Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 831: Which virus is known to cause a latent infection?

A. Rubella
B. Hepatitis B virus (HBV) (Correct Answer)
C. Pertussis
D. Rotavirus

Explanation: **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.

Question 832: Which of the following statements regarding respiratory viruses is FALSE?

A. RSV is the most common cause of bronchiolitis in infants.
B. Mumps virus can cause aseptic meningitis, not typically septic meningitis, in adults. (Correct Answer)
C. Measles virus can cause subacute sclerosing panencephalitis (SSPE).
D. Epstein-Barr virus (EBV) can be associated with pleuritis.

Explanation: ### Explanation The correct answer is **B**, as the statement provided is actually **TRUE**, making it an incorrect choice for a "find the false statement" question. In medical exams like NEET-PG, identifying the false statement requires verifying the clinical accuracy of each option. **1. Why Option B is the "Correct" Answer (Analysis of the Statement):** The statement "Mumps virus can cause aseptic meningitis, not typically septic meningitis" is a **true clinical fact**. Aseptic meningitis is the most common extra-salivary complication of Mumps. Since the question asks for the **FALSE** statement, and B is true, there is likely a typographical error in the question's premise or the provided options. However, in the context of standard virology: * **Aseptic meningitis** (viral) is characterized by lymphocytic pleocytosis and normal glucose. * **Septic meningitis** (bacterial) involves neutrophils and low glucose. Mumps never causes the latter. **2. Analysis of Other Options:** * **Option A (True):** Respiratory Syncytial Virus (RSV) is globally recognized as the #1 cause of bronchiolitis and pneumonia in infants under 1 year of age. * **Option C (True):** SSPE is a rare, progressive neurological disorder caused by a persistent infection with a mutant strain of the Measles virus, occurring years after the initial infection. * **Option D (False/Controversial):** EBV is primarily associated with Infectious Mononucleosis, Burkitt lymphoma, and Nasopharyngeal carcinoma. While it can rarely cause pneumonia in immunocompromised hosts, it is **not** typically associated with pleuritis. This makes Option D the technically false statement in most clinical textbooks. **High-Yield Clinical Pearls for NEET-PG:** * **Mumps:** Most common cause of spontaneous orchitis in post-pubertal males; can also cause pancreatitis. * **RSV:** Treatment for severe cases includes **Ribavirin** (aerosolized) and prophylaxis with **Palivizumab** (monoclonal antibody). * **SSPE Diagnosis:** Look for high titers of anti-measles antibodies in the CSF and "periodic complexes" on EEG. * **EBV:** Associated with "Downey cells" (atypical lymphocytes) and a positive Monospot test (heterophile antibodies).

Question 833: In which infection is transovarian transmission observed?

A. Plague
B. Filarial
C. Guinea
D. Yellow fever (Correct Answer)

Explanation: **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.

Question 834: A patient presents with keratoconjunctivitis. The differential diagnosis should include infection with which of the following viruses?

A. Parvovirus
B. Adenovirus (Correct Answer)
C. Epstein-Barr virus
D. Respiratory syncytial virus

Explanation: **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.

Question 835: Which of the following virus families exhibits the property of elution?

A. Myxovirus (Correct Answer)
B. Togavirus
C. Parvovirus
D. Adenovirus

Explanation: **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.

Question 836: Which of the following is NOT considered a hemorrhagic viral fever?

A. Dengue
B. Chikungunya
C. Rocky Mountain Spotted Fever (Correct Answer)
D. Kyasanur Forest Disease

Explanation: **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.

Question 837: Viruses can be isolated from clinical samples by cultivation in all of the following except:

A. Tissue culture
B. Embryonated eggs
C. Animals
D. Chemically defined media (Correct Answer)

Explanation: **Explanation:** The fundamental concept in virology is that **viruses are obligate intracellular parasites**. They lack the cellular machinery (ribosomes, enzymes, and metabolic pathways) required for independent replication and protein synthesis. Therefore, they can only grow within living cells. **1. Why "Chemically Defined Media" is the correct answer:** Chemically defined media (like agar or broth used for bacteria) consist of specific concentrations of pure chemical nutrients but lack living cells. Since viruses require a host cell's metabolic machinery to replicate, they **cannot** be cultured on inanimate, synthetic media. **2. Why the other options are incorrect (Methods of Viral Isolation):** * **Tissue Culture (Cell Culture):** This is the most common method used today. It involves growing mammalian or insect cells in vitro, which then serve as hosts for viral replication. Examples include Primary (Monkey kidney), Diploid (WI-38), and Continuous cell lines (HeLa, Vero). * **Embryonated Eggs:** A classic method (traditionally using 7–12 day old chick embryos). Different viruses have tropism for different sites, such as the **Chorioallantoic membrane (CAM)** for Poxvirus, the **Allantoic cavity** for Influenza, and the **Yolk sac** for Chlamydia or Rickettsia. * **Animals:** The oldest method, now largely replaced by cell culture due to ethical concerns. However, it remains essential for studying pathogenesis or for viruses that do not grow well in vitro (e.g., Suckling mice are used for Coxsackie and Arboviruses). **High-Yield Clinical Pearls for NEET-PG:** * **Pock formation:** Visible lesions on the CAM of an embryonated egg, characteristic of Variola or Vaccinia. * **Cytopathic Effect (CPE):** Morphological changes in cell culture (e.g., syncytia formation in RSV/Measles or "grape-like clusters" in Adenovirus) used to identify viral growth. * **Exceptions:** Prions and certain viruses (like Hepatitis B and C) are notoriously difficult or impossible to grow in standard routine cultures.

Question 838: Which virus is responsible for microcephaly, intracerebral calcifications, and hepatosplenomegaly when the fetus is exposed in utero?

A. Cytomegalovirus (Correct Answer)
B. Rubella
C. Varicella zoster
D. Rubeola

Explanation: **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.

Question 839: Parvovirus B19 usually causes a very mild disease. Two groups of people for whom it can be serious, however, are?

A. Teenagers and pregnant women
B. Pregnant women and sickle-cell anemics (Correct Answer)
C. The sexually promiscuous and drug addicts
D. Alcoholics and asplenics

Explanation: **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.

Question 840: What is the best laboratory test to diagnose HIV infection?

A. ELISA
B. Western blot (Correct Answer)
C. Complement fixation test
D. RIA

Explanation: **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.

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