Infectious Diseases Practice Questions

Q: Which geographical region has the highest prevalence of HIV-E?

Thailand. The question refers to **HIV-1 Subtype E** (now more accurately classified as the **CRF01_AE** recombinant form). While HIV-1 Subtype C is the most common globally, HIV-1 Subtype E (CRF01_AE) shows a distinct geographical clustering. **1. Why Thailand is Correct:** Thailand is the epicenter for **HIV-1 Subtype E (CRF01_AE)**. It was first identified among female sex workers and military recruits in Thailand in the late 1980s. This subtype is characterized by its high efficiency in heterosexual transmission and its specific tropism for the mucosal surfaces of the genital tract, which facilitated its rapid spread across Southeast Asia [1]. **2. Why other options are incorrect:** * **India:** The predominant strain in India is **Subtype C**, accounting for over 90% of infections. * **Africa:** Sub-Saharan Africa has the highest overall global burden of HIV, but the dominant strain is **Subtype C** (Southern Africa) and a mix of Subtypes A and D (East/Central Africa) [1]. * **Europe:** Western Europe and North America are dominated by **Subtype B**, which is historically associated with transmission among men who have sex with men (MSM) and intravenous drug users [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Most common subtype worldwide:** Subtype C. * **Most common subtype in India:** Subtype C. * **Subtype B:** Most common in the Americas, Europe, and Australia. * **Subtype E (CRF01_AE):** Associated with Southeast Asia (Thailand) and heterosexual transmission. * **HIV-2:** Primarily restricted to West Africa; it is less virulent and has a slower progression than HIV-1 [1].

Q: What is the most common cause of amoebic lung abscess?

Direct extension from the liver. **Explanation:** **Amoebic lung abscess** is almost always a secondary complication of **Amoebic Liver Abscess (ALA)**, caused by the protozoan *Entamoeba histolytica* [1]. **1. Why "Direct extension from the liver" is correct:** The most common mechanism is the **direct rupture** of a liver abscess (usually in the right lobe) through the diaphragm into the pleural space or the lung parenchyma [1]. This occurs because the superior surface of the liver is in close anatomical proximity to the base of the right lung. When an ALA reaches the diaphragmatic surface, it causes local inflammation, adhesion, and eventual penetration into the thoracic cavity. **2. Why other options are incorrect:** * **Hematogenous spread:** While *E. histolytica* can travel via the bloodstream (portal circulation) to reach the liver, primary hematogenous spread to the lungs without liver involvement is extremely rare. * **Lymphatic spread:** This is not a recognized primary route for the dissemination of amoebiasis to the thoracic cavity. * **Inhalation:** *E. histolytica* is transmitted via the fecal-oral route (ingestion of cysts). It is not an airborne pathogen and cannot be acquired through inhalation [1]. **High-Yield NEET-PG Pearls:** * **Most common site:** The **lower lobe of the right lung** is most frequently involved due to the anatomical position of the liver. * **Anchovy Sauce Sputum:** If the abscess ruptures into a bronchus (hepatobronchial fistula), the patient may expectorate "anchovy sauce" or "chocolate sauce" colored sputum, which is pathognomonic [1]. * **Treatment:** The drug of choice is **Metronidazole** (or Tinidazole), followed by a luminal amoebicide (e.g., Diloxanide furoate) to eradicate the intestinal carrier state.

Q: Which of the following statements about cysticercosis is true?

Human cysticercosis is transmitted by the ingestion of ova. Cysticercosis is a systemic parasitic infection caused by the larval stage (*Cysticercus cellulosae*) of the pork tapeworm, **Taenia solium** [1]. **1. Why Option C is correct:** Human cysticercosis occurs when a human acts as an **accidental intermediate host**. This happens via the **ingestion of T. solium eggs (ova)** through contaminated food or water (fecal-oral route) or via autoinfection [1], [2]. Once ingested, the eggs hatch in the intestine, releasing oncospheres that migrate to tissues (brain, muscles, eyes) to form cysticerci. **2. Why other options are incorrect:** * **Option A:** *Echinococcus granulosus* causes Hydatid disease, not cysticercosis [1]. * **Option B:** In the life cycle of *T. solium*, **man is the definitive host** only for the adult tapeworm (intestinal taeniasis, acquired by eating undercooked pork containing cysticerci) [1], [2]. However, for **cysticercosis**, man acts as the intermediate host. * **Option D:** The treatment of choice for neurocysticercosis (NCC) involves **Albendazole** (preferred) or Praziquantel, often administered with corticosteroids to reduce inflammation. Levamisole is an anthelmintic used primarily for Ascariasis. **High-Yield Clinical Pearls for NEET-PG:** * **Neurocysticercosis (NCC):** The most common cause of adult-onset seizures in developing countries. * **Imaging:** CT/MRI shows the "starry sky" appearance (multiple calcified cysts) or a "hole-with-dot" appearance (scolex within the cyst). * **Key Distinction:** Ingesting **larvae** (in pork) leads to **Taeniasis** (intestinal); ingesting **eggs** (fecal-oral) leads to **Cysticercosis** (tissue) [1], [2].

Q: Prophylactic therapy should be started against Pneumocystis carinii pneumonia in AIDS patients with CD4 counts below what threshold?

< 200/microL. The risk of opportunistic infections in HIV/AIDS patients is directly correlated with the decline in CD4+ T-lymphocyte counts. **Pneumocystis jirovecii (formerly P. carinii)** is the most common opportunistic respiratory infection in these patients [1]. Clinical data shows that the incidence of PCP increases significantly once the CD4 count drops below **200 cells/µL**. Therefore, primary prophylaxis with **Trimethoprim-Sulfamethoxazole (TMP-SMX)** is initiated at this threshold to reduce morbidity and mortality [1]. **Analysis of Options:** * **A (< 50/µL):** This is the threshold for initiating prophylaxis against **Mycobacterium avium complex (MAC)** (using Azithromycin) and is also the level where CMV retinitis becomes highly prevalent. * **B (< 150/µL):** This threshold is often associated with an increased risk for fungal infections like **Histoplasmosis** in endemic areas, but it is not the standard cutoff for PCP. * **C (< 200/µL):** **Correct.** This is the standard guideline for starting PCP prophylaxis [1]. It is also the threshold for starting prophylaxis against **Toxoplasma gondii** (if the patient is seropositive). * **D (< 400/µL):** At this level, patients are generally not at high risk for major opportunistic infections, though they may show signs of generalized lymphadenopathy or skin infections. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** TMP-SMX (Double strength, once daily). * **Alternative for Sulfa-allergic patients:** Dapsone, Atovaquone, or Pentamidine (aerosolized) [1]. * **Discontinuation:** Prophylaxis can be safely stopped if the CD4 count remains **>200 cells/µL for at least 3 months** in response to ART. * **Chest X-ray finding:** Classic "bat-wing" appearance or bilateral perihilar interstitial infiltrates [1].

Q: A nurse has been vaccinated against Hepatitis B and has no prior history of Hepatitis B infection. Which of the following would be found in a blood examination?

Anti-HBs Ag. The correct answer is **Anti-HBs Ag**. This question tests the ability to differentiate between immunity acquired through vaccination versus natural infection. **1. Why Anti-HBs Ag is correct:** Hepatitis B vaccines (like the recombinant Engerix-B) contain only the **Hepatitis B surface antigen (HBsAg)**. When a person is vaccinated, their immune system recognizes this surface protein and produces **Anti-HBs antibodies**. Since the vaccine does not contain the core of the virus, the body never produces antibodies against the core antigen. Therefore, a successfully vaccinated individual will be positive for Anti-HBs but negative for all other markers [1]. **2. Why the other options are incorrect:** * **HBsAg (Option A):** This is a marker of active infection (either acute or chronic) [1]. It would not be present in a healthy, vaccinated individual. * **Anti-HBc Ag (Option C):** These are antibodies against the **core antigen**. The core antigen is only found in the actual virus, not the vaccine. The presence of Anti-HBc indicates a **past or current natural infection** [1]. * **Anti-HBs and Anti-HBc (Option D):** This pattern is seen in individuals who have **recovered from a natural infection**. They develop Anti-HBs for immunity and Anti-HBc as a "scar" of the prior viral encounter [1]. **NEET-PG High-Yield Pearls:** * **Window Period:** The time when HBsAg has disappeared but Anti-HBs has not yet appeared. During this phase, **IgM Anti-HBc** is the only diagnostic marker. * **Chronic Infection:** Defined by the persistence of HBsAg for >6 months [1]. * **Infectivity:** **HBeAg** is the primary marker of high viral replication and high infectivity. * **Protective Titer:** An Anti-HBs level of **>10 mIU/mL** is considered protective after a full vaccination series.

Question 1

Which geographical region has the highest prevalence of HIV-E?

Accepted Answer

Thailand

Answer

India

Answer

Africa

Answer

Europe

Question 2

Which of the following is NOT a feature of dengue hemorrhagic fever?

Accepted Answer

Narrow pulse pressure

Answer

Thrombocytopenia

Answer

Elevated hematocrit

Answer

Positive tourniquet test

Question 3

A 29-year-old male is found to be HBsAg positive with highly increased SCOT levels but HBeAg negative. Which of the following is true about the status of the patient?

Accepted Answer

Precore mutant

Answer

Core-promoter mutant

Answer

Wild type mutant

Answer

Surface mutant

Question 4

A person had an episode of dengue serotype 1, followed by an infection with serotype 2 two years later. What is the likely effect of the second episode?

Accepted Answer

Increased chances of developing Dengue Hemorrhagic Fever (DHF).

Answer

Mild dengue fever due to the presence of neutralizing antibodies.

Answer

No chances of developing DHF.

Answer

No effect on the present illness.

Question 5

What is the most common cause of amoebic lung abscess?

Accepted Answer

Direct extension from the liver

Answer

Hematogenous spread

Answer

Lymphatic spread

Answer

Inhalation

Question 6

Which of the following statements about cysticercosis is true?

Accepted Answer

Human cysticercosis is transmitted by the ingestion of ova

Answer

The causative agent is Echinococcus granulosus

Answer

The definitive host is man

Answer

Levamisole is the treatment of choice

Question 7

Prophylactic therapy should be started against Pneumocystis carinii pneumonia in AIDS patients with CD4 counts below what threshold?

Accepted Answer

< 200/microL

Answer

< 50/microL

Answer

< 150/microL

Answer

< 400/microL

Question 8

Opportunistic lung infections in AIDS are most commonly caused by which of the following pathogens?

Accepted Answer

Pneumocystis jirovecii

Answer

Klebsiella pneumoniae

Answer

Mucor species

Answer

Mycoplasma pneumoniae

Question 9

What is the increased risk factor for developing tuberculosis (TB) in a patient with a positive Mantoux test?

Accepted Answer

Adrenal steroid therapy

Answer

Human Immunodeficiency Virus (HIV) infection

Answer

Diabetes Mellitus (DM)

Answer

All the above

Question 10

A nurse has been vaccinated against Hepatitis B and has no prior history of Hepatitis B infection. Which of the following would be found in a blood examination?

Accepted Answer

Anti-HBs Ag

Answer

HBsAg

Answer

Anti-HBc Ag

Answer

Anti-HBs Ag and Anti-HBc core antigen

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?