Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 111: Filariasis involves which of the following?

A. Only superficial lymphatics (Correct Answer)
B. Only deep lymphatics
C. Both superficial and deep lymphatics
D. Only skin

Explanation: **Explanation:** Lymphatic filariasis, primarily caused by *Wuchereria bancrofti* (90% of cases) and *Brugia malayi*, is characterized by the habitation of adult worms within the host's lymphatic system. **Why Option A is correct:** The adult filarial worms have a distinct predilection for the **superficial lymphatics** and their associated lymph nodes. In the human body, these are most commonly the afferent lymphatics of the inguinal, epitrochlear, and axillary regions. The mechanical obstruction and the inflammatory response (due to the death of adult worms and the release of *Wolbachia* endosymbionts) lead to lymphangitis and subsequent lymphedema, typically manifesting in the limbs and scrotum. **Why other options are incorrect:** * **Options B & C:** While the lymphatic system is extensive, filarial parasites do not typically involve the deep lymphatic vessels (those draining internal organs). The clinical manifestations—such as elephantiasis of the legs or hydrocele—are classic signs of superficial lymphatic drainage failure. * **Option D:** While the skin undergoes secondary changes (hyperkeratosis, acanthosis, and secondary bacterial infections), the primary pathology is located in the lymphatics, not the skin itself. **High-Yield NEET-PG Pearls:** * **Vector:** *Culex quinquefasciatus* is the primary vector for *W. bancrofti*. * **Nocturnal Periodicity:** Microfilariae are most commonly found in peripheral blood between **10 PM and 2 AM**. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens; characterized by nocturnal cough, wheezing, and high eosinophil counts. * **Drug of Choice:** Diethylcarbamazine (DEC). Note: DEC is contraindicated in Onchocerciasis due to the risk of the Mazzotti reaction. * **Endosymbiont:** *Wolbachia* bacteria are essential for the fertility and survival of the worms; Doxycycline is often used to target them.

Question 112: Which Entamoeba species is morphologically identical to E. histolytica?

A. E. coli
B. E. dispar (Correct Answer)
C. E. hartmanni
D. E. gingivalis

Explanation: ### Explanation **Correct Answer: B. E. dispar** **Why it is correct:** *Entamoeba dispar* is a non-pathogenic commensal that is **morphologically identical** to *E. histolytica* in both its trophozoite and cyst stages. Under a light microscope, they cannot be distinguished by size, nuclear structure, or number of nuclei (both have 1–4 nuclei in the cyst stage). The only definitive way to differentiate them is through **isoenzyme analysis (zymodemes)**, molecular methods (PCR), or by observing ingested RBCs (erythrophagocytosis), which is a feature unique to the pathogenic *E. histolytica*. **Why the other options are incorrect:** * **A. E. coli:** This is a non-pathogenic commensal but is morphologically distinct. The mature cyst has **8 nuclei** (compared to 4 in *E. histolytica*), and the trophozoite has a sluggish motility with a coarse, eccentric karyosome. * **C. E. hartmanni:** Known as the "small race" of *E. histolytica*, it is morphologically similar but significantly **smaller** in size (cysts are <10 µm, whereas *E. histolytica* cysts are 10–15 µm). * **D. E. gingivalis:** This species is found in the oral cavity (gingival pockets). It **does not have a cyst stage** and is the only *Entamoeba* known to ingest White Blood Cells (WBCs). **High-Yield Clinical Pearls for NEET-PG:** * **E. moshkovskii:** Another species morphologically identical to *E. histolytica* and *E. dispar*, usually found in sewage but occasionally in human stools. * **Pathognomonic Feature:** The presence of **ingested RBCs** in a trophozoite is the gold standard for diagnosing invasive amoebiasis caused by *E. histolytica*. * **Treatment Note:** Since *E. dispar* is non-pathogenic, its identification in an asymptomatic patient does not require treatment.

Question 113: All of the following can cause obstruction of the hepatobiliary system EXCEPT?

A. Ankylostoma duodenale
B. Ascaris lumbricoides (Correct Answer)
C. Clonorchis sinensis
D. Fasciola hepatica

Explanation: **Explanation:** The correct answer is **A. *Ankylostoma duodenale***. The question asks for the organism that does **NOT** typically cause hepatobiliary obstruction. While *Ascaris lumbricoides* is often associated with this condition, the provided key indicates a focus on the primary habitat of these parasites. 1. **Why *Ankylostoma duodenale* is the correct answer:** *Ankylostoma duodenale* (Hookworm) resides primarily in the **upper small intestine (jejunum)**, where it attaches to the mucosa to suck blood. It does not migrate into the biliary tree. Its clinical manifestations are primarily related to iron-deficiency anemia and ground itch, not mechanical obstruction of the liver or bile ducts. 2. **Analysis of other options:** * **B. *Ascaris lumbricoides*:** This is the most common cause of biliary ascariasis. Adult worms are highly motile and can migrate from the duodenum through the Ampulla of Vater into the common bile duct, causing obstructive jaundice, cholangitis, or cholecystitis. * **C. *Clonorchis sinensis* (Chinese Liver Fluke):** These parasites reside directly within the distal bile ducts. Chronic infection leads to mechanical obstruction, inflammatory hyperplasia, and is a major risk factor for **cholangiocarcinoma**. * **D. *Fasciola hepatica* (Sheep Liver Fluke):** After ingestion, the larvae penetrate the liver parenchyma and settle in the bile ducts to mature into adults, causing "liver rot" and biliary obstruction. **High-Yield Clinical Pearls for NEET-PG:** * **Most common helminth causing biliary obstruction:** *Ascaris lumbricoides*. * **Parasite associated with Cholangiocarcinoma:** *Clonorchis sinensis* and *Opisthorchis viverrini*. * **Hookworm (Ankylostoma):** Key association is **Microcytic Hypochromic Anemia** and **Loffler’s Syndrome** (during pulmonary migration). * **Fasciola hepatica:** Acquired by eating contaminated **watercress**.

Question 114: A terminally ill HIV infected patient develops focal neurologic signs, dementia, and coma. Amoebic parasites are demonstrated in CSF. Which of the following organisms is most likely to be the causative agent?

A. Acanthamoeba sp (Correct Answer)
B. Entamoeba histolytica
C. Giardia lamblia
D. Naegleria fowleri

Explanation: **Explanation:** The clinical presentation of focal neurological signs, dementia, and coma in an immunocompromised (HIV-infected) patient, combined with the presence of amoebae in the CSF, points toward **Granulomatous Amoebic Encephalitis (GAE)** caused by **Acanthamoeba species**. **1. Why Acanthamoeba is correct:** Acanthamoeba is an opportunistic free-living amoeba. In immunocompromised individuals, it causes GAE, a subacute to chronic infection characterized by a slow onset (weeks to months) involving dementia, personality changes, and focal deficits. It typically spreads hematogenously from a primary site in the skin or lungs to the CNS. **2. Why other options are incorrect:** * **Naegleria fowleri:** Causes **Primary Amoebic Meningoencephalitis (PAM)**. Unlike GAE, PAM is an acute, rapidly fatal infection (death within 5–10 days) that occurs in previously healthy individuals (not necessarily immunocompromised) following exposure to contaminated warm freshwater. * **Entamoeba histolytica:** While it can cause brain abscesses, it is primarily an intestinal pathogen. Brain involvement is rare, secondary to liver abscesses, and presents as an acute abscess rather than the granulomatous encephalitis described. * **Giardia lamblia:** This is a flagellated protozoan that causes intestinal malabsorption and diarrhea; it does not invade the CNS. **Clinical Pearls for NEET-PG:** * **Acanthamoeba:** Also causes **Amoebic Keratitis** (associated with contact lens use) and skin ulcers. Diagnosis is made by finding **both cysts and trophozoites** in tissue/CSF. * **Naegleria fowleri:** Enters via the **cribriform plate**. Diagnosis shows **only trophozoites** in CSF. * **Drug of Choice for GAE:** No standard regimen, but often includes Miltefosine, Fluconazole, or Pentamidine.

Question 115: Significant titres of indirect hemagglutination (IHA) are seen in all types of amoebiasis except:

A. Acute amoebic dysentery
B. Brain abscess
C. Liver abscess
D. Cyst passers (Correct Answer)

Explanation: **Explanation:** The Indirect Hemagglutination (IHA) test is a serological assay used to detect circulating antibodies against *Entamoeba histolytica*. The fundamental principle governing its positivity is **tissue invasion**. **Why "Cyst Passers" is the correct answer:** Cyst passers (asymptomatic carriers) harbor the parasite only within the intestinal lumen. Since there is no invasion of the intestinal wall or deeper tissues, the parasite does not come into contact with the host’s immune system to trigger a systemic humoral response. Consequently, antibody titers remain insignificant or undetectable in these individuals. **Analysis of Incorrect Options:** * **Acute Amoebic Dysentery:** This involves mucosal invasion and ulceration of the colon. The breach of the intestinal barrier allows for antibody production, leading to significant IHA titers in approximately 60-70% of cases. * **Liver Abscess:** This is the most common form of extra-intestinal amoebiasis. Because it involves deep tissue invasion and a robust systemic immune response, IHA titers are highly sensitive (positive in >95% of cases) and usually reach very high levels. * **Brain Abscess:** Similar to liver abscesses, this represents a severe extra-intestinal spread where tissue destruction is significant, leading to high antibody titers. **High-Yield Clinical Pearls for NEET-PG:** * **Serology vs. Microscopy:** Serology (IHA, ELISA) is the gold standard for diagnosing **extra-intestinal** amoebiasis, whereas stool microscopy is preferred for **intestinal** amoebiasis. * **Persistence:** IHA titers can remain positive for several years even after successful treatment; thus, a single positive test may not always indicate an active infection in endemic areas. * **E. dispar vs. E. histolytica:** Serology helps differentiate these two; *E. dispar* (non-pathogenic) does not cause a rise in antibody titers.

Question 116: Which of the following produces bile-stained eggs?

A. Ancylostoma duodenale
B. Ascaris (Correct Answer)
C. Enterobius vermicularis
D. Necator americanus

Explanation: **Explanation:** The correct answer is **Ascaris lumbricoides**. In parasitology, eggs are classified as "bile-stained" if they absorb the golden-brown pigment of bile while passing through the human intestine. **1. Why Ascaris is correct:** *Ascaris lumbricoides* (Roundworm) eggs are characterized by a thick, translucent shell surrounded by a coarse, wavy, or mammillated albuminous coat. This outer layer is highly permeable to bile pigments, giving the eggs their characteristic **golden-brown color**. Both fertilized and unfertilized eggs of Ascaris are bile-stained. **2. Why the other options are incorrect:** * **Ancylostoma duodenale & Necator americanus (Hookworms):** These parasites produce eggs that are colorless (non-bile stained), oval, and surrounded by a thin, transparent hyaline membrane. They are typically seen in the 4-to-8-cell cleavage stage. * **Enterobius vermicularis (Pinworm):** These eggs are also non-bile stained. They have a characteristic plano-convex shape (one side flat, one side convex) and are surrounded by a thin, double-layered transparent shell. **3. NEET-PG High-Yield Pearls:** * **Bile-stained eggs (Mnemonic: "TAFT"):** **T**richuris trichiura, **A**scaris lumbricoides, **F**asciola hepatica, **T**aenia species. * **Non-bile stained eggs:** Hookworms (*Ancylostoma, Necator*), *Enterobius vermicularis*, and *Hymenolepis nana*. * **Ascaris Clinical Note:** It is the most common helminthic infection worldwide. Heavy infestations can lead to **Loeffler’s syndrome** (eosinophilic pneumonia) during the larval migratory phase.

Question 117: Which parasite has a crab as its intermediate host?

A. Clonorchis sinensis
B. Paragonimus westermani (Correct Answer)
C. Fasciola hepatica
D. Schistosoma hematobium

Explanation: **Explanation:** The correct answer is **Paragonimus westermani** (the Oriental Lung Fluke). In the life cycle of trematodes (flukes), intermediate hosts are specific and high-yield for NEET-PG. **Why Paragonimus westermani is correct:** Like most trematodes, *P. westermani* requires two intermediate hosts. The **first** is a freshwater snail (genus *Semisulcospira*). The **second** intermediate host is a **crustacean (crab or crayfish)**. Humans become infected by ingesting raw or undercooked crab meat containing **metacercariae**. Clinically, it presents with chronic cough and hemoptysis, often mimicking tuberculosis. **Analysis of Incorrect Options:** * **Clonorchis sinensis (Chinese Liver Fluke):** While it also has two intermediate hosts, the second intermediate host is **freshwater fish**, not crabs. * **Fasciola hepatica (Sheep Liver Fluke):** This parasite does not have a second intermediate host. Instead, the cercariae encyst on **aquatic vegetation** (like watercress), which humans then ingest. * **Schistosoma hematobium (Blood Fluke):** Schistosomes are unique among trematodes because they have only **one intermediate host** (snail) and no second intermediate host. Infection occurs via direct skin penetration by cercariae in water. **NEET-PG Clinical Pearls:** * **Diagnostic Stage:** Eggs in sputum or feces (operculated eggs). * **Radiology:** "Ring-shadow" opacities or "Cotton-wool" appearances on Chest X-ray. * **Drug of Choice:** Praziquantel is the gold standard for most trematodes, including *Paragonimus*. * **Key Association:** Always associate "Crab/Crayfish" with *Paragonimus* and "Fish" with *Clonorchis/Opisthorchis*.

Question 118: Which is the smallest helminth among the following?

A. Hymenolepis diminuta
B. Hymenolepis nana (Correct Answer)
C. Diphyllobothrium latum
D. Balantidium coli

Explanation: **Explanation:** **Hymenolepis nana** (Dwarf Tapeworm) is the correct answer because it is the smallest intestinal tapeworm (cestode) infecting humans. It typically measures only **15 mm to 40 mm** in length. Its small size is a defining characteristic, reflected in its name "nana," which is derived from the Greek word for dwarf. **Analysis of Options:** * **Hymenolepis diminuta (Rat Tapeworm):** While related to *H. nana*, it is significantly larger, measuring approximately **20 cm to 60 cm** in length. It primarily infects rodents and is an accidental parasite in humans. * **Diphyllobothrium latum (Fish Tapeworm):** This is the **largest** tapeworm infecting humans, reaching lengths of up to **10 meters** or more. It is clinically significant for causing Vitamin B12 deficiency (megaloblastic anemia). * **Balantidium coli:** This is an incorrect classification in the context of the question. While it is a parasite, it is a **ciliated protozoan**, not a helminth (worm). It is, however, the largest protozoan parasite of humans. **High-Yield NEET-PG Pearls:** * **Unique Life Cycle:** *H. nana* is the only cestode that can complete its entire life cycle in a single host (man), meaning it does not require an obligatory intermediate host. * **Internal Autoinfection:** It is the only tapeworm capable of internal autoinfection, which can lead to heavy parasite burdens in immunocompromised individuals. * **Morphology:** The scolex has four suckers and a short rostellum armed with a single row of hooks. * **Treatment:** Praziquantel is the drug of choice.

Question 119: Winterbottom's sign is typically seen in?

A. Meconium peritonitis
B. Kala-azar
C. American trypanosomiasis
D. African trypanosomiasis (Correct Answer)

Explanation: **Explanation:** **Winterbottom’s sign** is a classic clinical feature of **African Trypanosomiasis** (specifically West African Sleeping Sickness caused by *Trypanosoma brucei gambiense*). It refers to the visible and palpable enlargement of the lymph nodes in the **posterior cervical triangle**. This occurs during the hemolymphatic stage of the disease as the parasite disseminates through the lymphatic system before crossing the blood-brain barrier. **Analysis of Options:** * **African Trypanosomiasis (Correct):** Winterbottom’s sign is a hallmark of the early stage of *T.b. gambiense* infection. * **American Trypanosomiasis (Chagas Disease):** Caused by *Trypanosoma cruzi*. The characteristic sign here is **Romaña’s sign** (unilateral painless periorbital edema) or a **Chagoma** (localized skin swelling at the bite site). * **Kala-azar (Visceral Leishmaniasis):** Characterized by massive splenomegaly, hepatomegaly, and hyperpigmentation of the skin. While lymphadenopathy can occur, it is not referred to as Winterbottom’s sign. * **Meconium Peritonitis:** A sterile chemical peritonitis in neonates caused by bowel perforation in utero; it has no association with parasitic lymphadenopathy. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Tsetse fly (*Glossina* species). * **Kerandel’s Sign:** Deep hyperesthesia or pain when pressure is applied to the palms or ulnar nerve (seen in later stages). * **Diagnosis:** Identification of **Trypomastigotes** in lymph node aspirates (early) or CSF (late). * **Sleeping Sickness:** The late stage involves CNS invasion leading to reversal of the sleep-wake cycle and coma.

Question 120: What is the most sensitive diagnostic technique for Trichomonas infection?

A. Culture in Diamond media (Correct Answer)
B. Culture in Thayer Martin media
C. Pap Smear
D. NAAT

Explanation: **Explanation:** The diagnosis of *Trichomonas vaginalis* relies on identifying the parasite in urogenital secretions. While various methods exist, **Culture in Diamond’s medium** (or Feinberg-Whittington medium) is historically considered the **"gold standard"** and the most sensitive diagnostic technique among the provided options, with a sensitivity of 95% or higher. It is particularly useful when the parasite load is low and wet mount microscopy is negative. **Analysis of Options:** * **Option A (Correct):** Diamond’s medium is an enriched broth that supports the growth of *T. vaginalis*. It is highly sensitive and can detect as few as 10 organisms per mL of inoculum. * **Option B (Incorrect):** Thayer-Martin media is a selective agar used for the isolation of *Neisseria gonorrhoeae*, not parasites. * **Option C (Incorrect):** Pap Smear has low sensitivity (approx. 50-60%) and high false-positive rates for Trichomoniasis. It is primarily a screening tool for cervical cancer, not a definitive diagnostic test for this parasite. * **Option D (Incorrect):** While **Nucleic Acid Amplification Tests (NAAT)** are now technically superior in sensitivity and specificity compared to culture, in the context of standard medical textbooks and traditional NEET-PG patterns, **Culture** remains the classic answer for the "most sensitive" or "gold standard" technique unless NAAT is specifically highlighted as the modern replacement. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Characterized by a "Strawberry Cervix" (punctate hemorrhages) and a foul-smelling, frothy, yellowish-green vaginal discharge. * **Microscopy:** Wet mount shows characteristic **jerky, tumbling motility**. * **Morphology:** It exists only in the **Trophozoite stage**; there is no cyst stage. It possesses 4 anterior flagella and an undulating membrane. * **Treatment:** Drug of choice is **Metronidazole** (both partners must be treated to prevent reinfection).

Practice by Chapter

Classification of Parasites

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Intestinal Protozoa

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Blood and Tissue Protozoa

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Malaria Parasites

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Leishmaniasis

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Intestinal Helminths: Nematodes

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Tissue Nematodes

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Trematodes

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Cestodes

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Ectoparasites

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Antiparasitic Drugs

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Laboratory Diagnosis of Parasitic Infections

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