Parasitic Skin Infections — MCQs

Parasitic Skin Infections Indian Medical PG Practice Questions and MCQs

Question 11: 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:

A. Antihistamines and scabicidal solution
B. Treat all family members
C. Dispose of contaminated clothing
D. Intravenous antibiotics (Correct Answer)

Explanation: This question describes a classic presentation of **Infantile Scabies**. In infants, the distribution often involves the groin, genitalia (prepuce), axillae, and even the palms and soles. The intense pruritus leads to irritability, poor feeding, and sleep disturbances. ### **Explanation of Options** * **Why D is the Correct Answer (Except):** Scabies is a parasitic infestation caused by *Sarcoptes scabiei*. The primary treatment is topical scabicides. **Intravenous (IV) antibiotics** are not indicated for uncomplicated scabies. While secondary bacterial infections (like impetigo) can occur due to scratching, they are typically managed with topical or oral antibiotics. IV antibiotics are reserved only for severe complications like cellulitis or sepsis, which are not suggested here. * **Option A (Incorrect):** Scabicidal solutions (e.g., 5% Permethrin) are the gold standard for killing the mites. Antihistamines are essential to manage the Type IV hypersensitivity reaction that causes the itching. * **Option B (Incorrect):** Scabies is highly contagious via skin-to-skin contact. To prevent "ping-pong" reinfection, all household members and close contacts must be treated simultaneously, even if asymptomatic. * **Option C (Incorrect):** Fomite transmission is possible. Bedding and clothing used in the last 3 days should be washed in hot water and dried at high heat (or sealed in plastic bags for 72 hours) to kill the mites. ### **NEET-PG High-Yield Pearls** * **Drug of Choice:** **Permethrin 5% cream** (applied neck down in adults; include face/scalp in infants). * **Nodular Scabies:** Often seen on the male genitalia (prepuce/scrotum) and axillae; these are hypersensitivity reactions and may persist for weeks after successful treatment. * **Norwegian (Crusted) Scabies:** Seen in immunocompromised patients; characterized by thousands of mites and minimal itching. Treatment requires oral **Ivermectin**. * **Burrow:** The pathognomonic lesion, most commonly found in finger webs and wrist creases.

Question 12: 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?

A. Crotamiton
B. Ivermectin (Correct Answer)
C. Lindane
D. Permethrin

Explanation: **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.

Question 13: 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?

A. Clindamycin solution
B. Oral erythromycin
C. Permethrin cream (Correct Answer)
D. Topical steroids

Explanation: ### Explanation **Diagnosis: Scabies** The clinical presentation of generalized pruritus with erythematous papules in classic locations—**finger webs, axillae, umbilicus, and groin**—is pathognomonic for Scabies, caused by the mite *Sarcoptes scabiei*. The involvement of a nursing home caretaker is a high-yield clue, as scabies often spreads in crowded or institutional settings via skin-to-skin contact. **Why Permethrin is Correct:** * **Permethrin (5% cream)** is the first-line treatment for scabies. It acts by disrupting the sodium channel conductance in the neuronal membranes of the mites, leading to paralysis and death. * **Application:** It must be applied from the neck down to the toes (including under nails) and left on for 8–12 hours before washing off. A repeat application after 1 week is often recommended to kill newly hatched nymphs. **Why Other Options are Incorrect:** * **A & B (Clindamycin/Erythromycin):** These are antibiotics. While secondary bacterial infections (like impetigo) can occur due to scratching, they do not treat the underlying parasitic infestation. * **D (Topical Steroids):** These may temporarily reduce inflammation and itching but will not kill the mites. In fact, using steroids alone can lead to *Scabies Incognito*, where the typical rash is suppressed while the infestation worsens. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic Sign:** The **Burrow** (a short, wavy, grayish line) is the most specific clinical sign. * **Distribution:** In adults, the scalp and face are typically **spared**. However, in infants and the elderly, the scalp and face may be involved. * **Nocturnal Exacerbation:** Pruritus is characteristically worse at night (Type IV hypersensitivity to mite feces/eggs). * **Nodular Scabies:** Persistent itchy nodules in the groin/axilla even after treatment; represents a hypersensitivity reaction, not active infection. * **Crusted (Norwegian) Scabies:** Seen in immunocompromised patients; presents with thousands of mites and thick crusts; highly contagious. Treatment requires **Oral Ivermectin** plus topical Permethrin.

Question 14: Which of the following drugs is most efficacious against Pediculosis humanus as well as Sarcoptes Scabiei?

A. Permethrin (Correct Answer)
B. Hexachlorocyclohexane
C. Monobenzone
D. Crotomiton

Explanation: **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.

Question 15: Which drug is used orally for treating scabies?

A. Levamisole
B. Ivermectin (Correct Answer)
C. Permethrin
D. Chloroquine

Explanation: **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.

Question 16: Vagabond's disease is caused by which of the following?

A. Scabies
B. Herpes genitalis
C. Pediculosis corporis (Correct Answer)
D. Ant bite reaction

Explanation: **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.

Question 17: Mark the false statement about Tungiasis.

A. Endo parasite skin infection (Correct Answer)
B. Tunga penetrans is also known as chigoe flea
C. Tunga penetrans is the smallest known flea, measuring 1 mm
D. Desquamation of the skin is always seen

Explanation: **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).

Question 18: 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?

A. Ivermectin
B. Topical permethrin (Correct Answer)
C. Prednisolone
D. Antibiotics

Explanation: ### **Explanation** The clinical presentation of a generalized itchy rash involving multiple family members is a classic hallmark of **Scabies**, caused by the mite *Sarcoptes scabiei*. The hallmark symptom is nocturnal pruritus, and the involvement of family members indicates a highly contagious infestation spread via skin-to-skin contact. **1. Why Topical Permethrin is the Correct Answer:** **5% Permethrin cream** is the **drug of choice (DOC)** for scabies. It acts by disrupting the sodium channel currents on the nerve cell membranes of the mites, leading to paralysis and death. It is preferred due to its high efficacy (>95% cure rate), low systemic toxicity, and safety profile in infants (above 2 months) and pregnant women. It should be applied from the neck down to the toes and left for 8–12 hours before washing off. **2. Why Other Options are Incorrect:** * **Ivermectin:** While oral Ivermectin (200 µg/kg) is effective and used as a second-line agent or in institutional outbreaks, it is not the primary DOC for uncomplicated scabies. It is, however, the DOC for **Crusted (Norwegian) Scabies**. * **Prednisolone:** This is a corticosteroid used for inflammatory conditions. While it may reduce itching, it does not treat the underlying parasitic infection and can worsen the infestation if used alone. * **Antibiotics:** These are only indicated if there is a secondary bacterial infection (e.g., impetigo) due to scratching. They do not treat the primary scabies infestation. ### **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic Sign:** The **Burrow** (a short, wavy, greyish line) is the classic lesion, most commonly found in finger webs, wrists, and genitals. * **Nodular Scabies:** Persistent itchy nodules seen in children, commonly on the axilla and groin. * **Treatment Rule:** Always treat **all close contacts** simultaneously, even if asymptomatic, to prevent re-infestation. * **Bedding/Clothes:** Should be washed in hot water (>60°C) or sealed in a plastic bag for 72 hours (mites die without human contact).

Question 19: Which of the following drugs or treatments are used in scabies?

A. Crotamiton
B. Permethrin
C. Lindane
D. All of the above (Correct Answer)

Explanation: 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.

Question 20: What is true about scabies?

A. It affects the palms and soles in adults.
B. Oral antibiotics are needed in every patient.
C. All family members should be treated together. (Correct Answer)
D. Itching is more pronounced in the morning.

Explanation: **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.

Practice by Chapter

Scabies

Practice Questions

Pediculosis

Practice Questions

Cutaneous Larva Migrans

Practice Questions

Leishmaniasis

Practice Questions

Onchocerciasis

Practice Questions

Myiasis

Practice Questions

Tungiasis

Practice Questions

Cutaneous Amebiasis

Practice Questions

Cutaneous Manifestations of Malaria

Practice Questions

Ectoparasitic Infestations

Practice Questions

Diagnosis of Parasitic Infestations

Practice Questions

Antiparasitic Therapy

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free