Virology Practice Questions

Q: Human immunodeficiency virus (HIV) has been isolated from many body fluids. Which of the following is a major source of transmission?

Semen. **Explanation:** The transmission of Human Immunodeficiency Virus (HIV) depends on the **viral load** (concentration of the virus) within a specific body fluid and the presence of infected CD4+ T-cells or macrophages. **Why Semen is Correct:** HIV is found in high concentrations in **semen** and **vaginal secretions**, both as free virus particles and within infected mononuclear cells. Sexual transmission (predominantly via semen) remains the most common mode of HIV spread globally. Other major high-risk fluids include blood, breast milk, and cerebrospinal fluid. **Why Other Options are Incorrect:** * **Tears, Sweat, and Urine:** While HIV has been isolated in trace amounts from these fluids in research settings, the viral concentration is **insignificantly low** to pose a risk of transmission. These are considered non-infectious fluids unless they are visibly contaminated with blood. **High-Yield Clinical Pearls for NEET-PG:** * **Risk of Transmission:** The highest risk of transmission per act is via **blood transfusion** (approx. 90%), followed by vertical transmission (mother-to-child) and receptive anal intercourse. * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2–8 weeks). During this time, the person is highly infectious despite a negative ELISA. * **Target Cells:** HIV primarily infects cells expressing the **CD4 receptor** and co-receptors **CCR5** (macrophages/early infection) or **CXCR4** (T-cells/late infection). * **Screening vs. Confirmation:** ELISA is the standard screening test (high sensitivity), while **Western Blot** was traditionally the confirmatory test (high specificity). However, current NACO guidelines emphasize the use of three different rapid antibody tests for diagnosis.

Q: Which geographical region is predominantly associated with HIV C subtype?

India. **Explanation:** The distribution of Human Immunodeficiency Virus (HIV) is characterized by significant genetic diversity, with **HIV-1 Group M** being responsible for the global pandemic. This group is further divided into several subtypes (clades). **1. Why India is Correct:** **Subtype C** is the most prevalent subtype of HIV-1 worldwide, accounting for nearly half of all global infections. It is the predominant strain in **India**, South Africa, and Ethiopia. In India, Subtype C is responsible for over 90% of HIV infections, making it a high-yield fact for community medicine and microbiology. **2. Analysis of Incorrect Options:** * **Europe and America (Options B & C):** These regions are predominantly associated with **Subtype B**. Most early research and clinical trials were conducted on this subtype, although other subtypes are now increasing due to migration. * **Thailand (Option D):** Southeast Asia, particularly Thailand, is uniquely associated with the **CRF01_AE** (a circulating recombinant form) and Subtype B. **High-Yield Clinical Pearls for NEET-PG:** * **Most common HIV type globally:** HIV-1. * **Most common HIV-1 Subtype globally and in India:** Subtype C. * **HIV-2 prevalence:** Primarily restricted to West Africa; in India, it is most commonly seen in Maharashtra and parts of Southern India. * **Transmission:** While Subtype B is often associated with MSM (men who have sex with men) in Western countries, Subtype C in India is primarily spread through **heterosexual transmission**. * **Diagnosis:** The "Window Period" for modern 4th generation ELISA (p24 antigen + antibody) is typically 14–21 days.

Q: All of the following are true about Ebola virus except?

Belongs to the Filoviridae family. **Explanation:** The question asks for the "Except" statement, but based on virological facts, **Option B is actually a true statement.** Ebola virus indeed belongs to the **Filoviridae** family. In the context of this question, if Option B is marked as the "correct answer" (the false statement), it is likely a typographical error in the question source, as all four options provided are technically correct descriptions of the Ebola virus. **Breakdown of Options:** * **Option A (True):** The incubation period for Ebola Virus Disease (EVD) typically ranges from **2 to 21 days**. This is a critical timeframe for quarantine and monitoring of suspected cases. * **Option B (True):** Ebola, along with Marburg virus, belongs to the **Filoviridae** family. They are enveloped, non-segmented, negative-sense RNA viruses. * **Option C (True):** Under Electron Microscopy (EM), Filoviruses exhibit a highly pleomorphic, **thread-like (filamentous)** appearance. They often fold into structures resembling a **'shepherd’s crook'**, the letter '6', or a 'U'. * **Option D (True):** **RT-PCR** (Reverse Transcription Polymerase Chain Reaction) is the **investigation of choice** for acute diagnosis, as it can detect the viral RNA in blood or body fluids shortly after symptom onset. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Primarily through direct contact with infected blood, secretions, or organs (including fruit bats, the natural reservoir). * **Pathogenesis:** Causes severe hemorrhagic fever by infecting endothelial cells and causing a "cytokine storm." * **Biosafety Level:** Ebola requires **BSL-4** containment (the highest level). * **Vaccine:** The **rVSV-ZEBOV** vaccine is used for prevention during outbreaks.

Q: A 24-hour history of fever in an infant is followed by the appearance of a maculopapular rash and erythema on the face. What other condition can be caused by the organism responsible for these symptoms?

Pure red cell aplasia. **Explanation:** The clinical presentation of fever followed by a facial maculopapular rash (classically described as a **"slapped-cheek" appearance**) in an infant is diagnostic of **Erythema Infectiosum (Fifth Disease)**. This condition is caused by **Parvovirus B19**, a small, non-enveloped DNA virus. **Why the correct answer is right:** Parvovirus B19 specifically targets and infects **erythroid progenitor cells** in the bone marrow by binding to the **P-antigen** (globoside). In healthy individuals, this causes a transient drop in hemoglobin. However, in patients with underlying hemolytic anemias (like Sickle Cell Disease) or immunocompromised states, it can lead to a cessation of red blood cell production, resulting in a **Transient Aplastic Crisis** or **Pure Red Cell Aplasia (PRCA)**. **Analysis of Incorrect Options:** * **A & D (Leukemias):** Acute myeloid leukemia and Hairy cell leukemia are neoplastic proliferations of leukocytes. Parvovirus B19 is not oncogenic and does not cause these malignancies. * **B (Cytomegalovirus):** While CMV is a common viral infection in infants, it typically presents with hepatosplenomegaly, jaundice, or mononucleosis-like symptoms, rather than the classic "slapped-cheek" rash. **High-Yield NEET-PG Pearls:** * **Receptor:** P-antigen (Globoside) on RBCs. * **Pregnancy:** Infection during pregnancy can lead to **Hydrops Fetalis** due to severe fetal anemia and high-output heart failure. * **Adults:** Often presents as symmetrical **arthralgia/arthritis** (mimicking Rheumatoid Arthritis). * **Morphology:** Look for **"Giant Pronormoblasts"** with viral inclusions in the bone marrow.

Q: Which virus is the leading cause of the croup syndrome in young children and, when infecting mammalian cells in culture, will hemadsorb red blood cells?

Parainfluenza virus. **Explanation:** The correct answer is **Parainfluenza virus (PIV)**. This virus belongs to the *Paramyxoviridae* family and is the most common cause of **Croup (Laryngotracheobronchitis)** in children aged 6 months to 3 years. **Why it is correct:** 1. **Clinical Presentation:** PIV (specifically Type 1 and 2) causes subglottic edema, leading to the classic triad of barking cough, inspiratory stridor, and hoarseness. 2. **Hemadsorption:** PIV possesses a **Hemagglutinin-Neuraminidase (HN) protein** on its envelope. When the virus infects a cell culture, these viral proteins are expressed on the host cell membrane. If red blood cells (RBCs) are added to the culture, they adhere to the surface of the infected cells—a phenomenon known as **hemadsorption**. This is a key diagnostic laboratory feature for Paramyxoviruses and Orthomyxoviruses. **Why other options are incorrect:** * **Group B Coxsackievirus:** Primarily associated with pleurodynia (Bornholm disease), myocarditis, and herpangina; it does not cause croup or exhibit hemadsorption. * **Rotavirus:** The leading cause of severe dehydrating diarrhea in infants; it is a non-enveloped Reovirus. * **Adenovirus:** While it can cause respiratory infections (pharyngoconjunctival fever), it is a DNA virus that does not typically cause croup and does not hemadsorb. **High-Yield NEET-PG Pearls:** * **Steeple Sign:** X-ray finding in Croup showing subglottic narrowing. * **Genome:** PIV is a pleomorphic, enveloped, negative-sense ssRNA virus. * **Syncytia formation:** Like other Paramyxoviruses, PIV induces cell-to-cell fusion (multinucleated giant cells) via its Fusion (F) protein.

Q: Which of the following cells are affected by HIV?

T helper cells and macrophages. **Explanation:** The Human Immunodeficiency Virus (HIV) primarily targets cells that express the **CD4 receptor** on their surface. The HIV envelope glycoprotein **gp120** binds specifically to the CD4 molecule to initiate entry. * **Why Option B is Correct:** While **T-helper (CD4+) lymphocytes** are the primary targets and their depletion leads to profound immunosuppression, HIV also infects **macrophages, monocytes, and dendritic cells**. These cells also express CD4 receptors (albeit at lower levels than T-cells) and various co-receptors (CCR5). Macrophages are particularly important as they are resistant to the cytopathic effects of the virus, acting as a **reservoir** for HIV and transporting it to the central nervous system (CNS). * **Why other options are incorrect:** * **Option A:** HIV does not *only* affect T-helper cells; excluding macrophages ignores a critical part of the viral pathogenesis and its persistence in the body. * **Option C & D:** Natural Killer (NK) cells and B lymphocytes do not typically express the CD4 receptor. While B-cell function is often deranged in AIDS (leading to polyclonal hypergammaglobulinemia), this is a secondary effect of the loss of T-helper cell regulation, not a result of direct viral infection. **High-Yield Clinical Pearls for NEET-PG:** * **Co-receptors:** HIV requires co-receptors for entry: **CCR5** (predominant in early infection/macrophage-tropic) and **CXCR4** (seen in late-stage infection/T-cell-tropic). * **Homozygous mutation of CCR5 (CCR5-Δ32)** provides immunity against HIV infection. * **Follicular Dendritic Cells** in the lymph nodes serve as major reservoirs for HIV. * **Microglial cells** are the primary targets of HIV in the brain, leading to HIV-associated dementia.

Q: Infectivity of Hepatitis B virus is best diagnosed by which marker?

HBeAg. **Explanation:** The infectivity of Hepatitis B Virus (HBV) is primarily determined by the rate of viral replication. **1. Why HBeAg is the correct answer:** **HBeAg (Hepatitis B e-antigen)** is a soluble protein produced during active viral replication. Its presence in the serum serves as a surrogate marker for high viral load and **maximal infectivity**. Clinically, if a patient is HBeAg-positive, they are considered highly infectious (e.g., a high risk of vertical transmission from mother to child). While HBV DNA is a more precise quantitative measure, HBeAg remains the classic diagnostic marker for assessing infectivity in standard examinations. **2. Why other options are incorrect:** * **HBsAg:** This is the first marker to appear and indicates **active infection** (either acute or chronic). However, it does not differentiate between high and low replication states; thus, it is a marker of "infection," not "infectivity." * **HBV DNA:** This is the most sensitive marker for viral replication and is used to monitor treatment. While it correlates with infectivity, in the context of standard MCQ patterns, HBeAg is the established "diagnostic marker" for infectivity. * **Anti-HBsAg:** These are protective antibodies that appear after the disappearance of HBsAg. They indicate **immunity** (via vaccination or recovery) and imply zero infectivity. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The interval where HBsAg and Anti-HBs are both negative; **Anti-HBc IgM** is the only marker present. * **Pre-core Mutant:** A condition where the patient is HBeAg negative but has high HBV DNA levels and high infectivity. * **Best marker of vaccination response:** Anti-HBs titers (>10 mIU/mL). * **First marker to appear:** HBsAg.

Q: Which of the following is not an RNA virus?

Hepatitis B. **Explanation:** The classification of Hepatitis viruses is a high-yield topic for NEET-PG. The correct answer is **Hepatitis B**, as it is the only member of the Hepatitis group that is a **DNA virus**. **1. Why Hepatitis B is the correct answer:** Hepatitis B virus (HBV) belongs to the **Hepadnaviridae** family. It possesses a **partially double-stranded circular DNA** genome. It is unique because it uses an enzyme called **reverse transcriptase** during its replication cycle to convert RNA back into DNA, a feature it shares with retroviruses. **2. Why the other options are incorrect:** * **Hepatitis A (Option A):** A member of the *Picornaviridae* family. It is a non-enveloped, **positive-sense single-stranded RNA (+ssRNA)** virus. * **Hepatitis C (Option C):** A member of the *Flaviviridae* family. It is an enveloped, **+ssRNA** virus. * **Hepatitis D (Option D):** Also known as the "Delta agent," it is a defective **ssRNA** virus that requires the HBsAg (Hepatitis B surface antigen) coat to replicate and cause infection. **Clinical Pearls for NEET-PG:** * **Mnemonic:** All Hepatitis viruses are RNA, **except B** (B = **B**oth strands of DNA, though partially). * **Transmission:** Hepatitis **A** and **E** are transmitted via the **Fecal-Oral** route (Vowels hit the bowels). Hepatitis **B, C, and D** are transmitted parenterally (Blood/Body fluids). * **Hepatitis E:** While it is an RNA virus (*Hepeviridae*), remember it is particularly associated with high mortality in **pregnant women** (fulminant hepatic failure). * **Hepatitis C:** Most common cause of post-transfusion hepatitis and chronic liver disease (cirrhosis/HCC) worldwide.

Q: Which of the following serum markers indicate a super carrier of Hepatitis B Virus (HBV)?

HBsAg + HBeAg + HBV DNA. ### Explanation The term **"Super Carrier"** in Hepatitis B refers to a chronic carrier who is highly infectious. To understand this, we must differentiate between simple carriage and high-level replication. **1. Why Option C is Correct:** A "Super Carrier" is characterized by the presence of three key markers: * **HBsAg (Hepatitis B Surface Antigen):** Indicates the presence of the virus (Chronic state if >6 months). * **HBeAg (Hepatitis B e-Antigen):** This is the hallmark of **active viral replication** and high infectivity. * **HBV DNA:** High levels of viral load in the serum confirm that the virus is actively multiplying. The combination of these three markers signifies that the individual has a high viral load and is most likely to transmit the infection to others (e.g., via needle-stick injuries or vertical transmission). **2. Why Other Options are Incorrect:** * **Option A (HBsAg):** This only indicates that the person is a carrier. It does not specify the level of infectivity or replication. * **Option B (HBsAg + HBV DNA):** While this shows the virus is present and replicating, the absence of **HBeAg** means it doesn't fulfill the classic definition of a "super carrier," as HBeAg is the primary clinical marker for high infectivity. * **Option D (Anti-HBsAg + HBV DNA):** This is a contradictory profile. Anti-HBs indicates immunity/recovery, which usually does not coexist with active HBV DNA (except in rare escape mutants). **3. NEET-PG High-Yield Pearls:** * **Window Period Marker:** Anti-HBc IgM is the only positive marker. * **Best Indicator of Prognosis:** HBV DNA levels. * **Marker of Recovery/Immunity:** Anti-HBs. * **Low Infectivity Carrier:** HBsAg positive but **Anti-HBe** positive (indicates replication has slowed down). * **Pre-core Mutants:** These patients are HBeAg negative but still have high HBV DNA and high infectivity.

Question 1

Human immunodeficiency virus (HIV) has been isolated from many body fluids. Which of the following is a major source of transmission?

Accepted Answer

Semen

Answer

Tears

Answer

Sweat

Answer

Urine

Question 2

Which of the following statements regarding viral replication and diseases is FALSE?

Accepted Answer

DNA viruses include Adenovirus, Human papilloma virus, Parvovirus B-19, BK and JC polyomavirus, and Poliovirus.

Answer

The general stages of viral replication include penetration, uncoating, macromolecular synthesis (transcription, protein synthesis, replication), assembly, and release by budding and lysis.

Answer

Ganciclovir is used for Cytomegalovirus (CMV) infections and acts on viral DNA.

Answer

Viruses that can cause congenital and neonatal disease include HSV-2, Echovirus, CMV, Parvovirus B19, VZV, HIV, and Hepatitis viruses.

Question 3

Which geographical region is predominantly associated with HIV C subtype?

Accepted Answer

India

Answer

Europe

Answer

America

Answer

Thailand

Question 4

All of the following are true about Ebola virus except?

Accepted Answer

Belongs to the Filoviridae family

Answer

Incubation period is 2-21 days

Answer

Under electron microscopy, virions show a characteristic 'shepherd's crook' or 'thread-like' morphology

Answer

Investigation of choice is RT-PCR

Question 5

A 24-hour history of fever in an infant is followed by the appearance of a maculopapular rash and erythema on the face. What other condition can be caused by the organism responsible for these symptoms?

Accepted Answer

Pure red cell aplasia

Answer

Acute myeloid leukemia

Answer

Cytomegalovirus infection

Answer

Hairy cell leukemia

Question 6

Which virus is the leading cause of the croup syndrome in young children and, when infecting mammalian cells in culture, will hemadsorb red blood cells?

Accepted Answer

Parainfluenza virus

Answer

Group B coxsackievirus

Answer

Rotavirus

Answer

Adenovirus

Question 7

Which of the following cells are affected by HIV?

Accepted Answer

T helper cells and macrophages

Answer

Only T helper cells

Answer

NK cells

Answer

B lymphocytes

Question 8

Infectivity of Hepatitis B virus is best diagnosed by which marker?

Accepted Answer

HBeAg

Answer

HBsAg

Answer

HBV DNA

Answer

Anti-HBsAg

Question 9

Which of the following is not an RNA virus?

Accepted Answer

Hepatitis B

Answer

Hepatitis A

Answer

Hepatitis C

Answer

Hepatitis D

Question 10

Which of the following serum markers indicate a super carrier of Hepatitis B Virus (HBV)?

Accepted Answer

HBsAg + HBeAg + HBV DNA

Answer

HBsAg

Answer

HBsAg + HBV DNA

Answer

Anti-HBsAg + HBV DNA

Virology — MCQs

Virology — MCQs

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