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The name chlamydiae is derived from the Greek word “chlamys” representing the cloak-like mantle worn by men in Ancient Greece.1 Upon initial discovery, chlamydiae were thought to be intracellular pathogens that cloaked the nucleus of an infected cell. Scientists have since discovered that chlamydiae are nonmotile, gram-negative, obligatory intracellular bacteria. These organisms cannot produce energy and thus survive by acting as a parasite using the energy mechanics of its infected host. The appearance of the cloak is now known to represent the host’s cytoplasmic vesicle with numerous individual chlamydia organisms inside.

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The four recognized species within the genus of Chlamydia are C psittaci, C pneumoniae, and C trachomatis, all of which cause disease in humans (Table 259-1), and C pecorum which causes disease in pigs, sheep, and cattle, but not in humans.1Chlamydia psittaci is responsible for psittacosis (ornithosis). Chlamydia pneumoniae causes pneumonia, pharyngitis, and bronchitis. Chlamydia 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 infection acquired by passage through an infected mother’s genital tract.

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Table 259-1. Chlamydial Infections in Humans 
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Chlamydiae all have biphasic cycles of replication.1 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.

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Chlamydia psittaci or the new proposed name Chlamydophila psittaci is an obligate intracellular, gram-negative bacterium.2 The pathogen causes psittacosis which is also referred to as ornithosis. Psittacosis is contracted by human beings 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.2-8 The birds show a spectrum of disease as they can have no evidence of disease or could appear ill and die. Birds transmit the disease to humans by the respiratory route from feces, fecal dust, ...

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