Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 971: Paramyxoviruses are most commonly associated with which of the following diseases?

A. Fifth disease
B. Rubella
C. Croup (Correct Answer)
D. Tonsillitis

Explanation: **Explanation:** **Croup (Laryngotracheobronchitis)** is the correct answer because it is most commonly caused by **Parainfluenza virus type 1 and 2**, which belong to the **Paramyxoviridae** family. The virus causes subglottic edema and airway narrowing, leading to the classic clinical triad of a barking cough, inspiratory stridor, and hoarseness. On imaging, this is characterized by the "Steeple sign" (subglottic narrowing). **Analysis of Incorrect Options:** * **Fifth Disease (Erythema Infectiosum):** Caused by **Parvovirus B19** (a single-stranded DNA virus). It is characterized by a "slapped-cheek" rash and can cause aplastic crisis in patients with chronic hemolytic anemias. * **Rubella (German Measles):** Caused by the **Rubella virus**, which belongs to the **Togaviridae** family. While it presents with a rash and lymphadenopathy, it is not a Paramyxovirus. * **Tonsillitis:** Most commonly caused by **Group A Streptococcus** (bacterial) or viruses like Adenovirus and EBV. While Paramyxoviruses can cause upper respiratory symptoms, they are not the primary or "most common" association for isolated tonsillitis. **NEET-PG High-Yield Pearls:** * **Paramyxoviridae Family:** Includes Measles (Morbillivirus), Mumps (Rubulavirus), Parainfluenza, and RSV (Pneumovirus). * **Key Feature:** All Paramyxoviruses are **enveloped, negative-sense, single-stranded RNA viruses**. * **Surface Proteins:** They possess **Hemagglutinin-Neuraminidase (HN)** and **Fusion (F) proteins**. The F-protein is responsible for forming **syncytia** (multinucleated giant cells), a hallmark histological finding. * **Palivizumab:** A monoclonal antibody against the F-protein used for RSV prophylaxis in high-risk infants.

Question 972: Which hepatitis virus was previously referred to as enterovirus?

A. Hepatitis A virus (HAV) (Correct Answer)
B. Hepatitis B virus (HBV)
C. Hepatitis C virus (HCV)
D. Hepatitis E virus (HEV)

Explanation: **Explanation:** **Hepatitis A virus (HAV)** was historically classified as **Enterovirus 72** within the family *Picornaviridae*. This classification was based on its physical and chemical properties, which closely resemble other enteroviruses (like Poliovirus): it is a small, non-enveloped, positive-sense single-stranded RNA virus that is transmitted via the **fecal-oral route** and is resistant to low pH. However, due to unique genetic sequencing and its primary tropism for the liver, it was later reclassified into its own genus, ***Hepatovirus***. **Analysis of Incorrect Options:** * **Hepatitis B virus (HBV):** A member of the *Hepadnaviridae* family. It is a DNA virus transmitted parenterally and sexually, never classified as an enterovirus. * **Hepatitis C virus (HCV):** A member of the *Flaviviridae* family. It is an enveloped RNA virus transmitted primarily through blood. * **Hepatitis E virus (HEV):** Although transmitted via the fecal-oral route (like HAV), it belongs to the *Hepeviridae* family. It was never classified as an enterovirus. **High-Yield Clinical Pearls for NEET-PG:** * **HAV:** Most common cause of acute viral hepatitis in children; never causes chronic infection; associated with "Councilman bodies" (acidophilic bodies) on liver biopsy. * **Transmission:** HAV and HEV are transmitted by the **fecal-oral route** (Vowels go with the Bowels), while HBV, HCV, and HDV are parenteral. * **HEV:** High mortality rate (up to 20%) in **pregnant women** due to fulminant hepatic failure. * **Shellfish:** Consumption of raw steamed oysters/clams is a classic board-style risk factor for HAV.

Question 973: A patient has been diagnosed with HBeAg and HBsAg in their serum. What is the most likely condition?

A. Chronic hepatitis B
B. Active and infectious Hepatitis B disease (Correct Answer)
C. HBV and HBe coinfection
D. Recovery from Hepatitis B

Explanation: ### Explanation The presence of **HBsAg** (Hepatitis B surface Antigen) and **HBeAg** (Hepatitis B envelope Antigen) in a patient's serum indicates an **active and highly infectious** state of Hepatitis B virus (HBV) infection. * **HBsAg:** This is the first marker to appear in the blood during infection. Its presence indicates that the virus is currently in the body (either acute or chronic). * **HBeAg:** This is a marker of **active viral replication**. When HBeAg is positive, it signifies a high viral load and high infectivity, meaning the patient is more likely to transmit the virus to others. #### Why other options are incorrect: * **A. Chronic Hepatitis B:** While HBsAg is present in chronic cases (defined as >6 months), the presence of HBeAg specifically highlights the *active/infectious* status. Chronic HBV can be either "HBeAg-positive" (replicative) or "HBeAg-negative" (non-replicative). Without a time frame, "Active and infectious" is the more precise description of the markers provided. * **C. HBV and HBe coinfection:** This is a distractor. HBe is not a separate virus; it is a protein (antigen) produced by the Hepatitis B virus itself. * **D. Recovery from Hepatitis B:** Recovery is characterized by the disappearance of HBsAg and the appearance of **Anti-HBs** (protective antibodies). #### NEET-PG High-Yield Pearls: * **Window Period:** The time when neither HBsAg nor Anti-HBs are detectable. The only marker present is **Anti-HBc IgM**. * **Anti-HBs:** The only marker present after successful **vaccination**. * **HBV DNA:** The most sensitive marker for monitoring viral load and response to antiviral therapy. * **Pre-core Mutants:** Patients who have high HBV DNA but are HBeAg negative (due to a mutation in the pre-core region).

Question 974: Which virus is noted for genetic reassortment?

A. Adenovirus
B. Herpesvirus
C. HIV
D. Influenza virus (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Influenza virus** The underlying medical concept here is **Genetic Reassortment**, which occurs only in viruses with **segmented genomes**. When two different strains of a segmented virus infect the same host cell simultaneously, they can exchange entire gene segments during assembly. This process leads to **Antigenic Shift**, resulting in the emergence of novel subtypes that can cause pandemics. **Influenza virus** (Orthomyxoviridae) has a segmented RNA genome (8 segments in Influenza A and B). This allows for the rapid shuffling of segments encoding surface glycoproteins (Hemagglutinin and Neuraminidase). **Why other options are incorrect:** * **Adenovirus (A):** It is a double-stranded DNA virus with a **linear, non-segmented** genome. It undergoes genetic recombination but not reassortment. * **Herpesvirus (B):** These are large, enveloped dsDNA viruses with **linear, non-segmented** genomes. * **HIV (C):** While HIV is diploid (two identical copies of (+)ssRNA), its genome is **not segmented**. It achieves high genetic diversity through **recombination** (via template switching during reverse transcription) and a high mutation rate, but not reassortment. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Segmented Viruses:** "**BOAR**" – **B**unyavirus (3), **O**rthomyxovirus (8), **A**renavirus (2), and **R**eovirus (10-12). * **Antigenic Shift vs. Drift:** * **Shift:** Reassortment of segments (Major change $\rightarrow$ Pandemics). * **Drift:** Point mutations in HA/NA genes (Minor change $\rightarrow$ Epidemics/Seasonal flu). * **Rotavirus** (Reovirus family) is another common exam topic that undergoes reassortment due to its 11 segments.

Question 975: A neonate is born in very poor condition with severe, generalized encephalitis. Which of the following viruses is the most likely pathogen in this setting?

A. Eastern equine encephalitis virus
B. Herpes simplex type II (Correct Answer)
C. Herpes zoster-varicella virus
D. Poliomyelitis virus

Explanation: **Explanation:** The correct answer is **Herpes simplex type II (HSV-2)**. **Why HSV-2 is correct:** Neonatal herpes simplex virus infection is a life-threatening condition typically acquired during delivery through an infected birth canal (vertical transmission). HSV-2 is responsible for approximately 70-80% of neonatal herpes cases. It presents in three patterns: Skin-Eye-Mouth (SEM) disease, Disseminated disease, or **Central Nervous System (CNS) disease**. Neonatal HSV encephalitis causes severe, generalized destruction of brain parenchyma, leading to high mortality and significant neurological sequelae if the infant survives. **Why the other options are incorrect:** * **Eastern Equine Encephalitis (EEE):** While it causes severe encephalitis, it is an arbovirus transmitted via mosquito bites. It is not a classic neonatal pathogen and depends on geographical exposure. * **Herpes Zoster-Varicella Virus (VZV):** Congenital Varicella Syndrome occurs due to maternal infection in early pregnancy (limb hypoplasia, scarring). While neonatal varicella can occur if the mother has active lesions at birth, it typically presents with a disseminated vesicular rash rather than isolated severe encephalitis. * **Poliomyelitis Virus:** Polio is an enterovirus that targets the anterior horn cells of the spinal cord, leading to flaccid paralysis. It does not typically cause generalized encephalitis in neonates. **Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** PCR of the Cerebrospinal Fluid (CSF). * **Treatment:** High-dose intravenous **Acyclovir** is the drug of choice. * **Key Distinction:** In adults, HSV encephalitis is usually caused by **HSV-1** and localized to the **temporal lobes**. In neonates, it is usually **HSV-2** and is **generalized**. * **Prevention:** Cesarean section is indicated if the mother has active genital lesions at the time of labor.

Question 976: The Paul Bunnell test is used to diagnose which of the following conditions?

A. Malta fever
B. Typhus fever
C. Enteric fever
D. Infectious mononucleosis (Correct Answer)

Explanation: **Explanation:** The **Paul Bunnell Test** is a classic diagnostic tool for **Infectious Mononucleosis (IM)**, caused by the Epstein-Barr Virus (EBV). The test is based on the detection of **heterophile antibodies** in the patient's serum. These are IgM antibodies produced during an EBV infection that, while not specific to the virus itself, have the unique property of agglutinating red blood cells (RBCs) from other species, specifically **sheep RBCs**. **Analysis of Options:** * **Infectious Mononucleosis (Correct):** The Paul Bunnell test is the gold standard heterophile antibody test. A more specific version used today is the **Monospot test** (using horse RBCs). * **Malta Fever (Brucellosis):** Diagnosed via the Standard Agglutination Test (SAT) or Rose Bengal Plate Test, detecting antibodies against *Brucella* species. * **Typhus Fever:** Historically diagnosed using the **Weil-Felix test**, which utilizes cross-reactivity between *Rickettsia* antibodies and *Proteus* antigens (OX19, OX2, OXK). * **Enteric Fever (Typhoid):** Diagnosed using the **Widal test**, which detects antibodies against the O and H antigens of *Salmonella Typhi*. **High-Yield Clinical Pearls for NEET-PG:** * **Differential Absorption:** To distinguish IM from serum sickness or Forssman antibodies, the **Davidsohn Differential Test** is used. IM antibodies are absorbed by beef RBCs but **not** by guinea pig kidney cells. * **Atypical Lymphocytes:** Peripheral blood smears in IM characteristically show **Downey cells** (activated T-cells). * **Clinical Triad:** Fever, pharyngitis, and lymphadenopathy. * **Warning:** Avoid prescribing Ampicillin/Amoxicillin in suspected IM, as it often triggers a characteristic maculopapular rash.

Question 977: Infection with Hepatitis B virus is associated with the appearance in the blood of all of the following except?

A. Hepatitis B antibody
B. Hepatitis B surface antigen
C. Core of the Dane particle (Correct Answer)
D. DNA polymerase activity

Explanation: ### Explanation The correct answer is **C. Core of the Dane particle**. **1. Why "Core of the Dane particle" is the correct answer:** The Hepatitis B virus (HBV) exists in the blood in three forms: the complete infectious virion (Dane particle), and spherical or tubular forms of excess surface antigen (HBsAg). While the **Dane particle** itself is found in the blood, its **internal core** (containing HBcAg and the viral genome) is never found circulating freely. The core is always sequestered within its outer envelope (HBsAg). Therefore, while HBsAg and HBeAg are detectable, the free core particle is not. **2. Analysis of Incorrect Options:** * **A. Hepatitis B antibody:** Various antibodies (Anti-HBs, Anti-HBc, Anti-HBe) appear in the blood at different stages of infection or recovery. * **B. Hepatitis B surface antigen (HBsAg):** This is the first serological marker to appear in the blood during acute infection and is produced in massive excess by hepatocytes. * **D. DNA polymerase activity:** The Dane particle contains a partially double-stranded DNA genome and its own DNA polymerase. During periods of active viral replication, this enzymatic activity is detectable in the serum. **3. NEET-PG High-Yield Pearls:** * **HBcAg (Core Antigen):** It is **never** detected in the serum. It can only be demonstrated in infected hepatocytes via biopsy/immunofluorescence. * **Window Period:** The interval where HBsAg has disappeared but Anti-HBs hasn't appeared yet. The only marker present is **Anti-HBc IgM**. * **Infectivity Marker:** **HBeAg** is the primary marker of high viral replication and high infectivity. * **Ground Glass Hepatocytes:** Histological hallmark of chronic HBV infection caused by the accumulation of HBsAg in the endoplasmic reticulum.

Question 978: Which one of the following viruses is least likely to cross the placenta?

A. Rubella
B. Herpes Simplex Virus
C. HIV
D. HBV (Correct Answer)

Explanation: **Explanation:** The ability of a virus to cross the placenta depends on its size, the presence of specific receptors on trophoblasts, and the mechanism of transmission. **Why HBV is the correct answer:** Hepatitis B Virus (HBV) is a large DNA virus that **rarely crosses the placenta** during pregnancy. The primary mode of mother-to-child transmission (MTCT) for HBV is **perinatal (vertical)**, occurring during delivery through contact with infected maternal blood or vaginal secretions. Because it does not typically cross the placenta, it is not considered a classic "TORCH" pathogen and does not cause congenital malformations. **Analysis of Incorrect Options:** * **Rubella:** A classic member of the TORCH group. It readily crosses the placenta, especially during the first trimester, leading to **Congenital Rubella Syndrome (CRS)** characterized by cataracts, PDA, and sensorineural deafness. * **Herpes Simplex Virus (HSV):** While most HSV infections are acquired during delivery (neonatal herpes), HSV-2 can cross the placenta (transplacental) in rare cases, leading to skin vesicles, chorioretinitis, and microcephaly. * **HIV:** This virus can cross the placenta at any stage of pregnancy (in utero), though transmission is more common during labor or breastfeeding. Antiretroviral therapy (ART) is used to minimize this risk. **NEET-PG High-Yield Pearls:** * **TORCH Complex:** Toxoplasmosis, Others (Syphilis, Parvovirus B19, VZV), Rubella, CMV, and HSV. Note that HBV is notably absent from this list. * **HBV Management:** To prevent perinatal transmission, the neonate must receive both the **HBV vaccine** and **Hepatitis B Immunoglobulin (HBIG)** within 12 hours of birth. * **HBeAg Status:** The risk of vertical transmission is highest (up to 90%) if the mother is HBeAg positive, indicating high viral replication.

Question 979: Which of the following viruses shows hemagglutination?

A. Respiratory syncytial virus
B. Influenza virus (Correct Answer)
C. Paramyxovirus
D. None of these

Explanation: **Explanation:** **1. Why Influenza Virus is Correct:** The Influenza virus (Orthomyxoviridae family) possesses a specific surface glycoprotein called **Hemagglutinin (HA)**. This protein has the unique ability to bind to N-acetylneuraminic acid (sialic acid) receptors on the surface of red blood cells (RBCs), causing them to clump together—a process known as **hemagglutination**. This property is utilized in the laboratory for the Hemagglutination Inhibition (HI) test to detect antibodies and for viral quantification. **2. Why the Other Options are Incorrect:** * **Respiratory Syncytial Virus (RSV):** Unlike other members of the Paramyxoviridae family, RSV lacks both Hemagglutinin and Neuraminidase activities. It uses a **G-protein** for attachment, which does not cause hemagglutination. * **Paramyxovirus:** While some genera within the Paramyxoviridae family (like *Mumps* or *Parainfluenza*) do show hemagglutination, the term "Paramyxovirus" in this context is often considered a broad category or refers specifically to the genus that may or may not exhibit this property as consistently as the "classic" example, Influenza. In NEET-PG, **Influenza** is always the primary and most definitive answer for hemagglutination. **3. High-Yield Clinical Pearls for NEET-PG:** * **HA vs. NA:** Hemagglutinin (HA) is for **attachment/entry**, while Neuraminidase (NA) is for **viral release** (budding). * **Antigenic Shift vs. Drift:** Point mutations in HA/NA cause *Antigenic Drift* (epidemics); reassortment of segments causes *Antigenic Shift* (pandemics). * **Other Hemagglutinating Viruses:** Remember the mnemonic **"PATH"** (Pox, Adeno, Toga, Hepadna) and others like Measles, Mumps, and Orthomyxoviruses. * **RSV Fact:** It is the most common cause of **bronchiolitis** and pneumonia in infants; it is characterized by the formation of **syncytia** (multinucleated giant cells).

Question 980: AIDS is not transmitted by which of the following routes?

A. Blood transfusion
B. Cryoprecipitate (Correct Answer)
C. Breast milk
D. Plasma

Explanation: **Explanation:** The transmission of Human Immunodeficiency Virus (HIV) occurs through specific body fluids, including blood, semen, vaginal secretions, and breast milk. The correct answer is **Cryoprecipitate** because of the modern manufacturing processes used in its preparation. **1. Why Cryoprecipitate is the correct answer:** While cryoprecipitate is a blood-derived product (containing Factor VIII, von Willebrand factor, and fibrinogen), modern preparation involves rigorous screening and, most importantly, **viral inactivation steps** (such as heat treatment or solvent-detergent processing). These processes effectively eliminate lipid-enveloped viruses like HIV and Hepatitis B/C. Therefore, in the context of modern medical practice, treated cryoprecipitate is not a route for AIDS transmission. **2. Analysis of Incorrect Options:** * **Blood Transfusion (Option A):** This remains the most efficient mode of transmission (over 90% risk per unit of infected blood). Even with screening, the "window period" poses a residual risk. * **Breast Milk (Option C):** Vertical transmission can occur via the placenta, during delivery, or through breastfeeding. Post-natal transmission via breast milk accounts for a significant percentage of pediatric HIV cases. * **Plasma (Option D):** Fresh Frozen Plasma (FFP) contains cell-free HIV particles. If the donor is infected and the plasma is not virally inactivated, it serves as a potent vehicle for transmission. **Clinical Pearls for NEET-PG:** * **Most common route worldwide:** Heterosexual transmission. * **Most efficient route:** Blood transfusion. * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2–8 weeks). * **Viral Inactivation:** Enveloped viruses (HIV, HBV, HCV) are susceptible to detergents and heat, whereas non-enveloped viruses (HAV, HEV) are more resistant.

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