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Chlamydiae and Chlamydia-Like Infections

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A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Medical Microbiology".

Deadline for manuscript submissions: closed (30 April 2026) | Viewed by 30350

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Prof. Dr. Servaas A. Morré

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Institute for Public Health Genomics (IPHG), Department of Genetics and Cell Biology, Research Institute GROW, Faculty of Health, Medicine & Life Sciences, University of Maastricht, 4-6, 6211 LK Maastricht, The Netherlands
Interests: epidemiology; diagnostics; immunogenetics; infectious diseases; valorization and translation; Chlamydia trachomatis
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Dr. Stephan Verweij

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Department of Pulmonology, St. Antonius Hospital, Koekoekslaan 1, 3435 CM Nieuwegein, The Netherlands
Interests: Chlamydia; Chlamydia trachomatis infections; infectious disease; immunogenetics; pulmonary infection; lung transplantation

Special Issue Information

Dear Colleagues,

Members of the Chlamydiales order are remarkably diverse, and include species pathogenic for humans, animals and the environment. Human-pathogenic species generally cause ocular, pulmonary or urogenital infection, and due to the mostly asymptomatic clinical presentation cause major morbidity due to the development of late sequelae, which is especially the case for Chlamydia trachomatis. Several species infecting animals have zoonotic potential and thus pose a risk for public health. The incidence of infection among both humans and animals remains high, warranting an integrated scientific and clinical approach for aiding in the development of primary preventive measures.

This Special Issue will gather relevant studies ranging from basic research to translational, clinical or epidemiological studies, in relation to human ocular, pulmonary and urogenital Chlamydiae and Chlamydia-like infection, as well as animal infections and zoonotic infections. We invite you to submit your contribution to this Special Issue (original research papers, reviews, case reports/case series, valorization studies, policy manuscripts, or large funded study designs) to further our understanding of Chlamydiae and Chlamydia-like infections in humans, animals and the environment.

Prof. Dr. Servaas A. Morré
Dr. Stephan Verweij
Guest Editors

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Keywords

Chlamydiales
Chlamydia infection
molecular and cell biology
genetics and genomics
host–pathogen interaction
diagnostics
vaccine development
epidemiology
prevention and policy
zoonosis
Chlamydia-like
model systems to study Chlamydiae and Chlamydia-like infections

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Published Papers (8 papers)

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Research

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12 pages, 692 KB

Open AccessArticle

High Burden of Chlamydia trachomatis and Human Papillomavirus Infections in Low-Income Female University Students from Public Schools in the Brazilian Amazon

by Leonardo Miranda dos Santos, Rodrigo Covre Vieira, Louise de Souza Canto Covre, Milena Cristina Martins da Silva, Thiago de Matos Bezerra, Geraldo Mariano Moraes de Macedo, Edna Aoba Yassui Ishikawa, Karla Valéria Batista Lima, Maísa Silva de Sousa and Rodrigo Vellasco Duarte Silvestre

Microorganisms 2026, 14(6), 1176; https://doi.org/10.3390/microorganisms14061176 - 23 May 2026

Viewed by 459

Abstract

Sexually transmitted infections (STIs) caused by C. trachomatis and HPV are the most prevalent worldwide. College students are characterized by being young women of reproductive age who may have risky sexual behavior. To describe the prevalence and factors associated with endocervical infection by C. trachomatis and HPV in college women in the Brazilian Amazon. Endocervical secretions were collected. The ompA gene of C. trachomatis and the L1 gene of HPV were detected. The Chi-square test, Fisher’s exact test, G test, Odds Ratio, and Multiple Logistic Regression were used with 95% confidence interval and p ≤ 0.05. The overall prevalence of endocervical infection by C. trachomatis was 8.3% (25/302) and by HPV was 28.9% (87/302). Low income was associated with sexually transmitted infection by C. trachomatis (14.8%, p = 0.0336). Those under 25 years old had twice the chance of HPV infection [39.3%, (OR: 2.6989), 95% CI: 1.6054–4.5371, p = 0.0002], as did women without children [31.8%, (OR: 2.333), CI: 1.1235–4.8461, p = 0.0307]. Women who did not study in a public school had 63% reduced risk of acquiring HPV infection [45.8% (OR: 0.3713), CI: 0.1951–0.7064, p = 0.0035]. C. trachomatis and HPV infections were present in low-income, childless young women who attended public schools, requiring the intensification of STI prevention policies in the Amazon region. Full article

(This article belongs to the Special Issue Chlamydiae and Chlamydia-Like Infections)

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19 pages, 1160 KB

Open AccessArticle

Prevalence and Tetracycline Susceptibility of Chlamydia suis in Different Intestinal Sections of Pigs from Commercial Farms

by Margaux Verhaeghe, Charlotte De Bruyne, Anne De Meyst, Toon Rombouts, Jeroen Degroote, Bert Devriendt and Daisy Vanrompay

Microorganisms 2026, 14(2), 361; https://doi.org/10.3390/microorganisms14020361 - 3 Feb 2026

Cited by 1 | Viewed by 564

Abstract

Chlamydia suis, a close relative of the human pathogen C. trachomatis, can be detected in the porcine gut, yet its prevalence and viability across intestinal segments remain poorly defined. This study aimed to assess the segment-specific prevalence, isolation success, and tetracycline susceptibility of C. suis in grower-finisher pigs. Jejunal, ileal, and colonic samples (n = 200 per intestinal segment) were collected from 600 pigs at slaughter and analyzed using C. suis-specific real-time PCR and culture. PCR revealed significantly higher detection rates in the colon (40%) than in the jejunum or ileum (both 4.5%), accompanied by significantly higher calculated bacterial loads in colonic samples. In contrast, viable C. suis was most frequently isolated from ileal material, indicating that the ileum may provide a more favorable condition for active bacterial replication. Among 24 culture-confirmed isolates, 75% were susceptible to tetracycline (MIC/MBC < 2 µg/mL), 12.5% exhibited an intermediate phenotype (2 µg/mL < MIC/MBC < 4 µg/mL) and another 12.5% were resistant (MIC/MBC > 4 µg/mL). Intermediate phenotypes were recovered from the jejunum and ileum, whereas resistant isolates were found in the ileum and colon. These findings suggest that the porcine colon may serve as an intestinal reservoir for C. suis, while the ileum supports more robust bacterial replication. Overall, these data contribute to our understanding of the intestinal ecology of C. suis under field conditions and its tetracycline susceptible patterns. Full article

(This article belongs to the Special Issue Chlamydiae and Chlamydia-Like Infections)

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11 pages, 264 KB

Open AccessArticle

Characteristics and Clinical Predictors of Chlamydia trachomatis Infections Sustained by LGV Serovars Among Men Who Have Sex with Men

by Alessia Siribelli, Angelo Roberto Raccagni, Sara Diotallevi, Riccardo Lolatto, Francesca Alberton, Emanuela Messina, Michela Sampaolo, Nicola Clementi, Roberto Burioni, Antonella Castagna and Silvia Nozza

Microorganisms 2026, 14(2), 262; https://doi.org/10.3390/microorganisms14020262 - 23 Jan 2026

Cited by 1 | Viewed by 1225

Abstract

This study aims to explore characteristics and clinical predictors of Lymphogranuloma venereum (LGV) and non-LGV Chlamydia trachomatis (Ct) serovars. We conducted a retrospective study on men who have sex with men (MSM) diagnosed with rectal or urethral Ct between 2015 and 2022 at the Infectious Diseases Unit of San Raffaele Scientific Institute, Milan, Italy. Nucleic acid amplification test with sequencing was used for Ct serovar determination. Individuals’ characteristics were described by median (interquartile, IQR) or frequency (%) and compared using Kruskal–Wallis or Chi-Square tests, as appropriate. Logistic regression model was used to identify predictors of LGV; multinomial logistic regression model, with LGV group as reference category, investigated factors associated with the LGV group (serovars L1, L2B, L2C), specific highly prevalent non-LGV serovars (D, E, G) or the non-amplifiable group. Overall, 211 MSM were included: 29.8% with LGV, 50.2% non-LGV and 19.9% non-amplifiable. Symptomatic cases were 46% of which 48% LGV; rectal infection was the most common (86%), followed by urethral (10%) and both sites (4%). People living with HIV were 91.5%; 31.3% had ≥1 concomitant STI and 65.4% ≥1 previous one. According to logistic regression analysis, after adjustment for the diagnosis of ≥1 concomitant and previous STI, LGV serovars were significantly associated with symptomatic infections (adjusted odds ratio, aOR = 6.05; 95%CI = 2.92, 13.13; p < 0.001) and anorectal site (aOR = 17.12; 95%CI = 3.17–319.17, p = 0.007) compared to non-LGV. Among MSM, almost 30% of Ct infections were due to LGV serovars. Presence of symptoms and anorectal site involvement, identified as clinical predictors of LGV, should guide clinicians during diagnosis. Full article

(This article belongs to the Special Issue Chlamydiae and Chlamydia-Like Infections)

10 pages, 789 KB

Open AccessCommunication

Female Sex Workers in the Amazon Region of Brazil Are at High Risk of Chlamydia trachomatis Infection: A Retrospective Study

by Leonardo Gabriel Campelo Pinto de Figueiredo, Paula do Socorro de Oliveira da Costa Laurindo, Daniela Assunção Pantoja, Maurimélia Mesquita da Costa, Diogo Oliveira de Araújo, Felipe Bonfim Freitas, Jacqueline Cortinhas Monteiro, Ricardo Roberto de Souza Fonseca, Rosimar Neris Martins Feitosa, Rogério Valois Laurentino, Leonardo Miranda dos Santos, Aldemir Branco Oliveira-Filho and Luiz Fernando Almeida Machado

Microorganisms 2025, 13(8), 1815; https://doi.org/10.3390/microorganisms13081815 - 3 Aug 2025

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Abstract

Background: Chlamydia trachomatis is the most prevalent bacterial sexually transmitted infection (STI) globally, linked to severe complications such as pelvic inflammatory disease and infertility. In the Brazilian Amazon, socioeconomic vulnerability and the absence of screening policies exacerbate risks, particularly among female sex workers (FSWs). Objective: This study aimed to determine the seroprevalence of anti-C. trachomatis IgG antibodies among FSWs in five municipalities of Pará State, Brazilian Amazon, and identify epidemiological factors associated with infection. Methods: A retrospective cross-sectional study (2005–2007) included 348 FSWs recruited via convenience sampling. Sociodemographic and behavioral data were collected through questionnaires, and blood samples were analyzed by ELISA for anti-C. trachomatis IgG. Statistical analyses included Fisher’s exact tests, odds ratios (ORs), and 95% confidence intervals (CIs), using SPSS 21.0. Results: Overall seroprevalence was 93.9% (327/348; 95% CI: 83.1–90%). Significant associations included a household income of 1–3 minimum wages (98.4%; p = 0.0002), sexual partners from the same region (98.8%; p = 0.0421), and age >42 years (96.3%). Most reported inconsistent condom use (43.7%), multiple monthly partners (54.6%), and illicit drug use (53.4%). Discussion: The extremely high seroprevalence reflects chronic C. trachomatis exposure, driven by socioeconomic deprivation and limited healthcare access. Comparisons with global data underscore the urgent need for screening policies, absent in Brazil for FSWs, and highlight the vulnerability of this population. Conclusions: The findings reveal an alarming burden of C. trachomatis exposure among Amazonian FSWs. Integrated strategies, including routine screening, sexual health education, and inclusion of FSWs in priority health programs, are critical to reduce transmission and associated complications. Full article

(This article belongs to the Special Issue Chlamydiae and Chlamydia-Like Infections)

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12 pages, 877 KB

Open AccessArticle

Clinically Defined Lymphogranuloma Venereum among US Veterans with Human Immunodeficiency Virus, 2016–2023

by Gina Oda, Joyce Chung, Cynthia Lucero-Obusan and Mark Holodniy

Microorganisms 2024, 12(7), 1327; https://doi.org/10.3390/microorganisms12071327 - 29 Jun 2024

Cited by 1 | Viewed by 2980

Abstract

We applied lymphogranuloma venereum (LGV) clinical case criteria to a cohort of 1381 Veterans positive for HIV and Chlamydia trachomatis (CT) from 2016 from 2023 and analyzed variables to ascertain risk factors for LGV and factors associated with the use of standard treatment regimens. In total, 284/1381 (20.6%) met the criteria for LGV. A total of 179/284 (63%) were probable cases, and 105/284 (37%) were possible cases (those meeting clinical criteria but with concurrent sexually transmitted infections (STI) associated with LGV-like symptoms). None had confirmatory CT L1–L3 testing. A total of 230 LGV cases (81%) presented with proctitis, 71 (25%) with ulcers, and 57 (20.1%) with lymphadenopathy. In total, 66 (23.2%) patients had >1 symptom of LGV. A total of 43 (15%) LGV cases were hospitalized. Primary risk factors for LGV were male birth sex (p = 0.004), men who have sex with men (p < 0.001), and the presence of STIs other than gonorrhea or syphilis (p = 0.011). In total, 124/284 (43.7%) LGV cases received standard recommended treatment regimens. Probable cases were more likely to receive standard treatment than possible cases (p = 0.003). We report that 20.6% of CT cases met clinical criteria for LGV among HIV-infected Veterans and that less than half of cases received recommended treatment regimens, indicating that LGV is likely underestimated and inadequately treated among this US population. Full article

(This article belongs to the Special Issue Chlamydiae and Chlamydia-Like Infections)

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8 pages, 245 KB

Open AccessCommunication

Challenges in Chlamydial Serology: Insights from a Belgian and a Dutch Population Cohort

by Anne De Meyst, Zoïe Alexiou, Tinne Lernout, Servaas A. Morré and Daisy Vanrompay

Microorganisms 2024, 12(4), 658; https://doi.org/10.3390/microorganisms12040658 - 26 Mar 2024

Cited by 3 | Viewed by 2145

Abstract

Serology routinely serves as a diagnostic tool to confirm Chlamydia infections in humans. Particularly in delayed settings, such as post-outbreak scenarios where the acute phase of infection has subsided, serology is invaluable. Multiple studies, nonetheless, indicate deficiencies in specificity and sensitivity of current chlamydial antibody detection assays. Incorporation of multiple antigens per target is known to improve the accuracy of chlamydial serological assays. We, therefore, used the recomLine test (Mikrogen diagnostics) on serological samples of two cohorts, as it is the only commercially available test allowing detection of antibodies against three human pathogenic Chlamydia species (C. trachomatis, C. pneumoniae and C. psittaci) using multiple antigens per target. The first cohort (n = 156; samples collected between 2008 and 2022 during a C. trachomatis screening initiative) comprised women from the Netherlands (NL) with past exposure to C. trachomatis, while the second cohort (n = 44; samples collected in 2018 in a health examination survey) consisted of Belgian citizens (BE) with occupational or recreational exposure to chickens, representing a risk population for C. psittaci. The test indicated a statistically equivalent C. pneumoniae seroprevalence in both cohorts (39.10% in NL and 34.09% in BE; p = 0.337). As expected C. trachomatis seroprevalence was significantly higher (p < 0.001) in the Dutch cohort (48.72%), as compared to the Belgian cohort (4.55%). Lastly, C. psittaci seroprevalence did not significantly differ between the two groups (2.27% in BE and 1.92% in NL; p = 0.633), even though a higher prevalence was expected for the Belgian cohort. This prompts us to question whether the Belgian cohort truly constituted a C. psittaci risk population or whether the recomLine test is susceptible to cross-reaction of species-specific antibodies, thereby increasing C. psittaci prevalence in the Dutch cohort. We advocate for the development of affordable, highly sensitive antibody detection assays that can effectively distinguish between chlamydial species, addressing the increasing demand for enhanced serological testing methodologies. Full article

(This article belongs to the Special Issue Chlamydiae and Chlamydia-Like Infections)

Review

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21 pages, 1525 KB

Open AccessReview

Study Models for Chlamydia trachomatis Infection of the Female Reproductive Tract

by Jaehyeon Kim, Milena Ślęczkowska, Beatriz Nobre and Paul Wieringa

Microorganisms 2025, 13(3), 553; https://doi.org/10.3390/microorganisms13030553 - 28 Feb 2025

Cited by 4 | Viewed by 6785

Abstract

Chlamydia trachomatis (Ct) is a leading cause of sexually transmitted infections globally, often resulting in inflammatory disorders, ectopic pregnancies, and infertility. Studying Ct’s pathogenesis remains challenging due to its unique life cycle and host-specific interactions, which require diverse experimental models. Animal studies using mouse, guinea pig, pig, and non-human primate models provide valuable insights into immune responses, hormonal influences, and disease progression. However, they face limitations in terms of translational relevance due to physiological differences, as well as ethical concerns. Complementing these, in vitro systems, ranging from simple monolayer to advanced three-dimensional models, exhibit improved physiological relevance by replicating the human tissue architecture. This includes the detailed investigation of epithelial barrier disruptions, epithelium–stroma interactions, and immune responses at a cellular level. Nonetheless, in vitro models fall short in mimicking the intricate tissue structures found in vivo and, therefore, cannot faithfully replicate the host–pathogen interactions or infection dynamics observed in living organisms. This review presents a comprehensive overview of the in vivo and in vitro models employed over the past few decades to investigate Ct and its pathogenesis, addressing their strengths and limitations. Furthermore, we explore emerging technologies, including organ-on-chip and in silico models, as promising tools to overcome the existing challenges and refine our understanding of Ct infections. Full article

(This article belongs to the Special Issue Chlamydiae and Chlamydia-Like Infections)

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14 pages, 1088 KB

Open AccessReview

Deciphering the Puzzle: Literature Insights on Chlamydia trachomatis-Mediated Tumorigenesis, Paving the Way for Future Research

by Rafaela Rodrigues, Carlos Sousa and Nuno Vale

Microorganisms 2024, 12(6), 1126; https://doi.org/10.3390/microorganisms12061126 - 31 May 2024

Cited by 5 | Viewed by 2636

Abstract

Some infectious agents have the potential to cause specific modifications in the cellular microenvironment that could be propitious to the carcinogenesis process. Currently, there are specific viruses and bacteria, such as human papillomavirus (HPV) and Helicobacter pylori, that are well established as risk factors for neoplasia. Chlamydia trachomatis (CT) infections are one of the most common bacterial sexually transmitted infections worldwide, and recent European data confirmed a continuous rise across Europe. The infection is often asymptomatic in both sexes, requiring a screening program for early detection. Notwithstanding, not all countries in Europe have it. Chlamydia trachomatis can cause chronic and persistent infections, resulting in inflammation, and there are plausible biological mechanisms that link the genital infection with tumorigenesis. Herein, we aimed to understand the epidemiological and biological plausibility of CT genital infections causing endometrial, ovarian, and cervical tumors. Also, we covered some of the best suitable in vitro techniques that could be used to study this potential association. In addition, we defend the point of view of a personalized medicine strategy to treat those patients through the discovery of some biomarkers that could allow it. This review supports the need for the development of further fundamental studies in this area, in order to investigate and establish the role of chlamydial genital infections in oncogenesis. Full article

(This article belongs to the Special Issue Chlamydiae and Chlamydia-Like Infections)

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