How do lice manifest in humans? - briefly
Infestation produces intense itching, visible live insects and attached eggs (nits) on hair shafts or clothing fibers, and localized redness or irritation. Severe cases can lead to secondary bacterial infection from scratching.
How do lice manifest in humans? - in detail
Lice infestations become evident through a combination of skin irritation, visible insects, and secondary skin changes. The three species that affect people—head lice, body lice, and pubic lice—each have characteristic patterns of presentation.
Head lice (Pediculus humanus capitis) cause intense pruritus, especially behind the ears and at the nape of the neck. The itching results from the saliva injected while feeding. Repeated scratching produces erythematous papules and excoriations. Live nymphs and adult insects can be seen attached to hair shafts, often near the scalp. Nits—unhatched eggs—appear as firm, oval, white structures cemented to the hair shaft about 1 mm from the scalp; they may be mistaken for dandruff but do not detach easily.
Body lice (Pediculus humanus corporis) inhabit clothing seams rather than the skin itself. Infestation manifests as a rash on the shoulders, lower back, and abdomen where clothing contacts the body. The rash consists of small, red papules or pustules that develop at bite sites. Persistent scratching can lead to crusted lesions and, in severe cases, secondary bacterial infection such as impetigo or cellulitis. Nits are deposited on fabric fibers and may be visible as tiny, whitish specks.
Pubic lice (Pthirus pubis), commonly called crab lice, produce itching in the genital region, perianal area, and occasionally on coarse body hair (e.g., chest, abdomen, armpits). The insects are visible to the naked eye as dark, crab‑shaped bodies attached to hair shafts. Bite marks appear as small, erythematous papules that may develop into excoriated lesions. Inflammation can spread to surrounding skin, causing edema and, rarely, secondary infection.
Additional clinical signs across all types include:
- Excoriated skin from persistent scratching
- Secondary bacterial infection indicated by pus, warmth, and increased pain
- Lymphadenopathy in the groin (pubic lice) or cervical region (head lice) when inflammation is pronounced
- Dermatitis from allergic reaction to louse saliva or feces
Diagnosis relies on direct visualization of live lice or nits using a fine‑toothed comb for head lice, inspection of clothing seams for body lice, and careful examination of affected hair-bearing areas for pubic lice. Laboratory confirmation is rarely required but may involve microscopic identification of specimens.
Effective management includes mechanical removal of insects and eggs, thorough cleaning of personal items (e.g., laundering clothing and bedding at ≥60 °C for body lice), and topical or oral pediculicidal agents prescribed according to the specific louse species. Prompt treatment reduces symptom duration and prevents complications such as bacterial superinfection.