Scabies: Symptoms, Causes, Treatment, and Prevention
What is Scabies?
Scabies is a skin infestation caused by the mite Sarcoptes scabiei var hominis of the Sarcoptidae family.
Morphologic Classification
- Arthropoda: Non-segmented, small body size, with 4 pairs of legs, dorsoventrally flattened, no eyes or trachea.
- Females: 300-500 microns long by 230-420 microns wide.
- Males: 213-285 microns long by 162-210 microns wide.
- Eggs: 160 microns in length.
Etiology and Life Cycle
- Parasitism Level: Obligate, living all or a phase of their life cycle inside or on the surface of the host.
- Topographical Location: Ectoparasites.
- Life Cycle: Monoxenic.
- Reservoir: Humans. The mites do not live more than 2 to 4 days in the environment.
- Transmission:
- Direct skin-to-skin contact (minimum 10 minutes).
- Sexual transmission.
- Sometimes indirectly through sheets, towels, and clothes.
- In some cases, it can be acquired through contact with infected animals, especially dogs (Sarcoptes scabiei var. canis), but the mites cannot reproduce in humans.
- Incubation Period:
- Primary infection: 2 to 6 weeks before the onset of itching in persons without prior exposure to the mite.
- Reinfestation: 1 to 4 days in people who have been previously infested.
Scabies Life Cycle
The scabies life cycle occurs in the stratum corneum of the epidermis. Fertilized females dig narrow tunnels where they lay eggs for 4 to 6 weeks, laying about 3 eggs per day. The eggs hatch in about 8 days, rising to the surface and becoming nymphs. Complete development takes 8 to 14 days. The female lives for 4 to 6 weeks, and the male dies after mating. The contagious forms are nymphs and adults.
Epidemiology
Scabies is more common in cold and temperate countries. In 1987, 30 out of 1000 people were treated. In 1985, Sarcoptes scabiei infestation was found in 7.3% of schoolchildren in the metropolitan area.
Clinical Manifestations
- Symptoms: Itching, which increases progressively in intensity at night and with heat.
- Signs: Furrows, pearly vesicles.
- Location of Injuries: Interdigital spaces, flexor surfaces of wrists, extensor aspects of elbows, armpits, waist.
- In children younger than 2 years, a vesicular rash usually occurs on the palmoplantar regions, head, face, and neck.
Norwegian or Crusted Scabies
This form occurs in immunodeficient patients and is highly contagious because each crust contains millions of mites.
Risk Group
Prevalent in children under 2 years. No significant differences in gender or race.
Diagnosis
Background: Clinical and epidemiological studies.
Treatment
Treatment should be administered to the affected person, all people over two months old living in the same house, and close contacts, even if they are asymptomatic. Change and wash clothes and bedding at 60°C or store them in a closed bag for 3 days to prevent reinfestation.
Medications (Scabicides)
- Topical medications should be applied throughout the body in infants and from the neck down in children over 2 years.
- Permethrin 5%
- Lindane 1%
- Ivermectin
Prevention
Mechanisms of transmission must be disseminated continuously in populations at risk to avoid contact with suspected cases. Perform timely diagnosis and effective treatment.