How do human lice live? - briefly
Human lice subsist by feeding on scalp blood, inhabiting hair shafts, and depositing eggs (nits) that cling to hair fibers. They depend on direct head-to-head contact for spread and die within a day without a host.
How do human lice live? - in detail
Human lice are obligate ectoparasites that depend entirely on a human host for nutrition, reproduction, and shelter. Their life cycle consists of three stages: egg (nit), nymph, and adult. Eggs are glued to hair shafts or fibers with a cementing protein and hatch after 7–10 days at temperatures between 30 °C and 35 °C. Nymphs emerge as miniature adults, undergo three molts over 9–12 days, and become capable of blood feeding after the second molt.
Adult females lay 5–10 eggs per day, producing up to 150 eggs during a lifespan of 30–40 days. Mating occurs shortly after the final molt; males die within a week, while females continue laying eggs until death. Feeding occurs every 30–60 minutes, with each blood meal lasting 5–10 minutes. Blood ingestion supplies the protein required for egg production and sustains metabolic activity.
Three distinct species occupy specific niches on the human body:
- Head lice (Pediculus humanus capitis) – reside on the scalp, attaching to hair shafts near the scalp. They thrive in warm, humid environments and are transmitted primarily by direct head‑to‑head contact.
- Body lice (Pediculus humanus humanus) – inhabit clothing seams and lay eggs on fabric. They move to the skin only to feed, preferring crowded, unhygienic conditions where clothing is not changed regularly.
- Pubic lice (Pthirus pubis) – colonize coarse hair in the genital region, eyebrows, or chest. Transmission occurs mainly through sexual contact or close personal contact.
Off‑host survival is limited. Eggs remain viable for up to 10 days without a host, while nymphs and adults survive no more than 24–48 hours in the absence of blood. Temperature extremes above 45 °C or below 0 °C are lethal within minutes.
Transmission pathways include:
- Direct physical contact (head‑to‑head, sexual contact, skin‑to‑skin).
- Indirect contact via contaminated personal items (combs, hats, clothing, bedding).
- Infestation of clothing or bedding by body lice, leading to spread among individuals sharing the same garments.
Population density on a host can reach 200–300 individuals per square centimeter of scalp, causing itching, irritation, and secondary bacterial infection if the skin is breached.
Control measures focus on removing all life stages:
- Mechanical removal of eggs and nymphs with fine‑toothed combs.
- Application of topical pediculicides that disrupt the nervous system of lice; efficacy depends on correct dosage and repeat treatment after 7–10 days to target newly hatched nymphs.
- Regular laundering of clothing and bedding at temperatures ≥60 °C to eliminate body‑lice eggs.
- Maintaining personal hygiene and avoiding shared personal items reduce transmission risk.
In summary, human lice survive exclusively on blood, reproduce rapidly within a month, and persist in environments that provide warmth, humidity, and direct host contact. Their limited off‑host endurance underscores the importance of prompt detection and thorough eradication to prevent spread.