Public Health Vectors and Pests

Pubic Lice

Pubic lice or "crabs"

Pubic lice in genital area

Public lice on eye-lashes
Common Name Pubic or Crab Louse


Scientific Name Phthirus pubis
Size 1-2 mm
Colour Immediately after oviposition they are shiny, round and transparent
Description The dorso-ventrally flattened body of the louse is divided into head, thorax and abdomen. A pair of eyes and a pair of antennae are clearly visible on the head. The mouthparts are adapted to piercing the skin and sucking blood. The second and third pair of legs, with their terminal claws are adapted to holding the hair-shaft, while the first pair of leg holds the skin during feeding. Abdominal protuberances on the side of the body are characteristic of this species. Males are slightly smaller than females. The eggs are oval-shaped and ca. 0.8 mm in length. Immediately after oviposition they are shiny, round, and transparent. Pubic lice are 1-2- mm in size, varying according to the stage of their development. They are usually whitish-grayish in color though they become reddish-brown for some time after a blood-meal.

Head Lice

Head lice (Pediculus humanus capitis) are about the size of a sesame seed, and can easily be seen, although they hide quickly when exposed to light. Their eggs, called nits, are barely visible whitish ovals cemented to hair shafts.
Head lice are spread by personal contact and by shared brushes, combs, hats and other personal items. The infestation sometimes extends into the eyebrows, eyelashes, and beard. Head lice are a common scourge of school children of all social strata.

Body Lice

Body lice (Pediculus humanus corporis) look very much like those found on the head, but are actually a different species. While they aren’t as easily transmitted as head lice are, they are more difficult to spot, hiding in the seams of clothing and folds of bedding when not actually feeding.
Body lice infestation is usually found in people who have poor hygiene and those living in close quarters or crowded institutions. These lice can carry diseases such as typhus, trench fever and relapsing fever.

Public Lice

Pubic lice (Phthirius pubis) are yellow-grey insects found in the pubic region, and are typically spread during sexual contact. The size of a pinhead, they are slightly translucent and barely visible against light-coloured skin. With their shorter, rounder body shape and crab-like claws with which they cling to hair, they resemble crabs – hence their popular name. The eggs, which are barely visible, are tiny white particles glued so firmly to hair shafts that they cannot be removed by normal washing.

Habitat Although any part of the body may be colonized, crab lice favor the hairs of the genital (Fig. 1) and peri-anal region. Especially in male patients, pubic lice and eggs can also be found in hair on the abdomen (Fig. 2) and under the armpits as well as on the beard and mustache, while in children they are usually found in eye-lashes (Fig. 3). Infestation with pubic lice is called Phthiriasis or Pediculosis pubis, while infestation of eye-lashes with pubic lice is called Phthriasis palpebrarum.
Lifecycle Pubic lice are insect parasites, spending their entire life on the host's hair and skin and feeding exclusively on blood, 4-5 times daily. The life-cycle from egg to adult is 22-27 days. The egg hatches producing the first nymphal stage, which after three moltings develops to nymph 2, nymph 3 and subsequently to either a male or female louse. The incubation period of the egg is 7-8 days, while the rest of the cycle is taken up with the development of nymphal stages. The average adult female lives for 17 and the male for 22 days.
Disease Transmitted Several species of Culicoides spp are also important as intermediary hosts of Onchocerca cervicalis, and as vectors of certain viral diseases such as horse sickness in Africa.
Symptoms The main symptom is itching, usually in the pubic hair area. This itch is frequently worse at night. It results from hypersensitivity to louse saliva, and it becomes strong enough two or more weeks following initial infestation. Sometimes the bite can cause an inflammatory skin reaction that is bluish gray in color. Although the lice do not cause a rash, the constant scratching and digging can cause the skin to become raw, and secondary infections can develop.

In the majority of infestations a characteristic grey-blue or slate coloration appears (maculae caeruleae) at the feeding site, which may last for days and is also characteristic for the infestation. Pubic lice are primarily spread through sweat and body contact or sexual contact. Therefore, all partners with whom the patient has had sexual contact within the previous 30 days should be evaluated and treated, and sexual contact should be avoided until all partners have successfully completed treatment and are thought to be cured. Because of the strong association between the presence of pubic lice and classic sexually transmitted diseases (STD), patients diagnosed with pubic lice should undergo evaluation for other STDs. Infection in a young child or teenager may indicate sexual abuse.

Head Lice:
Intense itching on the scalp, especially behind the ears and at the nape of the neck. Children may hardly notice head lice or may have only a vague scalp irritation in the beginning. With advanced infestation, the scalp may become red and inflamed, with swollen glands near the area where the lice are living.

Body Lice:
Itching is generally most intense on the shoulders, buttocks and abdomen. Signs of lice include unexplained scratch marks on the body, hives, eczema, or small red pimples on the shoulders or torso. If the lice are not treated, welts may develop.

Pubic Lice:
Pubic lice cause continual itching around the penis, vagina and anus, and perhaps a rash.

Type of Damage These parasites cause infection in humans that produces dermatitis and skin lesions because the adult worms are located in the skin.
Prevention Prevention of head lice is difficult, especially among children, since lice spread quickly from head to head. To help prevent lice, prevent children from sharing hats, hooded coats, scarves, combs, brushes, pillows, and soft toys. If you discover lice on your child, notify school or day-care authorities immediately, since classmates are likely to be infected. Infected children should be kept home from school until they are treated.

The best way to prevent lice in the genital area is monogamy or avoidance of intimate sexual contact. Condoms are not a good protection against lice because they do not cover the hairy areas where the lice live. You should also avoid contact with contaminated clothing, bed linen and toilet seats. Avoid sexual or intimate contact with infected people. If sexually active, use safer sex behaviours to avoid getting lice. Good personal hygiene is always recommended. If possible, avoid trying on bathing suits. However, if you must, be sure to wear your underwear while trying them on. This may prevent transmission.
Control Permethrin 1% cream rinse and pyrethrins can be used for this purpose and are the drugs of choice for pregnant or lactating women. These agents should be applied to the affected areas and washed off after 10 minutes. Shaving off or grooming any hair in the affected areas with a fine-toothed comb is necessary to ensure full removal of the dead lice and / or nits, though it does not suffice as treatment on its own. Resistance of pubic lice to pyrethroids must be if at all very rare. A second treatment after 10 days is recommended. Pubic lice on the eyelashes can be treated with a permethrin formulation by applying the solution to the infested hair with an applicator. It is dangerous to remove lice or eggs in the eyelashes by plucking or cutting the hairs.

Lindane shampoo (1%), a pediculocide, is FDA approved as safe and effective when used as directed for the second-line treatment of pubic lice (crabs). While serious side effects have been reported, they are considered to be rare and have almost always resulted from misuse of medication, such as excessive application and oral ingestion. To minimize this risk, Lindane medications are now dispensed in small single-use bottles. The Centers for Disease Control and Prevention (CDC) notes that lindane should not be used immediately after a bath or shower, and it should not be used by persons who have extensive dermatitis, women who are pregnant or lactating or children aged under 2 years. The FDA similarly warns against use in patients with a history of uncontrolled seizures disorders and premature infants, and recommends cautious use in infants, children, the elderly, and individuals with other skin conditions (e.g., atopic dermatitis, psoriasis) and in those who weigh less than 110 lbs (50 kg).

Head Lice
The most common treatment for head lice is to kill the adults with an insecticidal shampoo and to clear out the nits with a special fine-toothed comb. Of the medications for lice, permethrin is the safest, most effective, and most pleasant to use, and is available over the counter. For best results, follow the directions exactly. Other family members should be treated too – about 60% of infected children have relatives who carry lice.
To eliminate all lice and successfully prevent reinfection, wash all clothing, towels and bed linen in hot, soapy water, and dry them in a hot dryer. You can also disinfect bedding and other items such as hats and clothing by placing them in a sealed plastic bag for 14 days; the nits will hatch in about a week and die of starvation. Brushes and combs can be disinfected by soaking them in hot, soapy water for 10 minutes.

If you prefer to avoid the use of insecticides, try a "combing only" technique. Wash the hair with an ordinary shampoo and conditioner and leave wet. With a fine-toothed comb, stroke slowly outward from the roots through one lock of hair at a time. Lice will land on the back of the comb, get caught between the teeth, or fall off. Space at least 30 strokes over the head. Repeat every three days. Because new-born lice do not lay eggs for the first week, all lice should disappear after about two weeks of combing.

Body Lice
To treat body lice, wash the entire body with soap and water. If this is not effective, you may have to use an insecticidal preparation, which usually kills all the lice. Wash all clothing and bedding in hot water and dry them in a hot dryer. Store clothes for two weeks in sealed plastic bags or place them in dry heat of 60 C for three to five days.

Pubic Lice
Pubic lice can be treated with non-prescription medications containing pyrethrins (natural insecticides). Sexual partners will also have to be treated. "Crabs" are sometimes found on eyelashes and eyebrows, where they are difficult to treat. Remove them with tweezers, or use an ophthalmic ointment such as physostigmine. Ordinary petroleum jelly may kill or weaken lice on eyelashes too.

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