Scabies in Human - Transmission, Symptoms and Treatment

Scabies is a skin disease caused by a mite called Sarcoptes scabiei. Scabies is a contagious infection that can spread quickly through close physical contact, like between people who live in the same house or children in daycare.

Scabies in human
Scabies in human

Mite - Sarcoptes scabiei

Dust mites are microscopic eight-legged beings, the class of arachnids. The Sarcoptes scabiei has an average size of 0.3 mm, which is essentially the limit, which the naked human eye can see.

The Sarcoptes scabiei is a parasite that lives, feeds and reproduces on our skin. The life cycle of the mite lasts about 30 days. After copulation, the male mite dies while the female pierces through the superficial layers of the skin, creating a microscopic tunnel, where it is burrowed, depositing its eggs throughout its life, which lasts about 30 to 60 days. The female Sarcoptes scabiei releases 2 to 3 eggs per day. The eggs hatch in three or four days, and newborn larvae make their way back toward the skin surface, where they mature and can spread to other areas of the body.

The mite Sarcoptes scabiei produce enzymes that degrade the skin proteins, particularly keratin, which is used to feed them. As they move through the epidermis, they leave behind their feces, creating linear lesions in the skin. The lesions and itching of scabies are the result of an allergic skin reaction against the mite, their eggs and feces.

Transmission of scabies

Having scabies is not necessarily a sign of poor hygiene. Scabies is an infection transmitted between people through close contact. The most common cases are between relatives living in the same house. The sexual route is another common way of acquiring scabies. Army, nursing homes, daycare centers and prisons are places where there are often outbreaks of scabies.

Sarcoptes scabiei
Sarcoptes scabiei
The contact between children and teenagers in school is often not close enough to cause the transmission, which in no way means there is no risk. Similarly, a simple handshake or a quick hug is often not sufficient for transmission.

The mite Sarcoptes scabiei can survive in the environment for 24 to 48 hours, which makes the transmission possible through clothing, bedding or towels, although this route is not the most common.

Pets such as dogs and cats, can also have mange mite but that infection is different, making transmission to humans uncommon. When it occurs it is usually in really mite-infested animals. However, as the man does not have normal canine or feline, the mite does not reproduce the infection and it lasts only a few days (the life time of the mite).

Symptoms of scabies

Symptoms of scabies
Symptoms of scabies
The classic symptom of scabies is an itchy diffuse through the body, which tends to be more severe at night.

The average incubation period of scabies is about 6 weeks. However, in reinfected patients, symptoms can appear in just 24 hours. An infected person can transmit scabies, even if it is without symptoms, during the incubation period.

The typical lesions of scabies are small red papules (small dots or beads in relief) from 1 to 3 mm in diameter. The lesions sometimes are so small they can go unnoticed or camouflaged by scratches caused by intense itching.

The lesions of scabies may be diffuse. The sites involved are the hands (especially between the fingers), wrists, elbows, armpits, nipples (especially in women), areas around the umbilicus, genitalia (especially in men), knees, buttocks, thighs and feet. The back and head are usually spared, palms and soles are usually affected in children.

The tunnels produced by females of Sarcoptes scabiei can also be seen, although not as vivid as papules. They usually present as fine traces on the skin, slightly elevated, which can be up to 10 mm in length.

Crusted scabies (Norwegian scabies)

Norwegian scabies
Norwegian scabies
In most patients with psoriasis the total number of mites does not usually exceed one hundred. After an exponential increase in early disease, the patient's immune system can stop the multiplication of Sarcoptes scabiei, keeping its population more or less stable.

In patients with a weakened immune system, mites can multiply indefinitely, reaching a population of over one million in some cases. This super infestation of Sarcoptes scabiei is called crusted scabies or Norwegian scabies, which is the most severe form of scabies.

Patients at greatest risk are the elderly or those with problems such as AIDS (AIDS), leprosy, lymphoma, Down syndrome or other diseases that cause changes in the immune system.

The crusted scabies causes large red scabs on the skin, which spread easily if not treated. The scalp, hands and feet are frequently affected, although the spots may occur anywhere in the body. Crusted lesions do not generally itch and contain few numbers of mites.

Treatment of scabies

Drugs against scabies
Drugs against scabies
The two most widely used options for the treatment of scabies are Permethrin 5% or Ivermectin tablet.

Permethrin 5% should be applied all over the body from the neck down (in children it can be applied to the face, being careful not to reach the eyes), and rinsed in the shower after 8 to 14 hours. After 1 or 2 weeks the process can be repeated.

The Ivermectin is used orally in a single dose, repeated after 14 days. The success rate of both treatments is similar, but Ivermectin is the most appropriate treatment for outbreaks in nursing homes, prisons or households with many residents because a pill is much simpler than applying a cream all over the body.

Scabies is treated with a crusted combination of the two drugs: Permethrin 5% is applied daily for 7 days and then Ivermectin for one dose on days 1, 2, 8, 9 and 15.

It is important to remember the person infected with the scabies mite usually shows symptoms after 6 weeks. Therefore, treatment is also recommended for family members and sexual contacts, even if they do not show scabies symptoms.

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