Scabies: Causes, Symptoms, Diagnostic Tests, and Treatment a complete analysis for medical students as well as for doctors. Itching is a skin infection caused by a tiny particle called Sarcoptes scabies. If left untreated, these microscopic mites can live on your skin for months. They regenerate on the surface of your skin and then penetrate and lay eggs. This causes itchy, red rashes on the skin.
Table of Contents
Scabies is characterized by an intensely itchy, erythematous rash that may include papules, nodules, vesicles, or blisters and is caused by the burrowing of adult female mites in the upper layers of the epidermis, creating serpentine burrows. The itching is more intense at night. In older children and adults, the predilection sites are the interdigital folds, the flexor aspects of the wrists, the extensor surfaces of the elbows, the anterior axillary folds, the waist, the thighs, the navel, the genitalia, the areolas, the abdomen, gluteal cleft and buttocks. In children under 2 years of age, the rash is most often vesicular and often occurs in areas not usually seen in older children and adults, such as the scalp, face, neck, palms, and soles. from the feet. The rash is caused by a hypersensitivity reaction to the parasite’s proteins.
What does scabies look like?
Here is a picture of scabies infected area of the human body.
After initial exposure to scabies, symptoms can take up to six weeks to appear. Symptoms generally develop more quickly in people who have had scabies before.
Characteristic symptoms of scabies include a rash and severe itching that is worse at night. Continuous scratching of the infected area can create sores that become infected. If this occurs, additional antibiotic treatment may be recommended for the skin infection.
Common parts of the body where scribes effects
- between the fingers
- soles of the feet
Types of scabies:
Typical scabies: This is the most type of scabies, this infestation causes itchiness on the hands, wrists, and other areas, This type does not affect on face or scalp.
Nodular scabies: This causes itchy, raised bumps that usually develop trusted Source in the armpits or around the genital area.
Crusted scabies: People with typical scabies who have weakened immune systems can develop this type. It produces thick, gray crusts of skin that contain thousands of scabies mites. It is extremely contagious.
Characteristic scabetic burrows appear as fine lines, gray or white, serpentine and threadlike. Excoriations are common, and most burrows are cleared by scratching before the patient seeks medical attention. Occasionally, 2 to 5 mm reddish-brown nodules are present, particularly on the covered parts of the body, such as the genitals, groin, and armpit. These scabies nodules are a granulomatous response to antigens and feces from dead mites; nodules can persist for weeks and even months after effective treatment. Secondary skin bacterial infection is a common complication and is usually caused by Streptococcus pyogenes or Staphylococcus aureus. Studies have shown a correlation between post-streptococcal glomerulonephritis and scabies.
Crusted (formerly called Norwegian) scabies is an uncommon clinical syndrome characterized by a large number of mites and widespread, crusted, hyperkeratotic lesions. Crusted scabies usually occurs in people with debilitating conditions, people with developmental disabilities, or people who are immunocompromised, including patients receiving biologic response modifiers. It also can occur in healthy children using prolonged topical corticosteroid therapy.
Post-scabietic pustulosis is a reactive phenomenon that may follow the successful treatment of primary infestation with scabies. Affected infants and young children have episodic crops of sterile, pruritic papules and pustules predominantly in an acral distribution, but lesions may extend to a lesser degree onto the torso.
Etiology Or Cause
The Sarcoptes scabiei subspecies hominis mite is the cause of scabies. The adult female burrows into the stratum corneum of the skin and lay eggs. The larvae emerge from the eggs in 2 to 4 days, molt into nymphs, and then adults, which mate and produce new eggs.
The complete cycle lasts between 10 and 17 days. Scabies subspecies canis, acquired from dogs (with mange), can cause a mild, self-limited infestation in humans that generally involves the area in direct contact with the infected animal.
Epidemiology of Scabies
Humans are the source of infestation. Transmission generally occurs through close and prolonged personal contact. Due to a large number of mites in the exfoliating scales, even minimal contact with crusty scabies patients or their immediate surroundings can lead to transmission. Acquired infestation from dogs and other animals is rare; these mites do not replicate in humans.
Human scabies can be transmitted as long as the patient remains infested and untreated, even during the interval before symptoms appear. Scabies is endemic in many countries and occurs around the world in cycles believed to last 15 to 30 years. Scabies affects people of all socioeconomic levels regardless of age, gender, or standards of personal hygiene.
Scabies in adults is often acquired sexually. The incubation period in inexperienced people is usually 4 to 6 weeks. People who were previously infested become sensitized and develop symptoms 1 to 4 days after exposure to the mite; however, these reinfestations are usually milder than the original episode.
The diagnosis of scabies is usually made through a clinical examination. The diagnosis can be confirmed by identifying the mites or mite or scybala eggs (feces) from scrapings of intact papules or burrows, preferably from the terminal part where the mite is usually found. Mineral oil, microscope immersion oil, or water applied to the skin facilitate collection of scrapings. A broad-bladed scalpel is used to scrape the burrow. Scrapings and oil can be placed on a slide under a glass coverslip and examined microscopically at low power.
Adult female mites have an average length of 330 to 450 µm. Skin scrapings provide definitive evidence of infection but have low sensitivity.
Manual dermoscopy (epiluminescence microscopy) has been used to identify in vivo the pigmented parts of the mite or air bubbles corresponding to the mites that infest within the stratum corneum. In vivo reflectance microscopy and polymerase chain reaction assays on rubbed skin material are promising techniques with improved sensitivity and specificity.
Topical permethrin 5% cream or off-label use of oral ivermectin both are effective agents. Most experts recommend topical 5% permethrin cream as the drug of choice, particularly for infants, young children, and pregnant or nursing women. Permethrin cream should be removed by bathing after 8 to 14 hours. Children and adults with infestation should apply lotion or cream containing this scabicide over their entire body below the head.
Permethrin kills scabies eggs and mites. It may take two (or more) applications, each one week apart, to eliminate all the mites. Because scabies can affect the face, scalp, and neck in infants and young children, treatment of the entire head, neck, and body is required in this age group. Nails should be trimmed and medications applied to the head, neck, and body.
Because ivermectin is not ovicidal, it is given in 2 doses, 7 to 14 days apart. Oral ivermectin should be considered for patients who have failed treatment or who cannot tolerate topical treatment. The safety of ivermectin in children weighing less than 15 kg (33 lb) has not been established. Ivermectin is not recommended for pregnant or nursing women. Alternative drugs include cream or lotion of crotamiton 10% or precipitated sulfur 5% to 10% mixed with petroleum jelly.
Because scabetic lesions are the result of a hypersensitivity reaction to the mite, the itching may not go away for several weeks despite successful treatment. Using oral antihistamines and topical corticosteroids can help relieve this itching. Topical or systemic antimicrobial therapy is indicated for secondary bacterial infections of excoriated lesions. Lindane lotion should not be used in the treatment of scabies.
Example of Scabies
A 2-year-old baby with scabies
A 12 to 13 – year-old with itching in the axillae and groin for 2 weeks. She recently returned from a family camping trip, where she shared a tent with “dozens of cousins.” Since returning home, she has had itching in the armpits and in her pubic area. She now has papules and pustules on the fingers, toes, and her gluteal furrow.
The family is reluctant to inquire about relatives with similar lesions. Examination of scrapings of the lesions indicated a few oval structures suggestive of scabies eggs. She responded to treatment with topical sulfur and oil in lieu of pesticide-based therapy. Courtesy of Will Sorey, MD.A 12-year-old with itching in the axillae and groin for 2 weeks.
She recently returned from a family camping trip, where she shared a tent with “dozens of cousins.” Since returning home, she has had itching in the armpits and in her pubic area. She now has papules and pustules on the fingers, toes, and her gluteal furrow. The family is reluctant to inquire about relatives with similar lesions. Examination of scrapings of the lesions indicated a few oval structures suggestive of scabies eggs. She responded to treatment with topical sulfur and oil in lieu of pesticide-based therapy. Courtesy of Will Sorey, MD.