Parasitology — MCQs
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What is the selective medium for Naegleria fowleri?
What is the infectious stage of Plasmodium?
A 6-year-old boy presented with intermittent abdominal cramps and loose stools. Stool examination revealed ova approximately 100 micrometers in size. Which of the following is NOT a causative organism for these findings?
Which of the following is characterized by sheathed microfilariae?
Which disease can be transmitted by Pediculus humanus?
Which disease is transmitted by the Culex mosquito?
Accole forms are seen in which species of Plasmodium?
Visceral larva migrans is caused by which organism?
Unsegmented eggs are seen in which of the following parasites?
A male patient presented with pain and discomfort in the upper abdominal region. His abdomen has enlarged, and he has experienced significant weight loss. The Casoni test is positive. What is the most likely diagnosis?
Parasitology Indian Medical PG Practice Questions and MCQs
Question 311: What is the selective medium for Naegleria fowleri?
- A. Nutrient agar rich with E. coli
- B. NNN media
- C. Non-nutrient agar with E. coli (Correct Answer)
- D. Diamond media
Explanation: **Explanation:** *Naegleria fowleri*, the causative agent of **Primary Amoebic Meningoencephalitis (PAM)**, is a free-living amoeba. In the laboratory, it is cultured using a specialized technique known as the **"Amoebic Enrichment"** method. **Why Option C is Correct:** *Naegleria fowleri* is a bacterivorous organism (it feeds on bacteria). The selective medium used is **Non-nutrient agar (NNA)** seeded with a lawn of **heat-killed or live *Escherichia coli***. The NNA provides a solid substrate but no nutrients for the amoeba itself; instead, the amoebae graze on the *E. coli*. As they multiply, they create visible "tracks" or clearing zones on the agar surface, which is a diagnostic hallmark. **Analysis of Incorrect Options:** * **A. Nutrient agar rich with E. coli:** Nutrient agar allows the overgrowth of contaminating bacteria and fungi, which outcompete the slow-growing amoebae. Non-nutrient agar is essential to limit this overgrowth. * **B. NNN (Novy-MacNeal-Nicolle) media:** This is the classic blood-based medium used for culturing **Leishmania** and **Trypanosoma**. * **D. Diamond media:** This is a specialized liquid medium used for the axenic cultivation of **Entamoeba histolytica** and **Trichomonas vaginalis**. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** PAM is a rapidly fatal fulminant meningoencephalitis occurring in healthy individuals with a history of swimming in warm freshwater. * **Diagnostic Clue:** CSF shows "purulent meningitis" picture (high neutrophils) but **no bacteria** on Gram stain. * **Microscopy:** Look for actively motile trophozoites in a **wet mount** of fresh CSF. * **Transformation Test:** When placed in sterile water, *Naegleria* trophozoites transform into a **pear-shaped flagellated form** (diagnostic feature).
Question 312: What is the infectious stage of Plasmodium?
- A. Trophozoite
- B. Cryptozoite
- C. Sporozoite (Correct Answer)
- D. Merozoite
Explanation: ### Explanation **Correct Answer: C. Sporozoite** The life cycle of *Plasmodium* involves two hosts: the female *Anopheles* mosquito (definitive host) and the human (intermediate host). The **sporozoite** is the infectious stage for humans. When an infected mosquito bites a human, it injects sporozoites from its salivary glands into the bloodstream. These sporozoites quickly migrate to the liver to initiate the exo-erythrocytic cycle. **Analysis of Incorrect Options:** * **A. Trophozoite:** This is the metabolically active, feeding stage found within human Red Blood Cells (RBCs). It is responsible for the clinical symptoms of malaria but is not the stage that initiates infection upon entry. * **B. Cryptozoite:** These are the progeny produced after the first round of replication (schizogony) within the liver cells (hepatocytes). They are a developmental stage within the human host, not the primary infectious stage. * **C. Merozoite:** These are released when a liver cell or an RBC ruptures. Merozoites infect new RBCs to continue the erythrocytic cycle. While they "infect" cells, they do not represent the stage transmitted from the vector to the human. **High-Yield NEET-PG Pearls:** * **Infectious stage for Mosquito:** Gametocytes (taken up during a blood meal). * **Site of Sporogony:** Occurs in the mosquito (sexual cycle). * **Site of Schizogony:** Occurs in the human (asexual cycle). * **Hypnozoites:** Dormant liver stages found in *P. vivax* and *P. ovale*, responsible for late relapses. * **Gold Standard Diagnosis:** Peripheral blood smear (Leishman or Giemsa stain). Thick smears are for detection; thin smears are for species identification.
Question 313: A 6-year-old boy presented with intermittent abdominal cramps and loose stools. Stool examination revealed ova approximately 100 micrometers in size. Which of the following is NOT a causative organism for these findings?
- A. Fasciola gigantica
- B. Echinostoma ilocanum
- C. Gastrodiscoides hominis
- D. Opisthorchis viverrini (Correct Answer)
Explanation: **Explanation:** The core of this question lies in the **morphology and size of helminth eggs**. In parasitology, egg size is a critical diagnostic feature. **Why Opisthorchis viverrini is the correct answer:** *Opisthorchis viverrini* (Southeast Asian liver fluke) produces some of the **smallest** eggs among human helminths, measuring approximately **25–30 μm x 10–15 μm**. They are operculated, flask-shaped, and contain a mature miracidium. Since the question specifies an egg size of **100 μm**, *Opisthorchis* is excluded as a causative agent. **Analysis of Incorrect Options (Large-sized eggs):** * **Fasciola gigantica:** Known for producing very large, operculated, unembryonated eggs, typically measuring **160–190 μm**. * **Echinostoma ilocanum:** This intestinal fluke produces large, operculated eggs measuring approximately **80–120 μm**. * **Gastrodiscoides hominis:** An amphistome fluke where the eggs are large, operculated, and measure about **150 μm x 60–90 μm**. **Clinical Pearls for NEET-PG:** * **Large Eggs (>100 μm):** *Fasciola hepatica/gigantica*, *Fasciolopsis buski*, *Gastrodiscoides hominis*, and *Schistosoma* species. * **Small Eggs (<30 μm):** *Opisthorchis* species, *Clonorchis sinensis*, and *Heterophyes heterophyes*. * **Bile-stained eggs:** Remember the mnemonic **"ABC"** – *Ascaris*, *Bile-stained* (most flukes), and *Capillaria*. * **Opisthorchis/Clonorchis** are high-yield because they are strongly associated with **Cholangiocarcinoma** (bile duct cancer).
Question 314: Which of the following is characterized by sheathed microfilariae?
- A. Wuchereria bancrofti (Correct Answer)
- B. Loa loa
- C. Mansonella perstans
- D. Brugia malayi
Explanation: **Explanation:** The presence or absence of a **sheath** (a delicate, translucent covering) and the arrangement of nuclei in the tail are the primary morphological features used to differentiate microfilariae in peripheral blood smears. **1. Why Wuchereria bancrofti is correct:** *Wuchereria bancrofti* is a classic example of a **sheathed** microfilaria. A key diagnostic feature is that its nuclei do not extend to the tip of the tail (the tail tip is "empty"). This distinguishes it from other sheathed species. **2. Analysis of Options:** * **Brugia malayi:** This is also a **sheathed** microfilaria. However, in the context of single-choice questions where *W. bancrofti* is the primary representative of lymphatic filariasis, it is often the preferred answer. *Note: If this were a multiple-select question, both A and D would be correct.* * **Loa loa:** This is also **sheathed**, but it is primarily associated with African eye worm and Calabar swellings. Its nuclei extend to the very tip of the tail. * **Mansonella perstans:** This species is **unsheathed**. Other unsheathed species include *Mansonella ozzardi* and *Onchocerca volvulus*. **3. NEET-PG Clinical Pearls:** * **Sheathed Microfilariae:** *Wuchereria bancrofti, Brugia malayi, Loa loa.* * **Unsheathed Microfilariae:** *Mansonella* species, *Onchocerca volvulus.* * **Tail Tip Nuclei (High Yield):** * *W. bancrofti:* No nuclei at the tip. * *B. malayi:* Two distinct terminal nuclei. * *Loa loa:* Continuous row of nuclei to the tip. * **Diurnal vs. Nocturnal:** *W. bancrofti* shows **nocturnal periodicity** (10 PM – 2 AM), which is why blood collection is recommended at night. * **Drug of Choice:** Diethylcarbamazine (DEC) is the mainstay of treatment for *W. bancrofti*.
Question 315: Which disease can be transmitted by Pediculus humanus?
- A. Sleeping sickness
- B. Plague
- C. Chaga's disease
- D. Relapsing fever (Correct Answer)
Explanation: **Explanation:** The correct answer is **Relapsing fever**. Specifically, *Pediculus humanus corporis* (the human body louse) is the vector for **Louse-borne relapsing fever (LBRF)**, caused by the spirochete ***Borrelia recurrentis***. Transmission occurs not through a bite, but when a person crushes an infected louse, allowing the bacteria-laden hemolymph to enter the skin through abrasions or mucous membranes. **Analysis of Incorrect Options:** * **A. Sleeping sickness (African Trypanosomiasis):** Transmitted by the **Tsetse fly** (*Glossina* species). It is caused by *Trypanosoma brucei*. * **B. Plague:** Primarily transmitted by the **Oriental rat flea** (*Xenopsylla cheopis*). It is caused by the bacterium *Yersinia pestis*. * **C. Chagas disease (American Trypanosomiasis):** Transmitted by **Triatomine bugs** (Reduviid or "kissing" bugs). It is caused by *Trypanosoma cruzi*. **High-Yield Clinical Pearls for NEET-PG:** * **The "Louse Trio":** *Pediculus humanus corporis* transmits three major diseases: 1. **Epidemic Typhus** (*Rickettsia prowazekii*) 2. **Trench Fever** (*Bartonella quintana*) 3. **Louse-borne Relapsing Fever** (*Borrelia recurrentis*) * **Tick-borne Relapsing Fever (TBRF):** In contrast to LBRF, TBRF is transmitted by **Ornithodoros** (soft ticks) and is caused by various other *Borrelia* species. * **Antigenic Variation:** The hallmark of *Borrelia* infections is "antigenic variation" of surface proteins, which leads to the characteristic febrile relapses seen clinically.
Question 316: Which disease is transmitted by the Culex mosquito?
- A. Malaria
- B. Filariasis (Correct Answer)
- C. Dengue
- D. Japanese encephalitis
Explanation: **Explanation:** The **Culex mosquito** (specifically *Culex quinquefasciatus*) is the primary vector for **Lymphatic Filariasis** caused by *Wuchereria bancrofti*. In this transmission cycle, the mosquito ingests microfilariae from an infected human; these larvae undergo developmental changes (L1 to L3 stage) within the mosquito before being transmitted to a new host during a subsequent blood meal. **Analysis of Options:** * **Filariasis (Correct):** *Culex* is the most common vector for Bancroftian filariasis, particularly in urban and semi-urban areas. It breeds in stagnant, polluted water (e.g., sewage, drains). * **Malaria (Incorrect):** Transmitted exclusively by the female **Anopheles** mosquito. * **Dengue (Incorrect):** Transmitted by **Aedes aegypti** and *Aedes albopictus*. These mosquitoes are "day-biters" and breed in clean, artificial water containers. * **Japanese Encephalitis (Incorrect):** While *Culex* (specifically *Culex tritaeniorhynchus*) does transmit Japanese Encephalitis (JE), in the context of standard medical examinations, **Filariasis** is the classic association for *Culex* unless the question specifies viral encephalitis. *Note: If this were a "multiple correct" type question, both B and D would be technically accurate, but Filariasis is the primary textbook association for Culex quinquefasciatus.* **High-Yield Clinical Pearls for NEET-PG:** * **Culex Breeding:** Prefers "dirty" water (sewage/sullage). * **Biting Habit:** Culex is a nocturnal (night) biter. * **Other diseases by Culex:** West Nile Virus and St. Louis Encephalitis. * **Vector for Brugia malayi:** Unlike *W. bancrofti*, *Brugia malayi* is primarily transmitted by **Mansonia** mosquitoes. * **Control:** The "Floating Deck" method and use of *Gambusia* fish are common larval control strategies.
Question 317: Accole forms are seen in which species of Plasmodium?
- A. P. falciparum (Correct Answer)
- B. P. vivax
- C. P. ovale
- D. P. malariae
Explanation: **Explanation:** The correct answer is **P. falciparum**. **1. Why P. falciparum is correct:** In *Plasmodium falciparum* infections, the early trophozoites (ring forms) are often found at the very periphery of the host erythrocyte, appearing as if they are stuck to the outer margin of the red blood cell membrane. These are known as **Accole or Applique forms**. This occurs because *P. falciparum* rings are particularly small and delicate compared to other species. Additionally, *P. falciparum* is characterized by "multiple infection" (more than one ring per RBC) and the presence of **Maurer’s dots** in later stages. **2. Why other options are incorrect:** * **P. vivax:** Characterized by enlarged RBCs, the presence of **Schüffner’s dots**, and amoeboid trophozoites. It does not typically show marginal attachment. * **P. ovale:** Similar to *P. vivax* (Schüffner’s dots present), but the RBCs are often oval-shaped with fimbriated (tufted) edges. * **P. malariae:** Known for **"Band forms"** of trophozoites and **Ziemann’s dots**. The RBCs are usually normal or smaller in size. **3. NEET-PG High-Yield Pearls:** * **P. falciparum:** Look for "Banana-shaped" or crescentic gametocytes and the absence of late stages (schizonts) in peripheral blood due to sequestration. * **P. vivax:** Most common cause of malaria in India; prefers young RBCs (reticulocytes). * **P. malariae:** Associated with "Quartan malaria" (72-hour cycle) and can cause Nephrotic Syndrome (quartan malarial nephropathy). * **P. knowlesi:** A zoonotic malaria (monkeys) that follows a 24-hour (quotidian) cycle.
Question 318: Visceral larva migrans is caused by which organism?
- A. Ascariasis
- B. Toxocara canis (Correct Answer)
- C. Schistosomiasis
- D. Clonorchis Buski
Explanation: **Explanation:** **Visceral Larva Migrans (VLM)** is a clinical syndrome caused by the migration of second-stage larvae of non-human nematodes through the internal organs of humans. The most common causative agent is **Toxocara canis** (the dog roundworm), followed by *Toxocara cati* (the cat roundworm). **Why Toxocara canis is correct:** Humans, particularly children, are accidental hosts who ingest embryonated eggs from soil contaminated with dog feces. Since humans are not the definitive host, the larvae cannot complete their life cycle to become adult worms in the intestine. Instead, they penetrate the intestinal wall and migrate through the circulatory system to various organs (liver, lungs, brain, and eyes), causing inflammatory damage and marked **peripheral eosinophilia**. **Analysis of Incorrect Options:** * **A. Ascariasis (*Ascaris lumbricoides*):** This is a human parasite. Larvae do migrate through the lungs (Loeffler’s syndrome), but they eventually return to the intestine to mature into adult worms. It does not cause the persistent larval migration syndrome seen in VLM. * **C. Schistosomiasis:** Caused by blood flukes (trematodes). Their life cycle involves skin penetration by cercariae and residence in the venous plexuses, not the wandering larval migration characteristic of VLM. * **D. Clonorchis sinensis:** This is the Chinese liver fluke. It is acquired by eating undercooked fish and resides in the biliary tract, causing biliary obstruction or cholangiocarcinoma, rather than larva migrans. **High-Yield NEET-PG Pearls:** * **Ocular Larva Migrans (OLM):** When *Toxocara* larvae migrate to the eye; it can mimic retinoblastoma. * **Cutaneous Larva Migrans (CLM):** Most commonly caused by *Ancylostoma braziliensis* (dog hookworm). * **Diagnosis:** Characterized by high eosinophilia, high IgE levels, and positive ELISA for *Toxocara* antigens. Stool examination is **negative** because the worms never reach maturity in the human gut. * **Treatment:** Albendazole or Mebendazole.
Question 319: Unsegmented eggs are seen in which of the following parasites?
- A. Trichuris trichura (Correct Answer)
- B. Necator americanus
- C. Ankylostoma
- D. Dracunculus
Explanation: **Explanation:** The classification of helminth eggs based on their stage of development at the time of excretion is a high-yield topic for NEET-PG. Eggs are generally categorized as **unsegmented** (single-celled zygote), **segmented** (containing multiple blastomeres), or **embryonated** (containing a fully formed larva). **Correct Answer: A. Trichuris trichiura** *Trichuris trichiura* (Whipworm) eggs are laid in an **unsegmented stage**. They are characterized by a distinct barrel shape with bipolar mucus plugs. These eggs require a period of incubation in the soil (usually 2–3 weeks) to become embryonated and infective. **Analysis of Incorrect Options:** * **B & C. Necator americanus & Ancylostoma duodenale (Hookworms):** Hookworm eggs are **segmented** when passed in fresh feces. They typically contain 4 to 8 blastomeres (cleavage stages) surrounded by a thin, transparent hyaline shell. * **D. Dracunculus medinensis:** This parasite is **viviparous**. It does not lay eggs; instead, the gravid female releases fully formed, active motile larvae (L1) directly into water. **High-Yield Clinical Pearls for NEET-PG:** * **Unsegmented eggs:** *Trichuris trichiura*, *Ascaris lumbricoides* (fertilized), and *Fasciola hepatica*. * **Segmented eggs:** Hookworms (*Ancylostoma* and *Necator*). * **Embryonated eggs (containing larva):** *Enterobius vermicularis*, *Strongyloides stercoralis* (rarely seen in stool as they hatch in the mucosa), and *Hymenolepis nana*. * **Bipolar plugs:** Pathognomonic for *Trichuris trichiura*. * **Bile-stained eggs:** *Ascaris*, *Trichuris*, and *Taenia* (Mnemonic: **ATT**). Hookworm eggs are **non-bile stained**.
Question 320: A male patient presented with pain and discomfort in the upper abdominal region. His abdomen has enlarged, and he has experienced significant weight loss. The Casoni test is positive. What is the most likely diagnosis?
- A. Diphtheria
- B. Scarlet fever
- C. Echinococcosis (Correct Answer)
- D. Kala Azar
Explanation: **Explanation:** The clinical presentation and the positive **Casoni test** point directly toward **Echinococcosis** (Hydatid cyst disease), caused by the larval stage of the cestode *Echinococcus granulosus*. 1. **Why Echinococcosis is correct:** The liver is the most common site for hydatid cysts (70% of cases), leading to hepatomegaly (enlarged abdomen) and right upper quadrant pain. Significant weight loss occurs in chronic or advanced cases. The **Casoni test** is an immediate hypersensitivity skin test used to detect *Echinococcus* antigens. While largely replaced by imaging (USG/CT) and serology (ELISA) in modern practice, it remains a classic high-yield diagnostic marker in medical exams. 2. **Why other options are incorrect:** * **Diphtheria:** A respiratory infection caused by *Corynebacterium diphtheriae*, characterized by a pseudomembrane in the throat and bull-neck appearance. The diagnostic test is the **Schick test**. * **Scarlet Fever:** Caused by Group A Streptococcus; presents with a "strawberry tongue" and sandpaper rash. The diagnostic test is the **Dick test**. * **Kala Azar (Visceral Leishmaniasis):** While it causes massive splenomegaly and weight loss, it is diagnosed via bone marrow/splenic aspirate (LD bodies) or the **Montenegro skin test** (which is negative in active disease). **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Dog; **Intermediate Host:** Sheep (Humans are accidental intermediate hosts/dead-end hosts). * **Microscopy:** "Hydatid sand" (brood capsules and protoscolices) is found in the cyst fluid. * **Imaging:** Look for "Water lily sign" or "Camelot sign" on USG/CT. * **Management:** PAIR (Puncture, Aspiration, Injection, Re-aspiration) technique and Albendazole. Avoid cyst rupture to prevent life-threatening **anaphylaxis**.
Practice by Chapter
Classification of Parasites
Practice Questions
Intestinal Protozoa
Practice Questions
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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