Diagnosis of Parasitic Infestations — MCQs
Which physical finding is most useful in diagnosing scabies in genital lesions?
A child of 7-8 years of age presents with scalp swelling and alopecia. What is the most appropriate diagnostic investigation?
A girl who is staying in a hostel presented with severe itching all over her body for two days. The intense itching worsens at night and after a hot shower. Burrows are seen between the fingers. Approximately how many live mites are there in an adult with scabies?
A child presented with asymptomatic lesions on the forearm and on the shaft of the penis. The lesions on the forearm are shown below. What is the most likely diagnosis?
Identify the diagnosis based on the dermatology immunofluorescence (IF) image provided.
A Giemsa stain of a thin peripheral blood smear is prepared. Which of the following cannot be diagnosed?
A child presents with grouped vesicles on the lips. What is the bedside investigation that you would like to do?
All of the following are true regarding Norwegian scabies except
Mass Drug Administration is not helpful for:
JSB stain is used for which parasite?
Diagnosis of Parasitic Infestations Indian Medical PG Practice Questions and MCQs
Question 1: Which physical finding is most useful in diagnosing scabies in genital lesions?
- A. Vesicular lesions on shaft of penis
- B. Burrows in genital area (Correct Answer)
- C. Pustules on glans penis
- D. Excoriated nodules on scrotum
Explanation: ***Burrows in genital area*** - The presence of **burrows** is the **pathognomonic sign of scabies**, representing the tunnels dug by the female mite. - While scabies can cause varied lesions, identifying these **serpiginous, thread-like burrows** is the most diagnostic physical finding. *Vesicular lesions on shaft of penis* - **Vesicular lesions** can be seen in various conditions like **herpes simplex virus (HSV)** infection, making them less specific for scabies. - While scabies can sometimes present with vesicles, they are not the primary diagnostic feature. *Pustules on glans penis* - **Pustules on the glans penis** are more indicative of conditions like **bacterial folliculitis** or other sexually transmitted infections (STIs), such as **gonorrhea**. - Scabies typically does not present with pustules as its primary lesion. *Excoriated nodules on scrotum* - While **scabietic nodules**, particularly on the scrotum, are a recognized manifestation of scabies, especially in chronic cases, they are often **excoriated due to intense itching**. - These nodules are a common sign but are not as specific as finding a burrow, which directly demonstrates the mite's activity.
Question 2: A child of 7-8 years of age presents with scalp swelling and alopecia. What is the most appropriate diagnostic investigation?
- A. KOH staining of the scrapings (Correct Answer)
- B. Blood culture
- C. PAS staining
- D. Gram staining
Explanation: ***KOH staining of the scrapings*** - This presentation is highly suggestive of **tinea capitis**, a fungal infection of the scalp. **Potassium hydroxide (KOH) staining** of hair and scalp scrapings is the primary diagnostic method to identify fungal elements (hyphae and spores). - KOH dissolves keratinous material, making it easier to visualize the **fungal hyphae or spores** under a microscope. *Blood culture* - **Blood culture** is used to diagnose **systemic infections**, particularly bacterial or fungal infections that have entered the bloodstream. - It is **not indicated** for the initial diagnosis of localized skin and hair infections like tinea capitis. *PAS staining* - **Periodic acid–Schiff (PAS) staining** is primarily used for **histopathological examination** of tissue biopsies to detect fungi or other carbohydrates. - While it can identify fungi in tissue sections, it is **not the first-line diagnostic investigation** for tinea capitis, which typically uses direct microscopic examination of scrapings. *Gram staining* - **Gram staining** is a differential staining technique used to classify **bacteria** based on their cell wall properties (Gram-positive or Gram-negative). - It is **not effective** for identifying fungal organisms, which have different cell wall compositions.
Question 3: A girl who is staying in a hostel presented with severe itching all over her body for two days. The intense itching worsens at night and after a hot shower. Burrows are seen between the fingers. Approximately how many live mites are there in an adult with scabies?
- A. 20-25
- B. 5-15 (Correct Answer)
- C. 30-50
- D. 25-30
Explanation: ***Approximately 5-15*** - In an adult with typical scabies, the **mite burden is usually low**, with an average of 5-15 live mites. - The intense itching is primarily due to a **hypersensitivity reaction** to the mites and their products, rather than the sheer number of mites. - This is the **characteristic range for classic, uncomplicated scabies** in immunocompetent individuals. *20-25* - This number is generally **higher than the typical mite count** found in classic scabies infestations. - A burden this high might be seen in cases approaching **crusted scabies**, or in prolonged untreated cases. *25-30* - This number is significantly higher than the average mite count for typical scabies. - Such a high burden is characteristic of **crusted (Norwegian) scabies**, a severe form often seen in immunocompromised individuals with widespread crusted lesions. *30-50* - This represents a very high mite burden far exceeding typical scabies. - Such numbers are seen in **crusted (Norwegian) scabies**, which can harbor hundreds to thousands of mites and occurs primarily in immunocompromised patients, elderly, or those with neurological conditions preventing scratching.
Question 4: A child presented with asymptomatic lesions on the forearm and on the shaft of the penis. The lesions on the forearm are shown below. What is the most likely diagnosis?
- A. Lichen planus
- B. Lichen nitidus (Correct Answer)
- C. Scabies
- D. Scrofuloderma
Explanation: ***Lichen nitidus*** - Presents as **multiple, asymptomatic, tiny (1-2 mm), shiny, dome-shaped papules** that are often skin-colored or slightly hypopigmented, as seen in the image and described. - Common sites include the **forearms, penis, abdomen, and flexural areas**, consistent with the case presentation. *Lichen planus* - Characterized by **purplish, polygonal, planar, pruritic papules and plaques**, often with **Wickham's striae**, which are not seen in the image. - While it can affect the penis, its lesions are typically more intensely colored and often symptomatic (**itchy**), unlike the asymptomatic lesions described. *Scabies* - Presents with intensely **pruritic papules, vesicles, and burrows**, especially in the web spaces of fingers, wrists, axillae, and genitalia, which are very symptomatic and not usually described as shiny papules. - The primary symptom is **severe itching**, which is absent in this patient. *Scrofuloderma* - A form of **cutaneous tuberculosis** presenting as cold abscesses that eventually rupture to form ulcers, sinuses, and scars. - The image shows distinct, small papules, not ulcerating or scarring lesions characteristic of scrofuloderma.
Question 5: Identify the diagnosis based on the dermatology immunofluorescence (IF) image provided.
- A. Pemphigus vulgaris
- B. Pemphigus foliaceus
- C. Bullous pemphigoid
- D. Dermatitis herpetiformis (Correct Answer)
Explanation: ***Dermatitis herpetiformis*** - The immunofluorescence image shows **granular IgA deposits** at the **dermal papillae region**, which is characteristic of dermatitis herpetiformis. - This condition is strongly associated with **celiac disease** and presents with intensely pruritic papules and vesicles. *Pemphigus vulgaris* - Immunofluorescence in pemphigus vulgaris typically shows a **fishnet pattern** of IgG deposits throughout the **epidermis**, reflecting antibodies against desmoglein 3 and 1. - This pattern is an intercellular deposition, not granular at the dermal papillae. *Pemphigus foliaceus* - Similar to pemphigus vulgaris, pemphigus foliaceus also exhibits **intercellular IgG deposits** in the epidermis, but it is usually more superficial, targeting desmoglein 1. - The image does not show this intercellular epidermal staining. *Bullous pemphigoid* - Bullous pemphigoid is characterized by **linear IgG and C3 deposits along the dermal-epidermal junction** (basement membrane zone). - The image distinctly shows granular IgA, not linear IgG/C3, and specifically in the dermal papillae.
Question 6: A Giemsa stain of a thin peripheral blood smear is prepared. Which of the following cannot be diagnosed?
- A. Coxiella burnettii (Correct Answer)
- B. Bartonella henselae
- C. Ehrlichia chaffeensis
- D. Toxoplasma gondii
Explanation: ***Coxiella burnettii*** - *Coxiella burnettii* causes **Q fever** and is an **obligate intracellular bacterium** that resides primarily in **tissue macrophages** (lungs, liver, bone marrow), not in circulating blood cells. - It is **not found in peripheral blood smears** because it does not infect circulating leukocytes in significant numbers that would allow microscopic visualization. - Diagnosis requires **serology** (most common), **PCR**, or specialized culture in BSL-3 facilities—direct microscopic visualization in blood smears is not possible. *Bartonella henselae* - Causes **Cat scratch disease** and can invade **red blood cells**, making it potentially visible on Giemsa-stained blood smears, particularly in immunocompromised patients with bacillary angiomatosis or bacteremia. - While difficult and not the primary diagnostic method, it *can* be visualized in peripheral blood, unlike *Coxiella*. *Ehrlichia chaffeensis* - Causes **human monocytotropic ehrlichiosis (HME)** and forms characteristic **morulae** (berry-like clusters) within the cytoplasm of **monocytes**. - These morulae are readily visible on **Giemsa-stained peripheral blood smears** and are a key diagnostic finding, making this condition easily diagnosed by this method. *Toxoplasma gondii* - An **intracellular parasite** whose **tachyzoites** can occasionally be found in **peripheral blood leukocytes** during acute infection, especially in immunocompromised patients. - While rare and not the primary diagnostic method (serology/PCR preferred), tachyzoites *can* be observed in blood smears during active parasitemia.
Question 7: A child presents with grouped vesicles on the lips. What is the bedside investigation that you would like to do?
- A. Wood's lamp
- B. Slit skin smear
- C. Tzanck smear (Correct Answer)
- D. KOH
Explanation: ***Tzanck smear*** - A **Tzanck smear** is a rapid bedside test that can identify **multinucleated giant cells**, which are seen in herpes simplex virus infections. - The presence of **grouped vesicles on the lips** is highly suggestive of **herpes labialis** (HSV-1), which is primarily a **clinical diagnosis**. - Among the options provided, Tzanck smear is the only relevant bedside investigation, though it has **limited sensitivity and specificity** and **cannot distinguish between HSV and VZV**. - In modern practice, **PCR or direct immunofluorescence** are preferred when laboratory confirmation is needed, but Tzanck smear remains a low-cost option in resource-limited settings. *Wood's lamp* - A Wood's lamp uses **ultraviolet light** to detect certain fungal or bacterial infections by revealing characteristic fluorescence. - It is useful for conditions like **tinea capitis** (green fluorescence) and **erythrasma** (coral-red fluorescence), but has no role in diagnosing viral vesicular lesions. *Slit skin smear* - A **slit skin smear** is used to detect **acid-fast bacilli** in the diagnosis of **leprosy**. - It is not indicated for vesicular lesions and is irrelevant to herpes simplex infection. *KOH* - A **KOH (potassium hydroxide) mount** is used to diagnose **fungal infections** by dissolving keratinocytes and revealing fungal hyphae or spores. - It has no utility in diagnosing viral infections such as herpes simplex.
Question 8: All of the following are true regarding Norwegian scabies except
- A. Large number of parasites present
- B. Psoriasiform plaques common
- C. Itching is mild or absent
- D. Children commonly affected (Correct Answer)
Explanation: ***Children commonly affected*** - **Norwegian scabies** (also known as **crusted scabies**) primarily affects individuals with **immunocompromise**, **neurological impairment**, or the **elderly**. - While scabies can affect children, the crusted form is **uncommon** in healthy children. *Large number of parasites present* - This statement is true; **crusted scabies** is characterized by an **exceedingly high mite burden**, sometimes numbering in the millions. - The large number of mites leads to the characteristic **crusting and hyperkeratosis**. *Psoriasiform plaques common* - This statement is true; the extensive **hyperkeratosis** and **crusting** in Norwegian scabies often manifest as **thick, scaly plaques** that can resemble **psoriasis**. - These lesions are typically found on the **extremities**, **trunk**, and often involve the **nails** and **scalp**. *Itching is mild or absent* - This statement is true; despite the massive mite load, patients with crusted scabies often experience **surprisingly little or no pruritus**. - This reduced or absent itching is thought to be due to an impaired immune response that also prevents the typical inflammatory reaction to the mites.
Question 9: Mass Drug Administration is not helpful for:
- A. Lymphatic Filariasis
- B. Vitamin A Deficiency
- C. Worm infestation
- D. Scabies (Correct Answer)
Explanation: ***Scabies*** - **Mass Drug Administration (MDA)** for scabies is primarily an emergency intervention in high-prevalence settings, but it's generally not a sustainable or long-term solution for control due to high re-infection rates and the need for concomitant treatment of household contacts and environmental measures. - **Ivermectin** MDA can be effective in reducing prevalence in some communities, but it often needs to be combined with other strategies due to the risk of drug resistance and the importance of topical treatments, hygiene, and environmental sanitation. *Lymphatic Filariasis* - **MDA with anti-filarial drugs** (e.g., albendazole, ivermectin, diethylcarbamazine citrate) is a cornerstone of global **lymphatic filariasis elimination programs**. - It aims to reduce microfilariae in the blood to interrupt transmission by mosquitoes, and has been proven highly effective in many endemic regions. *Vitamin A Deficiency* - **Vitamin A supplementation** through MDA is a highly effective, widely implemented strategy to combat **Vitamin A Deficiency (VAD)** in young children and pregnant women in areas where VAD is a public health problem. - It significantly reduces childhood morbidity and mortality from infectious diseases and prevents **xerophthalmia**. *Worm infestation* - **Deworming programs** using MDA, particularly for **soil-transmitted helminths (STH)**, are highly effective in controlling intestinal worm infestations in school-aged children and other high-risk groups. - Regular administration of **albendazole** or **mebendazole** drastically reduces worm burden, improving nutritional status and school performance.
Question 10: JSB stain is used for which parasite?
- A. Kala azar
- B. Sleeping sickness
- C. Malaria
- D. Filaria (Correct Answer)
Explanation: ***Filaria*** - The **JSB stain (Jaswant Singh Battacharya stain)** is a rapid Romanowsky-type stain specifically developed for the diagnosis of **microfilariae** in blood films. - It allows for clear visualization of the sheaths and nuclei of microfilariae, which is crucial for species identification and diagnosis of **filariasis**. *Malaria* - **Giemsa stain** is the gold standard for identifying malaria parasites in thick and thin blood smears, not JSB stain. - Giemsa allows for detailed morphological differentiation of malaria species and stages within **red blood cells**. *Kala azar* - **Kala-azar (visceral leishmaniasis)** is diagnosed by detecting **Leishman bodies (amastigotes)** in bone marrow, splenic, or lymph node aspirates. - Stains like **Giemsa** or **Leishman stain** are traditionally used for visualizing these amastigotes. *Sleeping sickness* - **Sleeping sickness (African trypanosomiasis)** is diagnosed by identifying **trypomastigotes** in blood smears, lymph node aspirates, or cerebrospinal fluid. - **Giemsa stain** is commonly used for the microscopic examination of these specimens to detect the parasites.
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