Parasitic infection caused by mite Sarcoptes scabei variety hominis, an arthropod of the Acarina order.
World prevalence about 300 million cases per year.
An extremely contagious skin infestation.
May be endemic in impoverished communities.
Often affects children, with varying presentations in different age groups.
Transmitted primarily through person to person contact.
In resource poor settings, especially in tropical regions, it is a major underlying cause of high rates of bacterial skin infection.
Prevalence varies by season, state of war, population movements and crowding.
Causes rash and itching and may also be associated with a superinfection.
Risk of severe outbreaks increased in hospitals and nursing homes as well as among socially disadvantaged and immunocompromised patients.
Associated with an obligate parasite that completes its entire life cycle in humans.
Transmission requires close contact among individuals.
Infection secondary to direct skin-skin contact.
Transmitted through close personal contact with an infected individual or his or her personal items, including clothing, bedding, towels, and gloves.
Symptoms develop within 2-6 weeks after infection.
Fomite transmission via mite attachment to clothing, bedding and towels is not common (Mellanby K).
Live mites can be found in the environs of patients, where they survive for 2-3 days.
Only the female mites can burrow into the skin.
The female burrows tunnels into the skin and lays her eggs which hatch in about 1 week.
About 5-15 female mites live on a host with scabies infection, but hundreds to millions can be present in crusted scabies.
Maturation process lasts about 15 days with larval emergence 2-3 days after the eggs are laid.
Skin eruption a result of infestation and hypersensitivity reaction to the mite.
Incubation period prior to symptoms occur 3-6 weeks for primary infestation, but may be as short as 1-3 days in cases of reinfestation.
Classically lesions are most often present on the interdigital finger webs and flexor surfaces of the wrist.
Frequently elbows, axillae, buttocks and genitalia may be involved.
The scalp may be involved in infants and the elderly.
Neonates with scabies are ineffective scratchers and fussiness, irritability, and restlessness at night, rather than scratching with secondary excoriations are common in neonatal scabies
Chronic hypersensitivity reactions lead to nodular scabies, and pruritic nodules can be seen in axilla, groin and genitalia.
Crusted scabies occurs when mite replication is not controlled by the patients immune system and a hyper infection develops.
Crusted scabies occurs mainly in immunocompromised individuals such as patients with AIDS patients on immunosuppressive treatments.
Crusted scabies are highly infectious lesions and can be responsible for community outbreaks, and secondary bacterial septic lesions with high death rates.
Crusted scabies is a severe form of scabies occurring when immunity fails to controls mite proliferation and results in
Large quantity of mites trigger an inflammatory and hyperkeratotic reaction to the epidermis in crusted scabies.
Typical clinical findings in crusted scabies include erythematous patches that evolve into 3-15 mm thick gray or tan crusts.
Crusted scabies are most prominent over the palms, soles, extensor surfaces, and under the fingernails.
Crusted scabies classically presents without pruritus due to the hosts impaired immune response.
50% of patients with hcrusted scabies have some degree of itch, particularly in those with HIV.
Crusted scabies risk factors include AIDS, T-cell leukemia, lymphoma, systemic steroids, transplantation, diabetes, other immunocompromised states, severe mental or physical disabilities or neurologic disorders.
Associated with generalized itching, which is particularly more intense at night.
May lead to secondary infections with Streptococcus pyogenes or Sytaphylococcus aureus.
Diagnosis is generally made by looking for burrows, or rash, on a person’s skin.
The diagnosis can be confirmed by examining a skin scraping for mites, eggs, or mite fecal matter under a microscope.
Diagnosis can be done by removing the mite from the end of its burrow using the tip of a needle or by obtaining a skin scraping to examine under a microscope for mites, eggs, or mite fecal matter.
By scraping burrows from multiple sites, microscopic evidence of mites and ova can confirm the diagnosis, which are easily detected with or without smears or stains such as Tzanck and KOH preparation.
Patients can be infested even if mites, eggs, or fecal matter cannot be found
Fewer then 10-15 mites may be present on an infested person who is otherwise healthy.
Permethrin is a synthetic pyrethroid agent used as a topical 5% cream that disrupts the function of voltage gated sodium channels of arthropods prolonging depolarization of nerve cell membranes and disrupt neurotransmission (Zlotkin E).
Ivermectin is an oral semisynthetic macrolytic lactone antibiotic that disrupts ligand chloride ion channels, causing persistent opening of the channels (Geary TG).
Invermectin does not sterilize scabies eggs.
In a trial of topical permethrin compared to ivermectin in 85 patients, the former drug was associated with a 98% cure rate compared to 70% for ivermectin., however, a second dose of ivermectin increased the cure rate to 95%.
Ivermectin is an effective therapy in crusted scabies in patients who do not have a response to topical treatment.
Permethrin 5% topical is the pref2242ed treatment for classical scabies.
Evaluating treatment to ensure resolution is important, and weekly skin scraping is recommended to ensure eradication of all mites.
It is essential in the management of crusted scabies to address the risk of transmission to healthcare workers and patient contacts.
Recommended are outbreak management teams to oversee infection control.