An affected host harbors approximately 11 adult female mites during a typical infestation, with eggs hatching in 3-4 days. This reaction is responsible for the intense pruritus that is the hallmark of the disease. Individuals who already are sensitized from a prior infestation can develop symptoms within hours. A distinctive highly contagious form of scabies, known as Norwegian scabies, has a predilection for individuals who are immunocompromised, aged, physically debilitated, or mentally impaired. Extensive widespread crusted lesions appear with thick hyperkeratotic scales over the elbows, knees, palms, and soles.
Extensive proliferation occurs in immunocompromised patients.
These individuals can be infested with thousands of mites at a time. Scabies is unlikely to cause long-term morbidity or mortality in an otherwise healthy individual. Before the introduction of antibiotics, secondarily infected scabies could cause death or serious disability from septicemia, glomerulonephritis, or acute rheumatic fever. No population appears immune to scabietic infestation. Children younger than 15 years have the highest prevalence of scabies.