Virology Practice Questions

Q: A 64-year-old man with a travel history to Southern Minnesota presents with a 2-day history of fever, headache, and vomiting. Today, he appears confused and is disoriented to simple questions. His cerebrospinal fluid analysis shows 75% neutrophils (PMNs) and is otherwise clear. A head CT scan is normal. What is the most likely cause of his symptoms?

West Nile virus. ### Explanation **Correct Answer: D. West Nile virus** The patient presents with **Encephalitis** (fever, headache, altered mental status/confusion). The key diagnostic clue is the **CSF pleocytosis with a predominance of neutrophils (PMNs)**. While most viral encephalitides present with lymphocytic pleocytosis, **West Nile Virus (WNV)** is a classic exception where an early neutrophilic shift is frequently observed. The travel history to the Midwestern United States (Minnesota) during summer/fall months is highly suggestive of WNV, which is the most common cause of epidemic viral encephalitis in the US. **Analysis of Incorrect Options:** * **A. California Encephalitis virus:** While also an arbovirus found in the Midwest, it primarily affects children (La Crosse strain) and is less common in the elderly compared to WNV. * **B. Enterovirus:** This is the most common cause of viral *meningitis*. While it can cause encephalitis, the CSF typically shows a rapid shift to lymphocytes, and the clinical severity in an elderly patient with profound confusion points more strongly toward WNV. * **C. Herpes Simplex Virus (HSV):** HSV is the most common cause of sporadic (non-epidemic) encephalitis. However, it typically presents with **temporal lobe involvement** on imaging (CT/MRI) and hemorrhagic CSF (RBCs), neither of which are present here. **NEET-PG High-Yield Pearls:** * **WNV Vector:** *Culex* mosquito; **Reservoir:** Birds (Crow/Blue Jay deaths are sentinels). * **CSF Paradox:** WNV is a "High-Yield" exception—think neutrophils in the CSF for early viral presentation. * **Clinical Sign:** Look for "West Nile Poliomyelitis" (acute flaccid paralysis) as a specific complication. * **Diagnosis:** IgM antibody capture ELISA (MAC-ELISA) in CSF is the gold standard.

Q: Creutzfeldt-Jakob disease is due to a mutation causing the misfolding of which protein?

Prion protein. **Explanation:** **Creutzfeldt-Jakob disease (CJD)** is a fatal neurodegenerative disorder caused by **Prions** (proteinaceous infectious particles). The disease arises when the normal cellular prion protein (**PrPc**), which is primarily alpha-helical, undergoes a conformational change into an abnormal, misfolded pathogenic form called **PrPsc** (rich in beta-pleated sheets). This misfolded protein is resistant to proteases, accumulates in the brain, and induces further misfolding of healthy PrPc, leading to neuronal death and the characteristic "spongiform" appearance of the brain. **Analysis of Options:** * **Option A (Beta-amyloid):** While beta-amyloid plaques are a hallmark of **Alzheimer’s disease**, they are not the primary cause of CJD. * **Option C & D (Muscle/Structural proteins):** These are general categories of proteins. CJD specifically involves the PrP protein found in the central nervous system, not systemic structural or contractile proteins. **High-Yield Clinical Pearls for NEET-PG:** * **Triad of CJD:** Rapidly progressive dementia, myoclonus (startle-induced), and characteristic periodic sharp wave complexes (PSWC) on EEG. * **Diagnosis:** The **14-3-3 protein** in CSF is a significant marker. MRI typically shows "pulvinar sign" or "hockey-stick sign" in the thalamus. * **Resistance:** Prions are highly resistant to standard sterilization (autoclaving). They require specific protocols like **1N NaOH** or **sodium hypochlorite** for 1 hour, followed by autoclaving at 134°C. * **Variant CJD (vCJD):** Associated with "Mad Cow Disease" (Bovine Spongiform Encephalopathy) and typically affects younger patients.

Q: Cell fusion of HIV with target cell is mediated by which component?

gp41. The entry of HIV into a host cell is a two-step process involving the envelope glycoprotein complex (**gp160**), which is cleaved into two subunits: **gp120** and **gp41**. ### **Why gp41 is the Correct Answer** **gp41** is the transmembrane subunit of the HIV envelope. Once gp120 binds to the CD4 receptor and a co-receptor (CCR5 or CXCR4), a conformational change occurs that exposes gp41. gp41 then acts as a "fusion peptide," inserting itself into the host cell membrane and pulling the viral and cellular membranes together. This **cell-to-cell fusion** allows the viral capsid to enter the cytoplasm. ### **Analysis of Incorrect Options** * **gp120 (Option A):** This is the surface subunit responsible for **attachment/docking**. It binds to the CD4 receptor. While essential for the process, it does not mediate the actual fusion of membranes. * **p24 (Option B):** This is the **capsid protein**. It forms the inner conical core of the virus. It is a major diagnostic marker (p24 antigenemia) but is not involved in membrane fusion. * **p18 (Option D):** This is the **matrix protein** (also known as p17) that lies just beneath the viral envelope, providing structural integrity. ### **High-Yield Clinical Pearls for NEET-PG** * **Enfuvirtide:** A fusion inhibitor drug that works by binding to gp41, preventing the conformational change required for viral entry. * **Maraviroc:** A drug that binds to the **CCR5 co-receptor** on the host cell, preventing gp120 binding. * **Mnemonic:** gp**120** is for **Attachment** (120 is "outside"), gp**41** is for **Fusion** (41 "penetrates" the membrane). * **Screening vs. Confirmatory:** p24 is the earliest marker detected in blood (Screening/Early diagnosis); Western Blot (detecting gp120, gp41, p24) was traditionally the confirmatory test.

Q: Which virus has more than one serotype?

Influenza. **Explanation:** The correct answer is **Influenza**. This is due to the unique genetic structure and high mutation rate of the Influenza virus, which belongs to the *Orthomyxoviridae* family. **Why Influenza is Correct:** Influenza viruses (Types A, B, and C) exhibit significant antigenic variation. **Influenza A**, in particular, has multiple serotypes based on two surface glycoproteins: **Hemagglutinin (H1–H18)** and **Neuraminidase (N1–N11)**. This diversity is driven by two mechanisms: 1. **Antigenic Drift:** Point mutations causing minor changes (responsible for seasonal epidemics). 2. **Antigenic Shift:** Genetic reassortment of segmented RNA leading to major changes and new serotypes (responsible for pandemics). **Why Other Options are Incorrect:** * **Measles (Rubeola):** Despite being highly infectious, the Measles virus is **antigenically stable**. There is only **one serotype**, which is why the live-attenuated vaccine (MMR) provides lifelong immunity. * **Mumps:** This virus also exists as a **single serotype**. Infection or vaccination confers long-lasting protection. * **Rubella (German Measles):** Similar to the above, Rubella has only **one serotype**. It is a Togavirus that does not undergo significant antigenic variation. **High-Yield NEET-PG Pearls:** * **Segmented Genomes:** Remember the mnemonic **"BOAR"** (Bunyavirus, Orthomyxovirus, Arenavirus, Reovirus). These viruses can undergo reassortment. * **Vaccine Strategy:** Because Measles, Mumps, and Rubella have single serotypes, the **MMR vaccine** is highly effective. In contrast, the Influenza vaccine must be reformulated annually to match circulating serotypes. * **Poliovirus:** Often compared in this context, Polio has **three serotypes** (1, 2, and 3).

Q: A 9-month-old child presents for the second dose of oral polio vaccine, two weeks after the first vaccination. The child has mild diarrhea, and the decision is made to defer further immunizations. Bacteriological examination of a stool culture is unremarkable; however, a small, single-stranded, positive RNA virus that is not inactivated by ether is isolated from the specimen. Which of the following viruses was most likely isolated?

Poliovirus. **Explanation:** The correct answer is **D. Poliovirus**. This question tests the integration of clinical immunization schedules with the microbiological characteristics of the vaccine virus. **Why Poliovirus is correct:** The child recently received the first dose of the **Oral Polio Vaccine (OPV)**, which contains live-attenuated Sabin strains. These viruses replicate in the oropharynx and intestine and are excreted in the feces for several weeks. * **Microbiology:** Poliovirus belongs to the *Picornaviridae* family. It is a **small (27-30 nm), single-stranded, positive-sense RNA virus**. * **Ether Resistance:** Because it is **non-enveloped (naked)**, it is resistant to lipid solvents like ether, which only inactivate enveloped viruses. * **Clinical Context:** Mild diarrhea is not a contraindication for OPV, but the virus isolated is clearly the vaccine strain being shed. **Why other options are incorrect:** * **A. Adenovirus:** While it causes diarrhea and is non-enveloped, it is a **double-stranded DNA** virus. * **B. Hepatitis C:** Although it is a positive-sense RNA virus, it is **enveloped**, meaning it would be inactivated by ether. * **C. Parvovirus B19:** This is a **single-stranded DNA** virus (the only one of clinical importance). **High-Yield Pearls for NEET-PG:** 1. **OPV Shedding:** Vaccine virus can be excreted in stools for 4–6 weeks, contributing to "contact immunity" in the community. 2. **Ether Sensitivity Test:** Used to differentiate viruses; **Enveloped viruses** (e.g., HIV, Herpes, HBV) are ether-sensitive, while **Non-enveloped viruses** (e.g., Polio, HAV, HEV) are ether-resistant. 3. **Contraindications:** Minor respiratory infections or diarrhea are **NOT** contraindications for immunization. 4. **Pulse Polio:** Uses bOPV (Type 1 and 3) to eliminate the risk of VDPV2 (Vaccine-Derived Poliovirus Type 2).

Q: Which virus is responsible for causing cataracts, cardiac defects, and deafness when the fetus is exposed in utero?

Rubella. **Explanation:** The correct answer is **Rubella**. This classic triad of clinical findings—**Cataracts, Cardiac defects (most commonly Patent Ductus Arteriosus), and Sensorineural Deafness**—is known as **Gregg’s Triad**, the hallmark of **Congenital Rubella Syndrome (CRS)**. The virus is most teratogenic when the mother is infected during the first trimester of pregnancy. **Why the other options are incorrect:** * **Cytomegalovirus (CMV):** While it is the most common congenital infection, its classic presentation includes periventricular calcifications, microcephaly, and chorioretinitis (rather than cataracts). * **Varicella Zoster Virus (VZV):** Congenital Varicella Syndrome is characterized by cicatricial skin scarring (zigzag patterns), limb hypoplasia, and rudimentary digits. * **Rubeola (Measles):** This virus is not typically considered a major teratogen. Maternal infection is associated with spontaneous abortion or preterm labor, but not a specific constellation of congenital malformations. **High-Yield Clinical Pearls for NEET-PG:** * **Cardiac defect:** Patent Ductus Arteriosus (PDA) is the most common, followed by peripheral pulmonary artery stenosis. * **Ocular findings:** "Salt and pepper" retinopathy is another high-yield finding in CRS. * **Dermatological finding:** "Blueberry muffin" spots (extramedullary hematopoiesis) can be seen in Rubella and CMV. * **Diagnosis:** Detection of Rubella-specific IgM in the neonate or persistence of IgG beyond 6 months. * **Prevention:** The MMR vaccine is a live-attenuated vaccine and is **contraindicated** during pregnancy. Women should avoid pregnancy for 1 month after vaccination.

Q: Which positive test does not necessarily indicate HIV infection in a newborn?

ELISA for HIV IgG antibody. **Explanation:** The diagnosis of HIV in newborns requires distinguishing between maternal antibodies and actual neonatal infection. **1. Why ELISA for HIV IgG is the correct answer:** IgG is the only immunoglobulin class that can cross the placenta from the mother to the fetus. If a mother is HIV-positive, her IgG antibodies will be present in the newborn’s blood regardless of whether the baby is infected. These maternal antibodies can persist for up to **18 months**. Therefore, a positive ELISA for HIV IgG in a newborn only confirms maternal exposure, not necessarily neonatal infection. **2. Why the other options are incorrect:** * **p24 antigen:** This is a viral structural protein. Its presence indicates active viral replication within the infant’s body. * **Virus culture:** This is a definitive (though slow) method to detect the live virus in the infant's blood, confirming infection. * **ELISA for HIV IgA antibody:** Unlike IgG, **IgA and IgM antibodies do not cross the placenta**. If these are detected in the newborn, it indicates that the infant’s own immune system has produced them in response to an active infection. **Clinical Pearls for NEET-PG:** * **Gold Standard for Diagnosis ( 18 months):** After 18 months, maternal antibodies have waned, so standard ELISA/Western Blot can be used for diagnosis just like in adults. * **Prophylaxis:** Nevirapine or Zidovudine is typically administered to the newborn to prevent vertical transmission.

Q: What occurs when a temperate bacteriophage enters a state called lysogeny?

The virus may become integrated into the host genome.. ### Explanation **1. Why the Correct Answer is Right:** Lysogeny is a hallmark of **temperate bacteriophages** (e.g., Lambda phage). Unlike the lytic cycle, where the virus immediately replicates and kills the host, in lysogeny, the viral DNA is incorporated into the bacterial chromosome. Once integrated, the viral genome is referred to as a **prophage**. The prophage replicates synchronously with the host DNA without causing immediate harm, allowing the virus to persist in a latent state for generations. **2. Why the Other Options are Incorrect:** * **Option A & B:** These describe the **Lytic Cycle**. In this phase, the phage hijacks the host machinery to produce new virions, eventually leading to the rupture (lysis) of the bacterial cell wall to release the progeny. * **Option C:** During lysogeny, the bacterium continues its normal physiological functions. In fact, the presence of a prophage can sometimes grant the bacterium new phenotypic traits (Lysogenic Conversion) rather than turning functions off. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Lysogenic Conversion:** This is a high-yield concept where a non-pathogenic bacterium becomes pathogenic due to the prophage. * *Classic Examples:* **Diphtheria toxin** (*C. diphtheriae*), **Cholera toxin** (*V. cholerae*), **Botulinum toxin** (*C. botulinum*), and **Shiga toxin** (*S. dysenteriae*). * **Induction:** The transition from the lysogenic to the lytic cycle is called induction, often triggered by environmental stress or UV light. * **Transduction:** Lysogenic phages are responsible for **Specialized Transduction**, where specific bacterial genes adjacent to the integration site are transferred to another bacterium.

Q: Rabies can be confirmed in patients early in illness by?

Antigen detection by immunofluorescence of skin biopsy. **Explanation:** The diagnosis of Rabies in a living patient (antemortem) relies on detecting the virus before the onset of advanced neurological symptoms. **Why Option B is correct:** Rabies virus is highly neurotropic. After replicating in muscle cells, it travels via retrograde axonal transport to the CNS and subsequently spreads centrifugally to highly innervated peripheral sites. The **skin of the nape of the neck** is rich in hair follicles surrounded by sensory nerve networks. **Direct Fluorescent Antibody (DFA)** testing of a full-thickness skin biopsy from this region can detect viral antigens in these cutaneous nerves with high sensitivity and specificity early in the clinical course. **Why other options are incorrect:** * **Option A:** While corneal impression smears were historically used, they are no longer preferred due to low sensitivity and the risk of procedural injury to the patient. * **Option C:** Neutralizing antibodies usually appear late in the disease (often after the first week of symptoms) or may not appear at all in unvaccinated individuals until they are near death. They are not reliable for "early" confirmation. * **Option D:** Negri bodies (intracytoplasmic eosinophilic inclusions) are the pathological hallmark of Rabies but are typically identified during **post-mortem** examination of the brain (hippocampus/Purkinje cells). They are present in only about 70% of cases. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for Post-mortem diagnosis:** DFA of brain tissue. * **Most sensitive antemortem tests:** RT-PCR of saliva or DFA of skin biopsy. * **Negri Bodies:** Found in the Hippocampus (Ammon’s horn) and Cerebellum. * **Incubation Period:** Usually 1–3 months; determined by the distance of the bite from the CNS.

Question 1

A 64-year-old man with a travel history to Southern Minnesota presents with a 2-day history of fever, headache, and vomiting. Today, he appears confused and is disoriented to simple questions. His cerebrospinal fluid analysis shows 75% neutrophils (PMNs) and is otherwise clear. A head CT scan is normal. What is the most likely cause of his symptoms?

Accepted Answer

West Nile virus

Answer

California Encephalitis virus

Answer

Enterovirus

Answer

Herpes Simplex Virus (HSV)

Question 2

Creutzfeldt-Jakob disease is due to a mutation causing the misfolding of which protein?

Accepted Answer

Prion protein

Answer

Beta-amyloid protein

Answer

Muscle proteins

Answer

Structural proteins

Question 3

Cell fusion of HIV with target cell is mediated by which component?

Accepted Answer

gp41

Answer

gp 120

Answer

p24

Answer

p 18

Question 4

Which virus has more than one serotype?

Accepted Answer

Influenza

Answer

Measles

Answer

Mumps

Answer

Rubella

Question 5

A 9-month-old child presents for the second dose of oral polio vaccine, two weeks after the first vaccination. The child has mild diarrhea, and the decision is made to defer further immunizations. Bacteriological examination of a stool culture is unremarkable; however, a small, single-stranded, positive RNA virus that is not inactivated by ether is isolated from the specimen. Which of the following viruses was most likely isolated?

Accepted Answer

Poliovirus

Answer

Adenovirus

Answer

Hepatitis C

Answer

Parvovirus B19

Question 6

What is true about HIV transmission?

Accepted Answer

HIV transmission is more common from male to female than from female to male.

Answer

HIV is not transmitted through semen.

Answer

There are more chances of HIV transmission during LSCS than during normal labour.

Answer

HIV is more infectious than hepatitis B.

Question 7

Which virus is responsible for causing cataracts, cardiac defects, and deafness when the fetus is exposed in utero?

Accepted Answer

Rubella

Answer

Cytomegalovirus

Answer

Varicella zoster

Answer

Rubeola

Question 8

Which positive test does not necessarily indicate HIV infection in a newborn?

Accepted Answer

ELISA for HIV IgG antibody

Answer

p24 antigen

Answer

Virus culture

Answer

ELISA for HIV IgA antibody

Question 9

What occurs when a temperate bacteriophage enters a state called lysogeny?

Accepted Answer

The virus may become integrated into the host genome.

Answer

The bacterial cell is lysed.

Answer

Many new viruses are produced.

Answer

Most normal bacterial functions are turned off.

Question 10

Rabies can be confirmed in patients early in illness by?

Accepted Answer

Antigen detection by immunofluorescence of skin biopsy

Answer

Antigen detection by corneal smears immunofluorescence

Answer

Demonstration of neutralizing antibodies

Answer

Demonstration of Negri bodies in hippocampus

Virology — MCQs

Virology — MCQs

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