Chlamydiae are obligate intracellular bacteria, possess both DNA and RNA (a characteristic that distinguishes them from viruses), and have a cell wall similar to that of gram-negative bacteria.
These organisms have a complex reproductive cycle and exist in two forms.
– The elementary body (the infective form) is adapted for extracellular survival, while the reticulate body is adapted for intracellular survival and multiplication.
– Within 18–24 h after infection of the cell, reticulate bodies have replicated and begun to condense into elementary bodies that are released to infect other cells or people.
Three chlamydial species infect humans: Chlamydia trachomatis, C. psittaci, and C. pneumoniae.
– CF tests and enzyme immunoassays that detect lipopolysaccharide identify chlamydiae only to the genus level.
– The microimmunofluorescence (MIF) test can differentiate among the three species.
– For a discussion of C. pneumoniae, see Chap. 100.
C. TRACHOMATIS INFECTIONS
GENITAL INFECTIONS, INCLUDING LYMPHOGRANULOMA VENEREUM
TRACHOMA AND ADULT INCLUSION CONJUNCTIVITIS (AIC)
Trachoma is a chronic conjunctivitis caused by C. trachomatis serovars A, B, Ba, and C. Transmission occurs through contact with ocular discharge from infected pts, which is sometimes transferred by flies.
AIC is an acute eye infection occurring in adults exposed to infected genital secretions and in their newborns. This infection is caused by sexually transmitted C. trachomatis strains, usually serovars D–K.
Trachoma is a leading cause of preventable infectious blindness, with ∼6 million pts having been affected. In the hyperendemic regions of northern and sub-Saharan Africa, the Middle East, and parts of Asia, the prevalence of trachoma is ∼100% by the third year of life. Reinfection and persistent infection are common.
Both trachoma and AIC present clinically as conjunctivitis characterized by small lymphoid follicles in the conjunctiva; trachoma usually starts insidiously before 2 years of age.
With progression of trachoma, there is inflammatory leukocytic infiltration and superficial vascularization (pannus formation) of the cornea.
– Scarring eventually distorts the eyelids, turning lashes inward and abrading the eyeball (trichiasis and entropion).
– The corneal epithelium eventually ulcerates, with subsequent scarring and blindness.
– Destruction of goblet cells, lacrimal ducts, and glands causes dry-eye syndrome (xerosis), with resultant corneal opacity and secondary bacterial corneal ulcers.
AIC is an acute unilateral follicular conjunctivitis with preauricular lymphadenopathy and presents similarly to acute conjunctivitis due to adenovirus or HSV.
– Corneal inflammation is evidenced by discrete opacities, punctate epithelial erosions, and superficial corneal vascularization.
– Left untreated, the disease may persist for 6 weeks to 2 years.
Clinical diagnosis of trachoma is based on the presence of ...