Virology Practice Questions

Q: All of the following statements about parvovirus B19 are true except?

It crosses the placenta in less than 10% of cases.. **Explanation:** Parvovirus B19 is a clinically significant pathogen in the NEET-PG curriculum, known for its specific tropism for erythroid progenitor cells. **1. Why Option B is the correct answer (The "Except" statement):** While Parvovirus B19 is a well-known cause of vertical transmission, the statement that it crosses the placenta in less than 10% of cases is incorrect. In reality, if a non-immune pregnant woman is infected, the virus crosses the placenta in approximately **30% to 50%** of cases. While most fetuses are unaffected, infection can lead to **Hydrops Fetalis** (due to severe fetal anemia and high-output heart failure) or fetal death, particularly during the second trimester. **2. Analysis of Incorrect Options:** * **Option A (DNA Virus):** This is true. Parvovirus B19 is unique as it is the only **Single-Stranded DNA (ssDNA)** virus that causes disease in humans. It is also non-enveloped and icosahedral. * **Option C & D (Severe Anemia/Aplastic Crisis):** These are true. The virus binds to the **P-antigen** (globoside) on erythroblasts, leading to cell lysis. In patients with high red cell turnover (e.g., Sickle Cell Anemia, Hereditary Spherocytosis), this causes a life-threatening **Transient Aplastic Crisis**. In immunocompromised patients, it can lead to pure red cell aplasia and chronic anemia. **High-Yield Clinical Pearls for NEET-PG:** * **Erythema Infectiosum (Fifth Disease):** Characterized by the classic **"Slapped Cheek"** rash in children. * **Arthropathy:** More common in adults, presenting as symmetrical small joint arthritis (mimicking Rheumatoid Arthritis). * **Diagnosis:** Detection of **IgM antibodies** or PCR for viral DNA. * **Receptor:** P-antigen (Globoside) is the essential cellular receptor.

Q: Congenital rubella syndrome is most prominent in an infant when a pregnant woman becomes infected during which period?

The first trimester of pregnancy. **Explanation:** The risk of fetal damage in **Congenital Rubella Syndrome (CRS)** is inversely proportional to the gestational age at the time of maternal infection. [1] **1. Why the First Trimester is Correct:** The first trimester (specifically the first 8–12 weeks) is the period of **organogenesis**. During this window, the Rubella virus can cross the placenta and cause chronic fetal infection, leading to cell death and inhibition of mitosis. If infection occurs within the first 8 weeks, the risk of congenital malformations is as high as **85%**. After the 16th week, the risk of major structural defects drops significantly as organs are already formed. **2. Why Other Options are Incorrect:** * **Options B, C, and D:** Infections occurring in the late second or third trimester (including the weeks or hours before delivery) rarely result in the classic triad of CRS. While late-term infection can lead to fetal infection, it usually results in a subclinical infection or a "blueberry muffin" rash at birth, rather than permanent structural defects like cataracts or heart disease. [1] **3. High-Yield Clinical Pearls for NEET-PG:** * **Gregg’s Triad:** The classic presentation of CRS includes **Cataracts** (most common eye finding), **Sensorineural Deafness** (most common overall finding), and **Congenital Heart Disease** (most commonly Patent Ductus Andreas/PDA). * **Diagnosis:** Detection of **Rubella-specific IgM** in the neonate’s cord blood or persistent IgG levels beyond 6 months is diagnostic. * **Vaccination:** Rubella is a **Live Attenuated Vaccine** (RA 27/3 strain). It is strictly contraindicated during pregnancy, and pregnancy should be avoided for 1 month (4 weeks) after vaccination. * **Blueberry Muffin Rash:** This represents extramedullary hematopoiesis and is a characteristic skin finding in CRS.

Q: Which type of sample can be used to isolate poliovirus earliest?

Stool. **Explanation:** Poliovirus is an enterovirus transmitted primarily via the fecal-oral route. Understanding its pathogenesis is key to identifying the correct diagnostic sample. **Why Stool is Correct:** After ingestion, the virus multiplies in the lymphoid tissues of the pharynx and the Peyer’s patches of the small intestine. It is excreted in the **stool** for several weeks, starting as early as **2–5 days after infection** (often before the onset of paralysis). Because the viral load is highest and persists longest in the gastrointestinal tract, stool is the most reliable and earliest sample for isolation. **Analysis of Incorrect Options:** * **Throat Swab:** While the virus can be isolated from the throat during the first week of illness, it disappears rapidly (usually within 7 days), making it less reliable than stool. * **Blood:** Viremia occurs early in the "minor illness" phase (pre-paralytic). However, it is transient and usually subsides by the time clinical symptoms of meningitis or paralysis appear, making it difficult to capture. * **Cerebrospinal Fluid (CSF):** Paradoxically, poliovirus is **rarely isolated from CSF**, even in patients with paralytic polio. Diagnosis of CNS involvement is usually clinical or via PCR, but not primary isolation from CSF. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard:** Virus isolation from stool (two samples collected 24 hours apart). * **Culture:** Poliovirus is typically grown on Monkey Kidney or human cell lines (e.g., HeLa, HEp-2), showing characteristic **cytopathic effects (CPE)** like cell rounding and pyknosis. * **Specimen Transport:** Stool samples should be sent at **4°C** (Reverse Cold Chain) to maintain viral viability. * **Key Fact:** Polio is a positive-sense, single-stranded RNA virus belonging to the *Picornaviridae* family.

Q: Suckling mice are used in the isolation of which virus?

Arbovirus. **Explanation:** The use of **suckling mice** (mice less than 48 hours old) is a classic method for the isolation of **Arboviruses** (e.g., Dengue, Japanese Encephalitis) and certain **Coxsackieviruses**. These viruses are often difficult to grow in standard cell lines or embryonated eggs. Suckling mice are preferred because they lack a mature immune system and possess specific undifferentiated tissues that are highly susceptible to viral replication. For Arboviruses, the specimen is typically inoculated **intracerebrally**, leading to encephalitis, paralysis, or death, which confirms viral presence. **Analysis of Incorrect Options:** * **Herpes virus (B):** These are typically isolated using **cell cultures** (e.g., Human embryonic lung fibroblasts) where they produce characteristic Cowdry Type A intranuclear inclusion bodies. * **Pox virus (C):** The gold standard for isolation is the **Chorioallantoic Membrane (CAM)** of embryonated hen’s eggs, where they produce visible "pocks." * **HIV (D):** As a retrovirus, HIV is isolated using **co-culture of patient’s PBMCs** (Peripheral Blood Mononuclear Cells) with stimulated healthy T-lymphocytes. Diagnosis is primarily via ELISA, Western Blot, or p24 antigen detection. **High-Yield Clinical Pearls for NEET-PG:** * **Suckling mice** are also the specific medium to differentiate **Coxsackie A** (diffuse myositis/flaccid paralysis) from **Coxsackie B** (focal myositis/spastic paralysis). * **Intracerebral inoculation** in mice is the most sensitive method for isolating the **Rabies virus** (though Negri bodies in brain tissue is the classic histological finding). * Modern virology has largely replaced animal inoculation with **Cell Culture**, but suckling mice remain the "gold standard" for primary isolation of unknown Arboviruses in many reference labs.

Q: All of the following are examples of enveloped viruses EXCEPT:

Adenovirus. **Explanation:** The classification of viruses into **enveloped** and **non-enveloped (naked)** is a high-yield concept in NEET-PG Microbiology. Enveloped viruses derive their outer lipid bilayer from host cell membranes, making them more susceptible to heat, detergents, and lipid solvents (like alcohol). **1. Why Adenovirus is the Correct Answer:** Adenovirus is a **non-enveloped (naked) DNA virus**. It possesses a characteristic icosahedral capsid with "penton fibers" (spikes) projecting from the vertices. Because it lacks a lipid envelope, it is relatively stable in the environment and can survive the acidic conditions of the GI tract, which is why it can cause both respiratory infections and gastroenteritis. **2. Analysis of Incorrect Options:** * **Coronavirus:** An enveloped, positive-sense single-stranded RNA virus. Its envelope is derived from the endoplasmic reticulum-Golgi intermediate compartment (ERGIC). * **Molluscum Contagiosum Virus:** A member of the **Poxviridae** family. Poxviruses are unique, complex-shaped DNA viruses that possess an envelope, though they do not acquire it by budding from the plasma membrane. * **Herpes Virus:** A large, enveloped DNA virus. It acquires its envelope by budding through the **inner nuclear membrane** of the host cell. **Clinical Pearls for NEET-PG:** * **Mnemonic for Naked DNA Viruses:** "**P**apova, **A**deno, **P**arvo" (**PAP**). (Note: Parvovirus is the only one that is single-stranded). * **Mnemonic for Naked RNA Viruses:** "**P**icorna, **R**eo, **C**alici, **H**epe" (**P**e**RCH**). * **High-Yield Fact:** All DNA viruses are double-stranded except Parvovirus; all are icosahedral except Poxvirus; and all replicate in the nucleus except Poxvirus.

Q: Oral hairy leukoplakia is associated with which virus?

Epstein-Barr virus. **Explanation:** **Oral Hairy Leukoplakia (OHL)** is a clinical condition characterized by white, corrugated (hairy), non-scrapable patches typically found on the lateral margins of the tongue. **1. Why Epstein-Barr Virus (EBV) is correct:** OHL is caused by the **opportunistic replication of EBV (Human Herpesvirus 4)** in the squamous epithelium of the tongue. It occurs almost exclusively in immunocompromised individuals, particularly those with HIV/AIDS. Unlike oral candidiasis, these lesions **cannot be scraped off**. The diagnosis is confirmed by detecting EBV DNA or proteins within the epithelial cells. **2. Why the other options are incorrect:** * **Cytomegalovirus (CMV):** While CMV causes opportunistic infections in HIV patients (like retinitis or esophagitis), it does not cause leukoplakia. * **Human Immunodeficiency Virus (HIV):** While OHL is a classic clinical marker for HIV progression and low CD4 counts, HIV itself is the underlying cause of immunosuppression, not the direct viral cause of the leukoplakia. * **Human Papillomavirus (HPV):** HPV is associated with oral warts (verruca vulgaris) and oropharyngeal cancers, but not with the "hairy" white patches of OHL. **Clinical Pearls for NEET-PG:** * **Diagnostic Marker:** OHL is often the first clinical sign of HIV infection or a signal that a patient’s CD4 count has dropped below **200 cells/mm³**. * **Histology:** Look for **Koilocytes** (ballooning cells) in the upper layers of the epithelium and "Cowdry type A" inclusions. * **Treatment:** Usually not required unless for cosmetic reasons; however, it often resolves with **Highly Active Antiretroviral Therapy (HAART)** as the immune system recovers. * **Differential Diagnosis:** Must be distinguished from **Oral Candidiasis** (which scrapes off) and **Leukoplakia** (a premalignant lesion associated with tobacco). OHL is **not** premalignant.

Q: A child presents with fever and redness of a cheek. What is the causative organism for this condition?

Parvovirus B-19. ### Explanation The clinical presentation of fever followed by a characteristic redness of the cheek (often described as a **"slapped-cheek" appearance**) is the hallmark of **Erythema Infectiosum**, also known as **Fifth Disease**. **1. Why Parvovirus B-19 is correct:** Parvovirus B-19 is a DNA virus that infects erythroid progenitor cells. In children, it typically presents with a mild prodromal fever followed by a bright red exanthem on the cheeks (sparing the nasolabial folds). As the facial rash fades, a secondary **"lace-like" or reticular rash** often appears on the trunk and extremities. The rash is immune-mediated and usually appears once the child is no longer contagious. **2. Why the other options are incorrect:** * **Herpes virus:** HSV-1 typically causes gingivostomatitis or herpetic whitlow. While it causes skin lesions, they are vesicular (fluid-filled) rather than a diffuse erythematous "slapped-cheek" rash. * **Adenovirus:** Commonly causes pharyngoconjunctival fever (fever, sore throat, and conjunctivitis). While it can cause a nonspecific rash, it does not present with the classic malar erythema of Fifth disease. * **Rubella:** Also known as German Measles, it presents with a maculopapular rash that starts on the face and spreads downward (cephalocaudal progression) along with characteristic **Forchheimer spots** on the soft palate and retroauricular lymphadenopathy. **Clinical Pearls for NEET-PG:** * **Aplastic Crisis:** Parvovirus B-19 can cause a life-threatening cessation of red blood cell production in patients with high RBC turnover (e.g., **Sickle Cell Anemia**, Hereditary Spherocytosis). * **Pregnancy:** Infection in pregnancy can lead to **Hydrops Fetalis** due to severe fetal anemia. * **Adults:** Often presents with arthralgia or symmetric arthritis rather than a rash. * **Receptor:** The virus enters cells via the **P-antigen** (globoside) on erythrocytes.

Q: A 32-year-old woman seeking to become pregnant visits her physician for a pre-pregnancy examination. Routine prenatal laboratory testing demonstrates the following profile: HBsAg (-), anti-HBsAg (+), anti-HBcAg (-), anti-HBeAg (-), and HBV DNA (-). Which of the following likely represents the status of the patient?

Immunized against hepatitis B. ### Explanation The patient’s serological profile indicates immunity acquired through **vaccination**. **1. Why the Correct Answer is Right:** The presence of **anti-HBsAg (+)** in the absence of other markers is the hallmark of successful immunization. * **HBsAg (-):** Indicates no active infection [1]. * **Anti-HBsAg (+):** Indicates protective immunity. * **Anti-HBcAg (-):** This is the "crucial differentiator." Anti-HBc (Antibody to Core antigen) is only produced in response to an actual viral infection (natural infection). Since vaccines contain only the recombinant surface protein (HBsAg) and no core components, a vaccinated person will be **Anti-HBc negative** [1]. **2. Why the Other Options are Wrong:** * **Option A (Carrier):** A chronic carrier would be **HBsAg (+)** for more than 6 months and **Anti-HBc (+)** (IgG) [1]. * **Option C (Window Period):** During the "window period," HBsAg has disappeared but Anti-HBs has not yet appeared. The only marker typically positive is **Anti-HBc IgM** [1]. * **Option D (Highly Transmissible):** High infectivity is characterized by the presence of **HBsAg (+)** and **HBeAg (+)**, along with high levels of **HBV DNA**. **3. NEET-PG High-Yield Pearls:** * **Natural Infection (Recovered):** HBsAg (-), **Anti-HBc (+)**, Anti-HBs (+) [1]. * **Vaccinated:** HBsAg (-), **Anti-HBc (-)**, Anti-HBs (+). * **HBeAg:** Represents active viral replication and high infectivity. * **Anti-HBs Titer:** A level of **≥10 mIU/mL** after a 3-dose vaccine series is considered protective. * **Isolated Anti-HBc (+):** Can represent a "resolved" infection where Anti-HBs has waned, a "window period," or a false positive.

Q: AIDS was first diagnosed in patients suffering from which of the following conditions?

Pneumocystis carinii pneumonia. **Explanation:** The correct answer is **Pneumocystis carinii pneumonia (PCP)**. The medical recognition of AIDS began in **June 1981**, when the CDC’s *Morbidity and Mortality Weekly Report (MMWR)* described five cases of previously healthy young men in Los Angeles who developed pneumonia caused by *Pneumocystis carinii* (now renamed *Pneumocystis jirovecii*). This was highly unusual as PCP is an opportunistic infection that typically only affects severely immunocompromised individuals. Shortly thereafter, a cluster of **Kaposi Sarcoma** cases was also reported, leading to the identification of the syndrome initially termed "GRID" (Gay-Related Immune Deficiency) before being renamed AIDS in 1982. **Analysis of Options:** * **B (Correct):** PCP was the very first opportunistic infection reported in the 1981 MMWR report that alerted the medical community to the epidemic. * **C (Incorrect):** While Kaposi Sarcoma (caused by HHV-8) was reported very shortly after the initial PCP cases (July 1981), it was the second major condition associated with the outbreak. * **A & D (Incorrect):** While *Cryptococcus neoformans* and *Tuberculosis* are major AIDS-defining illnesses, they were not the index conditions that led to the initial discovery of the disease. **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agent:** HIV is a retrovirus (Lentivirus family) that targets **CD4+ T-cells**. * **Pneumocystis jirovecii:** It is now classified as a **fungus**, not a protozoan. The drug of choice is **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. * **Diagnosis:** The gold standard for HIV screening is **ELISA**, and the confirmatory test (historically) is **Western Blot**, though current protocols favor the **4th Gen p24 antigen/antibody combo assay**. * **CD4 Count:** PCP typically occurs when the CD4 count falls below **200 cells/mm³**.

Question 1

All of the following statements about parvovirus B19 are true except?

Accepted Answer

It crosses the placenta in less than 10% of cases.

Answer

It is a DNA virus.

Answer

It can cause severe anemia.

Answer

It can cause aplastic crisis.

Question 2

Congenital rubella syndrome is most prominent in an infant when a pregnant woman becomes infected during which period?

Accepted Answer

The first trimester of pregnancy

Answer

One week before a full-term delivery

Answer

One month before a full-term delivery

Answer

Hours before childbirth

Question 3

All of the following infections may be transmitted via blood transfusion, except?

Accepted Answer

Dengue virus

Answer

Parvovirus B-19

Answer

Cytomegalovirus

Answer

Hepatitis G virus

Question 4

Which type of sample can be used to isolate poliovirus earliest?

Accepted Answer

Stool

Answer

Blood

Answer

Throat swab

Answer

Cerebrospinal fluid

Question 5

Suckling mice are used in the isolation of which virus?

Accepted Answer

Arbovirus

Answer

Herpes virus

Answer

Pox virus

Answer

HIV

Question 6

All of the following are examples of enveloped viruses EXCEPT:

Accepted Answer

Adenovirus

Answer

Coronavirus

Answer

Molluscum contagiosum virus

Answer

Herpes virus

Question 7

Oral hairy leukoplakia is associated with which virus?

Accepted Answer

Epstein-Barr virus

Answer

Cytomegalovirus

Answer

Human immunodeficiency virus

Answer

Human papillomavirus

Question 8

A child presents with fever and redness of a cheek. What is the causative organism for this condition?

Accepted Answer

Parvovirus B-19

Answer

Herpes virus

Answer

Adenovirus

Answer

Rubella

Question 9

A 32-year-old woman seeking to become pregnant visits her physician for a pre-pregnancy examination. Routine prenatal laboratory testing demonstrates the following profile: HBsAg (-), anti-HBsAg (+), anti-HBcAg (-), anti-HBeAg (-), and HBV DNA (-). Which of the following likely represents the status of the patient?

Accepted Answer

Immunized against hepatitis B

Answer

Hepatitis B carrier

Answer

Infected and within the window period

Answer

Infected with hepatitis B and highly transmissible

Question 10

AIDS was first diagnosed in patients suffering from which of the following conditions?

Accepted Answer

Pneumocystis carinii pneumonia

Answer

Cryptococcus neoformans meningitis

Answer

Kaposi sarcoma

Answer

Tuberculosis

Virology — MCQs

Virology — MCQs

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