Ectoparasitic Infections

Question 1

Cause of scabies

Answer 1

Sarcoptes scabiei

Question 2

Scabies morphology

Answer 2

Small mite with short legs

Question 3

Female vs male scabies

Answer 3

Female:

• Fertilized on the skin surface
• Burrows into the epidermis
• Completes life cycle in 5 weeks, dies in burrow

Male:

• Shorter life span
• Remains on skin surface or shallow burrows

Question 4

Main clinical manifestation of scabies

Answer 4

PRURITIS (worse at night)

Question 5

Crusted norwegian scabies

Answer 5

More common in immunocompromised (HIV)

Intense superinfection of scabies with thousands of mites

Question 6

Pediatric scabies

Answer 6

Similar to Norwegian scabies, but lesions may be blood filled

Question 7

Transmission of scabies

Answer 7

Usually direct person contact (likely an STI in adults)

Question 8

Diagnosis of scabies

Answer 8

Mineral oil prep with microscopy

-Look for mite, mite parts, eggs, or fecal pellets

Question 9

Treatment considerations with scabies

Answer 9

May need to retreat!

• Permethrin only kills what’s on the surface
• Ivermectin does not kill eggs

Wash all bedding and clothes in hot water
Examine all sexual partners

Question 10

Cause of pubic lice

Answer 10

Phthirus pubis

Question 11

Transmission of pubic lice

Answer 11

Sexual contact

Contaminated bedding

Question 12

Diagnosis of pubic lice

Answer 12

Visualize louse or nit (much larger than scabies)

Question 13

Name for lice (non pubic)

Answer 13

Pediculosis

Question 14

Cause of pediculosis

Answer 14

Pediculus humanus

• P. humanus capitis = head louse
• P. humanus humanus = body louse

Question 15

Disease transmitted by lice

Answer 15

Epidemic typhus

Question 16

Pathogenicity of lice

Answer 16

Bloodsucking! (differs from pubic)

“Vagabond’s disease”

Question 17

Human flea

Answer 17

Pulex irritans

Question 18

Flea morphology

Answer 18

1-4 mm length
Laterally compressed
Short spikes on legs to allow attachment

Question 19

Pathogenicity of fleas

Answer 19

Need blood for survival!

Question 20

Bloodsuckers

Answer 20

Pediculus humanus

Pulex irritans

Question 21

Pimple like rash

Answer 21

Scabies

Question 22

Raised halo shaped bumps

Answer 22

Fleas

Question 23

Extremely pruritic (especially at night)

Answer 23

Scabies

Question 24

Concentrated in lower extremities

Answer 24

Fleas

Question 25

Multiple bites in a linear pattern

Answer 25

Fleas

Question 26

Burrow beneath the skin

Answer 26

Scabies

Question 27

Prefer to live in hairy, warm environments

Answer 27

Fleas

Question 28

Contagious by skin contact

Answer 28

Scabies

Question 29

Cause of rocky mountain spotted fever (RMSF)

Answer 29

Rickettsia rickettsii

Question 30

Vector for RMSF

Answer 30

American dog tick Rocky mountain wood tick BROWN DOG TICK (Arizona)

Question 31

Rickettsia rickettsii morphology

Answer 31

Gram negative* Obligate intracellular* Non motile Pleomorphic (cocci, rods, thread-like)

Question 32

Symptom onset of RMSF

Answer 32

2-14 days after tick bite

Question 33

RMSF Symptoms

Answer 33

``` Fever Rash (2 types) ```

Question 34

Rash types in RMSF

Answer 34

1. Small, flat pink non itchy spots: - On wrists, forearms, and ankles. - Spreads to trunk, palms, and soles - 2-5 days post infection (may not be present) 2. Red to purple spotted petechial rash: - Pinpoint hemorrhages (60% of pts) - 6 days post infection (late infection/severe disease)

Question 35

RMSF Diagnosis

Answer 35

Clinical Do not delay treatment! (within 5 days) No good/quick tests available Gold Standard - Indirect immunofluorescence with a R. rickettsii antigen (2 samples, 2-4 weeks apart)