Virology Practice Questions

Q: Which virus is known to cause a latent infection?

Hepatitis B virus (HBV). **Explanation:** **Hepatitis B Virus (HBV)** is the correct answer because it establishes latency through the formation of **cccDNA (covalently closed circular DNA)** in the nucleus of infected hepatocytes. This episomal form persists indefinitely, acting as a template for viral transcription even when the patient is clinically asymptomatic or under antiviral therapy. Reactivation can occur during periods of immunosuppression (e.g., chemotherapy or HIV co-infection). **Analysis of Incorrect Options:** * **Rubella:** This is an enveloped RNA virus (Togaviridae) that causes an acute self-limiting infection (German measles). While it can cause persistent infection in the fetus (Congenital Rubella Syndrome), it does not undergo a true latent phase in the general population. * **Pertussis:** This is caused by the bacterium *Bordetella pertussis*, not a virus. It causes an acute respiratory infection (Whooping cough) and does not exhibit latency. * **Rotavirus:** A Reovirus that causes acute gastroenteritis, primarily in children. It is a non-enveloped RNA virus that is shed in feces during the acute phase but does not establish a latent reservoir in the body. **High-Yield Clinical Pearls for NEET-PG:** * **Latency vs. Persistence:** Latency involves the maintenance of the viral genome without active replication (e.g., HBV, HSV, VZV, EBV). * **HBV Markers:** The disappearance of HBsAg and the appearance of Anti-HBs signify recovery; however, cccDNA may still persist in the liver. * **Other Latent Viruses:** Always remember the "Big Three" families: **Herpesviridae** (all members), **Retroviridae** (HIV), and **Hepadnaviridae** (HBV). * **Reactivation Risk:** Before starting biologicals (like Rituximab), patients must be screened for latent HBV to prevent fulminant hepatic failure.

Q: In which infection is transovarian transmission observed?

Yellow fever. **Explanation:** **Transovarian transmission** is a process where a pathogen is passed from a female vector to its offspring via the eggs. This mechanism allows the virus to persist in the environment even in the absence of an active host. **Why Yellow Fever is Correct:** Yellow fever is caused by a Flavivirus and is transmitted primarily by the *Aedes aegypti* mosquito. In this cycle, the virus can infect the ovaries of the female mosquito, ensuring that the next generation of mosquitoes is born already carrying the virus. This is a crucial survival strategy for the virus, especially during dry seasons when the adult mosquito population decreases. **Analysis of Incorrect Options:** * **Plague:** Caused by *Yersinia pestis*, it is transmitted by the rat flea (*Xenopsylla cheopis*). The transmission is mechanical (via the "blocked flea" mechanism) and does not involve the flea's eggs. * **Filarial (Filariasis):** Caused by nematodes like *Wuchereria bancrofti*. The larvae (microfilariae) must undergo a developmental cycle within the mosquito (L1 to L3 stage) but do not infect the eggs. * **Guinea (Dracunculiasis):** Caused by *Dracunculus medinensis*. It is transmitted by ingesting water containing infected copepods (Cyclops). There is no insect vector or transovarian route involved. **High-Yield Clinical Pearls for NEET-PG:** * **Other pathogens showing transovarian transmission:** Dengue virus, Japanese Encephalitis, and *Rickettsia rickettsii* (Rocky Mountain Spotted Fever). * **Yellow Fever Key Facts:** Look for "Councilman bodies" (acidophilic degeneration of hepatocytes) on histopathology and the "Faget sign" (pulse-temperature dissociation). * **Vector:** *Aedes aegypti* is also known as the "Tiger mosquito" due to its striped appearance.

Q: A patient presents with keratoconjunctivitis. The differential diagnosis should include infection with which of the following viruses?

Adenovirus. **Explanation:** **Adenovirus** is the most common viral cause of **epidemic keratoconjunctivitis (EKC)**, typically associated with serotypes 8, 19, and 37. The virus has a predilection for mucous membranes, including the conjunctiva and respiratory tract. EKC is characterized by sudden onset of watery discharge, pain, and "foreign body sensation," often followed by subepithelial corneal infiltrates which can impair vision. Adenoviruses also cause **Pharyngoconjunctival Fever** (triad of fever, pharyngitis, and conjunctivitis), usually linked to serotypes 3 and 7. **Analysis of Incorrect Options:** * **Parvovirus (B19):** Primarily causes Erythema Infectiosum (Fifth disease) in children, characterized by a "slapped-cheek" rash, and aplastic crisis in patients with chronic hemolytic anemias. It does not typically involve the cornea. * **Epstein-Barr virus (EBV):** The causative agent of Infectious Mononucleosis. While it can cause mild conjunctivitis or eyelid edema (Hoagland sign), it is not a classic cause of keratoconjunctivitis. * **Respiratory Syncytial Virus (RSV):** A major cause of bronchiolitis and pneumonia in infants. Its pathology is localized to the lower respiratory tract; ocular involvement is not a standard clinical feature. **High-Yield Clinical Pearls for NEET-PG:** * **Shipyard Eye:** A historical name for Adenoviral EKC due to industrial outbreaks. * **Transmission:** Highly contagious; spread via respiratory droplets, contaminated fingers, or ophthalmic instruments (tonometers). * **Other Viral Causes:** Herpes Simplex Virus (HSV) is another major cause of keratoconjunctivitis, typically presenting with characteristic **dendritic ulcers** on fluorescein staining. * **Structure:** Adenovirus is a non-enveloped, dsDNA virus with fiber spikes projecting from the penton bases, which are essential for attachment.

Q: Which of the following virus families exhibits the property of elution?

Myxovirus. **Explanation:** **1. Why Myxovirus is correct:** The property of **elution** is a hallmark of the **Orthomyxoviridae** (Influenza) and **Paramyxoviridae** families (collectively known as Myxoviruses). These viruses possess two specific surface spikes: **Hemagglutinin (HA)** and **Neuraminidase (NA)**. * **Hemagglutination:** The HA spikes bind to sialic acid receptors on Red Blood Cells (RBCs), causing them to clump. * **Elution:** After binding, the enzyme **Neuraminidase** cleaves the sialic acid receptors, releasing the virus from the RBC surface. This spontaneous release of the virus from the agglutinated RBCs is termed "elution." **2. Why other options are incorrect:** * **Togavirus & Adenovirus:** While some viruses in these families (like Rubella or certain Adenovirus serotypes) can cause hemagglutination, they **lack the Neuraminidase enzyme**. Therefore, once they bind to RBCs, they do not spontaneously elute. * **Parvovirus:** Specifically B19, binds to the P-antigen on erythroid progenitor cells. It causes hemagglutination but lacks the enzymatic machinery for elution. **Clinical Pearls for NEET-PG:** * **H-N Spikes:** In Influenza, HA is for **attachment/entry**, while NA is for **release/elution**. * **Antiviral Link:** Oseltamivir and Zanamivir are **Neuraminidase inhibitors**; they work by preventing elution, thereby trapping the virus within the host cell or on the cell surface. * **Receptor:** The specific receptor for Myxoviruses is **N-acetylneuraminic acid (Sialic acid)**. * **Diagnostic Test:** The Hemagglutination Inhibition (HAI) test is used to detect antibodies against these viruses.

Q: Which of the following is NOT considered a hemorrhagic viral fever?

Rocky Mountain Spotted Fever. **Explanation:** The core concept of this question lies in distinguishing between **Viral Hemorrhagic Fevers (VHFs)** and **Rickettsial diseases**. **Why Rocky Mountain Spotted Fever (RMSF) is the correct answer:** RMSF is caused by *Rickettsia rickettsii*, which is an **obligate intracellular bacterium**, not a virus. While it presents with fever and a characteristic petechial rash that can mimic hemorrhagic symptoms, it is classified as a rickettsial tick-borne disease. In the context of NEET-PG, distinguishing between viral, bacterial, and rickettsial etiologies of febrile illnesses is a frequent high-yield topic. **Analysis of Incorrect Options:** * **Dengue:** Caused by the Dengue virus (Flavivirus). Severe cases can progress to Dengue Hemorrhagic Fever (DHF), characterized by plasma leakage and bleeding manifestations. * **Chikungunya:** Caused by the Chikungunya virus (Togavirus). While primarily known for severe arthralgia, it is taxonomically grouped under viral fevers that can occasionally present with hemorrhagic manifestations in severe neonatal or elderly cases. * **Kyasanur Forest Disease (KFD):** Known as "Monkey Fever," it is caused by a Flavivirus endemic to Karnataka, India. It is a classic example of a viral hemorrhagic fever characterized by biphasic fever and mucosal bleeding. **High-Yield Clinical Pearls for NEET-PG:** * **Major VHF Families:** Arenaviridae (Lassa), Filoviridae (Ebola, Marburg), Bunyaviridae (Hantavirus, Crimean-Congo), and Flaviviridae (Yellow Fever, Dengue, KFD). * **KFD Vector:** *Haemaphysalis spinigera* (Hard tick). * **RMSF Vector:** *Dermacentor* ticks. * **Diagnostic Tip:** If a question asks for a "viral" cause and includes a Rickettsia or Coxiella species, always check the pathogen type first.

Q: Which virus is responsible for microcephaly, intracerebral calcifications, and hepatosplenomegaly when the fetus is exposed in utero?

Cytomegalovirus. **Explanation:** The clinical triad of **microcephaly, intracerebral calcifications, and hepatosplenomegaly** is the classic presentation of **Congenital Cytomegalovirus (CMV) infection**, the most common intrauterine infection worldwide. 1. **Why Cytomegalovirus is correct:** CMV has a predilection for the central nervous system and the reticuloendothelial system. A key diagnostic feature is the pattern of intracranial calcifications, which are characteristically **periventricular** (around the ventricles). Other features include sensorineural hearing loss (the most common non-genetic cause), chorioretinitis, and a "blueberry muffin" rash (extramedullary hematopoiesis). 2. **Why other options are incorrect:** * **Rubella:** While it causes microcephaly and hepatosplenomegaly, its classic triad is **Cataracts, Sensorineural deafness, and Congenital Heart Disease** (PDA or Pulmonary artery stenosis). * **Varicella Zoster:** Congenital Varicella Syndrome is characterized by **cicatricial skin scarring**, limb hypoplasia, and rudimentary digits, rather than isolated calcifications. * **Rubeola (Measles):** This is not a classic TORCH infection and does not typically cause this constellation of congenital malformations. **High-Yield Pearls for NEET-PG:** * **CMV:** Most common cause of sensorineural hearing loss in neonates. Look for **"Owl’s eye"** intranuclear inclusion bodies on histology. * **Calcification Patterns:** CMV = Periventricular; Toxoplasmosis = Diffuse/Scattered. * **Treatment:** Ganciclovir or Valganciclovir is used to reduce the severity of hearing loss and developmental delays. * **Diagnosis:** Best confirmed by PCR of saliva or urine within the first 3 weeks of life.

Q: Parvovirus B19 usually causes a very mild disease. Two groups of people for whom it can be serious, however, are?

Pregnant women and sickle-cell anemics. **Explanation:** Parvovirus B19 is a small, non-enveloped DNA virus that specifically targets and replicates in **erythroid progenitor cells** (precursors of red blood cells) by binding to the **P-antigen**. While it causes the mild "Slapped Cheek" rash (Erythema Infectiosum) in healthy children, it is life-threatening for two specific groups: 1. **Sickle-cell Anemics (and other chronic hemolytic anemias):** Because Parvovirus B19 temporarily halts erythropoiesis (red cell production), patients who already have a shortened RBC lifespan cannot compensate for the drop. This leads to a life-threatening **Aplastic Crisis**, characterized by a sudden drop in hemoglobin and a low reticulocyte count. 2. **Pregnant Women:** The virus can cross the placenta and infect the fetal bone marrow. This leads to severe fetal anemia, high-output cardiac failure, and generalized edema, a condition known as **Hydrops Fetalis**, which can result in intrauterine fetal death. **Analysis of Incorrect Options:** * **Option A:** While teenagers can get the virus (often presenting with arthralgia), it is rarely "serious" compared to the risks in pregnancy or anemia. * **Option C & D:** Parvovirus B19 is transmitted via respiratory droplets, not primarily through sexual contact or IV drug use. While asplenics are at risk for encapsulated bacteria, their risk with Parvovirus is not as specific as those with high RBC turnover (sickle cell). **High-Yield Clinical Pearls for NEET-PG:** * **Receptor:** P-antigen (Globoside) on RBCs. * **Diagnosis:** Low reticulocyte count is the hallmark of an aplastic crisis. * **Pure Red Cell Aplasia:** Can occur in immunocompromised patients (e.g., HIV) due to chronic Parvovirus infection. * **Arthropathy:** Common in adult females, mimicking Rheumatoid Arthritis.

Q: What is the best laboratory test to diagnose HIV infection?

Western blot. **Explanation:** The diagnosis of HIV infection traditionally follows a two-step algorithmic approach: **Screening** and **Confirmation**. 1. **Why Western Blot is correct:** While ELISA is the initial test used, the **Western Blot** is considered the "Gold Standard" confirmatory test for diagnosing HIV-1. It is highly specific because it detects antibodies against specific viral antigens of different molecular weights (e.g., gp120/160, gp41, and p24). A positive result requires the presence of antibodies against at least two of these major gene products (Env, Gag, or Pol). 2. **Why other options are incorrect:** * **ELISA (Option A):** This is the **best screening test** due to its high sensitivity. However, it can yield false positives (e.g., in autoimmune diseases or multiparous women), necessitating a more specific confirmatory test like Western Blot. * **Complement Fixation Test (Option C):** This is an older serological method used for certain viral and bacterial infections but lacks the sensitivity and specificity required for HIV diagnosis. * **RIA (Option D):** Radioimmunoassay is highly sensitive but involves radioactive isotopes, making it cumbersome and less practical compared to modern enzyme-based assays. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2–8 weeks). During this phase, ELISA and Western Blot may be negative. * **Best test in the Window Period/Neonates:** **p24 Antigen assay** or **HIV DNA PCR** (Qualitative). * **Best test for Prognosis/Monitoring:** **HIV RNA PCR** (Quantitative/Viral Load). * **Current CDC/NACO Update:** Modern 4th generation ELISA (detecting both p24 antigen and antibodies) has significantly shortened the window period.

Question 1

Which virus is known to cause a latent infection?

Accepted Answer

Hepatitis B virus (HBV)

Answer

Rubella

Answer

Pertussis

Answer

Rotavirus

Question 2

Which of the following statements regarding respiratory viruses is FALSE?

Accepted Answer

Mumps virus can cause aseptic meningitis, not typically septic meningitis, in adults.

Answer

RSV is the most common cause of bronchiolitis in infants.

Answer

Measles virus can cause subacute sclerosing panencephalitis (SSPE).

Answer

Epstein-Barr virus (EBV) can be associated with pleuritis.

Question 3

In which infection is transovarian transmission observed?

Accepted Answer

Yellow fever

Answer

Plague

Answer

Filarial

Answer

Guinea

Question 4

A patient presents with keratoconjunctivitis. The differential diagnosis should include infection with which of the following viruses?

Accepted Answer

Adenovirus

Answer

Parvovirus

Answer

Epstein-Barr virus

Answer

Respiratory syncytial virus

Question 5

Which of the following virus families exhibits the property of elution?

Accepted Answer

Myxovirus

Answer

Togavirus

Answer

Parvovirus

Answer

Adenovirus

Question 6

Which of the following is NOT considered a hemorrhagic viral fever?

Accepted Answer

Rocky Mountain Spotted Fever

Answer

Dengue

Answer

Chikungunya

Answer

Kyasanur Forest Disease

Question 7

Viruses can be isolated from clinical samples by cultivation in all of the following except:

Accepted Answer

Chemically defined media

Answer

Tissue culture

Answer

Embryonated eggs

Answer

Animals

Question 8

Which virus is responsible for microcephaly, intracerebral calcifications, and hepatosplenomegaly when the fetus is exposed in utero?

Accepted Answer

Cytomegalovirus

Answer

Rubella

Answer

Varicella zoster

Answer

Rubeola

Question 9

Parvovirus B19 usually causes a very mild disease. Two groups of people for whom it can be serious, however, are?

Accepted Answer

Pregnant women and sickle-cell anemics

Answer

Teenagers and pregnant women

Answer

The sexually promiscuous and drug addicts

Answer

Alcoholics and asplenics

Question 10

What is the best laboratory test to diagnose HIV infection?

Accepted Answer

Western blot

Answer

ELISA

Answer

Complement fixation test

Answer

RIA

Virology — MCQs

Virology — MCQs

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