Gram Negative: Chlamydia & Rickettsia Flashcards
What do Chlamydia and Rickettsia have in common? What’s the major difference between them?
- these are OBLIGATE intracellular parasites (they require the host’s ATP to fuel their own cellular activity; they pump in ATP and pump out ADP via an ATP/ADP translocator)
- Gram negative, pleomorphic
- very small (about the same size as a large virus)
- they cause different diseases; Chlamydia spreads via person-to-person contact, while Rickettsia requires an arthropod vector
Chlamydia and Rickettsia are both obligate intracellular parasites - how come they aren’t considered viruses?
- they aren’t viruses because they contain both DNA and RNA (viruses only contain one or the other), they are sensitive to antibiotics, and they create their own proteins (they just can’t create their own energy)
What type of cell does Chlamydia have a high affinity for? What are the two forms the organism exists in?
- Chlamydia has a high affinity for columnar epithelial cells that line mucous membranes
- it exists in 2 forms: an elementary body (EB) and initial body (IB)
- EB: a metabolically inactive, highly infectious particle that invades host cells
- IB: develops once inside the host cell, metabolically active, forms more EBs to spread infection
What are the major pathogenic species of Chlamydia? What disease does each cause?
- C. trachomatis: eyes (trachoma, inclusion conjunctivitis), genitals (urethritis, cervicitis, pelvic inflammatory disease, epididymitis), and lungs (infantile pneumonia)
- Chlamydophila psittaci and Chlamydophila pneuomoniae: lungs (atypical pneumonias)
What is trachoma? What is it the leading cause of?
- trachoma is a chronic infection of the conjunctiva via Chlamydia trachomatis
- it is the leading cause of preventable blindness
- blindness slowly develops over 10-15 years due to chronic scarring of the cornea
What is inclusion conjunctivitis? What other disease is it similar to? How can we prevent it?
- inclusion conjunctivitis is a conjunctival infection in neonates via Chlamydia trachomatis; presents 5-14 days after birth
- conjunctiva become inflamed, with a yellow purulent discharge and swelling of the eyelids
- very similar to ophthalmia neonatorum via Neisseria gonorrhoeae (usually presents 2-3 days after birth)
- prevent both by giving prophylactic neonatal erythromycin eyedrops
What is the most common STD? How do patients classically present? How do we treat this disease?
- urethritis via Chlamydia (nongonococcal urethritis; NGU) is the most common STD
- it is largely asymptomatic, but patients may present with dysuria and a mucoid discharge
- because NGU and gonococcal urethritis often occur together, treatment is empirical (penicillin or ceftriaxone for gonorrhea, doxycycline or azithromycin for chlamydia)
Why is Chlamydia resistant to penicillin?
- because it lacks a peptidoglycan layer!
- (this peptidoglycan layer is the target for penicillin)
What is cervicitis and pelvic inflammatory disease?
- cervicitis is inflammation of the cervix and can be caused by infection with Chlamydia trachomatis; cervix is red, swollen, tender, with a yellow purulent discharge
- the infection can ascend to involve the uterus, Fallopian tubes, and ovaries; this is known as pelvic inflammatory disease (PID); abnormal vaginal discharge/bleeding, pain with sex, nausea, vomiting, fever, and severe lower abdominal/pelvic pain and tenderness
What are some major complications of PID? What other organism besides Chlamydia trachomatis can cause PID?
- (PID: pelvic inflammatory disease)
- complications: infertility (occurs in 25% of patients!), ectopic pregnancy, chronic pelvic pain (complications are largely due to scarring of the Fallopian tubes), abscess formation, peritonitis, and peri-hepatitis (infection of the liver capsule, AKA Fitz-Hugh-Curtis syndrome)
- also caused by Neisseria gonorrhoeae
What is epididymitis?
- inflammation of the epididymis that can occur in men with urethritis via Chlamydia trachomatis
- presents with unilateral scrotal swelling, tenderness, pain, and fever
What other three diseases/syndromes is Chlamydia trachomatis also associated with?
- Reitier’s syndrome (conjunctivitis/uveitis, urethritis, and arthritis)
- Fitz-Hugh-Curtis syndrome (infection of liver capsule causing RUQ pain, also caused by N. gonorrhoeae)
- lymphogranuloma venereum (LGV; painless papule/ulceration of the genitals with spontaneous healing and followed by gradual regional lymph node involvement)
Which serotypes of Chlamydia trachomatis cause lymphogranuloma venereum? What are some of the major differentials of this disease?
- serotypes L1, L2, and L3 can cause LGV
- chancroid via Haemophilus ducreyi: painful genital ulcer with rapid progression to coexistent painful lymph node involvement
- syphilis via Treponoma pallidum: painless genital ulcer with bilateral painless lymph node involvement
- herpes via HSV: lesions are initially blisters (vesicles), systemic signs are common
Chlamydophila psittaci and Chlamydophila pneumoniae
- these organisms cause atypical pneumonia
- C. psittaci infects birds and transmission occurs via inhalation of dried feces or feather dust
- C. pneumoniae’s TWAR strain is found in Taiwan
Which organisms cause atypical pneumonia?
- viruses, Mycoplasma, Legionella, and Chlamydophila species
