|
| Fig. 34.5 Pediculosis. Young girl with pruritic papules on posterior scalp and lower neck. The diagnosis was established by finding nits attached to hair shafts. (Courtesy of the Fitzsimons Army Medical Center teaching files.) |
The head louse (
Pediculus humanus var. capitus) is 2 to 4 mm long with three pairs of legs that are of equal length. The body is dorsoventrally flattened. The entire life cycle is spent in the scalp hair. The visible eggs or nits are deposited on the hair shaft, singly and close to the scalp. Pruritus of the scalp with secondary infection is common. Associated cervical and occipital lymphadenopathy is common. Head lice are more common in school-aged children, especially young females with longer hair (Fig. 34-5).
The large
body louse (
Pediculus humanus var. corporis) resembles the head louse in configuration, only being larger. It lives and reproduces in the lining of the clothes and leaves the clothing only for feeding, being rarely found on the skin. The patient presents with pruritic papules and areas of hyperpigmentation from healing. This problem occurs in the setting of poverty, overcrowding, and poor hygiene in individuals who rarely change or clean their clothes.
The
pubic louse (
Phthirus pubis), or crabs, is smaller, broad-shouldered, and has a narrow head. The major crablike body is dorsoventrally flattened and has three pairs of legs. Eggs are found on the hair shaft. The pubic louse may also be found on short occipital scalp, body, eyebrow, eyelash, and axillary hair. One third of sexually active patients with pediculosis pubis have other sexually transmitted diseases.
