Pediculosis: causes, symptoms, diagnosis, and treatment

Pediculosis is a parasitic disease caused by lice and can be divided into pediculosis capitis, pediculosis humanus, and pediculosis pubis. The latter includes pediculosis palpebrarum and phthiriasis capitis.


Causes

Lice are ectoparasites that never leave the host for life. Both nymphs and adults can suck blood. The nymphs suck blood at least once a day, while the adults suck blood several times daily. A female louse can suck 1μL of blood each time. They release the venom through saliva while sucking blood, and have the habit of defecation while sucking blood. Lice dislike strong light, and they often suck blood at night or when quiet. The optimal temperature for the lice is 29℃ - 30℃. When the human body temperature rises, humans sweat, or the body temperature declines after human die, the lice automatically fall off the human body and seek a new host. The host of human lice can only be humans, and they cannot be parasitic on other animals.

Head lice are 2 - 3mm long and parasitic on the hair, especially the postauricular hairline and the dorsal head. They are hidden in the hairs or adhered to the hair. Pinpoint sized, white lice eggs are often seen. Female lice discharge gels while laying eggs, sticking the eggs to the hairs. Larvae are hatched in 5 - 9 days, and crawl out of the operculum. Some head lice can be parasitic on eyelashes and beards, predominantly in children or females with poor hygiene.

Body lice are larger than head lice. Male lice are 2.7mm - 3.6mm long, and female lice are 2.7mm - 4mm long. They are usually hidden in the underclothes, and are more common in the crotches and bedclothes.

Pubic lice are small in size, about 1mm long, grayish white, parasitic on the pubic or perianal hair, occasionally invading the eyebrows or eyelashes.


Signs and Symptoms

Head lice bites can cause papules and subcutaneous bleeding. Scratches often cause scratch marks, exudates, blood scabs, or secondary infections of the scalp, forming furuncles or abscesses. Local lymph nodes may be enlarged. In severe patients, dandruff, blood scabs, exudates, and dust are adhered to the hairs, with odors, and there may be bleached hair, hair loss, or scar formation over time.

Body lice pierce the skin with their mouthpart and suck blood. There are often erythema, papules or wheals caused by body lice bites on the shoulders, waist, and buttocks, with a bleeding point in the center. The body lice discharge saliva into the human skin while sucking blood. The saliva contains anticoagulant substances and hemolysins, resulting in skin reactions. Linear scratch marks, blood scabs or secondary infections may be seen on the skin due to scratches, and there may be lichenification or pigmentation on the skin over time. The condition often affects human rest due to severe pruritus, mostly in winter.

Pubic lice are often tightly on the skin or firmly adhered to the pubic hairs. There are severe pruritus, erythema or papules after bites, and scratches may cause erosion, scratch marks, blood scabs, folliculitis, and secondary infections. There may be about 0.5cm in diameter, blueish gray, non-blanching livedos, without pruritus, mostly on the inner thighs and abdomen. The livedos can last for several months. Pediculosis pubis is mainly transmitted through sexual contacts.


Diagnosis

If there are localized pruritus, blood scabs, and scratch marks on the skin, the disease should be considered. If adult lice or lice eggs are found on the hairs, underclothes, bedclothes, or pubic hairs, the disease can be definitively diagnosed.


Treatment

Pediculosis capitis can be treated with topical 50% stemona tincture, benzyl benzoate cream, or permethrin cream

If there are pubic lice, the pubic hairs should be removed fully and burned, and the pubic skin should be cleaned carefully.

If there are body lice, the clothes and bedclothes can be boiled, steamed or ironed with high heat.

Secondary infections can be treated with topical antibiotics.