Parasitology Practice Questions

Q: Which organism serves as an intermediate host for the Guinea worm?

Guinea worm. **Explanation:** The correct answer is **Guinea worm** (*Dracunculus medinensis*). In the context of the question, the organism that serves as the essential intermediate host for the transmission of Dracunculiasis is the **Cyclops** (water flea). *Note: The options provided in the prompt appear to list the diseases/pathogens themselves rather than the hosts. In NEET-PG, the specific intermediate host for Guinea worm is always identified as **Cyclops**.* **Why the correct answer is right:** The life cycle of *Dracunculus medinensis* requires a crustacean of the genus **Cyclops**. When a person drinks stagnant water containing Cyclops infected with L3 larvae, the larvae are released in the stomach, penetrate the intestinal wall, and mature into adults. The female worm eventually migrates to the subcutaneous tissue (usually the lower limbs) to release larvae into the water, completing the cycle. **Why the other options are wrong:** * **Malaria:** This is caused by *Plasmodium* species. The definitive host is the female *Anopheles* mosquito, and the intermediate host is the human. * **Rabies:** This is a viral zoonosis. It does not have an "intermediate host" in the parasitological sense; it is transmitted via the saliva of infected mammals (dogs, bats). * **Salmonella:** This is a bacterium causing enteric fever or gastroenteritis. It is transmitted via the fecal-oral route and does not require an intermediate host. **High-Yield Clinical Pearls for NEET-PG:** * **Intermediate Host:** Cyclops (Water flea). * **Infective Form:** L3 larvae inside the Cyclops. * **Diagnosis:** Step-ladder appearance of the worm under the skin or the "string test" (visualizing the worm upon water contact). * **Prevention:** Filtering water through a fine cloth or boiling. * **Eradication:** India was declared Guinea worm-free by the WHO in **2000**. The last case in India was reported in 1996 (Rajasthan).

Q: Endemic hemoptysis is caused by which parasite?

Paragonimus westermanii. **Explanation:** **Paragonimus westermani**, also known as the **Oriental Lung Fluke**, is the causative agent of **Endemic Hemoptysis**. The term refers to the characteristic clinical presentation of chronic cough and blood-stained sputum (hemoptysis) seen in endemic regions (primarily East Asia and parts of India like Manipur). * **Pathogenesis:** Humans are infected by ingesting metacercariae in undercooked **crabs or crayfish** (second intermediate hosts). The larvae migrate from the intestines, through the diaphragm, into the lungs. Here, they induce a granulomatous reaction, forming cystic cavities. When these cysts rupture into the bronchioles, the patient expectorates eggs, blood, and inflammatory debris, mimicking pulmonary tuberculosis. **Analysis of Incorrect Options:** * **Hymenolepis nana (Dwarf Tapeworm):** The smallest intestinal cestode. It causes abdominal pain and diarrhea but does not involve the lungs. It is unique for its "internal autoinfection" cycle. * **Diphyllobothrium latum (Fish Tapeworm):** Acquired by eating raw freshwater fish. It is clinically significant for causing **Vitamin B12 deficiency** and megaloblastic anemia. * **Clonorchis sinensis (Chinese Liver Fluke):** Inhabits the biliary tract. It is associated with cholangitis, biliary stones, and is a known risk factor for **cholangiocarcinoma**. **NEET-PG High-Yield Pearls:** * **Intermediate Hosts:** 1st – Snail (*Melania* spp.); 2nd – Crab/Crayfish. * **Diagnosis:** Presence of golden-brown, operculated eggs in sputum or stool. * **Radiology:** May show "ring shadows" or "cotton-wool" opacities, often confused with TB. * **Drug of Choice:** Praziquantel.

Q: Which of the following is the infective form of Plasmodium falciparum for humans?

Sporozoites. **Explanation:** The life cycle of *Plasmodium falciparum* involves two hosts: the female *Anopheles* mosquito (definitive host) and the human (intermediate host). **Why Sporozoites is the correct answer:** The **Sporozoite** is the infective stage for humans. When an infected female *Anopheles* mosquito takes a blood meal, it inoculates sporozoites from its salivary glands into the human dermis. These sporozoites enter the bloodstream and reach the liver within 30–60 minutes to initiate the **pre-erythrocytic (exo-erythrocytic) schizogony**. **Analysis of Incorrect Options:** * **Merozoites:** These are released when hepatic or red blood cell schizonts rupture. They are responsible for infecting new erythrocytes but are not the form introduced by the mosquito. * **Hypnozoites:** These are dormant hepatic stages found **only** in *P. vivax* and *P. ovale*. They are responsible for clinical relapses. *P. falciparum* does not have a hypnozoite stage. * **Trophozoites:** This is the intracellular feeding stage within the red blood cells (e.g., the "ring form"). It is a diagnostic stage, not the infective stage. **High-Yield Clinical Pearls for NEET-PG:** * **Infective form for Mosquito:** Gametocytes (taken up during a blood meal). * **Exo-erythrocytic cycle:** Absent in *P. falciparum* (once the liver stage is over, it does not recur from the liver). * **Recrudescence:** Seen in *P. falciparum* due to sub-optimal treatment or drug resistance (not to be confused with "Relapse" caused by hypnozoites). * **Gold Standard Diagnosis:** Peripheral blood smear (Giemsa stain) showing multiple ring forms per RBC and crescent-shaped (banana-shaped) gametocytes.

Q: Two nuclei at the tail tip is seen in which of the following?

Brugia malayi. The identification of microfilariae in peripheral blood smears is a high-yield topic for NEET-PG, primarily based on two morphological features: the presence of a **sheath** and the arrangement of **nuclei in the tail tip**. ### **Explanation of the Correct Answer** **A. Brugia malayi:** This microfilaria is characterized by being **sheathed** and having a tail that tapers significantly. Crucially, it possesses **two distinct, terminal nuclei** at the very tip of the tail that are separated from the rest of the nuclear column. This "double nuclei" feature is the pathognomonic diagnostic hallmark of *B. malayi*. ### **Analysis of Incorrect Options** * **B. Wuchereria bancrofti:** While it is also sheathed, the tail tip is **devoid of nuclei** (the nuclear column does not extend to the end). This is the most important feature distinguishing it from *Brugia*. * **C. Onchocerca volvulus:** This microfilaria is **unsheathed** and is typically found in skin snips, not blood. Its tail is pointed and **devoid of nuclei**. * **D. Mansonella ozzardi:** This is an **unsheathed** microfilaria found in blood. Its tail is long and slender, and the nuclei **do not extend** to the tip. ### **High-Yield Clinical Pearls for NEET-PG** * **Sheathed Microfilariae:** *Wuchereria bancrofti, Brugia malayi, Loa loa*. * **Unsheathed Microfilariae:** *Onchocerca volvulus, Mansonella spp.* * **Tail Nuclei Memory Aid:** * **B**rugia = **B**i-nucleated (2 nuclei at the tip). * **L**oa loa = **L**oaded with nuclei (nuclei extend in a continuous row to the tip). * **W**uchereria = **W**ithout nuclei (at the tip). * **Nocturnal Periodicity:** Both *W. bancrofti* and *B. malayi* show maximum density in blood between 10 PM and 2 AM.

Q: What is the infective stage of Plasmodium vivax for mosquitoes?

Gametocyte. **Explanation:** The life cycle of *Plasmodium vivax* involves two hosts: the female *Anopheles* mosquito (definitive host) and the human (intermediate host). **Why Gametocyte is correct:** When a mosquito bites an infected human, it ingests various stages of the parasite present in the blood. However, only the **Gametocytes** (male microgametocytes and female macrogametocytes) are capable of surviving and initiating the sexual cycle (sporogony) within the mosquito's midgut. Therefore, gametocytes are the **infective stage for the mosquito**. **Why the other options are incorrect:** * **Sporozoite:** This is the **infective stage for humans**. Sporozoites are stored in the mosquito's salivary glands and injected into the human bloodstream during a bite. * **Zygote:** This stage is formed **inside the mosquito's midgut** after the fusion of male and female gametes. It is not the stage that enters the mosquito from the human. * **Merozoite:** These are released from ruptured liver cells (exo-erythrocytic) or red blood cells (erythrocytic). While they circulate in human blood, they are digested in the mosquito's gut and do not contribute to further transmission. **High-Yield Clinical Pearls for NEET-PG:** * **Relapse:** *P. vivax* and *P. ovale* can persist in the liver as **hypnozoites**, causing clinical relapse months later. **Primaquine** is the drug of choice to eradicate these stages. * **Duffy Antigen:** *P. vivax* requires the Duffy blood group antigen on RBCs for attachment; individuals who are Duffy-negative are resistant to *P. vivax* infection. * **Schüffner’s dots:** These are characteristic stippling seen in RBCs infected with *P. vivax*.

Q: Which of the following statements regarding filariasis is FALSE?

Man is an intermediate host.. ### 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.

Q: In occult filariasis, all are true except?

Microfilaria is demonstrable in blood. **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).

Q: Regarding cysticercosis, all are true except?

Commonest sites are meninges and cerebral ventricles. **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*).

Q: 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?

Liver. **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**.

Q: Which of the following is true about Giardiasis?

Only the cyst form is infective.. **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 1

Which organism serves as an intermediate host for the Guinea worm?

Accepted Answer

Guinea worm

Answer

Malaria

Answer

Rabies

Answer

Salmonella

Question 2

Endemic hemoptysis is caused by which parasite?

Accepted Answer

Paragonimus westermanii

Answer

Hymenolepis nana

Answer

Diphyllobothrium latum

Answer

Clonorchis sinensis

Question 3

Which of the following is the infective form of Plasmodium falciparum for humans?

Accepted Answer

Sporozoites

Answer

Merozoites

Answer

Hypnozoite

Answer

Trophozoites

Question 4

Two nuclei at the tail tip is seen in which of the following?

Accepted Answer

Brugia malayi

Answer

Wuchereria bancrofti

Answer

Onchocerca volvulus

Answer

Mansonella ozzardi

Question 5

What is the infective stage of Plasmodium vivax for mosquitoes?

Accepted Answer

Gametocyte

Answer

Sporozoite

Answer

Zygote

Answer

Merozoite

Question 6

Which of the following statements regarding filariasis is FALSE?

Accepted Answer

Man is an intermediate host.

Answer

It is caused by Wuchereria bancrofti.

Answer

It involves the lymphatic system.

Answer

DEC is used in its treatment.

Question 7

In occult filariasis, all are true except?

Accepted Answer

Microfilaria is demonstrable in blood

Answer

Microfilaria is demonstrable in lungs

Answer

Eosinophilia is present

Answer

Thrombophlebitis can occur

Question 8

Regarding cysticercosis, all are true except?

Accepted Answer

Commonest sites are meninges and cerebral ventricles

Answer

Calcification is common

Answer

Caused by the larval stage of Taenia solium

Answer

Causes focal neurological complications

Question 9

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?

Accepted Answer

Liver

Answer

Lungs

Answer

Kidneys

Answer

Spleen

Question 10

Which of the following is true about Giardiasis?

Accepted Answer

Only the cyst form is infective.

Answer

The trophozoites reside in the cecum.

Answer

Transmission occurs only from man to man.

Answer

The parasite exists in only one phase.

Parasitology — MCQs

Parasitology — MCQs

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