Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 481: Human Papillomavirus (HPV) belongs to which family of viruses?

A. Papovavirus (Correct Answer)
B. Parvovirus
C. Herpesvirus
D. Poxvirus

Explanation: **Explanation:** **Correct Option: A. Papovavirus** Human Papillomavirus (HPV) is a member of the **Papovaviridae** family. The name "Papova" is an acronym derived from the first two letters of its three main genera: **Pa**pillomavirus, **Po**lyomavirus, and **Va**cuolating agent (SV40). These viruses are characterized by being small, non-enveloped, icosahedral viruses with a circular, double-stranded DNA genome. **Incorrect Options:** * **B. Parvovirus:** These are the smallest DNA viruses. Unlike HPV, they have a **single-stranded** DNA genome (e.g., Parvovirus B19). * **C. Herpesvirus:** These are large, **enveloped** viruses with linear double-stranded DNA. They exhibit latency (e.g., HSV, VZV, CMV). * **D. Poxvirus:** These are the largest and most complex DNA viruses. Unlike most DNA viruses (including HPV) which replicate in the nucleus, Poxviruses replicate in the **cytoplasm**. **High-Yield Clinical Pearls for NEET-PG:** * **Oncogenic Potential:** HPV types **16 and 18** are high-risk and strongly associated with cervical carcinoma, oropharyngeal cancer, and anal cancer. * **Mechanism:** Oncogenesis is driven by viral proteins **E6** (inhibits p53) and **E7** (inhibits Retinoblastoma/Rb protein). * **Diagnosis:** Characterized histologically by **Koilocytes** (squamous epithelial cells with perinuclear halos and wrinkled nuclei). * **Vaccination:** The Quadrivalent vaccine (Gardasil) targets types 6, 11, 16, and 18. Types 6 and 11 are primarily responsible for genital warts (Condyloma acuminata).

Question 482: What is the most definitive method for laboratory diagnosis of poliomyelitis?

A. Virus isolation from blood
B. Virus isolation from CSF
C. Virus isolation from feces or throat
D. Serological diagnosis (Correct Answer)

Explanation: **Explanation:** The laboratory diagnosis of poliomyelitis relies on identifying the virus or a significant rise in antibody titers. While virus isolation is common, **Serological diagnosis** is considered the most definitive method for confirming an acute infection in a clinical setting. **1. Why Serological Diagnosis is Correct:** A definitive diagnosis is established by demonstrating a **four-fold rise in neutralizing antibody titers** between acute and convalescent sera. This confirms that the virus isolated is the cause of the current illness rather than incidental shedding, which is crucial in endemic areas or in vaccine-associated cases. **2. Why Other Options are Incorrect:** * **Virus isolation from blood (A):** Viremia in polio is transient and occurs during the "minor illness" (prodromal phase). By the time neurological symptoms appear, the virus has usually cleared from the bloodstream. * **Virus isolation from CSF (B):** Unlike other enteroviruses, Poliovirus is **rarely isolated from the CSF**. Its presence in the CNS is brief, and it primarily resides in the anterior horn cells of the spinal cord. * **Virus isolation from feces or throat (C):** While these are the most common sites for isolation (feces being the best source for several weeks), isolation alone does not prove causation, as asymptomatic carriage or recent vaccination (OPV) can lead to viral shedding. **Clinical Pearls for NEET-PG:** * **Specimen of choice:** Feces (highest yield; excreted for 3–6 weeks). * **Culture:** Poliovirus is typically grown on **Monkey Kidney** or **HEp-2** cell lines, showing characteristic "apple-core" CPE (cytopathic effect). * **Gold Standard for Surveillance:** The WHO recommends **Acute Flaccid Paralysis (AFP) surveillance**, which requires two stool samples collected 24 hours apart within 14 days of onset.

Question 483: Echoviruses are cytopathogenic human viruses that mainly infect which system?

A. Respiratory system
B. Central nervous system
C. Blood and lymphatic systems
D. Intestinal tract (Correct Answer)

Explanation: **Explanation:** **Echoviruses** (Enteric Cytopathic Human Orphan viruses) belong to the genus *Enterovirus* within the family *Picornaviridae*. The correct answer is the **Intestinal tract** because, like other enteroviruses (Poliovirus, Coxsackievirus), Echoviruses primarily replicate in the mucosal cells of the **gastrointestinal tract** and the nasopharynx. They are transmitted via the fecal-oral route and are shed in the feces for several weeks, making the gut their primary site of infection and colonization. **Analysis of Options:** * **A. Respiratory system:** While Echoviruses can cause minor upper respiratory symptoms, it is not their primary site of infection or replication. * **B. Central nervous system:** This is a common site of **secondary** involvement. Echoviruses are a leading cause of aseptic meningitis, but they reach the CNS only after primary replication in the gut and subsequent viremia. * **C. Blood and lymphatic systems:** These serve as the **route of dissemination** (viremia) to target organs like the skin, heart, or meninges, rather than being the primary site of infection. **High-Yield Clinical Pearls for NEET-PG:** * **Nomenclature:** The name "Orphan" was originally given because these viruses were not initially associated with any specific disease. * **Clinical Spectrum:** They are the most common cause of **aseptic (viral) meningitis** and can cause neonatal sepsis-like syndromes, exanthems (rashes), and infantile diarrhea. * **Diagnosis:** Viral culture (showing characteristic cytopathic effects) or PCR from stool or CSF is the gold standard. * **Acid Stability:** Like all enteroviruses, Echoviruses are acid-stable, allowing them to survive the gastric pH to reach the intestinal tract.

Question 484: Rabies diagnosis is best done by which of the following methods?

A. Brain biopsy (Correct Answer)
B. Blood culture
C. Electron microscopy
D. None of the above

Explanation: **Explanation:** **1. Why Brain Biopsy is Correct:** The definitive diagnosis of Rabies (post-mortem) is established by demonstrating **Negri bodies** in the brain tissue. Negri bodies are pathognomonic intracytoplasmic, eosinophilic inclusion bodies found most commonly in the **Purkinje cells of the cerebellum** and the **pyramidal cells of the hippocampus (Ammon’s horn)**. While modern techniques like Direct Fluorescent Antibody (DFA) testing on brain tissue are the "gold standard" for sensitivity, the identification of Negri bodies via brain biopsy remains the classic diagnostic hallmark in medical examinations. **2. Why Other Options are Incorrect:** * **Blood Culture:** Rabies is a neurotropic virus. It travels via retrograde axonal transport to the CNS and does not cause a significant viremic phase. Therefore, blood cultures are useless for diagnosis. * **Electron Microscopy:** While EM can visualize the characteristic **bullet-shaped** morphology of the Rhabdoviridae family, it is not a routine or practical diagnostic method due to its low sensitivity and high cost compared to DFA or histopathology. **3. NEET-PG High-Yield Pearls:** * **Antemortem Diagnosis:** In living patients, the best samples are **full-thickness skin biopsy from the nape of the neck** (testing for viral antigen in hair follicle nerves) or **corneal impression smears**. * **Morphology:** Rabies virus is a single-stranded, negative-sense RNA virus, bullet-shaped, with a lipoprotein envelope containing G-spikes. * **Incubation Period:** Highly variable (usually 1–3 months); it depends on the distance of the bite site from the CNS. * **Fixed vs. Street Virus:** "Street virus" is the freshly isolated strain from natural cases; "Fixed virus" is the strain attenuated by serial passages in rabbits (used for vaccine production).

Question 485: Which fungal infection is commonly seen in patients with AIDS?

A. Mucormycosis
B. Aspergillosis
C. Disseminated candidiasis (Correct Answer)
D. Mucocutaneous candidiasis

Explanation: **Explanation:** In patients with HIV/AIDS, the risk of specific fungal infections is directly correlated with the decline in CD4+ T-lymphocyte counts. **Why Disseminated Candidiasis is correct:** While *Candida albicans* is a common commensal, the profound immunosuppression in advanced AIDS (typically CD4 <100 cells/mm³) allows the fungus to breach mucosal barriers and enter the bloodstream. **Disseminated (systemic) candidiasis** involves multiple organs (kidneys, liver, spleen, and eyes) and is a significant cause of morbidity and mortality in these patients. While mucosal forms are more frequent, dissemination represents the severe systemic manifestation characteristic of late-stage AIDS. **Analysis of Incorrect Options:** * **Mucocutaneous Candidiasis:** While extremely common in AIDS (e.g., oral thrush, esophageal candidiasis), it is often considered an "opportunistic" sign rather than a life-threatening systemic infection. Esophageal candidiasis is an AIDS-defining illness, but "disseminated" implies a more severe, multi-organ involvement. * **Mucormycosis:** This is primarily associated with **uncontrolled Diabetes Mellitus** (especially ketoacidosis) and neutropenia, rather than specifically being a hallmark of AIDS. * **Aspergillosis:** Invasive aspergillosis is more commonly seen in patients with **prolonged neutropenia** (e.g., leukemia, transplants) rather than isolated T-cell defects seen in AIDS. **NEET-PG High-Yield Pearls:** * **AIDS-Defining Fungal Infections:** Esophageal candidiasis, Cryptococcosis (extrapulmonary), and *Pneumocystis jirovecii* pneumonia (PCP). * **Most common fungal infection in AIDS:** Candidiasis (Mucocutaneous). * **Most common life-threatening fungal infection in AIDS:** Cryptococcal meningitis. * **CD4 Thresholds:** * <200: *Pneumocystis jirovecii* * <100: *Toxoplasma gondii*, Cryptococcosis * <50: *Mycobacterium avium* complex (MAC), CMV retinitis.

Question 486: Hetch giant cell pneumonia is caused by which virus?

A. Mumps virus
B. Rubella
C. Rubeola (Correct Answer)
D. Varicella

Explanation: **Explanation:** **Rubeola (Measles virus)** is the correct answer. In immunocompromised individuals (such as those with T-cell deficiencies, leukemia, or HIV), the measles virus can cause a severe, often fatal, interstitial pneumonia known as **Hecht’s Giant Cell Pneumonia**. The underlying pathophysiology involves the formation of characteristic **Warthin-Finkeldey giant cells**, which are large multinucleated cells formed by the fusion of infected cells. Unlike typical measles, Hecht’s pneumonia often occurs **without the characteristic maculopapular rash**, as the rash is an immune-mediated response which is absent in these patients. **Analysis of Incorrect Options:** * **Mumps virus:** Primarily causes parotitis, orchitis, and aseptic meningitis. While it can cause respiratory symptoms, it does not produce Hecht’s giant cells. * **Rubella (German Measles):** A togavirus that typically causes a mild rash and lymphadenopathy. Its most serious complication is Congenital Rubella Syndrome (CRS), not giant cell pneumonia. * **Varicella (VZV):** Can cause viral pneumonia, especially in adults, but the histopathology shows intranuclear inclusions (Cowdry type A) rather than the specific Hecht’s giant cell morphology. **High-Yield Clinical Pearls for NEET-PG:** * **Warthin-Finkeldey Cells:** Pathognomonic for Measles; found in lymphoid tissue (tonsils/adenoids) and lungs. * **Koplik’s Spots:** Small white spots on buccal mucosa (opposite 2nd molars); the earliest diagnostic sign of Measles. * **Vitamin A:** Supplementation reduces morbidity and mortality in children with Measles. * **SSPE (Subacute Sclerosing Panencephalitis):** A late, progressive neurological complication caused by a defective measles virus.

Question 487: Which of the following viruses is characterized by double-stranded RNA?

A. Rotavirus
B. Reovirus (Correct Answer)
C. Picornavirus
D. Myxovirus

Explanation: **Explanation:** The correct answer is **Reovirus**. In the world of virology, most RNA viruses are single-stranded (ssRNA). However, the **Reoviridae** family is the notable exception, characterized by a **segmented, double-stranded RNA (dsRNA)** genome and a double-layered icosahedral capsid without an envelope. **Why the options are right/wrong:** * **Reovirus (Option B):** This is the prototype of the Reoviridae family. Its name is an acronym for "Respiratory Enteric Orphan" virus. It contains 10–12 segments of dsRNA. * **Rotavirus (Option A):** While Rotavirus *is* a member of the Reoviridae family and also possesses dsRNA, in the context of standard MCQ hierarchy, "Reovirus" serves as the broader taxonomic classification often used in exams to test the family characteristic. (Note: In many clinical exams, both could be technically correct, but Reovirus is the classic textbook answer for the family trait). * **Picornavirus (Option C):** These are small, non-enveloped viruses with **single-stranded, positive-sense RNA** (e.g., Poliovirus, Hepatitis A). * **Myxovirus (Option D):** This group (Orthomyxoviridae like Influenza) consists of **single-stranded, negative-sense, segmented RNA** viruses. **High-Yield Clinical Pearls for NEET-PG:** 1. **Mnemonic for dsRNA:** "A **Double**-stranded **REO** speedwagon" (REOviridae = dsRNA). 2. **Segmentation:** Reoviruses (10–12 segments) and Orthomyxoviruses (8 segments) undergo **genetic reassortment**, leading to antigenic shifts. 3. **Rotavirus:** The most common cause of severe infantile diarrhea worldwide; characterized by a "wheel-like" appearance on electron microscopy. 4. **Replication:** Unlike most RNA viruses, Reoviruses replicate their dsRNA within the cytoplasm using their own RNA-dependent RNA polymerase.

Question 488: A resident doctor sustained a needlestick injury while sampling blood of a patient who is HIV positive. A decision is taken to offer him post-exposure prophylaxis. Which one of the following would be the best recommendation?

A. Zidovudine + Lamivudine for 4 weeks
B. Zidovudine + Lamivudine + Nevirapine for 4 weeks
C. Zidovudine + Lamivudine + Indinavir for 4 weeks (Correct Answer)
D. Zidovudine + Stavudine + Nevirapine for 4 weeks

Explanation: **Explanation:** The management of occupational exposure to HIV (Needlestick Injury) is a high-yield topic. The goal of Post-Exposure Prophylaxis (PEP) is to prevent viral replication before it becomes established in the host. **1. Why Option C is Correct:** According to standard guidelines (including NACO and CDC), the preferred regimen for "Expanded PEP" (used for high-risk exposures like deep injuries or source patients with high viral loads) consists of **two Nucleoside Reverse Transcriptase Inhibitors (NRTIs) plus a Protease Inhibitor (PI)**. * **Zidovudine (AZT) + Lamivudine (3TC)** form the backbone. * **Indinavir** (or Lopinavir/Ritonavir) is added as the third drug to increase potency. * The duration of treatment is strictly **4 weeks (28 days)**. **2. Why Other Options are Incorrect:** * **Option A:** This is a "Basic Regimen." While used for low-risk exposures, in a clinical scenario involving a known HIV-positive patient, the expanded regimen (3 drugs) is preferred for maximum efficacy. * **Option B & D:** These include **Nevirapine** (an NNRTI). Nevirapine is **contraindicated** in PEP because it is associated with a high risk of severe hepatotoxicity and Stevens-Johnson Syndrome (SJS) in HIV-negative individuals receiving it for prophylaxis. * **Option D:** Also uses Stavudine + Zidovudine; these two drugs are antagonistic and should never be used together. **Clinical Pearls for NEET-PG:** * **Timing:** PEP should ideally be started within **2 hours**, but can be given up to **72 hours** post-exposure. It is not recommended after 72 hours. * **Testing Schedule:** Follow-up HIV testing for the healthcare worker should be done at baseline, 6 weeks, 12 weeks, and 6 months. * **Current Preferred Regimen (Update):** While older questions focus on Indinavir, modern NACO guidelines now prefer **Tenofovir + Lamivudine + Dolutegravir (TLD)** as a single-pill daily regimen for 28 days.

Question 489: Epstein-Barr virus causes all of the following conditions except?

A. Hodgkin's lymphoma
B. Kaposi's sarcoma (Correct Answer)
C. Nasopharyngeal carcinoma
D. Burkitt's lymphoma

Explanation: **Explanation:** **1. Why Kaposi’s Sarcoma is the correct answer:** Kaposi’s sarcoma is caused by **Human Herpesvirus 8 (HHV-8)**, also known as Kaposi’s Sarcoma-associated Herpesvirus (KSHV). While Epstein-Barr Virus (EBV) is a potent oncogenic virus, it is not the causative agent for this specific vascular neoplasm. **2. Why the other options are incorrect (EBV Associations):** EBV (HHV-4) has a strong tropism for B-lymphocytes and epithelial cells, leading to several malignancies: * **Hodgkin’s Lymphoma:** EBV is found in approximately 40-50% of cases, particularly the Mixed Cellularity subtype. The virus resides in the characteristic Reed-Sternberg cells. * **Nasopharyngeal Carcinoma:** There is a 100% association with the undifferentiated type (Type III), common in South China. It involves the clonal expansion of EBV-infected epithelial cells. * **Burkitt’s Lymphoma:** EBV is associated with nearly all cases of the **Endemic (African)** variant, which typically presents as a jaw swelling in children. **3. High-Yield Clinical Pearls for NEET-PG:** * **EBV Receptor:** It enters B-cells via the **CD21** receptor (also the receptor for C3d complement). * **Diagnosis:** Look for **atypical lymphocytes (Downey cells)** on peripheral smear and a positive **Monospot test** (Heterophile antibodies). * **Other EBV conditions:** Infectious Mononucleosis (Glandular fever), Oral Hairy Leukoplakia (in HIV), and Gastric Carcinoma. * **HHV-8 Mnemonic:** Remember "K" for **K**aposi and **8** (looks like a "K" if split).

Question 490: Both intranuclear and intracytoplasmic inclusions are present in which of the following viruses?

A. Pox Virus
B. Measles virus (Correct Answer)
C. Hepatitis B virus
D. HIV

Explanation: ### Explanation The presence of inclusion bodies is a hallmark of viral infections, representing sites of viral replication or accumulation of viral proteins. **1. Why Measles Virus is Correct:** Measles virus (a member of the *Paramyxoviridae* family) is unique because it produces **both intranuclear and intracytoplasmic inclusion bodies**. These are known as **Warthin-Finkeldey cells**, which are multinucleated giant cells containing these characteristic inclusions. This occurs because the virus replicates in the cytoplasm but its nucleocapsid proteins also accumulate within the nucleus. **2. Analysis of Incorrect Options:** * **Pox Virus:** These are large DNA viruses that replicate entirely in the cytoplasm. Therefore, they produce **only intracytoplasmic** inclusions (e.g., **Guarnieri bodies** in Smallpox or **Molluscum bodies** in Molluscum contagiosum). * **Hepatitis B Virus (HBV):** HBV is associated with "ground-glass hepatocyte" appearance due to HBsAg accumulation in the cytoplasm, but it does not typically present with the classic dual inclusion pattern described in the question. * **HIV:** As a retrovirus, HIV integrates into the host genome. While it causes syncytia formation in cell cultures, it is not characterized by the diagnostic dual inclusion bodies seen in Measles. **3. High-Yield Clinical Pearls for NEET-PG:** * **Dual Inclusions (Both):** Measles virus and Cytomegalovirus (CMV). *Note: CMV is famous for "Owl’s eye" intranuclear inclusions, but also has small cytoplasmic inclusions.* * **Intracytoplasmic Only:** Poxvirus (Guarnieri bodies), Rabies (Negri bodies), Reovirus. * **Intranuclear Only:** Herpes Simplex Virus (Cowdry Type A), Adenovirus (Cowdry Type B), Papovavirus. * **Measles Mnemonic:** Remember the **3 C's** (Cough, Coryza, Conjunctivitis) + **Koplik spots** (pathognomonic).

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