Manual of Dermatologic Therapeutics
7th Edition

Pediculosis. There are two species of blood-sucking lice specific to the human host: Phthirius pubis and Pediculus humanus. These wingless, six-legged insects are obligate parasites and are host-specific for humans. The lice that inhabit the head or body are both types of P. humanus (P. humanus humanus and P. humanus capitis); only the body louse is capable of transmission of disease-endemic typhus (Rickettsia prowazekii), trench fever (Bartonella quintana), and relapsing fever (Borrelia recurrentis, Borrelia duttoni). P. capitis is not known to be a disease vector. Head and body lice look similar to one another and will interbreed; however, they do have different physiologic feeding habits and head lice prefer to confine themselves to the scalp. The head louse is transmitted through shared clothing and brushes; the body louse, by bedding or clothing; and the pubic louse, from person-to-person contact and not infrequently through clothing, bedding, or towels.

The adult body louse (Pediculosis humanis) is 2- to 4 mm-long, has three pairs of legs with delicate hooks at the tarsal extremities, and is gray-white in appearance. The adult female louse has a lifespan of approximately 25 days, lays up to 10 eggs each day, and will die after 10 days away from a host. Body lice prefer to live in clothing, particularly seams, and move to the body to feed. As the lice feed, they inject their digestive juices and fecal material into the skin; it is this, plus the puncture wound itself, that causes pruritus. Their saliva also contains a unique anticoagulant and vasodilator that produce some of the symptoms of irritation and pruritus. Heavy infestation is common in crowded, unhygienic surroundings such as military personnel and refugees during wartime, prisons, chronic health care institutions, and homelessness. Chronic infection may lead to lichenification and hyperpigmentation from repeated scratching.

Head lice (P. capitis) most commonly affect white children, between the ages of 3 and 11. Head lice prefer clean healthy heads and will leave a host if conditions are not optimal. Lice transmission usually begins at home in larger families and is then spread to the school environment. Straight hair is more vulnerable than curly hair and African American children are less commonly affected, presumably secondary to the oval-shaped hair shaft. However, new head lice variants have been found with a stronger cuticle and angular curved claws as an adaptation to the variety of hair structure. The incubation period from exposure to pruritus is approximately 30 days. The ova (nits), which are oval, 1-mm long and gray, and firmly attached to the hair, hatch in approximately 7 to 9 days and become mature in another week. Ova are laid very close to the scalp and hatch before the hair grows more than 1/4 in. If no nits are found within 1/2 in. of the scalp and no lice are seen, treatment is not necessary because nits more than 1/2 in. from the scalp are eggshells from a past infection. Head lice do not jump or fly from one person to another. They adapt to their surroundings; darker skin types and hair color have red/black lice whereas lighter skin or hair types have gray/white lice. Egg production occurs ideally at 84°F; in warmer climates, the viable eggs can be found further down the hair shaft.

The crab or pubic louse (P. pubis), which usually inhabits the genital region, is short (1 to 2 mm) and broad, and the first pair of legs is shorter than the claw-like second and third pairs. Infestation may occur in other areas including the moustache, beard, axillae, chest, and even scalp hair. Pediculosis palpebrarum or “phthiriasis palpebrarum” is the name given to infestation of the eyelashes. Pubic
lice are found in most ethnic groups except Asians, perhaps because of sparser pubic hair. Homosexual men have a high rate of infestation. Crab lice usually lay only three eggs per day. Adult lice can live off the host for up to 36 hours and viable eggs, for 10 days. The chance of acquiring pediculosis pubis from one sexual exposure with an infected person is approximately 95%. Transmission of crab lice can occur without body contact, especially in warmer environments. Through the use of polymerase chain reaction (PCR), the previous host of a crab louse can be identified (a possible forensic tool). The human immunodeficiency virus (HIV) has also been detected by PCR in collected crab louse specimens, but it is unclear whether any of the louse subtypes can transmit the virus.

Scabies is caused by infestation with the mite Sarcoptes scabiei var hominis. S. scabiei has four pairs of legs and transverse corrugations and bristles on its dorsal aspect. The 1.3-mm by 0.4-mm female mite, just visible to the human eye, excavates a burrow in the stratum corneum and travels as much as 5 mm everyday for 1 to 2 months before dying. Each female lays a total of 10 to 38 eggs, which hatch in approximately 1 week, reach maturity in approximately 3 weeks, and start a new cycle. Mating occurs only once, after which the male dies. Fewer than 10% of deposited eggs produce adult mites. Most infected adults will harbor 10 to 12 mites. Live mites have been recovered from dust and fomites. Twenty-five percent of surveyed chronic-care facilities reported problems with scabies outbreaks over a 1-year period.

Crusted or Norwegian scabies occurs in debilitated or immunocompromised patients and patients with adult T-cell lymphoma associated with human T lymphotrophic virus type I (HTLV-1); the infestation often presents as a generalized dermatitis with crusted hyperkeratosis of the palms and soles. Deep fissures between the crusted plaques are a source for bacterial invasion of the blood and also allow for the penetration of antiscabetic treatments into the blood. This variant of scabies is highly contagious, because the skin is infested with thousands of mites. Patients with HIV disease may present with scabies as their first acquired immunodeficiency syndrome (AIDS) defining illness, especially as the CD4 count drops below 200.

Scabies is acquired principally through close personal contact but may be transmitted through clothing, linens, furniture, or towels. The female can survive away from humans for at least 96 hours. The incubation period is usually <1 month but can be as long as 2 months. The severe pruritus is probably caused by an acquired sensitivity to the organism and its saliva, eggs, and feces and is first noted 3 to 4 weeks after primary infestation but sooner (24 to 48 hours) in subsequent infections. S. scabiei has cross-antigenicity with the house dust mite; this may play a role in the susceptibility to scabies and its clinical manifestations. Immunofluorescent studies suggest a cutaneous vasculitis-like pattern in dermal vessels, with the presence of immunoglobulin M (IgM) and C3 conjugates; skin-biopsy specimens can demonstrate immunoreactants indistinguishable from bullous pemphigoid. The delayed host response and these findings suggest a humoral component to the disease. Canine scabies (sarcoptic mange) causes crusting and hair loss over the ear margins, legs, and abdomen of dogs. This is highly communicable and may result in small epidemics in humans, although the mite is unable to reproduce in the human host.

Ticks are large mites covered by a tough integument. These ectoparasites live by sucking blood from mammals, birds, and reptiles. They are found in trees, grass, bushes, or on animals (dogs, cattle). After attaching to the human skin, the female tick feeds, becomes engorged after 7 to 14 days, and then drops off. The three most medically important ticks in the United States are the Lone Star tick (Amblyomma americanum), Dermacentor, and Ixodes ticks. The Lone Star and Dermacentor ticks can transmit Rocky Mountain spotted fever (Rickettsia rickettsii), ehrlichiosis (Ehrlichia chaffeensis), and tularemia (Francisella tularensis). Ixodes ticks can transmit Lyme disease (Borrelia burgdorferi) and babesiosis.

Lyme disease is often overdiagnosed and overtreated because of its protean manifestations and unreliable serologic tests. The risk of Lyme disease is low from deer tick bites that are attached for <24 hours. Early Lyme disease can be divided into localized (Stage 1) and disseminated (Stage 2) types. The localized rash develops in 60% to 80% of patients, usually at the tick bite site within
days to 1 month of the bite. The tick bite is often not recognized. Systemic symptoms are present in most patients with erythema migrans (EM) (fatigue, arthralgias, myalgia, headache, stiff neck, and anorexia). Forty-two percent of patients will have either lymphadenopathy or fever. Disseminated disease indicates spread of the disease to other organs, usually with central nervous system (CNS), cardiac, or rheumatologic symptoms. Late disease (Stage 3) occurs in untreated individuals with manifestations involving the CNS and/or the musculoskeletal system.

Extreme pruritus is the primary characteristic of pediculosis. It takes 4 to 6 weeks for the pruritus to develop in a nonsensitized individual and only 24 to 48 hours with repeat exposures. In some sensitized patients, generalized pruritus, urticaria, and eczematous changes may develop. In some cases, children may be totally asymptomatic. Sleeplessness may be reported, because lice are more active during nocturnal hours.

Scabies is noted for severe itching, which becomes most marked shortly after the patient goes to bed or for children during naptime. Pruritus may be delayed or overlooked in the immunocompromised or elderly patient. Early in the course, only the sites of burrows are pruritic; later, the itching may become generalized.

Tick bites are painless; ticks are often discovered several days later when itching develops or the engorged tick is found. Occasionally, symptoms of fever, headache, and abdominal pain may occur while the feeding tick remains attached. Minor or major constitutional symptoms can be associated with early-stage Lyme disease. Multiple symptoms can accompany both the early-disseminated disease and late-stage disease, depending on which system is involved (CNS, cardiac, or musculoskeletal). Very rarely, children can develop a reversible flaccid paralysis that starts after the tick has been attached for several days.

Ticks. The engorged tick, often the size of a large pea, may resemble a vascular tumor or wart.

Unexplained pyoderma of the scalp, inflammatory cervical or occipital adenopathy, or itching with mild inflammation of the occipital scalp and nuchal area should be attributed to pediculosis until proved otherwise. It is necessary to be persistent in searching for nits. If suspicion is high, a therapeutic trial or reexamination in 2 to 3 days is indicated.

Unexplained pubic pruritus is very often a manifestation of pediculosis. In fastidious individuals, few adult lice and nits will be found, and a careful search—ideally employing a hand lens—should be made, with special attention to the genital area. The possibility of other coexisting venereal diseases must be kept in mind.

The diagnosis of scabies is made by demonstrating the presence of the organisms, the eggs, or the oval, brown-black fecal concretions called scybala in a burrow or
papule. A superficial epidermal shave biopsy is the best method. The best papules for examination are often small but very itchy. Raise the burrow or papule between the forefinger and thumb and use a No. 15 scalpel blade to “saw” off the top of the papule or entire burrow. This procedure is almost painless. Place the material on a glass slide, cover with immersion oil, and examine under scanning power. Burrows or papules are found most often between the fingers, on the flexor aspect of the wrists, or on the ulnar aspect of the hands. It may sometimes be difficult to find either the burrow or the mite, especially in elderly or infirm patients, and in such cases, the clinical picture of intense pruritus and papular and excoriated lesions will lead one to the correct diagnosis. The addition of potassium hydroxide (KOH) to the preparation can be helpful in removing the keratinous debris in crusted scabies; prompt microscopic examination is required as the KOH also dissolves the mites and eggs. The mite of canine scabies is easily demonstrated in scrapings from the dog but rarely seen in preparations taken from human lesions. Epiluminescence microscopy may help detect the mite in vivo.

Lyme disease is often diagnosed with the EM skin lesion. The presence of other acute symptoms (fever, myalgia, arthralgias, headache, and stiff neck) is helpful. A history of a tick bite is not required. Laboratory confirmation is established with isolation of the spirochete from serum or cerebrospinal fluid (CSF), or a change in antibody levels in acute and convalescent serum. Skin-biopsy culture or PCR can also be useful.

Serologic testing is not helpful in early disease because of the low sensitivity. Positive or equivocal results of an enzyme-linked immunosorbent assay (ELISA), immunofluorescent assay (IFA), or immunodot assay require supplemental testing with a Western blot assay.

The treatment of choice for pediculosis capitis or pubis is pyrethrins with piperonyl butoxide (RID, A-200 Pyrinate), permethrin (Nix), or lindane (Kwell).

Protection against tick infestation is best accomplished by applying repellents to clothing. The most efficient agent is diethyltoluamide (DEET). Use the recommended amount of insect repellent but avoid frequent reapplications; do not use repellents on infants; on the hands or face of young children; or on cuts, abrasions, or sunburned skin. Repellents containing >10% to 15% DEET should not be used in children; concentrations no higher than 30% to 35% should be used in adults.

Tick removal methods are multiple, and each has its advocates. The important consideration is that the organism not be crushed while being taken off the skin.

Treatment recommendation for Lyme Borreliosis

A new Lyme disease vaccine has been approved by the FDA and is manufactured by Smith Kline Beecham. The vaccine should be considered for individuals over the age of 18 who are at moderate or high risk for acquiring Lyme disease.

This vaccine is 70% to 80% effective in individuals who have received the three doses of the vaccine (initial dose, followed by second dose 1 month later, and the final booster dose at 12 months). This vaccine offers no protection against other tick-borne diseases.