Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 31: A 3-year-old child presents with coryza, conjunctivitis, low-grade fever, and Koplik's spots. The causative agent of this disease belongs to which group of viruses?

A. Paramyxovirus
B. Morbillivirus (Correct Answer)
C. Rubulavirus
D. Pneumovirus

Explanation: ### Explanation **1. Why the Correct Answer is Right:** The clinical presentation of **coryza, conjunctivitis, fever, and Koplik’s spots** is pathognomonic for **Measles (Rubeola)**. Koplik’s spots (small white spots on the buccal mucosa opposite the lower molars) are the hallmark pre-eruptive sign. The Measles virus belongs to the family *Paramyxoviridae* and specifically to the genus **Morbillivirus**. It is a pleomorphic, enveloped virus with a single-stranded, negative-sense RNA genome. **2. Why the Other Options are Incorrect:** * **Paramyxovirus (Option A):** While Measles belongs to the *Paramyxoviridae* family, "Paramyxovirus" is a broad family name (and formerly a genus name now split). In NEET-PG, when a specific genus like *Morbillivirus* is provided, it is the more precise and correct answer. * **Rubulavirus (Option C):** This genus includes the **Mumps virus** and Parainfluenza viruses 2 and 4. Mumps typically presents with parotitis, not Koplik’s spots or a maculopapular rash. * **Pneumovirus (Option D):** This genus (now often classified under the family *Pneumoviridae*) includes **Respiratory Syncytial Virus (RSV)**, which is a leading cause of bronchiolitis and pneumonia in infants, lacking the systemic rash and oral signs of Measles. **3. High-Yield Clinical Pearls for NEET-PG:** * **Sequence of Symptoms:** Fever → 3 C’s (Cough, Coryza, Conjunctivitis) → Koplik’s spots → Exanthem (starts behind ears). * **Vitamin A:** Supplementation reduces morbidity and mortality in Measles. * **Complications:** The most common complication is **Otitis Media**; the most common cause of death is **Pneumonia** (Hecht’s giant cell pneumonia); the most dreaded late complication is **SSPE** (Subacute Sclerosing Panencephalitis). * **Warthin-Finkeldey Cells:** Multinucleated giant cells found in lymphoid tissue, characteristic of Measles.

Question 32: Which of the following hepatitis viruses is cultivable in vitro?

A. Hepatitis A virus (Correct Answer)
B. Hepatitis B virus
C. Hepatitis C virus
D. Hepatitis D virus

Explanation: **Explanation:** The correct answer is **Hepatitis A virus (HAV)**. Among the primary hepatitis viruses, HAV is the only one that can be routinely grown in cell culture (in vitro). **Why Hepatitis A is correct:** Hepatitis A virus (a Picornavirus) can be cultivated in various human and primate cell lines, such as **fetal rhesus monkey kidney cells (FRhK-4)** and human diploid cell lines (MRC-5). Although the virus is often slow-growing and non-cytopathic (meaning it doesn't always kill the host cell), its ability to be cultured was instrumental in the development of the **inactivated (killed) HAV vaccine**. **Why the other options are incorrect:** * **Hepatitis B (HBV):** HBV is highly fastidious. While specific transfected cell lines can produce viral particles, the virus cannot be propagated in standard routine cell cultures. * **Hepatitis C (HCV):** For decades, HCV was notoriously difficult to culture. While specialized "replicon" systems and specific strains (JFH-1) exist in high-level research settings, it is not considered "cultivable" in the standard diagnostic or general virology context. * **Hepatitis D (HDV):** As a defective virus, HDV requires the presence of HBV (HBsAg) to replicate and assemble. It cannot be cultured independently. **NEET-PG High-Yield Pearls:** * **HAV:** Most common cause of acute viral hepatitis in children in India. It is transmitted via the **fecal-oral route**. * **Culture Fact:** HAV does not produce a cytopathic effect (CPE) in most cultures; growth is detected by immunofluorescence or RIA. * **Vaccine:** The HAV vaccine is a **killed vaccine** (derived from cell culture), unlike the HBV vaccine which is a **recombinant (subunit) vaccine** produced in yeast (*Saccharomyces cerevisiae*).

Question 33: Which of the following viruses causes tick-borne hemorrhagic fever?

A. Omsk hemorrhagic fever virus (Correct Answer)
B. Chandipura virus
C. Vesicular stomatitis virus
D. Yellow fever virus

Explanation: **Explanation:** **1. Why Omsk Hemorrhagic Fever (OHF) Virus is Correct:** Omsk hemorrhagic fever virus belongs to the family **Flaviviridae**. It is a classic **Arbovirus** (Arthropod-borne) transmitted primarily by the bite of infected **Dermacentor ticks** (*D. reticulatus* and *D. marginatus*). It is endemic to western Siberia and presents clinically with a biphasic fever, headache, and hemorrhagic manifestations. **2. Analysis of Incorrect Options:** * **Chandipura Virus:** This is a **Rhabdovirus** transmitted by the **Sandfly** (*Phlebotomus*). It is known for causing outbreaks of acute encephalitis in children in India, not hemorrhagic fever. * **Vesicular Stomatitis Virus (VSV):** Also a **Rhabdovirus**, it primarily affects livestock. In humans, it causes a mild, self-limiting flu-like illness with vesicular lesions; it is not a hemorrhagic fever virus. * **Yellow Fever Virus:** While this is a Flavivirus that causes hemorrhagic symptoms, it is transmitted by **Mosquitoes** (*Aedes aegypti*), not ticks. **3. High-Yield Clinical Pearls for NEET-PG:** * **Tick-borne Flaviviruses:** Include OHF, Kyasanur Forest Disease (KFD), and Tick-borne Encephalitis (TBE). * **KFD (Kyasanur Forest Disease):** Often called "Monkey Fever," it is the Indian counterpart to OHF, found in Karnataka and transmitted by *Haemaphysalis spinigera* ticks. * **Crimean-Congo Hemorrhagic Fever (CCHF):** Another high-yield tick-borne hemorrhagic fever, but it belongs to the **Bunyaviridae** family (transmitted by *Hyalomma* ticks). * **Rule of Thumb:** If the question mentions "Tick + Hemorrhagic Fever + Russia/Siberia," think **OHF**. If it mentions "Tick + Hemorrhagic Fever + India/Monkeys," think **KFD**.

Question 34: Which virus causes a mononucleosis-like syndrome caused by a latent herpesvirus, is often a congenital infection, and is frequently diagnosed by detecting large amounts of virus excreted in urine?

A. Epstein-Barr virus
B. Cytomegalovirus (Correct Answer)
C. HHV-6
D. Parvovirus

Explanation: **Explanation:** The correct answer is **Cytomegalovirus (CMV)**. This question highlights three classic clinical pillars of CMV infection: 1. **Mononucleosis-like Syndrome:** CMV is the most common cause of heterophile-antibody negative (Monospot negative) mononucleosis. While it presents similarly to EBV (fever, lymphadenopathy, atypical lymphocytosis), pharyngitis and splenomegaly are typically less severe. 2. **Congenital Infection:** CMV is the most common intrauterine infection worldwide. It presents with the classic triad of periventricular calcifications, microcephaly, and sensorineural hearing loss. 3. **Viral Shedding:** CMV establishes lifelong latency in mononuclear cells (monocytes). During primary infection or reactivation, the virus is excreted in high titers in the **urine (viruria)** and saliva, making urine culture or PCR a primary diagnostic tool, especially in neonates. **Analysis of Incorrect Options:** * **A. Epstein-Barr virus (EBV):** While it causes classic infectious mononucleosis, it is **Heterophile positive** and is not a major cause of congenital infections or diagnosed via urine excretion. * **C. HHV-6:** This virus causes **Roseola Infantum** (Exanthem Subitum), characterized by high fever followed by a rash. It does not typically cause a mononucleosis syndrome or significant congenital disease. * **D. Parvovirus B19:** A single-stranded DNA virus (not a herpesvirus) that causes Erythema Infectiosum (Fifth disease) and hydrops fetalis, but not a mononucleosis-like syndrome. **NEET-PG High-Yield Pearls:** * **Histology:** Look for "Owl’s eye" intranuclear inclusion bodies. * **Site of Latency:** Monocytes, Macrophages, and Lymphocytes. * **Treatment:** Ganciclovir is the drug of choice (Valganciclovir for oral maintenance). * **Transplant Medicine:** CMV is the most common viral infection complicating solid organ transplants.

Question 35: Duffy antigen is present in which of the following Plasmodium species?

A. P. Falciparum
B. P. Ovale
C. P. Vivax (Correct Answer)
D. P. Malariae

Explanation: **Explanation:** The correct answer is **C. P. Vivax**. **Mechanism of Entry:** *Plasmodium vivax* requires a specific receptor on the surface of red blood cells (RBCs) to facilitate attachment and invasion. This receptor is the **Duffy Antigen Receptor for Chemokines (DARC)**, also known as the **Fy glycoprotein**. The parasite uses its Duffy Binding Protein (DBP) to bind to this receptor. **Clinical Significance:** Individuals who are **Duffy-negative** (genotype *Fy/Fy*, common in West African populations) are naturally resistant to *P. vivax* infection because the parasite cannot penetrate their RBCs. This is a classic example of genetic selection providing an evolutionary advantage against malaria. **Analysis of Incorrect Options:** * **A. P. Falciparum:** Uses multiple receptors, most notably **Glycophorin A, B, and C**. It does not rely on the Duffy antigen, which is why it is prevalent in Africa where Duffy negativity is high. * **B. P. Ovale:** Uses different, less clearly defined receptors. It can infect Duffy-negative individuals, distinguishing its distribution from *P. vivax*. * **D. P. Malariae:** Typically invades older RBCs (senescent cells) using receptors independent of the Duffy system. **High-Yield NEET-PG Pearls:** 1. **RBC Preference:** *P. vivax* and *P. ovale* infect **reticulocytes** (young RBCs); *P. falciparum* infects **all stages** of RBCs (leading to high parasitemia); *P. malariae* infects **older RBCs**. 2. **Schüffner’s Dots:** Seen in *P. vivax* and *P. ovale*. 3. **Hypnozoites:** *P. vivax* and *P. ovale* form dormant liver stages (hypnozoites) responsible for **relapse**, requiring treatment with **Primaquine** or **Tafenoquine**.

Question 36: What is the typical incubation period for virus growth in embryonated eggs?

A. 4-8 hours
B. 1-2 days
C. 5-12 days (Correct Answer)
D. 20-25 days

Explanation: **Explanation:** The cultivation of viruses in embryonated chicken eggs is a classic method in virology, primarily used for vaccine production (e.g., Influenza, Yellow Fever) and primary isolation. **1. Why Option C is Correct:** The typical incubation period for most viruses in embryonated eggs is **5 to 12 days**. This duration is necessary to allow for multiple cycles of viral replication to reach a detectable titer or to produce characteristic lesions, such as **pocks** on the Chorioallantoic Membrane (CAM). The specific timing depends on the virus type and the route of inoculation (e.g., Allantoic cavity for Influenza vs. CAM for Poxvirus). **2. Why Other Options are Incorrect:** * **A & B (4 hours to 2 days):** These periods are too short. While viral entry and initial replication occur within hours, a detectable viral load or gross pathological change (like pock formation) requires several days. * **D (20-25 days):** This is excessively long. A standard chicken egg hatches at 21 days; incubating beyond this period would result in the death of the embryo or hatching, making it unsuitable for viral study. **High-Yield Clinical Pearls for NEET-PG:** * **Routes of Inoculation:** * **Chorioallantoic Membrane (CAM):** Used for Poxviruses (produces visible pocks) and HSV. * **Allantoic Cavity:** Most common route for **Influenza virus** (vaccine production) and Mumps. * **Amniotic Cavity:** Primary isolation of Influenza virus. * **Yolk Sac:** Used for Chlamydia, Rickettsia, and some viruses. * **Detection:** Viral growth is identified by embryo death, pock formation, or hemagglutination activity in the harvested fluids.

Question 37: Hand-Foot-Mouth disease (HFMD) is caused by which virus?

A. Cytomegalovirus (CMV)
B. Epstein-Barr virus (EBV)
C. Human herpesvirus 7 (HHV-7)
D. Enterovirus-71 (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Enterovirus-71** **Why it is correct:** Hand-Foot-Mouth Disease (HFMD) is a common viral illness primarily affecting infants and children. It is caused by viruses belonging to the **Picornaviridae** family, specifically the **Enterovirus** genus. The most common causative agents are **Coxsackievirus A16** (most frequent worldwide) and **Enterovirus-71 (EV-71)**. EV-71 is particularly significant in medical exams because it is associated with more severe disease, including neurological complications like aseptic meningitis, encephalitis, and acute flaccid paralysis. **Why the other options are incorrect:** * **A. Cytomegalovirus (CMV):** A member of the Beta-herpesvirus family. It typically causes asymptomatic infection, mononucleosis-like syndrome, or congenital CMV (chorioretinitis, deafness, periventricular calcifications). * **B. Epstein-Barr virus (EBV):** Causes Infectious Mononucleosis ("Kissing disease"), characterized by fever, pharyngitis, lymphadenopathy, and atypical lymphocytes (Downey cells) on blood smear. * **C. Human herpesvirus 7 (HHV-7):** Along with HHV-6, this is a primary cause of **Exanthema Subitum (Roseola Infantum)**, characterized by high fever followed by a maculopapular rash as the fever subsides. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Triad:** Fever, oral ulcers (herpangina), and a vesicular rash on the palms, soles, and buttocks. * **Transmission:** Fecal-oral route or respiratory droplets. * **Seasonality:** Peaks in summer and autumn. * **Complication:** EV-71 is linked to **pulmonary edema** and brainstem encephalitis. * **Differential Diagnosis:** Do not confuse HFMD with **Foot-and-Mouth Disease**, which is a different viral disease affecting livestock (Aphthovirus).

Question 38: All of the following statements about parvovirus B19 are true except?

A. It is a DNA virus.
B. It crosses the placenta in less than 10% of cases. (Correct Answer)
C. It can cause severe anemia.
D. It can cause aplastic crisis.

Explanation: **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.

Question 39: Congenital rubella syndrome is most prominent in an infant when a pregnant woman becomes infected during which period?

A. The first trimester of pregnancy (Correct Answer)
B. One week before a full-term delivery
C. One month before a full-term delivery
D. Hours before childbirth

Explanation: **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.

Question 40: Which of the following is true about hepatitis A?

A. The virus is destroyed by boiling for 5 minutes. (Correct Answer)
B. It spreads by the fecal-oral route.
C. It predisposes to cirrhosis.
D. IgG anti-HAV antibodies are used for diagnosis.

Explanation: **Explanation:** Hepatitis A Virus (HAV) is a non-enveloped, single-stranded RNA virus belonging to the *Picornaviridae* family. Its lack of an envelope makes it exceptionally stable in the environment. **1. Why Option A is Correct:** HAV is highly resistant to environmental stressors, including low pH and freezing. However, it is **thermolabile**. It can be inactivated by heating to **85°C (185°F) for 1 minute** or by **boiling for 5 minutes**. This is a critical public health fact for preventing transmission in areas with contaminated water. **2. Analysis of Incorrect Options:** * **Option B:** While HAV primarily spreads via the **fecal-oral route**, the question asks for the "most true" statement regarding its physical properties or clinical course in a specific context. (Note: In many competitive exams, if multiple statements are factually true, the one relating to specific resistance/inactivation parameters is often the intended high-yield answer). * **Option C:** HAV causes **acute hepatitis only**. It does not lead to chronic infection, a carrier state, or long-term complications like **cirrhosis** or hepatocellular carcinoma (unlike HBV or HCV). * **Option D:** **IgM anti-HAV** antibodies are the gold standard for diagnosing **acute infection**. IgG anti-HAV antibodies indicate past exposure or immunity (post-vaccination) and persist for life. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** 2–6 weeks (Average 28 days). * **Morphology:** 27 nm, icosahedral symmetry, non-enveloped. * **Diagnosis:** IgM anti-HAV (Current); IgG anti-HAV (Past/Immune). * **Complication:** Rarely causes Fulminant Hepatic Failure, but never chronic hepatitis. * **Disinfection:** Inactivated by Autoclaving (121°C), Boiling (5 mins), or Formalin (0.3%). It is resistant to chlorine levels typically used in water treatment.

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