, whereas all genital isolates encode a functional enzyme. Moreover, functional enzyme activity was directly correlated to IFN-gamma resistance through an indole rescue mechanism. Hence, a strong selective pressure exists for genital strains to maintain a functional synthase capable of using indole for tryptophan biosynthesis. The fact that ocular serovars (serovar B) isolated from the genital tract were found to possess a functional synthase provided further persuasive evidence of this association. These results argue that there is an important host-parasite relationship between chlamydial genital strains and the human host that determines organotropism of infection and the pathophysiology of disease. We speculate that this relationship involves the production of indole by components of the vaginal microbial flora, allowing chlamydiae to escape IFN-gamma-mediated eradication and thus establish persistent infection.

Elimination of blinding trachoma

PURPOSE OF REVIEW

A recently initiated major effort to eliminate blinding trachoma as a public health problem is discussed.

RECENT FINDINGS

Mass (community-wide) treatment with a short course of oral azithromycin has been shown to be at least as effective as long courses (42 doses over a 6-week period) of topical tetracycline in reducing clinically active trachoma and the prevalence of chlamydial infection. The beneficial effects last for more than a year, in contrast to the short-lived results typically seen after previous control programs that used topical therapy. Azithromycin is a key element in the integrated approach towards eliminating blinding trachoma summarized as the 'SAFE' strategy (surgery for deformed eyelids; antibiotic treatment of whole communities with azithromycin, to control infection; face washing and improved hygiene of young children; and environmental improvements, particularly the provision of water and latrines). The first regional application of this strategy has shown dramatic results, producing a reduction in trachoma activity of more than 70% in Morocco.

SUMMARY

The goal of eliminating blinding trachoma may be reachable. Further research is needed to determine how best to use azithromycin and which environmental improvements will be most effective. The important questions are as follows: how often antibiotic treatment programs will be required in the endemic areas; how best to evaluate the effects of treatment; and when (and perhaps whom) do we retreat.