General Characteristics of the Pathogen
Chlamydia trachomatis can infect various organ systems, including the visual, respiratory, and urogenital tracts. A key pathogenetic feature of the microorganism is its ability to persist long-term within the host organism. This infection causes allergic and immune alterations (e.g., triggering Reiter's syndrome).
A distinctive biological marker of this chlamydial species is its ability to accumulate glycogen inside specific cellular inclusions.
Serovar Classification
Currently, 20 serovars of C. trachomatis are known, 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): 11 serovars responsible for urogenital chlamydia (non-gonococcal urethritis) and capable of causing extragenital complications, including Reiter's syndrome.
- Lymphogranuloma venereum serovars (L1, L2, L2a, L2b, L3): cause lymphogranuloma venereum.
Infection Epidemiology
Trachoma is a strict anthroponosis, meaning humans are the sole source of infection.
Transmission occurs via direct and indirect contact through contaminated hands and items contacting the face. Susceptibility to infection is extremely high, with children being the primary risk group. Familial clustering is characteristic of the disease.
Trachoma is endemic to states with hot climates (Africa, Asia, South and Central America), where low hygiene standards serve as a risk factor. Worldwide, over 400 million people are infected, of whom 10–20 million suffer severe consequences up to blindness. Only sporadic imported cases are reported in developed countries.
Pathogenesis and Clinical Presentation
The pathogen invades the corneal and conjunctival epithelium, multiplying intracellularly and destroying the host cells.
Follicular keratoconjunctivitis develops (bilateral in most cases). Morphologically, this manifests as the formation of specific lymphoid follicles—trachomatous granules—in the subepithelial tissue. In late stages, the conjunctiva acquires a bumpy appearance resembling "cooked sago" (hence the disease name from Greek trachys — rough).
The disease frequently starts in early childhood and progresses slowly over years. The ultimate outcome is replacement of tissues with fibrous scar tissue and loss of vision.
Immunity is not established after recovering from the infection. Re-infections are common, and repeated infections run a significantly more severe course than primary ones.
Microbiological Diagnosis and Treatment
Conjunctival scrapings serve as the specimen for testing.
Main diagnostic methods:
- Microscopy: Giemsa staining reveals 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 fluorescent antibody (DFA) tests.
- Culture method: Rarely used (inoculation of cell cultures or chicken embryos).
Serological methods are uninformative due to weak antigenic load in localized disease.
Treatment includes antibiotic therapy (tetracyclines) and immunomodulators (interferons). Specific prophylaxis (a vaccine) is unavailable, making personal hygiene the primary preventive measure.