Infectious Diseases Practice Questions

Q: Which of the following waterborne diseases is characterized by rice water stools?

Cholera. ***Typhoid fever*** - **Rice water stools** are a classic symptom of **cholera**, not typhoid fever. Typhoid fever is characterized by a **step-ladder fever pattern**, **bradycardia**, and abdominal pain, eventually leading to a rose-spot rash. - The causative agent of typhoid fever is **Salmonella typhi**, which primarily invades the gastrointestinal tract and then disseminates systemically. *Giardiasis* - Giardiasis is caused by the parasite **Giardia lamblia**, and its typical symptoms include **fatty**, **foul-smelling stools**, **bloating**, cramps, and weight loss, not rice water stools. - This infection is often acquired through the ingestion of **cysts** from contaminated water or food. *Cholera* - **Cholera** is the correct answer and is classically characterized by the production of **massive watery diarrhea** with **“rice water” stools**, which are gray, turbid, and flecked with mucus. - This severe dehydration is due to the action of **cholera toxin**, which causes electrolyte and fluid secretion into the intestinal lumen. *Hepatitis A* - **Hepatitis A** is primarily a **viral liver infection** characterized by **jaundice**, dark urine, fatigue, and nausea, and it does not typically present with diarrhea, especially not rice water stools. - It is transmitted via the **fecal-oral route**, often through contaminated food or water, but its primary target is the liver.

Q: Most common extra-cutaneous manifestation of varicella is involvement of

Lungs. **Lungs** - **Varicella pneumonia** is the most common and serious extra-cutaneous manifestation, particularly in adults, immunocompromised individuals, and pregnant women [1]. - It can lead to severe respiratory distress and has a significant mortality rate. *CNS* - **Aseptic meningitis** and **encephalitis** can occur, but less frequently than pulmonary involvement, and are often mild [1]. - Other neurological complications like **cerebellar ataxia** are also less common than pneumonia. *Kidneys* - **Renal involvement** in varicella is rare and typically mild, such as transient hematuria or proteinuria. - Serious renal complications like acute kidney injury are not characteristic features. *CVS* - **Cardiac complications** like myocarditis or pericarditis are exceedingly rare in varicella infections. - They are not considered a common extra-cutaneous manifestation of the disease.

Q: Acute endocarditis with abscess is most commonly associated with which organism?

Staphylococcus aureus. ***Staphylococcus aureus*** - **_Staphylococcus aureus_** is the most common cause of **acute infective endocarditis** and is notorious for its rapid destruction of heart valves and its frequent association with **abscess formation** (e.g., peri-annular abscesses, myocardial abscesses). [1] - Its virulence factors, such as hemolysins and coagulase, contribute to its aggressive nature and ability to cause **severe, rapidly progressive disease**. [3] *Listeria* - **_Listeria monocytogenes_** is an uncommon cause of endocarditis, typically seen in immunocompromised individuals or those with prosthetic valves, but it is not the most common organism associated with acute endocarditis and abscess formation. - While it can cause severe systemic infections, **abscess formation** in the context of endocarditis is not its hallmark clinical feature compared to _S. aureus_. *Streptococcus* - **_Streptococcus_ species**, particularly **_Streptococcus viridans_**, are common causes of **subacute infective endocarditis**, often affecting previously damaged valves. [1] - While they can cause complications, they are less frequently associated with **acute onset**, rapid valve destruction, and primary abscess formation compared to _S. aureus_. [2] *Enterococcus* - **_Enterococcus_ species** (e.g., _E. faecalis_, _E. faecium_) are important causes of endocarditis, especially in healthcare-associated infections and in older patients, but are not the leading cause of **acute endocarditis with abscess**. [1] - **Enterococcal endocarditis** tends to be more subacute to chronic in presentation and, while serious, does not commonly feature the aggressive **abscess formation** seen with _S. aureus_.

Q: Cyroglobulinemia is associated with:

Hepatitis C. ***Hepatitis C*** - **Cryoglobulinemia** is most strongly associated with chronic **Hepatitis C virus (HCV)** infection [1]. - HCV infection can lead to the formation of **cryoglobulins**, which are immunoglobulins that precipitate in the cold and can cause systemic vasculitis [1]. *Hepatitis A* - **Hepatitis A** is an acute, self-limiting viral infection that is not typically associated with chronic complications like cryoglobulinemia. - It primarily causes **acute hepatitis** and does not lead to chronic carrier states or immune complex diseases. *Hepatitis B* - While **Hepatitis B virus (HBV)** can be associated with immune complex diseases, such as **polyarteritis nodosa (PAN)** and **glomerulonephritis**, it is less commonly linked to cryoglobulinemia than HCV. - HBV-associated immune complex diseases generally involve different pathogenesis and clinical presentations than HCV-associated cryoglobulinemia. *Hepatitis D* - **Hepatitis D virus (HDV)** infection occurs only in individuals already infected with HBV. - While HDV can worsen the progression of HBV-related liver disease, it is not independently associated with cryoglobulinemia.

Q: What is the primary aim of tuberculosis treatment?

Achieving complete bacteriological cure. ***Achieving complete bacteriological cure*** - The primary aim of tuberculosis treatment is to **eliminate all Mycobacterium tuberculosis bacteria** from the patient's body to prevent relapse and further transmission [1]. - This involves a multi-drug regimen administered for a prolonged period to target both actively replicating and dormant bacteria [1]. *Prevention of complications* - While an important aspect of TB management, preventing complications like **pleural effusion** or **meningitis** is a secondary goal that naturally follows effective bacteriological cure [3]. - If the bacteria are not eradicated, **complications can still arise** even if initial symptoms improve. *Prevention of disease spread* - Preventing transmission to others is a crucial public health goal, directly linked to achieving bacteriological cure in the infected individual [1]. - A patient is no longer infectious once **bacteriologically cured**, making this a consequence rather than the primary *aim* of treatment for the individual [1]. *Achieving clinical improvement* - **Symptom resolution** (e.g., fever, cough, weight loss) indicates clinical improvement, but it does not guarantee the eradication of all bacteria. - Patients can feel better with some remaining bacteria, which could lead to **relapse** or **drug resistance** if treatment is stopped prematurely [2].

Q: A 3-year-old child presented with fatigue, malaise, fever, sore throat, headache, nausea, abdominal pain, and myalgia. On examination, generalized lymphadenopathy, hepatosplenomegaly, tonsillar enlargement, palatal petechiae, rashes, and edema of the eyelids were observed. Some unusual cells were seen in the peripheral blood. A specific serological test was performed. What is the receptor involved in the pathogenesis of the disease associated with these symptoms?

CD21. ***CD21*** - The constellation of symptoms (fatigue, fever, sore throat, lymphadenopathy, hepatosplenomegaly, tonsillar enlargement, palatal petechiae, edema of eyelids, and atypical lymphocytes) in a child strongly suggests **infectious mononucleosis**, which is most commonly caused by the **Epstein-Barr Virus (EBV)** [1]. - EBV primarily infects **B lymphocytes** by binding to the **CD21 receptor** (also known as complement receptor type 2, CR2) on the B cell surface. *CD20* - **CD20** is another transmembrane protein found on the surface of B lymphocytes, but it is not the primary receptor used by EBV for entry. - It plays a role in B cell activation and is a target for immunotherapy in some B cell malignancies. *CD19* - **CD19** is a B-cell specific surface marker that is part of a receptor complex involved in B cell activation and growth. - While present on B cells, it is not the direct receptor that EBV uses to enter the cell. *CD117* - **CD117** (c-Kit receptor) is a receptor tyrosine kinase primarily found on hematopoietic stem cells, mast cells, and interstitial cells of Cajal. - It is not expressed on B lymphocytes and is therefore not involved in EBV infection.

Q: The most common site for amoebiasis is:

Caecum. ***Caecum*** - The **caecum** is the most common site for intestinal amoebiasis because it provides an ideal environment for the **trophozoites** of *Entamoeba histolytica* to embed and colonize [1]. - The slower transit time and abundant bacterial flora in the caecum contribute to its susceptibility to **amoebic invasion and ulceration**. *Sigmoid colon* - While the sigmoid colon can be affected by amoebiasis, leading to symptoms like **dysentery**, it is not the initial or most frequent site of colonization [1]. - Involvement of the sigmoid colon typically indicates more widespread or severe intestinal infection. *Transverse colon* - The transverse colon can also be involved in amoebiasis, especially in cases of extensive disease, but it is less commonly the primary site compared to the caecum. - Symptoms related to transverse colon involvement are often diffuse and can include **abdominal pain** and **tenderness**. *Liver* - The **liver** is the most common site for **extraintestinal amoebiasis**, leading to an **amoebic liver abscess** [1]. - However, the question asks for the most common site for amoebiasis in general, implying initial infection, which is typically in the intestine (specifically the caecum).

Q: Loeffler's syndrome occurs in all except:

Giardia. ***Giardia*** - **Giardia lamblia** is an intestinal flagellate that causes **giardiasis**, primarily presenting with gastrointestinal symptoms such as diarrhea, abdominal cramps, and malabsorption [1]. - It does not undergo a **pulmonary migration phase** in its life cycle, which is a prerequisite for causing eosinophilic pneumonitis (Loeffler's syndrome). *Toxocara* - **Toxocara canis** and **Toxocara cati** larvae migrate through the lungs, causing **visceral larva migrans (VLM)** and pulmonary eosinophilia [1]. - This migration can trigger an immune response in the lungs, leading to symptoms consistent with **Loeffler's syndrome**. *Strongyloides* - **Strongyloides stercoralis** larvae migrate through the lungs as part of their life cycle (both in initial infection and in auto-infection), which can cause **eosinophilic pneumonitis** [1]. - This pulmonary migration commonly results in respiratory symptoms and is associated with **Loeffler's syndrome**. *Ascaris* - **Ascaris lumbricoides** larvae undergo essential **pulmonary migration** after ingestion, breaking out of capillaries into the alveoli before being coughed up and swallowed [1]. - This larval migration through the lungs is a classic cause of **Loeffler's syndrome**, characterized by transient pulmonary infiltrates and eosinophilia [1].

Q: According to WHO, what is the recommended treatment for uncomplicated Plasmodium falciparum malaria?

Artemether + lumefantrine. ***Artemether + lumefantrine*** - The **World Health Organization (WHO)** strongly recommends **Artemisinin-based combination therapies (ACTs)** as the first-line treatment for uncomplicated **Plasmodium falciparum malaria** due to their high efficacy and ability to overcome drug resistance. - **Artemether + lumefantrine** is one of the most widely used and effective ACTs, combining a fast-acting artemisinin derivative with a longer-acting partner drug. *Mefloquine* - While effective against some malaria strains and used for prophylaxis, **mefloquine** is not the primary recommended first-line treatment for uncomplicated *P. falciparum* malaria due to potential neuro-psychiatric side effects and existing resistance in some regions. - It is typically reserved for situations where other ACTs are unavailable or contraindicated. *Chloroquine* - **Chloroquine** resistance is widespread globally for *P. falciparum* malaria, making it largely ineffective as a first-line treatment for this species. - It remains effective for uncomplicated *P. vivax, P. ovale*, and *P. malariae* infections in non-resistant areas. *Artemisinin only* - Treating **uncomplicated malaria** with **artemisinin monotherapy** is **strongly discouraged** by the WHO because it promotes the rapid development of drug resistance. - Artemisinin derivatives should always be used in combination with a partner drug to protect their efficacy and prevent resistance.

Q: Mucormycosis of the paranasal sinus is most common in?

Diabetes. Diabetes - **Diabetic ketoacidosis** significantly impairs neutrophil function, reducing the body's ability to resist fungal infections like mucormycosis. [1] - The **hyperglycemic** and **acidotic** environment in uncontrolled diabetes promotes the growth and invasiveness of Mucorales fungi. [1] *Individuals with HIV* - While HIV can lead to **immunocompromise**, mucormycosis is less common in this population than in those with diabetes; other opportunistic infections are more prevalent with HIV. - HIV primarily affects **CD4+ T-lymphocytes**, whereas mucormycosis is more often associated with defects in phagocytic function. *Individuals on immunosuppressive therapy* - **Immunosuppressive therapy**, such as corticosteroids or chemotherapy, can increase the risk of fungal infections, but **uncontrolled diabetes** is the most significant risk factor for rhinocerebral mucormycosis. [1] - The type of immunosuppression and underlying condition are critical; while relevant, it is not as uniquely predisposing as diabetic ketoacidosis. [1] *Patients who have undergone surgery* - Surgical patients, especially those with prolonged hospital stays or extensive wounds, can be susceptible to various infections, but mucormycosis is not specifically or most commonly linked to surgery as an isolated risk factor. - **Nosocomial infections** after surgery are often bacterial; fungal infections, when they occur, are typically associated with profound immunosuppression or specific device-related issues, not surgery alone.

Question 1

Which of the following waterborne diseases is characterized by rice water stools?

Accepted Answer

Cholera

Answer

Giardiasis

Answer

Typhoid fever

Answer

Hepatitis A

Question 2

Most common extra-cutaneous manifestation of varicella is involvement of

Accepted Answer

Lungs

Answer

Kidneys

Answer

CVS

Answer

CNS

Question 3

Acute endocarditis with abscess is most commonly associated with which organism?

Accepted Answer

Staphylococcus aureus

Answer

Listeria

Answer

Streptococcus

Answer

Enterococcus

Question 4

Cyroglobulinemia is associated with:

Accepted Answer

Hepatitis C

Answer

Hepatitis A

Answer

Hepatitis B

Answer

Hepatitis D

Question 5

What is the primary aim of tuberculosis treatment?

Accepted Answer

Achieving complete bacteriological cure

Answer

Prevention of complications

Answer

Prevention of disease spread

Answer

Achieving clinical improvement

Question 6

A 3-year-old child presented with fatigue, malaise, fever, sore throat, headache, nausea, abdominal pain, and myalgia. On examination, generalized lymphadenopathy, hepatosplenomegaly, tonsillar enlargement, palatal petechiae, rashes, and edema of the eyelids were observed. Some unusual cells were seen in the peripheral blood. A specific serological test was performed. What is the receptor involved in the pathogenesis of the disease associated with these symptoms?

Accepted Answer

CD21

Answer

CD20

Answer

CD19

Answer

CD117

Question 7

The most common site for amoebiasis is:

Accepted Answer

Caecum

Answer

Sigmoid colon

Answer

Transverse colon

Answer

Liver

Question 8

Loeffler's syndrome occurs in all except:

Accepted Answer

Giardia

Answer

Toxocara

Answer

Strongyloides

Answer

Ascaris

Question 9

According to WHO, what is the recommended treatment for uncomplicated Plasmodium falciparum malaria?

Accepted Answer

Artemether + lumefantrine

Answer

Mefloquine

Answer

Chloroquine

Answer

Artemisinin only

Question 10

Mucormycosis of the paranasal sinus is most common in?

Accepted Answer

Diabetes

Answer

Individuals with HIV

Answer

Individuals on immunosuppressive therapy

Answer

Patients who have undergone surgery

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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