Trachoma

Therapeutic approaches toChlamydiainfections

Chlamydia trachomatis ocular and urogenital infections represent major public health problems, whereas Chlamydophila pneumoniae is a common aetiological agent of community-acquired pneumonia. The obligate intracellular lifestyle of these established pathogens poses challenges to both their diagnosis and treatment. Tetracyclines, macrolides and quinolones remain the antimicrobials of choice for the treatment of infections due to Chlamydiaceae.

Risk of trachomatous scarring and trichiasis in Gambians varies with SNP haplotypes at the interferon-gamma and interleukin-10 loci

Experimental evidence implicates interferon gamma (IFNgamma) in protection from and resolution of chlamydial infection. Conversely, interleukin 10 (IL10) is associated with susceptibility and persistence of infection and pathology. We studied genetic variation within the IL10 and IFNgamma loci in relation to the risk of developing severe complications of human ocular Chlamydia trachomatis infection. A total of 651 Gambian subjects with scarring trachoma, of whom 307 also had potentially blinding trichiasis and pair-matched controls with normal eyelids, were screened for associations between single-nucleotide polymorphisms (SNPs), SNP haplotypes and the risk of disease. MassEXTEND (Sequenom) and MALDI-TOF mass spectrometry were used for detection and analysis of SNPs and the programs PHASE and SNPHAP used to infer haplotypes from population genetic data. Multivariate conditional logistic regression analysis identified IL10 and IFNgamma SNP haplotypes associated with increased risk of both trachomatous scarring and trichiasis. SNPs in putative IFNgamma and IL10 regulatory regions lay within the disease-associated haplotypes. The IFNgamma +874A allele, previously linked to lower IFNgamma production, lies in the IFNgamma risk haplotype and was more common among cases than controls, but not significantly so. The promoter IL10-1082G allele, previously associated with high IL10 expression, is in both susceptibility and resistance haplotypes.

Participatory evaluations of trachoma control programmes in eight countries

OBJECTIVES

Trachoma is a major cause of blindness. The objective of this initiative was to conduct participatory process evaluations of the trachoma control programmes receiving support from the International Trachoma Initiative in eight countries.

METHODS

During each 2- to 4-week evaluation we analysed information collected at the central, district and community level through interviews, focus groups, questionnaires, direct observation of trachoma control activities, and existing data.

RESULTS

Mapping and assessment of disease prevalence had been completed in four of eight countries. Integration of trachoma control activities into national planning and district-level service provision varied. Intersectoral partnerships to implement the SAFE strategy (i.e. surgery, antibiotics, facial cleanliness and environmental change) were well established in a few countries. In all eight countries, the number of surgeries performed annually was insufficient; and quality of surgery was rarely monitored. Mass distribution of antibiotics was carried out well in extremely resource-poor settings and good coverage was achieved, although the strategy for antibiotic distribution varied. Inadequate water and sanitation remained a major problem in all programme areas. Monitoring of programme activities was generally inadequate. The Morocco programme is an example from which lessons and processes can be learnt and adapted to other programme countries.

CONCLUSIONS

Significant achievements have been made in implementing the SAFE strategy. Scaling up of activities to true national coverage should be planned and implemented provided the resources can be made available. Further standardization of how to assess, implement and monitor trachoma control activities will facilitate expansion of the programme.

PAX6 expression identifies progenitor cells for corneal keratocytes

Keratocytes of the corneal stroma produce a transparent extracellular matrix required for vision. During wound-healing and in vitro, keratocytes proliferate, becoming fibroblastic, and lose biosynthesis of unique corneal matrix components. This study sought identification of cells in the corneal stroma capable of assuming a keratocyte phenotype after extensive proliferation. About 3% of freshly isolated bovine stromal cells exhibited clonal growth. In low-mitogen media, selected clonal cultures displayed dendritic morphology and expressed high levels of keratan sulfate, aldehyde dehydrogenase 3A1, and keratocan, molecular markers of keratocyte phenotype. In protein-free media, both primary keratocytes and selected clonal cells aggregated to form attachment-independent spheroids expressing elevated levels of those marker molecules. The selected clonal cells exhibited normal karyotype and underwent replicative senescence after 65-70 population doublings; however, they continued expression of keratocyte phenotypic markers throughout their replicative life span. The progenitor cells expressed elevated mRNA for several genes characteristic of stem cells and also for genes expressed during ocular development PAX6, Six2, and Six3. PAX6 protein was detected in the cultured progenitor cells and a small number of stromal cells in intact tissue but was absent in cultured keratocytes and fibroblasts. Cytometry demonstrated PAX6 protein in 4% of freshly isolated stromal cells. These results demonstrate the presence of a previously unrecognized population of PAX6-positive cells in adult corneal stroma that maintain the potential to assume a keratocyte phenotype even after extensive replication. The presence of such progenitor cells has implications for corneal biology and for cell-based therapies targeting corneal scarring.

Effects of a probiotic strain of Enterococcus faecium on the rate of natural chlamydia infection in swine

Chlamydiae are obligately intracellular pathogens which cause infections associated with a broad range of diseases in both livestock and humans. In addition, a large proportion of animals may become persistently infected asymptomatic carriers and serve as reservoirs for other animals which also shed these potential zoonotic pathogens. Reducing the chlamydial load of animals is therefore of major importance, and since large-scale antibiotic treatment is neither desired nor feasible, alternative means of prevention are needed. Here we performed a study comparing the efficacy of a probiotic strain of Enterococcus faecium on the reduction of both the rate of natural infection and the shedding of chlamydiae in swine. The presence of Chlamydiaceae was detected by species-specific PCR of fecal samples of sows taken at three times prior to the birth of piglets. Piglets delivered from chlamydia-positive sows in either the control or the probiotic group were also examined for the frequency of chlamydiae at various ages. Eighty-five percent of the piglets from the control group were found to be chlamydia positive, whereas chlamydiae were found in only 60% of piglets from the probiotic group, results confirmed by fluorescence in situ hybridization and immunohistology, which showed higher rates of infection in the control group. In addition to the reduced frequency of chlamydia-positive piglets in the probiotic group, the time of appearance of positive samples was delayed. To our knowledge, these data show for the first time that a probiotic strain of E. faecium can reduce the rate of carryover infections of piglets by obligate intracellular pathogens.

Chlamydia trachomatis persistence: an update

Chlamydial persistence is a reversible state generated during conditions deleterious to growth. In persistence, Chlamydia trachomatis remains viable but atypical, with an enlarged, aberrant form and quiescent metabolism. It favours chronic chlamydiosis, leading to serious sequelae. Although the mechanism of persistence formation is still unknown, more reliable molecular approaches tend to confirm that its occurs in vivo, even lasting 3 years. One approach consists of identifying unprocessed rRNA found only in viable Chlamydia, when infection is not apparent. Another approach, referring to the fact that immunity is type-specific, consists of showing by genotyping that multiple recurrences are due to the same genovar. At the molecular level, persistence is characterized by increased expression of ct755, one of the three heat shock protein (hsp60)-coding genes. In addition, chromosomal replication occurs continuously, and cell division is blocked possibly due to the repression of genes such as ftsW and amiA. At the immunological level, persistence reveals the failure of host-defence mechanisms because of reduced or suppressed pro-inflammatory or cytotoxic responses.

Analysis of incidence rates in cluster-randomized trials of interventions against recurrent infections, with an application to trachoma

A method is developed for the Bayesian analysis of rate ratios of repeated events in matched cluster-randomized trials, and applied to the Flies and Eyes trial against trachoma in The Gambia. A non-mechanistic analysis estimates the incidence rate ratio for insecticide spray, relative to no intervention, as 0.59 (95 per cent credible interval 0.37--0.92), and for latrine provision as 0.67 (0.41--1.01). The method also yields incidence and clearance rate ratios for age. In the Flies and Eyes trial, the former rates are estimated to decrease with age, although no clear pattern is seen in the latter. Using clinical active trachoma as a marker of infection, and net catches to measure fly density, a mechanistic model is developed to estimate the proportion of transmission due to flies. However, it was not possible to estimate this proportion accurately, and a lack of association was noted between the magnitudes of reductions in fly density and in trachoma. The lack of knowledge on the relative importance of different transmission routes is a constraint on the current global programme for the elimination of trachoma.

Antibodies to Chlamydia trachomatis heat shock proteins Hsp60 and Hsp10 and subfertility in general population at age 31

PROBLEM

To assess the association between antibodies to Chlamydia trachomatis heat shock proteins 60 and 10 (Hsp60 and Hsp10) and subfertility in a general population sample.

METHOD OF STUDY

A nested case (n = 146)-control (n = 278) study in a population-based birth cohort. Serum immunoglobulin (Ig)G and IgA antibodies against C. trachomatis Hsp60 and Hsp10, explanatory factors, were measured by enzyme immunoassay, using recombinant proteins as antigens. The main outcome variable was subfertility (time to pregnancy > or =12 months).

RESULTS

The prevalence and medians of serum IgA antibodies to Hsp60 and Hsp10 were significantly higher in the female partners of subfertile couple than in their fertile controls. On the contrary, among male partners of subfertile couple, especially among smokers serum antibody levels to Hsp antigens were lower than in the controls.

CONCLUSION

The results indicate a serological association of antibodies to chlamydial Hsp antigens with female subfertility in a population-based sample.

Mass treatment with single-dose azithromycin for trachoma

BACKGROUND

Trachoma, caused by repeated ocular infection with Chlamydia trachomatis, is an important cause of blindness. Current recommended dosing intervals for mass azithromycin treatment for trachoma are based on a mathematical model.

METHODS

We collected conjunctival swabs for quantitative polymerase-chain-reaction assay of C. trachomatis before and 2, 6, 12, 18, and 24 months after mass treatment with azithromycin in a Tanzanian community in which trachoma was endemic. For ethical reasons, at 6, 12, and 18 months, we gave tetracycline eye ointment to residents who had clinically active trachoma.

RESULTS

At baseline, 956 of 978 residents (97.8 percent) received either one oral dose of azithromycin or (if azithromycin was contraindicated) a course of tetracycline eye ointment. The prevalence of infection fell from 9.5 percent before mass treatment to 2.1 percent at 2 months and 0.1 percent at 24 months. The quantitative burden of ocular C. trachomatis infection in the community was 13.9 percent of the pretreatment level at 2 months and 0.8 percent at 24 months. At each time point after baseline, over 90 percent of the total community burden of C. trachomatis infection was found among subjects who had been positive the previous time they were tested.

CONCLUSIONS

The prevalence and intensity of infection fell dramatically and remained low for two years after treatment. One round of very-high-coverage mass treatment with azithromycin, perhaps aided by subsequent periodic use of tetracycline eye ointment for persons with active disease, can interrupt the transmission of ocular C. trachomatis infection.

Diagnosis and assessment of trachoma

Trachoma is caused by Chlamydia trachomatis. Clinical grading with the WHO simplified system can be highly repeatable provided graders are adequately trained and standardized. At the community level, rapid assessments are useful for confirming the absence of trachoma but do not determine the magnitude of the problem in communities where trachoma is present. New rapid assessment protocols incorporating techniques for obtaining representative population samples (without census preparation) may give better estimates of the prevalence of clinical trachoma. Clinical findings do not necessarily indicate the presence or absence of C. trachomatis infection, particularly as disease prevalence falls. The prevalence of ocular C. trachomatis infection (at the community level) is important because it is infection that is targeted when antibiotics are distributed in trachoma control campaigns. Methods to estimate infection prevalence are required. While culture is a sensitive test for the presence of viable organisms and nucleic acid amplification tests are sensitive and specific tools for the presence of chlamydial nucleic acids, the commercial assays presently available are all too expensive, too complex, or too unreliable for use in national programs. There is an urgent need for a rapid, reliable test for C. trachomatis to assist in measuring progress towards the elimination of trachoma.

Current problems of perinatal Chlamydia trachomatis infections

Chlamydia trachomatis has been recognized as a pathogen of trachoma, nongonococcal urethritis, salpingitis, endocervicitis, pelvic inflammatory disease, inclusion conjunctivitis of neonates, follicular conjunctivitis of adults, infantile pneumonia and associated conditions. Chlamydial infections during pregnancy may also cause a variety of perinatal complications. Different antigenic strains of C. trachomatis from endocervical, nasopharyngeal and conjunctival origins have been associated with different clinical conditions. Control programs emphasizing early diagnosis, targeted screening, and effective treatment will lead to an eventual decline in the incidence of perinatal chlamydial infection. This review focuses on current problems of perinatal C. trachomatis infections in the aspects of microbiological and immunological pathogenesis.

The possibility of eliminating blinding trachoma

Global elimination of blinding trachoma, the world's leading preventable cause of blindness, now seems possible. The disease, which persists most severely in the poorest parts of Africa and Asia, is already eliminated in North America and Europe. On a scientific basis, the case for elimination was outlined at a WHO global scientific meeting in 1996. To facilitate action, WHO founded the Alliance for Global Elimination of Trachoma by 2020 (GET 2020) in 1997. In 1998 a World Health Assembly resolution called for member states to take steps to eliminate blinding trachoma by 2020 using the WHO recommended SAFE strategy (surgery of late stage disease, antibiotics for acute infection, and improved facial hygiene and environmental change-ie, improved access to water and sanitation). These developments contributed to the decision by Pfizer Inc to donate azithromycin in support of national programmes implementing SAFE and, with the Edna McConnell Clark Foundation, to found the International Trachoma Initiative as a charity dedicated to the elimination of blinding trachoma by 2020. Reports of the early programme scope and impact are encouraging. In ten national programmes currently underway (constituting about 50% of the global burden) more than 55,000 lid surgeries have halted further corneal damage and prevented blindness, and more than 6 million treatments with azithromycin have been given with reductions in acute infections of around 50% in children. Morocco, one of the first countries to implement SAFE with azithromycin, has achieved remarkable results and expects to eliminate blinding trachoma by 2005. If political will and public-health support can be mobilised, the goal of eliminating this cause of blindness can become a reality by 2020.