A mite infestation leads to the skin disorder known as scabies, which is highly contagious. Burrowing under the skin, the Sarcoptes scabiei mite produces excruciating itching. This itching is constant, particularly at night. Family members and intimate skin-to-skin relationships provide the greatest danger because skin-to-skin contact is how the infectious organism is spread.
The World Health Organization (WHO) designated scabies as a neglected skin disease in 2009, and it remains a serious health issue in many underdeveloped nations. People who are infested need to be identified and treated right away, since a false positive can result in outbreaks, increased morbidity, and higher costs.
Etiology and Causative Agent
Sarcoptes scabiei var. Hominis is the mite responsible for scabies. It is an arthropod that is a member of the Acarina order. It is a member of the family Sarcoptidae, order Astigmata, and class Arachnida. In terms of clinical presentation, it can manifest as either the typical, nodular, or infectious crusted variety known as Norwegian scabies. In both humans and animals, Sarcoptes scabiei lives in the dermal and epidermal layers. Scabies is a widespread skin ailment that is found all over the world. The female mite initiates the infestation by digging a hole in its host’s stratum corneum to deposit its eggs. Afterwards, it gives rise to larvae, nymphs, and adults.
In the traditional form of scabies, one individual may have anywhere from 10 to 15 mites in their population. In cases of classic scabies, mites usually need 10 minutes of skin-to-skin contact to spread to a new human host. Additionally, the sickness may spread through bed linens or clothing that has been contaminated with fomite. Hyperkeratotic plaques, which can be diffuse or restricted to the palms, soles, and under nails, are a common presentation of scabies.
One variation of the traditional form of scabies is the nodular form. This type is characterized by erythematous nodules that are more common in the groin and axilla. The itchy nodules are thought to represent an allergic reaction to the female mite.
A single person with Norwegian scabies, the crusted variety, may have up to millions of mites on them. Patients with impaired immune systems as a result of immunosuppressive medication, diabetes, HIV infection, or advanced age are susceptible to crusted scabies. For infection to develop in this high density, there needs to be brief interaction between patients and contaminated things. The quantity of infesting mites is often determined by the host’s immune status and the degree of mite dissemination.
Epidemiology
An estimated 300 million people get scabies annually around the world. The World Health Organization classified it as a neglected skin condition in 2009, and it is a major health concern in many underdeveloped nations. Southeast Asia, Africa, South America, and Australia are among the continents where scabies is most common. Homelessness, poor nutrition, poverty, and poor cleanliness all have a correlation with the high frequency.
It is more prevalent in young adults and children. Cases in these nations are linked to considerable morbidity because of follow-up infections and sequelae. Abscesses, lymphadenopathy, and post-streptococcal glomerulonephritis are a few examples of these. In developed nations, scabies outbreaks can happen seldom or as institutional outbreaks in places like jails, retirement homes, schools, nursing homes, long-term acute care (LTAC) institutions, and overcrowded regions.
Pathophysiology and Histopathology
Every day, two to three eggs are laid by adult female mites who excavate tunnels that are between one and ten millimeters long inside the epidermis’ outer layers. After 30 to 60 days, the mites die, and the eggs hatch in around two to three weeks. It is important to note that not every therapy modality can reach the eggs kept under the skin. Within two to five weeks, papules may appear if an infestation takes place. These papules have a length of several millimeters to one centimeter and are shaped like a tunnel or comma. Infestations usually arise beneath the epidermis in regions like the male penis shaft, areolae, navel, and interdigital folds.
Rarely is a punch biopsy required for the diagnosis of scabies. Scabies is frequently diagnosed clinically. With the exception of crusted scabies, there are often relatively few mites on the body, hence the biopsy will not typically yield a mite. If you’re lucky, you can observe the mite and the egg in the reticular dermis combined with an inflammatory infiltrate. Significant scale and crust, a serous discharge, neutrophils, and eosinophils are frequently visible in the epidermis.
Symptoms: History and Physical
The beltline, nipples, buttocks, areolae of female breasts, flexural surfaces of the wrists, penile shaft, axillae, umbilicus, between digits, and intertriginous areas are common places for mite burrowing. Where two patches of skin may rub or touch one another is known as an intertriginous area. There may be type IV hypersensitivity reactions resulting in erythematous papules in response to the mite, eggs, or excrement. Scratching, encrustation, and even impetigo result from the itching associated with scabies.
After the mites tunnel, secondary bacterial infections frequently develop. Because Streptococcus pyogenes bacterium and the scabies mite work in harmony, impetigo is particularly prevalent. Complement-inhibiting proteins are released by burrowing mites to stop S. pyogenes from opsonizing, which permits the bacteria to grow and avoid the immune system.
It can be difficult to diagnose scabies as not everyone displays the typical symptoms of an infestation. Patients may not exhibit the traditional indicators, such as a history of exposure, acute pruritis at night, or close contacts exhibiting a similar presentation, or they may only exhibit mild symptoms. When multiple family members or close contacts have pruritus, the practitioner should always consider scabies.
Evaluation and Diagnosis
The standard method of diagnosing scabies involves looking at the rash and taking the patient’s medical history. By observing mites in skin scrapings from the stratum corneum, scabies can be identified. The significant likelihood of sample mistake in this method frequently results in the incorrect diagnosis being missed.
During the physical examination, other techniques like non-invasive videodermatoscopy can be used. In the field of dermatology, this method is still relatively new. In videodermatoscopy, a video camera that is outfitted with optic fibers, lenses that can magnify up to 1000 times, a light source, and an immersion liquid is used. In the great majority of American offices, this technique is unavailable. Videodermatoscopy makes it possible to examine the skin’s surface all the way down to the superficial dermis, making it useful for identifying mites, burrows, eggs, larvae, and excrement. There are various benefits of videodermatoscopy over conventional skin scrapings.
First off, kids, delicate patients, and others who might object to skin scrapings are more likely to embrace its noninvasive nature. In addition, it is faster and easier to execute than the conventional microscope method. Additionally, the noninvasive method reduces the chance of unintentional infections from blood-transmissible pathogens such the hepatitis C virus (HCV) or the human immunodeficiency virus (HIV). Additionally helpful in assessing patients for follow-up following therapy, videodermatoscopy can show the existence of living mites in cases of recurrent infection or unsatisfactory treatment outcomes [2]. Nowadays, videodermatoscopy is rarely utilized in clinical settings.
Dermoscopy, also known as dermatoscopy, is a portable alternative to videodermatoscopy that doesn’t require a computer connection. Nowadays, dermoscopy is a standard procedure in the majority of US dermatology practices. The lens used in dermoscopy can magnify objects up to 10 times. A dermatoscope can be used to view the “jetliner trail,” or burrow structure, in cases of scabies. Furthermore, in locations with dark skin or hair, it is difficult to see the burrows. A skin biopsy can be utilized to confirm the diagnosis if it is unclear. A recently discovered serologic test can help diagnose scabies in addition to biopsy.
Treatment / Management
There are various treatments available for scabies. Evidence shows that when medications are used as directed, the efficacy of standard treatment options is comparable. These include topical permethrin, topical crotamiton, and systemic ivermectin. Adverse reactions are rare to these medications.
Topical permethrin 5% cream is effective and widely used. The cream is typically applied once a week for two weeks (total of 2 treatments). However, this treatment is occasionally associated with scabies resistance, poor patient compliance, and rare allergic reactions.
Oral ivermectin is another option, although the United States Food and Drug Administration has not approved its use for scabies treatment. It is administered to individuals ten years and older and given one time. An additional dose is given two weeks later if symptoms persist. Two doses of ivermectin are scabistatic; the second treatment kills mites that have hatched since the first treatment. Oral ivermectin is recommended due to convenience, ease of administration, favorable side effect profile, and safety.
Rates of compliance are higher with this treatment modality than with topical permethrin, and the tablet form of ivermectin reduces the likelihood of misuse or inadequate application, as may occur with the topical permethrin. Systemic ivermectin is superior to topical permethrin when treating scabies outbreaks. Ensuring adequate treatment is especially pertinent to the treatment of individuals living in close proximity, such as in homeless shelters, prisons, and healthcare facilities.
Other options are topical lindane, 5% precipitated sulfur, malathion, and topical ivermectin. Treatment choices may be limited in those with S. scabiei resistance or with limitations due to cost, availability, or potential toxicity, especially among pregnant women and children.
Treatment failure/recurrence is common, and isolating the cause can help prevent further infection and limit outbreaks in communities. Reasons for treatment failure include not treating close contacts simultaneously, not decontaminating beddings and clothes at the time of treatment, and nonadherence to the treatment regimen. Treatment failure of crusted scabies can result from ivermectin-resistant Sarcoptes mites. Moxidectin is the recommended therapy for known ivermectin-resistance [4].
Differential Diagnosis, Prognosis and Complications
The clinical presentation of scabies may resemble infections caused by other sources such as bacteria, fungi, parasites, and viruses. Scabies often gets misdiagnosed as eczema, dermatitis prurigo nodularis, or lupus erythematosus. Treating the patient along with close contacts and family members is associated with a good prognosis. With adequate treatment, patients can be expected to recover fully. Without treatment, the infection can spread to other members of the community and cause an outbreak within the population. Possible complications of a scabies infection include persistent itching, insomnia, secondary bacterial infection, and outbreaks of the disease to the community.
Source
Murray RL, Crane JS. Scabies. [Updated 2023 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK544306/