A 30 year old female developed pruritic papules with excoriated plaques in the interdigital web spaces. Later the lesion spread to the groin and under the surface of the breasts. The lady gives a history of intense pruritus which is more severe at night. Given below is the organism responsible for this condition. Identify the wrong statement about the same.

Correct Answer: D. Male parasite burrows into the epidermis

The clinical presentation—pruritic papules with excoriated plaques in interdigital webs, groin, and inframammary folds with nocturnal pruritus—is pathognomonic for scabies caused by Sarcoptes scabiei. The question asks for the WRONG statement about the organism. Option D is incorrect because only the gravid female mite burrows into the epidermis to lay eggs; the male does not burrow. Males remain on the skin surface, mate with emerging females, and die after copulation. This is a critical distinction in scabies biology. The female creates tortuous burrows in the stratum corneum where she deposits 40–50 eggs over 4–6 weeks, triggering the intense pruritus through hypersensitivity reaction (Type IV). Males play no role in burrowing or egg-laying. Understanding this sex-specific behavior is essential for recognizing that scabies is fundamentally a female-driven infestation, which has implications for understanding transmission and the pathophysiology of the itch.

Why the other options are wrong

A. Life history has 4 stages — This is CORRECT. Sarcoptes scabiei has four life-cycle stages: egg, larva, nymph, and adult. This is a true statement about the organism and not the wrong answer. The question specifically asks for the wrong statement, so this option is a true fact. B. The entire life cycle takes about 15 days — This is CORRECT. The complete life cycle of Sarcoptes scabiei takes approximately 14–21 days (commonly cited as ~15 days in Indian textbooks). Eggs hatch in 3–4 days, larvae develop in 3–4 days, and nymphs mature in 4–6 days. This is a true statement and not the wrong answer. C. Larvae have 3 pairs of legs — This is CORRECT. Larval mites have 3 pairs of legs (6 legs total), while nymphs and adults have 4 pairs (8 legs). This morphological feature is a standard identifying characteristic in parasitology. This is a true statement and not the wrong answer.

High-Yield Facts

Mnemonics

FEMALE BURROWS (Scabies Biology) Female burrows into epidermis | Eggs laid in tunnels | Male mates on surface | Adult life ~15 days | Larvae have 3 legs | Excoriation from scratching SCABIES Sites (Classic Distribution) Space between fingers (interdigital) | Crease of groin | Armpit | Breast (inframammary) | Instep of feet | Elbow | Scrotum/genitals

NBE Trap

NBE pairs "male parasite burrows" with the correct clinical picture of scabies to trap students who memorize only the clinical presentation without understanding the sex-specific biology of the mite. Students may assume both sexes burrow because both are present in the infection.

Clinical Pearl

In Indian clinical practice, scabies is often misdiagnosed as eczema or dermatitis because the nocturnal itch and secondary excoriation dominate the presentation. The key bedside clue is the burrow—a thin, tortuous, grayish line in the interdigital web or wrist—which is pathognomonic and confirms the diagnosis. Treating only the symptomatic patient while missing household contacts is a common error; all close contacts must be treated simultaneously to prevent reinfection.

_Reference: Jawetz, Melnick & Adelberg's Medical Microbiology (Parasitology section on Acari); Park's Textbook of Preventive and Social Medicine (Scabies epidemiology); Harrison's Principles of Internal Medicine Ch. 215 (Ectoparasites)_