Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 361: Outright or full-blown AIDS is characterized by which of the following CD4 T-cell counts?

A. CD4 T-cell count < 800 cells/mm³
B. CD4 T-cell count < 600 cells/mm³
C. CD4 T-cell count < 400 cells/mm³
D. CD4 T-cell count < 200 cells/mm³ (Correct Answer)

Explanation: **Explanation:** The diagnosis of **AIDS (Acquired Immunodeficiency Syndrome)**, the advanced stage of HIV infection, is defined by the CDC based on two criteria: the presence of an AIDS-defining illness (e.g., Pneumocystis pneumonia, Kaposi sarcoma) or a **CD4+ T-lymphocyte count of < 200 cells/mm³**. **Why Option D is correct:** In a healthy adult, the normal CD4 count ranges from 500 to 1,500 cells/mm³. As HIV replicates, it progressively destroys CD4 cells. When the count drops below **200 cells/mm³**, the immune system is severely compromised, leading to "full-blown AIDS." At this threshold, the risk of life-threatening opportunistic infections increases exponentially. **Why other options are incorrect:** * **Options A & B (< 800 and < 600 cells/mm³):** These counts are often seen in the early or asymptomatic stages of HIV. While they represent a decline from the physiological peak, they do not meet the clinical definition of AIDS. * **Option C (< 400 cells/mm³):** While this indicates significant immune suppression and may warrant the initiation of certain prophylaxis, the official diagnostic cutoff for AIDS remains 200 cells/mm³. **High-Yield NEET-PG Pearls:** * **CD4 < 200:** Start prophylaxis for *Pneumocystis jirovecii* (Trimethoprim-Sulfamethoxazole). * **CD4 < 100:** High risk for *Toxoplasma gondii* and Cryptococcosis. * **CD4 < 50:** High risk for *Mycobacterium avium* complex (MAC) and CMV retinitis. * **Inversion of Ratio:** In HIV, the normal CD4:CD8 ratio (typically 2:1) is **reversed** (becomes < 1:1). * **Monitoring:** CD4 count is the best indicator of **immune status**, while Viral Load (HIV RNA) is the best predictor of **disease progression** and response to ART.

Question 362: Which serological marker indicates acute Hepatitis B infection?

A. HBsAg and HBeAg
B. HBsAg and Core antibody (Correct Answer)
C. HBsAg
D. HBeAg

Explanation: **Explanation:** The diagnosis of acute Hepatitis B virus (HBV) infection relies on identifying markers that appear during the early phase of the disease. **Why Option B is correct:** Acute infection is characterized by the presence of **HBsAg** (Hepatitis B surface antigen) and **Anti-HBc IgM** (IgM antibody to Hepatitis B core antigen). * **HBsAg:** The first marker to appear in the blood, indicating the presence of the virus. * **Anti-HBc IgM:** This is the hallmark of **acute** infection. It is the only marker present during the "window period" (the gap between the disappearance of HBsAg and the appearance of Anti-HBs). Therefore, the combination of HBsAg and the core antibody (specifically IgM) is the definitive serological profile for acute HBV. **Why other options are incorrect:** * **Option A (HBsAg and HBeAg):** While both are present in acute infection, HBeAg specifically indicates high viral replication and infectivity, not necessarily the "acute" status itself. * **Option C (HBsAg):** HBsAg alone only indicates that the person is currently infected; it does not differentiate between acute and chronic states (as HBsAg persists in chronic carriers for >6 months). * **Option D (HBeAg):** This is a marker of active replication and high transmissibility, but it is not used as a primary diagnostic marker for acute infection. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period Marker:** Anti-HBc IgM is the **only** positive marker during the window period. * **Chronic Infection:** Defined by the persistence of HBsAg for more than 6 months and the presence of **Anti-HBc IgG**. * **Immunity via Vaccination:** Only **Anti-HBs** is positive; all other markers (including core antibodies) are negative. * **Immunity via Natural Infection:** Both **Anti-HBs** and **Anti-HBc IgG** are positive.

Question 363: Hepatitis A virus belongs to which of the following viral families?

A. Flavivirus
B. Calicivirus
C. Enterovirus (Correct Answer)
D. Defective virus

Explanation: **Explanation:** **Hepatitis A Virus (HAV)** is a non-enveloped, single-stranded, positive-sense RNA virus. It is taxonomically classified under the family **Picornaviridae** and the genus **Hepatovirus**. In many standardized exams, including NEET-PG, HAV is traditionally grouped with **Enteroviruses** (specifically Enterovirus 72) because it shares similar structural characteristics and is transmitted via the fecal-oral route, much like Poliovirus. **Analysis of Options:** * **Option C (Enterovirus):** Correct. HAV was formerly classified as Enterovirus 72. It is acid-stable, allowing it to survive the gastric passage and replicate in the intestine before reaching the liver. * **Option A (Flavivirus):** Incorrect. This family includes Hepatitis C virus (HCV), as well as Yellow Fever, Dengue, and Zika viruses. Flaviviruses are enveloped RNA viruses. * **Option B (Calicivirus):** Incorrect. While Hepatitis E virus (HEV) was previously classified here due to morphological similarities, it is now placed in the *Hepeviridae* family. Caliciviruses include Noroviruses. * **Option D (Defective virus):** Incorrect. This refers to Hepatitis D virus (HDV), which requires the HBsAg (from HBV) for its envelope and replication. HAV is a fully functional, autonomous virus. **Clinical Pearls for NEET-PG:** * **Transmission:** Fecal-oral route (commonly via contaminated water or shellfish). * **Incubation Period:** Short (2–6 weeks). * **Diagnosis:** Detection of **IgM anti-HAV** is the gold standard for acute infection. IgG indicates past infection or vaccination. * **Prognosis:** HAV never causes chronic hepatitis or a carrier state. It is usually self-limiting but can rarely cause fulminant hepatic failure. * **Vaccination:** Inactivated vaccines are available and highly effective.

Question 364: Infection with herpes simplex virus, a common human pathogen, is best described by which of the following statements?

A. The central nervous system and visceral organs are usually involved.
B. It rarely recurs in a host who has a high antibody titre.
C. It can be reactivated by emotional disturbances or prolonged exposure to sunlight. (Correct Answer)
D. Initial infection usually occurs by intestinal absorption of the virus.

Explanation: ### Explanation **1. Why the Correct Answer is Right:** Herpes Simplex Virus (HSV-1 and HSV-2) is characterized by its ability to establish **latency** in sensory nerve ganglia (Trigeminal for HSV-1; Sacral for HSV-2). Following the primary infection, the viral genome remains dormant. Reactivation occurs when the immune system's surveillance is temporarily compromised or triggered by specific stimuli. Common triggers include **emotional stress, UV light (sunlight exposure)**, fever, hormonal changes (menstruation), or local trauma. These triggers cause the virus to travel back down the axon to the skin/mucosa, leading to recurrent lesions (e.g., herpes labialis). **2. Why the Other Options are Wrong:** * **Option A:** In immunocompetent hosts, HSV usually causes localized mucocutaneous lesions. Involvement of the **CNS (Encephalitis)** or **visceral organs (Hepatitis/Pneumonitis)** is rare and typically seen in neonates or severely immunocompromised patients. * **Option B:** Recurrence is a hallmark of HSV. **Humoral immunity (antibodies) does not prevent reactivation** because the virus spreads via cell-to-cell contact and remains sequestered within neurons, shielded from circulating antibodies. * **Option D:** Initial infection occurs through **direct contact** with infected secretions (saliva or genital fluids) via abraded skin or mucous membranes, not through intestinal absorption. **3. NEET-PG High-Yield Pearls:** * **Site of Latency:** HSV-1 (Trigeminal ganglion); HSV-2 (Sacral ganglia S2-S3). * **Diagnosis:** **Tzanck Smear** showing Multinucleated Giant Cells with Cowdry Type A intranuclear inclusions. * **Gold Standard:** Viral Culture or PCR (PCR is the investigation of choice for HSV Encephalitis). * **Drug of Choice:** Acyclovir (inhibits viral DNA polymerase).

Question 365: Which of the following types of viruses is MOST likely to undergo an abrupt major antigenic shift, permitting reinfection in a previously exposed individual?

A. Coxsackie viruses
B. Hepadna viruses
C. Herpes viruses
D. Orthomyxo viruses (Correct Answer)

Explanation: **Explanation:** The correct answer is **Orthomyxo viruses** (specifically Influenza A). The underlying medical concept is **Antigenic Shift**, which occurs due to the **segmented genome** of the virus. 1. **Why Orthomyxo viruses are correct:** Influenza A viruses have a genome consisting of 8 distinct RNA segments. When two different strains infect the same host cell (e.g., in a pig or bird), these segments can undergo **reassortment**. This results in a major, abrupt change in the surface glycoproteins (Hemagglutinin and Neuraminidase), creating a novel subtype. Because the population has no pre-existing immunity to this new subtype, it frequently leads to **pandemics**. 2. **Why other options are incorrect:** * **Coxsackie viruses (Picornaviridae):** These are non-enveloped, positive-sense single-stranded RNA viruses. They lack a segmented genome and do not undergo reassortment/antigenic shift. * **Hepadna viruses (Hepatitis B):** These are DNA viruses that replicate via reverse transcription. While they have various genotypes, they do not exhibit abrupt major antigenic shifts. * **Herpes viruses:** These are large, double-stranded DNA viruses. They are known for **latency** rather than antigenic shift. Their surface antigens remain relatively stable over time. **High-Yield Clinical Pearls for NEET-PG:** * **Antigenic Shift:** Major change (Reassortment) $\rightarrow$ Segmented genome $\rightarrow$ Causes **Pandemics** (Only Influenza A). * **Antigenic Drift:** Minor change (Point mutations) $\rightarrow$ Occurs in both Influenza A and B $\rightarrow$ Causes **Epidemics** and necessitates annual vaccine updates. * **Segmented Viruses Mnemonic (BOAR):** **B**unyaviridae, **O**rthomyxoviridae, **A**renaviridae, **R**eoviridae. These are the viruses capable of reassortment.

Question 366: Persistent diarrhea in AIDS is caused by which of the following?

A. Microspora
B. Cryptococcus
C. Cryptosporidia (Correct Answer)
D. Isospora belli

Explanation: **Explanation:** **Cryptosporidium parvum** is the most common cause of chronic, persistent, and life-threatening watery diarrhea in patients with AIDS, particularly when CD4 counts drop below 100 cells/mm³. It is an acid-fast obligate intracellular protozoan that infects the intestinal epithelium, leading to malabsorption and severe dehydration. **Analysis of Options:** * **Cryptosporidium (Correct):** It is the classic "high-yield" pathogen associated with intractable diarrhea in HIV/AIDS. Diagnosis is typically made via **Modified Acid-Fast staining** (showing red oocysts) or Enzyme Immunoassay (EIA). * **Microspora:** While *Enterocytozoon bieneusi* causes diarrhea in AIDS, it is less common than Cryptosporidium. It requires specialized stains like Chromotrope 2R or electron microscopy for detection. * **Isospora belli (Cystoisospora):** This also causes diarrhea in AIDS, but it is less frequent globally than Cryptosporidium. A key differentiator is that *Isospora* responds well to **Trimethoprim-Sulfamethoxazole (TMP-SMX)**, whereas Cryptosporidium is often refractory to treatment until HAART improves the CD4 count. * **Cryptococcus:** *Cryptococcus neoformans* is a fungus primarily associated with **meningitis** and pulmonary infections in AIDS patients, not primary diarrheal disease. **NEET-PG High-Yield Pearls:** 1. **Staining:** Cryptosporidium, Isospora, and Cyclospora are all **Acid-Fast**. Cryptosporidium oocysts are small (4-6 µm), while Isospora oocysts are larger (20-30 µm) and oval. 2. **Treatment:** The drug of choice for Cryptosporidiosis in immunocompetent patients is **Nitazoxanide**, but in AIDS patients, the definitive treatment is **HAART** to restore immunity. 3. **Transmission:** Often associated with contaminated water supplies (oocysts are resistant to chlorination).

Question 367: Which of the following statements is FALSE regarding Hepatitis C Virus?

A. It has single-stranded RNA.
B. It is associated with hepatocellular carcinoma.
C. Hepatocellular injury is caused by viral replication. (Correct Answer)
D. Serologic testing detects antibody to HCV.

Explanation: **Explanation:** The correct answer is **C**. In Hepatitis C Virus (HCV) infection, hepatocellular injury is primarily **immune-mediated** rather than a direct cytopathic effect of viral replication. The damage to hepatocytes is caused by the host’s cytotoxic T-lymphocytes (CD8+ T cells) and inflammatory cytokines attempting to clear the infected cells. This chronic inflammatory state leads to fibrosis, cirrhosis, and eventually malignancy. **Analysis of other options:** * **Option A:** HCV is a member of the *Flaviviridae* family. It is an enveloped, **positive-sense, single-stranded RNA** virus. * **Option B:** HCV is a major risk factor for **Hepatocellular Carcinoma (HCC)**. Unlike HBV, HCV does not integrate into the host genome; instead, it promotes carcinogenesis through chronic inflammation and the action of non-structural proteins (like NS5A). * **Option D:** The primary screening tool for HCV is the **anti-HCV antibody test** (ELISA). A positive result is then confirmed by HCV RNA PCR to distinguish between active infection and prior cleared infection. **High-Yield Clinical Pearls for NEET-PG:** * **"The Silent Epidemic":** HCV has the highest rate of chronicity (75–85%) among hepatitis viruses. * **Extrahepatic Manifestations:** Strongly associated with **Mixed Cryoglobulinemia**, Membranoproliferative Glomerulonephritis (MPGN), and Porphyria Cutanea Tarda. * **Treatment:** The goal is "Sustained Virologic Response" (SVR), now highly achievable with Direct-Acting Antivirals (DAAs) like Sofosbuvir. * **Vaccine:** There is **no vaccine** for HCV due to the high antigenic variation of its envelope glycoproteins (E1/E2) and the lack of proofreading by its RNA polymerase.

Question 368: What is the most common route of transmission of HIV from mother to child?

A. Vertical transmission during pregnancy
B. During vaginal delivery (Correct Answer)
C. Breast milk
D. Constant touch and handling

Explanation: **Explanation:** Mother-to-child transmission (MTCT) of HIV, also known as vertical transmission, can occur at three stages: in utero (transplacental), during labor and delivery (intrapartum), or via breastfeeding (postpartum). **Why Option B is correct:** The majority of HIV transmissions from mother to child (**approximately 50-65%**) occur **during labor and delivery**. This is primarily due to the infant's direct contact with infected maternal blood and cervicovaginal secretions in the birth canal, as well as "ascending infection" following the rupture of membranes. **Analysis of Incorrect Options:** * **Option A:** Transplacental transmission during pregnancy accounts for about 20-25% of cases. While significant, it is less frequent than intrapartum transmission. * **Option B:** Breastfeeding accounts for roughly 12-15% of transmissions. The risk increases with the duration of breastfeeding and the presence of mastitis. * **Option D:** HIV is not transmitted through casual contact, such as touching, hugging, or handling, as the virus is not present in sufficient quantities on the skin or transmitted via respiratory droplets. **NEET-PG High-Yield Pearls:** * **Most important determinant of transmission:** Maternal viral load. * **Prevention of Parent-to-Child Transmission (PPTCT):** The current WHO/National guideline (Option B+) recommends lifelong **ART (Tenofovir + Lamivudine + Efavirenz)** for all pregnant and breastfeeding women living with HIV, regardless of CD4 count. * **Zidovudine (AZT):** Historically the first drug used to reduce MTCT; now part of combination regimens. * **Delivery Mode:** Elective Cesarean section (before labor/rupture of membranes) significantly reduces the risk if the maternal viral load is >1000 copies/mL.

Question 369: Coxsackie group A does not cause which of the following?

A. Conjunctivitis
B. Aseptic meningitis (Correct Answer)
C. Hepatitis
D. Hand, Foot, and Mouth Disease

Explanation: **Explanation:** The correct answer is **B. Aseptic meningitis**. While both Coxsackie Group A and Group B are Enteroviruses, they exhibit different clinical tropisms. **Aseptic meningitis** is primarily associated with **Coxsackie Group B** and Echoviruses. While Group A can occasionally cause it, Group B is the classic and more frequent cause of central nervous system infections and pleurodynia. **Analysis of Options:** * **A. Conjunctivitis:** Specifically, **Coxsackie A24** is a well-known cause of Acute Hemorrhagic Conjunctivitis (along with Enterovirus 70). * **C. Hepatitis:** Enteroviruses, including Coxsackie A, are known causes of viral hepatitis, particularly in neonates or immunocompromised individuals. * **D. Hand, Foot, and Mouth Disease (HFMD):** This is the classic clinical presentation of **Coxsackie A16** (and Enterovirus 71). It presents with vesicular eruptions on the palms, soles, and oral mucosa. **High-Yield Clinical Pearls for NEET-PG:** * **Coxsackie A:** Think "Surface/Skin" – Herpangina (A1-A6, A8, A10), HFMD (A16), and Hemorrhagic Conjunctivitis (A24). * **Coxsackie B:** Think "Body/Organs" – **B**ornholm disease (Pleurodynia), Myocarditis, Pericarditis, and Aseptic meningitis. * **Herpangina vs. Herpes:** Herpangina (Coxsackie A) typically involves the **posterior** pharynx (soft palate/tonsils), whereas Herpes Gingivostomatitis involves the **anterior** mouth and gums. * **Myocarditis:** Coxsackie B is the most common viral cause of myocarditis and dilated cardiomyopathy.

Question 370: What is the marker used to determine the efficacy of hepatitis B vaccination?

A. Hepatitis B surface antigen (HBsAg)
B. IgM antibody to Hepatitis B core antigen (IgM Anti-HBc)
C. IgG antibody to Hepatitis B core antigen (IgG Anti-HBc)
D. Antibody to Hepatitis B surface antigen (Anti-HBsAg) (Correct Answer)

Explanation: ### Explanation The correct answer is **D. Antibody to Hepatitis B surface antigen (Anti-HBsAg).** **1. Why Anti-HBsAg is the correct marker:** The Hepatitis B vaccine (a recombinant vaccine) contains only the **HBsAg protein** (surface antigen). When injected, the body’s immune system recognizes this antigen and produces protective antibodies against it, known as **Anti-HBs**. A titer of **≥10 mIU/mL** is clinically considered indicative of protective immunity and successful vaccination. **2. Why the other options are incorrect:** * **HBsAg (Option A):** This is the first marker to appear during an **active infection**. Its presence for more than 6 months defines chronic hepatitis B. It is never found in a successfully vaccinated individual. * **IgM Anti-HBc (Option B):** This is a marker of **acute infection** or a recent "window period." Since the vaccine does not contain the "core" antigen, vaccinated individuals will never develop anti-HBc antibodies. * **IgG Anti-HBc (Option C):** This indicates a **past or chronic infection**. The presence of Anti-HBc (Total) is the key differentiator between "natural immunity" (Anti-HBs + Anti-HBc positive) and "vaccine-induced immunity" (Only Anti-HBs positive). **3. NEET-PG High-Yield Pearls:** * **Window Period Marker:** IgM Anti-HBc is the only serological marker positive during the "window period" (the gap between HBsAg disappearance and Anti-HBs appearance). * **Infectivity Marker:** **HBeAg** (Envelope antigen) indicates high viral replication and maximum infectivity. * **Vaccine Schedule:** Standard 0, 1, and 6-month intramuscular injections (usually in the deltoid; gluteal injection is avoided due to lower immunogenicity). * **Non-responders:** Individuals who fail to develop a titer of ≥10 mIU/mL after two complete vaccination series.

Practice by Chapter

Virus Structure and Classification

Practice Questions

Viral Replication

Practice Questions

Pathogenesis of Viral Infections

Practice Questions

DNA Viruses: Herpesviruses

Practice Questions

DNA Viruses: Poxviruses and Adenoviruses

Practice Questions

Hepatitis Viruses

Practice Questions

RNA Viruses: Orthomyxoviruses

Practice Questions

RNA Viruses: Paramyxoviruses

Practice Questions

Enteroviruses and Rhinoviruses

Practice Questions

Arboviruses

Practice Questions

HIV and Retroviruses

Practice Questions

Oncogenic Viruses

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free

Virology — MCQs

Virology — MCQs

On this page

Practice by Chapter

Want unlimited practice?