Virology Practice Questions

Q: What are the primary hosts in the natural life cycle of the Japanese Encephalitis (JE) virus?

Pigs and Mosquitoes. ### Explanation Japanese Encephalitis (JE) is a zoonotic viral infection caused by a **Flavivirus**. Understanding its transmission cycle is crucial for NEET-PG, as it involves distinct roles for different species. **Why Option A is Correct:** The natural life cycle of the JE virus is maintained primarily between **Pigs** and **Mosquitoes** (specifically the *Culex tritaeniorhynchus* group). * **Pigs** act as the **amplifier hosts**; they develop high-titer viremia without getting sick, allowing mosquitoes to pick up the virus easily. * **Mosquitoes** are the **vectors** that transmit the virus between hosts. * **Ardeid birds** (herons, egrets) also serve as natural reservoirs, but the pig-mosquito cycle is the primary driver of human outbreaks. **Analysis of Incorrect Options:** * **B (Cattle and Birds):** While birds are reservoirs, cattle are "dead-end" hosts. They may develop antibodies but do not produce enough viremia to infect mosquitoes. * **C (Pigs and Humans):** Humans are **accidental, dead-end hosts**. The level of viremia in humans is transient and insufficient to infect a biting mosquito; therefore, human-to-mosquito-to-human transmission does not occur. * **D (Birds and Pigs):** While both are vertebrate hosts, this option excludes the **Mosquito**, which is a "primary host" (biological vector) essential for the virus's life cycle and transmission. **High-Yield Clinical Pearls for NEET-PG:** 1. **Vector:** *Culex tritaeniorhynchus* (breeds in stagnant water/paddy fields; "outdoor" biters). 2. **Amplifier Host:** Pig (The "Link" between nature and humans). 3. **Dead-end Hosts:** Humans and Horses. 4. **Sentinel Animals:** Pigs are used for surveillance to monitor the presence of the virus in a community. 5. **Vaccination:** Live attenuated (SA-14-14-2) and Inactivated vaccines are available under the Universal Immunization Programme (UIP) in endemic districts.

Q: Reassortment has enabled the development of live vaccines, which is a feature of the following virus?

Rotavirus. ### Explanation The correct answer is **Rotavirus**. **Why Rotavirus is correct:** The underlying concept here is **Genetic Reassortment**, which occurs only in viruses with **segmented genomes**. When two different strains of a segmented virus infect the same cell, they can exchange entire gene segments during assembly, creating a new progeny with a novel genetic mix. Rotavirus belongs to the *Reoviridae* family and possesses a genome of **11 segments of double-stranded RNA (dsRNA)**. This feature was exploited to develop live-attenuated vaccines like the **RotaTeq (RV5)** vaccine, which is a pentavalent human-bovine reassortant vaccine. **Why the other options are incorrect:** * **Hepadnavirus (e.g., Hepatitis B):** These are DNA viruses with a partially double-stranded circular genome. They do not have segments and thus cannot undergo reassortment. * **Herpesvirus:** These are large, enveloped viruses with a single, continuous piece of linear double-stranded DNA. They undergo recombination but not reassortment. * **Astrovirus:** These are small, non-enveloped viruses with a single-stranded, positive-sense RNA genome (ssRNA+). Since the genome is non-segmented, reassortment is impossible. **High-Yield Clinical Pearls for NEET-PG:** * **Segmented Viruses Mnemonic:** **BOAR** (**B**unyavirus - 3 segments, **O**rthomyxovirus/Influenza - 8 segments, **A**renavirus - 2 segments, **R**eovirus/Rotavirus - 11 segments). * **Antigenic Shift:** Reassortment is the mechanism behind "Antigenic Shift" in Influenza A, leading to pandemics. * **Rotavirus Vaccine:** Note that **Rotarix** is a monovalent human attenuated vaccine, while **RotaTeq** is the reassortant one. * **Clinical Presentation:** Rotavirus is the most common cause of severe diarrhea in infants and young children worldwide ("Winter diarrhea").

Q: Which virus is documented to cause fetal damage?

Varicella. **Explanation:** The correct answer is **Varicella (B)**. **Why Varicella is correct:** Varicella-Zoster Virus (VZV) is a well-documented teratogen. When a pregnant woman contracts primary varicella (chickenpox) during the first 20 weeks of gestation, the virus can cross the placenta and cause **Congenital Varicella Syndrome**. This syndrome is characterized by skin scarring (cicatricial lesions in a dermatomal distribution), limb hypoplasia, microcephaly, chorioretinitis, and cataracts. **Why the other options are incorrect:** * **Hepatitis A (A):** This is an enterically transmitted virus (fecal-oral). While it can cause acute hepatitis in the mother, it is not associated with congenital malformations or direct fetal damage. * **Measles (C):** While measles infection during pregnancy is associated with adverse outcomes like spontaneous abortion, premature labor, and low birth weight, it is **not** documented to be teratogenic (it does not cause structural fetal malformations). * **Arbovirus (D):** Most arboviruses (like Dengue or West Nile) do not typically cause fetal damage. *Note:* While Zika virus (an arbovirus) is a known teratogen, it is not the standard answer in this classic MCQ context compared to the established risk of Varicella. **NEET-PG High-Yield Pearls:** * **Congenital Rubella Syndrome (CRS):** The most common viral cause of fetal damage (Classic triad: Cataract, Deafness, Cardiac defects like PDA). * **Cytomegalovirus (CMV):** The most common *infectious* cause of sensorineural hearing loss and mental retardation in neonates. * **Varicella Prophylaxis:** If a susceptible pregnant woman is exposed to VZV, **Varicella-Zoster Immunoglobulin (VZIG)** should be administered within 96 hours to prevent maternal and fetal complications.

Q: Cytomegalovirus (CMV) infection is common. Which one of the following statements best characterizes CMV?

It can be transmitted across the placental barrier. **Explanation:** **1. Why Option A is Correct:** Cytomegalovirus (CMV), a member of the *Betaherpesvirinae* subfamily, is the most common cause of **congenital viral infection**. It can cross the placental barrier during both primary maternal infection and reactivation. Transmission can occur in utero (transplacental), during delivery (birth canal), or postpartum (breast milk). Congenital CMV is a leading cause of sensorineural hearing loss and intellectual disability. **2. Why the Other Options are Incorrect:** * **Option B:** Most CMV infections in immunocompetent individuals are **asymptomatic** or present as a mild mononucleosis-like syndrome (heterophile antibody negative). Symptomatic disease is primarily seen in neonates and immunocompromised patients. * **Option C:** CMV has a tropism for **mononuclear cells** (lymphocytes and monocytes) and polymorphonuclear leukocytes, not red blood cells. It establishes latency in myeloid progenitor cells in the bone marrow. * **Option D:** CMV is notorious for **reactivation** during periods of immunosuppression. It is a major cause of morbidity in transplant recipients (causing "CMV syndrome," pneumonia, or hepatitis) and AIDS patients (causing retinitis or colitis). **Clinical Pearls for NEET-PG:** * **Histology:** Look for **"Owl’s eye" appearance** (large intranuclear inclusion bodies with a clear halo). * **Congenital CMV Triad:** Chorioretinitis, periventricular calcifications, and microcephaly. * **Diagnosis:** PCR is the gold standard for systemic infection; Shell vial culture is a rapid culture technique. * **Treatment:** **Ganciclovir** is the drug of choice; Foscarnet is used for resistant cases.

Q: What are the most common types of human papillomavirus (HPV) causing cervical cancer?

16 and 18. **Explanation:** Cervical cancer is primarily caused by persistent infection with **High-Risk Human Papillomavirus (hrHPV)**. Among the various oncogenic strains, **HPV 16 and 18** are the most significant, accounting for approximately **70% of all cervical cancer cases** worldwide. HPV 16 is the most common (linked to squamous cell carcinoma), while HPV 18 has a higher association with adenocarcinoma. These strains produce E6 and E7 oncoproteins, which inhibit the tumor suppressor proteins p53 and pRb, respectively, leading to uncontrolled cell proliferation. **Analysis of Options:** * **Option A (Correct):** HPV 16 and 18 are the primary high-risk types responsible for the majority of cervical malignancies. * **Option B:** While HPV 33 is a high-risk type, HPV 1 is associated with benign cutaneous warts (verruca plantaris). * **Option C:** HPV 6 and 11 are **Low-Risk types**. They cause approximately 90% of genital warts (Condyloma acuminata) and recurrent respiratory papillomatosis, but they do not typically cause cancer. * **Option D:** HPV 2 is associated with common skin warts (verruca vulgaris); HPV 14 is not a major clinical subtype in this context. **High-Yield Clinical Pearls for NEET-PG:** * **Most common HPV type in Cervical Cancer:** HPV 16. * **Most common HPV type in Adenocarcinoma:** HPV 18. * **HPV Vaccines:** The Quadrivalent vaccine (Gardasil) targets 6, 11, 16, and 18. The Nonavalent vaccine adds 31, 33, 45, 52, and 58. * **Screening:** The primary screening tool is the Pap smear (cytology) and hrHPV DNA testing. The transformation zone is the most common site for cervical carcinogenesis.

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

Tick-borne encephalitis virus. ### 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*).

Q: Which hepatitis virus is notorious for causing chronic hepatitis evolving to cirrhosis?

HCV. **Explanation:** The correct answer is **HCV (Hepatitis C Virus)**. The hallmark of HCV infection is its high propensity for chronicity. Unlike other hepatitis viruses, approximately **75%–85%** of individuals infected with HCV fail to clear the virus and develop chronic infection. Over a period of 20 years, about 20% of these chronic cases progress to **cirrhosis**, which significantly increases the risk of Hepatocellular Carcinoma (HCC). **Analysis of Options:** * **HBV (Hepatitis B Virus):** While HBV is a major cause of chronic hepatitis and cirrhosis worldwide, the rate of chronicity in adults is relatively low (only **5%–10%**). It is more notorious for causing cirrhosis in neonatal transmissions (90% chronicity). * **HEV (Hepatitis E Virus):** This is typically an acute, self-limiting infection spread via the fecal-oral route. It does not cause chronic hepatitis in immunocompetent individuals, though it is notorious for high mortality in **pregnant women**. * **HAV (Hepatitis A Virus):** HAV causes only acute hepatitis and **never** progresses to a chronic state or cirrhosis. **High-Yield NEET-PG Pearls:** * **Most common indication for liver transplant:** HCV-induced cirrhosis [1]. * **HCV Screening:** Anti-HCV antibody is the screening test; **HCV-RNA** (PCR) is the gold standard for confirming active infection [1]. * **Extrahepatic manifestations of HCV:** Mixed cryoglobulinemia, Membranoproliferative glomerulonephritis (MPGN), and Porphyria cutanea tarda. * **Rule of 80s for HCV:** 80% become chronic, 80% are asymptomatic, and (historically) 80% were genotype 1 [1].

Q: What is the least common cause of sporadic encephalitis?

Rhinovirus. The correct answer is **D. Rhinovirus**. **Medical Concept:** Sporadic encephalitis refers to isolated cases of brain inflammation occurring year-round, independent of seasonal outbreaks. While many viruses are neurotropic (capable of infecting nerve tissue), **Rhinovirus** is primarily restricted to the upper respiratory tract. It thrives at temperatures slightly below core body temperature (33–35°C) and lacks the typical mechanisms to cross the blood-brain barrier. While extremely rare case reports exist in immunocompromised individuals, it is not considered a standard or recognized cause of sporadic encephalitis in clinical practice. **Analysis of Options:** * **HSV (Option A):** Herpes Simplex Virus-1 is the **most common cause** of sporadic fatal encephalitis worldwide [1]. It typically involves the temporal lobes [1]. * **VZV (Option B):** Varicella-Zoster Virus is a significant cause of sporadic encephalitis, often occurring during primary infection (chickenpox) or reactivation (shingles), frequently associated with vasculopathy. * **Arboviruses (Option C):** While many arboviruses (like Japanese Encephalitis) are epidemic/seasonal, several can present sporadically depending on geographic location and vector prevalence. They are well-established neurotropic pathogens. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of sporadic encephalitis:** HSV-1. * **Most common cause of epidemic encephalitis in India:** Japanese Encephalitis (JE) virus. * **Gold Standard Diagnosis:** CSF PCR for viral DNA/RNA. * **Imaging Choice:** MRI is superior to CT; look for temporal lobe involvement in HSV [1]. * **Treatment:** Empiric Acyclovir should be started immediately if encephalitis is suspected.

Q: What is the most specific diagnostic test for AIDS?

Western blot. **Explanation:** The diagnosis of HIV/AIDS follows a specific two-step algorithm: screening followed by confirmation. **Why Western Blot is the Correct Answer:** Western blot is considered the **gold standard confirmatory test** for HIV because of its high **specificity**. While screening tests look for general reactivity, the Western blot detects specific antibodies against individual HIV proteins (such as gp120, gp41, and p24). A positive result requires the presence of bands against multiple specific viral antigens, virtually eliminating false positives. **Analysis of Incorrect Options:** * **ELISA (Option C):** This is the **standard screening test**. It is highly sensitive (to ensure no cases are missed) but has lower specificity than Western blot, meaning it can occasionally yield false positives due to cross-reacting antibodies. * **Southern Blot (Option B):** This laboratory technique is used to detect specific **DNA** sequences. It is not used in the routine clinical diagnosis of HIV/AIDS. * **Note on Current Trends:** While Western blot remains the traditional "most specific" answer for exams, modern NAAT (Nucleic Acid Amplification Test) for HIV RNA is now frequently used for early diagnosis and confirmation in clinical practice. **NEET-PG High-Yield Pearls:** 1. **Screening Test of Choice:** ELISA (High sensitivity). 2. **Confirmatory Test of Choice:** Western blot (High specificity). 3. **Window Period Test:** p24 antigen assay or HIV RNA (PCR) are the earliest markers detectable. 4. **Diagnosis in Infants (<18 months):** PCR is the gold standard because maternal IgG antibodies can cause false positives on ELISA/Western blot. 5. **Monitoring Progression:** CD4+ T-cell count is the best predictor of clinical progression, while Viral Load (HIV RNA) is the best monitor of treatment (ART) efficacy.

Question 1

What are the primary hosts in the natural life cycle of the Japanese Encephalitis (JE) virus?

Accepted Answer

Pigs and Mosquitoes

Answer

Cattle and Birds

Answer

Pigs and Humans

Answer

Birds and Pigs

Question 2

Reassortment has enabled the development of live vaccines, which is a feature of the following virus?

Accepted Answer

Rotavirus

Answer

Hepadnavirus

Answer

Herpesvirus

Answer

Astrovirus

Question 3

Which virus is documented to cause fetal damage?

Accepted Answer

Varicella

Answer

Hepatitis A

Answer

Measles

Answer

Arbovirus

Question 4

Cytomegalovirus (CMV) infection is common. Which one of the following statements best characterizes CMV?

Accepted Answer

It can be transmitted across the placental barrier

Answer

While a common infection, CMV is almost always symptomatic

Answer

The CMV can be cultured from red blood cells of infected patients

Answer

Unlike other viral infections, CMV is not activated by immunosuppressive therapy

Question 5

What are the most common types of human papillomavirus (HPV) causing cervical cancer?

Accepted Answer

16 and 18

Answer

1 and 33

Answer

6 and 11

Answer

2 and 14

Question 6

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

Accepted Answer

Tick-borne encephalitis virus

Answer

Human papillomavirus

Answer

West Nile virus

Answer

Polyomavirus

Question 7

Which hepatitis virus is notorious for causing chronic hepatitis evolving to cirrhosis?

Accepted Answer

HCV

Answer

HBV

Answer

HEV

Answer

HAV

Question 8

Viruses have various ways of entering the human body and producing disease. Which of the following descriptions accurately describes the route of transmission and target disease for the virus indicated?

Accepted Answer

Echovirus: fecal-oral; aseptic meningitis

Answer

Coronavirus: fecal-oral; peptic ulcers

Answer

HIV: respiratory droplet; anemia

Answer

Influenza virus: blood-borne; maculopapular rash

Question 9

What is the least common cause of sporadic encephalitis?

Accepted Answer

Rhinovirus

Answer

Herpes Simplex Virus (HSV)

Answer

Varicella-Zoster Virus (VZV)

Answer

Arbovirus

Question 10

What is the most specific diagnostic test for AIDS?

Accepted Answer

Western blot

Answer

Southern blot

Answer

ELISA

Answer

None of the above

Virology — MCQs

Virology — MCQs

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