Scabies, Sarcoptes scabiei var. hominis, continues to plague mankind despite our best attempts to eradicate it. The creatures, small mites, are related to spiders, with eight legs in their adult form, which live off flakes of dead skin. People become infected when a gravid female passes from person to person after direct, prolonged, skin-to-skin contact. That female digs into the skin to form a “permanent” burrow and lays eggs which hatch in 3 to 5 days as nymphs. The nymphs locate their own “molting pouches,” where they undergo several transformations into an adult males and females. Adult mites then mate and the females go off to establish new “permanent” burrows.
Because it takes some time to complete the cycle and develop a sufficient adult population, symptoms may begin 2 to 6 weeks after exposure. The host reacts to the presence of the burrowing adults with a local allergic reaction, resulting in intense itching, often worse at night. Sites of infestation include the wrists, elbows, armpits, hands, waistline, buttocks and external genitalia. Because of this latter predilection, scabies is often included as a sexually transmitted disease.
Usually, there are only 10 to 15 adults mites on normal host, but when scabies occurs on someone who is profoundly immune-compromised (very low immunity, such as with the use of steroids, chemotherapy, uncontrolled AIDS or bad diabetes), there may be thousands or millions of mites. This results in unsightly thick layers of skin, “Crusted Scabies or Norwegian Scabies,” which is highly contagious to caregivers given the sheer number of organisms.
Scabies is usually relatively easy to treat with topical products such as Permethrin Cream (Elimite) or Crotamiton lotion or cream. When itching continues over 2 to 4 weeks in normal individuals, a second application may be necessary. Lindane lotion is sometimes used in difficult cases, although it can be neurotoxic in children. Ivermectin, an oral agent, is occasionally required in cases of unresponsive “Crusted Scabies.”
Since the mites can only live 2 to 3 days away from a host body, the environment does not remain infectious. Washing clothing and sheets in hot water and drying in a hot dryer kills the organisms, because mites are very sensitive to heat and will die at 122 degrees Fahrenheit or higher. Although animals can get scabies, they have their own species and human scabies does not infect animals or vice versa.
Once treatment is begun, the infected individual should be able to return to work the next day. If they were symptomatic with itching, especially between the fingers, then gloves should be used for a few days. Family members should be treated because of the possibility of prolonged skin-to-skin contact, but co-workers do not need to be treated if contact has only been casual.
The exception is for “Crusted Scabies,” where the numbers of mites is so large that contagion is very likely. Affected individuals must be isolated and all contacts (and their families) should be aggressively treated. Such cases are the exception and not the rule. Prior to effective treatments, scabies infestations tormented those infested as well as their entire extended family. Today, a simple application (or two) will clear up this pesky acarian, which nonetheless remains a constant, if unwanted, human companion.