General characteristics of the pathogen
Chlamydia trachomatis can affect various body systems: the visual and respiratory tracts, as well as the urogenital system. An important pathogenetic feature of the microorganism is its ability to persist in the host organism for a long time. This infection causes allergic and immune alterations (e.g., triggering Reiter's syndrome).
A distinct biological marker of this chlamydial species is the ability to accumulate glycogen within specific cellular inclusions.
Serovar classification
To date, 20 serovars of C. trachomatis are known, which are divided into three clinical groups:
- "Ocular" serovars (A, B, Ba, C): directly cause trachoma.
- "Genital" serovars (D, Da, E, F, G, H, I, Ia, J, Ja, K): there are 11 of them; they are responsible for urogenital chlamydia (nongonococcal urethritis) and can cause extragenital complications, including Reiter's disease.
- Lymphogranuloma venereum serovars (L1, L2, L2a, L2b, L3): are the causative agents of lymphogranuloma venereum.
Infection epidemiology
Trachoma is a strict anthroponosis, meaning the source of infection is exclusively human.
Transmission occurs via the contact-household route through dirty hands and objects coming into contact with the face. Susceptibility to the infection is extremely high, and children are the main risk group. The disease is characterized by the formation of family foci.
Trachoma is endemic to states with hot climates (Africa, Asia, South and Central America), where low hygiene standards serve as a risk factor. More than 400 million people are infected worldwide, of whom 10–20 million suffer from severe consequences up to and including blindness. Only sporadic imported cases are recorded in Russia.
Pathogenesis and clinical presentation
The pathogen invades the corneal and conjunctival epithelium, multiplying inside cells and destroying them.
Follicular keratoconjunctivitis develops (in most cases bilateral). Morphologically, this manifests as the formation of specific lymphoid follicles—trachomatous granules—in the subepithelial tissue. In later stages, the conjunctiva acquires a bumpy appearance resembling "cooked sago" (hence the disease name from the Greek trachys — rough).
The disease often starts in early childhood and progresses slowly over years. The ultimate outcome is the replacement of tissue with fibrous scar tissue and vision loss.
Immunity is not formed after a past infection. Reinfections are common, and recurrent infections are significantly more severe than primary ones.
Microbiological diagnostics and treatment
The material for examination is a conjunctival scraping.
Main diagnostic methods:
- Microscopy: Romanowsky–Giemsa staining allows the detection of Halberstaedter–Prowazek bodies—purple inclusions with a red center located near the nucleus in the cytoplasm of epithelial cells.
- Antigen tests: enzyme-linked immunosorbent assay (ELISA) and direct immunofluorescence assay (DFA) are used.
- Culture method: rarely used (inoculation of cell cultures or chicken embryos).
Serological methods are uninformative due to low antigenic load during a localized process.
Treatment includes antibiotic therapy (tetracycline group drugs) and the use of immunomodulators (interferons). Specific prophylaxis (a vaccine) is absent, so adherence to personal hygiene remains the primary measure.
Briefly: answers to topical questions
What joint complications does Chlamydia trachomatis cause?
Chlamydia trachomatis causes extragenital autoimmune joint complications in the form of Reiter's disease (syndrome) and probable reactive arthritis.
- Reiter's disease is urethrocoxosynovial syndrome, including combined involvement of joints, urethra, and eyes. It develops due to an autoimmune process and molecular mimicry: the chlamydial heat shock protein (HSP) is similar to human proteins, which triggers an immune attack on the body's own tissues.
- Probable reactive arthritis is a form of the disease manifesting as asymmetric involvement of the lower extremity joints without classic extra-articular symptoms.
Additionally, joint involvement can result from hematogenous dissemination, where the pathogen is phagocytosed by monocytes, carried via the bloodstream, and settles in tissues, causing multifocal lesions.
The phrase "TRI eyes" will help you remember the trachoma pathogen: TRAchoma — Due to chlamydia, causes Infection And Blindness.
Class and exam questions
Who discovered the trachoma pathogen?
The pathogen was discovered in 1907 by S. Prowazek and L. Halberstaedter upon detecting specific intracellular inclusions in corneal cells.
Is immunity formed after having trachoma?
No, post-infection immunity is not formed. Reinfections are possible and run a more severe course.
Why is serological diagnosis not used in trachoma?
The serological method is uninformative because the infection is localized and does not create sufficient antigenic load to produce a high antibody titer.
What else to study on this topic
- Mechanisms of intracellular chlamydial persistence
- Pathogenesis of trachomatous follicle formation
- Differences between ocular and genital serovars of Chlamydia trachomatis
- Principles of Romanowsky–Giemsa staining for chlamydia detection
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