Infestations and Bites

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Infestations and Bites

Medical Student Core Curriculum in Dermatology

Last updated August, 2011

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Goals and Objectives The purpose of this module is to help medical students

develop a clinical approach to the evaluation and initial management of patients presenting with bites and infestations

After completing this module, the learner will be able to:• Recognize risk factors for lice infestation and scabies• Identify nits and adult lice as diagnostic of pediculosis• Identify a burrow as the primary morphology of scabies• Identify common causes and clinical presentations of insect bite

reactions, with an emphasis on bedbugs and brown recluse spider bites

• Discuss treatment options and patient education for pediculosis capitis, scabies, and insect bite reactions

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Case OneMary Thompson

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Case One: History

HPI: Mary is a 6-year-old girl with a two week history of an itchy scalp. It has not been relieved by over-the-counter dandruff shampoo. She recently stayed over at her cousin’s house who now has the same problem.

PMH: no chronic illnesses or prior hospitalizations Allergies: no known allergies Medications: none Family history: noncontributory Social history: lives at home with parents and attends first

grade ROS: negative

Case One, Question 1

What information is relevant in Mary’s history?

a. Recent contact with similar complaintb. Scalp pruritus (itching)c. School-aged childd. All of the above

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Answer: d What information is relevant in Mary’s

history?a. Recent contact with similar complaintb. Scalp pruritusc. School-aged childd. All of the above

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Pediculosis (Lice): The Basics

Three different varieties of lice may infest humans• Head louse – Pediculus humanus var. capitis• Body louse – Pediculus humanus var. corporis• Pubic or crab louse – Phthirus pubis

Head lice are spread by close physical contact and may be transferred by use of head gear, combs, brushes, and pillows

Commonly affects school-age children

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Pediculosis Capitis: The Basics Affects all ethnic and socioeconomic groups, but is less

common in African-Americans. Frequently has associated scalp pruritus and may also have

posterior cervical lymphadenopathy. Live adult lice and nits (ova or eggs) may be noted on

examination.• Most common sites to find nits are the retroauricular and

occipital scalp.• Nits within 0.6 cm of the scalp are typically viable. In warm

environments the distance may be greater.• Nits must be distinguished from hair casts. Hair casts encircle

the hair shaft and move freely in contrast to the nit which is cemented to the hair.

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Back to Case One

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Skin Exam Findings

Exam of occipital scalp: Structures on the hair are not freely movable

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How would you describe Mary’s exam?a. Multiple hair casts present in the occipital

scalp. No nits or lice noted.b. Multiple nits present in the occipital scalp. No

lice noted. c. Negative exam, no nits or lice noted.

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Answer: b How would you describe Mary’s exam?

a. Multiple hair casts present in the occipital scalp. No nits or lice noted.

b. Multiple nits present in the occipital scalp. No lice noted.

c. Negative exam, no nits or lice noted.

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Skin Exam Findings

Exam of occipital scalp: numerous nits

Pediculosis: Pathogenesis

Female adult lice live 30 days and lay 5-10 eggs (nits) per day at the base of the hair where it meets the scalp.

Eggs hatch in 8-12 days. Lice typically survive 1-2 days away from the scalp. Eggs

may survive up to 10 days away from the scalp. Live eggs remain close to the scalp to maintain warmth

and moisture but as the hair grows, the nits move off the scalp with the hair.

Because hair grows at a rate of ~ 1cm per month, the duration of infestation can be estimated by the distance of the nit from the scalp.

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Pediculosis: Pathogenesis

The adult louse at the right typically is 2-3 mm in length.

The presence of live adult lice, immature nymphs, and/or viable eggs indicates active infection.

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Back to Case One

Follow-up

Mary returns to clinic in four weeks for follow-up. Therapy was completed as directed but she still has nits present on exam which are approximately one inch from the scalp. A sample is on the slide that follows.

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Hair Mount

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This image shows a nit without an intact cap (operculum) and is not viable (no larva inside).

Continued presence of nits does not always represent treatment failure.

Pediculosis: Treatment

Physical removal of nits may be facilitated by using a fine-toothed comb (or nit picker) on wet, well-conditioned hair.

Occlusive methods have also been used to suffocate head lice using substances such as petroleum jelly and mayonnaise, but study results have been variable.

Over-the-counter and prescription topical therapies are listed on the following slide.

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Therapy Use Risks Other

Over-the counter pyrethrins (natural botanical)

Topically to clean, dry hair for 10 minutes

+resistanceAllergic reaction (chrysanthemum, ragweed, etc)

Lotion, shampoo, foam mousse, cream rinse

1% permethrin lotion(synthetic pyrethrin)

Topically to clean, dry hair for 10 minutes +resistance Over age 2 months

5% permethrin cream (synthetic pyrethrin)

Topically to clean, dry hair overnight +resistance Over age 2 months

0.5% malathion lotion Topically to clean, dry hair for 8-12 hours

Alcohol base is flammable Over age 6 years


Individual patient risks should be assessed prior to choosing a topical therapy (age, allergy history, prior treatment, etc.).

It is prudent to retreat with topical therapies one week after initial therapy to kill the newly hatched lice.

Patients with refractory lice should be referred to a dermatologist.

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Back to Case One

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If Mary had live lice in the scalp on follow-up, what would be possible causes of treatment failure?

a. Not treating contacts (reinfestation)b. Not properly cleaning the environmentc. Not retreating in 7-10 daysd. Incorrect application of the medicatione. Resistance of the organism to medicationf. All of the above

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Answer: f If Mary had live lice in the scalp on follow-up, what

would be possible causes of treatment failure?a. Not treating contacts (reinfestation)b. Not properly cleaning the environmentc. Not retreating in 7-10 daysd. Incorrect application of the medicatione. Resistance of the organism to medicationf. All of the above

Pediculosis: Patient Education

All persons living in the home should be examined to avoid reinfestation. • If it is not possible to examine household members,

treat without an exam if the treatment is not contraindicated.

Clothing and bedding should be washed and dried on the hot cycle.

Non-washable items may be placed in the dryer or stored in a sealed plastic bag for two weeks.

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Pediculosis: Patient Education

Combs and brushes should also be washed in hot water and may be treated with a pediculocide.

Floors, furniture, and vehicles should be vacuumed to remove hair with potentially viable nits attached.

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Case TwoMichael Miller

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Case Two: History

HPI: Mike is a 21-month-old boy who was referred to the dermatology clinic for a rash that has been present for two weeks. He has been having problems sleeping due to itching.

PMH: no history of major illness or hospitalizations Allergies: no known drug allergies Medications: none Family history: noncontributory Social history: lives in the city and attends day

care ROS: pruritus

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Case Two: Skin Exam

Multiple erythematous papules throughout the trunk, extremities. Also involving the scrotum.

Burrows present in the 2nd-3rd web space on the right hand.

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Case Two, Question 1

What in-office procedure would best help to confirm the diagnosis?

a. KOH preparationb. Nail clipping c. Skin scraping (mineral oil prep)d. Wood’s light examination

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Answer: c What in-office procedure would best help

to confirm the diagnosis?a. KOH preparationb. Nail clipping c. Skin scraping (mineral oil prep)d. Wood’s lamp examination


You perform a skin scraping on the patient and see the image on the following slide when you look through the microscope. What is present on the slide?

a. Eggsb. Scabies mitec. Scybala (scabies feces)d. All of the above

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Answer: d You perform a skin scraping on the patient and see

the image on the following slide when you look through the microscope. What is present on the slide?

a. Eggsb. Scabies mitec. Scybala (scabies feces)d. All of the above

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mite

eggscybala (feces)

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Scabies: The Basics

Sarcoptes scabiei (scabies) affects patients of all ages and all socioeconomic classes, although more common in women and children.

Patients in congregated facilities are more prone to the infestation, such as nursing homes.

Most infections occur from direct contact with an infected individual. However, fomites can transmit the infection.

Females lay about three eggs per day, which hatch in four days. Most patients have less than 20 mites on the skin at a time.

Scabies: The Basics

The time from initial infestation to symptoms is 3-4 weeks because the rash is caused by hypersensitivity to the mites.

Papules may commonly involve the breasts, umbilicus, penis, scrotum, finger webs, wrists, and axilla.

The scalp and head are more frequently involved in infants, elderly, and immunosuppressed.

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Which of the following clinical findings are considered pathognomonic for scabies?

a. Burrowsb. Diffuse involvementc. Erythematous papulesd. Sparing of the groin

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Answer: a Which of the following clinical findings are

considered pathognomonic for scabies?a. Burrowsb. Diffuse involvementc. Erythematous papulesd. Sparing of the groin

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Scabies

Burrows are linear markings in the skin due to the movement of the mite. They are 1-10 mm in length and may be found most readily in the interdigital spaces, wrists, and elbows.

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Back to Case Two


Mike’s mother tells you his uncle has AIDS and is currently hospitalized. Why is this important?

a. His uncle may have been the source of infection

b. If his uncle has scabies, it could cause an institutional outbreak

c. If his uncle gets scabies, it may be a more severe form

d. All of the above

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Answer: d Mike’s mother tells you his uncle has AIDS and is

currently hospitalized. Why is this important?a. His uncle may have been the source of infection

(Immunosuppressed patients are at increased risk for infection)

b. If his uncle has scabies, it could cause an institutional outbreak (Patients with crusted scabies harbor more mites)

c. If his uncle gets scabies, it may be a more severe form (Immunosuppressed patients may develop crusted scabies)

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Crusted Scabies

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Refer to the HIV Dermatology module for more information on crusted scabies

Scabies: Treatment

As in pediculosis, scabies treatment includes a two-pronged approach. The patient and the environment must both be treated.

Environmental care includes washing all clothing and linens in hot water, sealing items which may not be washed in bags for two weeks, and vacuuming.

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Therapy Use Risks/Side effects Other

5% permethrin cream

Apply from the neck down, leave on overnight

Low, only 2% systemic absorption. May burn or sting on application.

First-line treatment in patients over 2 months old. Pregnancy category B

5-10% precipitated sulfur

Apply for three days, then wash off

Greasy, strong odor, stains clothing

Safe in pregnancy and children under 2 months. Must be compounded

Oral Ivermectin200mcg/kg by mouth, repeat dose two weeks later

Diarrhea, itching, joint pain, skin irritation

Most useful for immunocompromised patients or when topical therapy is impractical (outbreaks). Not recommended for pregnant or lactating women.

Scabies: Treatment

For difficult to treat or severe scabies, refer to a dermatologist

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Case ThreeMrs. Marsha Koehler

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Case Three: History HPI: Mrs. Koehler is a 33-year-old woman who

presented to clinic with “itchy bumps” which started over the weekend. No one else at home has a similar complaint.

PMH: GERD Allergies: none Medications: Omeprazole Family history: not contributory Social history: works in a diner as a waitress ROS: negative

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Case Three: Skin Exam

Edematous papules scattered over the body. Some with signs of excoriation.

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Case Three, Question 1

What is the most likely diagnosis?a. Bedbug bitesb. Brown recluse spider bitec. Chickenpoxd. Methicillin-resistant S. aureus folliculitise. Pediculosis corporis

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Answer: a What is the most likely diagnosis?

a. Bedbug bitesb. Brown recluse spider bite (normally single site)c. Chickenpox (presents as dewdrop on a rose petal

papules, vesicles, crusts in various stages more common in children)

d. Methicillin-resistant S. aureus folliculitis (follicular-based, may be pustular)

e. Pediculosis corporis (body lice) (normally blue-colored macules or excoriations are seen)

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Bedbugs: The Basics

Cimex lectularius (most common type) affect people from all racial and socioeconomic groups

May be spread via clothing and bedding while traveling, on mattresses, laundry, etc.

Stay hidden during the day and feed at night Attracted to the warmth and carbon dioxide

emitted by the patient Bites may be multiple in a linear array

referred to as “breakfast, lunch, and dinner”

Bedbugs: Pathogenesis

Typically have a blood meal every 3-5 days for 4-10 minutes

Saliva keeps blood meal flowing due to: • Nitrophorin, leading to vasodilation • An anticoagulant which prevents conversion of

factor X to factor Xa• Apyrase, leading to inhibition of platelet

aggregation May live over a year without feeding

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Cimex lectularius

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Back to Case Three

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Which finding favors a diagnosis of bedbug bites?

a. Flecks of blood or feces on the bed sheetsb. Nocturnal assaultc. Sweet, pungent odor in the roomd. All of the above

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Answer: d Which finding favors a diagnosis of bedbug

bites?a. Flecks of blood or feces on the bed sheetsb. Nocturnal assaultc. Sweet, pungent odor in the roomd. All of the above

Bedbugs: Treatment

Bites will typically resolve within 1-2 weeks Symptomatic care may include topical.

antipruritics such as corticosteroids and/or antibiotics (if secondary infection occurs).

Bed linens should be laundered and furniture vacuumed.

A professional exterminator may be needed to treat the home.

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Insect Presentation Characteristics Risks OtherFlea (rat flea: Xenopsylla cheopis, X. brasiliensiscat flea: Ctenocephalides felis)

Linear or clustered pruritic papules. May be bullous. Frequently on lower legs

Wingless. May jump 18 cm

May transmit disease such as bubonic plague (rat flea), endemic typhus (cat flea)

Mosquito bites Papular urticaria typically

Males lack mouthparts. Females inflict human bites

Pruritus, secondary infection. May transmit malaria, Dengue fever, etc.

Gypsy moth caterpillar (Lymantria dispar)

Erythematous papules in a linear streak

Keratoconjunctivitis and respiratory symptoms from airborne hairs

Hairs cause clinical findings

Harvest mite (chigger – Trombicula)

Erythematous macules, papules on waist, ankles, folds

Less than 0.5 mm long, reddish

Intense pruritus hours after bites

Southern states in U.S.

Insect Bites: Differential

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Case FourMiss Stacey Dean

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Case Four: History

HPI: Miss Dean is a 23-year-old woman who presented to clinic with a “painful bump” which started yesterday in the evening. She was cleaning out her attic earlier that day.

PMH: Asthma Allergies: Penicillin Medications: Albuterol inhaler Family history: not contributory Social history: college student ROS: malaise

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Case Four: Skin Exam

Hemorrhagic bulla with surrounding ischemia and peripheral erythema

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Case Four, Question 1

What is the most likely diagnosis?a. Brown recluse spider biteb. Ecthyma gangrenosumc. MRSA infectiond. Snake bite

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Answer: a What is the most likely diagnosis?

a. Brown recluse spider biteb. Ecthyma gangrenosumc. MRSA infectiond. Snake bite

Arachnid Bites: The Basics

Only three genera of spiders found in the United States have bites toxic to humans: Latrodectus, Loxosceles, and Tegeneria.

Approximately 12,500 spider bites were reported to the American Association of Poison Control Centers and zero deaths secondary to spider bites in 2008.

This module will review the characteristics of the Loxosceles reclusa, or brown recluse spider.

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Brown Recluse: The Basics

Characteristic violin-shaped dark brown marking on the cephalothorax seen at the left

Found in the Midwest and Southeast

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Brown Recluse: The Basics

As noted by the name, the spider is typically not aggressive, but is reclusive.

Bites frequently occur when patients are disturbing areas where the spiders seek shelter (attics, closets, etc.) or putting on clothing containing the spiders.

Cardboard boxes may harbor the spiders as the corrugated structure mimics their natural habitat.

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Back to Case Four

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Brown Recluse: Clinical Presentation

This case shows the characteristic

“Red (peripheral erythema), White (blanching), and

Blue (central violaceous area)” sign of the brown recluse bite.

Brown Recluse: Clinical Presentation

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The initial wound may progress to necrosis and deep ulcer formation.

Brown Recluse: DifferentialHistory/Finding MRSA Infection Brown Recluse Bite

Insect seen - -/+

History of similar occurrence Common Uncommon

Close personal contacts affected Common Uncommon

Multiple areas affected on exam Common Uncommon

Progression Days to weeks Hours to days

Red, white, and blue sign - +

Geographic location Throughout the U.S. Southeast and Midwest (endemic areas)

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MRSA infections may frequently be mistaken for spider bites. Pyoderma gangrenosum and erythema migrans (Lyme disease) may be considered also.

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Back to Case Four

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What leads to tissue destruction in the brown recluse bite?

a. Amylaseb. Keratolyticsc. Solenopsin Dd. Sphingomyelinase D

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Answer: d What leads to tissue destruction in the

brown recluse bite?a. Amylaseb. Keratolyticsc. Solenopsin Dd. Sphingomyelinase D

Brown Recluse: Complications

Tissue necrosis may occur due to the presence of multiple proteins in the venom.

In addition, some patients may develop systemic symptoms including malaise, nausea, vomiting, etc.

Uncommonly significant hemolysis, renal failure, anemia, and/or hypotension may occur.

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Brown Recluse: Management

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Supportive care including cleansing the wound, cold compresses, and pain control is important.

Multiple treatments have been suggested, but not consistently shown to be beneficial.

The wound at right healed with close monitoring, topical therapy with antibiotic ointment, and nonstick wound dressings without requiring surgical debridement.

Take Home Points Pediculosis capitis commonly affects school-aged children. Nits and/or adult lice are diagnostic of pediculosis capitis. Pediculosis capitis therapy includes physical removal and over-

the-counter or prescription topical therapy. Scabies affects all classes of patients, but those in group settings

or in an immunocompromised state are at increased risk of infestation.

The primary morphology of scabies is a burrow. Pruritic papules and areas of crusting may be seen as well.

The primary diagnostic test for scabies is the skin scraping, or mineral oil prep.

First-line treatment for scabies in patients over two months of age who are not pregnant is permethrin 5% cream.

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Take Home Points Bedbugs infest all populations. They typically feed at night. Bedbug bites cause edematous papules which are frequently

arranged in a “breakfast, lunch, and dinner” pattern. Insect bite reactions may be treated with topical corticosteroids and

antibiotics if indicated. Brown recluse spiders are only found in the Midwest and

Southeast. They have a characteristic violin-shaped marking on their cephalothorax.

MRSA infection is frequently misdiagnosed as brown recluse spider bites.

The primary therapy for a brown recluse spider bite is supportive care.

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Acknowledgements This module was developed by the American Academy of

Dermatology Medical Student Core Curriculum Workgroup from 2008-2012.

Primary author: Jennifer Swearingen, MD. Peer reviewers: Susan K. Ailor, MD, FAAD; Cory A. Dunnick, MD,

FAAD, Timothy G. Berger, MD, FAAD. Revisions and editing: Jennifer Swearingen, MD; Sarah D.

Cipriano, MD, MPH; Jillian W. Wong. Last revised in August 2011. Thank you to Dr. Bahar Dasgeb, Dr. Steven Daveluy, Dr.

Stephanie Diamond,Dr. Dirk Elston, Dr. Darius Mehregan, Dr. David Mehregan, and Dr. Robert Schoenfeld for their assistance in obtaining images for the module.

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References Bronstein AC, Spyker DA, Cantilena LR, et al. 2008 Annual Report of the

American Association of Poison Control Centers’ National Poison Data System (NPDS): 26th Annual Report. Clinical Toxicology. 2009; 47: 1027.

Chosidow O. Scabies and pediculosis. Lancet. 2000; 355(9206): 819-26. Epocrates Rx [database for PDA]. Version 9.0. San Mateo (CA): Epocrates, Inc.

c2009 [updated 2010 Sept; cited 2010 Sept]. Available from: http://www.epocrates.com.

Goldstein BG, Goldstein AO. Scabies. In: UpToDate, Basow, DS (Ed), UpToDate, Waltham, MA, 2011.

James WD, Berger TG, Elston DM, “Chapter 20. Parasitic Infestations, Stings, and Bites” (chapter). Andrews’ Diseases of the Skin Clinical Dermatology. 10th ed. Philadelphia, Pa: Saunders Elsevier; 2006: 446-448.

Kolb A, Needham GR, Neyman KM, High WA. Bedbugs. Dermatol Ther. 2009; 22 (4):347-52.

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References Meinking TL, Burkhart CN, Burkhart CG, Elgart G. Infestations. In: Bolognia JL,

Jorizzo, JL, Rapini RP, eds. Dermatology. 2nd ed. Spain: Elsevier; 2008. MD Consult Web site. Available at http://www.mdconsult.com/books/page.do?eid=4-u1.0-B978-1-4160-2999-1..50088-6&isbn=978-1-4160-2999-1&sid=1055850616&type=bookPage&sectionEid=4-u1.0-B978-1-4160-2999-1..50088-6--cesec2&uniqId=219284186-4#4-u1.0-B978-1-4160-2999-1..50088-6--cesec2 Accessed September 20, 2010.

Steen Christopher J, Schwartz Robert A, "Chapter 210. Arthropod Bites and Stings" (Chapter). Wolff K, Goldsmith LA, Katz SI, Gilchrest B, Paller AS, Leffell DJ: Fitzpatrick's Dermatology in General Medicine, 7e: http://www.accessmedicine.com/content.aspx?aID=3000969.

Stone Stephen P, Goldfarb Jonathan N, Bacelieri Rocky E, "Chapter 208. Scabies, Other Mites, and Pediculosis" (Chapter). Wolff K, Goldsmith LA, Katz SI, Gilchrest B, Paller AS, Leffell DJ: Fitzpatrick's Dermatology in General Medicine, 7e: http://www.accessmedicine.com/content.aspx?aID=2971870.

Wolf R, Davidovici B. Treatment of scabies and pediculosis: facts and controversies. Clin Dermatol. 2010; 28(5): 511-8.

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