Parasitology Practice Questions

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.

Q: What is the main reservoir for Entamoeba histolytica?

Man. **Explanation:** **1. Why the Correct Answer is Right:** *Entamoeba histolytica* is an obligate human parasite. **Man is the only natural host and the primary reservoir** for this infection. The life cycle is simple and does not require an intermediate host. The reservoir consists primarily of "asymptomatic cyst passers" (chronic carriers) who discharge mature, quadrinucleated cysts in their feces. These cysts are the infective stage, and since humans are the sole source, the maintenance of the parasite in nature depends entirely on human-to-human transmission via the fecal-oral route. **2. Why the Incorrect Options are Wrong:** * **B, C, and D (Drinking water, Soil, Ponds):** These are **vehicles of transmission** or environmental media, not reservoirs. While cysts can survive in moist soil or water for several weeks, the parasite cannot multiply or maintain its population within these elements. They serve as the route through which the parasite reaches a new human host but are not the biological source. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Infective Form:** Mature quadrinucleated cyst. * **Pathogenic Form:** Trophozoite (shows "crawling" pseudopodial movement and may contain ingested RBCs—a pathognomonic feature). * **Primary Site:** Large intestine (Caecum and Sigmoid colon). * **Classic Lesion:** Flask-shaped ulcer. * **Extra-intestinal Site:** Liver is the most common site (Amoebic Liver Abscess), characterized by "Anchovy sauce" pus. * **Drug of Choice:** Metronidazole or Tinidazole (followed by a luminal amoebicide like Diloxanide furoate to eradicate the carrier state).

Q: A patient presents with subcutaneous nodules over the right iliac crest. Lymph node and skin smears show microfilariae. The patient also has eye manifestations. What is the most common filarial species involved?

Onchocerca volvulus. ### Explanation **Correct Option: B. *Onchocerca volvulus*** The clinical triad of **subcutaneous nodules** (Onchocercomas), **skin manifestations** (dermatitis/atrophy), and **ocular involvement** (River Blindness) is classic for *Onchocerca volvulus*. Unlike other filarial worms, the adult worms reside in subcutaneous nodules, and the microfilariae are found primarily in the **skin and eyes**, rather than the blood. The iliac crest is a common site for these nodules in African variants. **Analysis of Incorrect Options:** * **A. *Brugia timori*:** Primarily causes lymphatic filariasis (elephantiasis) confined to the lower limbs. Microfilariae are found in the **blood**, not skin smears. * **C. *Loa loa* (African Eye Worm):** Characterized by transient **Calabar swellings** and the migration of the adult worm across the conjunctiva. While it involves the eye, it does not typically cause the permanent blindness or the specific subcutaneous nodules (Onchocercomas) seen here. * **D. *Mansonella ozzardi*:** Generally considered non-pathogenic or causes mild symptoms like arthralgia. Microfilariae circulate in the blood. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Transmitted by the **Blackfly (*Simulium*)**, which breeds in fast-flowing rivers (hence "River Blindness"). * **Diagnosis:** The gold standard is the **Skin Snip Test** to demonstrate microfilariae. * **Mazzotti Reaction:** A severe inflammatory response (fever, rash, hypotension) occurring after treatment with Diethylcarbamazine (DEC) as microfilariae die. * **Drug of Choice:** **Ivermectin** (Note: DEC is contraindicated due to the risk of ocular damage from the Mazzotti reaction). * **Wolbachia:** *Onchocerca* harbors symbiotic *Wolbachia* bacteria; Doxycycline can be used to sterilize adult female worms.

Q: What is the normal habitat of Giardia lamblia?

Duodenum and jejunum. **Explanation:** *Giardia lamblia* (also known as *G. duodenalis* or *G. intestinalis*) is a flagellated protozoan that primarily inhabits the **duodenum and the upper part of the jejunum**. This is the correct answer because the parasite thrives in an alkaline environment rich in nutrients. After ingestion of cysts, excystation occurs in the stomach due to gastric acid, but the resulting trophozoites migrate to and colonize the small intestine, where they attach to the mucosal surface using a ventral sucking disc. **Analysis of Incorrect Options:** * **Stomach (B):** The highly acidic environment of the stomach is lethal to trophozoites. While cysts pass through the stomach, it is not a site of colonization. * **Caecum (C):** This is the typical habitat for parasites like *Entamoeba histolytica* and *Trichuris trichiura*, not *Giardia*. * **Ileum (D):** While *Giardia* may occasionally be found in the ileum, its primary site of heavy colonization and clinical significance is the proximal small intestine (duodenum/jejunum). **Clinical Pearls for NEET-PG:** * **Pathogenesis:** *Giardia* causes malabsorption (especially of fats and fat-soluble vitamins) by "carpeting" the mucosa and causing blunting of villi. * **Clinical Feature:** Characterized by foul-smelling, frothy, non-bloody steatorrhea. * **Diagnosis:** The "String Test" (Entero-test) can be used to sample duodenal contents. Stool microscopy shows "falling leaf motility" (trophozoites) or oval cysts. * **Drug of Choice:** Metronidazole or Tinidazole.

Q: Which of the following is TRUE about antigen detection tests in the diagnosis of Plasmodium falciparum, EXCEPT?

Detection of histidine-rich protein 1.. **Explanation:** Rapid Diagnostic Tests (RDTs) for Malaria are primarily based on **immunochromatographic methods** (Option A) that detect specific parasite antigens in the blood. The correct answer is **Option B** because the specific antigen detected in *Plasmodium falciparum* is **Histidine-Rich Protein 2 (HRP-2)**, not HRP-1. HRP-2 is a water-soluble protein produced by the asexual stages and young gametocytes of *P. falciparum*. It is highly specific and can remain in the bloodstream for up to 2–4 weeks even after successful treatment, sometimes leading to false-positive results during follow-up. **Analysis of other options:** * **Option C:** **Parasite Lactate Dehydrogenase (pLDH)** is an enzyme produced by the glycolytic pathway of all four human malaria species. Tests detecting pLDH can differentiate between *P. falciparum* and non-falciparum species. * **Option D:** **Plasmodium Glutamate Dehydrogenase (pGDH)** is another metabolic enzyme used as a diagnostic marker for all *Plasmodium* species. * **Option A:** These tests are indeed **immunochromatographic** "dipstick" or "cassette" tests, providing results within 15–20 minutes without the need for microscopy. **High-Yield Clinical Pearls for NEET-PG:** * **HRP-2:** Specific to *P. falciparum* only. * **pLDH & pGDH:** Common to all species (Pan-malarial markers). * **Prozone Phenomenon:** Very high parasitemia can lead to false-negative RDT results. * **Gold Standard:** Peripheral Blood Smear (Thin for species identification, Thick for parasite density) remains the gold standard for malaria diagnosis.

Q: What is the diagnostic method for cryptosporidiosis in fecal matter?

Ziehl-Neelsen stain of the stool. **Explanation:** **1. Why Option A is Correct:** *Cryptosporidium parvum* is a coccidian parasite that causes self-limiting diarrhea in immunocompetent individuals and life-threatening, chronic watery diarrhea in immunocompromised patients (e.g., HIV/AIDS). The diagnostic stage is the **oocyst**, which is excreted in feces. These oocysts are **acid-fast**, meaning they contain mycolic acid-like substances in their cell walls that retain carbol fuchsin stain even after decolorization with acid. Therefore, a **Modified Ziehl-Neelsen (ZN) stain** (using a weaker decolorizer like 1-3% sulfuric acid) is the gold standard for visualizing bright red/pink spherical oocysts against a blue background. **2. Why Other Options are Incorrect:** * **B. Gram stain:** This is used for bacteria. While *Cryptosporidium* may appear as Gram-positive "ghost cells," it is not a definitive or reliable diagnostic method. * **C. Normal saline suspension:** Used primarily to detect motile trophozoites (e.g., *Giardia* or *E. histolytica*). *Cryptosporidium* oocysts are too small (4-6 µm) and colorless to be reliably identified in a simple saline wet mount. * **D. Iodine suspension:** Used to highlight nuclear details of protozoal cysts. However, *Cryptosporidium* oocysts do not take up iodine well and remain indistinguishable from yeast cells or debris. **3. NEET-PG High-Yield Pearls:** * **Size:** *Cryptosporidium* oocysts are **4-6 µm** (smaller than *Cyclospora* at 8-10 µm and *Isospora* at 25-30 µm). * **Acid-fastness:** All three intestinal coccidia (*Cryptosporidium, Cyclospora, Isospora*) are acid-fast. * **Infective dose:** Very low (as few as 10-100 oocysts). * **Treatment:** **Nitazoxanide** is the drug of choice for immunocompetent patients; HAART is the priority for HIV patients. * **Alternative Diagnosis:** Enzyme-linked immunosorbent assay (ELISA) or Immunofluorescence (DFA) are more sensitive than microscopy.

Q: Which of the following parasites does not enter the body by skin penetration?

Dracunculus. The correct answer is **Dracunculus medinensis** (Guinea worm). ### 1. Why Dracunculus is the Correct Answer Unlike the other parasites listed, *Dracunculus medinensis* is transmitted via the **fecal-oral (ingestion) route**. Infection occurs when a person drinks unfiltered water containing **Cyclops** (water fleas) infected with L3 larvae. Once ingested, the larvae are released in the stomach, penetrate the intestinal wall, and mature in the retroperitoneal space. While the adult female eventually creates a blister to *exit* through the skin, it never *enters* via skin penetration. ### 2. Analysis of Incorrect Options (Skin Penetrators) The other three options are classic examples of parasites that enter the body by penetrating intact skin (usually the feet): * **Ancylostoma duodenale & Necator americanus (Hookworms):** The filariform larvae (L3) penetrate the skin, causing "ground itch," and migrate via the lungs to the small intestine. * **Strongyloides stercoralis:** Similar to hookworms, the filariform larvae penetrate the skin. It is unique because it can also cause **autoinfection**, where larvae penetrate the perianal skin or intestinal mucosa. ### 3. NEET-PG High-Yield Pearls To remember parasites that penetrate the skin, use the mnemonic **"SANN"**: * **S**trongyloides stercoralis * **A**ncylostoma duodenale * **N**ecator americanus * **N**on-human hookworms (causing Cutaneous Larva Migrans) * *Note:* **Schistosoma** (Cercariae) also enters via skin penetration. **Key Fact:** India was declared free of Guinea worm disease by the WHO in 2000. The intermediate host is **Cyclops**, and the definitive host is **Humans**.

Question 1

Which of the following can cause spinal cord compression?

Accepted Answer

Cysticercosis

Answer

Ankylostomiasis

Answer

Echinococcus Granulosus

Answer

Visceral larva migrans

Question 2

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 3

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

Accepted Answer

Toxoplasmosis

Answer

Hydatid disease

Answer

Kala-azar

Answer

Toxocara canis

Question 4

What is the main reservoir for Entamoeba histolytica?

Accepted Answer

Man

Answer

Drinking water

Answer

Soil

Answer

Ponds

Question 5

A patient presents with subcutaneous nodules over the right iliac crest. Lymph node and skin smears show microfilariae. The patient also has eye manifestations. What is the most common filarial species involved?

Accepted Answer

Onchocerca volvulus

Answer

Brugia timori

Answer

Loa loa

Answer

Mansonella ozzardi

Question 6

Which of the following statements is true about toxoplasmosis?

Accepted Answer

Maximum damage in the 1st trimester and maximum transmission in the 3rd trimester

Answer

Maximum transmission and damage in the 1st trimester

Answer

Maximum transmission in the 1st trimester and maximum damage in the 3rd trimester

Answer

Maximum transmission and damage in the 3rd trimester

Question 7

What is the normal habitat of Giardia lamblia?

Accepted Answer

Duodenum and jejunum

Answer

Stomach

Answer

Caecum

Answer

Ileum

Question 8

Which of the following is TRUE about antigen detection tests in the diagnosis of Plasmodium falciparum, EXCEPT?

Accepted Answer

Detection of histidine-rich protein 1.

Answer

It is an immunochromatographic test.

Answer

Detection of lactate dehydrogenase antigen.

Answer

Detection of glutamate dehydrogenase antigen.

Question 9

What is the diagnostic method for cryptosporidiosis in fecal matter?

Accepted Answer

Ziehl-Neelsen stain of the stool

Answer

Gram stain of the stool

Answer

Normal saline suspension of stool

Answer

Iodine suspension of stool

Question 10

Which of the following parasites does not enter the body by skin penetration?

Accepted Answer

Dracunculus

Answer

Necator americanus

Answer

Ancylostoma duodenale

Answer

Strongyloides

Parasitology — MCQs

Parasitology — MCQs

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