Head lice

Case scenario

Jane and her 5-year-old son visit the pharmacy. Jane believes her child has head lice for the first time and needs advice. You comb through the child’s hair using a fine-tooth comb and find moving lice. After confirming the child has no allergies, you recommend KP24 (malathion) lotion, which is a first-line treatment for head lice. You explain how to use the treatment: apply to dry hair, massage the lotion in for 6 minutes and leave it on the scalp for 30 minutes before washing. You advise Jane not to use hot tools while using this product (e.g. a blow dryer), as it is flammable. You emphasise that at least two applications are needed, at least 7–10 days apart. It should be followed up with daily wet combing to identify remaining or newly hatched live lice.

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Introduction

Head lice (Pediculus humanus capitis) infestation is a global public health issue — the prevalence estimates range from 5% in Europe to 33% in Central and South America.¹ Prevalence of head lice infestation in Australian schools has been reported to be as high as 34%.^1–5 

Most head lice treatments are over-the-counter medicines, available without a prescription and readily available in pharmacies. It is essential that pharmacists have the knowledge and skills to assess, counsel and recommend appropriate evidence-based treatments for head lice. 

What are the symptoms?

Head lice infestation can be asymptomatic, particularly in first-time cases or light infestations.^6–8 The main symptom is pruritus (itch) on the scalp, back of the neck and behind the ears, caused by an allergic reaction to louse saliva, which it injects while feeding.^6,9,10 Individuals who have never experienced a head lice infestation can experience a delayed onset of itching, as sensitisation to louse saliva can develop over 4–6 weeks.^6,9 Red to brown spots may be found on the scalp, which is blood excreted and digested by the lice.¹⁰ In rare cases, excessive scratching can lead to sores and secondary infections (e.g. impetigo), enlarged lymph nodes, alopecia, poor sleep and irritability.^6,10–12 While extremely rare, there are reports of iron deficiency anaemia from severe infestations.^13,14   

What are the causes and risk factors?

Head lice can affect individuals of all age groups, irrespective of socioeconomic status, personal hygiene and hair type.^15–17 It is mostly seen in children aged 3–11 years,^15,18 and females (2.5 times higher risk).¹ 

Head lice are commonly transmitted through direct head-to-head contact.^6,9 Indirect transmission through sharing of clothes and personal care items is rare.⁶ Animals are not a vector for head lice transmission.⁹

The life cycle of head lice 

The adult head louse is an arthropod insect (Phthiraptera), whitish grey to pale brown in colour, 2–3 mm in length, equipped with mouth parts to suck blood and 6 legs to attach to hair strands.^6,7,9 Lice cannot jump or fly; they can only crawl from head to head,^{7, 9} and the average life span of an adult louse is 32–35 days.^6,19 Lice can only survive 1–2 days away from the scalp but can become non-viable due to dehydration before death occurs.^6,20 

The louse requires a protein blood meal to produce eggs and will feed from its host every few hours.⁹ Its saliva aids feeding by acting as an anticoagulant and vasodilator.⁹

Nits (louse eggs) are 1 mm in size, oval, and yellow to white in colour.⁷ The louse produces a glue-like substance which allows the nits to stick firmly to hair strands; they are commonly found near the scalp margins, behind the ears and back of the neck.^7,9,12 They are incubated by the heat of the scalp; eggs cannot hatch if they are not kept at temperatures close to the scalp and can die within a week.^7,9 Nymphs (immature lice) hatch after 7–10 days.^6,15,16 Once hatched, the nit shell becomes more visible, a dull yellow to white in colour, and remains attached to the hair shaft.^6,15 Nymphs pass through three maturation stages, known as moults, which takes anywhere from 2 to 10 days.¹⁹ The female louse can mate and lay eggs about 1–2 days after becoming an adult and can lay 3–8 eggs per day.^6,19 

Identifying head lice infestation 

Diagnosis of head lice infestation can be challenging, as it can be easily misdiagnosed (see Table 1). Visual identification of a live louse on the scalp is required for diagnosis.^6,7 Itching, or the presence of eggs, does not always indicate an active infestation. 

Wet combing is a commonly used diagnostic tool and is preferred over visual inspection.^7,21 Conditioner is applied to the hair to immobilise the lice, and a head lice comb (fine-tooth comb) is used to brush through the hair to collect the lice and eggs.⁷ 

1. Apply hair conditioner liberally to wet hair (conditioner immobilises lice for about 20 minutes).
2. Detangle the hair, divide it into 3–4 cm sections, and comb each section from close to the scalp through to the tips of the hair using a fine-tooth comb.
3. Wipe the conditioner from the comb onto a paper towel after each stroke and inspect for lice and eggs.
4. Repeat combing at least twice for each hair section.
5. Thoroughly rinse the hair.

Adapted from Therapeutic Guidelines and Australian Pharmaceutical Formulary (APF) 25. ^{6, 7}

Other causes of head lice-like symptoms and their differentiating features are listed in Table 1.

Table 1 – Other causes of head lice-like symptoms

When is referral required?

The following are red flag symptoms that may require referral to a doctor:^7,11

• Unclear diagnosis
• Signs of secondary infection (e.g. weeping or crusting of skin, swollen glands, fever)
• Infestation is affecting quality of life (e.g. sleep)
• Treatment failure 
• Has occurred 3 or more times in a year.

Management of head lice infestation

Neurotoxic agents are the first-line treatment option for head lice infestation,²² though there are reports of increasing resistance.^10,23 Physical insecticides like dimethicone are emerging to become favourable alternative options, and wet combing is an effective but labour-intensive mechanical approach.²⁴ 

The treatment goals for head lice infestation are to eliminate the active infestation and prevent transmission of lice to others.⁷ Treatment choice should be guided by local patterns of insecticide resistance, prior use of treatments, patient characteristics (age, pregnancy, breastfeeding, history of hypersensitivity or adverse effects), and individual preference.⁷ 

Treatment should only be commenced if live lice are identified on the individual. Prophylactic treatment is not recommended and can contribute to insecticide resistance, treatment failure and adverse effects.^{7, 12} 

Close contacts of the infested individual should be screened using the wet combing method, repeated daily.⁷ Most treatments do not kill eggs and require a second or third application after 7–10 days to ensure the lice that have hatched since the first application are killed off.^7,23 Dead eggs, lice or egg casings can be removed via fingernails or a fine-tooth comb.⁷ 

Treatment failure is defined as lice being present after the administration of treatment; this can be attributed to a variety of reasons: insecticide resistance, improper or inadequate application, re-infestation, failure to re-treat, or misdiagnosis.⁷

Treating head lice^7,8: 

1. Confirm the presence of live lice on the scalp using wet combing or visual identification method. Identify close contacts of the patient, and recommend daily screening by wet combing while infestation is active.
2. Recommend a treatment based on patient characteristics and preference. Neurotoxic insecticides are suitable from age >6 months.⁸
   • See individual product information for specific instructions on how long product should be left in the hair.
   • Protect the eyes, mouth and nose with a towel or face cloth.
   • Do not apply insecticides to hair after conditioner or hair product has been applied.
   • Apply the product over the entire head, coating all hairs from root to tip.
   • Dry hair with a towel, not a hair dryer. Heat can inactivate the product.
   • Avoid rewashing the hair for 1–2 days after treatment.
   • Wash hands thoroughly after use.
   • Close contacts with live head lice should be treated at the same time to prevent re-infestation.
3. Wet combing is an effective, labour intensive treatment for head lice and may be preferred in pregnant or breastfeeding patients.^{7, 8} Wet comb every 1–2 days until no lice are found for 10 consecutive days.^7,22 (See “Identifying head lice infestation” section for wet combing method)
4. Following each treatment, wet-comb hair daily to check for newly hatched or resistant lice.
5. Re-treat hair after 7–10 days and continue surveillance with wet combing and re-treatment, if necessary, until no more lice are found.
6. Resistant infestations may respond to a change in treatment. Recurrent treatment failure requires referral to a medical practitioner.  

Head lice treatment options are outlined in Table 2. 

Table 2 – Head lice treatments

References: APF 25⁷, TG⁸, AMH²², Department of Health²³, Public health medicine environmental group²⁴, TGA (DAEN)²⁵, Consumer Medicines Information (CMI) for Ivermectin²⁶

*Refer to product information for instructions on individual product use

Non-pharmacological treatments

As head lice can only survive 1–2 days away from the scalp, and there being little evidence of indirect transmission, the following interventions may be recommended; however, they have limited effectiveness in reducing infestations^7,11:

• Soak combs and brushes in very hot water (>60 °C) for 5 minutes.
• Items used by the individual 2 days before the initiation of treatment (e.g. hats, scarves, pillowcases, bedding, clothing and towels) should be washed in hot water, and dried using the hot air cycle or hung in direct sunlight.
• Dry-clean items that cannot be washed, or seal them in a plastic bag for 2 weeks.
• Vacuum furniture and floors to remove hairs that may have attached nits.  

Drug interactions

Malathion can be absorbed through the skin, though risk of systemic exposure is low.^22,27 If ingested, there is a risk of respiratory depression.¹⁹ 

Malathion when used in combination with anticholinesterases (e.g. donepezil, pyridostigmine) can result in additive toxicity.²² 

Prevention of infestation

There are no preventive treatments for head lice, though the following strategies can be used to reduce the transmission of head lice⁷:

• Regularly inspect the hair using the wet combing method.
• Avoid playing with other people’s hair.
• Tie hair back or plait long hair.
• Avoid head-to-head contact with other people.
• Avoid sharing personal items (e.g. clothes, towels, bedding, pillowcases, hairbrushes, combs, hair accessories and helmets).
• Avoid lying on beds, couches, pillows, carpets or stuffed animals that have recently come into contact with an infested person. 

Exclusion periods

Children identified with active lice need to inform the school and close contacts to ensure appropriate screening can be implemented. Children should be excluded from school until the day after appropriate treatment has been administered and no live lice are detected.⁷ 

Key points

• Head lice is a common health problem, most often affecting school-aged children, irrespective of their socioeconomic status and personal hygiene. 
• Head lice is transmitted through direct head-to-head contact. Indirect transmission through clothing or furniture is rare.
• Diagnosis of head lice infestation is established by the identification of live lice on the scalp, which can be done through wet combing.
• Repeated treatment application, at least 7–10 days apart, is required to eliminate the lice that did not hatch in the first application. Increasing resistance may require another treatment with a different neurotoxic medicine.

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References

1. Hatam-Nahavandi K, Ahmadpour E, Pashazadeh F, et al. Pediculosis capitis among school-age students worldwide as an emerging public health concern: a systematic review and meta-analysis of past five decades. Parasitol Res 2020;119(10):3125-43.
2. Speare R, Thomas G, Cahill C. Head lice are not found on floors in primary school classrooms. Aust N Z J 2002;26(3):208-11.
3. Currie MJ, Ciszek K, Kljakovic M, Bowden FJ. Prevalence of head lice among children entering school in the ACT 2006-08. Aust N Z J Public Health 2011;35(2):195–6.
4. Counahan M, Andrews R, Büttner P, et al. Head lice prevalence in primary schools in Victoria, Australia. J Paediatr Child Health 2004;40(11):616–9.
5. Speare R, Buettner PG. Head lice in pupils of a primary school in Australia and implications for control. Int J Dermatol. 1999;38(4):285–90.
6. Centres for Disease Control and Preventation. Head lice. 2013. At: cdc.gov/parasites/lice/head/index.html
7. Sansom L, ed. Australian pharmaceutical formulary and handbook. 25th ed. Canberra: PSA; 2021
8. Therapeutic Guidelines. Melbourne: Therapeutic Guidelines Limited. 2021
9. Devore CD, Schutze GE; AAP, Council on School Health, Committee on Infectious Diseases. Head Lice. Pediatrics 2015;135(5):e1355–e1365
10. Lamb, S. Head lice. 2018. At: https://dermnetnz.org/topics/head-lice
11. Raising Children Network (Australia) Limited. Head lice. At: https://raisingchildren.net.au/guides/a-z-health-reference/head-lice
12. Whybrew C. Detection and recommended treatment of head lice. Prescriber 2017;28(1):32–6.
13. Guss DA, Koenig M, Castillo EM. Severe iron deficiency anemia and lice infestation. J Emerg Med 2011;41(4):362–5.
14. Lowenstein EJ, Parish LC, Van Leer-Greenberg M, et al. The darker side of head lice infestations. Clin Dermatol 2022;40(1):81–4
15. Children’s Health Queensland Hospital and Health Service. Head lice. 2018. At: childrens.health.qld.gov.au/fact-sheet-head-lice/
16. Government of South Australia. Head lice-including symptoms treatment and prevention. At: www.sahealth.sa.gov.au/wps/wcm/connect/public+content/sa+health+internet/conditions/bites+stings+and+pests/head+lice+-+including+symptoms+treatment+and+prevention
17. Healthy WA. Head lice. 2019. At: healthywa.wa.gov.au/Articles/F_I/Head-lice
18. Johns Hopkins Medicine. No-panic guide to head lice treatment. At: www.hopkinsmedicine.org/health/treatment-tests-and-therapies/no-panic-guide-to-head-lice-treatment
19. Department of Health. Pediculosis (head lice). At: www.health.vic.gov.au/infectious-diseases/pediculosis-head-lice
20. Canyon DV, Speare R. Indirect transmission of head lice via inanimate objects. The Open Dermatology Journal 2010;4(1):72–6.
21. Jahnke C, Bauer E, Hengge U, et al. Accuracy of diagnosis of pediculosis capitis visual inspection vs wet combing. Arch Dermatol 2009;145:309–13.
22. Rossi S, ed. Australian medicines Adelaide: AMH; 2021.
23. Government of South Australia, Department of Health. Healthy heads without headlice: Management guidelines for the control of headlice in South Australia. 2005. At: sahealth.sa.gov.au/wps/wcm/connect/e1dc4180458f95fe92c3ff4ba88a01d5/headlice-book-jan06-web.pdf?MOD=AJPERES&CACHEID=ROOTWORKSPACE-e1dc4180458f95fe92c3ff4ba88a01d5-nKNDYcv
24. Public Health Medicine Environmental Group. Head lice: evidence-based guidelines based on the Stafford Report 2012 update. At: www.nhsggc.org.uk/media/239960/stafford-head-lice-2012.pdf
25. Therapeutic Goods Administration: Australian Government, Department of Health. Database of Adverse Event Notifications (DAEN). At: www.tga.gov.au/database-adverse-event-notifications-daen
26. Therapeutic Goods Administration: Australian Government, Department of Health. Consumer Medicines Information (CMI). At: www.tga.gov.au/consumer-medicines-information-cmi
27. Therapeutic Goods Administration. A review of the regulation of head lice treatments in Australia. 2003. At: www.tga.gov.au/publication/review-regulation-head-lice-preparations-australia

SANDRA RAJU BPharm (Hons) is an intern pharmacist.

DR WUBSHET TESFAYE BPharm, MSc, PhD is a project manager and post-doctoral researcher at the University of Sydney.

DR MARY BUSHELL BPharm (Hons), AACPA, GCTLHE, AFACP, MPS, PhD is a Clinical Assistant Pharmacist and the Professional Practice Convenor for the pharmacy discipline at the University of Canberra.

DR JACKSON THOMAS BPharm, MPharmSc,PhD is a pharmacist, trialist, NHMRC-funded pharmaceutical scientist and Associate Professor at the University of Canberra.