Phthiriasis pubis (crab louse infestation) is an ectoparasitosis transmitted mostly by skin to skin contact, primarily located in the genital areas and secondly, if treated late, expanding towards the armpits or other parts of the adult body with thick hair. In children before sexual maturation, the affected sites can include the eyelashes or head hair, usually after contact with an adult who has been sexually infected. Commonly, diagnosis is easy and requires finding eggs (nits) and/or insects, generally firmly hooked to hair shaft base. Because phthiriasis is included in sexually transmitted diseases, it is recommended to expand investigation to other venereal diseases.
Recent reports about Phthirus pubis seem to suggest a change of its usual behavior, favoring a primary scalp location without genital involvement, as already described by some authors and observed in a personal unpublished series.
Although fomites can carry parasites anywhere, cases considered in this letter refer to adults or school age children whose infestation was neither transmitted through objects or sexual intercourse, nor by non-sexual touching (i.e., when children sleep with a parent). A careful anamnestic reconstruction was only suggestive for a head-to-head direct contact modality.
This scenario, not yet fully investigated, could be partially explained with some hypotheses. One of the most probable could be related to the very popular practice of pubis and underarm trichotomy or laser epilation of any part of the body that eliminates the parasite’s natural habitat. Another suggestive hypothesis could regard some connection between terrestrial climatic changes and different receptivity of human skin to P. pubis. Anyway, in such unusual conditions, crabs appear to skip genital targets and going directly towards cephalic areas…Scanni, Gaetano. Anais Brasileiros de Dermatologia. 16 September 2020.
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