Micro: Pediculosis & Syphilis

Question 1

Pediculus humanus capitus

Answer 1

Head lice. Scalp, usually behind ears. Classically schoolchildren.

Question 2

Pediculus humanus corporis

Answer 2

Clothing, especially seams. Classically in homeless. Can also transmit typhus, trench fever, relapsing fever.

Question 3

Pthirus pubis

Answer 3

Pubic lice. Classically in sexually promiscuous. A marker for other STDs.

Question 4

Treponema pallidum bacteriology

Answer 4

• Motile in flagellar corkscrew motion
• NOT culturable
• Very slow growing
• Too slender to gram stain
• Too delicate to survive outside host

Question 5

Treponema pallidum pahogenesis

Answer 5

• Transmitted by sexual contact (very low infectious dose), transplacental, or blood-blood
• infects endothelium of small blood vessels
• Triphasic infection

Question 6

Primary syphilis infection

Answer 6

Weeks after contact

• initial replication at site of infection
• forms chancre, initiates bacteremia. Chancre heals in 3-12 weeks.

Question 7

Secondary syphilis infection

Answer 7

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

Question 8

Latent syphilis infecion

Answer 8

Early latency (1/3): symptoms come and go, patient remains infectious
Late latency (1/3): symptoms absent, patient not infectious

Question 9

Tertiary syphilis infection

Answer 9

1/3 enter this stage, very destructive

• Granulomatous gummas with necrotic center
• CNS involvement

Question 10

Neurosyphilis

Answer 10

Tertiary syphilis infection. 
Early: meningitis (~6 mos), low inflammation
Late: 
- meningovascular syphilis
- Parenchymal neurosyphilis

Question 11

Meningovascular syphilis

Answer 11

Late tertiary syphilis infection

- damage to blood vessels of meninges, brain, spinal cord

Question 12

Parenchymal neurosyphilis

Answer 12

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

Question 13

Congenital T. Pallidum pathogenesis

Answer 13

• Treponemes readily cross placenta and infect fetus
• Miscarriage/stillbirth/neonatal death 40-50%
• Within first two years, surviving infants develop severe secondary syphilis

Question 14

Diagnosis of syphilis (physical exam)

Answer 14

Chancre, rash, condylomata lata, patchy alopecia, CNS symptoms including meningitis, cardiovascular symptoms, Argyll-Robertson pupil

Question 15

Argyll Robertson pupil

Answer 15

bilateral small pupils that reduce in size on a near object, but do not constrict when exposed to bright light. Indicative of neurosyphilis.

Question 16

Diagnosis of syphilis (lab exam)

Answer 16

• 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)

Question 17

Yaws

Answer 17

• 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

Question 18

Syphilis treatment

Answer 18

• Single injection of benzathine penicillin G for primary and secondary syphilis
• Alternatively: long-term doxycycline, erythromycin, ceftriaxone (all much less effective)
• Jarisch-Herxheimer reaction

Question 19

Pinta

Answer 19

• 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

Question 20

Characteristic histology of syphilis

Answer 20

Plasma-cell-rich infiltrate: delayed hypersensitivity to T. pallidum, leads eventually to gummatous ulcerations/necrosis.