Introduction
Scabies is a highly contagious skin condition that is caused by the human itch mite Scaroptes scaibei var. Hominis . It is an obligate ectoparasite. The mite is spread by human contact, whereby it burrows eggs and lays its eggs that are responsible for the dermatological itch and rash. Sarcoptes Scaibei uses humans predominantly as an obligate human ectoparasite. This paper explains the classification of the causative agent in scabies, its morphology, lifecycle and virulence factors, pathophysiology and symptomatology and finally the diagnosis, management and prognosis.
Classification and Morphology
Sarcoptes Scaibei belongs to kingdom Animalia, phylyum Arthopoda, Subphylum Chelicerata, class Arachnida, subclass Acaria, order Sarcoptioformes, family Sarcoptidae and genus Sarcoptes ( Arlian & Morgan, 2017) .
Delegate your assignment to our experts and they will do the rest.
Morphologically, the parasite has a flat and ventral tortoise -like appearance, while dorsally it is convex ( Arlian & Morgan, 2017) . On average a female mite weighs about 5.62 to 6.87g, while males weight about 1.48 to 2.2 g. This indicates that females are larger than males ( Guillot, 2017). They only have two body parts: head (containing the gnathosoma) and the abdomen/idiosoma that carries the 4 pairs the legs. The gnathosoma has short chelicerae, and pedipllas ( Arlian & Morgan, 2017) . The anal opening is found posteriorly, with the bursa copulatrix appearing anterior to the anal opening as a nipple like papilla. Inferiorly they have suckers which they use to burrow the epidermis and lay eggs ( Salavastru et al., 2017) . The eggs are large and oval, and measure about half their own length.
Lifecycle
The average time for scabies mite to complete its full cycle in the human host varies from around 9 days, to around 21 days maximum ( Thomas et al., 2020). On average a female lays 20-40 eggs. These ectoparasites seek the nearest host closest to them through detection of the nearest hosts’ odor, temperature gradient and carbon di oxide exhaled during expiration ( Arlian & Morgan, 2017) . According to Thomas et al. (2020) these parasites’ optimum temperature ranges from 24-25 degrees. Sarcoptes Scaibei also have a photo responsive character here they tend to seek the source of light, rather than live in dark areas.
Female mites live in intimate relationship with the host, and thus transmission is often through direct contact or through beddings and toys ( Arlian & Morgan, 2017) . Females lay 1-3 eggs per day, which then take around 4 days to mature. In around 2-3 days, these larvae become nymphs, which then moult for a round 7 days, before becoming adults. The larvae then migrate from the burrowed holes, to the hair follicles ( Arlian & Morgan, 2017) . Adult males and females then mate on the surface, thereafter which the males die and the females start burrowing again in order to lay their eggs ( Arlian & Morgan, 2017) . Additionally, sexual contact has also been implicated in the spread of scabies ( Anderson & Strowd, 2017) .
Globally, scabies is estimated to affect around 200 million people at any time ( Anderson & Strowd, 2017). However, the disease doesn’t cause major disease burden economically. The disease mostly affects the tropical regions that are poorly resourced. This includes overcrowded areas, with poor treatment facilities. In children due to their playful nature, there is an increased prevalence by 5-10 percent when compared to adults ( Anderson & Strowd, 2017) . The rate of occurrence is also high in affected communities
Symptomatology
Symptoms of disease are dependent on the type of scabies namely: classical and crusted scabies.
Classical
Pruritus is the main presentation that is experienced by most affected patients. The pruritus intensifies at night as the mites wakeup to mate and feed ( Anderson & Strowd, 2017) . The increased skin irritation leads to frequent scraping. The skin areas affected mainly include between the fingers, the wrists, the auxiliary areas, the female breasts, the umbilicus, the male genitalia, the perianal region and ankles ( Anderson & Strowd, 2017) . The pattern of distribution indicates high fat areas, as well as where the skin overlaps.
The affected skin appears as crusty patches that may bleed. Due to the breach of the skin barriers, these skin lesions may become sites for secondary infections by gram positive bacteria such as staphylococcus and streptococcus ( Anderson & Strowd, 2017) . A study in Fiji found that the leading cause of sepsis was the impetigo that was caused by scabies ( Anderson & Strowd, 2017) .
Sarcoptes scaibei release chemicals and also possess factors that enhance their survival. These factors are often capable of triggering and hypersensitivity reaction after days, similar to that of the TB vaccine ( Salavastru, et al., 2017). The antigens are taken up by antigen presenting cells to the T helper cells, which them mediates the release of chemokine such interferon gamma and tumor necrosis factor, these in turn them mediates chronic inflammation at the site. The hallmark of this condition is the time taken and response by the body, which is around 2-3 days ( Bona & Bonilla, 2019) .
Crusted Scabies
Individuals who are immunocompromised such as HIV/Aids patients, those with diabetes, patients with malignancy and those who have human T- Cell leukemia virus are likely to develop a more complex condition called Norwegian scabies ( Anderson & Strowd, 2017) . The condition is characterized by thick and crusty skin erosions that mimic leprosy that are crusty at the top ( Anderson & Strowd, 2017) . These lesions are also ill defined, and are prominent on the dorsal end.
Diagnosis
The diagnosis of scabies is made through clinical suspicion initially. Thereafter, lab work and examination is the gold standard. A careful history indicating a history of an itch that worsens at night is often the start. Physical examination reveals the skin lesions. Finally, during Investigations, Physicians also scrape the surface skin and surface crust involved, and observes them under a microscope. Positive findings involve eggs and mites in the skin scrapings. Fecal pellets referred to as sycballa, may also be visualized.
Treatment
The treatment for scabies involves definitive, symptomatic and preventive measures. Treatment also is dependent on the type of scabies involved. Preventive measures include education on the mite spread, early identification and treatment of the condition and maintenance of hygiene. The affected clothing should be regularly washed with hot water, and dried with a hot air dryer for at least 72 hours. Insecticides are not recommended.
Definitively, scabies is managed through the administration of scabicides, which target the skin burrows where the eggs and mites live ( Salavastru, et al., 2017) . Permethrin and sulfur oil ointment are the two current therapies used. Permethrin works through inhibiting the sodium channels of animals, which eventually results in paralysis and death. Due to the odor, it causes discomfort to mites and acts as a repellant ( Salavastru, et al., 2017) . Permethrin should be applied for once a day and left to dry for around 8 hours, preferably in the night. The next dosage should be applied after a week ( Salavastru, et al., 2017) . One should also take bath before application of the ointment. Ivermectin has been administered orally for scabies that is systemic. Ivermectin also works through electrolyte alteration, which in turn inhibits muscular activity leading to paralysis. Classical scabies is managed through one drug only; while crusted involves both permethrin and an additional agent ( Salavastru, et al., 2017) .
The remaining symptoms such as rash and secondary bacterial infections can be managed through antihistamines and antibiotics respectively ( Salavastru, et al., 2017) . Topical steroids could also be administered to prevent itch severity and hypersensitivity exacerbations. An additional sexual history and testing for sexually transmitted diseases may also be recommended for sexual active patients, including a HIV test ( Salavastru, et al., 2017) .
Prognosis
In healthy individuals, the prognosis for scabies is excellent. However, in endemic regions, the likelihood of recurrence is high ( Salavastru, et al., 2017) . Children who are currently in their oral stage also have a high likelihood of disease occurrence due to suckling the ointment from their hands and arms, hence a poor prognosis and should be watched. Early treatment for patients with immunosuppression could also have good prognosis. Late treatment after dissemination could have a bad prognosis due to their weakened immunity. Superimposed bacterial infections could also worsen existing sepsis ( Salavastru, et al., 2017) .
Poor prognosis has also been associated with older drugs such as lindane and benzyl benzoate has been associated with microbial resistance ( Anderson & Strowd, 2017) .
Prophylaxis
The prophylactic measures against scabies involve avoiding skin to skin contact with affected patients and effected areas as well. This could involve wearing protective clothing such as gloves when handling patients ( Anderson & Strowd, 2017) . Contact tracing is also an effective method for prophylaxis to prevent spread ( Anderson & Strowd, 2017) .
The above paper outlines Sarcoptes Scaibei, as the causative organism in scabies. The paper further explains how the obligate ectoparasite burrows itself in the human dermis, and lays eggs that hatch in around 21 days. The symptomatology such as pruritus and type four hypersensitivity is well explained, and finally the treatment regimens with permethrin are also outlined. The paper concludes by indicating the prognosis and prophylactic measures that can be taken to prevent the spread of scabies.
References
Anderson, K. L., & Strowd, L. C. (2017). Epidemiology, diagnosis, and treatment of scabies in a dermatology office. The Journal of the American Board of Family Medicine , 30 (1), 78-84.
Arlian, L. G., & Morgan, M. S. (2017). A review of Sarcoptes scabiei: past, present and future. Parasites & vectors , 10 (1), 1-22.
Bona, C. A., & Bonilla, F. A. (2019). Textbook of immunology . CRC press.
Guillot, J. (2017). Sarcoptes scabiei: what kind of parasite is it? How is it transmitted and what could be its origin?. Bulletin de l'Académie Nationale de Médecine , 201 (1/3), 129-141.
Salavastru, C. M., Chosidow, O., Boffa, M. J., Janier, M., & Tiplica, G. S. (2017). European guideline for the management of scabies. Journal of the European Academy of Dermatology and Venereology , 31 (8), 1248-1253.
Thomas, C., Coates, S. J., Engelman, D., Chosidow, O., & Chang, A. Y. (2020). Ectoparasites: scabies. Journal of the American Academy of Dermatology , 82 (3), 533-548.
