Virology Practice Questions

Q: Which of the following viruses has an RNA genome and also produces an RNA replicative intermediate?

Togavirus. **Explanation:** The core concept tested here is the **replication strategy** of different virus families. **1. Why Togavirus is Correct:** Togaviruses (e.g., Rubella, Chikungunya) are **positive-sense single-stranded RNA (+ssRNA)** viruses. To replicate their genome, they must first synthesize a complementary **negative-sense RNA strand**, which serves as a **replicative intermediate**. This intermediate then acts as a template for the synthesis of multiple new positive-sense genomic RNA strands using the viral enzyme RNA-dependent RNA polymerase (RdRp). **2. Analysis of Incorrect Options:** * **Cytomegalovirus (CMV):** This is a member of the *Herpesviridae* family. It has a **double-stranded DNA (dsDNA)** genome and replicates in the nucleus using DNA-dependent DNA polymerase; it does not utilize an RNA replicative intermediate for genome doubling. * **Hepadnavirus (Hepatitis B):** While it involves an RNA step (pre-genomic RNA), it is a **DNA virus**. It uses **reverse transcription** to convert an RNA intermediate back into DNA. * **Retrovirus (HIV):** Although it has an RNA genome, it replicates via a **DNA intermediate** (provirus) integrated into the host genome using reverse transcriptase. It does not use an RNA-to-RNA replicative intermediate for genome replication. **Clinical Pearls for NEET-PG:** * **All RNA viruses** (except Retroviruses and Orthomyxoviruses) replicate in the **cytoplasm**. * **Positive-sense RNA viruses** (Toga, Flavi, Picorna, Corona) are directly infectious because their genome can function immediately as mRNA. * **Rubella (Togavirus)** is a classic "TORCH" infection characterized by the triad of cataracts, sensorineural deafness, and congenital heart disease (PDA).

Q: The likelihood of becoming an HBsAg carrier after acute HBV infection is high in which of the following groups?

All of the above. **Explanation:** The risk of progressing from an acute Hepatitis B Virus (HBV) infection to a chronic carrier state (defined as HBsAg persistence for >6 months) is inversely proportional to the **competence of the host’s cell-mediated immunity (CMI)**. 1. **Neonates (Option A):** This is the highest-risk group. Approximately **90%** of infants infected perinatally become chronic carriers. This is due to an immature immune system that develops "immune tolerance" to the virus, failing to clear the infected hepatocytes. 2. **Chronic Hemodialysis Patients (Option B):** Patients with end-stage renal disease (ESRD) often exhibit uremia-induced immune dysfunction. Their impaired T-cell response leads to a higher rate of chronicity (approx. 10–20%) compared to healthy adults. 3. **Persons with HIV Infection (Option C):** HIV-induced depletion of CD4+ T-cells severely impairs the body's ability to mount an effective cytotoxic T-lymphocyte response against HBV, significantly increasing the likelihood of persistent infection. **Conclusion:** Since all three groups have compromised or immature immune systems, they are all at a significantly higher risk of becoming HBsAg carriers compared to healthy immunocompetent adults (where the risk is Children aged 1-5 (25-30%) > Adults (<5%). * **Serological Marker:** Persistence of **HBsAg** for more than 6 months defines the carrier state. * **The "Window Period":** The interval when both HBsAg and Anti-HBs are negative; **Anti-HBc IgM** is the only marker present. * **Ground Glass Hepatocytes:** Histological hallmark of chronic HBV infection due to HBsAg accumulation in the endoplasmic reticulum.

Q: Which of the following is a leading cause of pneumonia primarily in infants?

Respiratory syncytial virus. **Explanation:** **Respiratory Syncytial Virus (RSV)** is the correct answer because it 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 (genus *Orthopneumovirus*). The virus causes the formation of **syncytia** (multinucleated giant cells) in the respiratory epithelium, leading to inflammation, edema, and excessive mucus production that easily obstructs the small airways of infants. **Analysis of Incorrect Options:** * **Rabies:** A neurotropic rhabdovirus that causes fatal encephalitis. It does not cause pneumonia; it is transmitted via animal bites and travels via retrograde axonal transport to the CNS. * **Rhinovirus:** The most frequent cause of the "common cold" (upper respiratory tract infection). While it can occasionally exacerbate asthma, it is rarely the primary cause of pneumonia in infants compared to RSV. * **Cytomegalovirus (CMV):** While CMV can cause interstitial pneumonia, it typically occurs in **immunocompromised** patients (e.g., post-transplant) or as part of congenital CMV syndrome, rather than being the leading cause of community-acquired pneumonia in healthy infants. **High-Yield Clinical Pearls for NEET-PG:** * **Seasonality:** RSV outbreaks typically occur in winter and early spring. * **Diagnosis:** Rapid antigen detection tests or RT-PCR from nasopharyngeal aspirates are preferred. * **Treatment:** Management is primarily supportive (oxygen, hydration). **Ribavirin** (aerosolized) is reserved for severe cases or high-risk infants. * **Prophylaxis:** **Palivizumab** (a monoclonal antibody against the RSV F-protein) is used for high-risk premature infants. * **Pathology:** Look for "Syncytia" and "intracytoplasmic inclusion bodies" in histopathology.

Q: Which of the following viruses is NOT implicated in the causation of Hand, Foot, and Mouth disease?

Coxsackie B4. **Explanation:** Hand, Foot, and Mouth Disease (HFMD) is a common viral illness primarily affecting children, characterized by a vesicular eruption on the palms, soles, and oral mucosa. It is caused by viruses belonging to the **Genus Enterovirus** (Family Picornaviridae). **Why Coxsackie B4 is the correct answer:** While **Coxsackievirus Group A** and **Enterovirus 71** are the classic causative agents of HFMD, **Coxsackievirus Group B** is generally not associated with this specific clinical syndrome. Coxsackie B viruses are more commonly implicated in conditions like pleurodynia (Bornholm disease), myocarditis, pericarditis, and pancreatitis. **Analysis of Incorrect Options:** * **Coxsackie A16:** This is the **most common** cause of HFMD worldwide. It typically presents as a mild, self-limiting illness. * **Coxsackie A5 (and A7, A9, A10):** These are less common but well-documented serotypes of the Coxsackie A group that can cause sporadic cases or small outbreaks of HFMD. * **Human Enterovirus 71 (EV-71):** This is a significant pathogen in HFMD, particularly in the Asia-Pacific region. It is high-yield because it is associated with **severe neurological complications** (like aseptic meningitis or encephalomyelitis) and pulmonary edema. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Fecal-oral route and respiratory droplets. * **Morphology:** Characteristically "elliptical" or "football-shaped" vesicles on an erythematous base. * **Atypical HFMD:** Often caused by **Coxsackie A6**, presenting with more widespread lesions, bullae, and subsequent nail shedding (onychomadesis). * **Differential Diagnosis:** Herpangina (also caused by Coxsackie A), which presents with posterior pharyngeal ulcers but *without* the skin rash on hands and feet.

Q: Which of the following is not a clinical manifestation of parvovirus infection?

Tropical sprue. **Explanation:** **Parvovirus B19** is a small, single-stranded DNA virus that specifically targets and replicates in **erythroid progenitor cells** by binding to the **P-antigen** (globoside) on the cell surface. **Why Tropical Sprue is the Correct Answer:** Tropical sprue is a malabsorption syndrome characterized by chronic diarrhea and megaloblastic anemia, primarily seen in tropical regions. Its etiology is linked to persistent bacterial overgrowth in the small intestine, not viral infections. Parvovirus B19 has no clinical association with intestinal malabsorption or tropical sprue. **Analysis of Incorrect Options:** * **Erythema Infectiosum (Fifth Disease):** This is the most common presentation in children, characterized by a "slapped-cheek" rash followed by a reticular, lace-like rash on the trunk and limbs. * **Polyarthropathy:** In adults (especially women), Parvovirus B19 often presents as symmetrical inflammatory arthritis affecting small joints, mimicking rheumatoid arthritis. * **Pure Red Cell Aplasia (PRCA):** Because the virus destroys erythroblasts, it can cause a transient aplastic crisis in patients with high red cell turnover (e.g., Sickle Cell Anemia). In immunocompromised individuals, it can lead to chronic PRCA and severe anemia. **High-Yield Clinical Pearls for NEET-PG:** * **Hydrops Fetalis:** If a pregnant woman is infected, the virus can cross the placenta, leading to severe fetal anemia, high-output cardiac failure, and fetal death. * **Receptor:** The cellular receptor for Parvovirus B19 is the **P-antigen**. Individuals lacking this antigen are naturally immune. * **Diagnosis:** IgM antibodies are used for acute infection; PCR is preferred for immunocompromised patients with PRCA.

Q: Susceptible cultured cells infected with which of the following viruses would exhibit hemadsorption with the appropriate erythrocyte?

Influenza virus. **Explanation:** The correct answer is **Influenza virus**. **Mechanism of Hemadsorption:** Hemadsorption is a phenomenon where erythrocytes (RBCs) adhere to the surface of virus-infected host cells. This occurs because certain viruses, primarily those in the **Orthomyxoviridae** and **Paramyxoviridae** families, express a viral protein called **Hemagglutinin (HA)** on the host cell membrane during the budding process. When appropriate RBCs are added to the culture, they bind to these HA spikes, creating a "clumping" effect on the cell surface. This serves as a rapid presumptive test for viral replication before a cytopathic effect (CPE) is visible. **Analysis of Options:** * **Influenza virus (Correct):** As a member of Orthomyxoviridae, it possesses Hemagglutinin which strongly mediates hemadsorption. * **Sindbis virus:** An Alphavirus (Togaviridae). While it has envelope glycoproteins, it is not typically identified via the hemadsorption test in standard diagnostic virology. * **Measles virus:** Although it belongs to Paramyxoviridae and has a hemagglutinin (H) protein, it typically causes characteristic **syncytia (multinucleated giant cells)** and inclusion bodies. In the context of standard NEET-PG questions, Influenza is the classic prototype for hemadsorption. * **Respiratory Syncytial Virus (RSV):** A Paramyxovirus that **lacks** Hemagglutinin and Neuraminidase (it only has the G-protein). Therefore, it cannot perform hemadsorption. **High-Yield Clinical Pearls for NEET-PG:** 1. **Hemadsorption vs. Hemagglutination:** Hemadsorption happens on the **surface of infected cells**, while hemagglutination is the clumping of RBCs by **free viral particles** in a solution. 2. **Viruses showing Hemadsorption:** Influenza, Parainfluenza, and Mumps. 3. **RSV Key Fact:** It is the most common cause of bronchiolitis in infants and is characterized by **syncytia formation**, not hemadsorption.

Q: Which of the following is NOT true of Kyasanur Forest Disease?

Caused by a retrovirus. **Kyasanur Forest Disease (KFD)**, commonly known as "Monkey Fever," is a viral hemorrhagic fever endemic to the Western Ghats of India. **Explanation of the Correct Answer:** * **Option B (Incorrect Statement):** KFD is **not** caused by a retrovirus. It is caused by the **Kyasanur Forest Disease Virus (KFDV)**, which belongs to the family **Flaviviridae** and the genus *Flavivirus*. It is a single-stranded RNA virus. **Analysis of Other Options:** * **Option A (Incorrect Statement in Question):** This is actually the **incorrect statement** regarding the vector. KFD is transmitted by **Hard Ticks** (*Haemaphysalis spinigera*), not soft ticks. However, in the context of this specific MCQ format where "Retrovirus" is marked as the primary key, it highlights that KFDV is a Flavivirus. (Note: In many exams, both A and B could be considered technically false, but B is a fundamental virological error). * **Option C (True):** The incubation period is typically **3 to 8 days**. The disease often presents with a sudden onset of high-grade fever, headache, and severe myalgia, sometimes followed by a biphasic illness involving neurological symptoms. * **Option D (True):** A **formalin-inactivated (killed) vaccine** is available and used in endemic areas of Karnataka. It requires two primary doses (1 month apart) and periodic boosters. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoirs:** Monkeys (*Black-faced Langur* and *Bonnet Macaque*) are the common hosts; their death is often an early warning sign of an outbreak. * **Vector:** *Haemaphysalis spinigera* (Hard tick). * **Diagnosis:** PCR (early phase) or IgM ELISA. * **Distribution:** First isolated in 1957 from the Kyasanur Forest in Shimoga district, Karnataka. * **Seasonality:** Peak incidence occurs during the dry season (January–June) when human activity in forests increases.

Q: Which virus spreads via the neural route?

Rabies virus. **Explanation:** The correct answer is **Rabies virus**. The defining characteristic of Rabies pathogenesis is its **centripetal spread** via the nervous system. After an animal bite, the virus replicates locally in muscle tissue before binding to nicotinic acetylcholine receptors at the neuromuscular junction. It then travels via **retrograde axonal transport** through the sensory or motor nerves to the spinal cord and eventually the brain, leading to fatal encephalitis. **Analysis of Options:** * **Poliovirus & Enteroviruses:** While Poliovirus is neurotropic (targeting the anterior horn cells of the spinal cord), its primary route of spread within the body is **hematogenous** (viremia). It enters via the feco-oral route, replicates in the Peyer’s patches, and reaches the CNS through the bloodstream, not primarily via peripheral nerves. * **Adenovirus:** This virus typically spreads via respiratory droplets or feco-oral routes and causes pharyngitis, conjunctivitis, or gastroenteritis. It does not exhibit neural spread. **High-Yield Clinical Pearls for NEET-PG:** * **Axonal Transport:** Rabies uses the dynein motor protein for retrograde transport to the CNS. * **Negri Bodies:** These are pathognomonic intracytoplasmic eosinophilic inclusions found in the hippocampus (Ammon’s horn) and Purkinje cells of the cerebellum. * **Other Neural Spreaders:** Besides Rabies, **Herpes Simplex Virus (HSV)** and **Varicella-Zoster Virus (VZV)** also utilize neural pathways to establish latency in sensory ganglia (e.g., Trigeminal or Dorsal Root Ganglia). * **Incubation Period:** The length of the incubation period in Rabies is directly proportional to the distance of the bite site from the CNS.

Q: Chandipura virus multiplies in which of the following vectors?

Sandfly. **Explanation:** **Chandipura Virus (CHPV)** is an emerging human pathogen belonging to the family **Rhabdoviridae** (Genus: *Vesiculovirus*). It is a significant cause of explosive outbreaks of acute encephalitis, particularly in children in India (notably in Maharashtra and Gujarat). **1. Why Sandfly is correct:** The primary vector for Chandipura virus is the **Sandfly** (specifically *Phlebotomus papatasi* and *Sergentomyia* species). The virus is transmitted to humans through the bite of an infected sandfly. It is unique among Rhabdoviruses for its rapid replication and high fatality rate in pediatric populations. **2. Why other options are incorrect:** * **Black fly (Simulium fly):** While Black flies are vectors for *Onchocerca volvulus* (River blindness) and certain animal Vesiculoviruses, they are not the vectors for Chandipura virus. Note: *Simulium* and Black fly are essentially the same entity (Option B and C). * **Rat flea:** *Xenopsylla cheopis* (the rat flea) is the classic vector for *Yersinia pestis* (Plague) and *Rickettsia typhi* (Endemic typhus), not viral encephalitis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Family:** Rhabdoviridae (Bullet-shaped virus, same family as Rabies). * **Clinical Presentation:** Rapid onset of high-grade fever, altered sensorium, and convulsions, often progressing to coma and death within 24–48 hours. * **Target Population:** Primarily affects children under 15 years of age. * **Reservoir:** Likely small rodents or domestic animals, though the sandfly acts as both vector and a potential reservoir through transovarial transmission. * **Diagnosis:** Real-time PCR or ELISA for IgM antibodies. There is currently no specific antiviral treatment or vaccine.

Question 1

Which of the following viruses has an RNA genome and also produces an RNA replicative intermediate?

Accepted Answer

Togavirus

Answer

Cytomegalovirus

Answer

Hepadnavirus

Answer

Retrovirus

Question 2

The likelihood of becoming an HBsAg carrier after acute HBV infection is high in which of the following groups?

Accepted Answer

All of the above

Answer

Neonates

Answer

Chronic hemodialysis patients

Answer

Persons with HIV infection

Question 3

Which of the following is a leading cause of pneumonia primarily in infants?

Accepted Answer

Respiratory syncytial virus

Answer

Rabies

Answer

Rhinovirus

Answer

Cytomegalovirus

Question 4

Which of the following viruses is NOT implicated in the causation of Hand, Foot, and Mouth disease?

Accepted Answer

Coxsackie B4

Answer

Coxsackie A16

Answer

Coxsackie A5

Answer

Human enterovirus 71

Question 5

Which of the following is not a clinical manifestation of parvovirus infection?

Accepted Answer

Tropical sprue

Answer

Erythema infectiosum

Answer

Polyarthropathy

Answer

Pure red cell aplasia

Question 6

Susceptible cultured cells infected with which of the following viruses would exhibit hemadsorption with the appropriate erythrocyte?

Accepted Answer

Influenza virus

Answer

Sindbis virus

Answer

Measles virus

Answer

Respiratory syncytial virus

Question 7

Which of the following is NOT true of Kyasanur Forest Disease?

Accepted Answer

Caused by a retrovirus

Answer

Transmitted by soft ticks

Answer

Incubation period is 3-8 days

Answer

A killed vaccine is available

Question 8

Which virus spreads via the neural route?

Accepted Answer

Rabies virus

Answer

Poliovirus

Answer

Adenovirus

Answer

Enterovirus

Question 9

Chandipura virus multiplies in which of the following vectors?

Accepted Answer

Sandfly

Answer

Black fly

Answer

Simulum fly

Answer

Rat flea

Question 10

Which of the following statements is true regarding the rabies virus?

Accepted Answer

Produces infection that is almost fatal to humans.

Answer

Can be isolated from the blood of infected patients.

Answer

Has multiple antigenic types.

Answer

Can be transmitted by a dog 4 weeks before the dog becomes noticeably ill.

Virology — MCQs

Virology — MCQs

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