Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 361: Which of the following statements regarding filariasis is FALSE?

A. Man is an intermediate host. (Correct Answer)
B. It is caused by Wuchereria bancrofti.
C. It involves the lymphatic system.
D. DEC is used in its treatment.

Explanation: ### Explanation **1. Why Option A is the Correct (False) Statement:** In the life cycle of filarial parasites like *Wuchereria bancrofti*, **Man is the Definitive Host**, not the intermediate host. By definition, a definitive host is one where the parasite reaches maturity and undergoes sexual reproduction. In humans, adult filarial worms reside in the lymphatic vessels and produce microfilariae. The **Mosquito (Culex/Aedes/Anopheles)** serves as the **Intermediate Host**, where the parasite undergoes essential developmental stages (L1 to L3 larvae) without sexual reproduction. **2. Analysis of Other Options:** * **Option B:** Correct. *Wuchereria bancrofti* is responsible for approximately 90% of lymphatic filariasis cases worldwide. * **Option C:** Correct. The adult worms reside in the **afferent lymphatic vessels** and lymph nodes, leading to inflammation (lymphangitis) and eventual obstruction (elephantiasis). * **Option D:** Correct. **Diethylcarbamazine (DEC)** is the drug of choice. It is effective against both microfilariae and adult worms. **3. High-Yield Clinical Pearls for NEET-PG:** * **Infective Stage:** Third-stage larvae (**L3**) introduced via mosquito bite. * **Diagnostic Stage:** **Microfilariae** found in peripheral blood (usually collected at night between 10 PM – 2 AM due to **nocturnal periodicity**). * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough, wheezing, and high peripheral eosinophilia. * **Drug of Choice for TPE:** DEC for 21 days. * **Ivermectin:** Used in the treatment of Onchocerciasis and Strongyloidiasis, but often co-administered with Albendazole in mass drug administration for filariasis.

Question 362: In occult filariasis, all are true except?

A. Microfilaria is demonstrable in blood (Correct Answer)
B. Microfilaria is demonstrable in lungs
C. Eosinophilia is present
D. Thrombophlebitis can occur

Explanation: **Explanation:** Occult filariasis (also known as **Tropical Pulmonary Eosinophilia - TPE**) is a distinct clinical syndrome resulting from a hypersensitivity reaction to the antigens of microfilariae (*W. bancrofti* or *B. malayi*). **1. Why Option A is the correct answer (The "Except"):** The hallmark of occult filariasis is the **absence of microfilariae in the peripheral blood**. In this condition, the body’s immune system becomes hyper-responsive, leading to the rapid destruction and clearance of microfilariae from the bloodstream. They are trapped and destroyed in the tissues (primarily the lungs and lymph nodes) rather than circulating freely. **2. Analysis of Incorrect Options:** * **Option B (Lungs):** Microfilariae are trapped in the pulmonary capillaries, where they trigger an eosinophilic inflammatory response. While difficult to find, they are pathologically present in the lungs, not the blood. * **Option C (Eosinophilia):** Massive peripheral blood eosinophilia (often >3000/µL) is a diagnostic criterion for TPE. * **Option D (Thrombophlebitis):** Occult filariasis can manifest in non-pulmonary forms (Meyers-Kouwenaar syndrome), involving lymphadenopathy, splenomegaly, or rare vascular complications like thrombophlebitis due to localized inflammatory responses. **Clinical Pearls for NEET-PG:** * **Classic Triad:** Paroxysmal cough (worse at night), massive eosinophilia, and high serum IgE levels. * **Serology:** High titers of anti-filarial antibodies are present. * **Treatment:** Excellent response to **Diethylcarbamazine (DEC)**; failure to respond usually suggests an alternative diagnosis. * **Contrast:** In "Classical Filariasis," microfilariae are present in the blood (nocturnal periodicity), and the primary pathology is lymphatic obstruction (elephantiasis).

Question 363: Regarding cysticercosis, all are true except?

A. Commonest sites are meninges and cerebral ventricles (Correct Answer)
B. Calcification is common
C. Caused by the larval stage of Taenia solium
D. Causes focal neurological complications

Explanation: **Explanation:** **1. Why Option A is the correct answer (The "Except" statement):** While *Cysticercus cellulosae* (the larval stage of *Taenia solium*) can affect any organ, the **most common site for cysticercosis is the brain parenchyma** (specifically the grey-white matter junction), not the meninges or ventricles. When it occurs in the brain, it is termed Neurocysticercosis (NCC). Extraparenchymal sites like the subarachnoid space (meninges) and ventricles are less common and often associated with higher morbidity due to hydrocephalus. **2. Analysis of other options:** * **Option B (Calcification is common):** This is true. As the larvae die, they undergo a degenerative process leading to the "calcified nodule" stage. On a CT scan, these appear as hyperdense punctate lesions, which are a hallmark of inactive NCC. * **Option C (Caused by the larval stage of *Taenia solium*):** This is true. Human cysticercosis occurs when humans act as the **intermediate host** by ingesting *T. solium* eggs (via contaminated food/water or autoinfection). In contrast, intestinal taeniasis occurs by ingesting larvae (cysticerci) in undercooked pork. * **Option D (Causes focal neurological complications):** This is true. NCC is the leading cause of acquired epilepsy in developing countries. Depending on the location of the cyst, it can cause focal seizures, focal neurological deficits, or signs of increased intracranial pressure. **Clinical Pearls for NEET-PG:** * **Drug of Choice:** Albendazole (preferred over Praziquantel as it has better CNS penetration). * **Diagnosis:** MRI is the gold standard (shows "hole-with-dot" appearance representing the scolex). * **Key Distinction:** Humans are the **definitive host** for the adult worm (*Taeniasis*) but the **accidental intermediate host** for the larvae (*Cysticercosis*).

Question 364: Which of the following is NOT seen in the cyst of Entamoeba histolytica?

A. Glycogen mass
B. Chromatid bars
C. Eccentric nucleus
D. Ingested RBC (Correct Answer)

Explanation: The correct answer is **D. Ingested RBC**. ### **Explanation** The life cycle of *Entamoeba histolytica* consists of two stages: the **Trophozoite** (feeding/pathogenic stage) and the **Cyst** (infective stage). * **Why Ingested RBC is the correct answer:** Erythrophagocytosis (ingestion of RBCs) is a hallmark feature of the **Trophozoite** stage of *E. histolytica*. It indicates invasive disease (amoebic dysentery). RBCs are never found in the cyst stage because the cyst is a non-feeding, dormant form designed for environmental survival. ### **Analysis of Incorrect Options** * **A. Glycogen mass:** This is a characteristic feature of the **immature (uninucleate/binucleate) cyst**. It serves as a food reserve and disappears as the cyst matures into the quadrinucleate stage. * **B. Chromatid bars:** These are cigar-shaped (rounded ends) aggregations of ribosomes found in **immature cysts**. Like the glycogen mass, they are consumed as the cyst matures. * **C. Eccentric nucleus:** The nucleus of *E. histolytica* (in both trophozoite and cyst stages) typically features a small, central karyosome and peripheral chromatin. However, in many preparations, the nucleus may appear slightly eccentric, and it is a standard morphological component of the cyst. ### **NEET-PG High-Yield Pearls** 1. **Infective Form:** Mature **Quadrinucleate cyst** (passed in formed stools). 2. **Diagnostic Form (Invasive):** Trophozoite with **ingested RBCs** (found in liquid/dysenteric stools). 3. **Chromatid Bars:** *E. histolytica* has **cigar-shaped** (rounded) bars, whereas *Entamoeba coli* has **filamentous/frayed** (pointed) ends. 4. **Nuclear Count:** *E. histolytica* cysts have a maximum of **4 nuclei**, while *E. coli* cysts have up to **8 nuclei**. 5. **Anchors:** The presence of RBCs in a trophozoite is the most reliable feature to differentiate *E. histolytica* from the morphologically identical non-pathogen *E. dispar*.

Question 365: A 52-year-old ex-military man presented with fever and abdominal pain. Imaging studies are suspicious of hydatid cyst. Which of the following is the commonest organ for forming a hydatid cyst?

A. Liver (Correct Answer)
B. Lungs
C. Kidneys
D. Spleen

Explanation: **Explanation:** Hydatid disease is caused by the larval stage of the cestode **_Echinococcus granulosus_**. The life cycle involves dogs as definitive hosts and sheep as intermediate hosts. Humans act as accidental intermediate hosts. **Why Liver is the correct answer:** After a human ingests the eggs (oncospheres), they hatch in the duodenum and penetrate the intestinal wall to enter the **portal circulation**. The **liver** acts as the first and most significant physiological filter. Consequently, approximately **60–70%** of hydatid cysts develop in the liver (most commonly the right lobe). **Analysis of Incorrect Options:** * **Lungs (Option B):** This is the **second most common** site (15–25%). Larvae that bypass the hepatic sinusoids enter the systemic venous circulation and reach the pulmonary capillaries, which act as the second filter. In children, the lungs are relatively more common sites than in adults. * **Kidneys (Option C) and Spleen (Option D):** These are considered uncommon or "ectopic" sites (approx. 2–3%). Larvae only reach these organs if they bypass both the hepatic and pulmonary filters to enter the systemic arterial circulation. **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agent:** *Echinococcus granulosus* (Cystic hydatid); *E. multilocularis* (Alveolar hydatid - more aggressive). * **Diagnosis:** Ultrasound is the primary modality (look for "Water lily sign" or "Grapes-like appearance"). Serology (ELISA) is used for confirmation. * **Casoni’s Test:** An immediate hypersensitivity skin test (now largely replaced by serology due to low specificity). * **Treatment:** Small cysts are treated with **Albendazole**. For larger cysts, the **PAIR** technique (Puncture, Aspiration, Injection of scolicidal agent like hypertonic saline, Re-aspiration) is used. * **Complication:** Rupture of the cyst can lead to life-threatening **anaphylactic shock**.

Question 366: Which of the following is true about Giardiasis?

A. Only the cyst form is infective. (Correct Answer)
B. The trophozoites reside in the cecum.
C. Transmission occurs only from man to man.
D. The parasite exists in only one phase.

Explanation: **Explanation:** **Giardia lamblia** (also known as *G. duodenalis* or *G. intestinalis*) is a flagellated protozoan that causes diarrheal illness. 1. **Why Option A is correct:** The life cycle of Giardia consists of two stages: the **cyst** and the **trophozoite**. The cyst is the **infective stage** because it is hardy and can survive outside the host in soil and water due to its thick wall. Trophozoites, if ingested, are immediately destroyed by gastric acid and are therefore not infective. 2. **Why Option B is incorrect:** Trophozoites reside in the **duodenum and upper jejunum**. They use a ventral sucking disc to attach to the mucosal surface. They do not typically inhabit the cecum (unlike *Entamoeba histolytica*). 3. **Why Option C is incorrect:** While man-to-man transmission (fecal-oral) is common, Giardiasis is a **zoonotic disease**. Animals like beavers (leading to the name "Beaver Fever"), dogs, and cats act as reservoirs. 4. **Why Option D is incorrect:** As mentioned, the parasite is **pleomorphic**, existing in two phases: the pear-shaped, flagellated **trophozoite** (feeding/replicating stage) and the quadrinucleated **cyst** (diagnostic/infective stage). **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Trophozoite has a characteristic **"Falling Leaf" motility** and a "Monkey face" or "Old man with glasses" appearance on microscopy. * **Clinical Feature:** Causes **Steatorrhea** (foul-smelling, greasy stools) due to malabsorption of fats. * **Diagnosis:** Stool microscopy (cysts/trophozoites) or **String Test (Entero-test)**. * **Association:** Increased incidence in patients with **Selective IgA deficiency**. * **Drug of Choice:** Tinidazole or Metronidazole.

Question 367: Which of the following organs is NOT affected by Plasmodium falciparum?

A. Lung
B. Liver
C. Kidney
D. Heart (Correct Answer)

Explanation: **Explanation:** The correct answer is **Heart**. While *Plasmodium falciparum* is known for causing multi-organ dysfunction, it primarily targets organs with extensive microvascular beds where **cytoadherence** and **sequestration** can occur. **1. Why Heart is the correct answer:** In severe malaria, the heart is typically spared from direct pathological damage. While systemic complications like severe anemia or fluid overload can indirectly strain the cardiovascular system, *P. falciparum* does not cause specific inflammatory or obstructive lesions in the myocardium. Therefore, "Malarial Myocarditis" is not a recognized clinical entity. **2. Why other options are incorrect:** * **Lung:** Can lead to **Acute Respiratory Distress Syndrome (ARDS)** due to increased capillary permeability and sequestration of parasites in pulmonary capillaries. This is a common cause of death in adults. * **Liver:** The liver is the site of the initial **pre-erythrocytic (exo-erythrocytic) cycle**. Severe infection causes centrilobular necrosis, leading to jaundice (biliary remittent fever). * **Kidney:** Causes **Acute Tubular Necrosis (ATN)** due to hemoglobinuria and ischemia. A classic presentation is **Blackwater Fever**, characterized by massive intravascular hemolysis and dark urine. **High-Yield Clinical Pearls for NEET-PG:** * **Sequestration:** Mediated by **PfEMP-1** (P. falciparum erythrocyte membrane protein 1) which binds to receptors like **ICAM-1** and **CD36** on vascular endothelium. * **Cerebral Malaria:** The most dreaded complication; characterized by "Dürck’s granulomas" (focal microglial proliferation). * **Hypoglycemia:** A common metabolic complication caused by both the parasite and quinine therapy. * **Spleen:** *P. falciparum* can cause "Tropical Splenomegaly Syndrome" (Hyperreactive Malarial Splenomegaly).

Question 368: Which of the following is NOT a liver fluke?

A. Paragonimus (Correct Answer)
B. Whipworm
C. Clonorchis sinensis
D. Gnathostoma spinigerum

Explanation: **Explanation:** The question asks to identify which organism is **not** a liver fluke. Liver flukes are trematodes (flukes) that primarily inhabit the bile ducts or liver parenchyma of their hosts. **1. Why Paragonimus is the correct answer:** *Paragonimus westermani* is known as the **Oriental Lung Fluke**. Its primary site of infection is the lungs, where it causes a clinical presentation mimicking pulmonary tuberculosis (cough, hemoptysis, and chest pain). Since it targets the respiratory system rather than the biliary system, it is not classified as a liver fluke. **2. Analysis of other options:** * **Clonorchis sinensis:** Known as the **Chinese Liver Fluke**. It is a classic liver fluke that inhabits the distal bile ducts. Chronic infection is a significant risk factor for **Cholangiocarcinoma** (bile duct cancer). * **Whipworm (*Trichuris trichiura*):** While this is a nematode (roundworm) and not a fluke, in the context of this specific question's phrasing and standard NEET-PG distractors, the focus is on identifying the fluke that doesn't belong to the "liver" category. However, note that *Fasciola hepatica* and *Opisthorchis* are the other major liver flukes. * **Gnathostoma spinigerum:** This is a nematode that causes **Larva Migrans**. While it can migrate through the liver (visceral larva migrans), it is not a "fluke." *(Note: In many standard versions of this MCQ, the options usually include Fasciola, Clonorchis, and Opisthorchis. Here, Paragonimus stands out as the definitive "Lung Fluke".)* **High-Yield Clinical Pearls for NEET-PG:** * **Intermediate Hosts:** All flukes require **snails** as their first intermediate host. *Paragonimus* requires **crabs/crayfish** as the second intermediate host. * **Drug of Choice:** **Praziquantel** is the treatment of choice for most flukes, except *Fasciola hepatica* (treated with Triclabendazole). * **Diagnostic Stage:** For *Paragonimus*, look for operculated eggs in **sputum** or feces.

Question 369: Which parasite is commonly referred to as the dragon or serpent worm?

A. Enterobius
B. Trichuris
C. Dracunculus (Correct Answer)
D. Taenia solium

Explanation: **Explanation:** The correct answer is **Dracunculus medinensis**, commonly known as the **Guinea worm**, **Dragon worm**, or **Fiery Serpent**. 1. **Why Dracunculus is correct:** The name is derived from the Latin *dracunculus* (little dragon). It earned the moniker "fiery serpent" due to the intense, burning pain caused by the blister the female worm creates on the skin (usually the lower limbs) to release larvae when the host enters water. It is the largest tissue nematode infecting humans. 2. **Why other options are incorrect:** * **Enterobius vermicularis:** Known as the **Pinworm** or **Seatworm**. It is characterized by perianal pruritus and diagnosed via the NIH swab/Scotch tape test. * **Trichuris trichiura:** Known as the **Whipworm** due to its whip-like shape (thin anterior and thick posterior). It is associated with rectal prolapse in children. * **Taenia solium:** Known as the **Pork Tapeworm**. It is a cestode that causes Taeniasis (adult worm) or Cysticercosis (larval stage). **High-Yield Clinical Pearls for NEET-PG:** * **Intermediate Host:** *Cyclops* (Water flea). Infection occurs by drinking unfiltered water containing infected Cyclops. * **Diagnosis:** Clinical observation of the worm emerging from a skin ulcer; larvae can be seen if cold water is poured over the ulcer. * **Treatment:** Slow, manual extraction of the worm by winding it around a small stick over several days. * **Global Status:** It is on the verge of eradication; India was declared Guinea worm-free in February 2000.

Question 370: What is the common host of Balantidium coli?

A. Cattle
B. Dog
C. Goat
D. Pig (Correct Answer)

Explanation: **Explanation:** *Balantidium coli* is the largest protozoan parasite and the only ciliate known to cause human disease (Balantidiasis). **1. Why Pig is the Correct Answer:** The **pig (swine)** is the natural reservoir and the most common definitive host for *Balantidium coli*. The parasite lives as a commensal in the large intestine of pigs. Humans are accidental hosts, typically acquiring the infection through the fecal-oral route—specifically by ingesting food or water contaminated with pig feces containing the infective **cysts**. Because of this, the disease is most prevalent in areas where humans live in close proximity to swine (e.g., pig farmers or slaughterhouse workers). **2. Why Other Options are Incorrect:** * **Cattle, Dogs, and Goats:** While these animals can occasionally harbor various intestinal parasites, they are not the primary or natural reservoirs for *B. coli*. For instance, cattle are more commonly associated with *Cryptosporidium*, and dogs are definitive hosts for *Echinococcus granulosus*. **3. High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** It exists in two stages: the **Trophozoite** (covered in cilia with a characteristic kidney-shaped/bean-shaped macronucleus) and the **Cyst** (the infective stage). * **Pathogenesis:** It produces the enzyme **hyaluronidase**, which allows it to invade the intestinal mucosa, creating ulcers similar to those in amoebiasis (flask-shaped ulcers). * **Clinical Feature:** It primarily causes large bowel involvement, leading to diarrhea or dysentery. * **Treatment of Choice:** **Tetracycline** is the first-line drug, followed by Metronidazole or Iodoquinol.

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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