Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 711: What is the characteristic appearance of Cowdry type A inclusion bodies?

A. Granular (Correct Answer)
B. Circumscribed
C. Seen in polio virus infections
D. None of the above

Explanation: **Explanation:** **Cowdry type A inclusion bodies** are characteristic intranuclear, eosinophilic (acidophilic) inclusions. The correct answer is **Granular** because these inclusions typically have a **granular or "ground-glass" appearance** and are surrounded by a clear halo (due to the peripheral displacement of chromatin), often referred to as the "owl's eye" appearance in certain contexts. * **Why Option A is correct:** Cowdry Type A inclusions are formed by the accumulation of viral proteins and nucleic acids within the nucleus. Morphologically, they appear as dense, granular masses that push the host cell chromatin toward the nuclear membrane (chromatin margination). * **Why Option B is incorrect:** **Circumscribed** (or "droplet-like") appearance is more characteristic of **Cowdry type B** inclusion bodies (seen in Poliovirus or Adenovirus), which are smaller, multiple, and do not show significant chromatin margination. * **Why Option C is incorrect:** Poliovirus produces Cowdry type B inclusions. Cowdry type A inclusions are classically associated with the **Herpesviridae family** (HSV-1, HSV-2, VZV) and **Yellow Fever virus** (Torres bodies). **High-Yield Clinical Pearls for NEET-PG:** * **Cowdry Type A:** Large, single, granular, eosinophilic. Associated with **HSV, VZV, and CMV** (though CMV is specifically known for "Owl's eye" inclusions). * **Cowdry Type B:** Multiple, small, circumscribed. Associated with **Poliovirus and Adenovirus**. * **Negri Bodies:** Pathognomonic for **Rabies** (intracytoplasmic, eosinophilic, found in Purkinje cells of the cerebellum). * **Guarnieri Bodies:** Intracytoplasmic inclusions seen in **Variola (Smallpox)** and Vaccinia. * **Henderson-Peterson Bodies:** Large, intracytoplasmic inclusions seen in **Molluscum Contagiosum**.

Question 712: Which of the following is seen in Rabies?

A. Cowdry A
B. Negri bodies (Correct Answer)
C. Guarneri bodies
D. Bollinger bodies

Explanation: **Explanation:** **Negri bodies** are the hallmark histopathological finding in Rabies. They are **intracytoplasmic, eosinophilic, round-to-oval inclusion bodies** found in the cytoplasm of neurons. They represent sites of viral replication (nucleocapsid assembly). They are most commonly found in the **Purkinje cells of the cerebellum** and the **pyramidal cells of the hippocampus (Ammon’s horn)**. Their presence is 100% diagnostic of Rabies, though they are absent in about 20% of cases. **Analysis of Incorrect Options:** * **Cowdry A bodies:** These are intranuclear, eosinophilic "dropped-in" inclusions surrounded by a clear halo. They are characteristic of **Herpes Simplex Virus (HSV)** and **Varicella-Zoster Virus (VZV)**. * **Guarneri bodies:** These are intracytoplasmic inclusions seen in **Variola (Smallpox)** and Vaccinia virus infections. * **Bollinger bodies:** These are large, granular intracytoplasmic inclusions seen in **Fowlpox**. (Note: Inside Bollinger bodies, smaller Borrel bodies are found). **High-Yield Clinical Pearls for NEET-PG:** * **Virus Structure:** Rabies is caused by a Rhabdovirus (Lyssavirus genus), which is a negative-sense, single-stranded RNA virus with a characteristic **bullet-shaped** appearance. * **Pathogenesis:** The virus travels via **retrograde axonal transport** (dynein motors) from the site of the bite to the CNS. * **Diagnosis:** While Negri bodies are classic for autopsy, the gold standard for diagnosis in animals/humans is the **Direct Fluorescent Antibody (DFA)** test on brain tissue or skin biopsy from the nape of the neck. * **Hydrophobia:** This pathognomonic sign is due to painful spasms of the pharyngeal muscles when attempting to swallow.

Question 713: Subacute sclerosing panencephalitis occurs as a complication of which of the following infections?

A. Pneumonia
B. Measles (Correct Answer)
C. Diphtheria
D. Pertussis

Explanation: ### Explanation **Correct Answer: B. Measles** **Subacute Sclerosing Panencephalitis (SSPE)**, also known as Dawson disease, is a rare, progressive, and fatal neurodegenerative disease caused by a persistent infection with a **defective Measles virus**. * **Pathophysiology:** SSPE occurs years (typically 7–10 years) after an initial measles infection. It is caused by a mutant strain of the virus that lacks the **M (Matrix) protein**, preventing the virus from budding. Instead, the virus spreads directly from cell to cell via syncytia formation, leading to widespread inflammation and demyelination in the CNS. * **Clinical Presentation:** It typically presents in children or young adults with behavioral changes, followed by myoclonic jerks, seizures, and eventually coma or death. **Why Incorrect Options are Wrong:** * **A. Pneumonia:** While measles can cause Hecht’s giant cell pneumonia (especially in immunocompromised patients), pneumonia itself is a clinical syndrome caused by various pathogens and does not lead to SSPE. * **C. Diphtheria:** Caused by *Corynebacterium diphtheriae*, it primarily leads to pseudomembranous pharyngitis. Neurological complications include cranial nerve palsies or peripheral neuropathy due to the exotoxin, not chronic encephalitis. * **D. Pertussis:** Caused by *Bordetella pertussis*, it leads to "whooping cough." While it can cause encephalopathy due to hypoxia or toxins, it does not cause a slow-virus infection like SSPE. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Characterized by high titers of **anti-measles antibodies** in the CSF and serum (intrathecal synthesis). * **EEG Finding:** Classic **periodic complexes** (high-voltage slow waves) occurring at regular intervals. * **Histology:** Presence of **Cowdry type A** intranuclear inclusion bodies in neurons and glial cells. * **Prevention:** The most effective way to prevent SSPE is through widespread **MMR vaccination**.

Question 714: Which virus possesses a positive-sense single-stranded RNA genome?

A. Poliovirus (Correct Answer)
B. Papovavirus
C. Influenza virus
D. All of the above

Explanation: **Explanation:** The classification of viruses based on their genome is a high-yield topic for NEET-PG. Viruses are categorized by the type of nucleic acid (DNA or RNA), strand number (single or double), and polarity (positive or negative sense). **1. Why Poliovirus is correct:** Poliovirus belongs to the **Picornaviridae** family. It possesses a **positive-sense single-stranded RNA (+ssRNA)** genome. "Positive-sense" means the viral RNA is identical to mRNA and can be directly translated into proteins by the host cell's ribosomes immediately upon entry. **2. Why the other options are incorrect:** * **Papovavirus (Option B):** These are **Double-Stranded DNA (dsDNA)** viruses. This family includes important human pathogens like Human Papillomavirus (HPV) and BK/JC viruses. Remember: Most DNA viruses are double-stranded (except Parvovirus). * **Influenza virus (Option C):** This belongs to the **Orthomyxoviridae** family. It possesses a **negative-sense single-stranded RNA (-ssRNA)** genome which is **segmented** (8 segments). Negative-sense viruses must carry their own RNA-dependent RNA polymerase to transcribe the negative strand into a positive mRNA strand before translation. **Clinical Pearls for NEET-PG:** * **Picornavirus Mnemonic:** "PERCH" – **P**olio, **E**cho, **R**hino, **C**oxsackie, and **H**epatitis A. All are +ssRNA. * **Segmented Genomes:** Remember **"BOAR"** – **B**unyavirus, **O**rthomyxovirus, **A**renavirus, and **R**eovirus. This feature allows for genetic reassortment (Antigenic Shift). * **Poliovirus specific:** It lacks an envelope (naked virus), making it resistant to acidic gastric pH, which facilitates its fecal-oral transmission.

Question 715: Which of the following mycobacteria can cause disease in an HIV-positive patient with a CD4 count of 600/cu.mm?

A. M. Tuberculosis (Correct Answer)
B. MAC
C. M. Chelonei
D. M. Fortuitum

Explanation: **Explanation:** The risk of specific opportunistic infections in HIV patients is strictly correlated with the **CD4 T-lymphocyte count**. This question tests your ability to distinguish between pathogens that require severe immunosuppression and those that can cause disease even when the immune system is relatively preserved. **1. Why M. Tuberculosis (MTB) is correct:** * **M. Tuberculosis** is the most common opportunistic infection in HIV patients worldwide. * Unlike Non-Tuberculous Mycobacteria (NTM), MTB is highly virulent. It can cause pulmonary or extrapulmonary disease at **any CD4 count**. * When the CD4 count is **>500 cells/cu.mm**, the clinical presentation of TB is similar to that in HIV-negative individuals (typical apical cavitary lesions). As the CD4 count drops, the presentation becomes "atypical" (lower lobe involvement, miliary spread, and lack of cavitations). **2. Why the other options are incorrect:** * **B. MAC (M. avium complex):** This is a late-stage opportunistic infection. It typically occurs only when the CD4 count falls **below 50 cells/cu.mm**. It usually presents as disseminated disease with fever, weight loss, and lymphadenopathy. * **C & D. M. Chelonei and M. Fortuitum:** These are "Rapid Growers" (Runyon Group IV). While they can cause skin and soft tissue infections, they rarely cause systemic disease in HIV patients unless there is profound immunosuppression (usually CD4 <100 cells/cu.mm). **High-Yield Clinical Pearls for NEET-PG:** * **CD4 >500:** MTB, Kaposi Sarcoma, Bacterial pneumonia. * **CD4 <200:** Pneumocystis jirovecii (PJP) — Start prophylaxis with Co-trimoxazole. * **CD4 <100:** Toxoplasmosis, Cryptococcosis, CMV (Retinitis), Esophageal Candidiasis. * **CD4 <50:** MAC, CNS Lymphoma. * **Rule of Thumb:** If an HIV patient has symptoms and a high CD4 count, always suspect **MTB** first.

Question 716: African Burkitt's lymphoma is caused by which virus?

A. Cytomegalovirus
B. Epstein-Barr virus (Correct Answer)
C. Herpes zoster virus
D. Infectious mononucleosis virus

Explanation: **Explanation:** **Epstein-Barr Virus (EBV)**, also known as Human Herpesvirus 4 (HHV-4), is the correct answer. It is a potent oncogenic virus that infects B-lymphocytes via the **CD21 receptor**. In equatorial Africa, EBV is strongly associated with the endemic (African) form of Burkitt’s lymphoma, typically presenting as a rapidly growing tumor of the jaw. The pathogenesis involves a specific chromosomal translocation, **t(8;14)**, which leads to the overexpression of the **c-myc** oncogene, driving uncontrolled B-cell proliferation. **Analysis of Incorrect Options:** * **A. Cytomegalovirus (CMV/HHV-5):** Primarily causes infectious mononucleosis-like syndrome (heterophile negative) and congenital infections (cytomegalic inclusion disease), but is not oncogenic. * **C. Herpes Zoster Virus (VZV/HHV-3):** Causes chickenpox (primary) and shingles (reactivation); it does not cause malignancies. * **D. Infectious Mononucleosis Virus:** This is actually another name for **EBV** itself. However, in medical examinations, when asked for the causative agent of a specific pathology, the formal taxonomic name (Epstein-Barr Virus) is the preferred answer over the clinical syndrome name. **High-Yield Clinical Pearls for NEET-PG:** * **EBV-Associated Malignancies:** Burkitt’s Lymphoma, Nasopharyngeal Carcinoma (undifferentiated type), Hodgkin’s Lymphoma (Mixed cellularity), and Oral Hairy Leukoplakia (in HIV). * **Burkitt’s Lymphoma Histology:** Characterized by a **"Starry sky appearance"** (tingible body macrophages against a sea of neoplastic B-cells). * **Diagnosis:** Monospot test (detects heterophile antibodies) and Paul-Bunnell test. * **Atypical Lymphocytes:** Also known as **Downey cells** (activated T-cells), seen on peripheral smears of EBV patients.

Question 717: In a patient with HIV infection, oral ulcer is most commonly due to which of the following?

A. Candida (Correct Answer)
B. Cryptococcosis
C. Histoplasma
D. Trichophyton

Explanation: **Explanation:** In patients with HIV/AIDS, **Candida albicans** is the most common opportunistic fungal infection of the oral cavity. It typically manifests when the CD4 count falls below 500 cells/mm³. Oral candidiasis (thrush) presents as pseudomembranous white patches that can be scraped off, leaving an erythematous base. It serves as a critical clinical marker for disease progression and is often the first sign of HIV-related immunosuppression. **Analysis of Options:** * **A. Candida (Correct):** It is the most frequent cause of oral lesions in HIV. While other viruses (like HSV or CMV) can cause ulcers, among the fungal options provided, Candida is the primary culprit. * **B. Cryptococcosis:** Caused by *Cryptococcus neoformans*, this typically presents as subacute meningitis or pneumonia in HIV patients (usually CD4 <100). Oral involvement is extremely rare. * **C. Histoplasma:** *Histoplasma capsulatum* can cause disseminated disease in AIDS patients (CD4 <150), which may occasionally manifest as painful oral ulcers, but it is far less common than Candidiasis. * **D. Trichophyton:** This is a dermatophyte responsible for superficial skin, hair, and nail infections (e.g., Tinea corporis). It does not cause mucosal oral ulcers. **High-Yield Clinical Pearls for NEET-PG:** * **Oral Candidiasis types:** Pseudomembranous (most common), Erythematous (atrophic), and Angular cheilitis. * **CD4 Thresholds:** Oral Thrush (<500), Esophageal Candidiasis (<100; an AIDS-defining illness). * **Treatment:** Topical Nystatin or Clotrimazole for mild cases; oral Fluconazole for moderate-to-severe or esophageal involvement. * **Hairy Leukoplakia:** Often confused with Thrush, it is caused by **EBV**, occurs on the lateral tongue, and **cannot** be scraped off.

Question 718: Rhinovirus is primarily transmitted by?

A. Droplet aerosolization
B. Sexual activity
C. Fecal-oral route
D. Fomites (Correct Answer)

Explanation: **Explanation:** **Rhinovirus**, the most common cause of the "common cold," belongs to the *Picornaviridae* family. While many respiratory viruses are primarily spread via large droplets, Rhinovirus is uniquely characterized by its high stability on environmental surfaces and human skin. 1. **Why Fomites are Correct:** The primary mode of transmission is through **direct contact with contaminated surfaces (fomites)** or self-inoculation via contaminated hands. Rhinovirus can survive on environmental surfaces (like doorknobs or toys) for several hours and on hands for up to 2 hours. Infection occurs when a person touches these surfaces and then touches their own nasal or conjunctival mucosa. 2. **Why Other Options are Incorrect:** * **Droplet aerosolization:** While possible, it is significantly less efficient than direct contact/fomites for Rhinovirus. In contrast, viruses like Influenza or RSV rely more heavily on droplets. * **Sexual activity:** Rhinovirus is a respiratory pathogen and is not classified as a sexually transmitted infection (STI). * **Fecal-oral route:** Although Rhinoviruses are Picornaviruses (like Poliovirus and Hepatitis A), they are **acid-labile**. They are destroyed by gastric acid and therefore cannot be transmitted via the fecal-oral route. **High-Yield Clinical Pearls for NEET-PG:** * **Acid Lability:** This is the key feature distinguishing Rhinoviruses from Enteroviruses. * **Temperature Sensitivity:** Rhinoviruses grow best at **33°C** (the temperature of the nasal mucosa) rather than 37°C (systemic body temperature). * **Receptor:** Most Rhinoviruses (90%) use **ICAM-1** (CD54) to enter host cells. * **Vaccine:** No vaccine is available due to the existence of over 100 distinct serotypes (antigenic diversity).

Question 719: Which of the following is/are arboviral diseases?

A. Japanese encephalitis
B. Dengue
C. Kyasanur Forest Disease (KFD)
D. Hand-foot-mouth disease (Correct Answer)

Explanation: **Explanation:** The term **Arbovirus** (Arthropod-borne virus) refers to a functional group of viruses that are transmitted to humans through the bite of infected arthropods, primarily mosquitoes and ticks. **Why Hand-foot-mouth disease (HFMD) is the correct answer (as the non-arboviral disease):** HFMD is caused by viruses belonging to the **Picornaviridae** family, most commonly **Coxsackievirus A16** and **Enterovirus 71**. Unlike arboviruses, these are transmitted via the **fecal-oral route**, respiratory droplets, or direct contact with lesion fluid. They do not require an arthropod vector for transmission. **Analysis of Incorrect Options (Arboviral Diseases):** * **Japanese Encephalitis (JE):** An arboviral disease caused by a Flavivirus. It is transmitted by the **Culex tritaeniorhynchus** mosquito. * **Dengue:** Caused by the Dengue virus (Flavivirus) and transmitted primarily by the **Aedes aegypti** mosquito. * **Kyasanur Forest Disease (KFD):** A viral hemorrhagic fever caused by a Flavivirus. It is a tick-borne disease transmitted by **Haemaphysalis spinigera**. **High-Yield Clinical Pearls for NEET-PG:** * **Arbovirus Families:** Most belong to *Flaviviridae* (Dengue, JE, KFD, West Nile, Zika), *Togaviridae* (Chikungunya), or *Bunyaviridae* (Crimean-Congo Hemorrhagic Fever). * **Vector Identification:** Always remember the specific vectors: *Aedes* (Dengue/Zika/Chikungunya), *Culex* (JE), and *Ticks* (KFD/CCHF). * **HFMD Presentation:** Characterized by a vesicular rash on the palms, soles, and oral ulcers (herpangina). It is a common pediatric infection and is **not** seasonal in the same way vector-borne diseases are.

Question 720: All are true about rabies except?

A. Vaccine virus has a fixed incubation period.
B. It is a DNA virus. (Correct Answer)
C. Incubation period depends upon the site of the bite.
D. All bites on fingers with laceration are class III injuries.

Explanation: **Explanation:** **1. Why Option B is the Correct Answer (The Exception):** Rabies virus belongs to the family **Rhabdoviridae** and the genus *Lyssavirus*. It is a single-stranded, negative-sense **RNA virus**, not a DNA virus. It is characterized by its distinct bullet-shaped morphology and the presence of a helical nucleocapsid. **2. Analysis of Other Options:** * **Option A:** In rabies research, "Fixed virus" refers to strains that have been stabilized by serial passage in brains of laboratory animals. These strains have a short, **fixed incubation period** (4–6 days) and are used for vaccine production. In contrast, "Street virus" (wild type) has a highly variable incubation period. * **Option C:** The incubation period of rabies is highly variable (typically 1–3 months) because it depends on the **distance of the bite site from the Central Nervous System (CNS)**. Bites on the face or head have a shorter incubation period compared to bites on the legs. * **Option D:** According to WHO and National guidelines, **Category III** (High risk) exposure includes single or multiple transdermal bites or scratches, licks on broken skin, or contamination of mucous membranes with saliva. Any bite on the fingers (highly innervated area) with lacerations is classified as Category III, requiring both vaccine and Rabies Immunoglobulin (RIG). **Clinical Pearls for NEET-PG:** * **Negri Bodies:** Pathognomonic intracytoplasmic eosinophilic inclusions found most commonly in **Hippocampus** (Ammon’s horn) and Purkinje cells of the cerebellum. * **Pathogenesis:** The virus travels via **retrograde axonal transport** (centripetal spread) to the CNS. * **Prophylaxis:** Post-exposure prophylaxis (PEP) includes wound washing, active immunization (vaccine), and passive immunization (RIG for Category III). The current preferred schedule is the **Essen regimen** (0, 3, 7, 14, 28 days).

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