eMedicine Specialties > Infectious Diseases > Skin and Soft-Tissue Infections

Pediculosis: Differential Diagnoses & Workup

Author: Lyn Guenther, MD, FRCP(C), Professor, Department of Medicine, Division of Dermatology, University of Western Ontario; Chief of Dermatology, London Health Sciences Center; Medical Director, The Guenther Dermatology Research Centre, Canada
Coauthor(s): Sheilagh Maguiness, BSc, MD, Department of Dermatology, University of Alberta; Thomas W Austin, MD, Professor Emeritus, Department of Medicine, Division of Infectious and Sexually Transmitted Diseases, University of Western Ontario, Canada
Contributor Information and Disclosures

Updated: May 5, 2009

Differential Diagnoses

Impetigo

Other Problems to Be Considered

P humanus capitis

Dried hairspray/gel
Hair cast (ie, pseudocyst)
Seborrheic dermatitis
Dermatophyte infection
Black piedra and white piedra, caused by Piedraia hortae and Trichosporon beigelii
Psocids
Hair shaft abnormalities (ie, Monilethrix, trichorrhexis nodosa)

P humanus corporis

Folliculitis
Insect Bites
Acne
Delusions of parasitosis
Xerosis with excoriations
Impetigo
Postinflammatory hyperpigmentation

P pubis

Dermatophyte infection
Folliculitis
Delusions of parasitosis
Contact dermatitis
Conjunctivitis (if eyelash involvement)

Lice may carry Staphylococcus aureus and group A Streptococcus pyogenes on their surface and transmit these coagulase-positive pathogens to others.

The body louse, P humanus corporis, is a known vector of 3 major bacterial diseases, all of which have caused epidemics.

  • Typhus: The intracellular pathogen Rickettsia prowazekii causes typhus. Typhus fever epidemics have consistently been related to times when overcrowded conditions and body louse infestations were prevalent. For example, mass migration, refugee camps, and times of war have been linked to body louse infestations and secondary epidemics of typhus. The illness begins with a high fever and progresses over hours to days with malaise, backache, headache, and myalgia. A petechial rash appears approximately on day 4, beginning in the flank and axillary regions and quickly spreading to the trunk and extremities. By the second week, the fever begins to wane, profuse sweating occurs, and convalescence ensues. CNS involvement during this period places the patient at high risk of mortality.
  • Trench fever: The extracellular pathogen Bartonella quintana causes trench fever. Although rarely fatal, this disease has been the cause of many epidemics and is believed to be related to bacterial infective endocarditis. Infection in humans results from autoinoculation of louse feces into abraded or scratched skin. The infection has a 10- to 30-day latency period and results in a fever similar to that of typhus, with headache, myalgia, and pain in the back and the legs.
  • Relapsing fever: The spirochete Borrelia recurrentis causes relapsing fever. This disease is highly fatal in malnourished persons. Although not common in North America, epidemics have been described during the last few decades in Asia, South America, Africa, and Europe. Human infection with this spirochete occurs only when a crushed louse comes into contact with an abrasion. The bacteria replicate in the louse hemolymph, not in the gut; therefore, no transmission occurs through the salivary glands or via the feces. The bacteria infection causes a high fever, headache, dizziness, and myalgia. Rash and sweating also appear and wane approximately on day 5. As the name indicates, this fever often returns several times.

No evidence indicates that any species of louse has the ability to transmit HIV.

Workup

Laboratory Studies

  • A Wood lamp examination of the area considered to be infested shows yellow-green fluorescence of lice and nits.
  • Because the diagnosis of infestation requires identification of a live louse and/or a viable nit, examining suggestive particles under the microscope confirms the diagnosis.
  • A fine-tooth "bug-busting" comb is useful to dislodge eggs and to remove live lice/nymphs. Cellulose tape can be applied over an infested area to pick up lice and place them on a microscopic slide to be examined.
  • Dermoscopy can be used to reliably differentiate nymph-containing eggs from empty cases or pseudonits.7
  • Scrapings for a fungal culture can be collected if dermatophyte infection is in the differential diagnoses. This is useful when the diagnosis is unclear, ie, no nits or lice have been identified.
  • In P pubis infestation, blood tests and a thorough examination for concomitant STDs, including HIV infection, are appropriate if the physician considers the individual to be at risk for these conditions.

Histologic Findings

Histology is rarely required for diagnosis. Examination of a bite shows intradermal hemorrhage and a deep, wedge-shaped infiltrate with many eosinophils and lymphocytes.

More on Pediculosis

Overview: Pediculosis
Differential Diagnoses & Workup: Pediculosis
Treatment & Medication: Pediculosis
Follow-up: Pediculosis
Multimedia: Pediculosis
References
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References

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Further Reading

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Keywords

pediculosis, lice, crabs, louse infestation, lice infestation, ectoparasites, pubic lice, pubic louse, head lice, head louse, body lice, body louse, Pediculus humanus capitis, P humanus capitis, Pediculus humanus corporis, P humanus corporis, Phthirus pubis, P pubis, Pediculus humanus humanus, P humanus humanus, human pests, Anoplura, sucking lice, insect infestation, insect bite, nit, vector-borne disease, typhus, relapsing fever, trench fever, plica polonica, vagabond disease, vagabond skin, pediculicide, permethrin, lindane, malathion, mercuric oxide ointment, pyrethrin, piperonyl butoxide, hexachlorocyclohexane

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Contributor Information and Disclosures

Author

Lyn Guenther, MD, FRCP(C), Professor, Department of Medicine, Division of Dermatology, University of Western Ontario; Chief of Dermatology, London Health Sciences Center; Medical Director, The Guenther Dermatology Research Centre, Canada
Lyn Guenther, MD, FRCP(C) is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Society for Dermatologic Surgery, Canadian Dermatology Association, Canadian Medical Association, College of Physicians and Surgeons of Ontario, International Society for Dermatologic Surgery, Ontario Medical Association, Royal College of Physicians and Surgeons of Canada, Society for Investigative Dermatology, and Society for Pediatric Dermatology
Disclosure: L'Oreale Consulting fee Consulting

Coauthor(s)

Sheilagh Maguiness, BSc, MD, Department of Dermatology, University of Alberta
Disclosure: Nothing to disclose.

Thomas W Austin, MD, Professor Emeritus, Department of Medicine, Division of Infectious and Sexually Transmitted Diseases, University of Western Ontario, Canada
Thomas W Austin, MD is a member of the following medical societies: American Venereal Disease Association, Canadian Infectious Disease Society, College of Physicians and Surgeons of Ontario, Ontario Medical Association, and Royal College of Physicians and Surgeons of Canada
Disclosure: Nothing to disclose.

Medical Editor

Jeffrey M Zaks, MD, Clinical Associate Professor of Medicine, Wayne State University School of Medicine; Vice President, Medical Affairs, Chief Medical Officer, Department of Internal Medicine, Providence Hospital
Jeffrey M Zaks, MD is a member of the following medical societies: American College of Cardiology, American College of Healthcare Executives, American College of Physician Executives, and American Medical Association
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Joseph F John Jr, MD, FACP, FIDSA, FSHEA, Clinical Professor of Medicine, Molecular Genetics and Microbiology, Medical University of South Carolina; Associate Chief of Staff for Education, Ralph H Johnson Veterans Affairs Medical Center
Disclosure: BioMerieux Honoraria Review panel membership; Cubist Honoraria Review panel membership; Pfizer Honoraria Speaking and teaching; Merck Stock dividends stock holdings

CME Editor

Eleftherios Mylonakis, MD, Clinical and Research Fellow, Department of Internal Medicine, Division of Infectious Diseases, Massachusetts General Hospital
Eleftherios Mylonakis, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Society for Microbiology, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Chief Editor

Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

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