Micro: Pediculosis & Syphilis Flashcards
Pediculus humanus capitus
Head lice. Scalp, usually behind ears. Classically schoolchildren.
Pediculus humanus corporis
Clothing, especially seams. Classically in homeless. Can also transmit typhus, trench fever, relapsing fever.
Pthirus pubis
Pubic lice. Classically in sexually promiscuous. A marker for other STDs.
Treponema pallidum bacteriology
- Motile in flagellar corkscrew motion
- NOT culturable
- Very slow growing
- Too slender to gram stain
- Too delicate to survive outside host
Treponema pallidum pahogenesis
- Transmitted by sexual contact (very low infectious dose), transplacental, or blood-blood
- infects endothelium of small blood vessels
- Triphasic infection
Primary syphilis infection
Weeks after contact
- initial replication at site of infection
- forms chancre, initiates bacteremia. Chancre heals in 3-12 weeks.
Secondary syphilis infection
Months after contact
- Macropapular rash on palms and soles
- Moist papules on skin and mucous membranes
- Highly infectious moist lesions on genitals (condylomata lata)
- patchy alopecia
- constitutional symptoms like fever, malaise, anorexia, weight loss, headache, myalgia, lymphadenopathy
Latent syphilis infecion
Early latency (1/3): symptoms come and go, patient remains infectious Late latency (1/3): symptoms absent, patient not infectious
Tertiary syphilis infection
1/3 enter this stage, very destructive
- Granulomatous gummas with necrotic center
- CNS involvement
Neurosyphilis
Tertiary syphilis infection. Early: meningitis (~6 mos), low inflammation Late: - meningovascular syphilis - Parenchymal neurosyphilis
Meningovascular syphilis
Late tertiary syphilis infection
- damage to blood vessels of meninges, brain, spinal cord
Parenchymal neurosyphilis
Late tertiary syphilis infection
- Tabes dorsalis: damage to spinal cord → impaired sensation, wide-based gait
- Disruption of doral roots → loss of pain and temperature sensation, areflexia
- General paresis: damage to cortical brain tissue → dementia
Congenital T. Pallidum pathogenesis
- Treponemes readily cross placenta and infect fetus
- Miscarriage/stillbirth/neonatal death 40-50%
- Within first two years, surviving infants develop severe secondary syphilis
Diagnosis of syphilis (physical exam)
Chancre, rash, condylomata lata, patchy alopecia, CNS symptoms including meningitis, cardiovascular symptoms, Argyll-Robertson pupil
Argyll Robertson pupil
bilateral small pupils that reduce in size on a near object, but do not constrict when exposed to bright light. Indicative of neurosyphilis.
Diagnosis of syphilis (lab exam)
- Won’t culture, too small to Gram stain
- Swab moist cutaneous lesions for darkfield microscopy or IF
- For neurosyphilis, use CSF for tests, specific but not sensitive
Serology:
- Reagin: nonspecific antibodies detectable by flocculation tests with cardiolipin (VDRL or RPR). Positivity decreases with treatment. False positives and negatives may occur; positives confirmed by specific tests.
- Specific antibodies: detectable by IF or hemagglutination, remain positive for life (tests exposure, not current infxn)
Yaws
- Treponema pertenue
- Tropical disease of overcrowding and poor sanitation
- Spread by direct contact with cutaneous lesions
- 3 phase disease like syphilis w/o neuro or cardio involvement
- Tests reagin positive
- Treat with penicillin
Syphilis treatment
- Single injection of benzathine penicillin G for primary and secondary syphilis
- Alternatively: long-term doxycycline, erythromycin, ceftriaxone (all much less effective)
- Jarisch-Herxheimer reaction
Pinta
- Treponema carateum
- Even rarer than Yaws, Central and S. America
- No constitutional symptoms, just hypo and hyper pigmented skin plaques
- Probably spread by direct contact
- Tests reagin-positive
- Treat w/ penicillin
Characteristic histology of syphilis
Plasma-cell-rich infiltrate: delayed hypersensitivity to T. pallidum, leads eventually to gummatous ulcerations/necrosis.
