Parasitology — MCQs
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Which organism serves as an intermediate host for the Guinea worm?
In which of the following diseases does the cat act as a reservoir?
Endemic hemoptysis is caused by which parasite?
What type of development cycle does microfilaria undergo in a mosquito?
Which of the following is the infective form of Plasmodium falciparum for humans?
The NIH swab is used to demonstrate which of the following parasites?
Megaloblastic anemia is caused by which of the following parasites?
Two nuclei at the tail tip is seen in which of the following?
Which vector transmits diseases caused by both Rickettsia and Orientia?
What is the infective stage of Plasmodium vivax for mosquitoes?
Parasitology Indian Medical PG Practice Questions and MCQs
Question 351: Which organism serves as an intermediate host for the Guinea worm?
- A. Malaria
- B. Guinea worm (Correct Answer)
- C. Rabies
- D. Salmonella
Explanation: **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).
Question 352: In which of the following diseases does the cat act as a reservoir?
- A. Toxoplasma gondii (Correct Answer)
- B. Rabies
- C. Streptocerca infection
- D. Plague
Explanation: **Explanation:** **Toxoplasma gondii (Correct Answer):** Cats (and other felids) are the **definitive hosts** and primary reservoirs for *Toxoplasma gondii*. This is the only host in which the parasite undergoes its sexual cycle, resulting in the excretion of infective **oocysts** in cat feces. Humans typically acquire the infection through the ingestion of these oocysts (via contaminated soil or water) or by consuming undercooked meat containing tissue cysts. **Analysis of Incorrect Options:** * **Rabies:** While cats can transmit rabies, the primary reservoirs are wild carnivores (like raccoons, skunks, and foxes) and bats. In urban settings, domestic dogs are the most significant source of human infection. * **Streptocerca infection:** *Mansonella streptocerca* is a filarial nematode. The reservoir is primarily humans and non-human primates (monkeys); it is transmitted by *Culicoides* biting midges. * **Plague:** The primary reservoirs for *Yersinia pestis* are **wild rodents** (e.g., rats, ground squirrels). Cats are highly susceptible and can transmit the disease to humans (pneumonic or bubonic), but they are considered accidental hosts rather than the primary reservoir. **High-Yield Clinical Pearls for NEET-PG:** * **Congenital Toxoplasmosis Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Diagnosis:** Sabin-Feldman Dye Test (Gold Standard) and Tachyzoites in Giemsa stain. * **HIV/Immunocompromised:** Most common cause of CNS mass lesions (Ring-enhancing lesions on MRI). * **Treatment:** Pyrimethamine + Sulfadiazine (with Folinic acid to prevent bone marrow suppression).
Question 353: Endemic hemoptysis is caused by which parasite?
- A. Hymenolepis nana
- B. Diphyllobothrium latum
- C. Clonorchis sinensis
- D. Paragonimus westermanii (Correct Answer)
Explanation: **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.
Question 354: What type of development cycle does microfilaria undergo in a mosquito?
- A. Cyclo-developmental (Correct Answer)
- B. Cyclo-propagative
- C. Propagative
- D. Cyclical
Explanation: ### Explanation In medical parasitology, the relationship between a parasite and its vector is classified based on whether the parasite undergoes structural changes (development) or increases in number (multiplication). **1. Why "Cyclo-developmental" is correct:** Microfilariae (e.g., *Wuchereria bancrofti*) undergo **Cyclo-developmental** transmission. This means the parasite undergoes essential morphological changes (from L1 to L3 larvae) within the mosquito, but **no multiplication** occurs. One microfilaria ingested by the mosquito results in only one infective larva. **2. Analysis of Incorrect Options:** * **Propagative (C):** The parasite undergoes multiplication but no structural change. Example: Plague bacilli (*Yersinia pestis*) in rat fleas. * **Cyclo-propagative (B):** The parasite undergoes both structural development and multiplication. Example: *Plasmodium* (Malaria) in the Anopheles mosquito. * **Cyclical (D):** This is a general term often used interchangeably with cyclo-developmental in some contexts, but "Cyclo-developmental" is the specific technical term required for filarial parasites in NEET-PG. **3. Clinical Pearls for NEET-PG:** * **Infective Stage:** The **L3 (filariform) larva** is the infective stage for humans, transmitted via the mosquito bite. * **Diagnostic Stage:** The **Microfilaria** (found in peripheral blood, usually with nocturnal periodicity). * **Mosquito Vectors:** *Culex quinquefasciatus* is the most common vector for *W. bancrofti* in India. * **Key Distinction:** Remember, for Filaria and Guinea worm (*Dracunculus*), the rule is: **Change in form, but no change in number.**
Question 355: Which of the following is the infective form of Plasmodium falciparum for humans?
- A. Merozoites
- B. Sporozoites (Correct Answer)
- C. Hypnozoite
- D. Trophozoites
Explanation: **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.
Question 356: The NIH swab is used to demonstrate which of the following parasites?
- A. Enterobius (Correct Answer)
- B. Trichuris
- C. Ancyclostoma
- D. Necator
Explanation: **Explanation:** The **NIH (National Institutes of Health) swab** is the diagnostic gold standard for **Enterobius vermicularis** (Pinworm/Threadworm). **Why Enterobius is correct:** Unlike most intestinal helminths, *Enterobius vermicularis* does not typically lay eggs in the lumen of the bowel. Instead, the gravid female migrates out of the anus at night to deposit eggs on the **perianal skin**. Therefore, routine stool examinations are often negative (only 5-10% sensitivity). The NIH swab—consisting of a glass rod tipped with cellophane tape—is used to scrape the perianal folds to collect these eggs for microscopic identification. **Why the other options are incorrect:** * **B. Trichuris (Whipworm):** Eggs are laid in the colon and passed directly in feces. Diagnosis is made via **stool microscopy** (identifying characteristic barrel-shaped eggs with bipolar plugs). * **C. Ancyclostoma & D. Necator (Hookworms):** These parasites reside in the small intestine and release eggs into the stool. Diagnosis is confirmed by **stool microscopy** or culture methods like Harada-Mori if larval identification is required. **Clinical Pearls for NEET-PG:** * **Clinical Presentation:** The hallmark symptom is **Pruritus ani** (nocturnal perianal itching) due to the allergic reaction to the female worm's migration. * **Diagnosis:** The swab should be taken **early in the morning** before bathing or defecation. * **Morphology:** Eggs are **planoconvex** (D-shaped) and contain a coiled larva. * **Treatment:** Albendazole or Mebendazole; it is crucial to **treat the entire family** simultaneously to prevent reinfection.
Question 357: Megaloblastic anemia is caused by which of the following parasites?
- A. Diphyllobothrium latum (Correct Answer)
- B. Hymenolepis nana
- C. Taenia saginata
- D. Echinococcus granulosus
Explanation: **Explanation:** The correct answer is **Diphyllobothrium latum** (the Fish Tapeworm). **Why Diphyllobothrium latum is correct:** *Diphyllobothrium latum* is the largest tapeworm infecting humans. It has a unique affinity for **Vitamin B12 (Cobalamin)**. The adult worm competes with the host for B12 absorption in the small intestine, absorbing up to 80-100% of the dietary intake. This leads to a secondary Vitamin B12 deficiency, resulting in **Megaloblastic Anemia** (also known as "Bothriocephalus anemia") and potential neurological symptoms similar to subacute combined degeneration of the spinal cord. **Why the other options are incorrect:** * **Hymenolepis nana (Dwarf Tapeworm):** It is the most common tapeworm but typically causes mild gastrointestinal symptoms or autoinfection. It does not interfere with B12 metabolism. * **Taenia saginata (Beef Tapeworm):** While it can grow very large, it generally causes vague abdominal pain or indigestion but does not cause megaloblastic anemia. * **Echinococcus granulosus (Dog Tapeworm):** This parasite causes **Hydatid cyst disease**, primarily affecting the liver and lungs. It does not reside in the intestinal lumen as an adult worm in humans and thus does not cause nutrient malabsorption. **High-Yield Clinical Pearls for NEET-PG:** * **Infection Source:** Consumption of undercooked/raw freshwater fish (containing **Plerocercoid larvae**). * **Diagnostic Feature:** Operculated eggs in stool (unembryonated). * **Treatment:** Praziquantel is the drug of choice. * **Key Association:** Always link "Fish Tapeworm" with "Vitamin B12 deficiency" and "Megaloblastic Anemia" in parasitology questions.
Question 358: Two nuclei at the tail tip is seen in which of the following?
- A. Brugia malayi (Correct Answer)
- B. Wuchereria bancrofti
- C. Onchocerca volvulus
- D. Mansonella ozzardi
Explanation: 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.
Question 359: Which vector transmits diseases caused by both Rickettsia and Orientia?
- A. Rat flea
- B. Tick
- C. Louse
- D. Trombiculid mite (Correct Answer)
Explanation: **Explanation** The correct answer is **D. Trombiculid mite**. **Why it is correct:** The genus *Orientia* (specifically *Orientia tsutsugamushi*) is the causative agent of **Scrub Typhus**, which is transmitted by the larval stage (chigger) of the **Trombiculid mite**. While *Orientia* was previously classified under the genus *Rickettsia*, it is now a separate genus. However, the Trombiculid mite also acts as a vector for certain *Rickettsia* species in specific ecological niches. Crucially, in the context of medical entrance exams, the Trombiculid mite is the definitive vector associated with the "Tsutsugamushi" group, bridging the clinical presentation of rickettsial-like illnesses. **Why other options are incorrect:** * **Rat flea (*Xenopsylla cheopis*):** Transmits *Rickettsia typhi* (Endemic/Murine typhus) and *Yersinia pestis* (Plague), but not *Orientia*. * **Tick:** Transmits *Rickettsia rickettsii* (Rocky Mountain Spotted Fever) and *Rickettsia conorii* (Indian Tick Typhus), but is not a vector for *Orientia*. * **Louse (*Pediculus humanus corporis*):** Transmits *Rickettsia prowazekii* (Epidemic typhus), but not *Orientia*. **High-Yield Clinical Pearls for NEET-PG:** * **Scrub Typhus Triad:** Fever, headache, and a characteristic **Eschar** (a black, necrotic scab at the mite bite site). * **Weil-Felix Test:** A heterophile agglutination test used for diagnosis. Scrub typhus (*Orientia*) shows a positive reaction with **OX-K**, while failing to react with OX-2 or OX-19. * **Drug of Choice:** Doxycycline is the gold standard treatment for both Rickettsial and Orientia infections. * **Transovarial Transmission:** In Trombiculid mites, the pathogen is passed from the adult to the egg, maintaining the reservoir in nature.
Question 360: What is the infective stage of Plasmodium vivax for mosquitoes?
- A. Gametocyte (Correct Answer)
- B. Sporozoite
- C. Zygote
- D. Merozoite
Explanation: **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*.
Practice by Chapter
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