Parasitology — MCQs
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A 30-year-old veterinarian presents for a first-trimester prenatal check-up with no complaints. Routine physical examination is significant only for mild cervical lymphadenopathy. She was prescribed spiramycin but was noncompliant. Her baby is born with hydrocephalus and cerebral calcifications. Which of the following organisms is most likely responsible?
Eosinophilic meningoencephalitis is caused by which of the following?
Which disease is transmitted by the Ixodid tick?
What is the most rapid test for the diagnosis of malaria?
Which of the following parasites does not pass through the liver during its life cycle?
Which of the following exhibits regressive metamorphosis?
A patient presents with diarrhea. Analysis of stool on a wet mount shows motile protozoa without red blood cells and pus cells. What is the most likely diagnosis?
Which organism, associated with fish consumption, also causes carcinoma of the gallbladder?
Which of the following is NOT typically seen in Plasmodium falciparum infection?
Trichomoniasis is caused by:
Parasitology Indian Medical PG Practice Questions and MCQs
Question 501: A 30-year-old veterinarian presents for a first-trimester prenatal check-up with no complaints. Routine physical examination is significant only for mild cervical lymphadenopathy. She was prescribed spiramycin but was noncompliant. Her baby is born with hydrocephalus and cerebral calcifications. Which of the following organisms is most likely responsible?
- A. Isospora belli
- B. Leishmania donovani
- C. Plasmodium vivax
- D. Toxoplasma gondii (Correct Answer)
Explanation: **Explanation:** The clinical presentation describes a classic case of **Congenital Toxoplasmosis**, caused by the protozoan **_Toxoplasma gondii_**. **Why the correct answer is right:** * **Transmission & Risk:** The patient is a veterinarian, an occupation with high exposure to cats (the definitive host). Primary infection during pregnancy (especially the first trimester) poses a significant risk of vertical transmission. * **Clinical Presentation:** While the mother was mostly asymptomatic (common), the presence of **cervical lymphadenopathy** is the most frequent clinical sign of acute toxoplasmosis in immunocompetent adults. * **Congenital Triad:** The neonate presents with two components of the classic **Sabin Triad**: **Hydrocephalus** and **Intracranial (diffuse) calcifications**. The third component is Chorioretinitis. * **Management:** **Spiramycin** is the drug of choice to prevent vertical transmission when maternal infection is suspected. Noncompliance in this case led to fetal infection. **Why incorrect options are wrong:** * **A. _Isospora belli_:** An opportunistic intestinal coccidian causing chronic watery diarrhea, primarily in HIV/AIDS patients. It does not cause congenital malformations. * **B. _Leishmania donovani_:** Causes Visceral Leishmaniasis (Kala-azar), characterized by massive splenomegaly, fever, and pancytopenia. It is not a classic TORCH pathogen. * **C. _Plasmodium vivax_:** Causes malaria. While it can lead to low birth weight or stillbirth due to placental malaria, it does not cause the specific triad of hydrocephalus and cerebral calcifications. **High-Yield NEET-PG Pearls:** * **Definitive Host:** Cat; **Intermediate Host:** Humans/Mammals. * **Infective forms:** Oocysts (cat feces), Bradyzoites (undercooked meat), Tachyzoites (transplacental). * **Imaging:** Intracranial calcifications in Toxoplasmosis are **diffuse/scattered**, whereas in CMV (the most common TORCH infection), they are **periventricular**. * **Treatment:** Maternal (prophylaxis) = Spiramycin; Fetal/Neonatal infection = Pyrimethamine + Sulfadiazine + Folinic acid.
Question 502: Eosinophilic meningoencephalitis is caused by which of the following?
- A. Gnathostoma spinigerum (Correct Answer)
- B. Naegleria
- C. Toxocara Canis
- D. All of the above
Explanation: **Explanation:** The hallmark of **Eosinophilic Meningoencephalitis (EME)** is the presence of $\ge$ 10 eosinophils/mm³ in the cerebrospinal fluid (CSF) or a CSF eosinophilia of at least 10%. **1. Why Gnathostoma spinigerum is correct:** *Gnathostoma spinigerum* is a nematode (roundworm) and a leading cause of EME, particularly in Southeast Asia. Humans are accidental hosts who ingest undercooked fish or poultry containing L3 larvae. The larvae undergo **larva migrans**, penetrating the CNS. This triggers a robust Type 1 hypersensitivity reaction, leading to high CSF eosinophilia, radiculitis, and hemorrhagic tracks in the brain. **2. Analysis of Incorrect Options:** * **Naegleria fowleri:** Causes **Primary Amoebic Meningoencephalitis (PAM)**. This is a fulminant, rapidly fatal infection characterized by a **neutrophilic** (purulent) pleocytosis, not eosinophilic. * **Toxocara canis:** Causes **Visceral Larva Migrans (VLM)** and Ocular Larva Migrans. While it can rarely involve the CNS, it is not a classic or primary cause of Eosinophilic Meningoencephalitis compared to *Gnathostoma* or *Angiostrongylus*. * **All of the above:** Incorrect because *Naegleria* specifically causes a neutrophilic response. **High-Yield NEET-PG Pearls:** * **Most common cause of EME worldwide:** *Angiostrongylus cantonensis* (Rat lungworm). * **Most common cause of EME in India:** *Gnathostoma spinigerum*. * **Key Diagnostic Clue:** History of consuming raw/undercooked freshwater fish or snails + severe "shooting" nerve pain + CSF eosinophilia. * **Other causes of EME:** *Baylisascaris procyonis*, Neurocysticercosis (rarely), and certain fungal infections (Coccidioidomycosis).
Question 503: Which disease is transmitted by the Ixodid tick?
- A. Listeriosis
- B. Leishmaniasis
- C. Lyme disease (Correct Answer)
- D. Malaria
Explanation: **Explanation:** **Lyme disease** is caused by the spirochete *Borrelia burgdorferi* and is primarily transmitted through the bite of the **Ixodid tick** (specifically *Ixodes scapularis* and *Ixodes ricinus*), also known as the hard-bodied tick. The tick must typically be attached for 36–48 hours to transmit the bacteria. **Analysis of Options:** * **Listeriosis (A):** Caused by *Listeria monocytogenes*, this is a foodborne illness typically acquired by consuming contaminated unpasteurized dairy products or deli meats. It is not vector-borne. * **Leishmaniasis (B):** Caused by *Leishmania* protozoa, it is transmitted by the bite of the female **Sandfly** (*Phlebotomus* species). * **Malaria (D):** Caused by *Plasmodium* species, it is transmitted by the bite of the female **Anopheles mosquito**. **High-Yield Clinical Pearls for NEET-PG:** * **Ixodid Tick Vectors:** Apart from Lyme disease, Ixodid ticks transmit **Babesiosis**, **Human Granulocytic Anaplasmosis**, and **Kyasanur Forest Disease (KFD)**. * **Lyme Disease Stages:** 1. *Early Localized:* Characterized by **Erythema Chronicum Migrans** (bull’s eye rash). 2. *Early Disseminated:* May present with **Bell’s palsy** (often bilateral) or AV nodal block. 3. *Late Disseminated:* Chronic arthritis and encephalopathy. * **Treatment:** **Doxycycline** is the drug of choice for early Lyme disease; Ceftriaxone is used for neurological or cardiac involvement.
Question 504: What is the most rapid test for the diagnosis of malaria?
- A. Thick blood smear
- B. HRP-2 antigen test (Correct Answer)
- C. Thin blood smear
- D. PCR
Explanation: **Explanation:** The **HRP-2 (Histidine-Rich Protein 2) antigen test** is the correct answer because it is a **Rapid Diagnostic Test (RDT)** based on immunochromatography. It can provide results within 15–20 minutes without the need for specialized laboratory equipment or high-level technical expertise, making it the fastest method for point-of-care diagnosis. **Analysis of Options:** * **Thick blood smear:** While it is the **Gold Standard** for detecting parasites (due to its high sensitivity in screening), it requires time for staining (Giemsa/JSB) and expert microscopic examination. * **Thin blood smear:** This is primarily used for **species identification** and calculating the parasite index. Like the thick smear, it is time-consuming compared to RDTs. * **PCR (Polymerase Chain Reaction):** This is the **most sensitive and specific** method. However, it is expensive, requires sophisticated thermal cyclers, and takes several hours to days to yield results, making it unsuitable for rapid diagnosis. **High-Yield Clinical Pearls for NEET-PG:** * **HRP-2** is specific to *Plasmodium falciparum*. * **pLDH (Parasite Lactate Dehydrogenase)** is used in RDTs to detect all four common species (*P. falciparum, P. vivax, P. ovale, P. malariae*). * **Prozone Phenomenon:** Very high parasitemia can sometimes lead to false-negative RDT results. * **Persistence:** HRP-2 can remain positive for up to 2 weeks even after successful treatment, potentially leading to false positives in follow-up cases.
Question 505: Which of the following parasites does not pass through the liver during its life cycle?
- A. Fasciolopsis buski (Correct Answer)
- B. Fasciola hepatica
- C. Clonorchis sinensis
- D. Opisthorchis felineus
Explanation: ### Explanation The correct answer is **Fasciolopsis buski**. **1. Why Fasciolopsis buski is correct:** *Fasciolopsis buski* is the **Giant Intestinal Fluke**. Its life cycle is confined primarily to the gastrointestinal tract. After humans ingest metacercariae (encysted on aquatic plants like water caltrop or chestnuts), the larvae excyst in the duodenum and attach directly to the **intestinal mucosa**. They mature into adult flukes in the small intestine without any extra-intestinal migration. Therefore, they do not pass through or reside in the liver. **2. Why the other options are incorrect:** * **Fasciola hepatica (Sheep Liver Fluke):** After excysting in the duodenum, the larvae penetrate the intestinal wall, migrate across the peritoneal cavity, and **bore through the liver parenchyma** to reach the bile ducts, where they mature. * **Clonorchis sinensis (Chinese Liver Fluke) & Opisthorchis felineus (Cat Liver Fluke):** These are "biliary flukes." Upon ingestion, the larvae migrate from the duodenum through the **Ampulla of Vater** directly into the common bile duct and distal biliary capillaries of the liver to mature. **3. High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** *F. buski* (Small Intestine) vs. *F. hepatica/Clonorchis* (Biliary tract). * **Intermediate Hosts:** All four flukes require **snails** as the 1st intermediate host. * **Infective Stage:** **Metacercariae** for all four. * **Diagnostic Stage:** Eggs in stool. Note that *F. buski* and *F. hepatica* eggs are operculated and morphologically identical (large, bile-stained). * **Complication:** *Clonorchis sinensis* is strongly associated with **Cholangiocarcinoma** (Biliary tract cancer).
Question 506: Which of the following exhibits regressive metamorphosis?
- A. Hydatid cyst (Correct Answer)
- B. Cysticercoid
- C. Cysticercus bovis
- D. Cysticercus cellulosae
Explanation: **Explanation:** **Regressive metamorphosis** is a biological process where an organism undergoes structural simplification or "degeneration" during its development, moving from a more complex larval form to a simpler one. **Why Hydatid Cyst is correct:** The **Hydatid cyst** (larval stage of *Echinococcus granulosus*) is the classic example of regressive metamorphosis in parasitology. When the hexacanth embryo (oncosphere) reaches the target organ (usually the liver), it loses its hooks and motility. It then transforms into a hollow, fluid-filled bladder. This transition from a complex, motile embryo with specialized attachment organs (hooks) to a simpler, stationary cystic structure defines regressive metamorphosis. **Why other options are incorrect:** * **Cysticercus cellulosae (*T. solium*) & Cysticercus bovis (*T. saginata*):** These are "bladder worms" that maintain a high degree of structural complexity. They develop an invaginated scolex with suckers (and hooks in *T. solium*) within the cyst. This is considered progressive development rather than regressive. * **Cysticercoid:** Found in *Hymenolepis nana*, this larval stage features a solid body and a developed scolex. It does not undergo the structural simplification seen in *Echinococcus*. **High-Yield Clinical Pearls for NEET-PG:** * **Hydatid Cyst Structure:** Consists of three layers: Pericyst (host-derived), Ectocyst (outer laminated), and Endocyst (inner germinal layer). * **Hydatid Sand:** Refers to the sediment found in the cyst fluid containing free scolices, daughter cysts, and hooks. * **Casoni’s Test:** An immediate hypersensitivity skin test used for diagnosis (though largely replaced by ELISA). * **Water Lily Sign:** A classic radiological finding on MRI/CT indicating a ruptured endocyst.
Question 507: A patient presents with diarrhea. Analysis of stool on a wet mount shows motile protozoa without red blood cells and pus cells. What is the most likely diagnosis?
- A. Balantidium coli (Correct Answer)
- B. Plasmodium
- C. Trichomonas hominis
- D. Entamoeba histolytica
Explanation: **Explanation** The correct answer is **Balantidium coli**. **1. Why Balantidium coli is correct:** *Balantidium coli* is the largest protozoan and the only ciliate known to infect humans. It typically causes **balantidiasis**, which manifests as diarrhea or dysentery. On a stool wet mount, the trophozoites are easily identified by their large size and characteristic **ciliary motility** (often described as a "boring" or "spiraling" motion). The absence of red blood cells (RBCs) and pus cells in the stool suggests a non-invasive or mildly inflammatory diarrheal process, which is common in many balantidial infections, although severe cases can mimic amoebic dysentery. **2. Why the other options are incorrect:** * **Plasmodium:** This is a blood parasite causing malaria; it is not found in stool and does not cause primary diarrheal illness. * **Trichomonas hominis:** While found in the large intestine and visible on wet mounts as motile flagellates, it is generally considered a **commensal** and does not typically cause clinical diarrhea. * **Entamoeba histolytica:** This is the causative agent of amoebic dysentery. A key diagnostic feature of *E. histolytica* trophozoites is the presence of **ingested RBCs** (erythrophagocytosis), and the stool typically contains blood and mucus. **3. High-Yield NEET-PG Pearls:** * **Reservoir:** Pigs are the primary reservoir for *B. coli*; infection is common in pig farmers. * **Morphology:** Look for a **kidney-shaped (reniform) macronucleus** in the trophozoite. * **Treatment:** The drug of choice for Balantidiasis is **Tetracycline** (Metronidazole is an alternative). * **Size:** It is the largest protozoan parasite of the human intestine (60–100 µm).
Question 508: Which organism, associated with fish consumption, also causes carcinoma of the gallbladder?
- A. Clonorchis sinensis (Correct Answer)
- B. Gnathostoma
- C. Strongyloides cantonensis
- D. Hymenolepis diminuta
Explanation: **Explanation:** **Clonorchis sinensis** (the Chinese Liver Fluke) is the correct answer. It is a trematode acquired by consuming undercooked or raw **freshwater fish** containing encysted metacercariae. Once ingested, the larvae migrate to the biliary tract. Chronic infection leads to mechanical irritation and the release of inflammatory cytokines, causing chronic biliary inflammation, hyperplasia, and fibrosis. This chronic state is a major risk factor for **Cholangiocarcinoma** (bile duct cancer) and is also strongly associated with **carcinoma of the gallbladder**. **Analysis of Incorrect Options:** * **Gnathostoma:** A nematode acquired from undercooked fish/poultry; it typically causes **larva migrans** (cutaneous or visceral), not biliary malignancy. * **Strongyloides cantonensis (Angiostrongylus):** Known as the rat lungworm, it is acquired from snails/slugs and is a leading cause of **eosinophilic meningitis**. * **Hymenolepis diminuta:** The rat tapeworm; it causes mild intestinal infection in humans via ingestion of infected insects (fleas/beetles) found in grain. It has no association with fish or biliary cancer. **High-Yield Clinical Pearls for NEET-PG:** * **IARC Classification:** *Clonorchis sinensis* and *Opisthorchis viverrini* are classified as Group 1 carcinogens. * **Intermediate Hosts:** 1st host = Snail; 2nd host = Freshwater fish (Cyprinidae family). * **Diagnosis:** Identification of characteristic "operculated eggs with a small knob (abopercular protuberance)" in stool or bile. * **Drug of Choice:** Praziquantel. * **Differential:** While *Clonorchis* causes biliary cancer, **Schistosoma haematobium** is associated with Squamous Cell Carcinoma of the **Urinary Bladder**.
Question 509: Which of the following is NOT typically seen in Plasmodium falciparum infection?
- A. Hemoglobinuria
- B. Cerebral malaria
- C. Relapses (Correct Answer)
- D. Malignant malaria
Explanation: **Explanation:** The correct answer is **Relapses**. In parasitology, a "relapse" specifically refers to the recurrence of symptoms due to the activation of dormant liver stages known as **hypnozoites**. 1. **Why Relapse is NOT seen in *P. falciparum*:** Relapses occur only in *Plasmodium vivax* and *Plasmodium ovale* infections because these species produce hypnozoites that can remain dormant in the liver for months or years. *P. falciparum* (and *P. malariae*) do not have a hypnozoite stage; therefore, once the parasite leaves the liver, no dormant forms remain to cause a true relapse. Any recurrence of *P. falciparum* after treatment is termed a **recrudescence**, which results from the survival of erythrocytic forms in the blood due to inadequate treatment or drug resistance. 2. **Analysis of Incorrect Options:** * **Cerebral Malaria:** This is the most common cause of death in *P. falciparum* infection, characterized by sequestration of parasitized RBCs in cerebral microvasculature. * **Hemoglobinuria:** Also known as **Blackwater Fever**, this is a severe complication of *P. falciparum* involving massive intravascular hemolysis and subsequent dark urine. * **Malignant Malaria:** *P. falciparum* is known as "Malignant Tertian Malaria" because of its high parasite load and potential for multi-organ failure. **High-Yield Clinical Pearls for NEET-PG:** * **Hypnozoites:** Only seen in *P. vivax* and *P. ovale*. Treatment requires **Primaquine** or **Tafenoquine** for radical cure. * **Maurer’s Clefts:** Seen in RBCs infected with *P. falciparum*. * **Multiple Rings & Accole Forms:** Characteristic peripheral smear findings for *P. falciparum*. * **Recrudescence:** Associated with *P. falciparum* and *P. malariae*.
Question 510: Trichomoniasis is caused by:
- A. Bacteria
- B. Virus
- C. Protozoa (Correct Answer)
- D. Chlamydia
Explanation: **Explanation:** **Trichomoniasis** is a common sexually transmitted infection (STI) caused by **_Trichomonas vaginalis_**. 1. **Why Protozoa is Correct:** _Trichomonas vaginalis_ is a flagellated **protozoan**. It is a single-celled eukaryotic parasite that lacks a cyst stage, existing only in the **trophozoite** form. It primarily infects the squamous epithelium of the urogenital tract (vagina, urethra, and prostate). 2. **Why Other Options are Incorrect:** * **Bacteria:** While many STIs like Syphilis and Gonorrhea are bacterial, Trichomoniasis is parasitic. * **Virus:** Viral STIs include HIV, HPV, and Herpes Simplex. Viruses are acellular and require a host cell to replicate, unlike the independent protozoan _Trichomonas_. * **Chlamydia:** Although _Chlamydia trachomatis_ is a major cause of urethritis and cervicitis, it is an obligate intracellular **bacterium**, not a parasite. **High-Yield NEET-PG Clinical Pearls:** * **Clinical Presentation:** Characterized by a profuse, **foul-smelling, yellowish-green frothy vaginal discharge**. * **Colposcopy Finding:** The "Strawberry Cervix" (punctate hemorrhages on the cervix) is a classic, pathognomonic sign. * **Diagnosis:** The gold standard is **Whiff test** (positive) and **Wet mount microscopy**, which shows "jerky" or "twitching" motility of the trophozoites. Culture (Diamond’s medium) is the most sensitive method. * **Treatment:** The drug of choice is **Metronidazole**. It is crucial to treat the **sexual partner** simultaneously to prevent "ping-pong" reinfection.
Practice by Chapter
Classification of Parasites
Practice Questions
Intestinal Protozoa
Practice Questions
Blood and Tissue Protozoa
Practice Questions
Malaria Parasites
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Leishmaniasis
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Intestinal Helminths: Nematodes
Practice Questions
Tissue Nematodes
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Trematodes
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Cestodes
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Ectoparasites
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Antiparasitic Drugs
Practice Questions
Laboratory Diagnosis of Parasitic Infections
Practice Questions
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