Which of the following is the causative organism of scabies?

Appeared in: BTSC Staff Nurse 30July-2025

Explanation

Scabies is a highly contagious skin infestation caused by the mite Sarcoptes scabiei var. hominis.
The female mite burrows into the superficial layer of the skin (stratum corneum) to lay its eggs, which triggers an allergic reaction.
This reaction leads to the characteristic symptoms of intense itching (pruritus), which is often worse at night, and a pimple-like rash.

Option A: Staphylococcus aureus is a bacterium, not a mite. It is a common cause of bacterial skin infections such as boils, impetigo, and cellulitis. While it can cause a secondary infection in scabies lesions due to scratching, it is not the primary causative agent of scabies.
Option B: Candida albicans is a type of fungus (yeast). It causes fungal infections known as candidiasis or thrush, which typically affect moist areas of the body like the mouth, throat, and genital area.
Option D: Pediculus humanus capitis is the scientific name for the head louse. This insect is an ectoparasite that infests the human scalp and causes pediculosis capitis (head lice), not scabies.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Identification of the causative agent for scabies as background academic context rather than a clinical decision trigger.
Scabies is highly contagious and spreads through direct, prolonged, skin-to-skin contact. Nurses must implement strict contact precautions to prevent outbreaks in healthcare settings.
Patient education is crucial. All family members and close contacts of an infected person must be treated at the same time, even if they show no symptoms, to prevent re-infestation.
What if? If a patient is immunocompromised, they may develop crusted (Norwegian) scabies, a severe and hyper-infested form. This condition is extremely contagious and requires more aggressive treatment with both topical and oral medications (e.g., ivermectin) and strict isolation protocols.

How to Approach the Question

First, identify the key term in the question stem, which is 'scabies'.
Recall the specific causative agent for this condition from your knowledge of microbiology and infectious diseases.
Analyze the four options provided. Classify each organism by its type (e.g., bacterium, fungus, mite, louse).
Match 'scabies' with its known cause, the mite Sarcoptes scabiei.
Eliminate the other options by correctly associating them with the different conditions they cause (e.g., Staphylococcus with boils, Candida with thrush, Pediculus with head lice).

Concept Tested & Keywords

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E6 Medicine Harrison 22e Part 2 p. 1633-1635

E6 Ghai Essential Pediatrics(pp 26-904 of 913) p. 741-743

Practise the full BTSC Staff Nurse 30July-2025

Attempt every question from this paper in a timed mock, then review the full solution for each one.