Parasitic Skin Infections Practice Questions

Q: A patient presents with itchy lesions over the wrist, which are worse at night. Which of the following drugs can be used orally for treatment in this case?

Ivermectin. **Explanation:** The clinical presentation of itchy lesions over the wrist that worsen at night is a classic description of **Scabies**, caused by the mite *Sarcoptes scabiei*. The nocturnal exacerbation of pruritus is due to a type IV hypersensitivity reaction to the mite, its eggs, and scybala (feces). **Why Ivermectin is correct:** **Ivermectin** is the only drug among the options that can be administered **orally**. It is an anthelmintic agent that works by binding to glutamate-gated chloride channels in the invertebrate nerve and muscle cells, leading to paralysis and death of the mite. The standard dose is **200 μg/kg** as a single dose, repeated after 1–2 weeks to kill mites that have hatched from eggs (as it is not ovicidal). **Why other options are incorrect:** * **Permethrin (5%):** This is the **topical drug of choice** for scabies. However, it is applied as a cream from neck to toe and is not administered orally. * **Lindane (1% Gamma Benzene Hexachloride):** A topical agent that is now less preferred due to potential neurotoxicity (seizures), especially in children and the elderly. * **Crotamiton (10%):** A topical scabicide and antipruritic agent with lower efficacy compared to Permethrin or Ivermectin. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic sign:** The **Burrow** (a short, wavy, dirty-looking line), most commonly found in finger webs and wrists. * **Nodular Scabies:** Itchy nodules found on male genitalia and axillae; these persist even after successful treatment. * **Crusted (Norwegian) Scabies:** Seen in immunocompromised patients; characterized by thousands of mites and minimal itching. **Treatment:** Combined oral Ivermectin and topical Permethrin. * **Contraindication:** Oral Ivermectin is generally avoided in children weighing <15 kg and during pregnancy.

Q: Which of the following drugs is most efficacious against Pediculosis humanus as well as Sarcoptes Scabiei?

Permethrin. **Explanation:** **1. Why Permethrin is the Correct Answer:** Permethrin (5% for Scabies, 1% for Pediculosis) is currently the **gold standard** and first-line treatment for both conditions. It is a synthetic pyrethroid that acts by disrupting the sodium channel currents in the neuronal membranes of parasites, leading to delayed repolarization, paralysis, and death. Its high efficacy (cure rates >95%), low systemic absorption, and excellent safety profile in infants (above 2 months) and pregnant women make it the drug of choice. **2. Analysis of Incorrect Options:** * **B. Hexachlorocyclohexane (Lindane):** Once widely used, it is now a second-line agent due to concerns regarding **neurotoxicity** (seizures), especially in children and underweight individuals. It is less efficacious than Permethrin due to emerging resistance. * **C. Monobenzone:** This is a **depigmenting agent** used in conditions like Vitiligo universalis to remove remaining normal skin pigment. It has no antiparasitic properties. * **D. Crotamiton:** While it has anti-scabietic and anti-pruritic properties, its efficacy is significantly lower than Permethrin, often requiring multiple applications over several days. **3. High-Yield Clinical Pearls for NEET-PG:** * **Application Rule:** For Scabies, Permethrin 5% cream should be applied from the **neck down to the toes** and left for 8–12 hours. In infants, the face and scalp must also be included. * **Ivermectin:** The oral drug of choice for **Crusted (Norwegian) Scabies** (used in combination with topical Permethrin) and for institutional outbreaks. * **Nits:** In Pediculosis, nits (eggs) within 1 cm of the scalp indicate active infection. * **Post-scabietic Pruritus:** Itching may persist for 2–4 weeks even after successful treatment due to a hypersensitivity reaction to dead mites; this does not necessarily indicate treatment failure.

Q: Which drug is used orally for treating scabies?

Ivermectin. **Explanation:** **Ivermectin** is the correct answer as it is the only drug among the options approved for the **systemic (oral) treatment** of scabies. It works by binding to glutamate-gated chloride channels in the nerve and muscle cells of the invertebrate, leading to paralysis and death of the *Sarcoptes scabiei* mite. The standard dosage is **200 μg/kg** as a single dose, repeated after 1–2 weeks to kill nymphs that have hatched from surviving eggs. **Analysis of Incorrect Options:** * **Permethrin (5%):** While it is the **gold standard/first-line treatment** for scabies, it is administered **topically** (as a cream), not orally. * **Levamisole:** This is an anthelmintic used for roundworm infections and sometimes as an immunomodulator, but it has no role in treating scabies. * **Chloroquine:** This is an antimalarial and DMARD; it is ineffective against ectoparasites like mites. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Topical **5% Permethrin** is the overall DOC for classical scabies. * **Crusted (Norwegian) Scabies:** Characterized by thousands of mites in immunocompromised patients; treatment requires a **combination** of oral Ivermectin and topical Permethrin. * **Contraindications:** Oral Ivermectin should be avoided in children weighing **<15 kg**, pregnant women, and lactating mothers (due to the blood-brain barrier concerns). * **Nodular Scabies:** Represents a hypersensitivity reaction; treated with intralesional or potent topical steroids, not just scabicides.

Q: Vagabond's disease is caused by which of the following?

Pediculosis corporis. **Explanation:** **Vagabond’s disease** (also known as Parasitosis corporis) is a chronic skin condition caused by a long-standing infestation of **Pediculosis corporis (Body lice)**. It typically affects individuals with poor personal hygiene, such as the homeless or those living in overcrowded conditions. **Why Pediculosis corporis is correct:** Body lice live and lay eggs in the seams of clothing, visiting the skin only to feed. Chronic scratching due to persistent bites leads to a triad of clinical features: 1. **Excoriations:** Linear scratch marks. 2. **Post-inflammatory Hyperpigmentation:** The skin becomes dark and thickened (lichenified). 3. **Secondary Infection:** Often present due to constant trauma to the skin barrier. The term "Vagabond" refers to the characteristic "dirty, bronze-pigmented skin" seen in neglected individuals. **Why other options are incorrect:** * **Scabies:** Caused by *Sarcoptes scabiei*. While it causes intense nocturnal itching and hyperpigmentation in chronic cases (Norwegian scabies), it does not produce the specific clinical picture of Vagabond’s disease. * **Herpes genitalis:** A viral infection (HSV-2) characterized by painful vesicles and ulcers in the genital region, not chronic generalized pigmentation. * **Ant bite reaction:** Presents as acute papular urticaria or pustules at the site of the sting; it is an acute allergic reaction, not a chronic dermatosis. **Clinical Pearls for NEET-PG:** * **Vector Potential:** Body lice are the only lice that transmit systemic diseases: **Epidemic Typhus** (*Rickettsia prowazekii*), **Trench Fever** (*Bartonella quintana*), and **Relapsing Fever** (*Borrelia recurrentis*). * **Diagnosis:** Lice are found in the **seams of clothes**, not on the body. * **Treatment:** Primary management involves laundering clothes in hot water (>60°C) or ironing; topical pediculicides (Permethrin) are secondary.

Q: Mark the false statement about Tungiasis.

Endo parasite skin infection. **Explanation:** **Tungiasis** is a skin infestation caused by the burrowing of the female sand flea, *Tunga penetrans*. 1. **Why Option A is the False Statement (Correct Answer):** *Tunga penetrans* is an **ectoparasite**, not an endoparasite. While the gravid female burrows into the epidermis to feed on blood and lay eggs, it remains in the cutaneous layers and maintains a small opening to the skin surface for breathing, defecation, and egg expulsion. Endoparasites, by definition, live inside the internal organs or tissues of the host (e.g., helminths in the gut). 2. **Analysis of Other Options:** * **Option B:** *Tunga penetrans* is commonly known as the **chigoe flea**, jigger, or sand flea. (Note: Do not confuse this with "chiggers," which are larval mites). * **Option C:** It is indeed the **smallest known flea** species, with non-gravid adults measuring approximately **1 mm** in length. * **Option D:** Clinical presentation typically involves a painful, pruritic, pearly-white nodule with a central black dot (the flea's posterior). As the flea dies and is sloughed off by the host's immune response, **desquamation** and crusting of the surrounding skin are characteristic features. **High-Yield Clinical Pearls for NEET-PG:** * **Common Site:** Most commonly affects the **periungual** region of the toes and the soles (areas in contact with soil). * **Kohl's Sign:** The characteristic white halo with a central black point. * **Treatment:** Surgical extraction of the flea under sterile conditions is the treatment of choice. Topical dimeticone can also be used. * **Prevention:** Wearing closed-toe shoes in endemic areas (Sub-Saharan Africa, Latin America).

Q: Which of the following drugs or treatments are used in scabies?

All of the above. Scabies is a contagious skin infestation caused by the mite *Sarcoptes scabiei* var. *hominis*. The management involves the use of topical or systemic **scabicides** to eradicate the mites and their eggs. **Explanation of Options:** * **Permethrin (5%):** This is the **drug of choice** for scabies. It acts by disrupting the sodium channel currents in the neuronal membranes of the mites, leading to paralysis and death. It has high efficacy and a superior safety profile, making it safe for infants over 2 months and pregnant women. * **Lindane (1% Gamma Benzene Hexachloride):** An organochlorine insecticide that was once a first-line treatment. However, due to risks of **neurotoxicity** (seizures), it is now considered a second-line agent and is contraindicated in children, the elderly, and patients with seizure disorders. * **Crotamiton (10%):** This agent has both scabicidal and anti-pruritic properties. While less effective than Permethrin, it is often used in pediatric cases or when other treatments fail. Since all three medications are recognized scabicidal agents, **Option D (All of the above)** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Ivermectin:** The oral drug of choice (200 μg/kg). It is the preferred treatment for **Crusted (Norwegian) Scabies** and for managing outbreaks in institutional settings. * **Application Rule:** Topical scabicides must be applied from the **neck down to the toes** and left on for 8–12 hours (usually overnight) before washing off. In infants, the face and scalp should also be included. * **Treatment of Contacts:** All close physical contacts and family members must be treated simultaneously, even if asymptomatic, to prevent re-infestation. * **Post-Scabietic Pruritus:** Itching may persist for 2–4 weeks even after successful treatment due to a hypersensitivity reaction to dead mites; this does not necessarily indicate treatment failure.

Q: What is true about scabies?

All family members should be treated together.. **Explanation:** Scabies is a contagious infestation caused by the mite *Sarcoptes scabiei* var. *hominis*. The hallmark of management is treating the "household unit" rather than just the symptomatic individual. **Why Option C is correct:** Scabies has an **incubation period of 3–6 weeks**. During this time, an infested person can be asymptomatic but still transmit the mites to others through close skin-to-skin contact. To prevent a "ping-pong" reinfection cycle within a household, all close contacts and family members must be treated simultaneously, regardless of whether they are itching. **Analysis of Incorrect Options:** * **Option A:** In adults, scabies typically spares the face, scalp, palms, and soles (the "Circle of Hebra"). However, in **infants** and the elderly, these areas are frequently involved. * **Option B:** Scabies is a parasitic infestation, not bacterial. The primary treatment involves **topical scabicides** (e.g., 5% Permethrin) or **oral Ivermectin**. Antibiotics are only indicated if there is a secondary bacterial infection (impetiginization) due to scratching. * **Option D:** Itching in scabies is a Type IV hypersensitivity reaction to the mite, its eggs, and scybala (feces). It characteristically **worsens at night** (nocturnal pruritus) due to increased mite activity and warmth under bedclothes. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic sign:** The **Burrow** (a linear or S-shaped track), most commonly found in finger webs and wrist flexures. * **Drug of Choice:** Topical **Permethrin 5%** (applied neck down, left for 8–12 hours). * **Crusted (Norwegian) Scabies:** Seen in immunocompromised patients; characterized by thousands of mites and minimal itching. It is highly contagious. * **Nodular Scabies:** Persistent itchy nodules (often on genitalia) that remain even after the mites are eradicated; treated with intralesional steroids.

Question 1

An 18-month-old boy presents with pruritic, papular lesions over the groin and prepuce. The infant has not been eating or sleeping well. All of the following are indicated in this patient, EXCEPT:

Accepted Answer

Intravenous antibiotics

Answer

Antihistamines and scabicidal solution

Answer

Treat all family members

Answer

Dispose of contaminated clothing

Question 2

A patient presents with itchy lesions over the wrist, which are worse at night. Which of the following drugs can be used orally for treatment in this case?

Accepted Answer

Ivermectin

Answer

Crotamiton

Answer

Lindane

Answer

Permethrin

Question 3

A caretaker in a nursing home presents with pruritus of her trunk and extremities. On physical examination, she has several erythematous papules in her finger webs, axillae, umbilicus, and groin areas. Her scalp is clear. Which of the following is the best treatment for this woman?

Accepted Answer

Permethrin cream

Answer

Clindamycin solution

Answer

Oral erythromycin

Answer

Topical steroids

Question 4

Which of the following drugs is most efficacious against Pediculosis humanus as well as Sarcoptes Scabiei?

Accepted Answer

Permethrin

Answer

Hexachlorocyclohexane

Answer

Monobenzone

Answer

Crotomiton

Question 5

Which drug is used orally for treating scabies?

Accepted Answer

Ivermectin

Answer

Levamisole

Answer

Permethrin

Answer

Chloroquine

Question 6

Vagabond's disease is caused by which of the following?

Accepted Answer

Pediculosis corporis

Answer

Scabies

Answer

Herpes genitalis

Answer

Ant bite reaction

Question 7

Mark the false statement about Tungiasis.

Accepted Answer

Endo parasite skin infection

Answer

Tunga penetrans is also known as chigoe flea

Answer

Tunga penetrans is the smallest known flea, measuring 1 mm

Answer

Desquamation of the skin is always seen

Question 8

An 8-year-old boy presents with an itchy rash affecting his entire body. All members of his family are also affected. What is the drug of choice for this condition?

Accepted Answer

Topical permethrin

Answer

Ivermectin

Answer

Prednisolone

Answer

Antibiotics

Question 9

Which of the following drugs or treatments are used in scabies?

Accepted Answer

All of the above

Answer

Crotamiton

Answer

Permethrin

Answer

Lindane

Question 10

What is true about scabies?

Accepted Answer

All family members should be treated together.

Answer

It affects the palms and soles in adults.

Answer

Oral antibiotics are needed in every patient.

Answer

Itching is more pronounced in the morning.

Parasitic Skin Infections — MCQs

Parasitic Skin Infections — MCQs

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