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Scabies is a skin rash caused by mites of the genus Sarcoptes that tends to appear in a population in 15-20 year cycles and during wars and other disasters. Service (2008) estimated that at lease 300-million humans suffer from scabies every year. Diagnosis is by detection of female mites in narrow twisting tunnels. Feces located in these tunnels are visible through the skin as dark spots. Usually not more than 14 female mites will infect a human, but extremes of over 50 can occur. A mite species that is regularly involved in scabies is Sarcoptes scabiei (Arlian 1989).
The rash is a papular allergic eruption that is found on the body where the mites are not present. First time mite infections are followed 2-6 weeks later by the rash, while those how have had previous infections will experience the rash within only 2-4 days (Service 2008). Itch and scratching can follow an infection, which can then lead to serious secondary bacterial infections. A very serious form of scabies known as "Crusted Scabies" or "Norwegian Scabies" can involve thousands of mites.
The mite females excavate below the skin's surface where it is thin as around wrists, fingers, feet, etc. However, most are found on the hands and wrists and sometimes they also infest the head region of their hosts. Once under the skin females create winding tunnels and feed on liquids produced by the dermal cells. About 1-3 eggs are laid daily in the tunnels, which then require about four days to hatch with small larvae that have only six legs. The larvae migrate to the skin's surface where most perish, but the survivors seek out a hair follicle where they moult and develop into a "protonymph) with eight legs. A "tritonymph" is produced after about 3-4 days. Service (2008) noted that female nymphs are much larger than male nymphs. About 3 days later the tritonymph moults to produce either a male or female adult. Mated females then increase their size and begin their penetration into skin. Males, on the other hand, are much smaller and wander about the skin surface and construct short dens for refuge. The total life cycle usually requires less than two weeks, and females may live up to six weeks on their hosts, but perish in a few days without hosts.
MEDICAL IMPORTANCE
Skin diseases, known as Scabies, Acariasis, Sarcoptic Itch, etc., are produced in humans and animals. Some of the Sarcoptes spp. actually inhabit tunnels underneath the skin. These mites may pass their entire lives on their hosts. Infestations among hosts are acquired by contact. It has been estimated that over 300 million cases of Scabies occur annually worldwide.
One family, Sarcoptidae, and genus, Sarcoptes, is of principal importance for humans. Sarcoptes scabiei is known as the "Human Itch Mite," of "Norwegian Itch" as it is sometimes called. Females that are larger than males have the dorsal part of the body marked with distinctive parallel lines. The mites locate in the upper layers of epidermis especially around the groin and more sequestered areas. Mature females that bore directly into skin where they remain concealed for a while construct egg tunnels. Enlarging the excavation and laying eggs follow this. Eggs hatch in 3-4 days and the larvae leave the tunnel for the skin surface where they enter hair follicles. Molting occurs in 2-3 days followed by two nymphal stages. Nymphs construct narrow tunnels where mating occurs. The life cycle varies from 8-15 days at room temperature. Adult longevity is 3-5 weeks.
A person may acquire 50 or more mites at any given time, and any infections that develop are not obvious for several weeks. Following an attack there are at first few symptoms. Gradually as one becomes sensitized an intense itching ensues, which is especially intense at night. Infections are more likely the more one scratches the infested areas.
Acquisition of mites is through close contact with infested persons or their clothing. Avoidance of infested areas is preferred, but if infected one should seek medical attention from a physician, for current products available for treatment.
There are also species (eg., Psoroptes communis and Notoedres cati itch mites attacking animals that do not tunnel bur rather possess suckers for exterior attachment to the skin. Humans only become affected from close contact with infested animals, such as cats and rats.
Scabies may be controlled by the application of medicated skin lotions, sulphur ointments and other compounds (Buffet & Dupin 2003, Service 2008). Because scabies is contagious it may be necessary to deploy control procedures to entire families or even communities. Relief from the rash only gradually disappears after treatments. The attention of a medical physician is advised for this group of mites, as medicinal treatment is usually required. Prevention involves the usual precautions of cleanliness and limiting contact with infected surfaces, animals and people. However, Service (2008) recommended that during epidemics clothing and bedding should be dry cleaned or washed in 50-deg. Centigrade water.
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