NEET-PG 2015 - Microbiology Practice Questions

Q: Trypanosoma cruzi is transmitted by which of the following?

Reduviid bug. ***Reduviid bug*** - *Trypanosoma cruzi*, the causative agent of **Chagas disease**, is primarily transmitted to humans through the feces of infected **reduviid bugs**, also known as **kissing bugs**. - The bug typically bites a person, often around the face, and then defecates near the bite wound, allowing the parasite to enter when the person scratches or rubs the area. *Tse tse fly* - The **tsetse fly** is the vector for **African trypanosomiasis** (sleeping sickness), caused by *Trypanosoma brucei*. - This fly is geographically restricted to sub-Saharan Africa, whereas *Trypanosoma cruzi* is prevalent in the Americas. *Culex mosquito* - **Culex mosquitoes** are known vectors for various diseases, including **West Nile virus**, **Japanese encephalitis**, and **filariasis**. - They are not involved in the transmission of *Trypanosoma cruzi*. *Sand fly* - **Sand flies** transmit **Leishmaniasis**, a parasitic disease caused by various species of *Leishmania*. - They are also responsible for transmitting **Bartonellosis** and some types of **Arboviruses**, but not Chagas disease.

Q: Duodenal aspirate is used in diagnosis of:

Giardia lamblia. ***Giardia lamblia*** - **Duodenal aspiration** is a highly sensitive method for detecting **Giardia lamblia trophozoites** or cysts, especially in cases where stool examination is inconclusive. - This parasite primarily inhabits the **duodenum** and **upper jejunum**, making aspirate from this region an ideal diagnostic sample. *E histolytica* - **Entamoeba histolytica** (causes amoebiasis) is typically diagnosed by identifying **trophozoites** or **cysts** in **stool samples**, or through serology for invasive disease. - While it can affect the gastrointestinal tract, its primary site of colonization and pathology is the **colon**, not the duodenum. *Taenia solium* - **Taenia solium** (pork tapeworm) is diagnosed by identifying **proglottids** or **eggs** in **stool samples**. - It resides in the **small intestine**, but **duodenal aspirate** is not a standard diagnostic method for its detection. *Leishmania* - **Leishmania species** cause **leishmaniasis**, a disease diagnosed by detecting **amastigotes** in tissue biopsies (e.g., bone marrow, spleen, skin lesions) or through serological tests. - These parasites are intracellular and do not inhabit the **duodenal lumen**, making duodenal aspirate irrelevant for diagnosis.

Q: Which of the following is not a recognized transmission route for amoebiasis?

Vector transmission. ***Vector transmission*** - Amoebiasis, caused by *Entamoeba histolytica*, is primarily an **intestinal infection** transmitted through the **fecal-oral route**. - Its life cycle **does not involve any arthropod vector** (e.g., mosquito, tick, fly) for transmission. - This is the **only route among the options that is definitively NOT recognized** for amoebiasis transmission. *Sexual transmission* - Amoebiasis **can be transmitted** through **oral-anal sexual contact**, particularly documented in men who have sex with men (MSM). - This represents an **indirect fecal-oral transmission** route and is a recognized mode of spread. *Blood and blood products* - While *E. histolytica* can disseminate to cause **amoebic liver abscesses** and rarely systemic disease, transmission via blood transfusion is **extremely rare and not well-documented**. - However, theoretically possible in cases of parasitemia during invasive disease. - Unlike vector transmission, this cannot be definitively ruled out as "not recognized." *Fecal-oral route* - This is the **primary and most important transmission route** for amoebiasis. - Infection occurs through ingestion of **cysts** from contaminated food, water, or through direct person-to-person contact with poor hand hygiene.

Q: Recrudescences are commonly seen in which type of malaria:

P. falciparum. ***P. falciparum*** - **Recrudescence** refers to the reappearance of malaria symptoms after a period of remission, due to the survival and subsequent increase of asexual parasites in the blood [1]. - This is common in *P. falciparum* due to the high parasite burden and its ability to sequester in deep capillaries, evading splenic clearance and developing drug resistance. *P. vivax* - *P. vivax* is known for **relapses**, which are caused by the activation of dormant liver stages called **hypnozoites**, rather than a recrudescence of blood-stage parasites [1]. - Relapses can occur months or years after the initial infection, even after the blood-stage parasites have been cleared. *P. malariae* - *P. malariae* is uniquely characterized by infections that can persist for many years, even decades, causing symptoms of **recrudescence**, although less frequently than *P. falciparum* [1]. - It has a prolonged erythrocytic cycle, which can lead to chronic low-level parasitemia and sporadic symptomatic episodes. *P. ovale* - Similar to *P. vivax*, *P. ovale* also causes **relapses** due to the presence of **hypnozoites** in the liver [1]. - While it can manifest with symptoms similar to *P. vivax*, it is generally less common and causes milder disease.

Q: River blindness is caused by?

Onchocerca volvulus. ***Onchocerca volvulus*** - **River blindness**, or **onchocerciasis**, is caused by the parasitic nematode *Onchocerca volvulus*. - This parasite is transmitted by the bite of infected **blackflies** (genus *Simulium*), which breed in fast-flowing rivers. *Loa loa* - *Loa loa* causes **Loiasis**, also known as African eye worm disease. - While it can manifest as an eye worm and cause itching and swelling, it does not typically lead to permanent blindness or the widespread skin lesions associated with river blindness. *Ascaris* - *Ascaris lumbricoides* causes **ascariasis**, an intestinal infection. - Symptoms are primarily gastrointestinal, such as abdominal pain, malnutrition, and, in severe cases, intestinal obstruction; it does not affect the eyes or cause blindness. *B. malayi* - *Brugia malayi* is one of the causes of **lymphatic filariasis**, also known as **elephantiasis**. - This disease primarily affects the lymphatic system, causing severe swelling in the limbs and genitals, but it does not cause blindness.

Q: What is required for precipitation in comparison to agglutination?

Soluble antigen. ***Soluble antigen*** - **Precipitation reactions** involve the interaction of antibodies with **soluble antigens** to form a detectable precipitate. - Unlike **agglutination**, which involves particulate antigens (e.g., cells), precipitation requires the antigen to be dissolved in a solution. *Increased temperature* - Most immunologic reactions, including precipitation and agglutination, are typically performed at **physiological temperatures** (e.g., 37°C) or room temperature. - An **increased temperature** is not a specific requirement that differentiates precipitation from agglutination. *Specific cofactor* - While some complex immunologic reactions might require **cofactors**, neither precipitation nor agglutination inherently requires a specific cofactor to occur. - The primary components are **antigen** and **antibody**. *Lower pH* - Both precipitation and agglutination reactions are sensitive to pH and typically occur within a **narrow pH range** close to neutral (e.g., pH 7.0-7.4). - A **lower pH** (acidic environment) could lead to antibody denaturation or non-specific aggregation, ultimately hindering the reaction rather than being a requirement.

Q: Which of the following statements about the VDRL test is LEAST accurate?

VDRL is a treponemal-specific test with high specificity. ***VDRL is a treponemal-specific test with high specificity*** - This statement is inaccurate because the **VDRL test** is a **non-treponemal** test, meaning it detects antibodies to cardiolipin, a lipid released from damaged host cells, rather than directly detecting antibodies to *Treponema pallidum*. - Non-treponemal tests like VDRL are known for their potential to produce **false-positive results** due to various conditions. *VDRL is a non-treponemal test and can give false positive results* - The **VDRL test** is indeed a **non-treponemal** test, detecting antibodies against cardiolipin, cholesterol, and lecithin. - Since it detects host-derived antibodies rather than specific *Treponema pallidum* antibodies, it is prone to **false-positive results** in conditions like autoimmune diseases, infections, and pregnancy. *RPR is better than VDRL for monitoring drug therapy* - Both **RPR (Rapid Plasma Reagin)** and VDRL are used to monitor response to therapy in syphilis, but **RPR is sometimes preferred** due to its ease of use (no need for a microscope), stability of reagents, and clearer macroscopic end-point. - The **titers of both VDRL and RPR typically decrease** after successful treatment, indicating a good response to therapy. *VDRL is a slide flocculation test for syphilis* - The **VDRL test** is a **flocculation test** where cardiolipin antigen mixed with a patient's serum (containing reagin antibodies) results in visible clumping or flocculation under a microscope. - It is used as a screening test for **syphilis**, caused by *Treponema pallidum*.

Q: What is the Rose Waaler test used for?

Passive hemagglutination test. ***Passive hemagglutination test*** - The **Rose Waaler test** is a historical **rheumatoid factor (RF)** detection method based on **passive hemagglutination**. - It uses sheep red blood cells coated with a subagglutinating dose of rabbit anti-sheep red blood cell antibody to detect RF in patient serum. *Complement fixation test* - This assay detects the presence of **antibody** or **antigen** by observing whether **complement** is consumed in an antigen-antibody reaction. - The Rose Waaler test does not involve the measurement of complement consumption. *Precipitation in gel* - This technique, such as **immunodiffusion**, involves the formation of a visible **precipitate** when soluble antigens and antibodies diffuse through a gel matrix and meet at optimal concentrations. - The Rose Waaler test relies on agglutination of red blood cells, not precipitation in gel. *Ring precipitation* - A **ring precipitation test** involves layering an antigen solution over an antibody solution, creating an antigen-antibody complex visible as a **precipitate ring** at the interface of the two solutions. - This method is distinct from the Rose Waaler test which uses red blood cell agglutination.

Q: In the context of diagnosing syphilis, which of the following is an example of a precipitation test?

Kahn test. ***Kahn test*** - The Kahn test is a **flocculation** or **precipitation** test used for diagnosing syphilis. - It detects **reagin antibodies** in the patient's serum that react with a non-treponemal antigen (cardiolipin antigen). *Rose waaler test* - The Rose Waaler test is an **agglutination test** used to detect **rheumatoid factor** in patients with rheumatoid arthritis, not syphilis. - It involves sheep red blood cells sensitized with rabbit anti-sheep erythrocyte antibody. *Widal test* - The Widal test is an **agglutination test** used for the diagnosis of **typhoid fever**, detecting antibodies against *Salmonella* O and H antigens. - It is not used for the diagnosis of syphilis. *Latex agglutination* - Latex agglutination is a general type of **agglutination test** where antigen or antibody is coated onto latex particles. - While used in various diagnoses, it is not a specific precipitation test for syphilis in the context of classic methods like the Kahn test.

Q: Haptens are immunogenic when they covalently bind to which type of carrier?

Protein carrier. ***Protein carrier*** - Haptens are small molecules that are **antigenic** but not **immunogenic** on their own; they acquire immunogenicity when covalently bound to a larger carrier molecule. - **Proteins** are highly effective carriers because their complex structures and multiple epitopes can induce strong T-cell help, which is crucial for a robust antibody response against the hapten. *Lipid carrier* - While some lipids can be antigenic (e.g., glycolipids), they generally do not serve as effective carriers for haptens to induce a strong adaptive immune response, especially T-cell-dependent responses. - **Lipids** are less likely to be processed and presented by MHC molecules in a way that generates potent helper T-cell activation. *Polysaccharide carrier* - Some polysaccharides can be immunogenic themselves (e.g., bacterial capsular polysaccharides) and can induce T-cell-independent antibody responses. - However, for haptens to become immunogenic and induce a **T-cell-dependent antibody response**, a protein carrier is typically required. *None of the above carrier* - This option is incorrect because haptens do require a carrier to become immunogenic, and specific types of carriers are more effective than others. - The type of carrier chosen significantly impacts the **strength and nature of the immune response** to the hapten.

Question 1

Trypanosoma cruzi is transmitted by which of the following?

Accepted Answer

Reduviid bug

Answer

Tse tse fly

Answer

Culex mosquito

Answer

Sand fly

Question 2

Duodenal aspirate is used in diagnosis of:

Accepted Answer

Giardia lamblia

Answer

E histolytica

Answer

Taenia solium

Answer

Leishmania

Question 3

Which of the following is not a recognized transmission route for amoebiasis?

Accepted Answer

Vector transmission

Answer

Sexual transmission

Answer

Blood and blood products

Answer

Fecal-oral route

Question 4

Recrudescences are commonly seen in which type of malaria:

Accepted Answer

P. falciparum

Answer

P. vivax

Answer

P. malariae

Answer

P. ovale

Question 5

River blindness is caused by?

Accepted Answer

Onchocerca volvulus

Answer

Loa loa

Answer

Ascaris

Answer

B. malayi

Question 6

What is required for precipitation in comparison to agglutination?

Accepted Answer

Soluble antigen

Answer

Increased temperature

Answer

Specific cofactor

Answer

Lower pH

Question 7

Which of the following statements about the VDRL test is LEAST accurate?

Accepted Answer

VDRL is a treponemal-specific test with high specificity

Answer

RPR is better than VDRL for monitoring drug therapy

Answer

VDRL is a non-treponemal test and can give false positive results

Answer

VDRL is a slide flocculation test for syphilis

Question 8

What is the Rose Waaler test used for?

Accepted Answer

Passive hemagglutination test

Answer

Ring precipitation

Answer

Precipitation in gel

Answer

Complement fixation test

Question 9

In the context of diagnosing syphilis, which of the following is an example of a precipitation test?

Accepted Answer

Kahn test

Answer

Rose waaler test

Answer

Widal test

Answer

Latex agglutination

Question 10

Haptens are immunogenic when they covalently bind to which type of carrier?

Accepted Answer

Protein carrier

Answer

Lipid carrier

Answer

Polysaccharide carrier

Answer

None of the above carrier

NEET-PG 2015 — Microbiology