Virology Practice Questions

Q: A patient develops clinical symptoms consistent with hepatitis. The patient recalls sticking themselves with a needle approximately 4 months prior after drawing blood from another patient. Serologic tests for HBsAg, antibodies to HBsAg, and hepatitis A virus (HAV) are all negative; however, the patient is positive for IgM core antibody. What is the most likely diagnosis?

Window period of hepatitis B infection. ### Explanation The correct answer is **D. Window period of hepatitis B infection.** **Understanding the Concept:** The "Window Period" is a specific phase in Hepatitis B virus (HBV) infection where **HBsAg** (the surface antigen) has disappeared because it is being cleared by the body, but **Anti-HBs** (the protective surface antibody) has not yet reached detectable levels. During this gap, both HBsAg and Anti-HBs are negative. The only reliable serologic marker of an acute infection during this phase is the **IgM anti-HBc (IgM core antibody)**. This patient’s profile (HBsAg negative, Anti-HBs negative, but IgM anti-HBc positive) is the classic definition of the window period. **Why other options are incorrect:** * **A. No hepatitis B infection:** The presence of IgM anti-HBc indicates a recent acute infection; it would be negative if the patient were never infected. * **B. Hepatitis A infection:** The patient tested negative for HAV serology, ruling this out. * **C. Late stage of hepatitis B infection:** In late/chronic stages or recovery, HBsAg would be negative but **IgG anti-HBc** would be present, and **Anti-HBs** would typically be positive (if recovered). IgM is specifically a marker of acute/recent infection. **NEET-PG High-Yield Pearls:** * **IgM anti-HBc:** The *only* marker positive during the window period. It is also the best marker for diagnosing **acute** HBV infection. * **HBsAg:** The first marker to appear (as early as 1–2 weeks post-exposure) and the first to disappear in recovery. * **Anti-HBs:** Indicates immunity (via recovery or vaccination). * **Anti-HBc:** Indicates a history of infection (never present in vaccinated individuals). * **HBeAg:** Indicates high viral replication and maximum infectivity.

Q: An HIV patient complains of visual disturbances. Fundal examination shows bilateral retinal exudates and perivascular hemorrhages. Which of the following viruses is most likely responsible for this retinitis?

Cytomegalovirus. ### Explanation **Correct Option: C. Cytomegalovirus (CMV)** **Why it is correct:** Cytomegalovirus (CMV) retinitis is the most common opportunistic ocular infection in HIV/AIDS patients, typically occurring when the **CD4 count falls below 50 cells/mm³**. The classic fundoscopic description provided—**"bilateral retinal exudates and perivascular hemorrhages"**—is characteristic of CMV. This is often referred to as the **"Pizza-pie"** or **"Tomato-sauce and cheese"** appearance. The virus causes a full-thickness necrotizing retinitis that leads to visual field defects and, if untreated, total blindness. **Why other options are incorrect:** * **A & B (HSV and VZV):** While both can cause retinitis in HIV patients (e.g., Acute Retinal Necrosis), they typically present with rapid, painful vision loss and peripheral necrotizing lesions rather than the classic perivascular "pizza-pie" hemorrhage seen in CMV. * **D (Epstein-Barr Virus):** EBV is primarily associated with Oral Hairy Leukoplakia and Primary CNS Lymphoma in HIV patients; it is not a standard cause of retinitis. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** **Ganciclovir** (Intravenous or intravitreal) or Valganciclovir. Foscarnet/Cidofovir are second-line. * **CD4 Threshold:** Always suspect CMV when CD4 < 50 cells/mm³. * **Histology:** Look for **"Owl’s eye"** intranuclear inclusion bodies. * **Other CMV manifestations in AIDS:** Intractable diarrhea (CMV Colitis) and painful esophageal ulcers (CMV Esophagitis). * **Differential:** Unlike Toxoplasmosis (which shows "headlight in the fog" due to vitritis), CMV retinitis usually has minimal vitreous inflammation.

Q: The human immunodeficiency virus (HIV) has a particularly high affinity for which of the following cell types?

CD4 T Lymphocytes and monocytes. **Explanation:** The hallmark of HIV pathogenesis is its high affinity for cells expressing the **CD4 receptor** on their surface. The viral envelope glycoprotein **gp120** binds specifically to the CD4 molecule, which acts as the primary receptor for viral entry. 1. **Why Option B is Correct:** While **CD4+ T Lymphocytes** (Helper T cells) are the primary targets and their depletion leads to profound immunodeficiency, **Monocytes and Macrophages** also express CD4 receptors on their surface (albeit in lower densities). These cells, along with dendritic cells, serve as significant reservoirs for the virus, transporting it to various organs like the brain and lymphoid tissues. 2. **Why Other Options are Incorrect:** * **Options A & C (B cells):** B lymphocytes do not express the CD4 receptor; therefore, HIV cannot directly infect them via the gp120-CD4 interaction. * **Options C & D (CD8 T Lymphocytes):** CD8+ T cells (Cytotoxic T cells) lack the CD4 receptor. In fact, CD8+ T cell counts often initially rise as the body attempts to control the HIV infection. **High-Yield NEET-PG Pearls:** * **Co-receptors:** Binding to CD4 is not enough; HIV also requires co-receptors: **CCR5** (found on macrophages/monocytes; "M-tropic" strains) and **CXCR4** (found on T-helper cells; "T-mropic" strains). * **CCR5 Mutation:** Individuals with a homozygous **CCR5-Δ32 mutation** are resistant to infection by the most common strains of HIV-1. * **Trojan Horse:** Macrophages are often called the "Trojan Horse" of HIV because they are resistant to the cytopathic effects of the virus, allowing it to persist and spread throughout the body.

Q: Which infection is common after organ transplantation?

Cytomegalovirus. **Explanation:** **Cytomegalovirus (CMV)** is the most common clinically significant viral infection following solid organ transplantation (SOT). The underlying medical concept is the **reactivation of latent virus** (or primary infection from the donor) during the period of maximal immunosuppression, typically occurring **1 to 6 months post-transplant**. CMV is a member of the Herpesviridae family and remains latent in myeloid progenitor cells and monocytes. It is a major cause of morbidity, leading to "CMV syndrome" (fever, malaise, cytopenia) or tissue-invasive disease (pneumonitis, hepatitis, colitis). **Analysis of Incorrect Options:** * **Pneumocystis jirovecii (A):** While a significant opportunistic fungal infection causing pneumonia in immunocompromised hosts, its incidence has drastically decreased due to the routine use of **TMP-SMX prophylaxis** in transplant recipients. * **Nocardia (B):** This is an opportunistic bacterial infection (Gram-positive, weakly acid-fast) that can cause pulmonary or CNS disease, but it is far less frequent than CMV. * **Toxoplasma gondii (D):** This protozoan infection is primarily a concern in heart transplant recipients (if the donor is seropositive) or HIV patients, but it does not match the overall prevalence of CMV across all organ types. **High-Yield Clinical Pearls for NEET-PG:** * **Timeline:** CMV typically appears in the "middle period" (1–6 months). Infections in the first month are usually bacterial/surgical; after 6 months, they are community-acquired. * **Diagnosis:** **PP65 antigenemia assay** or **Quantitative PCR** for CMV DNA. * **Histology:** Look for **"Owl’s eye" intranuclear inclusions**. * **Treatment:** **Ganciclovir** or Valganciclovir are the drugs of choice.

Q: What is the usual incubation period for hepatitis B virus infection?

1-6 months. **Explanation:** Hepatitis B Virus (HBV) is a DNA virus characterized by a **long and variable incubation period**, typically ranging from **30 to 180 days (1–6 months)**, with an average of about 60–90 days. This prolonged period is due to the virus's slow replication cycle and the time required for the host's immune system to mount a cell-mediated response against the hepatocytes, which causes the clinical symptoms. **Analysis of Options:** * **Option A (1-2 days):** This is characteristic of respiratory viruses (like Influenza) or bacterial gastroenteritis (like *Vibrio cholerae*). * **Option B (1-2 weeks):** This is typical for Hepatitis A (which has a total range of 2–6 weeks) or Arboviruses like Dengue. * **Option C (1-6 months):** **Correct.** HBV and HCV both share this long incubation window. * **Option D (1 year):** While some chronic infections or slow viruses (like Prions or Rabies in rare cases) can have incubation periods of a year or more, it is not the "usual" presentation for acute HBV. **NEET-PG High-Yield Pearls:** * **Hepatitis Incubation Periods:** * **HAV:** 2–6 weeks (Short) * **HBV:** 1–6 months (Long) * **HCV:** 2 weeks – 6 months (Variable) * **HEV:** 2–8 weeks (Similar to HAV) * **First Marker to Appear:** HBsAg is the first detectable serological marker, appearing even before the onset of symptoms (during the incubation period). * **Window Period:** The interval between the disappearance of HBsAg and the appearance of Anti-HBs. During this time, **Anti-HBc IgM** is the only diagnostic marker.

Q: Syncytium formation is the typical cytopathic effect (CPE) produced by which virus?

Measles virus. **Explanation:** The correct answer is **Measles virus**. Syncytium formation (also known as multinucleated giant cell formation) is a hallmark cytopathic effect (CPE) of certain enveloped viruses. **Why Measles is Correct:** Measles virus, a member of the *Paramyxoviridae* family, possesses a specialized **Fusion (F) protein** on its envelope. This protein allows the viral envelope to fuse with the host cell membrane. During replication, the F-protein is expressed on the surface of the infected cell, causing it to fuse with neighboring uninfected cells. This results in a large, cytoplasmic mass containing multiple nuclei, known as a **syncytium**. In clinical practice, these are identified in lymphoid tissue as **Warthin-Finkeldey giant cells**. **Analysis of Incorrect Options:** * **BK virus, JC virus, and SV 40 virus:** These are all members of the *Polyomaviridae* family. Polyomaviruses are small, non-enveloped DNA viruses. Because they lack a fusion protein and an envelope, they do not induce cell-to-cell fusion (syncytia). Instead, their typical CPE involves **intranuclear inclusions** (e.g., "decoy cells" in urine for BK virus). **High-Yield Clinical Pearls for NEET-PG:** * **Other Syncytia-forming viruses:** Remember the mnemonic **"MR. H"** — **M**easles, **R**SV (Respiratory Syncytial Virus), and **H**IV/Herpes Simplex Virus. * **Warthin-Finkeldey Cells:** Pathognomonic multinucleated giant cells found in the tonsils/lymph nodes of Measles patients. * **Koplik Spots:** The prodromal enanthem of Measles; look for "grains of salt on a red base" opposite the lower molars. * **Tzanck Smear:** Used to identify syncytia (multinucleated giant cells) in HSV or VZV infections.

Q: A child from a summer camp presents with a sore throat, rhinorrhoea, and bilateral conjunctival congestion. What is the most likely causative agent?

Adenovirus. **Explanation:** The clinical presentation of a **sore throat (pharyngitis)**, **rhinorrhoea**, and **bilateral conjunctival congestion** (conjunctivitis) in a child, especially in a setting like a summer camp, is the classic triad of **Pharyngoconjunctival Fever (PCF)**. **Why Adenovirus is correct:** Adenovirus (specifically serotypes 3, 4, and 7) is the primary cause of Pharyngoconjunctival Fever. It often occurs in outbreaks among children in close quarters, such as summer camps or schools, and is frequently associated with contaminated swimming pool water ("Swimming pool conjunctivitis"). The combination of respiratory symptoms and follicular conjunctivitis is a hallmark of Adenoviral infection. **Why other options are incorrect:** * **Rhinovirus:** The most common cause of the "common cold." While it causes rhinorrhoea and sore throat, it rarely causes significant conjunctivitis. * **Enterovirus:** While some Enteroviruses (like Coxsackievirus) cause hand-foot-and-mouth disease or herpangina, they are not the typical cause of the pharyngitis-conjunctivitis triad. (Note: Enterovirus 70 causes Acute Hemorrhagic Conjunctivitis, which is more severe and lacks the prominent pharyngitis). * **Coronavirus:** Primarily causes upper respiratory infections (common cold) or severe pneumonia (SARS/MERS/COVID-19), but conjunctivitis is not a primary diagnostic feature of the standard seasonal variants. **High-Yield Clinical Pearls for NEET-PG:** * **Adenovirus Structure:** Non-enveloped, dsDNA virus with a characteristic icosahedral shape and projecting fibers (penton bases). * **Epidemic Keratoconjunctivitis (EKC):** Caused by Adenovirus serotypes 8, 19, and 37; it is more severe than PCF and can lead to corneal opacities. * **Other manifestations:** Adenovirus is also a common cause of **Acute Hemorrhagic Cystitis** (serotypes 11, 21) and **infantile gastroenteritis** (serotypes 40, 41).

Q: Man is the primary host for which poxvirus?

Molluscum contagiosum. ### Explanation **Correct Answer: D. Molluscum contagiosum** **1. Why it is correct:** Poxviruses are generally **zoonotic**, meaning they primarily circulate in animals and only incidentally infect humans. **Molluscum contagiosum virus (MCV)** is the notable exception. It is an **obligate human pathogen** with no known animal reservoir. Humans are the primary and only natural hosts. It is transmitted via direct skin-to-skin contact, fomites, or sexual contact, leading to characteristic umbilicated papules. **2. Why the other options are incorrect:** * **A. Monkeypox:** The primary hosts are **rodents** (such as squirrels and Gambian pouched rats) and non-human primates in Central and West Africa. Human infection is accidental. * **B. Orf:** This is a parapoxvirus whose primary hosts are **sheep and goats**. It causes "contagious pustular dermatitis" in animals; humans (usually shearers or veterinarians) are accidental hosts. * **C. Tanapox:** This is a yatapoxvirus endemic to the Tana River valley in Kenya. The primary hosts are **monkeys**, and it is transmitted to humans via arthropod bites or direct contact. **3. High-Yield Clinical Pearls for NEET-PG:** * **Smallpox (Variola):** Like Molluscum, Variola also had humans as the only host, which is why global eradication was possible. * **Histopathology of Molluscum:** Look for **Henderson-Patterson bodies** (large, eosinophilic intracytoplasmic inclusion bodies) in the epidermis. * **Clinical Presentation:** Small, pearly, flesh-colored, **dome-shaped papules with central umbilication**. In HIV/immunocompromised patients, lesions can be giant or disseminated. * **Poxvirus General Feature:** They are the largest DNA viruses and are unique because they **replicate entirely in the cytoplasm** (carrying their own DNA-dependent RNA polymerase).

Q: A sexually active 17-year-old male presents with small, white papules with a central depression on his penis. There is no discharge or pain on urination. What is the virus most likely causing these lesions?

Molluscipoxvirus. ### Explanation **Correct Answer: D. Molluscipoxvirus** The clinical presentation of small, white, pearly papules with a **central depression (umbilication)** is the hallmark of **Molluscum Contagiosum**, caused by the **Molluscipoxvirus** (a member of the Poxviridae family). In adolescents and adults, it is frequently transmitted sexually, presenting on the genitals, lower abdomen, or inner thighs. The lesions are typically asymptomatic (painless and non-pruritic) and contain a curd-like core consisting of infected keratinocytes. **Analysis of Incorrect Options:** * **A. Adenovirus:** Typically causes respiratory infections, conjunctivitis (pink eye), or hemorrhagic cystitis, but does not present with umbilicated skin papules. * **B. Coxsackievirus A:** Known for causing **Hand-Foot-and-Mouth Disease** (vesicular eruptions on the palms, soles, and oral mucosa) or Herpangina, not chronic umbilicated genital papules. * **C. HPV type 6:** Causes **Condyloma acuminatum** (genital warts). These are typically cauliflower-like, fleshy, or filiform growths, lacking the central umbilication characteristic of Molluscum. **NEET-PG High-Yield Pearls:** * **Histopathology:** Look for **Henderson-Patterson bodies** (large, eosinophilic intracytoplasmic inclusion bodies) within the epidermis. * **Virology:** Molluscipoxvirus is a **dsDNA virus** that replicates in the **cytoplasm** (unique for DNA viruses). * **Clinical Association:** In adults, extensive or giant molluscum lesions should prompt an investigation for **HIV/immunodeficiency**. * **Transmission:** Occurs via direct contact or fomites (e.g., towels, gym equipment).

Q: Which of the following is true about hepatitis A, except?

Chronicity is the hallmark of the disease. **Explanation:** Hepatitis A Virus (HAV) is a leading cause of acute viral hepatitis worldwide. The hallmark of HAV infection is that it **never causes chronic infection**. It is an acute, self-limiting disease that does not lead to a carrier state, chronic hepatitis, or cirrhosis. **Analysis of Options:** * **Option D (Correct):** This is the false statement. Unlike Hepatitis B and C, HAV does not progress to chronicity. Once the acute phase resolves, the patient develops lifelong immunity. * **Option A:** HAV is notoriously **difficult to culture** in the laboratory. While it can be grown in certain primate cell lines (like fetal rhesus monkey kidney cells), it does not produce a cytopathic effect (CPE), making primary isolation impractical for diagnosis. * **Option B:** HAV is a non-enveloped, positive-sense RNA virus. It was formerly classified as **Enterovirus 72** but is now placed in its own genus, *Hepatovirus*, within the *Picornaviridae* family. * **Option C:** Both **Inactivated (killed)** and **Live-attenuated** vaccines are available. In India, the inactivated vaccine (e.g., Havrix) is commonly used, administered in two doses. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Fecal-oral route (most common). * **Incubation Period:** Short (average 2–4 weeks). * **Diagnosis:** Detection of **IgM anti-HAV** is the gold standard for acute infection. IgG indicates past infection or vaccination. * **Complication:** While it doesn't cause chronicity, it can rarely cause **Fulminant Hepatic Failure**, especially in adults or those with pre-existing liver disease. * **Shellfish:** Consumption of raw/undercooked shellfish is a classic risk factor mentioned in clinical vignettes.

Question 1

A patient develops clinical symptoms consistent with hepatitis. The patient recalls sticking themselves with a needle approximately 4 months prior after drawing blood from another patient. Serologic tests for HBsAg, antibodies to HBsAg, and hepatitis A virus (HAV) are all negative; however, the patient is positive for IgM core antibody. What is the most likely diagnosis?

Accepted Answer

Window period of hepatitis B infection

Answer

No hepatitis B infection

Answer

Hepatitis A infection

Answer

Late stage of hepatitis B infection

Question 2

An HIV patient complains of visual disturbances. Fundal examination shows bilateral retinal exudates and perivascular hemorrhages. Which of the following viruses is most likely responsible for this retinitis?

Accepted Answer

Cytomegalovirus

Answer

Herpes simplex virus

Answer

Varicella zoster virus

Answer

Epstein-Barr virus

Question 3

The human immunodeficiency virus (HIV) has a particularly high affinity for which of the following cell types?

Accepted Answer

CD4 T Lymphocytes and monocytes

Answer

CD4 T Lymphocytes and B cells

Answer

CD8 T Lymphocytes and B cells

Answer

CD8 T Lymphocytes and CD4 T Lymphocytes

Question 4

Which infection is common after organ transplantation?

Accepted Answer

Cytomegalovirus

Answer

Pneumocystis

Answer

Nocardia

Answer

Toxoplasma

Question 5

What is the usual incubation period for hepatitis B virus infection?

Accepted Answer

1-6 months

Answer

1-2 days

Answer

1-2 weeks

Answer

1 year

Question 6

Syncytium formation is the typical cytopathic effect (CPE) produced by which virus?

Accepted Answer

Measles virus

Answer

BK virus

Answer

JC virus

Answer

SV 40 virus

Question 7

A child from a summer camp presents with a sore throat, rhinorrhoea, and bilateral conjunctival congestion. What is the most likely causative agent?

Accepted Answer

Adenovirus

Answer

Rhinovirus

Answer

Enterovirus

Answer

Coronavirus

Question 8

Man is the primary host for which poxvirus?

Accepted Answer

Molluscum contagiosum

Answer

Monkey pox

Answer

Orf

Answer

Tanapox

Question 9

A sexually active 17-year-old male presents with small, white papules with a central depression on his penis. There is no discharge or pain on urination. What is the virus most likely causing these lesions?

Accepted Answer

Molluscipoxvirus

Answer

Adenovirus

Answer

Coxsackievirus A

Answer

HPV type 6

Question 10

Which of the following is true about hepatitis A, except?

Accepted Answer

Chronicity is the hallmark of the disease

Answer

It is difficult to culture

Answer

It belongs to enterovirus

Answer

Vaccines are available

Virology — MCQs

Virology — MCQs

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