Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 761: Rabies can be transmitted by all EXCEPT:

A. Bite of rabid dog
B. Bite of bats
C. Bite of fox
D. Bite of squirrel (Correct Answer)

Explanation: **Explanation:** Rabies is a fatal viral zoonosis caused by the **Lyssavirus (Rhabdoviridae family)**. The virus is primarily maintained in nature by mammalian reservoirs, specifically those in the orders **Carnivora** (dogs, foxes, raccoons) and **Chiroptera** (bats). **Why Option D is correct:** Small rodents such as **squirrels**, hamsters, guinea pigs, gerbils, rats, and mice, as well as lagomorphs (rabbits and hares), are almost never found to be infected with rabies. Furthermore, they have not been known to transmit rabies to humans. According to the CDC and WHO, bites from these animals are generally not considered an indication for Rabies Post-Exposure Prophylaxis (PEP). **Why other options are incorrect:** * **Option A (Dog):** Domestic dogs are the most common source of rabies transmission to humans worldwide (responsible for >99% of human cases). * **Option B (Bat):** Bats are a significant reservoir, especially in the Americas. They can transmit the virus through bites that are often so small they go unnoticed. * **Option C (Fox):** Foxes, along with wolves and jackals, are major sylvatic (wildlife) reservoirs of the virus. **High-Yield Clinical Pearls for NEET-PG:** 1. **Negri Bodies:** Pathognomonic intracytoplasmic inclusion bodies found in the hippocampus (Ammon’s horn) and cerebellum (Purkinje cells). 2. **Street Virus vs. Fixed Virus:** Street virus is the natural isolate with long incubation; Fixed virus is laboratory-attenuated (Pasteur) used for vaccine production. 3. **Hydrophobia:** Pathognomonic clinical sign caused by forceful spasms of the diaphragm and accessory respiratory muscles when attempting to swallow. 4. **Post-Exposure Prophylaxis (PEP):** Includes wound washing (most important), Rabies Immunoglobulin (RIG), and modern cell culture vaccines (Day 0, 3, 7, 14, 28).

Question 762: Which of the following is the pathogen responsible for blindness in advanced HIV infections?

A. Fungus
B. Toxoplasma
C. Epstein-Barr virus
D. Cytomegalovirus (Correct Answer)

Explanation: **Explanation:** **Cytomegalovirus (CMV)** is the most common cause of blindness in patients with advanced HIV/AIDS, typically occurring when the **CD4 count falls below 50 cells/mm³**. CMV retinitis is characterized by a full-thickness retinal necrosis and vasculitis. Clinically, it presents as painless vision loss, floaters, or blurred vision. On fundoscopy, it classically shows the **"Pizza-pie" or "Tomato-sauce and cheese" appearance**, consisting of perivascular hemorrhages and white fluffy exudates. **Analysis of Incorrect Options:** * **Fungus:** While *Cryptococcus neoformans* can cause visual loss due to increased intracranial pressure (papilledema), it is not the primary pathogen for direct retinal destruction leading to blindness. *Candida* endophthalmitis usually occurs in IV drug users or neutropenic patients. * **Toxoplasma gondii:** This parasite causes chorioretinitis, but it typically presents with focal necrotizing lesions and significant vitreous inflammation ("headlight in the fog" appearance). It is less common than CMV as a cause of blindness in advanced AIDS. * **Epstein-Barr virus (EBV):** In HIV patients, EBV is primarily associated with **Oral Hairy Leukoplakia** and **Primary CNS Lymphoma**, not retinitis or blindness. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** **Ganciclovir** (or Valganciclovir). Foscarnet is used for ganciclovir-resistant cases. * **CD4 Threshold:** Always associate CMV retinitis with **CD4 < 50**. * **Other CMV manifestations in AIDS:** Esophagitis (linear ulcers) and Colitis. * **Diagnosis:** Primarily clinical via fundoscopy; PCR of aqueous or vitreous humor can be used for confirmation.

Question 763: Two siblings, ages 2 and 4, experience fever, rhinitis, and pharyngitis that result in laryngotracheobronchitis. Both have a harsh, bark-like cough and hoarseness. Which of the following viruses is the leading cause of their syndrome?

A. Adenovirus
B. Coxsackievirus B
C. Parainfluenza virus (Correct Answer)
D. Rhinovirus

Explanation: ### Explanation **Correct Option: C. Parainfluenza virus** The clinical presentation described—fever, rhinitis, and pharyngitis progressing to **laryngotracheobronchitis** (commonly known as **Croup**) with a characteristic **bark-like cough** and hoarseness—is the classic hallmark of Parainfluenza virus infection. * **Mechanism:** Parainfluenza virus (specifically Type 1 and 2) causes subglottic edema and narrowing of the airway. * **Radiology:** On an X-ray, this narrowing produces the high-yield **"Steeple Sign"** due to subglottic tracheal constriction. It is the most common cause of croup in children aged 6 months to 3 years. **Incorrect Options:** * **A. Adenovirus:** Typically causes pharyngoconjunctival fever (sore throat + conjunctivitis), pneumonia, or hemorrhagic cystitis. While it can cause respiratory distress, it is not the primary cause of croup. * **B. Coxsackievirus B:** Most commonly associated with pleurodynia (Bornholm disease), myocarditis, and pericarditis. Coxsackievirus A is more famous for Herpangina and Hand-Foot-Mouth disease. * **D. Rhinovirus:** The leading cause of the "common cold." It primarily affects the upper respiratory tract (sneezing, nasal congestion) but rarely causes the subglottic inflammation seen in croup. **High-Yield Clinical Pearls for NEET-PG:** 1. **Croup vs. Epiglottitis:** Croup (Parainfluenza) presents with a barky cough and a "Steeple Sign." Epiglottitis (*H. influenzae*) presents with drooling, tripod positioning, and a **"Thumb Sign"** on X-ray. 2. **Virology:** Parainfluenza belongs to the **Paramyxoviridae** family (enveloped, negative-sense ssRNA). 3. **Treatment:** Management of croup usually involves cool mist, humidified oxygen, and **dexamethasone**. Nebulized epinephrine is used in severe cases to reduce airway edema.

Question 764: Phage typing is useful as an epidemiological tool in all, except?

A. Salmonella
B. Staph aureus
C. V. Cholerae
D. Shigella dysenteriae (Correct Answer)

Explanation: **Explanation:** Phage typing is a phenotypic method used to detect single strains of bacteria within a single species by utilizing their susceptibility to specific bacteriophages. It is primarily used as an **epidemiological tool** to trace the source of outbreaks and identify transmission patterns. **Why Shigella dysenteriae is the correct answer:** While phage typing exists for several enteric pathogens, it is **not** a standard or routinely used epidemiological tool for *Shigella dysenteriae*. For *Shigella*, **Colicin typing** (based on the production of bacteriocins) and biochemical reactions are the traditional phenotypic methods used for subtyping, though these have largely been replaced by molecular methods like PFGE and Whole Genome Sequencing (WGS). **Analysis of Incorrect Options:** * **Salmonella:** Phage typing is the gold standard for subtyping *Salmonella Typhi* (Vi-phage typing) and *Salmonella Typhimurium* (DT104) to track foodborne outbreaks. * **Staph aureus:** This was the first organism for which phage typing was developed. It is classically used to differentiate strains (e.g., identifying the source of a surgical site infection or nursery outbreak). * **V. Cholerae:** Phage typing is extensively used for *Vibrio cholerae* O1 (Basu and Mukerjee scheme) to differentiate between Classical and El Tor biotypes and for further epidemiological surveillance. **High-Yield Clinical Pearls for NEET-PG:** * **Bacteriocin Typing:** Most useful for *Shigella* (Colicin) and *Pseudomonas* (Pyocin). * **Vi-Phage Typing:** Specific for *Salmonella Typhi*; it uses the Vi antigen as a receptor for the phage. * **Reverse Typing:** Used in *Staphylococcus aureus* when the isolate is not typable by standard phages (the isolate's own phages are used against indicator strains).

Question 765: Which small nonparticulate protein leads to enhanced replication of HBV as well as HIV?

A. HBc Ag
B. HBs Ag
C. Hbe Ag
D. HBx Ag (Correct Answer)

Explanation: **Explanation:** The correct answer is **HBx Ag** (Option D). **Why HBx Ag is Correct:** The Hepatitis B virus (HBV) genome contains four overlapping open reading frames (ORFs): S, C, P, and X. The **X gene** encodes the **HBx protein**, a small, non-particulate protein that functions as a transcriptional transactivator. It does not bind to DNA directly but interacts with various host cellular proteins (like transcription factors and kinases) to upregulate the expression of both viral and host genes. Crucially, HBx Ag can transactivate the **HIV-1 Long Terminal Repeat (LTR)** promoter, thereby enhancing the replication of HIV in co-infected patients. Furthermore, HBx Ag plays a significant role in hepatocarcinogenesis by interfering with the p53 tumor suppressor gene. **Why Other Options are Incorrect:** * **HBc Ag (Hepatitis B core Antigen):** This is a particulate structural protein that forms the nucleocapsid. It is not secreted into the blood and does not possess transactivating properties. * **HBs Ag (Hepatitis B surface Antigen):** This is the envelope protein found on the surface of the virion and as non-infectious spherical or tubular particles. Its primary role is viral attachment and entry, not transcriptional regulation. * **HBe Ag (Hepatitis B e Antigen):** This is a soluble protein derived from the precore/core ORF. It serves as a marker of high viral infectivity and active replication but does not enhance the replication of other viruses like HIV. **High-Yield Clinical Pearls for NEET-PG:** * **HBx Ag** is the only HBV protein linked directly to the development of **Hepatocellular Carcinoma (HCC)** via p53 inhibition. * **HBe Ag** indicates high infectivity; its disappearance and the appearance of Anti-HBe (seroconversion) usually signify a favorable prognosis. * **Window Period:** The interval where HBsAg and Anti-HBs are both negative; **Anti-HBc IgM** is the sole diagnostic marker during this phase.

Question 766: What is the primary mode of transmission for enteroviruses?

A. Vector-mediated transmission
B. Droplet infection
C. Fecal-oral route (Correct Answer)
D. Direct skin contact

Explanation: **Explanation:** **Correct Answer: C. Fecal-oral route** Enteroviruses (a genus within the *Picornaviridae* family) include Poliovirus, Coxsackieviruses (A and B), Echoviruses, and numbered Enteroviruses. The primary mode of transmission is the **fecal-oral route**. These viruses are non-enveloped, making them exceptionally stable in acidic environments (like the stomach) and resistant to bile and detergents. They replicate initially in the pharynx and the Peyer’s patches of the distal ileum, after which they are shed in high concentrations in the feces for several weeks. **Analysis of Incorrect Options:** * **A. Vector-mediated transmission:** This is characteristic of Arboviruses (e.g., Dengue, Zika, Japanese Encephalitis), which require an arthropod host like mosquitoes or ticks. * **B. Droplet infection:** While some enteroviruses (like Polio or Coxsackie) can be found in oropharyngeal secretions early in the infection and transmitted via respiratory droplets, this is a secondary and less common route compared to the fecal-oral path. * **D. Direct skin contact:** This is typical for viruses like HPV (warts) or Molluscum contagiosum, but not the primary mechanism for systemic enteroviral infections. **High-Yield Clinical Pearls for NEET-PG:** * **Acid Stability:** Unlike Rhinoviruses (also Picornaviruses), Enteroviruses are **acid-stable**, allowing them to pass through the stomach. * **Seasonal Pattern:** Infections typically peak during **summer and autumn** in temperate climates. * **Clinical Spectrum:** They are the leading cause of **aseptic meningitis**. Specific associations include **Herpangina** and **Hand-Foot-Mouth Disease** (Coxsackie A) and **Myocarditis/Pleurodynia** (Coxsackie B). * **Polio Eradication:** India was declared Polio-free in 2014; the last case was reported in 2011 (Howrah, West Bengal).

Question 767: Coxsackie virus is implicated in which of the following conditions?

A. Herpes zoster
B. Measles
C. Smallpox
D. Hand, Foot, and Mouth disease (Correct Answer)

Explanation: **Explanation:** **1. Why the Correct Answer is Right:** **Hand, Foot, and Mouth Disease (HFMD)** is a common viral illness primarily caused by **Coxsackievirus A16** (most common) and **Enterovirus 71**. Coxsackieviruses belong to the *Picornaviridae* family (genus *Enterovirus*). The disease is characterized by a prodrome of fever followed by a vesicular eruption on the palms, soles, and oral mucosa (herpangina). **2. Why the Other Options are Incorrect:** * **A. Herpes Zoster:** This is caused by the reactivation of the **Varicella-Zoster Virus (VZV)**, a DNA virus belonging to the *Herpesviridae* family. It typically presents as a painful, unilateral dermatomal rash. * **B. Measles:** This is caused by the **Rubeola virus**, a member of the *Paramyxoviridae* family. It is clinically identified by the "3 Cs" (Cough, Coryza, Conjunctivitis) and pathognomonic **Koplik spots**. * **C. Smallpox:** This was caused by the **Variola virus**, a member of the *Poxviridae* family. It was officially declared eradicated by the WHO in 1980. **3. Clinical Pearls for NEET-PG:** * **Coxsackie A** is generally associated with **Herpangina** and **HFMD**. * **Coxsackie B** is the most common cause of **Myocarditis**, Pericarditis, and **Bornholm disease** (epidemic pleurodynia/Devil’s grip). * **Enterovirus 71** is significant because it can lead to severe neurological complications like aseptic meningitis or encephalitis. * **Transmission:** Fecal-oral route is the primary mode of spread for Enteroviruses.

Question 768: A pyrexial and neutropenic immunocompromised patient due to transplantation most likely has which of the following infections?

A. Herpes Simplex Virus (HSV)
B. Cytomegalovirus (CMV) (Correct Answer)
C. Gram-negative organisms
D. Gram-positive organisms

Explanation: **Explanation:** **Why Cytomegalovirus (CMV) is the correct answer:** In the context of post-transplant patients, **Cytomegalovirus (CMV)** is the most common and clinically significant viral pathogen. It typically manifests between 1 to 6 months post-transplant (the "middle period"). CMV is notorious for causing a systemic syndrome characterized by **fever (pyrexia)** and hematological abnormalities, specifically **neutropenia**, leukopenia, and thrombocytopenia. It can also lead to organ-specific invasive diseases like pneumonitis, hepatitis, or colitis. **Analysis of Incorrect Options:** * **Herpes Simplex Virus (HSV):** While common in immunocompromised hosts, HSV usually presents with mucocutaneous lesions (cold sores or genital ulcers) rather than systemic pyrexia and neutropenia. * **Gram-negative/Gram-positive organisms:** While bacterial infections are the leading cause of fever in neutropenic patients *immediately* after chemotherapy or in the very early post-transplant phase (<1 month), the specific combination of pyrexia *and* induced neutropenia in a stable transplant recipient is a classic hallmark of CMV infection. **High-Yield Clinical Pearls for NEET-PG:** * **CMV Timing:** Most common opportunistic infection 1–6 months post-solid organ transplant (SOT) or hematopoietic stem cell transplant (HSCT). * **Diagnosis:** The gold standard for tissue diagnosis is the presence of **"Owl’s eye" intranuclear inclusion bodies**. For monitoring, **CMV PCR** or pp65 antigenemia assay is used. * **Treatment:** **Ganciclovir** is the drug of choice; Foscarnet is used for resistant cases. * **Prophylaxis:** Valganciclovir is frequently used to prevent CMV disease in high-risk transplant recipients.

Question 769: What is the most common cause of the common cold?

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

Explanation: **Explanation:** The common cold, also known as **Acute Nasopharyngitis**, is a viral infectious disease of the upper respiratory tract. It is primarily caused by viruses, with **Rhinoviruses** being the most frequent causative agents (accounting for 30–50% of cases). Other common viral triggers include Coronaviruses, Respiratory Syncytial Virus (RSV), and Parainfluenza viruses. These viruses spread via respiratory droplets or direct contact, leading to inflammation of the nasal mucosa and throat. **Analysis of Options:** * **Bacteria (B):** While bacteria like *Streptococcus pneumoniae* or *Haemophilus influenzae* can cause secondary infections (e.g., sinusitis or otitis media) following a cold, they are not the primary cause of the common cold itself. * **Fungus (C):** Fungal infections of the upper respiratory tract (like Mucormycosis or Aspergillosis) are rare and typically occur in immunocompromised individuals. They present with much more severe symptoms than a common cold. * **Allergic Reaction (D):** Allergic rhinitis can mimic cold symptoms (sneezing, runny nose), but it is an inflammatory response to allergens (pollen, dust) rather than an infectious process. It lacks systemic symptoms like low-grade fever or sore throat. **High-Yield NEET-PG Pearls:** * **Most common cause:** Rhinoviruses (belong to the *Picornaviridae* family). * **Receptor:** Most Rhinoviruses use **ICAM-1** (CD54) to enter host cells. * **Seasonality:** Rhinoviruses peak in autumn and spring; Coronaviruses peak in winter. * **Management:** Treatment is purely symptomatic (decongestants, fluids); **antibiotics are ineffective** as the etiology is viral.

Question 770: Which of the following arboviruses is NOT transmitted by a tick?

A. Japanese encephalitis (Correct Answer)
B. Kyasanur forest disease
C. Russian spring summer encephalitis
D. Omsk hemorrhagic fever

Explanation: **Explanation:** Arboviruses (Arthropod-borne viruses) are classified based on their primary vectors. The question tests the ability to distinguish between **Mosquito-borne** and **Tick-borne** viruses within the Flaviviridae family. **1. Why Japanese Encephalitis (JE) is the correct answer:** Japanese Encephalitis is transmitted primarily by the bite of infected **Culex mosquitoes** (specifically *Culex tritaeniorhynchus*). It is the leading cause of viral encephalitis in Asia. Unlike the other options, it has no association with tick vectors. Its natural cycle involves pigs (amplifier hosts) and water birds (reservoirs). **2. Analysis of Incorrect Options (Tick-borne Viruses):** * **Kyasanur Forest Disease (KFD):** Known as "Monkey Fever" in India (Karnataka), it is transmitted by the **Hard tick (*Haemaphysalis spinigera*)**. * **Russian Spring-Summer Encephalitis (RSSE):** A classic tick-borne encephalitis (TBE) complex virus transmitted by ***Ixodes* ticks**. * **Omsk Hemorrhagic Fever (OHF):** Found in Siberia, this is also a member of the TBE complex transmitted by ***Dermacentor* ticks** and sometimes through contact with infected muskrats. **High-Yield Clinical Pearls for NEET-PG:** * **Vector Mnemonic:** Remember **"KRO"** for Tick-borne Flaviviruses: **K**yasanur, **R**ussian Spring-Summer, and **O**msk. * **JE Vector:** *Culex* mosquitoes are "night-biters" and breed in stagnant water like rice fields. * **JE Diagnosis:** The gold standard is the detection of **IgM antibodies in CSF** or serum using MAC-ELISA. * **KFD:** Important for Indian exams; look for a history of forest exposure and sudden high fever with prostration.

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