1. Chlamydia

Introduction
1. Obligate intracellular bacteria
2. C. trachomatis leading preventable cause of blindness
3. C. pneumoniae causes respiratory tract infections
4. C. psittaci causes pneumonia, arthritis, and sepsis
Encounter: sexually transmitted and vertical transmission
Entry: extracellular form (elementary body - EB) binds receptors on epithelial cells and endocytosed into intracellular vacuole
Spread/Multiplication: exits the cell in a reproductive form (reticulate body - RB) and replicates by fission
1. RB replicates within the vacuole to form new RBs
2. Later in infection, RBs redifferentiate into EBs, which then infect more cells
Damage and clinical manifestations: all species can cause arthritis
1. C. trachomatis
  1. types A-C: conjunctivitis and trachoma
  2. types D-K: urethritis, epididymitis, prostatitis, proctitis, cervicitis, endometritis, salpingitis, PID, ectopic pregnancy, infertility, infant conjunctivitis and pneumonia
  3. types L1-3: lymphgranuloma venereum
2. C. pneumonia: pneumonia, upper respiratory disease, cardiovascular disease
3. C. psittaci: abortion, heart tissue damage, psittacosis (flu-like)
Virulence Factors
1. Binds epithelial cells
2. Prevents phagosome-lysosome fusion mediated by Type III secretion system
3. Host immune response responsible for inflammation and scarring
Diagnosis/Identification
1. PCR and ligase chain reaction (LCR)
2. Fluorescent antibody staining and ELISA
Treatment/Prevention
1. RB form is metabolically active and therefore target of therapy
2. Drugs that enter host cells: tetracyclines, macrolides, and sulfonamides
3. Treat sexual partners
4. Concomitant gonorrheal treatment
5. Erythromycin eye drops for conjunctivitis and trachoma
6. Resistance is not a problem
Outcome: normally good prognosis, but can cause PID, infertility, and blindness

2. Rickettsia

Obligate intracellular pathogen
Encounter: transmitted by arthropod vector
1. R. rickettsii: dog ticks
2. R. typhi: fleas
3. R. prowazekii: louse feces
Entry: inoculated into skin over 6-24 hours and has a strong tropism for endothelial cells, inside which the bacteria escape from the phagosome into the cytosol
Spread/Multiplication: replicate within cytoplasm and have no extracellular phase
Damage and clinical manifestations
1. Rocky Mountain Spotted Fever (RMSF): fever, rash, andhistory of tick bite
  1. pinpoint hemorrhages may lead to encephalitis, cardiac arrhythmia, nausea, vomiting, and abdominal pain
2. Typhus group fevers: similar to RMSF
3. Query fever caused by C. burnetii
  1. transmitted as aerosol or through animal vectors
  2. forms spores and potential biowarfare agent
  3. varies from actue pneumonia to chronic endocarditis
  4. resembles flu, with fever, atypical pneumonia, or granulomatous hepatitis
4. Monocytic ehrlichiosis caused by Ehrlichia chaffeensis
  1. transmitted by Lone Star tick
  2. similar to RMSF and characterized by fever, headache, and multisystem involvement
5. Human granulocytic ehrlichiosis caused by E. equi
  1. transmitted by Lyme disease tick
  2. similar symptoms as monocytic ehrlichiosis
Virulence Factor
1. Phospholipase A: responsible for RBC vacuole rupture and release of R. rickettsii into the cytosol
2. Interact with actin to allow insertion into adjacent cells
Treatment/Prevention
1. Prevention with tick-repellent and adequate clothing
2. Responds well to doxycycline, tetracycline, or chloramphenicol
  1. sulfonamides exacerbate illness
  2. penicillins and aminoglycosides do not affect the course of illness
Outcome
1. Without treatment, 75% of patients survive due to host immune response
2. Risk factors for worse prognosis: males, elderly, alcohol abusers, and immuno- compromised patients

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