This post features links to and excerpts from the portion of the podcast on lice from Lice And Scabies, by Caleb.Botta, Sep 11, 2019 from PedsCases.*
This podcast was created by Caleb Botta, a senior medical student from the Medical College of Georgia, with the help of Dr. Julie Martin, an Assistant Professor of Pediatrics in the UA/UGA Medical Partnership System. This podcast will cover the manifestations, clinical approach, diagnostic methods, and treatment options for lice and scabies.
Here are excerpts from the transcript:
Introduction to the Human Louse – Key Takeaways
Lice are obligate ectoparasites. There are three different species of lice that infest humans. They are head lice, body lice, and pubic lice, also known as crab lice (1). I am going to start by giving you an overview of what you need to know in order to take care of patients with each type of lice. Then we will dive further into the topic of head lice since head lice are what you are most likely to see in children.
– Head lice
- Head lice is the most common type of lice in school-age children (2–4)
- They are not associated with poor hygiene (5–7)
- The louse eggshells, or nits (8), are found exclusively on the scalp (9). Key areas to look include both temples, behind the ears, and at the base at the neck (10).
- Patterns of treatment resistance have been seen worldwide (3)
- Body lice are vectors of human disease: Rickettsia prowazekii (epidemic typhus), Bartonella quintana (trench fever), Borrelia recurrentis (epidemic relapsing fever)(11)
- Fomite management is key (12)
- Nits found in clothing seams, bedding (12)
– Crab lice
- Not just the pubic area: beards, eyelashes, axilla (2,13)
- Maculae ceruleae are blue or slate colored lesions in patients with heavy crab lice infestations. They are typically on found chest, abdomen, and thighs (14)
- Patients with crab lice should be screened for other sexually transmitted infections (2)
Lice Background and Clinical Manifestations (LO#1)
First, it is important to know that each of these types of lice only infest humans (1). Therefore, treatments of family pets are not necessary (1,6,8,15). Lice are small insects that crawl but do not jump or fly (16). They get their energy from ingesting human blood. Each bite has an injection of anesthetic and anticoagulant along with other antigens (1). The characteristic itching associated with lice infestations occurs 3-4
weeks later and is an allergic reaction to these antigens (1). That being said, only 14-36% of patients experience itching (7). Those who have had lice previously may begin to itch in just two days (7).
Lice cannot survive apart from a human host, but how long they can survive depends on the type of louse and environmental factors. Head lice typically cannot survive more than one day at room temperature, and pubic lice can last about 48 hours (5,14). Body lice, in contrast, can survive for 5-7 days. They thrive in humid, cooler environments that prevent desiccation (11).
Head lice are what comes to mind when many people think of lice. They are associated with school-age children, and outbreaks often occur once children return to school after summer vacation (7). It is estimated that 6-12 million children ages 3-12 years old are infested annually in the United States (13). Thankfully, head lice are not thought to be vectors of human disease. Transmission of head lice occurs primarily via head to head contact. Giving another person lice through an object, called a “fomite”, such as a pillow, hat, or hairbrush typically does not occur (7). Hair lice nits are cemented firmly to the hair shaft by an adhesive at the scalp, and the height of a nit on the hair shaft can be used to approximate the amount of time it has been there. Hair grows roughly 1cm per month. Any nits found more than 1cm from the scalp should, therefore, be considered nonviable and not thought of as evidence of active infestation. In fact, empty egg sacs can persist for months after the clearing of a lice infestation (5).
Diagnostic Methods (LO#2)
Diagnosis is typically made by finding a louse or nit in a patient’s hair. Lice can move quickly and will try to avoid light (17). This, coupled with the fact that many patients do not experience the itching allergic reaction, can make the diagnosis difficult to make. An active infestation is defined as finding live lice in a patient’s hair or finding
a nit on a hair shaft within 1cm of the scalp. Visual inspection of the patient’s hair to detect active infestation has a low sensitivity of only 29% (18). This can be improved to 91% by the use of the wet combing method*, where the patient’s hair is washed with a conditioner to slow down the lice and then combed with a fine-toothed comb [Emphasis added].
Key areas to check are both temples, behind the ears, and at the base at the neck (10). Removing lice in this way also has a beneficial therapeutic advantage (13). It is important to teach parents to use the wet combing method in order to screen the patient’s other family members for lice. That being said, visual examination is 86% sensitive for the detection of nits indicating historical infestation, and it is reasonable to do this for this purpose. A Wood’s lamp will cause head lice to fluoresce a pale blue (19), and this can be helpful.
If you think that you have found evidence of lice in a child’s hair, it is important to confirm that what you have found is not actually something else. One study found that 35% of specimens thought to be lice or nits sent to a reference center were actually dandruff. A key difference is that a nit will be firmly fixed to the hair shaft (10,15). Light microscopy providing extra magnification can also be extremely helpful. Lice have six legs, are tan to grayish-white in color, and are about the size of a sesame seed (20).
Treatment begins with the initial management of symptoms. Antihistamines and topical steroids can be used to help alleviate any itching or burning caused by the lice or by the topical treatments that are given (16).
Eradication of lice can be somewhat complicated due to rising resistance to traditional first-line agents. First line is the neurotoxic agent permethrin and the pyrethrins which are chemically similar. The Canadian Pediatric Society recommends two permethrin applications 7 days apart before switching to another class of medication (6). Neurotoxins like permethrin require two treatments because developing
lice eggs will not be harmed (3,21). A second treatment during week two will kill any lice that were missed by the first treatment (16).
Permethrin is one of the cheapest options available to treat lice, and it can be used in patients older than 2 months (6). Different treatment options are used to treat children of different ages, but permethrin has the lowest age limit. Unfortunately, worldwide resistance is increasing to permethrin (7). A study in Great Britain showed a drop in efficacy from 97% in the 1990s to 13% in 2013 (22).
A promising newer therapy is the dimeticones. Dimeticones are synthetic
silicone oils. Lice have small breathing holes in their exoskeletons called spiracles, and dimeticones work by closing over these holes to suffocate the lice (7). They are considered biochemically inert and nontoxic (6). A benefit of dimeticones is that the development of resistance is very unlikely because of the physical mechanism of action. A drawback is that the dimeticone products available are different from each other and
not all products have the same level of efficacy. One product that is a mixture of two different dimeticones called NYDA was shown to have an efficacy of 97% (3).
While there are many options available, a few clear principles guide treatment. The synchronicity of treatment of close contacts is key to interrupting the exponential spread of lice infestations in a school, family, or community. An important part of every treatment regimen is wet combing. It is the most sensitive method for diagnosing and
monitoring a lice infestation to follow treatment progress, and it is intrinsically therapeutic as lice are removed by the process (23). Wet combing should be used to screen anyone who may be affected. It is recommended to treat any bedmates regardless of if any nits or lice are found (5). That being said, the American Academy of Pediatrics and the Canadian Pediatric Society both recommend against “no-nit” policies
for schools (6,16). Children should receive a full course of treatment and should avoid head-to-head contact, but they should not be kept from going to school, daycare, or spending time with friends.
Rising resistance to permethrin most likely will lead to limited usefulness of the drug in the future, but thankfully there are many more options available for treating lice.
The safety and efficacy of dimeticones may cause them to become the agent of the choice in the future. Other available agents should be considered based on their individual risks and benefits.