Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 831: All of the following helps in the diagnosis of leishmaniasis except:

A. Immobilisation test (Correct Answer)
B. Examination of the bone marrow
C. Blood smear
D. Aldehyde test

Explanation: ***Immobilisation test*** - The **immobilisation test** is used to detect antibodies that inhibit the motility of organisms like *Trypanosoma cruzi* (Chagas disease), not *Leishmania*. - This test is not relevant for the diagnosis of leishmaniasis, as it targets a different parasitic mobility mechanism. *Examination of the bone marrow* - **Bone marrow aspiration** is a highly sensitive and specific method for diagnosing visceral leishmaniasis because **amastigotes** of *Leishmania* parasites are found intracellularly within macrophages in the bone marrow. - Direct visualization of the parasites in bone marrow smears confirms the diagnosis. *Blood smear* - While generally less sensitive than bone marrow aspiration, a **peripheral blood smear** can occasionally reveal **amastigotes** in circulating monocytes during the acute phase of visceral leishmaniasis. - However, its diagnostic utility is limited as the parasitic load in peripheral blood is often low. *Aldehyde test* - The **formol gel test** (also known as the **aldehyde test** or Napier's aldehyde test) is a non-specific test for **hypergammaglobulinemia**, which is a common finding in long-standing visceral leishmaniasis. - A positive result (gelation of serum after adding formaldehyde) suggests chronic infection but does not specifically confirm leishmaniasis nor differentiate it from other chronic inflammatory conditions.

Question 832: 18 years old male developed meningitis 5 days after taking a bath in a pond. The likely causative organism -

A. Naegleria fowleri (Correct Answer)
B. Cryptococcus
C. Enterococcus
D. Meningococcus

Explanation: ***Naegleria fowleri*** - This amoeba is known to cause **primary amoebic meningoencephalitis (PAM)**, a rapidly fatal brain infection. - Infection typically occurs when individuals swim in **warm fresh water**, such as ponds or lakes, allowing the amoeba to enter the brain via the nasal passages. - The **incubation period is typically 1-9 days** (commonly around 5 days), which matches the clinical timeline in this case. *Cryptococcus* - **Cryptococcal meningitis** is an opportunistic infection typically seen in immunocompromised individuals, such as those with HIV/AIDS. - It is usually acquired by inhaling fungal spores from the environment, not directly from swimming in ponds. *Enterococcus* - **Enterococcus** is a bacterium that can cause meningitis, particularly in neonates, the elderly, or those with underlying medical conditions or hospital-acquired infections. - It is not typically associated with exposure to pond water as a primary risk factor for meningitis. *Meningococcus* - **Neisseria meningitidis (Meningococcus)** is a common bacterial cause of meningitis, often transmitted person-to-person through respiratory droplets. - While it causes meningitis, its transmission is not linked to swimming in ponds.

Question 833: All of the following are known to cause biliary obstruction EXCEPT:

A. Fasciola
B. Ancylostoma (Correct Answer)
C. Ascariasis
D. Clonorchis

Explanation: ***Ancylostoma*** - **Ancylostoma**, or **hookworm**, primarily infects the small intestine, causing **iron deficiency anemia** due to blood loss. - It does not directly obstruct the biliary tree as it does not migrate there. *Fasciola* - **Fasciola hepatica**, the **sheep liver fluke**, can migrate to the **biliary ducts** and cause inflammation, fibrosis, and obstruction. - Its presence can lead to **cholangitis**, **cholecystitis**, and **formation of gallstones**. *Ascariasis* - **Ascaris lumbricoides**, a large intestinal nematode, can **migrate from the gut** into the **biliary tree** through the ampulla of Vater. - This can cause **acute cholangitis**, **pancreatitis**, or even **biliary obstruction** due to the physical presence of the worms. *Clonorchis* - **Clonorchis sinensis**, the **Chinese liver fluke**, specifically inhabits the **biliary ducts** of its human host. - Chronic infection can lead to profound **biliary obstruction**, **cholangitis**, and is a significant risk factor for **cholangiocarcinoma**.

Question 834: Which component of breast milk provides the primary protection against gastrointestinal infections in newborns?

A. Lysozyme
B. Complement C3
C. Lactoferrin
D. Secretory IgA (Correct Answer)

Explanation: ***Secretory IgA*** - Breast milk contains **secretory IgA (sIgA)**, which is the **primary antibody** providing mucosal immunity in the infant's gastrointestinal tract. - sIgA **binds to pathogens** (bacteria, viruses, parasites) and prevents their adherence to the intestinal epithelium, thus offering the **most important protection** against gastrointestinal infections. - It is present in **high concentrations** in colostrum and mature breast milk, and is **resistant to gastric acid and proteolytic enzymes**. - Provides protection against pathogens like **rotavirus, E. coli, Giardia, Shigella**, and other enteric organisms. *Lactoferrin* - Lactoferrin is an **iron-binding glycoprotein** that has antimicrobial properties by sequestering iron needed by pathogenic bacteria. - While it provides some protection, it is **not the primary** protective component against GI infections. *Lysozyme* - Lysozyme is an **enzyme** that breaks down bacterial cell walls and has antimicrobial activity. - Present in breast milk but plays a **secondary role** compared to secretory IgA in gastrointestinal protection. *Complement C3* - While complement components are present in breast milk, they are in **lower concentrations** and are **not the primary** mechanism of GI protection in newborns. - Complement system provides more systemic immunity rather than mucosal protection.

Question 835: Hanging drop method is used for:

A. Toxoplasma
B. Cryptosporidium
C. Trichomonas (Correct Answer)
D. Plasmodium

Explanation: ***Trichomonas*** - The **hanging drop method** is a highly effective technique for visualizing the characteristic **motility** of *Trichomonas vaginalis*. - This method allows for the observation of living, unstained organisms directly from clinical samples, making it valuable for rapid diagnosis. *Toxoplasma* - **Toxoplasma gondii** is an intracellular parasite best identified through serological tests for **antibodies** or molecular diagnostics like **PCR**. - It does not exhibit characteristic motility in a hanging drop preparation that would aid in its direct identification. *Cryptosporidium* - **Cryptosporidium** species are typically identified by detecting **oocysts** in stool samples, often using **acid-fast staining** or **immunofluorescence assays**. - Their small size and lack of distinctive motility under a hanging drop method make this technique unsuitable for their diagnosis. *Plasmodium* - **Plasmodium** species, the causative agents of malaria, are diagnosed by visualizing **parasites within red blood cells** on **Giemsa-stained blood smears**. - The hanging drop method would not effectively identify these intracellular parasites for malaria diagnosis.

Question 836: Which among the following doesn't enter human body skin?

A. Trichinella (Correct Answer)
B. Necator
C. Strongyloides
D. Ancylostoma

Explanation: ***Trichinella*** - **Trichinella** species are acquired through ingestion of **undercooked meat** containing encysted larvae, primarily from pigs or wild game. They do not penetrate the skin. - The larvae mature in the intestine and then migrate to skeletal muscle, forming **cysts**. *Necator* - **Necator americanus** (New World hookworm) larvae invade the human body by **penetrating intact skin**, typically on the feet. - This invasion causes a characteristic **pruritic rash** known as "ground itch." *Strongyloides* - **Strongyloides stercoralis** larvae penetrate the skin, usually through the **feet**, to initiate infection in humans. - It is unique among intestinal nematodes due to its ability to cause **autoinfection**. *Ancylostoma* - **Ancylostoma duodenale** (Old World hookworm) larvae also enter the human body by **penetrating intact skin**, similar to Necator. - Skin penetration by Ancylostoma larvae can also lead to **ground itch**.

Question 837: All the following organisms can cause arthritis except

A. A parasitic worm causing dracunculiasis
B. A tapeworm causing hydatid disease
C. A filarial worm causing lymphatic filariasis (Correct Answer)
D. A protozoan causing malaria

Explanation: ***A filarial worm causing lymphatic filariasis*** - While **filarial infections** can cause lymphatic obstruction and systemic inflammation, they do not directly cause **arthritis**. Joint involvement is not a typical manifestation of lymphatic filariasis. - The primary pathology in **lymphatic filariasis** involves the lymphatic system, leading to lymphedema, hydrocele, and elephantiasis, rather than joint inflammation. *A parasitic worm causing dracunculiasis* - **Dracunculiasis**, caused by *Dracunculus medinensis* (Guinea worm), can lead to **arthritis** as the migrating worm or its lesions near joints cause significant inflammation and secondary bacterial infection. - The worm's migration and eventual emergence from the skin, often near joints, cause intense pain and an inflammatory response that can involve the joint space. *A tapeworm causing hydatid disease* - **Hydatid disease**, caused by *Echinococcus granulosus*, can form **hydatid cysts** in various tissues, including bone and occasionally periarticular soft tissues. - These cysts can erode into joints or cause a significant inflammatory reaction mimicking **arthritis** if they rupture or impinge on joint structures. *A protozoan causing malaria* - **Plasmodium species** causing malaria can trigger **reactive arthritis** through immune-mediated mechanisms, particularly in chronic or severe infections. - Arthralgias and frank arthritis have been documented in malaria cases, often involving multiple joints with synovial inflammation and immune complex deposition.

Question 838: Definitive host is one in which the parasite lives in which of the following forms?

A. Intermediate host
B. Asexual form
C. Larvae
D. Adult form (Correct Answer)

Explanation: ***Adult form*** - The **definitive host** is defined as the host in which the parasite reaches **sexual maturity** and undergoes **sexual reproduction**. - This typically means the **adult, sexually reproductive stage** of the parasite resides within the definitive host. *Intermediate host* - An **intermediate host** harbors the **larval** or **asexual stages** of a parasite. - It is crucial for the parasite's life cycle but does not involve sexual maturation. *Asexual form* - The **asexual form** of a parasite typically develops within an **intermediate host**. - While essential for multiplication, it does not represent the definitive host stage for sexual reproduction. *Larvae* - **Larvae** are immature forms of parasites that usually reside in an **intermediate host**. - They develop further but do not reach sexual maturity within this host.

Question 839: A 35 year old man presented with dry cough and rusty colored sputum. He has a history of eating in a Chinese restaurant very often with consumption of crabs. What is the probable causative agent in this condition?

A. Pneumocystis jirovecii
B. Paragonimus westermani (Correct Answer)
C. Strongyloides stercoralis
D. Diphyllobothrium latum

Explanation: ***Paragonimus westermani*** - The key clinical features are **dry cough**, **rusty-colored sputum**, and a history of consuming **crabs**. These are classic indicators of **paragonimiasis**. - *Paragonimus westermani* is a **lung fluke** acquired by eating undercooked freshwater crabs or crayfish. *Pneumocystis jirovecii* - This fungus typically causes pneumonia in **immunocompromised individuals**, like those with HIV/AIDS. - While it can cause a dry cough, **rusty-colored sputum** is not a characteristic sign, and there's no mention of immunocompromise. *Strongyloides stercoralis* - This parasite primarily causes **gastrointestinal symptoms** (e.g., abdominal pain, diarrhea) and can lead to cutaneous manifestations (larva currens). - While lung involvement can occur in severe cases (hyperinfection), it does not typically present with **rusty sputum** or a direct association with crab consumption. *Diphyllobothrium latum* - This is the **fish tapeworm**, acquired by eating undercooked freshwater fish. - It primarily causes **gastrointestinal symptoms** such as abdominal pain and diarrhea, and is known for causing **vitamin B12 deficiency** leading to megaloblastic anemia, not pulmonary symptoms.

Question 840: Flask-shaped ulcers in the intestine are caused by which of the following?

A. TB
B. Giardia
C. Entamoeba histolytica (Correct Answer)
D. Typhoid

Explanation: ***Entamoeba histolytica*** - *Entamoeba histolytica* is a protozoan that causes **amoebiasis**, which is characterized by **flask-shaped (bottle-shaped) ulcers** in the colon - this is the **pathognomonic feature** of intestinal amoebiasis. - The trophozoites invade the intestinal mucosa and submucosa, creating a **narrow neck at the mucosal surface** and a **wider base in the submucosa**, giving them their unique flask-like appearance. - These ulcers are most commonly found in the **cecum and ascending colon**. *TB* - Intestinal tuberculosis typically causes **transverse ulcers** (perpendicular to the bowel axis) due to lymphatic spread and caseous necrosis, often in the ileocecal region. - These ulcers are usually associated with **granulomas** and acid-fast bacilli, which are histologically distinct from flask-shaped ulcers. *Giardia* - *Giardia lamblia* (or *intestinalis*) is a flagellate that causes **giardiasis**, primarily adhering to the small intestinal villi and causing malabsorption and diarrhea. - It is **non-invasive** and does not penetrate the intestinal wall or cause ulcer formation; its pathology is mainly due to **mucosal inflammation** and villous blunting. *Typhoid* - Typhoid fever, caused by *Salmonella Typhi*, commonly leads to **longitudinal ulcers** (parallel to the bowel axis) in the **Peyer's patches** of the ileum due to bacterial invasion and necrosis of lymphoid tissue. - These ulcers may perforate but do not present with the flask-shaped morphology characteristic of amoebiasis.

Practice by Chapter

Classification of Parasites

Practice Questions

Intestinal Protozoa

Practice Questions

Blood and Tissue Protozoa

Practice Questions

Malaria Parasites

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Leishmaniasis

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Intestinal Helminths: Nematodes

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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

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