Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 811: All of the following statements about parvovirus B-19 are true, except?

A. Less than 10% spread by transplacental route (Correct Answer)
B. Respiratory route is the primary mode of transmission
C. It is a DNA virus
D. Affects erythroid progenitors

Explanation: **Explanation:** Parvovirus B19 is a clinically significant virus in the Parvoviridae family. The correct answer is **Option A** because the statement is factually incorrect regarding the efficiency of vertical transmission. **1. Why Option A is the "Except" (Correct Answer):** Transplacental transmission of Parvovirus B19 is actually quite efficient. If a non-immune pregnant woman (seronegative) develops a primary infection, the risk of the virus crossing the placenta to the fetus is approximately **33% (roughly one-third)**, which is significantly higher than the "less than 10%" stated in the option. **2. Analysis of Other Options:** * **Option B:** The **respiratory route** (via droplets) is indeed the primary mode of transmission in the general population, leading to outbreaks in schools and households. * **Option C:** Parvovirus B19 is a **single-stranded DNA (ssDNA) virus**. It is unique for being the smallest DNA virus and is non-enveloped. * **Option D:** The virus has a specific tropism for **erythroid progenitor cells** (specifically the P-antigen or globoside on proerythroblasts). It replicates in the bone marrow, leading to a temporary cessation of red blood cell production. **High-Yield Clinical Pearls for NEET-PG:** * **Erythema Infectiosum (Fifth Disease):** Characterized by the classic "slapped-cheek" rash in children. * **Aplastic Crisis:** Occurs in patients with high RBC turnover (e.g., Sickle Cell Anemia, Hereditary Spherocytosis). * **Hydrops Fetalis:** Severe fetal anemia and heart failure resulting from primary maternal infection during pregnancy (most common in the second trimester). * **Receptor:** It uses **P-antigen** as its cellular receptor; individuals lacking P-antigen are naturally immune.

Question 812: Rapid diagnosis of rabies is made with which test?

A. Skin biopsy with fluorescent antibody testing (Correct Answer)
B. Rabies virus specific antibodies
C. Inoculation in mice
D. Corneal impression smear

Explanation: **Explanation:** The diagnosis of Rabies in a living patient (antemortem) relies on detecting the virus before the onset of symptoms or during the early clinical phase. **Why Option A is Correct:** **Skin biopsy with Direct Fluorescent Antibody (DFA)** testing is considered the gold standard for rapid antemortem diagnosis. A full-thickness skin biopsy (usually 5-6 mm) is taken from the **nuchal area (nape of the neck)** at the hairline. This site is chosen because rabies virus is highly neurotropic and concentrates in the subepidermal nerve plexuses surrounding hair follicles. DFA provides high sensitivity and specificity, often yielding results within hours. **Analysis of Incorrect Options:** * **B. Rabies virus specific antibodies:** These usually appear late in the disease (often after the first week of symptoms) or only after vaccination. They are not useful for "rapid" or early diagnosis. * **C. Inoculation in mice:** This is a biological gold standard for virus isolation but takes **5–21 days** for the mice to show symptoms/death. It is far too slow for rapid clinical diagnosis. * **D. Corneal impression smear:** While historically used, it has **low sensitivity** and is technically difficult to perform correctly, making it less reliable than a skin biopsy. **NEET-PG High-Yield Pearls:** * **Negri Bodies:** Pathognomonic intracytoplasmic inclusion bodies found post-mortem, most commonly in the **Hippocampus (Ammon’s horn)** and **Cerebellum (Purkinje cells)**. * **Best Post-mortem Test:** DFA on brain tissue. * **Viral Characteristics:** Negative-sense, single-stranded RNA virus; Rhabdoviridae family; **Bullet-shaped** morphology. * **PCR:** RT-PCR of saliva or skin is increasingly used due to its extremely high sensitivity.

Question 813: Which of the following statements about viruses is false?

A. Ribosomes are absent
B. Mitochondria are absent
C. Motility is absent
D. Nucleic acid is absent (Correct Answer)

Explanation: ### Explanation **Core Concept:** Viruses are defined as **obligate intracellular parasites** that lack a cellular structure. The fundamental composition of a virus consists of a **nucleic acid genome** (either DNA or RNA, but never both) enclosed within a protein coat called a **capsid**. Therefore, the statement that "nucleic acid is absent" is false; without nucleic acid, a virus cannot replicate or carry genetic information. **Analysis of Options:** * **Option D (Correct - False Statement):** All viruses must possess a genome (DNA or RNA) to direct the synthesis of viral proteins within a host cell. An infectious particle lacking nucleic acids is not a virus but a **Prion** (which consists solely of protein). * **Option A (Incorrect - True Statement):** Viruses lack **ribosomes**. They are entirely dependent on the host cell's translational machinery (ribosomes, tRNA) to synthesize viral proteins. * **Option B (Incorrect - True Statement):** Viruses lack **mitochondria** and other metabolic organelles. They do not generate their own ATP and rely on the host cell's energy metabolism. * **Option C (Incorrect - True Statement):** Viruses are **non-motile**. They do not possess flagella or cilia; they move via passive diffusion or through the host's circulatory/lymphatic systems. **NEET-PG High-Yield Pearls:** * **DNA/RNA Rule:** A virus contains either DNA or RNA. The only exception is the *Mimivirus*, which may contain traces of both, but for exam purposes, the "either/or" rule holds. * **Smallest Virus:** Parvovirus (DNA) and Picornavirus (RNA). * **Largest Virus:** Poxvirus (resembles a brick under electron microscopy). * **Prions vs. Viroids:** Prions are infectious proteins (no nucleic acid); Viroids are infectious RNA strands (no protein coat).

Question 814: The classic triad of congenital rubella syndrome includes which of the following, except?

A. Cataract
B. Deafness
C. Retinal detachment (Correct Answer)
D. Congenital heart disease (CHD)

Explanation: **Explanation:** The classic triad of **Congenital Rubella Syndrome (CRS)**, also known as **Gregg’s Triad**, is a high-yield topic in NEET-PG. It occurs when the rubella virus crosses the placenta during the first trimester, leading to multi-organ malformations. **Why Retinal Detachment is the Correct Answer:** Retinal detachment is **not** part of the classic triad. While CRS causes significant ocular pathology, the characteristic finding is **"Salt and Pepper Retinopathy"** (mottled pigmentation of the retina), which usually does not affect vision. Other ocular features include microphthalmia and glaucoma, but not typically detachment. **Analysis of the Classic Triad (Incorrect Options):** * **Cataract (Option A):** This is the most common ocular manifestation. It is often bilateral and presents as a "pearly white" nuclear opacity. * **Sensorineural Deafness (Option B):** This is the **most common** overall manifestation of CRS. It may be the only finding in late-onset cases. * **Congenital Heart Disease (Option D):** The most characteristic cardiac lesion is **Patent Ductus Arteriosus (PDA)**, followed by peripheral pulmonary artery stenosis. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Period:** Maximum risk of fetal damage is during the first 12 weeks of gestation. * **Dermal Erythropoiesis:** Infants may present with a **"Blueberry muffin rash"** (purpuric skin lesions). * **Diagnosis:** Presence of **IgM antibodies** in the newborn or persistence of IgG beyond 6 months. * **Prevention:** Live attenuated **RA 27/3 vaccine**. It must be avoided during pregnancy, and pregnancy should be avoided for 1 month post-vaccination.

Question 815: Which of the following is non-cultivable in vivo?

A. Mycobacterium avium
B. HIV
C. Mycoplasma pneumoniae
D. Hepatitis-C virus (Correct Answer)

Explanation: **Explanation:** The term **"non-cultivable"** in this context refers to the inability to grow the pathogen in standard laboratory cell cultures or artificial media. **Hepatitis C Virus (HCV)** is the correct answer because it is notoriously difficult to grow in traditional *in vitro* cell culture systems. For decades, research was hindered because HCV does not replicate efficiently in standard cell lines. While specialized "replicon" systems and specific human hepatoma cell lines (like Huh7) have been developed for research, HCV remains clinically non-cultivable for routine diagnostic or vaccine production purposes. **Analysis of Incorrect Options:** * **Mycobacterium avium (A):** This is a bacterium belonging to the MAC complex. Unlike *M. leprae* (which is truly non-cultivable on artificial media), *M. avium* can be grown on liquid media (Middlebrook 7H12) or solid media (Lowenstein-Jensen), though it grows slowly. * **HIV (B):** Human Immunodeficiency Virus can be readily cultivated in the laboratory using primary human T-lymphocytes or established leukemic T-cell lines. * **Mycoplasma pneumoniae (C):** Although fastidious and requiring specialized media enriched with serum and yeast extract (e.g., PPLO agar), it is cultivable *in vitro*, typically showing characteristic "fried-egg" colonies. **High-Yield Clinical Pearls for NEET-PG:** * **M. leprae** and **T. pallidum** are classic examples of bacteria that are **non-cultivable** on artificial media. * HCV diagnosis relies on **Serology (ELISA)** for screening and **RT-PCR (Viral Load)** for confirmation, as culture is not an option. * HCV belongs to the **Flaviviridae** family and is the most common cause of post-transfusion hepatitis and chronic viral hepatitis leading to HCC.

Question 816: Which of the following is NOT a cause of viral hemorrhagic fever?

A. Arenaviridae
B. Marburg virus
C. Caliciviridae (Correct Answer)
D. Ebolavirus

Explanation: **Explanation:** Viral Hemorrhagic Fevers (VHFs) are a group of illnesses caused by four distinct families of RNA viruses: **Arenaviridae, Filoviridae, Bunyaviridae, and Flaviviridae**. These viruses share common features: they are zoonotic, cause multisystem syndrome, and damage the vascular system, leading to hemorrhage. **Why Caliciviridae is the Correct Answer:** **Caliciviridae** (e.g., Norovirus, Sapovirus) primarily causes **acute gastroenteritis**. They are non-enveloped, positive-sense RNA viruses transmitted via the fecal-oral route. They do not cause systemic vascular leakage or hemorrhagic manifestations, which are the hallmarks of VHFs. **Analysis of Other Options:** * **Arenaviridae (Option A):** This family includes viruses like **Lassa fever virus** and South American hemorrhagic fevers (e.g., Junin, Machupo). They are typically transmitted via rodent excreta. * **Marburg virus (Option B):** A member of the **Filoviridae** family, it causes severe hemorrhagic fever with high mortality rates. It was the first filovirus discovered (1967). * **Ebolavirus (Option C):** Also a member of the **Filoviridae** family, it is notorious for causing large-scale outbreaks of fatal hemorrhagic fever, characterized by severe coagulation abnormalities. **High-Yield Clinical Pearls for NEET-PG:** * **Filoviridae:** Characterized by "pleomorphic" or "filamentous" (U-shaped/6-shaped) morphology. * **Flaviviridae:** Includes Yellow Fever and Dengue (DHF/DSS). * **Bunyaviridae:** Includes Crimean-Congo Hemorrhagic Fever (CCHF), Hantavirus, and Rift Valley Fever. * **Vector Tip:** Most VHFs are transmitted by arthropods (ticks/mosquitoes) or rodents, except for Filoviruses (Ebola/Marburg), where **fruit bats** are the natural reservoir.

Question 817: Which of the following can be caused by Herpes genitalis?

A. Koilocytosis in a smear
B. Atypical cells
C. Cervical carcinoma (Correct Answer)
D. Sterility

Explanation: **Explanation:** **Herpes Simplex Virus Type 2 (HSV-2)**, the primary cause of **Herpes genitalis**, has been epidemiologically linked to the development of **Cervical Carcinoma**. While Human Papillomavirus (HPV) is the definitive primary oncogenic driver, HSV-2 is considered a significant **co-factor**. It is believed that HSV-2 infection promotes oncogenesis by inducing chronic inflammation and causing DNA damage in cervical cells already infected with high-risk HPV strains (like 16 and 18). **Analysis of Options:** * **A. Koilocytosis:** This is a pathognomonic histological finding for **HPV infection**, characterized by cells with perinuclear halos and nuclear wrinkling. It is not seen in HSV infections. * **B. Atypical cells:** While HSV causes cytopathic effects, the specific diagnostic finding is **Tzanck cells** (multinucleated giant cells with Cowdry Type A inclusion bodies), not generalized "atypical cells," which is a non-specific term often associated with dysplasia. * **D. Sterility:** While some sexually transmitted infections like Chlamydia and Gonorrhea lead to Pelvic Inflammatory Disease (PID) and subsequent tubal factor infertility, HSV-2 does not typically cause sterility. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Gold Standard:** Viral culture or PCR (most sensitive). * **Cytology (Tzanck Smear):** Look for multinucleated giant cells and **Cowdry Type A** intranuclear inclusion bodies (acidophilic). * **Neonatal Herpes:** Usually acquired during passage through the birth canal; often necessitates Cesarean section if active lesions are present. * **Drug of Choice:** Acyclovir (inhibits viral DNA polymerase).

Question 818: About parvovirus B19, which of the following statements is false?

A. It is spread by the respiratory route.
B. It has an affinity for erythrocyte progenitor cells.
C. It causes transient aplastic crisis.
D. Transplacental transfer occurs in only 10% of cases. (Correct Answer)

Explanation: **Explanation:** **Parvovirus B19** is a small, non-enveloped, single-stranded DNA virus. Understanding its pathogenesis is crucial for NEET-PG. **1. Why Option D is the Correct (False) Statement:** The statement that transplacental transfer occurs in "only 10%" of cases is incorrect. In reality, if a non-immune pregnant woman is infected with Parvovirus B19, the rate of **transplacental transmission is approximately 30%**. While the transmission rate is high, the risk of actual fetal loss or hydrops fetalis is relatively low (about 5-10%), occurring primarily when infection happens during the second trimester. **2. Analysis of Incorrect Options (True Statements):** * **Option A:** Parvovirus B19 is primarily transmitted via **respiratory droplets**, though it can also be spread through blood products and vertically. * **Option B:** The virus has a specific tropism for **erythroid progenitor cells** (specifically in the bone marrow) because it uses the **P-antigen** (globoside) as its cellular receptor. * **Option C:** Because it destroys red cell precursors, it causes a temporary halt in erythropoiesis. In healthy individuals, this is subclinical; however, in patients with high red cell turnover (e.g., Sickle Cell Anemia, Hereditary Spherocytosis), it leads to a life-threatening **Transient Aplastic Crisis**. **Clinical Pearls for NEET-PG:** * **Erythema Infectiosum (Fifth Disease):** Characterized by the classic **"slapped-cheek"** rash followed by a lace-like reticular rash on the trunk. * **Hydrops Fetalis:** Severe fetal anemia leading to high-output heart failure and generalized edema. * **Pure Red Cell Aplasia:** Can occur in immunocompromised patients. * **Receptor:** P-antigen (Globoside) is the key high-yield fact for its entry mechanism.

Question 819: What is the most effective method for testing Hepatitis C virus in a blood bank?

A. NS1 antigen testing
B. NS2 antigen testing
C. NS3 antigen testing (Correct Answer)
D. ELISA

Explanation: **Explanation:** The primary goal of blood bank screening is to minimize the "window period"—the time between infection and the appearance of detectable antibodies. While ELISA for anti-HCV antibodies is the standard screening tool, it has a significant window period of approximately 70 days. **Why NS3 Antigen Testing is Correct:** Hepatitis C Virus (HCV) core and non-structural proteins (like **NS3**) appear in the blood much earlier than antibodies. Testing for the **NS3 antigen** (often as part of a 4th generation combination ELISA or via specific antigen assays) significantly reduces the window period to about 12–15 days. In the context of blood banking, detecting the antigen directly is more effective for preventing transfusion-transmitted HCV than relying on antibodies alone. **Analysis of Incorrect Options:** * **NS1 Antigen:** This is the hallmark diagnostic marker for **Dengue virus**, not HCV. * **NS2 Antigen:** While NS2 is a functional protein in the HCV lifecycle (protease), it is not used as a standardized diagnostic marker in clinical or blood bank screening. * **ELISA:** While widely used, conventional 3rd generation ELISAs detect **antibodies**. These can yield false negatives during the early acute phase (window period), making them less "effective" than antigen detection for immediate safety in blood banks. **Clinical Pearls for NEET-PG:** * **Gold Standard for Diagnosis:** HCV RNA (PCR) is the most sensitive but expensive. * **Screening Sequence:** Antibody ELISA is done first; if positive, confirm with HCV RNA. * **HCV Characteristics:** It is a Flavivirus, (+) ssRNA, and has the highest tendency among hepatitis viruses to cause **chronic infection (70-85%)** and **Cryoglobulinemia**.

Question 820: Which of the following antigens is found within the nuclei of infected hepatocytes and not usually in the peripheral circulation in Hepatitis B infection?

A. HBeAg
B. HBcAg (Correct Answer)
C. Anti-HBc
D. HBsAg

Explanation: **Explanation:** The correct answer is **HBcAg (Hepatitis B core Antigen)**. **Why HBcAg is the correct answer:** HBcAg is a particulate antigen that forms the inner nucleocapsid of the Hepatitis B virus. During active viral replication, it is synthesized within the **nuclei of hepatocytes**. Unlike HBsAg or HBeAg, HBcAg is sequestered within the viral envelope as it buds from the cell. Consequently, free HBcAg does not circulate in the peripheral blood and cannot be detected by standard serum assays. Its presence can only be demonstrated through immunofluorescence or immunohistochemical staining of liver biopsy tissue. **Analysis of Incorrect Options:** * **HBeAg (Option A):** This is a soluble protein derived from the precore region. It is actively secreted by infected hepatocytes into the blood and serves as a marker of high viral infectivity and active replication. * **Anti-HBc (Option C):** This is an antibody produced by the host against the core antigen. It is easily detectable in the serum and is a crucial marker for the "window period" (IgM) or past exposure (IgG). * **HBsAg (Option D):** This is the surface antigen found on the outer envelope of the virus and as non-infectious spherical/tubular filaments in the blood. It is the primary screening marker for HBV infection. **High-Yield Clinical Pearls for NEET-PG:** * **The "Window Period":** The interval where HBsAg has disappeared and Anti-HBs has not yet appeared. During this time, **IgM Anti-HBc** is the only diagnostic marker of acute infection. * **Dane Particle:** The complete 42nm infectious virion consisting of an inner core (HBcAg) and an outer shell (HBsAg). * **Ground Glass Hepatocytes:** The characteristic histological appearance of hepatocytes in chronic HBV, caused by the accumulation of HBsAg in the endoplasmic reticulum.

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Virology — MCQs

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