Parasitology Practice Questions

Q: A dog trainer presented with recurrent fever and weight loss since a few days. The liver and spleen have enlarged. Blood investigations show eosinophilia. Visceral larva migrans is suspected. What is the causative organism?

Toxocara canis. **Explanation:** **1. Why Toxocara canis is correct:** Visceral Larva Migrans (VLM) is a clinical syndrome caused by the migration of second-stage larvae of nematodes through human tissues. The most common causative agent is **Toxocara canis** (dog roundworm). * **Pathogenesis:** Humans (accidental hosts) ingest embryonated eggs from soil contaminated with dog feces. The larvae hatch in the intestine, penetrate the wall, and migrate to the liver, lungs, and other organs. * **Clinical Presentation:** As seen in this case, it typically presents in individuals with close animal contact (dog trainer) with fever, hepatosplenomegaly, and marked **peripheral eosinophilia** (a hallmark of migrating helminths). **2. Why other options are incorrect:** * **Ascariasis (*Ascaris lumbricoides*):** While it can cause Loeffler’s syndrome (transient pulmonary eosinophilia), the adult worms typically reside in the human intestine. It does not cause the chronic systemic larval migration seen in VLM. * **Schistosomiasis:** This is a trematode infection (blood fluke) acquired through skin penetration in contaminated water. It causes "Swimmer's itch" or Katayama fever, but is not the cause of VLM. * **Loa Loa (African Eye Worm):** This filarial nematode is transmitted by the *Chrysops* fly. It is characterized by Calabar swellings (subcutaneous edema) and subconjunctival migration, not visceral organ involvement. **3. High-Yield Clinical Pearls for NEET-PG:** * **Ocular Larva Migrans (OLM):** Also caused by *Toxocara canis*; it can mimic retinoblastoma on fundoscopy. * **Diagnosis:** Primarily clinical and serological (ELISA for secretory-excretory antigens). Stool examination is **useless** because the larvae do not develop into egg-laying adults in humans. * **Treatment:** Albendazole is the drug of choice. * **Cutaneous Larva Migrans:** Most commonly caused by *Ancylostoma braziliense* (dog/cat hookworm).

Q: Which tapeworm can be transmitted directly from human to human?

Dwarf Tapeworm. **Explanation:** The correct answer is **Dwarf Tapeworm (*Hymenolepis nana*)**. **Why it is correct:** *Hymenolepis nana* is unique among tapeworms because it is the only one that does not mandatory require an intermediate host to complete its life cycle. It can be transmitted via the **fecal-oral route** (ingestion of eggs from contaminated hands or food). Furthermore, it is capable of **internal autoinfection**, where eggs hatch within the intestine and develop into larvae (cysticercoids) without ever leaving the host. This direct mode of transmission allows for easy human-to-human spread, especially in crowded environments or among children. **Why the other options are incorrect:** * **A. Fish Tapeworm (*Diphyllobothrium latum*):** Requires two intermediate hosts (Cyclops and freshwater fish). Humans are infected by eating undercooked fish. * **B. Beef Tapeworm (*Taenia saginata*):** Requires cattle as an intermediate host. Humans are infected by eating "measly beef" containing cysticerci. * **C. Dog Tapeworm (*Echinococcus granulosus*):** Humans are accidental intermediate hosts (dead-end) infected by ingesting eggs from dog feces. It does not spread human-to-human. **High-Yield Clinical Pearls for NEET-PG:** * **Smallest Cestode:** *H. nana* is the smallest tapeworm infecting the human intestine. * **Morphology:** The egg has a characteristic **double membrane** with **polar filaments** (a classic "basket-like" appearance). * **Treatment:** **Praziquantel** is the drug of choice. * **Life Cycle:** It is the only tapeworm that can complete its entire life cycle (egg to adult) in a single host.

Q: Which of the following is the vector for a disease characterized by specific findings on polarized microscopy?

Ixodes scapularis tick. The question hinges on identifying the disease associated with **polarized microscopy** and its corresponding vector. ### **1. Why Option B is Correct** The disease characterized by specific findings on polarized microscopy is **Babesiosis**, caused by *Babesia microti*. * **The Finding:** Under polarized light, the intraerythrocytic parasites (specifically the **Maltese Cross** or tetrad forms) exhibit **birefringence**. This is a high-yield diagnostic feature used to differentiate *Babesia* from *Plasmodium falciparum* in blood smears. * **The Vector:** *Babesia* is transmitted by the **Ixodes scapularis** tick (the same vector for Lyme disease and Anaplasmosis). ### **2. Why Other Options are Incorrect** * **A. Anopheles mosquito:** Vector for **Malaria**. While malaria presents with ring forms similar to Babesia, it does not show the "Maltese Cross" birefringence under polarized microscopy. Malaria is associated with *hemozoin* pigment, which is birefringent, but the question specifically points to the diagnostic "Maltese Cross" of Babesia. * **C. Louse:** Vector for **Epidemic Typhus** (*Rickettsia prowazekii*), Relapsing fever (*Borrelia recurrentis*), and Trench fever. None of these are diagnosed via polarized microscopy of RBCs. * **D. Rat flea:** Vector for **Bubonic Plague** (*Yersinia pestis*) and **Endemic Typhus** (*Rickettsia typhi*). Diagnosis is usually via culture, serology, or Wayson stain (safety-pin appearance). ### **3. High-Yield Clinical Pearls for NEET-PG** * **Babesia Triad:** Hemolytic anemia, jaundice, and fever in a patient from an endemic area (e.g., Northeastern USA). * **Maltese Cross:** Pathognomonic for *Babesia*. * **Co-infection:** Always remember that *Ixodes* ticks can co-transmit **Babesia, Borrelia burgdorferi (Lyme), and Anaplasma**. * **Treatment:** Atovaquone + Azithromycin (unlike Malaria, which uses Chloroquine/Artesunate).

Q: Which of the following is an infective form of Ascaris?

Embryonated egg. **Explanation:** The life cycle of *Ascaris lumbricoides* (Giant Roundworm) is unique because it does not require an intermediate host. The correct answer is **Embryonated egg** because the eggs passed in human feces are unsegmented and non-infective. They must undergo development in the soil for 2–3 weeks to become "embryonated," containing the **rhabditiform larva (L2 stage)**, which is the specific infective stage for humans upon ingestion. **Analysis of Incorrect Options:** * **Coracidium:** This is the ciliated first-stage larva of *Diphyllobothrium latum* (Fish Tapeworm), which hatches in water to be ingested by cyclops. * **Filariform larvae (L3):** This is the infective stage for Hookworms (*Ancylostoma duodenale*) and *Strongyloides stercoralis*. These larvae infect humans via active skin penetration, not ingestion. * **Rhabditiform larvae (L1):** In *Ascaris*, this larva develops inside the egg but is not infective if it hatches outside the host. In Hookworms/Strongyloides, this is the feeding, non-infective stage found in soil or feces. **High-Yield Clinical Pearls for NEET-PG:** * **Mode of Transmission:** Fecal-oral route (ingestion of contaminated water/vegetables). * **Loeffler’s Syndrome:** Characterized by fever, cough, and eosinophilia, occurring during the pulmonary migration phase of the larvae. * **Diagnosis:** Identification of bile-stained eggs (mammillated/albuminous coat) on stool microscopy. * **Complications:** Most common cause of intestinal obstruction due to worms in children; can also cause biliary ascariasis or appendicitis. * **Treatment:** Albendazole (Drug of Choice).

Q: Which parasite is associated with Charcot-Leyden crystals in stool but lacks pus cells?

E. histolytica. ### Explanation The correct answer is **C. *Entamoeba histolytica***. **1. Why *E. histolytica* is correct:** *E. histolytica* causes amoebic dysentery. A hallmark of the stool examination in this condition is the presence of **Charcot-Leyden crystals**, which are diamond-shaped crystals formed from the breakdown of eosinophils. Crucially, amoebic dysentery is characterized by a **lack of pus cells (neutrophils)**. This occurs because the parasite produces a potent toxin (amoebic pore-forming protein) that causes **lysis of host inflammatory cells**. Therefore, while the stool contains blood and mucus, it is notably "scanty" in cellular exudate compared to bacillary dysentery. **2. Why the other options are incorrect:** * **A. Giardia:** Causes malabsorption and steatorrhea (fatty, foul-smelling stools). It does not cause mucosal invasion or significant eosinophilic response; hence, no Charcot-Leyden crystals are seen. * **B. Taenia:** These are intestinal helminths (tapeworms). While helminthic infections can cause systemic eosinophilia, they do not typically present with the acute dysenteric picture or the specific stool findings associated with *E. histolytica*. * **C. Trichomonas:** *T. vaginalis* is a urogenital parasite causing vaginitis, not an intestinal pathogen. *T. hominis* is a non-pathogenic commensal in the gut. **3. NEET-PG High-Yield Pearls:** * **Amoebic vs. Bacillary Dysentery:** Bacillary dysentery (e.g., *Shigella*) contains **abundant pus cells** and lacks Charcot-Leyden crystals. * **Stool Microscopy:** In *E. histolytica*, look for "quadrinucleate cysts" (infective stage) or "trophozoites with ingested RBCs" (diagnostic of invasive disease). * **Charcot-Leyden Crystals:** These are also found in other conditions with high eosinophil turnover, such as **bronchial asthma** (in sputum) and **Isosporiasis**.

Q: A butcher develops fatigue and lymphadenopathy after years of consuming raw, ground meat. Examination reveals intensely white focal retinal lesions with vitritis and diagnosed chorioretinitis. An older laboratory test, the Sabin-Feldman dye test, is found positive. This patient is most likely infected with which of the following organisms?

Toxoplasma gondii. ### Explanation The correct answer is **Toxoplasma gondii**. **1. Why Toxoplasma gondii is correct:** The clinical triad of **raw meat consumption** (ingestion of tissue cysts), **lymphadenopathy**, and **chorioretinitis** (characterized by focal white retinal lesions and "headlight in the fog" vitritis) is classic for Toxoplasmosis. The **Sabin-Feldman dye test** is the historical gold standard serological test for *T. gondii*. It measures IgG antibodies; if antibodies are present, they neutralize the parasite, preventing methylene blue dye from staining the live tachyzoites. **2. Why the other options are incorrect:** * **Giardia lamblia:** An intestinal protozoan causing malabsorption and foul-smelling steatorrhea. It does not cause lymphadenopathy or chorioretinitis. * **Schistosoma species:** Trematodes associated with freshwater snails. They typically cause portal hypertension (S. mansoni/japonicum) or hematuria (S. haematobium), not ocular lesions. * **Trichinella spiralis:** Also associated with raw meat (especially pork), but presents with the triad of **periorbital edema, myositis, and eosinophilia**. While it affects muscles, it does not cause the specific focal chorioretinitis seen here. **3. High-Yield NEET-PG Pearls:** * **Definitive Host:** Domestic cat (sheds oocysts in feces). * **Intermediate Host:** Humans/Mammals (tissue cysts in muscle/brain). * **Congenital Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **HIV/Immunocompromised:** Most common cause of CNS mass lesions (Ring-enhancing lesions on MRI). * **Treatment:** Pyrimethamine + Sulfadiazine (plus folinic acid to prevent bone marrow suppression).

Q: Dogs are responsible for the transmission of all the following infections except:

Toxoplasmosis. **Explanation:** The correct answer is **Toxoplasmosis** because the definitive hosts for *Toxoplasma gondii* are members of the **Felidae family (cats)**, not dogs. 1. **Toxoplasmosis (Option B):** Cats acquire the infection by eating infected rodents. The parasite undergoes its sexual cycle in the feline gut, and infectious oocysts are shed in cat feces. Humans are accidental intermediate hosts, infected via ingestion of oocysts (from soil/cat litter) or tissue cysts (undercooked meat). While dogs can be mechanical carriers if they roll in contaminated soil, they play no biological role in the parasite's life cycle. 2. **Hydatid Disease (Option A):** Caused by *Echinococcus granulosus*. The **dog is the definitive host**, harboring the adult worm in its intestine. Humans are accidental intermediate hosts infected by ingesting eggs shed in dog feces. 3. **Kala-azar (Option C):** In the transmission of Visceral Leishmaniasis (especially the Mediterranean/Zoonotic type caused by *L. infantum*), **dogs serve as the primary reservoir host**. The sandfly transmits the parasite from dogs to humans. 4. **Toxocara canis (Option D):** This is the **dog roundworm**. It causes Visceral Larva Migrans (VLM) in humans when eggs from dog feces are accidentally ingested. **NEET-PG High-Yield Pearls:** * **Definitive Host:** Where the sexual cycle occurs (Cat for *Toxoplasma*; Dog for *Echinococcus*). * **Intermediate Host:** Where the asexual cycle occurs (Human for both *Toxoplasma* and *Echinococcus*). * **Toxoplasmosis Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications (Congenital infection). * **Hydatid Cyst:** Look for "Eggshell calcification" on X-ray and "Water lily sign" on USG/CT.

Question 1

A 36-year-old man with AIDS develops right-sided weakness involving the lower, but not the upper, limb. MRI scans reveal a ring-enhancing lesion within the white matter of the left frontal lobe. A biopsy showed coagulative necrosis of brain parenchyma with macrophage-rich chronic inflammatory infiltration admixed with microscopic cysts that contain characteristic bradyzoites. What is the most common source of this type of infection?

Accepted Answer

Cats

Answer

Anopheles mosquitoes

Answer

Bird droppings

Answer

Cooling systems

Question 2

A dog trainer presented with recurrent fever and weight loss since a few days. The liver and spleen have enlarged. Blood investigations show eosinophilia. Visceral larva migrans is suspected. What is the causative organism?

Accepted Answer

Toxocara canis

Answer

Ascariasis

Answer

Schistosomiasis

Answer

Loa Loa

Question 3

Which tapeworm can be transmitted directly from human to human?

Accepted Answer

Dwarf Tapeworm

Answer

Fish Tapeworm

Answer

Beef Tapeworm

Answer

Dog Tapeworm

Question 4

Which of the following is the vector for a disease characterized by specific findings on polarized microscopy?

Accepted Answer

Ixodes scapularis tick

Answer

Anopheles mosquito

Answer

Louse

Answer

Rat flea

Question 5

Which of the following is an infective form of Ascaris?

Accepted Answer

Embryonated egg

Answer

Coracidium

Answer

Filariform larvae

Answer

Rhabditiform larvae

Question 6

Which parasite is associated with Charcot-Leyden crystals in stool but lacks pus cells?

Accepted Answer

E. histolytica

Answer

Giardia

Answer

Taenia

Answer

Trichomonas

Question 7

A company executive, who travels worldwide, presents with an upper abdominal mass and a positive Casoni's test. What is the causative organism?

Accepted Answer

Echinococcus

Answer

Entamoeba histolytica

Answer

Hepatitis

Answer

Ascariasis

Question 8

Which of the following can cause spinal cord compression?

Accepted Answer

Cysticercosis

Answer

Ankylostomiasis

Answer

Echinococcus Granulosus

Answer

Visceral larva migrans

Question 9

A butcher develops fatigue and lymphadenopathy after years of consuming raw, ground meat. Examination reveals intensely white focal retinal lesions with vitritis and diagnosed chorioretinitis. An older laboratory test, the Sabin-Feldman dye test, is found positive. This patient is most likely infected with which of the following organisms?

Accepted Answer

Toxoplasma gondii

Answer

Giardia lamblia

Answer

Schistosoma species

Answer

Trichinella spiralis

Question 10

Dogs are responsible for the transmission of all the following infections except:

Accepted Answer

Toxoplasmosis

Answer

Hydatid disease

Answer

Kala-azar

Answer

Toxocara canis

Parasitology — MCQs

Parasitology — MCQs

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