Parasitic Skin Infections Practice Questions

Q: Which of the following statements about scabies is false?

Pruritus is predominantly absent.. ***Pruritus is predominantly absent.*** - This statement is false because **pruritus (itching)** is the **hallmark symptom** of scabies and is almost always present, often severe and worse at night. - The intense itching is caused by an **allergic reaction** to the mites, their eggs, and their feces. *Not exclusively transmitted sexually.* - This statement is true; while scabies can be transmitted sexually through **skin-to-skin contact**, it can also spread through **non-sexual close physical contact** with an infected person or contaminated items like bedding. - Transmission requires **prolonged skin-to-skin contact**, not just a brief touch. *Scabies is caused by the mite Sarcoptes scabiei* - This statement is true; the parasitic mite **_Sarcoptes scabiei_ var. _hominis_** is the causative agent of human scabies. - The female mite burrows into the **epidermis** to lay eggs, leading to characteristic lesions and symptoms. *Erythematous papules develop due to delayed type 4 hypersensitivity.* - This statement is true; the **erythematous papules**, vesicles, and intense itching associated with scabies are a result of a **delayed type IV hypersensitivity reaction** to the mite, its feces, and eggs. - The immune response typically develops **3-6 weeks** after primary exposure.

Q: A child has multiple itchy papular lesions on the genitalia and fingers, and similar lesions are also seen in the younger brother. Which of the following is the most possible diagnosis?

Scabies. ***Scabies*** - The presentation of **itchy papular lesions** (especially on the **genitalia and fingers**) in a child, along with similar lesions in a younger sibling, is highly suggestive of **scabies**. This pattern indicates an infectious, transmissible skin condition. - **Scabies** is caused by the *Sarcoptes scabiei* mite, which burrows into the skin, leading to intense itching, particularly at night, and characteristic lesions often found in interdigital spaces, wrists, elbows, axillae, umbilicus, belt line, buttocks, and genitalia. *Localized papular urticaria* - While characterized by **itchy papules**, **papular urticaria** usually represents an allergic reaction to insect bites and is typically localized and does not spread directly to other family members in the same manner as an infestation. - The **transmissible nature** and typical distribution (genitalia, fingers) described in the question are not characteristic of simple papular urticaria. *Chronic atopic dermatitis* - **Atopic dermatitis** is a chronic inflammatory skin condition characterized by **eczematous lesions**, severe itching, and dry skin, often with a history of allergies or asthma. - While it can cause itchy lesions, it typically presents with distinct **eczematous patches** or plaques, often in flexural areas, and is not directly transmissible between siblings in the way suggested by the scenario. *Irritant contact dermatitis* - **Irritant contact dermatitis** is caused by direct skin irritation from contact with a substance, leading to red, itchy, or burning rash, often with vesicles or blisters. - It is unlikely to cause a widespread rash involving specific areas like the genitals and fingers in two siblings simultaneously unless both were exposed to the same irritant, which is less likely than a transmissible infestation given the description.

Q: An infant presenting with itchy lesions over the groin and prepuce, all of the following are indicated except:

Dispose of all clothes by burning. ***Dispose of all clothes by burning*** - While **scabies mites** can survive off-host for a limited time, disposal of all clothes by burning is an **extreme and unnecessary measure**. - Proper laundering of clothes and linens in hot water, followed by hot drying, is sufficient to kill mites and prevent reinfestation. *Bath & apply scabicidal solution* - A bath helps to clean the skin before applying a **scabicidal solution**, which is the primary treatment for eradicating **scabies mites**. - The solution, usually permethrin cream, needs to be applied to the entire body (neck down) and left on for the recommended time to be effective. *Treatment of all family members* - **Scabies** is highly contagious, and asymptomatic family members can be carriers and a source of reinfestation for the infant. - Treating all close contacts, even if they show no symptoms, is crucial to prevent the spread and recurrence of the infestation. *IV antibiotics* - **Scabies** is caused by a mite infestation, not a bacterial infection, so **antibiotics are not indicated** for treating the scabies itself. - **IV antibiotics** would only be considered if there were a **secondary bacterial skin infection** (e.g., impetigo) that was severe enough to warrant intravenous administration.

Q: A 65-year-old man presented with skin lesions on his chest and left arm and shoulder, six weeks after returning from a vacation in Belize, where he spent time at the beach in the rainforest. The lesions occasionally stung, drained dark exudates, and enlarged despite two weeks of treatment with cephalexin. The patient had no constitutional symptoms. Physical examination revealed five nodules of varying sizes with surrounding erythema and a central pore through which a single, moving larva was observed. What is the cause of this condition?

Bot fly. ***Bot fly*** - The presence of a **single, moving larva** observed through a central pore in nodular skin lesions, after travel to a tropical region (Belize), is highly characteristic of **myiasis caused by the bot fly (Dermatobia hominis)**. - The symptoms like stinging, dark exudates, and enlargement despite antibiotics are consistent with the larva feeding and growing within the host. *Tungiasis* - Caused by the **sand flea Tunga penetrans**, which burrows into the skin, typically on the feet, causing intense itching and pain. - It presents as a **pigmented nodule** with a central black dot, but **no visible moving larva**. *Cutaneous leishmaniasis* - Presents as **chronic skin ulcers or nodules** that can be slow-healing and often have raised borders. - Diagnosis is confirmed by identifying **amastigotes** in tissue samples, not by observing a moving larva. *Onchocerciasis* - Caused by the filarial nematode **Onchocerca volvulus**, transmitted by blackflies, leading to **subcutaneous nodules (onchocercomas)** and skin changes. - It does not involve a single, macroscopic, moving larva visible through a central pore.

Question 1

Which of the following statements about scabies is false?

Accepted Answer

Pruritus is predominantly absent.

Answer

Scabies is caused by the mite Sarcoptes scabiei

Answer

Not exclusively transmitted sexually.

Answer

Erythematous papules develop due to delayed type 4 hypersensitivity.

Question 2

A child has multiple itchy papular lesions on the genitalia and fingers, and similar lesions are also seen in the younger brother. Which of the following is the most possible diagnosis?

Accepted Answer

Scabies

Answer

Localized papular urticaria

Answer

Chronic atopic dermatitis

Answer

Irritant contact dermatitis

Question 3

An infant presenting with itchy lesions over the groin and prepuce, all of the following are indicated except:

Accepted Answer

Dispose of all clothes by burning

Answer

IV antibiotics

Answer

Treatment of all family members

Answer

Bath & apply scabicidal solution

Question 4

A 65-year-old man presented with skin lesions on his chest and left arm and shoulder, six weeks after returning from a vacation in Belize, where he spent time at the beach in the rainforest. The lesions occasionally stung, drained dark exudates, and enlarged despite two weeks of treatment with cephalexin. The patient had no constitutional symptoms. Physical examination revealed five nodules of varying sizes with surrounding erythema and a central pore through which a single, moving larva was observed. What is the cause of this condition?

Accepted Answer

Bot fly

Answer

Cutaneous leishmaniasis

Answer

Tungiasis

Answer

Onchocerciasis

Parasitic Skin Infections — MCQs

Parasitic Skin Infections — MCQs

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