Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 611: Which of the following genes is associated with the encoding of reverse transcriptase?

A. Pol (Correct Answer)
B. Env
C. Gag
D. LTR

Explanation: The correct answer is **A. Pol**. ### **Explanation** The Human Immunodeficiency Virus (HIV) and other retroviruses possess three structural genes essential for their life cycle: **gag, pol, and env**. 1. **Pol (Polymerase) Gene:** This gene encodes the essential enzymes required for viral replication and integration. These include: * **Reverse Transcriptase:** Converts viral RNA into proviral DNA. * **Integrase:** Integrates the proviral DNA into the host cell genome. * **Protease:** Cleaves precursor polypeptides into functional proteins during viral maturation. 2. **Gag (Group-specific Antigen) Gene:** Encodes the inner structural proteins, primarily the **p24 capsid protein** (used for early diagnosis) and the p17 matrix protein. 3. **Env (Envelope) Gene:** Encodes the precursor glycoprotein **gp160**, which is cleaved by host proteases into **gp120** (attachment to CD4) and **gp41** (fusion and entry). 4. **LTR (Long Terminal Repeat):** These are non-coding sequences at both ends of the viral genome that act as promoters for gene transcription; they do not encode proteins. ### **High-Yield Clinical Pearls for NEET-PG** * **p24 Antigen:** The earliest serological marker of HIV infection (detected during the window period). * **gp120:** Responsible for tropism; it binds to the CD4 receptor and CCR5/CXCR4 co-receptors. * **Drug Targets:** * **NRTIs/NNRTIs** target Reverse Transcriptase. * **Raltegravir** targets Integrase. * **Maraviroc** targets the CCR5 co-receptor. * **Enfuvirtide** targets gp41 (fusion inhibitor).

Question 612: Recent Hepatitis infection is best diagnosed by?

A. HBsAg
B. IgG anti-HBe antibodies
C. Anti-HBsAg antibodies
D. IgM anti-HBc antibodies (Correct Answer)

Explanation: **Explanation:** The diagnosis of acute (recent) Hepatitis B infection relies on identifying markers that appear during the early phase of the disease. **IgM anti-HBc (Hepatitis B core antibody)** is the most reliable marker for recent infection because it is the first antibody to appear and remains positive during the **"Window Period"**—the interval when HBsAg has disappeared but Anti-HBs has not yet become detectable. **Analysis of Options:** * **IgM anti-HBc (Correct):** It indicates acute infection (within the last 6 months). It is the only marker positive during the window period, making it the gold standard for diagnosing recent/acute HBV. * **HBsAg:** While it is the first marker to appear in the blood, it only indicates that the virus is present (acute or chronic). It does not differentiate between a new infection and a long-term carrier state. * **IgG anti-HBe:** This antibody appears after the disappearance of the HBeAg, signaling reduced viral replication. It indicates a later stage of infection or convalescence, not an acute/recent onset. * **Anti-HBsAg:** These protective antibodies appear after recovery or vaccination. Their presence indicates immunity and the end of the acute phase. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** Defined as the time between the disappearance of HBsAg and the appearance of Anti-HBs. **IgM anti-HBc** is the diagnostic marker of choice here. * **HBeAg:** A marker of high infectivity and active viral replication ("e" for envelope/excess replication). * **Chronic Infection:** Defined by the persistence of HBsAg for >6 months. * **Vaccination:** Results in the presence of **Anti-HBs only** (Anti-HBc will be negative as there is no exposure to the core antigen).

Question 613: What types of human papillomavirus are associated with cervical carcinoma?

A. Types 6, 12, 18
B. Types 16, 18, 31 (Correct Answer)
C. Types 6, 8, 11
D. Types 3, 10, 19

Explanation: **Explanation:** Human Papillomavirus (HPV) is a double-stranded DNA virus with over 100 genotypes, categorized into "low-risk" and "high-risk" based on their oncogenic potential. **1. Why Option B is Correct:** Types **16, 18, 31, 33, and 45** are classified as **high-risk HPV**. These types produce the E6 and E7 oncoproteins, which inhibit tumor suppressor proteins p53 and pRb, respectively. HPV-16 is the most common type associated with squamous cell carcinoma, while HPV-18 is frequently linked to cervical adenocarcinoma. **2. Analysis of Incorrect Options:** * **Option A:** While 18 is high-risk, Type 6 is low-risk, and Type 12 is not typically associated with cervical malignancy. * **Option C:** Types **6 and 11** are the classic **low-risk** types. They are responsible for 90% of cases of **Condyloma acuminatum** (anogenital warts) and Recurrent Respiratory Papillomatosis (RRP). They rarely progress to malignancy. * **Option D:** Types 3 and 10 are usually associated with plane warts (verruca plana) and are not considered high-risk for cervical cancer. **High-Yield Clinical Pearls for NEET-PG:** * **Most common HPV type in Cervical Cancer:** HPV-16. * **Screening:** The Papanicolaou (Pap) smear looks for cytological changes (e.g., **Koilocytes**—cells with perinuclear halo and wrinkled nuclei). * **Vaccination:** * *Bivalent (Cervarix):* 16, 18. * *Quadrivalent (Gardasil):* 6, 11, 16, 18. * *Nonavalent (Gardasil-9):* 6, 11, 16, 18, 31, 33, 45, 52, 58. * **Oncogenesis:** E6 degrades **p53**; E7 binds and inactivates **pRb**.

Question 614: A patient presents with arthralgia, a rash, lymphadenopathy, and pneumonia, but no fever. Which of the following conditions is most likely given these symptoms?

A. Dengue fever (Correct Answer)
B. St. Louis encephalitis
C. Infectious mononucleosis
D. Hepatitis

Explanation: ### **Explanation** **Correct Option: A. Dengue Fever** Dengue fever, caused by the Dengue virus (Flavivirus), is classically known as **"Breakbone Fever"** due to severe arthralgia and myalgia. While high-grade fever is a hallmark of the typical presentation, the question highlights a constellation of symptoms—**arthralgia, maculopapular rash, lymphadenopathy, and respiratory involvement (pneumonia)**—that align with the systemic nature of the virus. In clinical practice and exams, Dengue is a primary differential for febrile illnesses with rash and joint pain. The mention of "no fever" in this specific vignette may refer to the **afebrile/critical phase** of the disease, where the temperature drops but complications like capillary leak or organ involvement (e.g., pneumonitis) can manifest. **Why Incorrect Options are Wrong:** * **B. St. Louis Encephalitis:** This Flavivirus primarily targets the Central Nervous System. The predominant clinical feature is **encephalitis** (altered mental status, seizures, or focal deficits), not pneumonia or generalized arthralgia. * **C. Infectious Mononucleosis (EBV):** While it presents with lymphadenopathy and rash (especially after amoxicillin), the classic triad is **fever, pharyngitis, and lymphadenopathy**. Pneumonia is an extremely rare complication. * **D. Hepatitis:** Viral hepatitis (A-E) primarily presents with **jaundice, hepatomegaly, and right upper quadrant pain**. While prodromal arthralgia can occur (especially in Hep B), pneumonia is not a standard feature. --- ### **NEET-PG High-Yield Pearls** * **Vector:** *Aedes aegypti* (Day biter; breeds in artificial collections of clean water). * **Serotypes:** 4 serotypes (DEN 1-4). Type 2 is most commonly associated with **Dengue Hemorrhagic Fever (DHF)**. * **Diagnosis:** * Day 1-5: **NS1 Antigen** (Gold standard for early detection). * After Day 5: **IgM ELISA**. * **Tourniquet Test:** Positive if >20 petechiae per square inch (indicates capillary fragility). * **Herman’s Sign:** "Islands of white in a sea of red" (characteristic rash appearance).

Question 615: What is the primary treatment for Herpes zoster?

A. Zidovudine
B. Valacyclovir (Correct Answer)
C. Ribavirin
D. Nevirapine

Explanation: **Explanation:** **Herpes zoster (Shingles)** is caused by the reactivation of the **Varicella-Zoster Virus (VZV)** latent in the sensory ganglia. The primary goal of treatment is to limit viral replication, accelerate healing, and reduce the risk of post-herpetic neuralgia (PHN). **Why Valacyclovir is correct:** Valacyclovir is a prodrug of Acyclovir with significantly higher oral bioavailability. It inhibits viral DNA polymerase, leading to chain termination. It is preferred over Acyclovir in clinical practice due to its **superior pharmacokinetic profile** and less frequent dosing (TID vs. 5 times/day for Acyclovir), which improves patient compliance. Famciclovir is another equivalent option. **Why the other options are incorrect:** * **A. Zidovudine (AZT):** A Nucleoside Reverse Transcriptase Inhibitor (NRTI) used exclusively in the treatment of **HIV/AIDS**. * **C. Ribavirin:** A broad-spectrum antiviral used primarily for **Hepatitis C** (in combination) and **RSV** (Respiratory Syncytial Virus) infections. * **D. Nevirapine:** A Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI) used in **HIV** management and for preventing mother-to-child transmission. **High-Yield Clinical Pearls for NEET-PG:** * **The "72-hour Rule":** Antiviral therapy is most effective when initiated within 72 hours of rash onset. * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusions (common to HSV and VZV). * **Complication:** Post-herpetic neuralgia is the most common complication; Ramsay Hunt Syndrome occurs when the Geniculate ganglion is involved. * **Vaccination:** The Recombinant Zoster Vaccine (Shingrix) is recommended for adults >50 years to prevent reactivation.

Question 616: What are the causes of antigenic drift in influenza viral infections?

A. Small mutations in neuraminidase and hemagglutinin (Correct Answer)
B. Large mutations in hemagglutinin only
C. Step mutations in viral genome
D. None of the above

Explanation: **Explanation:** Influenza viruses undergo two primary types of genetic changes: **Antigenic Drift** and **Antigenic Shift**. **Why Option A is correct:** Antigenic drift refers to the gradual accumulation of **point mutations** (small mutations) in the genes encoding the surface glycoproteins—**Hemagglutinin (HA)** and **Neuraminidase (NA)**. These mutations occur frequently because the viral RNA polymerase lacks proofreading ability. While the changes are minor, they eventually alter the antigenic sites enough that host antibodies from previous infections or vaccinations may no longer recognize the virus. This necessitates the annual update of the influenza vaccine and causes **seasonal epidemics**. **Why other options are incorrect:** * **Option B:** Antigenic drift involves both HA and NA, not just HA. Furthermore, "large mutations" or genetic reassortment (exchange of entire gene segments) describe **Antigenic Shift**, which leads to **pandemics**. * **Option C:** "Step mutations" is not a standard virological term used to describe this process. The mechanism is specifically point mutations leading to amino acid substitutions. **High-Yield Clinical Pearls for NEET-PG:** * **Antigenic Drift:** Seen in Influenza **A and B**. Responsible for **epidemics**. * **Antigenic Shift:** Seen **ONLY in Influenza A** (due to its wide host range including birds/pigs). Responsible for **pandemics**. * **Hemagglutinin (HA):** Responsible for viral attachment to sialic acid receptors and target of neutralizing antibodies. * **Neuraminidase (NA):** Facilitates the release of progeny virions from the host cell. * **Gold Standard Diagnosis:** Viral culture or RT-PCR.

Question 617: Which mosquito transmits Tritu enorrhynchus?

A. Dengue fever
B. Yellow fever
C. Kyasanur Forest Disease (KFD)
D. Japanese encephalitis (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Japanese Encephalitis** The question refers to the vector species **Culex tritaeniorhynchus**, which is the primary vector for **Japanese Encephalitis (JE)**. In the transmission cycle of JE, this mosquito acts as the bridge vector, carrying the virus from the amplifying hosts (primarily pigs and water birds) to humans. These mosquitoes typically breed in stagnant water, such as rice paddies and irrigation ditches, which explains the higher prevalence of JE in rural, agricultural areas. **Analysis of Incorrect Options:** * **A. Dengue Fever:** Transmitted primarily by **Aedes aegypti** (and secondarily by *Aedes albopictus*). These are "day-biters" that breed in clean, artificial water containers. * **B. Yellow Fever:** Also transmitted by the **Aedes aegypti** mosquito in urban cycles and *Haemagogus* species in jungle cycles. * **C. Kyasanur Forest Disease (KFD):** This is a viral hemorrhagic fever transmitted by **Hard ticks (Haemaphysalis spinigera)**, not mosquitoes. It is geographically limited to parts of Karnataka, India. **High-Yield Clinical Pearls for NEET-PG:** * **Vector Characteristics:** *Culex tritaeniorhynchus* is a **night-biter** (zoophilic) and prefers outdoor resting. * **Amplifying Host:** **Pigs** are the most important amplifying hosts for JE; humans are **dead-end hosts** because they do not develop sufficient viremia to infect mosquitoes. * **Diagnosis:** The gold standard for JE diagnosis is the detection of **IgM antibodies in CSF** or serum using MAC-ELISA. * **Vaccination:** The **Jenvac** (indigenous inactivated) and **SA-14-14-2** (live attenuated) vaccines are key preventive measures in endemic zones.

Question 618: What is the most common genital lesion observed in patients with HIV?

A. Chlamydia
B. Herpes (Correct Answer)
C. Syphilis
D. Candida

Explanation: **Explanation:** The correct answer is **Herpes Simplex Virus (HSV)**. In the context of HIV, Herpes Simplex Virus type 2 (HSV-2) is the most common cause of genital ulcer disease (GUD) worldwide. There is a synergistic relationship between HIV and HSV: HIV-induced immunosuppression leads to more frequent, severe, and prolonged herpetic outbreaks, while the presence of active herpetic ulcers increases the risk of HIV transmission and acquisition by providing a portal of entry and recruiting CD4+ cells to the site. **Analysis of Options:** * **A. Chlamydia:** While *Chlamydia trachomatis* is a common STI, it typically presents as urethritis or cervicitis rather than a primary genital lesion (ulcer), except in the case of Lymphogranuloma Venereum (LGV), which is less common than HSV. * **C. Syphilis:** Caused by *Treponema pallidum*, it presents as a painless chancre. While prevalent in HIV patients, studies consistently show that HSV accounts for a significantly higher percentage of genital ulcers in this population. * **D. Candida:** *Candida albicans* causes balanitis or vulvovaginitis (itching and discharge) rather than true ulcerative lesions. While common in HIV due to low CD4 counts, it is not classified as the primary "genital lesion" in the context of GUD. **Clinical Pearls for NEET-PG:** * **Most common cause of GUD in HIV:** Herpes Simplex Virus. * **Atypical presentation:** In advanced AIDS, HSV ulcers can become "chronic, giant, or necrotic" and may be resistant to standard Acyclovir therapy. * **Diagnostic Gold Standard:** PCR is the most sensitive test for HSV; however, the **Tzanck smear** (showing multinucleated giant cells) is a classic high-yield bedside test. * **Treatment:** Valacyclovir or Famciclovir are preferred for management and suppression.

Question 619: All of the following infections may be transmitted by dental instruments except?

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

Explanation: **Explanation:** The core concept tested here is the **mode of transmission** of various viral pathogens. Dental instruments pose a risk of transmission for infections spread via **blood and body fluids** (parenteral route) due to the potential for mucosal trauma and blood contamination during procedures. * **Why Hepatitis E is the correct answer:** Hepatitis E Virus (HEV) is primarily transmitted via the **fecal-oral route**, usually through contaminated water. It is an enteric virus and is not typically transmitted through blood-borne routes or contaminated medical/dental instruments. * **Why the other options are incorrect:** * **Hepatitis B (HBV):** This is the most significant occupational hazard in dentistry. It is highly infectious and transmitted through blood, saliva, and contaminated needles/instruments. * **Hepatitis C (HCV):** Primarily blood-borne. While the risk is lower than HBV, it can be transmitted via inadequately sterilized dental equipment. * **HIV:** Although the virus is fragile, it is present in blood and can theoretically be transmitted through percutaneous injury with contaminated dental instruments. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Hepatitis Transmission:** **Vowels (A, E)** are **Enteric** (Fecal-oral); **Consonants (B, C, D)** are **Blood-borne**. * **Hepatitis B** is the most resilient of these viruses on environmental surfaces; hence, strict adherence to **autoclaving** (Universal Precautions) is mandatory in dental practice. * **Hepatitis E** is particularly dangerous in **pregnant women**, where it can cause fulminant hepatic failure with a high mortality rate (~20%).

Question 620: Which of the following viruses is known for its high mutation rate?

A. Poliovirus
B. Influenza virus (Correct Answer)
C. Mumps virus
D. Measles virus

Explanation: The correct answer is **Influenza virus**. ### **Explanation** The high mutation rate of the Influenza virus is primarily attributed to two mechanisms: **Antigenic Drift** and **Antigenic Shift**. 1. **Antigenic Drift:** This involves point mutations in the genes encoding surface glycoproteins (**Hemagglutinin** and **Neuraminidase**). Because the viral RNA-dependent RNA polymerase lacks proofreading ability, mutations accumulate rapidly, leading to seasonal epidemics. 2. **Antigenic Shift:** This is a major genetic change due to the **segmented nature** of the Influenza genome (8 segments in Influenza A). When two different strains infect the same cell, they can exchange segments (reassortment), leading to entirely new subtypes and causing global pandemics. ### **Analysis of Incorrect Options** * **Poliovirus (Option A):** While it is an RNA virus and undergoes some mutation, it lacks the segmented genome required for reassortment. The three serotypes are highly stable, which is why the Salk and Sabin vaccines have remained effective for decades. * **Mumps (Option C) and Measles (Option D):** These are Paramyxoviruses. Although they are RNA viruses, they are **antigenically stable**. They exist as a single serotype, and infection or vaccination provides lifelong immunity. They do not exhibit the rapid surface protein variations seen in Influenza. ### **NEET-PG High-Yield Pearls** * **Segmented Genomes:** Remember the mnemonic **BOAR** (Bunyavirus, Orthomyxovirus [Influenza], Arenavirus, Reovirus). These are the viruses capable of **Genetic Reassortment**. * **Influenza A vs. B:** Only Influenza A undergoes both Drift and Shift (infects humans and animals); Influenza B undergoes only Drift (infects only humans). * **Vaccine Updates:** Due to high mutation rates (Drift), the WHO updates the Influenza vaccine composition annually.

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Virology — MCQs

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