What is the disease caused by lice called?

Understanding Lice Infestations

What Are Lice?

Types of Lice

Lice are obligate ectoparasites that feed on human blood or skin debris. The infection transmitted by certain lice species is known as epidemic typhus, caused by Rickettsia prowazekii and associated primarily with body lice.

Head louse (Pediculus humanus capitis) – inhabits the scalp, attaches eggs (nits) to hair shafts, spreads through direct head‑to‑head contact. Does not transmit serious bacterial disease but causes intense pruritus and secondary skin irritation.
Body louse (Pediculus humanus corporis) – lives in clothing seams, moves to the skin to feed. Serves as vector for Rickettsia prowazekii (epidemic typhus), Borrelia recurrentis (relapsing fever), and Bartonella quintana (trench fever). Outbreaks occur in crowded, unhygienic environments.
Pubic louse (Pthirus pubis) – infests the genital region and coarse body hair. Transmits the parasite through sexual contact; does not act as a vector for bacterial pathogens.
Crab louse (Pthirus pubis) – alternative name for the pubic louse; same biological characteristics and transmission routes.
Sucking lice of other mammals – various species infest animals; not relevant to human disease but illustrate the broader taxonomic diversity of the order Phthiraptera.

The disease linked to lice infestation is classified as a rickettsial infection, specifically epidemic typhus. Body lice constitute the primary vector, transmitting the pathogen when they defecate on the skin and the fecal material is introduced into abrasions. Control measures focus on improving personal hygiene, regular laundering of clothing at high temperatures, and prompt removal of all louse stages.

Life Cycle of Lice

The disease produced by lice infestation is medically termed pediculosis. Its persistence depends largely on the parasite’s development, which follows a predictable sequence of stages.

Lice begin life as eggs, commonly called nits, that are firmly attached to hair shafts near the scalp. Each egg measures about 0.8 mm and requires 7–10 days of incubation at normal body temperature before hatching.

After emergence, the juvenile stage, known as the nymph, appears. Nymphs resemble miniature adults but lack full reproductive capability. They undergo three successive molts, each lasting approximately 3–4 days, during which they grow and acquire the ability to feed on blood.

The final molt produces the adult louse. Adults measure 2–4 mm, live for 30 days on a host, and begin reproducing after about 5 days. A single female can lay 5–10 eggs per day, maintaining the infestation cycle.

Key points of the life cycle:

Egg (nit): 7–10 days incubation.
First nymphal stage: 3–4 days before first molt.
Second nymphal stage: 3–4 days before second molt.
Third nymphal stage: 3–4 days before third molt.
Adult: 30 days lifespan, reproductive after 5 days, 5–10 eggs daily.

Successful control of pediculosis requires interruption of this cycle, typically by eliminating nits, reducing nymphal populations, and preventing adult reproduction. Effective measures include thorough combing, topical agents that kill all stages, and environmental decontamination to remove detached eggs.

Common Conditions Caused by Lice

Pediculosis Capitis («Head Lice Infestation»)

Symptoms of Head Lice

Head lice infestation, medically termed pediculosis capitis, manifests primarily on the scalp and hair shafts. The parasite’s feeding activity and allergic reaction to its saliva generate a recognizable set of clinical signs.

Intense itching, especially behind the ears and at the nape of the neck
Presence of live lice, visible as small, grayish‑brown insects moving quickly across hair strands
Nits (lice eggs) firmly attached to hair shafts, appearing as tiny, oval, white or yellowish specks within 1 mm of the scalp
Red or inflamed skin patches caused by scratching or bite sites
Occasionally, secondary bacterial infection resulting from excoriated skin

Symptoms typically appear within 4–6 weeks after initial contact. Early detection relies on thorough visual inspection of the scalp under adequate lighting, often aided by a fine‑toothed comb. Persistent pruritus and the identification of nits close to the scalp are the most reliable indicators of an active infestation.

Transmission of Head Lice

Head lice (Pediculus humanus capitis) spread primarily through direct head‑to‑head contact. The insects cling to hair shafts and move quickly, allowing a single brief encounter to transfer viable nymphs or adult lice.

Key transmission routes include:

Physical contact: Sharing hair brushes, hats, helmets, or scarves creates a conduit for lice movement.
Environmental exposure: Lice can survive for 24–48 hours off the host; contact with contaminated bedding, upholstered furniture, or personal items may result in infestation.
Group settings: Close proximity in schools, daycare centers, camps, or sports teams increases the likelihood of rapid spread.

Transmission efficiency depends on hair length, grooming habits, and the density of individuals in a confined space. Preventive measures focus on minimizing shared personal items and maintaining regular head inspections, especially in environments where close contact is routine.

Diagnosis of Head Lice

Pediculosis capitis, the medical term for an infestation of the scalp with Pediculus humanus capitis, is identified primarily through clinical examination.

Typical findings include live lice adhered to hair shafts, viable nymphs, and brownish or dark oval eggs (nits) firmly attached near the hair root. Scalp irritation, itching, and secondary excoriations often accompany the infestation.

Diagnostic procedures focus on direct observation:

Visual inspection: Examine the scalp under good lighting, parting hair in sections to reveal lice or nits within 1 cm of the scalp surface.
Wet combing: Apply a conditioner to damp hair, then pass a fine-toothed lice comb from the scalp outward, wiping the comb after each pass to collect specimens.
Dermatoscopy: Use a handheld dermatoscope (10–20× magnification) to confirm the presence of adult lice, nymphs, or eggs without extensive hair manipulation.

If uncertainty persists, collect a sample of suspected lice or nits and submit to a laboratory for microscopic confirmation. The combination of symptom assessment and these targeted techniques yields a reliable diagnosis of head‑lice infestation.

Treatment Options for Head Lice

Effective management of head‑lice infestation relies on several evidence‑based strategies. Over‑the‑counter pediculicides containing permethrin 1 % or pyrethrins combined with piperonyl‑butoxide are first‑line options; they must be applied to dry hair for the recommended duration and repeated after seven days to eliminate newly hatched nymphs. Prescription agents such as malathion 0.5 % or benzyl alcohol 5 % lotion are reserved for cases where resistance to OTC products is suspected or confirmed. Both require precise dosing and adherence to safety guidelines, especially in children under two years of age.

Mechanical removal complements chemical treatment. Fine‑toothed nit combs, used on wet, conditioned hair, eliminate live lice and viable eggs when combed systematically from scalp to hair tip. Repeating the combing process every two to three days for two weeks ensures complete eradication. The method is safe for all ages and reduces reliance on insecticides.

Adjunctive measures prevent reinfestation. Washing bedding, clothing, and personal items in hot water (≥ 54 °C) or sealing them in airtight containers for two weeks destroys residual lice and eggs. Regular inspection of household members and immediate treatment of any new cases interrupt transmission cycles. In settings where chemical resistance is prevalent, rotating between different classes of pediculicides or combining chemical and mechanical approaches improves outcomes.

Pediculosis Corporis («Body Lice Infestation»)

Symptoms of Body Lice

Body lice infestation, medically termed pediculosis corporis, presents with a characteristic set of cutaneous and systemic manifestations. The infestation itself produces localized irritation, while the pathogens it can transmit generate additional clinical signs.

Intense pruritus, especially after prolonged periods of inactivity or heat exposure.
Erythematous papules or pustules at sites where lice attach, commonly the waist, hips, and thighs.
Linear or clustered excoriations resulting from scratching.
Hyperpigmented macules or post‑inflammatory streaks that persist after lesions heal.
Visible nits or adult lice attached to clothing fibers or directly to the skin.
Secondary bacterial infection indicated by purulent drainage, increased warmth, or spreading erythema.

When body lice act as vectors for infectious agents, patients may develop:

Sudden onset fever accompanied by chills.
Headache and generalized malaise.
Myalgia and arthralgia, often described as a “body ache.”
Transient rash distinct from the primary lice‑induced lesions, sometimes resembling a maculopapular eruption.

Recognition of these symptoms enables timely treatment and prevents complications associated with lice‑borne diseases.

Transmission of Body Lice

Body lice (Pediculus humanus corporeus) are vectors of the louse‑borne illness most commonly identified as epidemic typhus, along with trench fever and relapsing fever. The insects live in clothing seams and feed on human blood, creating a direct link between the host’s skin and the pathogens they carry.

Transmission occurs when infected lice or their excreta come into contact with a person’s skin or mucous membranes. The primary routes are:

Defecation of lice on the skin; scratching introduces fecal material that contains viable bacteria.
Crushing of lice; released internal fluids contaminate the surrounding area.
Contaminated clothing, bedding, or towels that harbor live lice or their waste.
Direct skin‑to‑skin contact in crowded, unhygienic environments, facilitating rapid spread.

Risk factors include prolonged wearing of unwashed clothing, overcrowding, limited access to clean water, and situations that impede regular laundering, such as refugee camps or disaster shelters. These conditions promote lice proliferation and increase exposure to the pathogens they transmit.

Control measures focus on eliminating the ectoparasite and its habitat: frequent laundering of garments at temperatures above 60 °C, thorough drying, replacement of infested clothing, and application of approved pediculicides when necessary. Maintaining personal hygiene and reducing crowd density are essential components of an effective prevention strategy.

Diagnosis of Body Lice

Body lice (Pediculus humanus corporis) are identified by their presence in clothing seams, especially in the waist and groin areas. Infestation manifests as itching, excoriations, and the appearance of nits attached to the fabric rather than the hair shaft. Direct visual inspection of the garment and skin reveals adult lice measuring 2–4 mm, translucent bodies, and elongated abdomens filled with blood.

Laboratory confirmation involves several methods:

Microscopic examination of collected specimens to verify morphological features such as the six‑segment antennae and the characteristic dorsal shield.
PCR assays targeting the mitochondrial cytochrome oxidase I gene to differentiate body lice from head lice with high specificity.
Serologic testing for antibodies against Rickettsia prowazekii, the pathogen responsible for louse‑borne typhus, when systemic symptoms accompany the infestation.

Clinical assessment should correlate cutaneous findings with epidemiologic risk factors, including homelessness, crowded living conditions, and inadequate hygiene. Absence of lice on the scalp helps distinguish body lice from head lice, which inhabit hair follicles. Prompt identification enables targeted treatment and reduces the likelihood of secondary infection and transmission of the associated rickettsial disease.

Treatment Options for Body Lice

Body lice infestation, medically termed pediculosis corporis, results from prolonged contact with contaminated clothing or bedding. Effective management requires eliminating the parasites and preventing re‑infestation.

Key interventions include:

Improved personal hygiene: Daily bathing and thorough washing of the entire body remove lice and eggs.
Laundering of garments and linens: Machine‑wash at ≥60 °C for at least 30 minutes; alternatively, dry‑clean or seal items in a plastic bag for 72 hours to starve lice.
Topical pediculicides: Apply FDA‑approved products containing permethrin 1 % or pyrethrins with piperonyl butoxide; follow label instructions for repeat application after 7–10 days to target newly hatched nymphs.
Oral ivermectin: Single dose of 200 µg/kg for adults; repeat after 7 days if live lice persist. Reserve for cases where topical agents fail or are contraindicated.
Environmental decontamination: Vacuum carpets, upholstery, and mattresses; discard heavily infested items that cannot be cleaned.

Adjunct measures—such as regular inspection of skin folds, prompt treatment of contacts, and education on avoidance of shared clothing—support long‑term control.

Phthiriasis Pubis («Pubic Lice Infestation» or «Crabs»)

Symptoms of Pubic Lice

Pediculosis pubis, commonly referred to as crab infestation, results from the ectoparasite Pthirus pubis colonizing the pubic region and adjacent hair‑bearing areas. The infestation manifests through a distinct set of clinical signs.

Persistent, localized itching that intensifies after bathing or sexual activity
Presence of live lice or translucent eggs (nits) attached to coarse hair near the base of the shaft, labia, thighs, buttocks, or abdomen
Small, bluish‑gray macules or papules caused by bite‑induced inflammation
Redness, swelling, or excoriation from scratching
Secondary bacterial infection indicated by pus, increased warmth, or foul odor

Symptoms may appear within one to two weeks after exposure and can spread to other body sites with sufficient hair growth. Prompt identification of these signs enables effective treatment and limits transmission.

Transmission of Pubic Lice

Pubic lice, scientifically Pthirus pubis, cause the condition known as phthiriasis pubis, a contagious ectoparasitosis of the genital region and adjacent body hair.

Transmission occurs primarily through direct human contact. The most common pathways include:

Vaginal, anal, or oral sexual intercourse, which provides immediate transfer of lice from one partner to another.
Prolonged skin‑to‑skin contact without sexual activity, such as sharing a bed or prolonged hugging.
Contact with contaminated objects (fomites) like towels, bedding, clothing, or sex toys that have not been disinfected.

Secondary factors that increase transmission risk are high‑density living environments, inadequate personal hygiene, and the presence of other sexually transmitted infections, which may facilitate lice acquisition.

Prevention relies on avoiding the aforementioned contact routes and implementing hygiene measures: regular laundering of personal fabrics at high temperatures, using disposable or thoroughly disinfected sexual aids, and prompt treatment of identified infestations with approved topical pediculicides. Early detection reduces spread and limits secondary infection.

Diagnosis of Pubic Lice

Pubic lice infestation, medically termed pediculosis pubis, is identified primarily through visual inspection. Adult lice appear as dark, crab‑shaped insects approximately 1–2 mm long, attached to hair shafts in the pubic region, perianal area, or coarse body hair. Nits (eggs) are ovoid, firmly cemented to the shaft near the base.

Key diagnostic criteria:

Live lice or viable nits observed under magnification.
Intense itching localized to infested zones, often worsening at night.
Erythematous papules or small pustules resulting from bite reactions.

Laboratory confirmation may involve:

Collecting hair samples with fine forceps.
Placing specimens on a glass slide with saline.
Examining under a light microscope at 10–40× magnification for characteristic morphology.

Absence of lice but presence of nits warrants treatment, as nits may hatch within 5–10 days. Accurate diagnosis relies on thorough physical examination and, when needed, microscopic verification.

Treatment Options for Pubic Lice

Pubic lice (Pthirus pubis) require prompt eradication to prevent reinfestation and secondary skin irritation. Effective management combines chemical agents, mechanical removal, and environmental decontamination.

Topical pediculicides are first‑line. Permethrin 1 % cream rinse applied to the affected area for ten minutes, then rinsed off, eliminates most insects. Pyrethrins combined with piperonyl butoxide provide an alternative for patients intolerant to permethrin. Malathion 0.5 % lotion, left on for eight to twelve hours before washing, is useful when resistance to pyrethrins is suspected.

Oral ivermectin (200 µg/kg) offers a systemic option for extensive infestations or when topical treatment fails. A single dose is usually sufficient; a repeat dose after seven days addresses newly hatched lice.

Mechanical methods supplement chemicals. Fine‑toothed combs remove live lice and nits after shaving or trimming the hair. Repeating combing every 48 hours for a week reduces residual organisms.

Environmental control prevents re‑exposure. Wash bedding, towels, and clothing in hot water (≥ 50 °C) or seal items in plastic bags for at least 72 hours. Treat sexual partners simultaneously; untreated contacts reintroduce the parasite.

A typical regimen:

Apply permethrin 1 % cream rinse; repeat after seven days.
If resistance suspected, substitute pyrethrins‑piperonyl butoxide or malathion.
Consider oral ivermectin for severe cases.
Comb affected area with a fine nit comb every two days for one week.
Launder all personal items; advise partners to undergo identical treatment.

Monitoring for adverse reactions, such as skin irritation or allergic response, ensures safe completion of therapy.

Potential Complications of Lice Infestations

Secondary Bacterial Infections

Lice infestations can compromise skin integrity, providing an entry point for pathogenic bacteria. When bacterial colonization follows a lice‑induced lesion, the condition is classified as a secondary bacterial infection.

Typical organisms include Staphylococcus aureus, Streptococcus pyogenes, and Pseudomonas aeruginosa. These pathogens may cause cellulitis, impetigo, or abscess formation at the site of infestation. Clinical signs comprise erythema, swelling, purulent discharge, and localized pain. Systemic manifestations such as fever may develop if the infection spreads.

Management requires both eradication of the ectoparasite and antimicrobial therapy. Recommended steps are:

Mechanical removal of lice and nits.
Topical or oral antibiotics targeting the identified bacteria.
Wound care with antiseptic dressings to reduce bacterial load.

Prevention relies on maintaining personal hygiene, regular inspection of high‑risk populations, and prompt treatment of lice to limit skin disruption. Early recognition of bacterial complications reduces the risk of tissue damage and systemic involvement.

Skin Irritation and Allergic Reactions

Lice infestation, medically termed pediculosis, triggers direct skin irritation through repeated bites and mechanical abrasion. Each bite injects saliva containing anticoagulants, provoking localized inflammation and persistent itching.

The cutaneous response typically includes:

Small, erythematous papules at bite sites
Linear or clustered lesions following the movement of the parasite
Secondary excoriations from scratching

In many individuals, the reaction progresses to a hypersensitivity response. Repeated exposure to lice saliva can sensitize the immune system, leading to contact dermatitis characterized by edema, erythema, and intense pruritus. The severity of allergic manifestations varies with host susceptibility and infestation load.

Effective control combines eradication of the ectoparasite with symptomatic relief. Topical insecticidal agents eliminate the source, while topical corticosteroids or oral antihistamines reduce inflammatory and allergic symptoms. Maintaining hygiene and regular inspection of hair and clothing prevent recurrence.

Psychological Impact

Pediculosis, the medical term for infestation by head, body, or pubic lice, is often perceived as a purely dermatological problem. Clinical observations demonstrate that the condition produces a range of psychological responses that extend beyond skin irritation.

Affected individuals commonly experience:

Persistent anxiety about visible lice or nits
Acute embarrassment when the infestation becomes apparent to others
Reduced self‑esteem due to perceived loss of personal hygiene
Social withdrawal driven by fear of judgment or exclusion
Heightened stress in caregivers responsible for detection and treatment

Research on school‑aged children indicates that peer teasing and isolation correlate with lower academic performance and increased depressive symptoms. Adults report comparable distress, particularly when infestation interferes with professional interactions or family responsibilities.

Effective management therefore incorporates mental‑health strategies alongside antiparasitic therapy. Counseling addresses shame and anxiety, while educational programs clarify transmission mechanisms and reinforce that lice are a common, treatable condition. Reducing stigma through transparent communication lessens the emotional burden and supports faster recovery.

Prevention and Control of Lice Infestations

Hygiene Practices

Pediculosis, the medical term for a lice infestation, spreads primarily through direct contact with contaminated hair or clothing. Effective hygiene measures interrupt transmission and reduce the risk of secondary infections.

Key hygiene practices include:

Regular washing of hair and scalp with medicated shampoo at least twice weekly during an outbreak.
Daily laundering of clothing, bedding, and towels in hot water (minimum 60 °C) followed by high‑heat drying.
Thorough combing of hair with a fine‑toothed lice comb after each wash to remove nits.
Avoidance of sharing personal items such as hats, brushes, headphones, and helmets.
Routine inspection of children’s hair, especially after school or group activities, to detect early signs of infestation.

When an infestation is confirmed, combine the above practices with appropriate topical or oral pediculicides as prescribed. Re‑treat after seven days to eliminate newly hatched lice. Maintaining the described hygiene routine for at least three weeks prevents recurrence and minimizes the likelihood of disease transmission.

Environmental Control

Pediculosis, the medical condition resulting from lice infestation, spreads primarily through direct contact and contaminated surroundings. Effective environmental control reduces the risk of transmission and supports treatment outcomes.

Control measures focus on eliminating viable lice and their eggs from the living environment. Key actions include:

Washing clothing, bedding, and towels in hot water (minimum 130 °F/54 °C) and drying on high heat for at least 20 minutes.
Sealing non‑washable items in airtight plastic bags for two weeks to starve surviving lice.
Vacuuming carpets, upholstered furniture, and vehicle seats, discarding vacuum bags or cleaning canisters immediately after use.
Cleaning personal items such as combs, brushes, and hair accessories by soaking in hot water or applying an alcohol‑based solution.
Restricting shared use of personal items and limiting close contact during active infestation periods.

Regular inspection of household members and immediate removal of infested items sustain a low‑risk environment. Documentation of cleaning cycles and adherence to the outlined protocols ensure consistent protection against re‑infestation.

Screening and Early Detection

Pediculosis, the medical term for an infestation of lice, can be identified before symptoms worsen through systematic screening and prompt detection.

Effective screening relies on direct observation and tactile assessment. Common techniques include:

Visual inspection of the scalp and hair for live lice, nits, or brown‑red spots indicating bites.
Fine‑toothed lice combs applied to dry or damp hair to capture specimens for microscopic confirmation.
Dermatoscopic examination to differentiate lice eggs from hair debris.
Structured questionnaires that capture recent exposure, travel history, and household contacts.

Early detection limits transmission, reduces the need for extensive treatment, and prevents secondary skin infections. Prompt identification enables immediate initiation of topical or oral pediculicides, combined with environmental measures such as laundering bedding and personal items.

Implementing routine checks in schools, childcare centers, and community health programs ensures rapid identification of cases. Training staff to perform standardized examinations and to recognize early signs improves overall control of pediculosis within populations.