Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 621: Which gene codes for the core proteins of HIV?

A. GAG (Correct Answer)
B. ENV
C. POL
D. TAT

Explanation: The HIV genome consists of three structural genes (**gag, pol, and env**) and several regulatory/accessory genes. Understanding these is high-yield for NEET-PG. ### **Correct Answer: A. GAG** The **gag (group-specific antigen)** gene encodes a polyprotein that is cleaved by viral proteases into the structural **core proteins** of the virus. These include: * **p24:** The major capsid protein (detected early in infection via ELISA). * **p17:** The matrix protein. * **p7/p9:** Nucleocapsid proteins. ### **Why the other options are incorrect:** * **B. ENV (Envelope):** This gene codes for the viral envelope glycoproteins. It produces **gp160**, which is cleaved into **gp120** (for attachment to CD4 receptors) and **gp41** (for fusion and entry). * **C. POL (Polymerase):** This gene codes for essential viral enzymes: **Reverse Transcriptase** (RNA to DNA), **Integrase** (integration into host genome), and **Protease** (cleavage of polyproteins). * **D. TAT (Trans-activator of transcription):** This is a regulatory gene that enhances the efficiency of viral transcription. ### **High-Yield Clinical Pearls for NEET-PG:** 1. **p24 Antigen:** This is the earliest serological marker of HIV infection, appearing before antibodies (the "window period"). 2. **Nef Gene:** It downregulates CD4 and MHC-I expression; it is the most important factor for viral virulence. 3. **LTR (Long Terminal Repeats):** Located at both ends of the genome, these are responsible for the integration of the provirus into the host DNA. 4. **Screening vs. Confirmation:** ELISA (p24 + antibodies) is used for screening, while Western Blot (detecting gp120/160, gp41, and p24) was traditionally used for confirmation.

Question 622: All of the following statements are true for rabies virus except:

A. Infection may be prevented by active and passive immunization.
B. The animal reservoir differs from country to country.
C. It can be diagnosed by direct fluorescent antibody (DFA) testing.
D. Rabies vaccine is a live attenuated vaccine. (Correct Answer)

Explanation: **Explanation:** The correct answer is **D** because the modern rabies vaccines used in humans (such as PCECV and HDCV) are **inactivated (killed) vaccines**, not live attenuated. Live attenuated vaccines are generally avoided in human rabies prophylaxis due to the risk of reversion to virulence in a disease that is virtually 100% fatal. **Analysis of Options:** * **Option A (Incorrect):** This is a true statement. Post-exposure prophylaxis (PEP) involves a combination of **active immunization** (vaccine) to induce long-term immunity and **passive immunization** (Rabies Immunoglobulin/RIG) to provide immediate neutralizing antibodies at the wound site. * **Option B (Incorrect):** This is true. While dogs are the primary reservoir in India and developing nations, wild animals like foxes, raccoons, and skunks are the main reservoirs in developed countries (e.g., USA). * **Option C (Incorrect):** This is true. The **Direct Fluorescent Antibody (DFA)** test on brain tissue (in animals) or skin biopsy from the nape of the neck (in humans) is the "gold standard" for rapid diagnosis, detecting viral antigens. **Clinical Pearls for NEET-PG:** * **Morphology:** Rabies virus is a **bullet-shaped**, negative-sense, single-stranded RNA virus (Rhabdoviridae). * **Pathognomonic Sign:** **Negri bodies** (intracytoplasmic eosinophilic inclusions) found typically in the Hippocampus and Cerebellum (Purkinje cells). * **Neural Spread:** The virus travels via **retrograde axonal transport** to the CNS. * **Vaccine Strains:** Fixed virus (e.g., Pitman-Moore strain) is used for vaccine production, whereas the naturally occurring virus is called the "Street virus." * **Classification:** It belongs to the genus *Lyssavirus*.

Question 623: German measles is the common name for which of the following conditions?

A. Rubella (Correct Answer)
B. Rubeola
C. Herpes simplex
D. Herpetic gingivostomatitis

Explanation: **Explanation:** **Rubella**, commonly known as **German measles**, is caused by the Rubella virus (a Togavirus). It is characterized by a three-day maculopapular rash, low-grade fever, and significant posterior cervical or post-auricular lymphadenopathy. It is termed "German measles" because it was first described by German physicians in the 18th century as a distinct entity from Rubeola. **Analysis of Incorrect Options:** * **Rubeola:** This is the medical term for **Measles** (caused by the Paramyxovirus). It is distinguished by the "3 Cs" (Cough, Coryza, Conjunctivitis) and pathognomonic **Koplik spots** on the buccal mucosa. * **Herpes simplex (HSV):** This virus causes vesicular lesions (Type 1 usually oral; Type 2 usually genital) and is unrelated to the childhood exanthems. * **Herpetic gingivostomatitis:** This is a clinical manifestation of a primary HSV-1 infection, typically presenting with painful oral ulcers and gum swelling in children. **High-Yield Clinical Pearls for NEET-PG:** * **Congenital Rubella Syndrome (CRS):** This is the most critical complication. The classic **Gregg Triad** includes: 1. Sensorineural deafness (most common), 2. Cataracts, and 3. Cardiac defects (Patent Ductus Arteriosus). * **Forchheimer spots:** Small red spots (petechiae) on the soft palate seen in Rubella (though not pathognomonic). * **Teratogenicity:** The risk is highest if the mother is infected during the **first trimester** (up to 85% risk). * **Vaccination:** Prevented by the live-attenuated **RA 27/3 strain** (MMR vaccine). It is contraindicated in pregnancy.

Question 624: Which RNA virus is inhibited by Actinomycin D?

A. Measles
B. Polio
C. Influenza (Correct Answer)
D. Rubella

Explanation: **Explanation:** The correct answer is **Influenza**. **1. Why Influenza is the correct answer:** Actinomycin D is an antibiotic that inhibits **DNA-dependent RNA polymerase**, thereby blocking transcription. Most RNA viruses replicate entirely in the cytoplasm and do not require host cell nuclear transcription, making them resistant to Actinomycin D. However, **Orthomyxoviruses (Influenza)** are unique among RNA viruses because they replicate their genome in the **nucleus**. They require host cell DNA transcription to produce "primers" (a process called cap-snatching) to initiate their own viral mRNA synthesis. Because Influenza depends on the host's nuclear DNA-directed RNA synthesis, Actinomycin D inhibits its replication. **2. Why the other options are incorrect:** * **Measles (Paramyxovirus):** Replicates entirely in the cytoplasm using its own RNA-dependent RNA polymerase. It does not depend on host DNA transcription. * **Polio (Picornavirus):** A positive-sense single-stranded RNA virus that replicates in the cytoplasm. It is independent of nuclear functions and thus resistant to Actinomycin D. * **Rubella (Togavirus):** Similar to Polio, it replicates in the cytoplasm and does not utilize the host cell nucleus for its primary replication cycle. **3. High-Yield Clinical Pearls for NEET-PG:** * **Exceptions to the Rule:** Most RNA viruses replicate in the cytoplasm *except* **Influenza** and **Retroviruses** (HIV). * **Exceptions to the Rule:** Most DNA viruses replicate in the nucleus *except* **Poxvirus** (replicates in the cytoplasm). * **Mechanism:** Influenza uses "Cap-snatching," where it steals the 5' methylated cap from host pre-mRNA in the nucleus to use as a primer for viral mRNA. * **Drug Target:** Actinomycin D is primarily used as a chemotherapy agent (Dactinomycin) for Wilms tumor and Rhabdomyosarcoma.

Question 625: Which of the following is a single-stranded DNA virus with no envelope?

A. Parvovirus B19 (Correct Answer)
B. Hepatitis A
C. Herpes simplex
D. Human reovirus

Explanation: **Explanation:** The correct answer is **Parvovirus B19**. In virology, there is a fundamental rule for DNA viruses: almost all are double-stranded (dsDNA) and show icosahedral symmetry, except for the **Parvoviridae** family, which is **single-stranded (ssDNA)**. Additionally, Parvovirus is a **non-enveloped (naked)** virus, making it highly resistant to environmental degradation. **Analysis of Options:** * **Hepatitis A (Option B):** While it is non-enveloped, it belongs to the Picornaviridae family and is a single-stranded **RNA** virus, not DNA. * **Herpes simplex (Option C):** This is a double-stranded DNA virus. Crucially, it is an **enveloped** virus (derived from the host nuclear membrane), which contradicts the question. * **Human reovirus (Option D):** Reoviruses are unique because they are **double-stranded RNA** viruses. Like Parvovirus, they are non-enveloped, but their genome type is different. **High-Yield Clinical Pearls for NEET-PG:** * **Smallest DNA Virus:** Parvovirus B19 is the smallest DNA virus (25 nm). * **Clinical Presentation:** It causes **Erythema Infectiosum (Fifth Disease)**, characterized by the classic "slapped-cheek" rash in children. * **Receptor:** It binds to the **P-antigen** (globoside) on erythroid progenitor cells. * **Complications:** It can lead to **Aplastic Crisis** in patients with chronic hemolytic anemias (e.g., Sickle Cell) and **Hydrops Fetalis** if a pregnant woman is infected. * **Mnemonic:** Remember "**HHAPPPPy**" for DNA viruses (Hepadna, Herpes, Adeno, Papova, Parvo, Pox). All are dsDNA except **Parvo** (ssDNA). All are icosahedral except **Pox** (complex).

Question 626: Which of the following statements is true about Herpes viruses?

A. Herpes Simplex Virus (HSV) encephalitis is treated with acyclovir. (Correct Answer)
B. Oropharyngeal involvement is common in HSV-1.
C. Recurrent genital involvement is seen in HSV-2.
D. Recurrence is rare in HSV-1.

Explanation: ### Explanation **1. Why Option A is Correct:** Intravenous **Acyclovir** is the gold standard and drug of choice for **HSV Encephalitis (HSE)**. HSE is a medical emergency, typically caused by HSV-1 in adults, involving the temporal lobes. Early initiation of acyclovir significantly reduces mortality (from 70% to ~20%) and improves neurological outcomes by inhibiting viral DNA polymerase. **2. Analysis of Incorrect Options:** * **Option B & C:** While these statements are clinically true (HSV-1 causes oropharyngeal lesions and HSV-2 causes recurrent genital herpes), in the context of a "single best answer" question, Option A represents a critical therapeutic fact. However, in many medical entrance exams, if multiple statements are factually correct, the most "definitive" or "clinically significant" one is chosen. *Note: In some versions of this question, Options B and C are phrased as "only seen in," making them false.* * **Option D:** This is incorrect because **latency and recurrence** are hallmark features of all Herpes viruses. After primary infection, HSV-1 remains latent in the **trigeminal ganglion** and can reactivate due to stress, fever, or UV light (causing herpes labialis). **3. High-Yield Clinical Pearls for NEET-PG:** * **Site of Latency:** HSV-1 (Trigeminal ganglion); HSV-2 (Sacral ganglia); Varicella-Zoster (Dorsal root ganglia). * **Diagnosis:** **Tzanck Smear** shows multinucleated giant cells with Cowdry Type A intranuclear inclusion bodies. **PCR** is the gold standard for CSF analysis in encephalitis. * **HSE Localization:** Characteristically affects the **temporal lobes**, often presenting with hemorrhagic necrosis, seizures, and aphasia. * **Drug Resistance:** In acyclovir-resistant cases (often in immunocompromised patients), **Foscarnet** is the preferred alternative.

Question 627: 'H5 N1' may be best described as a:

A. Bird flu virus (Correct Answer)
B. Vaccine for HIV
C. Agent for Japanese encephalitis
D. New strain of Plasmodium falciparum

Explanation: **Explanation:** **H5N1** is a highly pathogenic subtype of the **Influenza A virus** that primarily affects birds, hence it is commonly known as **Bird Flu (Avian Influenza)**. The nomenclature "H5N1" refers to the specific surface glycoproteins: **Hemagglutinin (H5)**, which facilitates viral entry into host cells, and **Neuraminidase (N1)**, which assists in the release of new viral progeny. While it primarily circulates among wild birds and poultry, it can occasionally cross the species barrier to infect humans, often resulting in severe respiratory illness with a high mortality rate. **Analysis of Incorrect Options:** * **Option B (Vaccine for HIV):** There is currently no approved vaccine for HIV. HIV research focuses on targets like gp120 and gp41, which are unrelated to the H and N proteins of Influenza. * **Option C (Agent for Japanese Encephalitis):** Japanese Encephalitis is caused by the **JE virus**, which is a member of the *Flaviviridae* family and is transmitted by *Culex* mosquitoes, not avian influenza strains. * **Option D (New strain of Plasmodium falciparum):** *P. falciparum* is a protozoan parasite responsible for malaria. Strains are categorized by drug resistance (e.g., chloroquine-resistant), not by viral surface proteins. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Oseltamivir (Tamiflu), a neuraminidase inhibitor, is the preferred treatment. * **Antigenic Shift vs. Drift:** H5N1 represents a potential source for **Antigenic Shift** (major genetic reassortment), which can lead to pandemics. * **Other Strains:** **H1N1** is responsible for Swine Flu, while **H3N2** is a common cause of seasonal human influenza. * **Diagnosis:** Real-time PCR is the gold standard for identifying the H5N1 viral RNA.

Question 628: All of the following are seen in active chronic hepatitis B except?

A. IgM against core antigen (Correct Answer)
B. Total core antibody
C. HBeAg
D. HBsAg

Explanation: In Hepatitis B serology, the presence of specific markers distinguishes between acute and chronic phases. **Explanation of the Correct Answer:** **Option A (IgM against core antigen/IgM anti-HBc)** is the hallmark of **acute infection** or the "window period." In chronic hepatitis B (defined as the persistence of HBsAg for >6 months), IgM anti-HBc is replaced by **IgG anti-HBc**. Therefore, IgM anti-HBc is typically absent in active chronic hepatitis, making it the correct "except" choice. **Explanation of Incorrect Options:** * **Option B (Total core antibody):** This includes both IgM and IgG. In chronic cases, the IgG component remains positive for life, meaning total core antibody will be positive. * **Option C (HBeAg):** This is a marker of active viral replication and high infectivity. It is frequently present in "active" chronic hepatitis (the HBeAg-positive chronic hepatitis phase). * **Option D (HBsAg):** This is the primary screening marker. Its persistence for more than 6 months is the very definition of chronic hepatitis B. **High-Yield Clinical Pearls for NEET-PG:** 1. **Window Period:** The period where HBsAg becomes negative but Anti-HBs hasn't appeared yet. The only positive marker here is **IgM anti-HBc**. 2. **Chronic Infection Marker:** Persistence of **HBsAg > 6 months**. 3. **Recovery/Immunity:** Presence of **Anti-HBs** indicates recovery or successful vaccination. 4. **Vaccination vs. Natural Infection:** Vaccinated individuals are **Anti-HBs positive** but **Anti-HBc negative**. Naturally immune individuals are positive for both.

Question 629: Which of the following statements regarding Rabies infection is FALSE?

A. Rabies is a dead-end infection in humans.
B. Rabies can be transmitted by aerosols.
C. Suturing is usually recommended for local wounds.
D. Human Rabies immunoglobulin dose is 10 IU/kg. (Correct Answer)

Explanation: **Explanation:** The correct answer is **D**, as the statement is incorrect. The standard dose for **Human Rabies Immunoglobulin (HRIG)** is **20 IU/kg** body weight. For Equine Rabies Immunoglobulin (ERIG), the dose is 40 IU/kg. HRIG is administered to provide immediate passive immunity by neutralizing the virus at the wound site before the vaccine-induced active immunity develops. **Analysis of other options:** * **A. Dead-end infection:** This is **True**. Humans do not typically transmit rabies to other humans or animals (except via rare organ transplants), as the viral load in human saliva is insufficient for transmission. * **B. Aerosol transmission:** This is **True**. While rare, rabies can be transmitted via aerosols in specific environments like bat-infested caves or through laboratory accidents. * **C. Suturing:** This is **True** (in the context of general management). Suturing of rabies-prone wounds should ideally be **avoided**. If functionally necessary, it must be delayed by 24–48 hours and performed only after infiltrating the wound with Rabies Immunoglobulin (RIG) to prevent "seeding" the virus deeper into nerves. **High-Yield Clinical Pearls for NEET-PG:** * **Negri Bodies:** Pathognomonic intracytoplasmic eosinophilic inclusions found in the hippocampus (Ammon’s horn) and cerebellum (Purkinje cells). * **Incubation Period:** Typically 1–3 months; depends on the distance of the bite from the CNS. * **Post-Exposure Prophylaxis (PEP):** Includes wound washing (15 mins with soap/water), RIG, and the modern vaccine schedule (Essen: 0, 3, 7, 14, 28 days or IDRV: 0, 3, 7, 28 days). * **Category III Bites:** Always require both Vaccine and RIG.

Question 630: Infectious mononucleosis is confirmed by which diagnostic test?

A. Blood smear
B. Monospot test (Correct Answer)
C. Frei’s test
D. Hess test

Explanation: **Explanation:** **Infectious Mononucleosis (IM)** is primarily caused by the **Epstein-Barr Virus (EBV)**. The definitive screening test for confirmation is the **Monospot test**, which detects **heterophile antibodies**. These are IgM antibodies produced during the acute phase of EBV infection that cross-react with antigens on the red blood cells of other species (e.g., sheep, horse, or bovine). A positive Monospot test (latex agglutination) is highly specific for IM in the presence of clinical symptoms. **Analysis of Incorrect Options:** * **A. Blood smear:** While a peripheral smear is a crucial initial step, it is not confirmatory. It typically shows **lymphocytosis** with characteristic **atypical lymphocytes (Downey cells)**—which are actually activated T-cells (CD8+) reacting against infected B-cells. * **C. Frei’s test:** This is a delayed hypersensitivity skin test historically used to diagnose **Lymphogranuloma Venereum (LGV)** caused by *Chlamydia trachomatis*. It is now largely obsolete. * **D. Hess test:** Also known as the capillary fragility test, it is used to assess capillary wall resistance and is classically positive in **Dengue hemorrhagic fever**. **High-Yield Clinical Pearls for NEET-PG:** * **Triad of IM:** Fever, Pharyngitis, and Lymphadenopathy (posterior cervical). * **Paul-Bunnell Test:** The classic tube agglutination test for heterophile antibodies (Monospot is the rapid version). * **EBV-Specific Serology:** If the Monospot is negative but IM is suspected (common in children <4 years), test for **Anti-VCA (Viral Capsid Antigen) IgM**. * **Ampicillin Rash:** Patients with IM misdiagnosed as strep throat who receive Ampicillin/Amoxicillin often develop a characteristic maculopapular rash.

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