Ectoparasites

Question 1

A 6-year-old girl is brought to the pediatrician’s office for an “itchy” head. She is actively scratching her hair.
She has no significant past medical history. Her mom reports that they live in a homeless shelter with crowded
living conditions. Several other children there also were seen scratching their head. Physical exam reveals
several non-viable nits > 1 cm away from the base of the hair shaft and viable nits < 1 cm away from the base of
the hair shaft. She is given topical permethrin. What is the most likely causative agent?
A, Phthirus pubis
B. Pediculus capitis
C. Dermatobia hominis
D. Pediculus corporis
E. Cimex lectularius

Answer 1

B

Question 2

A 9-year-old boy in Alabama presents with a pruritic red rash on his ankles and legs. He is currently on
summer vacation and often rides his bike outdoors. He often plays in the fields and rarely applies anti-bug
spray. He has had this rash for a few days now and reports that it is very itchy. Physical exam reveals multiple
pink papulovesicles with surrounding erythema. Some lesions have overlying excoriations from scratching. He
is given an oral antihistamine and told that this would resolve in time. What is the most likely causative agent?
A. Phthirus pubis
B. Trombicula autumnalis
C. Pediculus corporis
D. Latrodectus mactans
E. Loxosceles blanda

Answer 2

B

Question 3

A 2-year-old girl is brought in by her parents due to a rash on her armpit and belly for 2 weeks. Her major
complaint is itching. The lesions are so itchy that she cannot sleep at night and scratches her rashes constantly.
She goes to daycare 3 days a week. Skin exam reveals multiple polymorphous scaly papules on her hands, in
the axilla, and around the umbilicus. Linear markings can be seen amongst the rash. Which of the following is
the most likely causative agent?
A. Dermatobia hominis
B. Phthirus pubis
C. Latrodectus mactans
D. Sarcoptes scabiei
E. Trombicula autumnalis

Answer 3

D. The linear markings are the burrows left by the mite. Hallmark feature is that the itching is worse at night.

Question 4

An 18-year-old man presents to his primary care physician with an itchy rash. He recently backpacked through
Europe, staying at hostels along the way. He remembered that other people in his travel group complained of
itchiness but didn’t think much of it. Every day, he woke up with a few more lesions on different parts of his
body. The lesions were often in a linear pattern. Which of the following is the most likely causative agent?
A, Phthirus pubis
B. Pediculus capitis
C. Dermatobia hominis
D. Pediculus corporis
E. Cimex lectularius

Answer 4

E. Linear biting pattern of the bedbug is sometimes referred to as “breakfast, lunch and dinner pattern.”

Question 5

A 21-year-old female presents to her primary care physician after recently having unprotected sexual 
intercourse at a college party "a few weeks ago". She complains of intense genital pruritis that has been going on for the past 3 days. Nothing she has tried has alleviated the intense itching. Which of the following is the 
most likely causative agent?
A. Phthirus pubis
B. Trombicula autumnalis
C. Pediculus corporis
D. Latrodectus mactans
E. Loxosceles blanda

Answer 5

A