Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 251: Which of the following are transfusion-transmitted viruses?

A. Hepatitis B, Hepatitis C, HTLV-1 (Correct Answer)
B. CMV, Rubella, HHV-8
C. Hepatitis C, HTLV-1, HHV-8
D. Hepatitis B, Rubella, CMV

Explanation: **Explanation:** Transfusion-Transmitted Infections (TTIs) are pathogens that can be transmitted through blood or blood products. For a virus to be effectively transmitted via transfusion, it must typically have a phase of **viremia** (presence in the blood) and the ability to cause asymptomatic or chronic infections in the donor. **1. Why Option A is Correct:** * **Hepatitis B (HBV) & Hepatitis C (HCV):** These are the most common transfusion-transmitted hepatotropic viruses. They cause chronic carrier states with high viral loads in the plasma. * **HTLV-1 (Human T-lymphotropic virus):** This retrovirus is primarily cell-associated (found in lymphocytes). It is a recognized TTI, which is why leukoreduction (filtering white blood cells) is an important safety measure in blood banking. **2. Why Other Options are Incorrect:** * **Rubella (Options B & D):** Rubella is primarily transmitted via respiratory droplets. While transient viremia occurs, it is not considered a standard transfusion-transmitted virus in clinical practice. * **CMV & HHV-8 (Options B & C):** While CMV and HHV-8 *can* be transmitted via blood (especially in immunocompromised recipients), they are not grouped with the primary, high-risk TTIs like HBV and HCV in the context of standard screening panels. **NEET-PG High-Yield Pearls:** * **Mandatory Screening in India:** Under the Drugs and Cosmetics Act, all donated blood must be screened for **HIV, HBV (HBsAg), HCV, Syphilis, and Malaria.** * **Window Period:** The time between infection and detection. Nucleic Acid Testing (NAT) is used to reduce this window period for HIV, HBV, and HCV. * **Bacterial Contamination:** *Staphylococcus epidermidis* is the most common contaminant of blood products, while *Yersinia enterocolitica* is the most common cause of post-transfusion sepsis in red cell concentrates (due to its ability to grow at 4°C).

Question 252: Which virus is transmitted by the same arthropod that transmits babesiosis and ehrlichiosis?

A. Human papillomavirus
B. West Nile virus
C. Tick-borne encephalitis virus (Correct Answer)
D. Polyomavirus

Explanation: ### Explanation The core concept tested here is the identification of diseases sharing a common vector. **Babesiosis** (*Babesia microti*) and **Ehrlichiosis** (specifically Human Granulocytic Anaplasmosis caused by *Anaplasma phagocytophilum*) are both transmitted by **Ixodes ticks** (hard ticks). **Why Tick-borne encephalitis virus (TBEV) is correct:** TBEV belongs to the *Flaviviridae* family and is primarily transmitted by the bite of infected **Ixodes ticks** (*I. ricinus* and *I. persulcatus*). Since Babesiosis, Ehrlichiosis, and TBEV (along with Lyme disease) all utilize the *Ixodes* species as their primary arthropod vector, they are often found in the same geographical distributions and can occasionally cause co-infections. **Why the other options are incorrect:** * **A. Human papillomavirus (HPV):** Transmitted via direct skin-to-skin or sexual contact; it has no arthropod vector. * **B. West Nile virus:** While it is an arbovirus, it is transmitted by **Culex mosquitoes**, not ticks. * **D. Polyomavirus:** (e.g., JC and BK viruses) These are typically transmitted through respiratory droplets or contaminated water; they are not vector-borne. **NEET-PG High-Yield Pearls:** * **Ixodes Tick "Big Four":** Always remember the four major pathogens transmitted by *Ixodes*: **L**yme disease (*Borrelia burgdorferi*), **B**abesiosis, **E**hrlichiosis/Anaplasmosis, and **T**ick-borne encephalitis (**Mnemonic: BELT**). * **Vector Differentiation:** * *Culex:* West Nile, Japanese Encephalitis, Filariasis. * *Aedes:* Dengue, Chikungunya, Zika, Yellow Fever. * *Ticks:* Kyasanur Forest Disease (KFD) is the major tick-borne viral hemorrhagic fever in India (transmitted by *Haemaphysalis spinigera*).

Question 253: Which of the following strains caused the 1997 bird flu pandemic?

A. H1N1
B. H5N1 (Correct Answer)
C. H2N1
D. H4N1

Explanation: **Explanation:** The correct answer is **H5N1**. **1. Why H5N1 is correct:** The 1997 outbreak in Hong Kong marked the first documented instance of direct transmission of a highly pathogenic avian influenza (HPAI) virus from birds to humans. This strain, **H5N1**, caused severe respiratory illness with a high mortality rate. The "H" and "N" refer to the surface glycoproteins: **Hemagglutinin (H5)**, which mediates viral entry into host cells, and **Neuraminidase (N1)**, which facilitates the release of new virions. **2. Analysis of Incorrect Options:** * **H1N1:** This strain is responsible for the **1918 Spanish Flu** pandemic and the **2009 Swine Flu** pandemic. It is a common cause of seasonal flu in humans. * **H2N1:** This is a subtype of avian influenza but has not been associated with major human pandemics or the 1997 outbreak. (Note: **H2N2** caused the 1957 Asian Flu). * **H4N1:** This subtype is primarily found in wild birds and has not caused significant human outbreaks or pandemics. **3. NEET-PG High-Yield Pearls:** * **Antigenic Shift:** Major genetic changes (reassortment) leading to new H/N combinations, causing **pandemics**. * **Antigenic Drift:** Minor point mutations causing seasonal **epidemics**. * **Drug of Choice:** Oseltamivir (Neuraminidase inhibitor) is the preferred treatment for H5N1 and H1N1. * **Other notable strains:** **H3N2** (1968 Hong Kong Flu) and **H7N9** (2013 Avian Flu outbreak in China).

Question 254: The gag gene encodes for which of the following?

A. Reverse transcriptase
B. Core antigen (Correct Answer)
C. Envelope
D. Gene activation

Explanation: The genome of Retroviruses (like HIV) consists of three structural genes: **gag, pol, and env**. Understanding these is high-yield for NEET-PG as they form the basis of viral structure and diagnostic testing. **Explanation of the Correct Answer:** * **Option B (Core antigen):** The **gag** (group-specific antigen) gene encodes the internal structural proteins of the virus. In HIV, it is translated into a precursor protein (p55) which is then cleaved into the **core/capsid (p24)**, matrix (p17), and nucleocapsid (p7/p9) proteins. p24 is the most clinically significant core antigen used in early diagnosis (p24 antigen assay). **Analysis of Incorrect Options:** * **Option A (Reverse transcriptase):** This is encoded by the **pol** (polymerase) gene. The *pol* gene also encodes essential enzymes like Integrase and Protease. * **Option C (Envelope):** This is encoded by the **env** gene. It produces a precursor (gp160) that cleaves into the surface glycoprotein **gp120** (for attachment to CD4) and the transmembrane protein **gp41** (for fusion). * **Option D (Gene activation):** This is the function of regulatory genes like **tat** (transactivator of transcription) and **rev** (regulator of expression of virion proteins). **High-Yield Clinical Pearls for NEET-PG:** * **p24 Antigen:** The earliest marker to appear in blood after HIV infection (Window period). * **gp120:** Responsible for tropism; it binds to the CD4 receptor on T-cells and macrophages. * **gp41:** Targeted by the fusion inhibitor drug, Enfuvirtide. * **Western Blot:** Traditionally used for confirmation; it detects antibodies against gag (p24), pol (p31/p66), and env (gp120/gp160).

Question 255: What is the most common virus that causes the common cold?

A. Adenovirus
B. Rhinovirus (Correct Answer)
C. Influenza virus
D. Respiratory syncytial virus

Explanation: **Explanation:** **Rhinovirus** is the most common cause of the common cold (acute viral rhinosinusitis), accounting for approximately 30% to 50% of cases in adults and children. It belongs to the *Picornaviridae* family. The virus thrives at a temperature of **33°C**, which is the ambient temperature of the nasal mucosa, explaining its localization to the upper respiratory tract. **Analysis of Incorrect Options:** * **Adenovirus:** While a common cause of upper respiratory infections, it is more characteristically associated with **pharyngoconjunctival fever** (sore throat, fever, and conjunctivitis) and outbreaks in military recruits. * **Influenza virus:** Causes "the flu," a systemic illness characterized by high fever, myalgia, and significant malaise, rather than the localized, mild coryzal symptoms of a common cold. * **Respiratory Syncytial Virus (RSV):** Although it causes mild cold-like symptoms in adults, it is the most common cause of **bronchiolitis and pneumonia** in infants and young children (lower respiratory tract involvement). **High-Yield Clinical Pearls for NEET-PG:** * **Seasonality:** Rhinoviruses are most prevalent in the fall and spring. * **Transmission:** Primarily via direct contact (hand-to-hand) and large-particle aerosols. Handwashing is the most effective preventive measure. * **Receptor:** Most rhinoviruses (90%) utilize **ICAM-1** (CD54) to enter host cells. * **Second Most Common Cause:** Coronaviruses (non-SARS types) are the second most frequent cause of the common cold. * **Complications:** The common cold is the most frequent trigger for **asthma exacerbations** and can lead to secondary bacterial sinusitis or otitis media.

Question 256: Which of the following best describes the genetic material of Adenovirus?

A. Double-stranded DNA (Correct Answer)
B. Enveloped virus
C. Complex symmetry
D. None of the above

Explanation: ### Explanation **Correct Answer: A. Double-stranded DNA** Adenoviruses are characterized by a **linear, double-stranded DNA (dsDNA)** genome. In the Baltimore classification system, they belong to Group I. The DNA is associated with virus-encoded basic proteins (like protamines) that help pack the genome into the capsid. **Analysis of Options:** * **B. Enveloped virus (Incorrect):** Adenoviruses are **non-enveloped (naked)** viruses. This makes them relatively stable and resistant to chemical or physical agents, including gastric acid and bile, which is why they can cause gastrointestinal infections. * **C. Complex symmetry (Incorrect):** Adenoviruses exhibit **Icosahedral symmetry**. They have a unique structure consisting of 252 capsomeres, with specialized "fibers" (penton bases) protruding from the vertices that act as attachment proteins. Complex symmetry is characteristic of Poxviruses. **High-Yield Clinical Pearls for NEET-PG:** * **Serotypes:** There are over 50 serotypes. Types 3, 4, and 7 are commonly associated with **Pharyngoconjunctival fever** (often seen in outbreaks among swimmers). * **Ocular Infections:** Types 8, 19, and 37 cause **Epidemic Keratoconjunctivitis (EKC)**, which is highly contagious. * **Gastrointestinal:** Types 40 and 41 are major causes of **infantile gastroenteritis**. * **Cystitis:** Types 11 and 21 are associated with **Acute Hemorrhagic Cystitis** in children. * **Intranuclear Inclusions:** Histology shows characteristic **"Smudge cells"** (basophilic intranuclear inclusion bodies).

Question 257: What is the most common viral infection in kidney transplant recipients?

A. BK virus (BKV)
B. Herpes Simplex Virus (HSV)
C. Cytomegalovirus (CMV) (Correct Answer)
D. Hepatitis B Virus (HBV)

Explanation: **Explanation:** **Cytomegalovirus (CMV)** is the most common clinically significant viral infection in kidney transplant recipients, typically occurring within the first 1–6 months post-transplant. The primary reason for its prevalence is the use of potent immunosuppressive therapy (like T-cell depleting agents), which triggers the reactivation of latent CMV residing in the donor organ or the recipient’s myeloid progenitor cells. CMV is a major cause of morbidity, leading to "CMV syndrome" (fever, malaise, leukopenia) or tissue-invasive disease (pneumonitis, hepatitis, and colitis). **Analysis of Incorrect Options:** * **BK Virus (BKV):** While BKV is a significant cause of graft dysfunction (BKV-associated nephropathy), it is less common than CMV. It typically presents later and is characterized by decoy cells in urine and viral inclusions in renal tubular cells. * **Herpes Simplex Virus (HSV):** HSV infections (mucocutaneous lesions) are common but usually occur early and are effectively managed or prevented with routine acyclovir prophylaxis. * **Hepatitis B Virus (HBV):** HBV is a chronic infection. While it can reactivate under immunosuppression, it is not the most common post-transplant viral infection due to rigorous pre-transplant screening and vaccination. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Quantitative PCR for CMV DNA. * **Histopathology:** Characterized by **"Owl’s eye"** intranuclear inclusion bodies. * **Drug of Choice:** **Valganciclovir** (prophylaxis/mild disease) or **Ganciclovir** (treatment of choice for established disease). * **Risk Stratification:** The highest risk group is **D+/R-** (Seropositive Donor/Seronegative Recipient).

Question 258: Which of the following conditions is commonly caused by Coxsackie group A virus?

A. Conjunctivitis
B. Aseptic meningitis (Correct Answer)
C. Hepatitis B
D. Myocarditis

Explanation: **Explanation:** Coxsackieviruses are members of the **Picornaviridae** family (Genus: *Enterovirus*). They are divided into Groups A and B based on their pathogenicity in suckling mice. **Why Aseptic Meningitis is correct:** Enteroviruses, including both Coxsackie Group A and Group B, are the **most common cause of viral (aseptic) meningitis** worldwide. While Group B is more frequently associated with systemic infections, Group A is a classic cause of meningeal inflammation, presenting with fever, headache, and neck stiffness, but with clear CSF (negative for bacteria). **Analysis of Incorrect Options:** * **Conjunctivitis:** While Enterovirus 70 and Coxsackie A24 cause Acute Hemorrhagic Conjunctivitis, it is less "common" as a general manifestation compared to meningitis. * **Hepatitis B:** This is caused by the Hepatitis B virus (a DNA Hepadnavirus), which is unrelated to the Enterovirus genus. * **Myocarditis:** This is the classic "high-yield" association for **Coxsackie Group B**. Group B viruses are known for attacking specialized tissues like the myocardium and the pancreas (Bornholm disease/Pleurodynia). **NEET-PG High-Yield Pearls:** * **Coxsackie Group A:** Primarily associated with "surface" or vesicular lesions. Key diseases: **Herpangina** (vesicles on the posterior pharynx) and **Hand-Foot-and-Mouth Disease** (specifically A16). * **Coxsackie Group B:** Associated with "body" or internal organ involvement. Key diseases: **Myocarditis, Pericarditis**, and **Pleurodynia** (Devil’s Grip). * **Mnemonic:** Group **A** for **A**ngina (Herpangina); Group **B** for **B**ody (Heart/Pleura). Both cause aseptic meningitis.

Question 259: Regarding mumps, which of the following statements is true?

A. Causes subacute sclerosing panencephalitis (SSPE)
B. Causes aseptic meningitis in children (Correct Answer)
C. Involves the sublingual salivary gland commonly
D. All of the above

Explanation: **Explanation:** **Mumps virus**, a member of the *Paramyxoviridae* family, is a common cause of systemic viral infection primarily targeting glandular and nervous tissues. **Why Option B is Correct:** Aseptic meningitis is the most common extra-salivary complication of mumps, occurring in up to 10–15% of clinical cases. It is typically benign and self-limiting. The virus is neurotropic, and pleocytosis (increased white cells) in the cerebrospinal fluid (CSF) can be detected in nearly 50% of patients, even those without overt meningeal symptoms. **Analysis of Incorrect Options:** * **Option A:** Subacute sclerosing panencephalitis (SSPE) is a rare, progressive, and fatal demyelinating disease caused by a persistent infection with a mutant **Measles virus**, not Mumps. * **Option C:** While mumps affects salivary glands, it most commonly involves the **Parotid glands** (Parotitis), usually bilaterally. Involvement of the sublingual or submandibular glands is much less frequent. * **Option D:** Since options A and C are incorrect, "All of the above" is invalid. **High-Yield Clinical Pearls for NEET-PG:** * **Most common complication in children:** Aseptic meningitis. * **Most common complication in post-pubertal males:** Orchitis (usually unilateral; rarely leads to sterility). * **Other complications:** Pancreatitis (look for elevated serum amylase), Oophoritis, and permanent sensorineural deafness (usually unilateral). * **Diagnosis:** Primarily clinical; confirmed by RT-PCR or IgM serology. * **Prevention:** Live attenuated vaccine (Jeryl Lynn strain) as part of the MMR vaccine.

Question 260: Which serological marker indicates infectivity of Hepatitis B?

A. HBeAg
B. HBeAg (Correct Answer)
C. IgM anti HBc
D. HBcAg

Explanation: **Explanation:** The presence of **HBeAg (Hepatitis B e-antigen)** is the hallmark of active viral replication and high infectivity. It is a soluble protein derived from the precore/core gene and is secreted into the blood only when the virus is actively multiplying. Therefore, a patient positive for HBeAg is considered "highly infectious" to others. **Analysis of Options:** * **HBeAg (Correct):** It serves as a surrogate marker for high levels of HBV DNA. Its disappearance and subsequent "seroconversion" to anti-HBe usually indicate a transition to a low-replicative state. * **IgM anti-HBc:** This is the marker of **acute infection**. It is particularly useful during the "window period" when both HBsAg and anti-HBs are negative. While it indicates a recent infection, it does not directly quantify the degree of infectivity. * **HBcAg (Hepatitis B core antigen):** This is a structural protein that remains sequestered within the hepatocyte or inside the viral coat. It is **not detectable in the serum** under normal conditions; hence, it cannot be used as a routine serological marker for infectivity. **High-Yield Clinical Pearls for NEET-PG:** * **HBsAg:** The first marker to appear; indicates the presence of the virus (infection). If it persists for >6 months, the infection is defined as chronic. * **Anti-HBs:** Indicates **immunity** (either from recovery or vaccination). * **HBV DNA:** The most sensitive and quantitative marker for viral load and infectivity. * **Window Period:** The interval where **IgM anti-HBc** is the only detectable marker.

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