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Chlamydiae are nonmotile, gram-negative, obligate intracellular bacteria. These organisms cannot produce energy and thus survive by acting as a parasite using the energy mechanics of their infected host; they all have biphasic cycles of replication. The elementary body that represents the “infectious” particle enters the host cell and lives within the host’s cytoplasmic inclusion particles. The organism then begins its secondary vegetative state known as the reticulate body and replicates by binary fission. Each inclusion body begins to form multiple progeny that will be extruded as new infectious elementary bodies to begin the cycle once again.

Some controversy exists as to whether chlamydiae should be split into 2 genera; this discussion will use the more commonly used nomenclature for the 3 recognized species that cause human disease: Chlamydophila psittaci, Chlamydophila pneumoniae, and Chlamydia trachomatis (Table 254-1). C psittaci is responsible for psittacosis (ornithosis). C pneumoniae causes pneumonia, pharyngitis, and bronchitis. C trachomatis has at least 15 different serotypes, known as serovars, that are associated with a spectrum of diseases. Serovars A to C are associated with trachoma, D to K with genital infections, and L1 to L3 with lymphogranuloma venereum. The most common infections of C trachomatis are those of the genital tract, which present as urethritis and epididymitis in the male and cervicitis and salpingitis in the female. Neonates can present with conjunctivitis and pneumonia acquired by passage through an infected mother’s genital tract.



C psittaci causes psittacosis, also known as ornithosis. Psittacosis is contracted by humans from infected birds and their contaminated droppings. All birds, including pet birds (parrots, parakeets, macaws, and cockatiels) and poultry (turkeys, ducks, chickens, and other fowl), are most frequently involved in transmission to humans; however, mammals such as sheep, cattle, goats, and cats have also been shown to transmit infection to humans. The birds show a spectrum of disease that ranges from no evidence of illness to the severely ill. Birds transmit the disease to humans by the respiratory route from feces, fecal dust, or secretions of infected animals. The incidence among poultry workers, pet shop workers, and exotic bird importers can be high. Since 1996, the US Centers for Disease Control and Prevention (CDC) reports around 50 cases a year. This is likely an underestimate because C psittaci is difficult to diagnose and may not be considered in a differential diagnosis. Person-to-person transmission also is possible, and healthcare personnel can acquire the disease from patients. Children infrequently acquire the disease, perhaps because they are less likely to ...

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