Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 691: Creutzfeldt-Jacob disease is caused by?

A. Prion (Correct Answer)
B. JC virus
C. Genetic factors
D. Nutritional deficiency

Explanation: **Explanation:** **Creutzfeldt-Jakob Disease (CJD)** is a fatal neurodegenerative disorder caused by **Prions**. Prions are unique infectious agents composed entirely of protein (PrPSc), lacking any nucleic acids (DNA or RNA). They cause disease by inducing the misfolding of normal cellular prion proteins (PrPC) into a pathological, protease-resistant beta-sheet conformation. This leads to neuronal loss and a characteristic "spongiform" appearance of the brain parenchyma. **Analysis of Options:** * **Option A (Correct):** Prions are the established causative agents of CJD (sporadic, iatrogenic, and variant forms). * **Option B (Incorrect):** The **JC virus** (a Polyomavirus) causes **Progressive Multifocal Leukoencephalopathy (PML)**, typically in immunocompromised patients. While it affects the CNS, the pathology involves demyelination rather than spongiform change. * **Option C (Incorrect):** While a small percentage of CJD cases are familial (genetic mutations in the *PRNP* gene), the disease entity itself is defined by the presence of the prion protein. "Genetic factors" is too broad and not the primary causative agent for the general disease. * **Option D (Incorrect):** Nutritional deficiencies (like Vitamin B12 or Thiamine) cause neurological syndromes (Subacute Combined Degeneration or Wernicke-Korsakoff), but not CJD. **High-Yield Clinical Pearls for NEET-PG:** * **Triad of CJD:** Rapidly progressive dementia, myoclonus (startle-induced), and characteristic EEG findings (periodic sharp wave complexes). * **Diagnosis:** Gold standard is brain biopsy (spongiform vacuolation); supportive tests include **14-3-3 protein** in CSF and **MRI** (hyperintensity in the caudate/putamen or "pulvinar sign" in variant CJD). * **Resistance:** Prions are highly resistant to standard sterilization (autoclaving). They require specialized protocols like sodium hydroxide (NaOH) or extended gravity displacement autoclaving at 134°C.

Question 692: Which of the following statements is true of all paramyxoviruses?

A. They contain a single-stranded RNA genome of negative polarity. (Correct Answer)
B. Their envelope is derived from the host cell's plasma membrane.
C. They have a cytoplasmic site of replication.
D. They enter the body by the respiratory route.

Explanation: **Explanation:** The **Paramyxoviridae** family (including Measles, Mumps, RSV, and Parainfluenza viruses) is characterized by specific structural and replicative features essential for NEET-PG. **1. Why Option A is Correct:** All paramyxoviruses possess a **linear, non-segmented, single-stranded RNA genome of negative polarity**. Because they are negative-sense, they must carry their own **RNA-dependent RNA polymerase** within the virion to transcribe the negative strand into positive mRNA for protein synthesis. **2. Why Other Options are Incorrect:** * **Option B:** While paramyxoviruses are enveloped, this is not a unique or universal defining trait for *all* in the same way the genome is. More importantly, while most bud from the plasma membrane, the focus of the question is on the most fundamental taxonomic characteristic. * **Option C:** While paramyxoviruses do replicate in the **cytoplasm**, this is a shared feature with almost all RNA viruses (except Orthomyxoviruses and Retroviruses). However, the question asks for a statement that is true of *all* paramyxoviruses; while true, the genomic structure (Option A) is the primary taxonomic definition. * **Option D:** Most paramyxoviruses (Measles, Mumps, RSV) enter via the respiratory route. However, certain zoonotic paramyxoviruses (like **Nipah and Hendra viruses**) can be transmitted through contaminated food or direct contact with animal excreta, making "respiratory route" a general rule but not an absolute universal truth for the entire family. **High-Yield Clinical Pearls:** * **Surface Spikes:** They possess **HN** (Hemagglutinin-Neuraminidase) and **F (Fusion) proteins**. The F-protein is responsible for forming **multinucleated giant cells (syncytia)**, a classic histopathological finding. * **Rule of 6:** Paramyxovirus replication follows the "Rule of Six"—the genome length must be a multiple of six nucleotides to be efficiently packaged. * **Vitamin A:** Supplementation reduces mortality in Measles (a key Paramyxovirus).

Question 693: In the context of dengue virus, what does NS-1 refer to?

A. Non-specific
B. Non-significant
C. Non-structural (Correct Answer)
D. Non-stranded

Explanation: **Explanation:** The Dengue virus (DENV) is a single-stranded, positive-sense RNA virus belonging to the **Flaviviridae** family. Its genome encodes for a single polyprotein that is cleaved into three structural proteins (C, prM, E) and seven **non-structural (NS)** proteins. **1. Why "Non-structural" is correct:** **NS-1 (Non-structural protein 1)** is a highly conserved glycoprotein. Unlike structural proteins, which form the physical shell of the virus, non-structural proteins are involved in viral replication, assembly, and immune evasion. NS-1 is secreted into the bloodstream during the early phase of infection. It is a critical diagnostic marker because it can be detected in the patient's serum from **Day 1 to Day 9** of the fever, often before IgM antibodies appear. **2. Why other options are incorrect:** * **Non-specific:** While NS-1 is used for screening, it is highly specific to the Dengue virus (though cross-reactivity with other Flaviviruses like Zika can occur). * **Non-significant:** NS-1 is clinically significant for early diagnosis and is implicated in the pathogenesis of vascular leak (Dengue Hemorrhagic Fever). * **Non-stranded:** This is a non-medical term in this context; viruses are classified by their genomic strands (e.g., single-stranded or double-stranded). **3. High-Yield Clinical Pearls for NEET-PG:** * **Early Diagnosis:** NS-1 Antigen is the investigation of choice in the **first 5 days** of illness. * **Serology:** After day 5, **MAC-ELISA (IgM)** becomes the preferred test. * **Pathogenesis:** Secreted NS-1 triggers the release of cytokines, leading to the "capillary leak syndrome" seen in DHF/DSS. * **Vector:** *Aedes aegypti* (Day biter; breeds in artificial collections of clean water).

Question 694: Which hepatitis virus is enterically transmitted?

A. Hepatitis B virus
B. Hepatitis C virus
C. Hepatitis E virus (Correct Answer)
D. Hepatitis A virus

Explanation: **Explanation:** The correct answer is **Hepatitis E virus (HEV)**. Hepatitis viruses are primarily classified by their mode of transmission into two groups: **Enteric** (fecal-oral) and **Parenteral** (blood-borne/sexual). **1. Why Hepatitis E is correct:** Hepatitis E, along with Hepatitis A, is transmitted via the **fecal-oral route**, typically through contaminated water or food. It is a non-enveloped RNA virus. In the context of NEET-PG, HEV is specifically notorious for causing high mortality rates (up to 20%) in **pregnant women**, often leading to Fulminant Hepatic Failure. **2. Why the other options are incorrect:** * **Hepatitis B (HBV):** A DNA virus transmitted via parenteral routes (blood transfusion, needles), sexual contact, and vertical transmission (mother to child). * **Hepatitis C (HCV):** An RNA virus primarily transmitted through blood (IV drug use is a major risk factor). It has the highest tendency to progress to chronic hepatitis and cirrhosis. * **Hepatitis A (HAV):** While HAV is *also* enterically transmitted, the question asks to identify "which" virus among the choices is enteric. In many exam formats, if both A and E are present, the question may be testing specific clinical associations (like waterborne epidemics or pregnancy risks) often linked to HEV. **High-Yield NEET-PG Pearls:** * **Vowels go with the Bowels:** Hepatitis **A** and **E** are transmitted via the fecal-oral route. * **HEV Genotypes:** Genotypes 1 and 2 are human-restricted (epidemic), while 3 and 4 are zoonotic (pork consumption). * **Morphology:** All Hepatitis viruses are RNA viruses except **Hepatitis B**, which is a **DNA virus**. * **Chronicity:** HAV and HEV **do not** cause chronic infection (except HEV in immunocompromised patients).

Question 695: Which of the following viruses is the causative agent of one of the most common sexually transmitted diseases that may lead to cervical carcinoma?

A. Cytomegalovirus
B. Papillomavirus (Correct Answer)
C. Epstein-Barr virus
D. Herpes simplex virus

Explanation: **Explanation:** The correct answer is **Papillomavirus (specifically Human Papillomavirus - HPV)**. HPV is the most common sexually transmitted infection globally. High-risk genotypes, primarily **HPV 16 and 18**, are the principal causative agents of cervical carcinoma. The oncogenic potential of HPV is attributed to the viral oncoproteins **E6 and E7**, which inhibit the host tumor suppressor proteins **p53 and Rb**, respectively, leading to uncontrolled cell proliferation. **Analysis of Incorrect Options:** * **A. Cytomegalovirus (CMV):** While CMV can be transmitted sexually, it is primarily associated with congenital infections (TORCH), retinitis in AIDS patients, and mononucleosis-like syndrome. It is not linked to cervical cancer. * **C. Epstein-Barr virus (EBV):** EBV is associated with several malignancies, including Burkitt lymphoma, Nasopharyngeal carcinoma, and Hodgkin lymphoma, but it does not cause cervical carcinoma. * **D. Herpes simplex virus (HSV):** HSV-2 is a common cause of genital herpes (painful vesicles). While it was once considered a potential co-factor, it is not the primary causative agent of cervical cancer. **High-Yield Clinical Pearls for NEET-PG:** * **Screening:** Pap smear is used to detect **koilocytes** (cells with perinuclear halo and wrinkled nuclei), which are pathognomonic for HPV infection. * **Vaccination:** The Quadrivalent vaccine (Gardasil) targets types 6, 11 (genital warts) and 16, 18 (cancer). * **Genotypes:** HPV 6 and 11 cause **Condyloma acuminata** (genital warts) but have low oncogenic potential. * **Most common genotype in Cervical Cancer:** HPV 16 (Squamous cell carcinoma) and HPV 18 (Adenocarcinoma).

Question 696: In which cells does the Human Immunodeficiency Virus primarily replicate?

A. CD4 helper T cells (Correct Answer)
B. CD8 T cells
C. Natural killer cells
D. None of the above

Explanation: **Explanation:** The Human Immunodeficiency Virus (HIV) is a retrovirus that exhibits specific tropism for cells expressing the **CD4 molecule** on their surface. **1. Why CD4 helper T cells are correct:** The primary mechanism of HIV entry involves the binding of the viral envelope glycoprotein **gp120** to the **CD4 receptor** on the host cell. This interaction, along with co-receptors (**CCR5** on macrophages/early infection or **CXCR4** on T cells/late infection), triggers a conformational change in **gp41**, leading to membrane fusion and viral entry. CD4+ T helper cells are the principal targets because they express high densities of these receptors, making them the primary site for viral replication and subsequent depletion, which leads to AIDS. **2. Why the other options are incorrect:** * **CD8 T cells:** These are cytotoxic T cells that lack the CD4 receptor. While they play a role in the immune response *against* HIV, the virus cannot infect them directly. * **Natural Killer (NK) cells:** These are part of the innate immune system. Like CD8 cells, they do not express the CD4 receptor required for HIV entry. **High-Yield Clinical Pearls for NEET-PG:** * **Coreceptors:** **CCR5** is used by M-tropic strains (early stage); **CXCR4** is used by T-tropic strains (late stage). A mutation in the CCR5 gene (**CCR5-Δ32**) provides resistance to HIV infection. * **Other Target Cells:** Besides T cells, HIV infects **Macrophages, Dendritic cells, and Microglial cells** (the primary reservoir in the CNS), as these also express CD4. * **Markers:** The progression to AIDS is clinically defined when the CD4+ T cell count falls below **200 cells/mm³**.

Question 697: Which virus has a bullet shape?

A. Rabies virus (Correct Answer)
B. Coxsackie A
C. Coxsackie B
D. Polio virus

Explanation: **Explanation:** The correct answer is **Rabies virus (Option A)**. **Why Rabies Virus is Correct:** The Rabies virus belongs to the **Rhabdoviridae** family (Greek *rhabdos* meaning "rod"). Under electron microscopy, it exhibits a characteristic **bullet-shaped** morphology. This unique shape is due to its helical nucleocapsid being surrounded by a lipid envelope that is rounded at one end and flat at the other. The envelope is studded with glycoprotein spikes (G protein), which are essential for attachment to nicotinic acetylcholine receptors at the neuromuscular junction. **Why Other Options are Incorrect:** * **Options B, C, and D (Coxsackie A, B, and Polio virus):** All three belong to the **Picornaviridae** family (specifically the *Enterovirus* genus). These viruses are characterized by an **icosahedral** (spherical) symmetry and are non-enveloped. They do not possess the elongated, bullet-like structure seen in Rhabdoviruses. **High-Yield Clinical Pearls for NEET-PG:** * **Genome:** Single-stranded, negative-sense RNA (ssRNA). * **Histopathology:** Presence of **Negri bodies** (intracytoplasmic eosinophilic inclusions), most commonly found in the **Purkinje cells of the cerebellum** and pyramidal cells of the **Hippocampus** (Ammon’s horn). * **Pathogenesis:** Centripetal spread via retrograde axonal transport to the CNS. * **Prophylaxis:** The most common cell culture vaccine used in India is the **Purified Chick Embryo Cell Vaccine (PCECV)** or Human Diploid Cell Vaccine (HDCV). * **Category III Bite:** Requires both vaccine and Rabies Immunoglobulin (RIG).

Question 698: Which of the following is NOT transmitted by Aedes aegypti?

A. Filariasis (Correct Answer)
B. Yellow fever
C. Dengue fever
D. Chikungunya hemorrhagic fever

Explanation: **Explanation:** The correct answer is **Filariasis**. While *Aedes aegypti* is a notorious vector for several viral diseases, it is not the primary vector for Lymphatic Filariasis in most endemic regions. 1. **Why Filariasis is the correct answer:** Lymphatic Filariasis (caused by *Wuchereria bancrofti* and *Brugia malayi*) is primarily transmitted by the **Culex quinquefasciatus** mosquito (in urban/semi-urban areas) and certain species of *Anopheles* and *Mansonia*. While some *Aedes* species (like *Aedes polynesiensis*) can transmit filariasis in specific Pacific islands, *Aedes aegypti* is not a significant vector for this parasite. 2. **Why the other options are incorrect:** * **Yellow Fever:** *Aedes aegypti* is the principal urban vector for this Flavivirus. * **Dengue Fever:** This is the most common disease transmitted by *Aedes aegypti*. * **Chikungunya:** This alphavirus is transmitted to humans primarily by *Aedes aegypti* and *Aedes albopictus*. **High-Yield NEET-PG Pearls:** * **Aedes aegypti Characteristics:** Known as the "Tiger Mosquito" (due to white stripes), it is a **day-time biter** (mostly early morning and late afternoon) and breeds in **artificial collections of clean water** (coolers, flower pots, discarded tires). * **Nervous Feeding:** It is a "nervous feeder," meaning it bites multiple people to complete a single blood meal, leading to rapid outbreaks. * **Other Diseases:** *Aedes aegypti* also transmits **Zika virus** and **Rift Valley Fever**. * **Vector Control:** The most effective control measure is "source reduction" (eliminating stagnant water).

Question 699: The genome of paramyxoviruses consists of:

A. Single stranded segmented RNA
B. Single stranded non-segmented RNA (Correct Answer)
C. Double stranded segmented DNA
D. Double stranded non-segmented DNA

Explanation: **Explanation:** **1. Why Option B is Correct:** Paramyxoviruses (which include Measles, Mumps, Parainfluenza, and RSV) belong to the family *Paramyxoviridae*. Their genome is characterized as **single-stranded, negative-sense, non-segmented RNA**. The "non-segmented" nature is a critical taxonomic feature; unlike segmented viruses, paramyxoviruses do not undergo genetic reassortment (antigenic shift), which is why we do not see the rapid emergence of new pandemic strains as seen in Influenza. **2. Why the Other Options are Incorrect:** * **Option A (SS Segmented RNA):** This describes the **Orthomyxoviridae** (Influenza) family. Influenza has 8 segments, which allows for genetic reassortment. Other segmented RNA viruses include Reoviridae (Rotavirus), Bunyaviridae, and Arenaviridae (Mnemonic: **BOAR**). * **Option C (DS Segmented DNA):** This is rare in human pathology. Most DNA viruses are double-stranded but non-segmented. * **Option D (DS Non-segmented DNA):** This describes the majority of DNA viruses, such as **Herpesviridae, Adenoviridae, and Poxviridae**. **3. High-Yield Clinical Pearls for NEET-PG:** * **The "Rule of Six":** Paramyxovirus genomes must be a multiple of six nucleotides long to be efficiently replicated (due to the way the Nucleoprotein binds). * **Replication Site:** Unlike most RNA viruses that replicate in the cytoplasm, Orthomyxoviruses (Influenza) replicate in the **nucleus**. Paramyxoviruses follow the general rule and replicate in the **cytoplasm**. * **Key Proteins:** All Paramyxoviruses possess a **Fusion (F) protein** which causes host cells to fuse into multinucleated giant cells (syncytia), a classic histopathological finding (e.g., Warthin-Finkeldey cells in Measles). * **Surface Spikes:** They possess Hemagglutinin (H) and Neuraminidase (N) activities, often on the same spike (HN protein), unlike Influenza where they are separate.

Question 700: An immunologist is working on growing influenza virus for vaccine production. Which of the following sites is used for the production of vaccine in a fertilized egg?

A. Allantoic cavity (Correct Answer)
B. Chorioallantoic membrane
C. Yolk sac
D. Amniotic cavity

Explanation: **Explanation:** The cultivation of viruses in embryonated eggs is a classic virological technique. For **Influenza virus**, the site of inoculation depends on the purpose of the study. **1. Why Allantoic Cavity is Correct:** The **allantoic cavity** is the preferred site for the **mass production of vaccines**. It provides a large volume of allantoic fluid, allowing the virus to replicate to high titers. This makes it commercially viable for harvesting large quantities of viral antigen required for inactivated or live-attenuated influenza vaccines. **2. Analysis of Incorrect Options:** * **Amniotic Cavity:** This site is primarily used for the **primary isolation** of the Influenza virus from clinical samples (e.g., throat swabs). Once isolated, the virus is usually adapted to the allantoic cavity for further growth. * **Chorioallantoic Membrane (CAM):** This site is used for viruses that produce visible **pocks** (lesions), such as Variola (Smallpox), Vaccinia, and Herpes Simplex Virus (HSV). * **Yolk Sac:** This is the site of choice for cultivating **Chlamydia**, Rickettsiae, and some viruses like the St. Louis encephalitis virus. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Influenza Vaccine:** Most seasonal flu vaccines are still produced in eggs; hence, a history of **egg allergy** is a traditional contraindication (though modern guidelines allow for supervised administration in some cases). * **Age of Embryo:** For allantoic/amniotic inoculation, 10–12 day old embryos are used; for yolk sac, 5–8 day old embryos are used. * **Detection:** Viral growth in the allantoic fluid is typically detected via the **Hemagglutination (HA) test**.

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