Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 921: In chronic Hepatitis B infection, which one of the following markers is indicative of active viral replication and the corresponding risk of disease transmission?

A. HBe antigen (Correct Answer)
B. HBs antigen
C. Anti-HBe
D. Anti-HBs

Explanation: ### Explanation **Correct Option: A. HBe antigen (HBeAg)** HBeAg is a soluble protein derived from the precore/core gene. It is a surrogate marker for **active viral replication** and high viral load (HBV DNA levels). Its presence indicates that the virus is actively multiplying in the hepatocytes, making the patient **highly infectious** with a significant risk of transmission (e.g., vertical transmission or needle-stick injuries). **Analysis of Incorrect Options:** * **B. HBs antigen (HBsAg):** This is the first marker to appear and indicates **active infection** (either acute or chronic). While it confirms the presence of the virus, it does not distinguish between high-replicative and low-replicative states. * **C. Anti-HBe:** The appearance of these antibodies (seroconversion) usually signifies that the virus has entered a **low-replicative phase**. It correlates with lower infectivity and a reduced risk of transmission. * **D. Anti-HBs:** These are protective antibodies that appear after the clearance of HBsAg or following **vaccination**. They indicate immunity and the absence of active infection. **NEET-PG High-Yield Pearls:** * **Window Period:** The interval where both HBsAg and Anti-HBs are negative; **Anti-HBc IgM** is the only diagnostic marker during this phase. * **Chronic Infection:** Defined by the persistence of HBsAg for >6 months. * **Precore Mutants:** Some HBV strains do not produce HBeAg despite high replication. In these cases, **HBV DNA levels** are the gold standard to assess infectivity. * **Vertical Transmission:** If a mother is HBeAg positive, the risk of transmitting HBV to the newborn is approximately 90%.

Question 922: What is the primary vector for the Japanese encephalitis virus?

A. Anopheles mosquito
B. Culex mosquito (Correct Answer)
C. Aedes mosquito
D. All of the above

Explanation: **Explanation:** Japanese Encephalitis Virus (JEV) is a flavivirus and the leading cause of viral encephalitis in Asia. The correct answer is **Culex mosquito**, specifically the species ***Culex tritaeniorhynchus***. **1. Why Culex is Correct:** JEV is maintained in an enzootic cycle involving **pigs** (amplifier hosts) and **water birds** (natural reservoirs). *Culex tritaeniorhynchus* is the primary vector because it is "zoophilic," meaning it prefers feeding on animals. These mosquitoes breed extensively in stagnant water, such as **flooded rice paddies**, which brings them into contact with both the animal reservoirs and humans (accidental dead-end hosts). **2. Why Other Options are Incorrect:** * **Anopheles mosquito:** This is the primary vector for **Malaria**. While some Anopheles species can carry JEV, they are not the primary epidemiological drivers of the disease. * **Aedes mosquito:** *Aedes aegypti* and *Aedes albopictus* are the primary vectors for **Dengue, Chikungunya, Zika, and Yellow Fever**. They are "anthropophilic" (prefer humans) and breed in clean, stored water around households. **3. High-Yield Clinical Pearls for NEET-PG:** * **Reservoir/Amplifier Host:** Pigs are the most important amplifier hosts (they develop high viremia without getting sick). * **Dead-end Hosts:** Humans and horses (viremia is too low to infect a biting mosquito). * **Clinical Feature:** Look for "Thalamic involvement" on MRI (bilateral thalamic infarcts/hemorrhage are characteristic). * **Vaccination:** The **SA-14-14-2** (Live attenuated) vaccine is commonly used in the Universal Immunization Programme (UIP) in India. * **Seasonality:** Cases typically peak during the rainy season and pre-harvest period due to increased mosquito breeding in rice fields.

Question 923: The phenomenon of genetic reassortment can occur during the replication of which type of virus?

A. Reoviruses (Correct Answer)
B. This involves crossing over of genes within an RNA segment
C. Influenza viruses
D. This can occur only with RNA viruses of plus polarity

Explanation: **Explanation:** The correct answer is **Reoviruses** (Option A). **1. Underlying Medical Concept:** Genetic reassortment occurs when a host cell is co-infected with two different strains of a virus that possesses a **segmented genome**. During the assembly phase of viral replication, individual segments from both parent strains are randomly packaged into new virions. This results in progeny with a unique combination of genetic material, potentially leading to new antigenic properties. **2. Analysis of Options:** * **Option A (Correct):** Reoviruses (e.g., Rotavirus) have a segmented double-stranded RNA genome (10–12 segments), making them prime candidates for reassortment. * **Option B (Incorrect):** This describes **genetic recombination**, which involves the physical breaking and rejoining of nucleic acid strands (crossing over). Reassortment is the shuffling of whole segments, not intra-segmental crossing over. * **Option C (Incorrect in context):** While Influenza viruses *do* undergo reassortment (causing **Antigenic Shift**), the question asks for the type of virus where this occurs. In a single-choice format where "Reoviruses" is marked as the intended answer, it highlights that reassortment is a property of *all* segmented viruses, including Reoviridae, Orthomyxoviridae, Arenaviridae, and Bunyaviridae. * **Option D (Incorrect):** Reassortment is not limited to plus-polarity RNA viruses. It occurs in negative-sense RNA viruses (Influenza) and double-stranded RNA viruses (Rotavirus). **3. NEET-PG High-Yield Pearls:** * **Mnemonic for Segmented Viruses:** "**BOAR**" (**B**unvaviridae, **O**rthomyxoviridae, **A**renaviridae, **R**eoviridae). * **Antigenic Shift vs. Drift:** Reassortment leads to **Antigenic Shift** (major changes causing pandemics), whereas point mutations lead to **Antigenic Drift** (minor changes causing epidemics). * **Rotavirus:** The most common cause of severe diarrhea in infants; its reassortment capability is a key factor in its diversity and vaccine development.

Question 924: Which one of the following mosquitoes transmits West Nile fever?

A. Anopheles
B. Aedes
C. Mansonoides
D. Culex (Correct Answer)

Explanation: **Explanation:** **West Nile Virus (WNV)** is a member of the *Flaviviridae* family (genus Flavivirus) and is the causative agent of West Nile fever. The virus is maintained in a **bird-mosquito-bird** transmission cycle. 1. **Why Culex is correct:** The primary vectors for West Nile Virus are mosquitoes of the genus **Culex** (specifically *Culex pipiens*, *C. quinquefasciatus*, and *C. tarsalis*). These mosquitoes act as the bridge vector, carrying the virus from the primary reservoir (birds) to incidental hosts like humans and horses. Humans are considered **"dead-end hosts"** because they do not develop high enough viral titers in their blood to re-infect mosquitoes. 2. **Why other options are incorrect:** * **Anopheles:** Primarily known as the vector for **Malaria**. * **Aedes:** The principal vector for other Flaviviruses like **Dengue, Zika, and Yellow Fever**, as well as the Togavirus **Chikungunya**. * **Mansonoides:** Known for transmitting **Brugian Filariasis** (*Brugia malayi*). **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir:** Wild birds (Passerines/songbirds). * **Clinical Spectrum:** Most infections are asymptomatic (80%). About 20% develop West Nile Fever (flu-like symptoms), and <1% develop **Neuroinvasive disease** (Meningitis, Encephalitis, or Acute Flaccid Paralysis). * **Diagnosis:** Detection of **IgM antibodies** in serum or CSF via MAC-ELISA is the gold standard. * **Other Culex-transmitted diseases:** Japanese Encephalitis (JE) and Bancroftian Filariasis (*Wuchereria bancrofti*).

Question 925: An infant presents with fever and persistent cough. Physical examination and a chest x-ray suggest pneumonia. Which of the following is most likely the cause of this infection?

A. Rotavirus
B. Adenovirus
C. Coxsackievirus
D. Respiratory syncytial virus (Correct Answer)

Explanation: **Explanation:** The clinical presentation of fever, persistent cough, and pneumonia in an infant is a classic description of **Respiratory Syncytial Virus (RSV)** infection. RSV is the most common cause of lower respiratory tract infections (LRTI), including bronchiolitis and pneumonia, in infants and children under the age of one. It belongs to the *Paramyxoviridae* family and is characterized by the formation of syncytia (multinucleated giant cells) in host tissues. **Analysis of Options:** * **Respiratory Syncytial Virus (Correct):** It is the leading cause of viral pneumonia in infants. The small diameter of infant airways makes them highly susceptible to the inflammation and mucus plugging caused by RSV. * **Rotavirus:** This is the most common cause of severe diarrhea and dehydration in infants and young children worldwide, not respiratory infections. * **Adenovirus:** While it can cause pneumonia (Types 3, 7, 21), it more commonly presents with pharyngoconjunctival fever or hemorrhagic cystitis. It is a less frequent cause of infant pneumonia compared to RSV. * **Coxsackievirus:** A member of the *Picornaviridae* family, it typically causes Hand-Foot-and-Mouth disease, herpangina, or myocarditis, rather than primary pneumonia in infants. **High-Yield Clinical Pearls for NEET-PG:** * **RSV Seasonality:** Typically peaks during winter months. * **Diagnosis:** Rapid antigen detection tests or RT-PCR from nasopharyngeal swabs are the gold standards. * **Radiology:** Chest X-rays often show hyperinflation and peribronchial thickening. * **Treatment:** Primarily supportive; **Ribavirin** (aerosolized) may be used in severe cases or immunocompromised patients. **Palivizumab** (monoclonal antibody) is used for prophylaxis in high-risk preterm infants.

Question 926: Which virus causes hemorrhagic fever?

A. West-Nile fever
B. Sandfly fever
C. Ebola virus (Correct Answer)
D. All of the above

Explanation: **Explanation:** **Ebola Virus (Option C)** is the correct answer because it belongs to the **Filoviridae** family, which is a classic cause of Viral Hemorrhagic Fever (VHF). The pathophysiology involves severe endothelial damage, disruption of the coagulation cascade (leading to DIC), and increased vascular permeability, resulting in internal and external bleeding, multi-organ failure, and high mortality rates. **Analysis of Incorrect Options:** * **West Nile Fever (Option A):** Caused by a Flavivirus (transmitted by *Culex* mosquitoes), it primarily presents as a self-limiting febrile illness or neuroinvasive disease (meningitis/encephalitis). It does not typically cause hemorrhagic manifestations. * **Sandfly Fever (Option B):** Also known as Pappataci fever (caused by Phlebovirus), it is transmitted by *Phlebotomus papatasi*. It presents as a brief, self-limiting febrile illness with severe retro-orbital pain and conjunctival injection, but without hemorrhagic features. **High-Yield Clinical Pearls for NEET-PG:** * **Major VHF Families:** Remember the mnemonic **"FAB-R"**: **F**iloviridae (Ebola, Marburg), **A**renaviridae (Lassa), **B**unyaviridae (Crimean-Congo Hemorrhagic Fever - CCHF, Hantavirus), and **R**eoviridae/Flaviviridae (Dengue, Yellow Fever, Kyasanur Forest Disease - KFD). * **KFD (Kyasanur Forest Disease):** An important Indian context VHF found in Karnataka, transmitted by the tick *Haemaphysalis spinigera*. * **CCHF:** Transmitted by *Hyalomma* ticks; it is a significant cause of nosocomial hemorrhagic fever outbreaks in India. * **Ebola Transmission:** Occurs through direct contact with infected blood, secretions, or organs (including fruit bats, the natural reservoir).

Question 927: Which of the following statements about the influenza A virus is true?

A. It has a double-stranded segmented RNA genome.
B. Pandemics are caused by antigenic drift.
C. Nucleocapsid antibody is not strain-specific.
D. Hemagglutinin and neuraminidase are strain-specific. (Correct Answer)

Explanation: **Explanation:** **1. Why Option D is Correct:** The influenza A virus is classified into subtypes based on its surface glycoproteins: **Hemagglutinin (H)** and **Neuraminidase (N)**. These proteins are highly variable and undergo frequent mutations. Because they are the primary targets of the host immune response, the specific combination and structure of H and N define the particular **strain** (e.g., H1N1, H3N2). Antibodies against these surface antigens provide immunity only to that specific strain. **2. Why the Other Options are Incorrect:** * **Option A:** Influenza A belongs to the *Orthomyxoviridae* family. It has a **single-stranded**, negative-sense, segmented RNA genome (8 segments), not double-stranded. * **Option B:** Pandemics are caused by **Antigenic Shift**, which involves a major genetic reassortment leading to a completely new subtype. **Antigenic Drift** (point mutations) causes seasonal epidemics. * **Option C:** The **Nucleocapsid (NP)** and Matrix (M1) proteins are the internal type-specific antigens used to differentiate Influenza A, B, and C. They are **relatively stable** and do not vary between strains of the same type; therefore, NP antibodies are type-specific but **not strain-specific**. **High-Yield Clinical Pearls for NEET-PG:** * **Antigenic Shift:** Seen only in Influenza A (due to its wide animal reservoir). * **Hemagglutinin (H):** Responsible for cell attachment (via sialic acid receptors) and agglutination of RBCs. * **Neuraminidase (N):** Facilitates the release of progeny virions from infected cells; inhibited by **Oseltamivir**. * **Amantadine/Rimantadine:** Act by inhibiting the **M2 ion channel** (only effective against Influenza A).

Question 928: Which of the following viruses is labile to acid but heat stable?

A. Human enterovirus serotype 70
B. Human enterovirus serotype 68
C. Echovirus
D. Rhinovirus (Correct Answer)

Explanation: **Explanation:** The correct answer is **Rhinovirus**. This question tests the fundamental differentiation between genera within the *Picornaviridae* family based on physical properties. **1. Why Rhinovirus is correct:** Rhinoviruses are the primary cause of the common cold. A defining characteristic of Rhinoviruses is their **acid lability** (they are inactivated at a pH < 5.0–6.0). This property prevents them from surviving the acidic environment of the stomach, which is why they primarily infect the upper respiratory tract rather than the gastrointestinal tract. Conversely, they are relatively **heat stable**, surviving for long periods on environmental surfaces at room temperature, which facilitates transmission via fomites. **2. Why the other options are incorrect:** * **Options A, B, and C (Enteroviruses):** Human enterovirus 70, 68, and Echoviruses all belong to the genus *Enterovirus*. Unlike Rhinoviruses, Enteroviruses are **acid-stable** (resistant to pH 3.0). This allows them to pass through the stomach unharmed and colonize the intestine. While they are also relatively stable at room temperature, the distinguishing factor in this question is their resistance to acid. **High-Yield Clinical Pearls for NEET-PG:** * **Temperature Preference:** Rhinoviruses grow best at **33°C** (the temperature of the nasal mucosa) rather than 37°C (body temperature). * **Receptor:** Most Rhinoviruses (90%) use **ICAM-1** (CD54) as their cellular receptor. * **Transmission:** Hand-to-eye or hand-to-nose contact via contaminated surfaces is more common than aerosol transmission. * **Vaccination:** No vaccine is available due to the existence of over 100 distinct serotypes.

Question 929: Which disease is characterized by the presence of Torres bodies in the liver cells in its early stage?

A. Kala-azar
B. Q fever
C. Yellow fever (Correct Answer)
D. Lymphogranuloma venereum (LGV)

Explanation: **Explanation:** The correct answer is **Yellow Fever**. **Yellow Fever** is a viral hemorrhagic fever caused by a Flavivirus. The virus is hepatotropic, leading to significant liver pathology. **Torres bodies** are characteristic acidophilic (eosinophilic) intranuclear inclusion bodies found in hepatocytes during the early stages of the disease. As the disease progresses, these are often accompanied by **Councilman bodies**, which represent apoptotic, eosinophilic degeneration of hepatocytes. **Analysis of Incorrect Options:** * **Kala-azar (Visceral Leishmaniasis):** Caused by *Leishmania donovani*, it is characterized by the presence of **LD bodies** (Leishman-Donovan bodies), which are amastigote forms found within macrophages, not Torres bodies. * **Q Fever:** Caused by *Coxiella burnetii*, the classic liver finding is a **"doughnut granuloma"** (a fibrin-ring granuloma), not intranuclear inclusions. * **Lymphogranuloma venereum (LGV):** Caused by *Chlamydia trachomatis* (serotypes L1-L3), it is characterized by **Gamna-Favre bodies** (large intracytoplasmic inclusions) within lymph nodes, typically presenting as the "Groove sign." **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Aedes aegypti* mosquito is the primary vector. * **Councilman Bodies:** Though seen in Yellow Fever, they are not pathognomonic as they can also appear in viral hepatitis. * **Vaccine:** The **17D vaccine** is a live-attenuated vaccine providing immunity for life (International Certificate of Vaccination is valid starting 10 days after vaccination). * **Faget’s Sign:** A clinical hallmark of Yellow Fever where there is **relative bradycardia** despite a high fever.

Question 930: Which of the following does not possess both DNA and RNA?

A. Bacteria
B. Fungus
C. Virus (Correct Answer)
D. Spirochete

Explanation: ### Explanation **Core Concept:** The fundamental distinction between viruses and all other cellular life forms lies in their genetic composition. According to the **Lwoff-Horne-Tournier criteria**, a virus is defined by the presence of only **one type of nucleic acid**—either DNA or RNA—never both. This genetic material is encased in a protein coat (capsid) and requires a host cell's machinery for replication. **Why Virus is Correct:** Viruses are obligate intracellular parasites that lack a cellular structure. They contain either a DNA genome (e.g., Herpesvirus, Hepatitis B) or an RNA genome (e.g., HIV, Influenza). While some complex viruses (like Cytomegalovirus) may carry trace amounts of mRNA packaged within the virion for early protein synthesis, they do not possess a functional dual-genomic system like living cells. **Why Other Options are Incorrect:** * **Bacteria (A) and Spirochetes (D):** These are prokaryotic organisms. All bacteria, including spirochetes (like *Treponema pallidum*), possess a double-stranded DNA genome and utilize various types of RNA (mRNA, tRNA, rRNA) for protein synthesis simultaneously. * **Fungus (B):** Fungi are eukaryotic organisms. They contain a membrane-bound nucleus with DNA and a cytoplasm rich in RNA for translation and cellular metabolism. **NEET-PG High-Yield Pearls:** * **Exception to the Rule:** Mimiviruses are "giant viruses" that contain both DNA and several types of RNA, but for exam purposes, the classical definition (Only DNA or RNA) remains the standard. * **Prions:** These are even simpler than viruses; they are infectious proteins that contain **no nucleic acids** at all. * **Viroids:** These consist solely of a short strand of circular, single-stranded RNA without a protein coat. * **DNA Viruses:** Most are double-stranded (except Parvoviridae). * **RNA Viruses:** Most are single-stranded (except Reoviridae/Rotavirus).

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?