| disease | Scabies |
| alias | Scabies |
Scabies is a chronic pestilential skin disease caused by the human itch mite Chinese Taxillus Herb in the superficial layers of human skin. This Bingchuan is highly contagious, primarily transmitted through close contact pestilence, and can also spread indirectly through clothing pestilence, potentially causing outbreaks in families or collective populations.
bubble_chart Epidemiology
The epidemiology of scabies generally follows a 30-year cycle, with an interval of 15 years between the end of one epidemic and the start of the next. Each epidemic lasts approximately 15 years.
The exact causes of modern scabies epidemics remain unclear, though factors such as poverty, poor hygiene, promiscuous sexual behavior, misdiagnosis, increased travel, population growth, and ecological changes can contribute to its spread. The reasons are highly complex. While sexual transmission is relatively common in Europe and America, in our country, although possible, other modes of transmission—such as close contact, overcrowded living conditions, poor sanitation, communal living environments, and exposure in vehicles, ships, or hotels—also play a role.
Before liberation, scabies was prevalent in China. After liberation, as living standards improved and medical prevention efforts advanced rapidly, scabies was largely eradicated by the 1950s (except in Xinjiang). However, over the past 20 years, it has gradually resurged. Preliminary investigations suggest that residual scabies in Xinjiang never completely disappeared. In 1969, cases in Changsha were traced to Vietnamese interns, and in 1973, the disease spread to Guangdong from Hong Kong. Thus, the resurgence in Xinjiang may be attributed to the re-emergence of previously uneradicated scabies, while the nationwide resurgence is linked to global epidemics, specifically transmission from Vietnam. This outbreak has been characterized by its rapid and aggressive spread, moving from south to north and from urban to rural and pastoral areas within just a few years. It has now spread across the entire country, with higher prevalence in southern regions such as Guangdong, Guangxi, Fujian, Sichuan, Yunnan, Guizhou, Hunan, Jiangsu, Anhui, Jiangxi, and Zhejiang. In the north, cases are relatively rare except in Xinjiang.
bubble_chart PathogenThe scabies mite, commonly known as the itch mite, is a type of intradermal Chinese Taxillus Herb mite with many species. Human scabies is primarily caused by the human itch mite (Sarcoptes scabiei var. hominis). The mites are divided into males and females, with the female being about 400μm long, just visible to the naked eye. The mature female is oval-shaped, flat, and yellowish-white, lacking a distinct head, though its mouth protrudes from the front edge of the body, often mistaken for a head. It has four pairs of legs, each divided into five segments; the first two pairs end in suction cups, while the last two pairs have long, bristle-like hairs. There is an egg-laying pore in the center of the abdomen, and the anus is located in the middle of the trunk region. The male is half the size of the female. The mites crawl quickly on warm skin, moving at a speed of 2.5 cm per minute. Mature females burrow into the stratum corneum in suitable skin areas, using their front claws to tunnel between the stratum corneum and granular layer, where they feed on cells for nourishment.
The life cycle of the scabies mite consists of four stages: egg, larva, nymph, and adult. A mature female digs a tunnel 0.5-5 mm long and lays her first egg within hours, producing 40-50 eggs per day. While laying eggs, she also excretes feces and dies at the blind end of the tunnel after completing egg-laying. The average lifespan of a female is 6-8 weeks.
The eggs are oval, pale yellow, with a thin shell, about half the size of the female. After 3-4 days of incubation in the tunnel, the eggs hatch into larvae, which resemble adults but have only three pairs of legs. The larvae remain in the tunnel for about a day before moving to the skin surface, quickly burrowing back into the skin to hide and feed. After approximately three days, the larvae molt into nymphs, which have four pairs of legs and can be distinguished by sex. Male and female nymphs mate on the skin surface at night, after which most males die. The female nymph mates for 2-20 minutes before burrowing into the stratum corneum, soon molting into an adult. After fertilization of egg cells inside her body, she begins laying eggs in the tunnel within 2-3 days, moving forward as she lays eggs until she dies in the tunnel. The entire life cycle from egg to adult takes about 7-10 days.
The pathogenesis of scabies is significantly influenced by delayed hypersensitivity reactions. During the infection period of scabies, the detection of serum immunoglobulin levels can somewhat reflect B-cell activity. IgA levels are markedly decreased during infection, while IgG and IgM levels are significantly elevated, returning to normal after treatment. The IgE level in the serum of scabies patients is notably higher than in healthy individuals, and it decreases after the patients are cured. The IgE produced after scabies mite infection is specific and shows no cross-reactivity with dust mite antigens.
Hoefling, using immunofluorescence techniques, found deposits of IgM and C3 in the dermal blood vessel walls of patients, resembling manifestations of cutaneous vasculitis, while granular deposits of IgM and IgG were observed at the dermal junction, resembling lupus erythematosus. Neste et al. detected antigen-antibody complexes binding to complement C1q in the serum of patients. Further studies revealed that Langerhans cells in the epidermis of patients were injured, with reduced density, shortened or fewer dendrites, enlarged cell bodies, and the presence of vacuoles and disrupted mitochondrial cristae. Scabies patients treated for one year often exhibit hypersensitivity reactions to scabies mite extracts. In nodular scabies patients, there is a defect in the regulatory function of suppressor T cells on B cells.
bubble_chart Clinical Manifestations
Scabies mites often invade areas with thin and delicate skin, so lesions commonly occur in the finger webs, flexor aspects of the wrists, elbow fossae, armpits, women's breasts, around the navel, waist, lower abdomen, inner thighs, and external genitalia, usually appearing symmetrically. The head, face, and metatarsus are rarely affected, except in infants and young children. Those who frequently wash their hands may have no lesions or only a few on their hands.
The rash primarily consists of papules, blisters, burrows, and nodules. Papules are about the size of foxtail millet, pale red or skin-colored, with an inflammatory halo, often scattered or densely clustered, rarely merging, and some may evolve into papulovesicles. Blisters are generally the size of rice grains to mung beans, commonly seen between the fingers. Burrows appear as grayish-white or light black lines, about 3-15 mm long, slightly curved and raised, often ending in papules or blisters; some may not show typical burrows due to washing, scratching, or secondary sexually transmitted disease changes. Nodules frequently occur on the scrotum, penis, labia majora, etc., about the size of peas, hemispherical, pale red, and wheal-like.
Intense itching is felt, especially at night, likely due to the mites being more active in warm bedding or the toxic stimulation of their secretions. Scratching can lead to excoriations, crusting, eczematous changes, or secondary infections, resulting in impetigo, folliculitis, boils, lymphadenitis, or even nephritis.
Based on the history of exposure to pestilence, the predilection sites of skin lesions, intense itching, and a rash primarily characterized by burrows and papulovesicles, it is common for multiple family members to be affected simultaneously. The diagnosis is straightforward, and if scabies mites can be identified, the diagnosis is particularly definitive.
Methods for examining scabies mites:
(1) Method for locating burrows
Apply a drop of blue ink to the suspected burrow lesion, then rub gently with a cotton swab for 30 seconds to 1 minute. Afterward, wipe away the surface ink with an alcohol swab to reveal the faint blue trace of the burrow.
(2) Needle extraction method
Locate the scabies burrows on the sides of fingers, palmar wrist creases, vesicles, or pustules, and carefully identify the terminal end of the burrow where a white mite spot is found. This is the most likely site to detect the mite.
Procedure: Use a No. 6 injection needle, holding it at a 10°–20° angle to the skin surface with the bevel facing upward. At the mite spot at the end of the burrow, insert the needle approximately 1 mm away from the spot, perpendicular to the long axis of the burrow, until reaching the base of the mite spot and bypassing the mite body. Then, flatten the needle shaft (to a 5°–10° angle) and gently rotate it, causing the mite to fall into the needle's groove. Slowly withdraw the needle while lifting the skin (or simply withdraw it directly). Transfer the mite to a glass slide with water (or 10% KOH or normal saline) and examine it under a microscope.
(3) Scraping method
This method is recommended for examining papules. First, use a sterilized surgical blade coated with a small amount of mineral oil to locate newly formed inflammatory papules. Scrape the top keratinized layer of the papule horizontally several times until fine particles appear in the oil droplet. After scraping 6–7 papules, transfer the material to a glass slide. Microscopic examination often reveals larvae, and occasionally mite eggs or feces.
bubble_chart Treatment Measures
Generally, apply 10% sulfur ointment (5% sulfur ointment for infants and young children). Before treatment, take a bath with hot water and soap, then apply the medication from the neck downward, first to the affected areas and then to the entire body, 1-2 times daily for 3-4 days as one course of treatment. During the application period, avoid bathing and changing clothes to maintain the medication's efficacy and thoroughly eliminate scabies mites on the skin and clothing. After completing the course, change into clean clothes. If new rashes appear after two weeks, repeat the second course of treatment.
25% benzyl benzoate emulsion has strong killing power against worms and is non-irritating. It can be applied 1-2 times daily for 2-3 days, yielding better results.
10% Lindane cream, also known as gamma-666 cream, is the most commonly used and effective scabicide. This agent should not be used for infants and young children (under 10 years old), pregnant or breastfeeding women, or patients with epilepsy or other neurological disorders. The method of use involves applying 10% gamma-666 cream from the neck downward to the entire body, washing it off completely after 24 hours, and avoiding contact with the eyes and mucous membranes.
Pay attention to personal hygiene. Patients should be immediately isolated and treated, and those at home should receive simultaneous treatment. Avoid contact with others, including handshakes, before full recovery. Clothes and bedding used by patients must be disinfected or exposed to sunlight.
This disease should be differentiated from the following conditions:
1. Prurigo: Often begins in early childhood. Chronic course, with larger papules, predominantly on the extensor surfaces of the limbs.
2. Eczema: Presents with polymorphous skin lesions, often coalescing into patches with a tendency for moist exudation. No specific predilection sites.
3. Pediculosis: Lesions mainly consist of scratch marks. No rash between fingers, but lice and nits can be found in clothing seams.
