Parasitology — MCQs
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Which of the following statements about malaria transmission is correct?
Cutaneous larva migrans is due to ?
Which of the following amoebae does not have a neuropathogenic effect?
What does the hookworm primarily feed on?
Amoebic liver abscess can be diagnosed by demonstrating-
Cylindrical helminths are -
Persons with heterozygous sickle cell trait are protected from infection by:
What is the correct sequence of the sexual cycle in malaria?
The Hanging Drop method is primarily used for studying which of the following microorganisms?
Which of the following substances is toxic to parasites?
Parasitology Indian Medical PG Practice Questions and MCQs
Question 901: Which of the following statements about malaria transmission is correct?
- A. Individuals harboring gametocytes can transmit malaria. (Correct Answer)
- B. P. vivax always completely fills the infected RBC with schizonts.
- C. Malaria can only be transmitted through blood transfusions.
- D. All stages of P. falciparum are commonly seen in peripheral blood smears.
Explanation: ***Individuals harboring gametocytes can transmit malaria.*** - **Gametocytes** are the sexual stage of the malaria parasite that circulate in the human bloodstream and are infectious to mosquitos. - When an *Anopheles* mosquito feeds on an infected human, it ingests these gametocytes, allowing the parasite's life cycle to continue in the mosquito vector, leading to transmission. *P. vivax always completely fills the infected RBC with schizonts.* - While *P. vivax* does infect **reticulocytes** (young RBCs) and can enlarge them, the **schizonts** typically occupy a significant portion but not always completely fill the host cell. - The infected RBCs are often enlarged to about 1.5 to 2 times their normal size and contain numerous **Schüffner's dots**. *Malaria can only be transmitted through blood transfusions.* - The primary mode of malaria transmission is through the bite of an **infected female *Anopheles* mosquito**. - While **blood transfusions** can transmit malaria, it is a less common and secondary route compared to vector-borne transmission. *All stages of P. falciparum are commonly seen in peripheral blood smears.* - In *P. falciparum* infections, only the **ring forms** and **gametocytes** are commonly observed in the peripheral blood smear. - The more mature asexual stages (trophozoites and schizonts) typically sequester in the capillaries of internal organs, where they are not readily visible in peripheral circulation.
Question 902: Cutaneous larva migrans is due to ?
- A. W.bancrofti
- B. B. Malayi
- C. D. medinensis
- D. Ancylostoma braziliense (Correct Answer)
Explanation: ***Ancylostoma braziliense*** - **Cutaneous larva migrans** is primarily caused by the larvae of **dog and cat hookworms**, especially *Ancylostoma braziliense*. - Humans become **accidental hosts** when these larvae penetrate the skin but cannot complete their life cycle, leading to **serpiginous tracks**. *W. bancrofti* - This parasite, **Wuchereria bancrofti**, is a filarial nematode that causes **lymphatic filariasis** (elephantiasis). - Its effects are characterized by **lymphedema** and **hydrocele**, not migrating skin lesions. *B. Malayi* - **Brugia malayi** is another filarial nematode responsible for **lymphatic filariasis** in humans, similar to *W. bancrofti*. - It primarily causes **swelling of the limbs** and scrotum, not cutaneous larva migrans. *D. medinensis* - **Dracunculus medinensis** is the parasite that causes **dracunculiasis**, also known as **Guinea worm disease**. - This infection is characterized by a **painful blister** and subsequent emergence of the adult worm, which is distinct from creeping eruptions.
Question 903: Which of the following amoebae does not have a neuropathogenic effect?
- A. Naegleria
- B. Acanthamoeba
- C. Dientamoeba (Correct Answer)
- D. Balamuthia
Explanation: ***Dientamoeba*** - *Dientamoeba fragilis* is an intestinal flagellate (often mistakenly classified as an amoeba) that causes **gastrointestinal symptoms** like diarrhea and abdominal pain. - It has **no known neuropathogenic effects** and does not invade the central nervous system. *Naegleria* - *Naegleria fowleri* is a highly virulent amoeba that causes **primary amoebic meningoencephalitis (PAM)**, a rapidly fatal infection of the central nervous system. - It typically invades the brain after **nasal insufflation** of contaminated water. *Acanthamoeba* - *Acanthamoeba* species can cause **granulomatous amoebic encephalitis (GAE)**, a subacute to chronic central nervous system infection, particularly in immunocompromised individuals. - They are also known to cause **amoebic keratitis**, a severe eye infection. *Balamuthia* - *Balamuthia mandrillaris* causes **granulomatous amoebic encephalitis (GAE)**, similar to *Acanthamoeba*, but often in both immunocompetent and immunocompromised individuals. - It can also lead to **skin lesions** and has a tropism for the brain, causing severe neurological damage.
Question 904: What does the hookworm primarily feed on?
- A. Plasma proteins
- B. Lymphatic fluid
- C. Interstitial fluid
- D. Blood from intestinal mucosa (Correct Answer)
Explanation: ***Blood from intestinal mucosa*** - Hookworms attach to the **intestinal wall** and ingest host blood, leading to blood loss and potential **anemia**. - They produce **anticoagulants** to facilitate continuous feeding from the mucosal capillaries. *Plasma proteins* - While plasma contains proteins, hookworms primarily feed directly on **whole blood**, not just isolated plasma proteins. - Feeding mainly on plasma proteins would not explain the significant **iron-deficiency anemia** associated with hookworm infection. *Lymphatic fluid* - Hookworms reside in the **small intestine** and do not typically feed on lymphatic fluid. - Other parasites, like **filarial worms**, are known to inhabit and obstruct the lymphatic system. *Interstitial fluid* - Interstitial fluid is found in the spaces between cells; hookworms feed from the **vascular supply** within the intestinal mucosa. - Feeding on interstitial fluid would not cause the characteristic **blood loss** seen in hookworm infections.
Question 905: Amoebic liver abscess can be diagnosed by demonstrating-
- A. Trophozoites in the pus (Correct Answer)
- B. Trophozoites in the feces
- C. Cysts in the pus
- D. Cysts in the liver
Explanation: ***Trophozoites in the pus*** - **Amoebic liver abscesses** are caused by the invasive **trophozoite stage** of *Entamoeba histolytica*. - Demonstrating **trophozoites** in the characteristic **'anchovy paste' pus** aspirated from the abscess cavity is diagnostic. *Cysts in the pus* - **Cysts** are the **infective stage** of *Entamoeba histolytica* and are typically found in the **feces**, not in an abscess. - Cysts are responsible for transmission and survival outside the host, but they do not cause invasive disease. *Cysts in the liver* - The disease in the liver is caused by **trophozoites**, which invade the intestinal wall and then spread to the liver. - **Cysts** are never found within the liver parenchyma or abscesses. *Trophozoites in the feces* - While **trophozoites** can be found in the feces during acute amoebic dysentery, their presence alone does not confirm a liver abscess. - Furthermore, **trophozoites** are fragile and often difficult to detect in stool samples, especially once the stool has cooled.
Question 906: Cylindrical helminths are -
- A. Tapeworms
- B. Flukes
- C. Roundworms (Correct Answer)
- D. Hookworms
Explanation: ***Roundworms*** - **Roundworms**, also known as **nematodes**, are characterized by their **cylindrical body shape**. - Their unsegmented, tapered bodies distinguish them from flatworms like tapeworms and flukes. *Tapeworms* - **Tapeworms**, or **cestodes**, have **flat, ribbon-like bodies** segmented into proglottids. - They are not cylindrical but rather dorsoventrally flattened. *Flukes* - **Flukes**, or **trematodes**, have **flat, leaf-shaped bodies**, which are not cylindrical. - Their morphology includes suckers for attachment and they are not segmented. *Hookworms* - **Hookworms** are a type of **roundworm** (nematode), which means they are cylindrical. However, "Roundworms" is a broader and more accurate classification for the general term "cylindrical helminths." - While hookworms are indeed cylindrical, the option "Roundworms" encompasses all such cylindrical helminths, making it a more general and appropriate answer.
Question 907: Persons with heterozygous sickle cell trait are protected from infection by:
- A. Pneumococcus
- B. P. falciparum (Correct Answer)
- C. P. vivax
- D. Salmonella
Explanation: ***P. falciparum*** - Individuals with heterozygous sickle cell trait have a **protective effect** against severe malaria caused by *P. falciparum* due to altered red blood cell morphology [1][2]. - The sickle hemoglobin (HbAS) provides a **selective advantage**, reducing the severity of malaria infections and the parasitic load [2][3]. *P. vivax* - Sickle cell trait does not confer significant protection against *P. vivax*, which primarily infects non-sickled red blood cells [2]. - The infection still occurs in individuals with the trait because it specifically affects the reticulocyte count, which is less impacted by sickling. *Salmonella* - While sickle cell disease is linked with increased susceptibility to **Salmonella infections**, the sickle cell trait itself does not provide protection against it [2]. - The trait does not influence immunity or susceptibility to bacterial pathogens like *Salmonella*. *Pneumococcus* - Individuals with sickle cell trait still have a normal risk of **invasive pneumococcal disease**, similar to those without the trait [2]. - Protection against *Pneumococcus* primarily relates to vaccination status and not to hemoglobinopathies. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 398-400. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 598-599. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 50-51.
Question 908: What is the correct sequence of the sexual cycle in malaria?
- A. Sporozoites to gametocytes
- B. Gametocytes to gametes
- C. Gametocytes to sporozoites (Correct Answer)
- D. Gametes to zygote
Explanation: ***Gametocytes to sporozoites*** - The sexual cycle begins when a mosquito ingests **gametocytes** during a blood meal. - These gametocytes develop into **gametes**, which fuse to form a **zygote**. The zygote matures into an **oocyst** and then releases **sporozoites**, which migrate to the mosquito's salivary glands, ready to infect a new human host. *Gametocytes to gametes* - This is an initial step within the sexual cycle where gametocytes differentiate into **male and female gametes**, respectively. - However, it's not the complete *sequence* of the sexual cycle, as it omits subsequent crucial stages like fertilization and sporozoite formation. *Sporozoites to gametocytes* - **Sporozoites** are injected into a human host and initiate the asexual cycle by infecting liver cells, then red blood cells. - **Gametocytes** are formed later during the asexual cycle in the human host, ready to be picked up by another mosquito; this sequence describes part of the human infection, not the sexual cycle in the mosquito. *Gametes to zygote* - This step represents **fertilization**, where male and female gametes fuse, forming a **zygote** in the mosquito gut. - While essential, it is only one part of the overall sexual cycle and doesn't encompass the full transformation from gametocytes to infective sporozoites.
Question 909: The Hanging Drop method is primarily used for studying which of the following microorganisms?
- A. Trichomonas vaginalis (Correct Answer)
- B. Plasmodium falciparum
- C. Toxoplasma gondii
- D. Cryptosporidium parvum
Explanation: ***Trichomonas vaginalis*** - The **hanging drop method** is excellent for observing the **motility** of this parasite, which is crucial for its identification due to its characteristic jerky, tumbling movement. - This method helps differentiate it from other non-motile organisms in vaginal fluid samples. *Plasmodium falciparum* - This parasite is primarily identified through examination of **blood smears** (thick and thin films) for its characteristic **intraerythrocytic stages** (rings, trophozoites, schizonts, gametocytes). - It is an **intracellular parasite** and does not exhibit free motility in a hanging drop preparation. *Toxoplasma gondii* - Diagnosis typically involves **serological tests** for antibodies or **PCR** for detecting parasitic DNA, as well as histological examination of tissue biopsies. - While it can move, it's an **obligate intracellular parasite** and is not primarily identified by its motility in a simple hanging drop preparation from clinical samples. *Cryptosporidium parvum* - This parasite is diagnosed by detecting its **oocysts in stool samples** using specialized staining techniques like **acid-fast stain** or immunofluorescence assays. - The oocysts are non-motile and are not identified using the hanging drop method.
Question 910: Which of the following substances is toxic to parasites?
- A. Peroxidase (Correct Answer)
- B. Interferon-alpha
- C. IL-2 (Interleukin-2)
- D. IL-6 (Interleukin-6)
Explanation: ***Peroxidase*** - **Peroxidase** enzymes, especially those produced by **eosinophils**, generate toxic oxygen metabolites and hypohalous acids that are highly effective at damaging and killing parasites. - This enzyme plays a crucial role in the host's defense against larger parasites, such as **helminths (worms)**. *Interferon-alpha* - **Interferon-alpha** is an important cytokine primarily known for its **antiviral effects** and its role in activating natural killer (NK) cells. - While it modulates immune responses, it does not directly act as a toxic substance to parasites. *IL-2 (Interleukin-2)* - **IL-2** is a growth factor that primarily promotes the **proliferation and differentiation of T cells**, enhancing adaptive immune responses. - It does not directly kill parasites but rather supports the immune cells involved in parasite clearance. *IL-6 (Interleukin-6)* - **IL-6** is a pleiotropic cytokine involved in **inflammation, acute phase responses**, and the differentiation of B cells and T cells. - While it contributes to overall immune regulation, it lacks direct parasiticidal activity.
Practice by Chapter
Classification of Parasites
Practice Questions
Intestinal Protozoa
Practice Questions
Blood and Tissue Protozoa
Practice Questions
Malaria Parasites
Practice Questions
Leishmaniasis
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Intestinal Helminths: Nematodes
Practice Questions
Tissue Nematodes
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Trematodes
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Cestodes
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Ectoparasites
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Antiparasitic Drugs
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Laboratory Diagnosis of Parasitic Infections
Practice Questions
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