Which mite species is responsible for human scabies?

Question

Accepted Answer

C. Sarcoptes scabiei var. hominis. ## Causative Agent of Scabies

**Key Point:** Sarcoptes scabiei var. hominis is the obligate human parasite responsible for scabies infestation.

### Organism Characteristics

| Feature | Details |
| --- | --- |
| **Taxonomic classification** | Acari family, Sarcoptidae |
| **Size** | 0.3–0.4 mm (visible only under microscope) |
| **Morphology** | Oval body with 4 pairs of legs; anterior pair have suckers |
| **Host specificity** | Strictly human; var. hominis does not infect animals |
| **Lifecycle** | 10–14 days from egg to adult |

### Life Cycle & Pathogenesis

1. **Penetration:** Female mite burrows into stratum corneum
2. **Egg laying:** Deposits 2–3 eggs per day in burrow
3. **Larval development:** Larvae emerge, migrate to skin surface
4. **Mating:** Adults mate in follicles; cycle repeats
5. **Immune response:** Sensitization occurs after 4–6 weeks (explains delayed pruritus in primary infestation)

**High-Yield:** The burrow is pathognomonic — a linear or S-shaped tunnel in the stratum corneum, typically on wrists, finger webs, axillae, and genitalia.

**Clinical Pearl:** Norwegian (crusted) scabies occurs in immunocompromised patients and contains thousands of mites; highly contagious and often misdiagnosed as psoriasis or dermatitis.

### Why Other Mites Are Wrong

- **Demodex folliculorum:** Commensal mite; causes rosacea and perioral dermatitis, not scabies
- **Psoroptes ovis:** Veterinary mite infesting sheep and cattle; does not cause human disease
- **Cheyletiella blakei:** Cat mite; causes transient pruritic papules in humans but not true scabies

![Scabies diagram](https://mmcphlazjonnzmdysowq.supabase.co/storage/v1/object/public/blog-images/explanation/4186.webp)

Answer

A. Psoroptes ovis

Answer

B. Cheyletiella blakei

Answer

D. Demodex folliculorum

Which mite species is responsible for human scabies?

Explanation

Causative Agent of Scabies

Organism Characteristics

Life Cycle & Pathogenesis

Why Other Mites Are Wrong

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Feature	Details
Taxonomic classification	Acari family, Sarcoptidae
Size	0.3–0.4 mm (visible only under microscope)
Morphology	Oval body with 4 pairs of legs; anterior pair have suckers
Host specificity	Strictly human; var. hominis does not infect animals
Lifecycle	10–14 days from egg to adult