Parasitology Practice Questions

Q: What is the infective form of Plasmodium falciparum in the mosquito?

Gametocytes. **Explanation:** The life cycle of *Plasmodium falciparum* involves two hosts: the human (intermediate host) and the female *Anopheles* mosquito (definitive host). **Why Gametocytes are correct:** For the mosquito to become infected, it must ingest the sexual stages of the parasite present in human peripheral blood. These are the **Gametocytes** (male microgametocytes and female macrogametocytes). Once inside the mosquito's midgut, these gametocytes undergo fertilization to begin the sporogonic cycle, eventually leading to the production of sporozoites. Therefore, gametocytes are the **infective form for the mosquito**. **Why other options are incorrect:** * **Sporozoites (Option B):** These are the **infective form for humans**. They are inoculated into the human bloodstream via the mosquito's saliva during a blood meal. * **Merozoites (Option A):** These are released from hepatic cells (exo-erythrocytic stage) or red blood cells (erythrocytic stage). They infect new RBCs but are digested if ingested by a mosquito. * **Trophozoites (Option D):** This is the metabolically active, feeding stage within the human RBC (e.g., "ring forms"). Like merozoites, they do not survive the mosquito's digestive tract. **High-Yield NEET-PG Pearls:** * **Definitive Host:** Female *Anopheles* mosquito (where the sexual cycle occurs). * **Intermediate Host:** Humans (where the asexual cycle/schizogony occurs). * **P. falciparum Gametocytes:** Characteristically **crescent or banana-shaped**, appearing in peripheral blood 7–10 days after the initial infection. * **Primaquine:** The drug of choice for its gametocidal action against *P. falciparum*, used to prevent the transmission of malaria back to the mosquito.

Q: Which of the following diseases are transmitted by the sandfly?

Kala-azar. **Explanation:** The sandfly (genus *Phlebotomus* in the Old World and *Lutzomyia* in the New World) is a significant medical vector. The correct answer is **Kala-azar** (Visceral Leishmaniasis), caused by *Leishmania donovani*. The sandfly transmits the parasite in its **promastigote** stage through a bite, which then transforms into the **amastigote** stage within the host's macrophages. **Analysis of Options:** * **A. Kala-azar (Correct):** Transmitted by *Phlebotomus argentipes*. It is characterized by the classic triad of fever, hepatosplenomegaly, and pancytopenia. * **B. Oriental Sore:** While also transmitted by the sandfly (*P. papatasi*), it refers to **Cutaneous Leishmaniasis**. In many competitive exams, if "Kala-azar" is an option, it is prioritized as the primary disease associated with sandflies in the Indian subcontinent. * **C. Relapsing Fever:** Epidemic relapsing fever is transmitted by the **body louse** (*Pediculus humanus corporis*), while endemic relapsing fever is transmitted by **soft ticks** (*Ornithodoros*). * **D. Oroya Fever:** This is the acute febrile phase of **Carrion’s disease** (caused by *Bartonella bacilliformis*). It is indeed transmitted by the sandfly (*Lutzomyia*), but it is geographically restricted to the Andes region of South America, making Kala-azar the more globally and locally relevant answer for NEET-PG. **High-Yield Clinical Pearls:** * **Sandfly-borne diseases mnemonic (6 O's):** **O**roya fever, **O**riental sore, **O**ld world Leishmaniasis, **O**ndansetron (not related, but helps memory), **O**ther Leishmaniasis, and **O**ropouche virus. * **Sandfly characteristics:** They are small (1/4 size of a mosquito), crawl rather than fly (short hops), and are nocturnal. * **Drug of Choice for Kala-azar:** Liposomal Amphotericin B is currently the first-line treatment.

Q: Which of the following is most severely affected in Kala-azar?

Spleen. **Explanation:** **Kala-azar (Visceral Leishmaniasis)**, caused by *Leishmania donovani*, is characterized by the massive proliferation of the parasite within the **Reticuloendothelial System (RES)**. **Why the Spleen is the correct answer:** The spleen is the organ most severely affected in Kala-azar. The amastigote form of the parasite multiplies within the splenic macrophages, leading to intense reactive hyperplasia of the lymphoid tissue and congestion. This results in **massive splenomegaly** (often extending to the iliac fossa), which is a hallmark clinical feature of the disease. The spleen becomes soft, friable, and dark (hence the name "Black Fever"). **Analysis of Incorrect Options:** * **B. Liver:** While the liver is frequently enlarged (hepatomegaly) due to the proliferation of Kupffer cells, the degree of enlargement and structural alteration is significantly less than that of the spleen. * **C. Adrenal gland:** Though the RES is involved systemically, the adrenal glands are not a primary site of pathology in Visceral Leishmaniasis. * **D. Bone marrow:** The bone marrow is indeed involved, leading to pancytopenia (anemia, leucopenia, and thrombocytopenia). However, in terms of gross organ pathology and severity of enlargement, the spleen remains the most prominently affected organ. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Splenic aspiration is the most sensitive diagnostic method (>95% yield) but carries a risk of hemorrhage. Bone marrow aspiration is safer and more commonly performed. * **Hematological Finding:** Characterized by **pancytopenia** and **hypergammaglobulinemia** (reversed Albumin:Globulin ratio). * **Vector:** Transmitted by the bite of the female **Sandfly (*Phlebotomus argentipes*)**. * **Drug of Choice:** Liposomal Amphotericin B is currently the preferred treatment.

Q: Ascariasis causes which of the following complications?

All of the above. **Explanation:** *Ascaris lumbricoides* (the giant roundworm) is the most common helminthic infection worldwide. The complications of Ascariasis are primarily due to the **mechanical effects** of the adult worms, which are large (20–35 cm), highly mobile, and have a tendency to migrate into narrow openings. 1. **Intestinal Obstruction:** This is the most common serious complication. A heavy worm burden can lead to the formation of a "bolus" or tangled mass of worms that physically blocks the lumen of the small intestine (usually the ileum), leading to acute mechanical obstruction. 2. **Bile Duct Obstruction:** Adult worms are known for their "wandering" nature. They can migrate through the Ampulla of Vater into the biliary tract, causing biliary colic, cholecystitis, or obstructive jaundice. 3. **Appendicitis:** If a wandering worm enters the narrow lumen of the appendix, it can cause luminal obstruction, leading to acute appendicitis. **Why "All of the above" is correct:** Since *Ascaris* is a large, motile parasite capable of both mass-aggregation and ectopic migration, it can cause mechanical blockage in the intestine, the biliary tree, and the appendix simultaneously or independently. **High-Yield Clinical Pearls for NEET-PG:** * **Loeffler’s Syndrome:** Characterized by transient pulmonary infiltrates and peripheral eosinophilia during the larval migration phase through the lungs. * **Diagnosis:** The gold standard is the detection of characteristic bile-stained (brown), mamillated eggs in stool microscopy. * **Imaging:** On Barium meal, a "String sign" or "Railway track appearance" may be seen due to the presence of worms in the intestine. * **Drug of Choice:** Albendazole (single dose) or Mebendazole.

Q: Which of the following parasites is known to cause anemia?

Diphyllobothrium latum. ### Explanation **Correct Answer: D. Diphyllobothrium latum** **Medical Concept:** *Diphyllobothrium latum*, also known as the **Fish Tapeworm**, is the largest parasite infecting humans. It causes a specific type of anemia known as **Megaloblastic Anemia** (Vitamin B12 deficiency). The parasite competes with the host for Vitamin B12 (Cyanocobalamin) in the proximal small intestine. It absorbs approximately 80–100% of the dietary B12, leading to host depletion. This results in macrocytic anemia and, in severe cases, neurological symptoms similar to Subacute Combined Degeneration of the Spinal Cord (SCD). **Analysis of Incorrect Options:** * **A. Entamoeba histolytica:** This protozoan causes amoebic dysentery and liver abscesses. While chronic dysentery can lead to iron deficiency, it is not classically associated with a specific anemia syndrome like *D. latum*. * **B. Isospora belli (Cystoisospora):** An opportunistic coccidian parasite primarily causing self-limiting or chronic watery diarrhea, especially in HIV/AIDS patients. It does not cause anemia. * **C. Trichomonas vaginalis:** A flagellated protozoan that causes urogenital infections (vaginitis/urethritis). It is a localized infection and does not have systemic hematological effects. **NEET-PG High-Yield Pearls:** * **Infection Source:** Consumption of undercooked/raw freshwater fish (containing **Plerocercoid larvae**). * **Diagnosis:** Presence of **operculated eggs** (bile-stained) in stool. * **Other Parasites causing Anemia:** * **Hookworms** (*Ancylostoma duodenale/Necator americanus*): Iron Deficiency Anemia (Microcytic Hypochromic). * **Malaria** (*Plasmodium*): Hemolytic Anemia. * **Trichuris trichiura**: Microcytic anemia due to mucosal bleeding in heavy infestations (Whipworm). * **Drug of Choice:** Praziquantel.

Q: A 30-year-old patient developed high fever of sudden onset. Peripheral blood smear showed crescent-shaped gametocytes. Malaria pigment was dark brown in color. Which of the following malarial parasites is the causative agent?

Plasmodium falciparum. ### Explanation The correct answer is **Plasmodium falciparum**. **1. Why Plasmodium falciparum is correct:** The diagnosis is based on two pathognomonic morphological features described in the peripheral blood smear: * **Crescent-shaped (Banana-shaped) Gametocytes:** This is the most characteristic diagnostic feature of *P. falciparum*. Other species have spherical or rounded gametocytes. * **Dark Brown Pigment:** Malarial pigment (hemozoin) in *P. falciparum* is typically dark brown to black. * **Clinical Presentation:** Sudden onset of high fever is consistent with the aggressive nature of falciparum malaria, which often causes "malignant tertian" malaria. **2. Why other options are incorrect:** * **P. vivax:** Gametocytes are large and **round/oval**. The pigment is yellowish-brown. It typically shows Schüffner’s dots and enlarged RBCs. * **P. malariae:** Gametocytes are **round** and smaller. A key feature is the "Ziemann’s dots" and the characteristic "Band form" trophozoites. The pigment is often dark brown but coarser. * **P. ovale:** Gametocytes are **round/oval**. RBCs are often oval with fimbriated (tufted) edges and contain James’ dots. **3. NEET-PG High-Yield Pearls:** * **Maurer’s Clefts:** Coarse granulations seen in RBCs infected with *P. falciparum*. * **Multiple Rings & Appole Forms:** *P. falciparum* often shows multiple ring forms per RBC and "appliqué" forms (parasite at the periphery of the RBC). * **Sequestration:** *P. falciparum* is the only species where mature trophozoites and schizonts are rarely seen in peripheral blood (except in severe cases) because they sequester in deep capillaries, leading to complications like Cerebral Malaria. * **Recrudescence** is seen in *P. falciparum* and *P. malariae*, whereas **Relapse** (due to hypnozoites) is seen in *P. vivax* and *P. ovale*.

Q: A 50-year-old man presents with a history of abdominal pain, weakness, lightheadedness, palpitations, and shortness of breath. On examination, glossitis, hyperpigmentation of the skin of the dorsum of hands and feet, and abnormal pigmentation of hair were observed. The patient's family reports frequent episodes of increased irritability over the past year. Laboratory findings include Hb: 9gm%, MCV: 110fL, MCH: 36Pg, MCHC: 34gm/dL, Reticulocyte count: 0.1 x 10^9/L, LDH: 600 U/L, Indirect bilirubin: 1 mg/dL, S. iron: Normal, S. Ferritin: Normal, WBC: 2 x 10^9/L, and Platelet count: 90 x 10^9/L. Peripheral blood smear and bone marrow aspiration were also performed. What is the infective form of the organism causing the above condition?

Plerocercoid. ### Explanation The clinical presentation and laboratory findings point towards **Megaloblastic Anemia** caused by **Vitamin B12 deficiency** [1]. **Clinical Reasoning:** * **Hematology:** The patient has macrocytic anemia (MCV 110 fL), pancytopenia (low WBC and Platelets), and a low reticulocyte count. Elevated LDH and indirect bilirubin indicate **ineffective erythropoiesis** (intramedullary hemolysis). * **Physical Findings:** Glossitis and hyperpigmentation (dorsum of hands/feet) are classic cutaneous markers of B12 deficiency. * **Neuropsychiatric:** Irritability and cognitive changes are common in B12 deficiency. The question asks for the infective form of the organism causing this condition. In the context of parasitic causes of B12 deficiency, the culprit is **_Diphyllobothrium latum_** (Fish Tapeworm). It competes with the host for Vitamin B12 in the proximal jejunum. Humans acquire the infection by consuming undercooked fish containing the **Plerocercoid larva**. **Analysis of Options:** * **C. Plerocercoid (Correct):** This is the third-stage larva found in the muscles of freshwater fish and is the **infective stage** for humans. * **A. Miracidium:** The first larval stage of **Trematodes** (flukes), which infects the intermediate host (snail). * **B. Coracidium:** The ciliated first-stage larva of _D. latum_ that hatches from the egg and is ingested by the first intermediate host (Cyclops). * **D. Procercoid:** The second-stage larva of _D. latum_ that develops inside the Cyclops. **High-Yield Clinical Pearls for NEET-PG:** * **_D. latum_** is the largest tapeworm infecting humans (up to 10 meters). * **Mechanism:** It absorbs ~80-100% of dietary B12, leading to megaloblastic anemia. * **Diagnosis:** Identification of operculated eggs in stool. * **Treatment:** Praziquantel is the drug of choice.

Q: Arc-C-5 in countercurrent electrophoresis of serum is diagnostic of?

Hydatidosis. **Explanation:** **Hydatidosis (Cystic Echinococcosis)** is caused by the larval stage of *Echinococcus granulosus*. The diagnosis relies heavily on imaging and serology. The **Arc-5 (or Arc-C-5)** is a specific precipitation line formed during immunoelectrophoresis or countercurrent immunoelectrophoresis (CIEP) when patient serum reacts with hydatid cyst fluid (antigen 5). 1. **Why Hydatidosis is correct:** Antigen 5 is a major lipoprotein found in the hydatid cyst fluid. When subjected to electrophoresis, it forms a characteristic "Arc-5" precipitation band. This finding is considered highly specific and **diagnostic** for *E. granulosus* infection, although cross-reactivity can rarely occur with *Taenia solium*. 2. **Why other options are incorrect:** * **Cysticercosis:** Diagnosis typically involves neuroimaging (MRI/CT) and Enzyme-linked Immunoelectrotransfer Blot (EITB) for detecting antibodies against glycoprotein antigens, not Arc-5. * **Cryptococcosis:** Diagnosis is confirmed by India ink preparation, CrAg (Cryptococcal Antigen) lateral flow assay, or culture. * **Brucellosis:** Diagnosis relies on blood culture (Castaneda medium) and serological tests like the Standard Agglutination Test (SAT) or Rose Bengal Plate Test. **Clinical Pearls for NEET-PG:** * **Antigen 5 and Antigen B** are the two most important immunogenic proteins in hydatid fluid. * **Casoni’s Test:** An immediate hypersensitivity skin test formerly used for Hydatidosis, now largely replaced by serology due to low sensitivity and specificity. * **PAIR technique:** (Puncture, Aspiration, Injection, Re-aspiration) is a minimally invasive treatment for hydatid cysts. * **Echinococcus multilocularis:** Causes Alveolar Hydatid Disease (more aggressive/malignant presentation).

Q: Where does Schistosoma Japonicum reside?

Ileocecal plexus. **Explanation:** *Schistosoma japonicum* is a blood fluke that primarily inhabits the **superior mesenteric veins**, which drain the small intestine and the ascending/transverse colon. The **ileocecal plexus** is the specific anatomical site within this drainage system where the adult worms reside and deposit their eggs. **Why the other options are incorrect:** * **Vesical Plexus:** This is the primary habitat for ***Schistosoma haematobium***. It leads to urinary schistosomiasis, characterized by terminal hematuria and an increased risk of squamous cell carcinoma of the bladder. * **Systemic Circulation:** While cercariae travel through the blood to reach the liver (where they mature), the adult worms do not reside in the general systemic circulation. They live specifically in the portal venous system. * **Gallbladder:** This is a common site for liver flukes like *Clonorchis sinensis* or *Fasciola hepatica*, but not for Schistosomes. **High-Yield NEET-PG Pearls:** 1. **Habitat Mnemonic:** * *S. haematobium*: **H**ematobium = **H**ole (Bladder/Vesical plexus). * *S. mansoni*: **M**ansoni = **M**inferior (Inferior mesenteric veins/Sigmoid-rectal area). * *S. japonicum*: **J**aponicum = **J**uperior (Superior mesenteric veins/Ileocecal area). 2. **Egg Morphology:** *S. japonicum* eggs are unique for being **rounded/oval with a rudimentary lateral knob** (often difficult to see), unlike the prominent terminal spine of *S. haematobium* or the large lateral spine of *S. mansoni*. 3. **Pathology:** *S. japonicum* is associated with "Katayama Fever" and has the highest egg output, often leading to severe hepatic fibrosis and portal hypertension.

Question 1

What is the infective form of Plasmodium falciparum in the mosquito?

Accepted Answer

Gametocytes

Answer

Merozoites

Answer

Sporozoites

Answer

Trophozoites

Question 2

Which of the following diseases are transmitted by the sandfly?

Accepted Answer

Kala-azar

Answer

Oriental sore

Answer

Relapsing fever

Answer

Oraya fever

Question 3

Microscopic examination of a thin blood smear from a patient suspected of having malaria reveals numerous normal size erythrocytes without stippling but with ring stages, many with multiple ring stages and applique forms. Several erythrocytes show developing trophozoites that are spread across the erythrocytes in a band fashion. Which of the following is the most likely cause of infection?

Accepted Answer

A mixed infection with two plasmodium species

Answer

Plasmodium vivax

Answer

Plasmodium malariae

Answer

Plasmodium falciparum

Question 4

Which of the following is most severely affected in Kala-azar?

Accepted Answer

Spleen

Answer

Liver

Answer

Adrenal gland

Answer

Bone marrow

Question 5

Ascariasis causes which of the following complications?

Accepted Answer

All of the above

Answer

Appendicitis

Answer

Intestinal obstruction

Answer

Bile duct obstruction

Question 6

Which of the following parasites is known to cause anemia?

Accepted Answer

Diphyllobothrium latum

Answer

Entamoeba histolytica

Answer

Isospora belli

Answer

Trichomonas vaginalis

Question 7

A 30-year-old patient developed high fever of sudden onset. Peripheral blood smear showed crescent-shaped gametocytes. Malaria pigment was dark brown in color. Which of the following malarial parasites is the causative agent?

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium vivax

Answer

Plasmodium malariae

Answer

Plasmodium ovale

Question 8

A 50-year-old man presents with a history of abdominal pain, weakness, lightheadedness, palpitations, and shortness of breath. On examination, glossitis, hyperpigmentation of the skin of the dorsum of hands and feet, and abnormal pigmentation of hair were observed. The patient's family reports frequent episodes of increased irritability over the past year. Laboratory findings include Hb: 9gm%, MCV: 110fL, MCH: 36Pg, MCHC: 34gm/dL, Reticulocyte count: 0.1 x 10^9/L, LDH: 600 U/L, Indirect bilirubin: 1 mg/dL, S. iron: Normal, S. Ferritin: Normal, WBC: 2 x 10^9/L, and Platelet count: 90 x 10^9/L. Peripheral blood smear and bone marrow aspiration were also performed. What is the infective form of the organism causing the above condition?

Accepted Answer

Plerocercoid

Answer

Miracidium

Answer

Coracidium

Answer

Procercoid

Question 9

Arc-C-5 in countercurrent electrophoresis of serum is diagnostic of?

Accepted Answer

Hydatidosis

Answer

Cysticercosis

Answer

Cryptococcosis

Answer

Brucellosis

Question 10

Where does Schistosoma Japonicum reside?

Accepted Answer

Ileocecal plexus

Answer

Vesical Plexus

Answer

Systemic Circulation

Answer

Gallbladder

Parasitology — MCQs

Parasitology — MCQs

On this page

Practice by Chapter

Want unlimited practice?