Infectious Diseases Practice Questions

Q: A man presents with fever and chills 2 weeks after a louse bite. There was a maculo-papular rash on the trunk which spread peripherally. The cause of this infection can be

Epidemic typhus. ***Epidemic typhus*** - This condition is characterized by **fever**, **chills**, and a **maculopapular rash** that spreads centrally to peripherally, often following a **louse bite**. - It is caused by **Rickettsia prowazekii** and transmitted by the human body louse (Pediculus humanus corporis), making it common in crowded, unhygienic conditions. *Scrub typhus* - Scrub typhus is typically transmitted by the bite of **chiggers (larval mites)** and is caused by **Orientia tsutsugamushi**. - A characteristic feature is an **eschar** at the site of the bite, which is not mentioned in the patient's presentation. *Endemic typhus* - Also known as **murine typhus**, this disease is caused by **Rickettsia typhi** and transmitted by the **rat flea**. - While it causes fever and rash, its transmission vector (**flea**) and typical epidemiology (associated with rodents) differ from the louse bite described. *Rickettsial pox* - Rickettsial pox is caused by **Rickettsia akari** and transmitted by the **house mouse mite**. - It presents with an initial **papule** at the bite site that develops into an eschar, followed by fever and a **vesicular rash**, which is different from the maculopapular rash described.

Q: Rickettsialpox is caused by?

Rickettsia akari. ***Rickettsia akari*** - **Rickettsia akari** is the specific etiologic agent responsible for causing **rickettsialpox**. - This Rickettsia species is transmitted to humans by the bite of the **mouse mite**, particularly *Liponyssoides sanguineus*. *Rickettsia conorii* - **Rickettsia conorii** is the pathogen that causes **Mediterranean spotted fever** (also known as boutonneuse fever), which is distinct from rickettsialpox. - It is typically transmitted by ticks, such as *Rhipicephalus sanguineus*. *Rickettsia rickettsii* - This bacterium is the causative agent of **Rocky Mountain spotted fever**, a severe and potentially fatal tick-borne disease. - It is not associated with rickettsialpox, which presents with different clinical features and epidemiology. *Rickettsia typhi* - **Rickettsia typhi** is the cause of **murine (endemic) typhus**, a flea-borne disease primarily associated with rats. - Murine typhus has different clinical manifestations and epidemiology compared to rickettsialpox.

Q: Brain abscess in immunodeficient person is due to :

Toxoplasma gondii. ***Toxoplasma gondii*** - **Toxoplasma gondii** is a very common cause of **brain abscesses** (cerebral toxoplasmosis) in individuals with compromised immune systems, especially those with AIDS. - The parasite is usually latent in many people and reactivates when the immune system weakens. *Aspergillus* - While *Aspergillus* can cause central nervous system infections, including brain abscesses, this is usually seen in severely **neutropenic** or transplant patients. - *Aspergillus* typically invades via **hematogenous spread** from a primary pulmonary infection or directly from sinusitis. *Cryptococcus* - *Cryptococcus neoformans* is a significant cause of **meningitis** in immunocompromised patients, particularly those with HIV/AIDS. - While it can cause **cryptococcomas** (focal lesions), pure abscess formation is less common than with *Toxoplasma*. *Candida* - *Candida* species can cause **brain microabscesses** or multifocal lesions, especially in patients with disseminated candidiasis originating from prolonged hospitalization or indwelling catheters. - However, large, solitary brain abscesses are less typical for *Candida* compared to *Toxoplasma gondii*.

Q: All the diseases caused by transfusion EXCEPT:

Plague. ***Plague*** - Plague is caused by the bacterium **Yersinia pestis** and is primarily transmitted through the bite of infected fleas or direct contact with infected animals, not via blood transfusion. - While extremely rare, it is **not a recognized transfusion-transmitted infection (TTI)** due to its epidemiology and the standard screening processes for blood products. *Hepatitis-C* - **Hepatitis C virus (HCV)** is a well-established transfusion-transmitted infection, as the virus can persist in donated blood and cause infection in recipients. - Prior to routine screening, **post-transfusion hepatitis** was a significant concern, with HCV being a major culprit. *HIV* - **Human Immunodeficiency Virus (HIV)** is highly transmissible through infected blood products and was a major concern for transfusions before robust screening methods were implemented. - All donated blood is now rigorously tested for **HIV antibodies and antigens** to prevent transmission. *Hepatitis-B* - **Hepatitis B virus (HBV)** is another well-known transfusion-transmitted infection, capable of causing acute and chronic liver disease in recipients. - Extensive **screening for HBV surface antigen (HBsAg)** and other markers is conducted on all donated blood to minimize transmission risk.

Q: Wells' disease is caused by?

Leptospira. ***Leptospira*** - **Wells' disease**, also known as severe leptospirosis, is caused by infection with bacteria belonging to the genus **Leptospira**. - This zoonotic disease is transmitted through contact with infected animal urine or contaminated water and can cause a wide range of symptoms, from mild flu-like illness to severe organ damage. *Mycoplasma* - **Mycoplasma** are bacteria known to cause various infections such as atypical pneumonia, urinary tract infections, and genital infections. - They are not associated with Wells' disease or leptospirosis. *Legionella* - **Legionella** is a bacterium notorious for causing **Legionnaires' disease**, a severe form of pneumonia, and Pontiac fever. - These infections are typically acquired through inhalation of contaminated aerosols from water systems, not from animal urine or contaminated water in the context of Wells' disease. *Listeria* - **Listeria monocytogenes** is a bacterium that causes **listeriosis**, a serious infection typically contracted from contaminated food. - It primarily affects pregnant women, newborns, older adults, and immunocompromised individuals, and is not responsible for Wells' disease.

Q: Which of the following is not transmitted transplacentally –

Mumps. ***Mumps*** - **Mumps virus** is NOT considered a clinically significant cause of congenital infection via transplacental transmission. - While the virus may theoretically cross the placenta in rare cases, mumps is **not part of the TORCH infections** and does not cause the characteristic pattern of congenital abnormalities seen with other transplacental infections. - Maternal mumps during pregnancy is associated with an increased risk of **first-trimester abortion**, but not with a recognizable congenital syndrome. *Toxoplasma* - **Toxoplasma gondii** readily crosses the placenta, causing **congenital toxoplasmosis** (part of TORCH). - This results in the classic triad: **chorioretinitis, hydrocephalus, and intracranial calcifications**. - Risk and severity depend on the trimester of infection. *Rubella* - **Rubella virus** crosses the placenta, causing **congenital rubella syndrome (CRS)** (part of TORCH). - Classic manifestations include **cataracts, congenital heart disease (PDA), and sensorineural deafness**. - Maximum risk occurs with infection in the **first trimester**. *Syphilis* - **Treponema pallidum** crosses the placenta, causing **congenital syphilis** (part of TORCH - "Other"). - Manifestations include **stillbirth, hydrops fetalis, hepatosplenomegaly, rash, and bone abnormalities** (saddle nose, saber shins). - Can be prevented with **adequate maternal treatment before 16-18 weeks**.

Q: Septic shock is primarily due to

Lipopolysaccharide. ***Lipopolysaccharide*** - **Lipopolysaccharide (LPS)**, an endotoxin found in the outer membrane of **Gram-negative bacteria**, is the primary mediator of **septic shock**. - LPS binding to immune cells triggers a massive release of **pro-inflammatory cytokines**, leading to systemic inflammation, vasodilation, and organ dysfunction characteristic of septic shock. *Protein* - While some bacterial proteins can be **virulence factors**, they are not the primary cause of overwhelming systemic inflammation seen in **septic shock**. - Proteins are the building blocks of all cells and have diverse functions, but they don't exclusively trigger the septic shock cascade in the same way as LPS. *Peptidoglycan* - **Peptidoglycan** is a major component of the bacterial cell wall found in both **Gram-positive** and **Gram-negative bacteria**. - It can stimulate an immune response, but its role in triggering the full cascade of **septic shock** is less pronounced and less direct compared to LPS from Gram-negative bacteria. *Teichoic acid* - **Teichoic acids** are cell wall components specific to **Gram-positive bacteria**. - They can elicit an inflammatory response, but they are generally less potent in inducing the severe, life-threatening systemic effects associated with **septic shock** compared to LPS.

Q: Genital ulcers are seen in all except:

H. aegyptius. ***H. aegyptius*** - *Haemophilus aegyptius* is primarily known to cause **conjunctivitis (pinkeye)**, especially in children, and **Brazilian purpuric fever**, which is a severe systemic illness. - It does **not typically cause genital ulcers**, differentiating it from other listed pathogens. *H. ducreyi* - *Haemophilus ducreyi* is the causative agent of **chancroid**, which typically presents as painful **genital ulcers** with soft, friable bases. - These ulcers are often accompanied by **inguinal lymphadenopathy (buboes)**. *HSV* - **Herpes Simplex Virus (HSV)**, particularly HSV-2, is a common cause of **genital herpes**, characterized by painful, vesicular eruptions that progress to **ulcers** on the genitals. - These lesions often recur and are associated with **neuropathic pain and tenderness**. *Chlamydia* - While *Chlamydia trachomatis* is known for causing **genital infections** like urethritis and cervicitis, specific serovars (L1, L2, L3) are responsible for **lymphogranuloma venereum (LGV)**. - LGV typically begins with a **transient, often unnoticed, small genital ulcer** or papule, followed by marked **inguinal lymphadenopathy** and systemic symptoms.

Q: Which of the following doesn't cause urethritis in males?

H. Ducreyi. ***H. Ducreyi*** - *Haemophilus ducreyi* is the causative agent of **chancroid**, a sexually transmitted infection characterized by painful **genital ulcers** and **lymphadenopathy**. - It does not primarily cause **urethritis**, which is inflammation of the urethra. *Trichomonas vaginalis* - **Trichomonas vaginalis** is a protozoan parasite that commonly causes **trichomoniasis**, a sexually transmitted infection. - In males, it can lead to **urethritis** with symptoms such as dysuria and urethral discharge. *Chlamydia trachomatis* - **Chlamydia trachomatis** is a very common bacterial cause of **urethritis** in males, often presenting with a **mucopurulent discharge** and dysuria. - It is frequently asymptomatic, making it a significant cause of undiagnosed sexually transmitted infections. *N. gonorrhoeae* - **Neisseria gonorrhoeae** is the bacterium responsible for **gonorrhea**, a well-known cause of **purulent urethritis** in males. - Symptoms typically include a profuse, **purulent urethral discharge** and painful urination.

Q: Which microorganism causes pseudomembranous colitis?

C. difficile. ***C. difficile*** - **Clostridioides difficile** (formerly Clostridium difficile) infection is the most common cause of **pseudomembranous colitis**, characterized by inflammation of the colon and formation of pseudomembranes. - This infection often occurs after **antibiotic use**, which disrupts the normal gut flora, allowing C. difficile to proliferate and produce toxins. *Shigella* - **Shigella** species cause **shigellosis**, a type of dysentery characterized by bloody diarrhea, fever, and abdominal cramps. - While it can cause severe colitis, it typically does not lead to the distinct pseudomembranous lesions seen in C. difficile infection. *E. coli* - Various strains of **Escherichia coli** can cause different gastrointestinal illnesses, such as traveler's diarrhea (enterotoxigenic E. coli) or hemorrhagic colitis (enterohemorrhagic E. coli O157:H7). - However, E. coli is not the causative agent of **pseudomembranous colitis**. *Salmonella* - **Salmonella** species cause salmonellosis, which can manifest as **gastroenteritis** (food poisoning) or **typhoid fever**. - While it causes enterocolitis, it does not typically result in the formation of **pseudomembranes** that characterize C. difficile infection.

Question 1

A man presents with fever and chills 2 weeks after a louse bite. There was a maculo-papular rash on the trunk which spread peripherally. The cause of this infection can be

Accepted Answer

Epidemic typhus

Answer

Scrub typhus

Answer

Endemic typhus

Answer

Rickettsial pox

Question 2

Rickettsialpox is caused by?

Accepted Answer

Rickettsia akari

Answer

Rickettsia conorii

Answer

Rickettsia rickettsii

Answer

Rickettsia typhi

Question 3

Brain abscess in immunodeficient person is due to :

Accepted Answer

Toxoplasma gondii

Answer

Aspergillus

Answer

Cryptococcus

Answer

Candida

Question 4

All the diseases caused by transfusion EXCEPT:

Accepted Answer

Plague

Answer

Hepatitis-C

Answer

HIV

Answer

Hepatitis-B

Question 5

Wells' disease is caused by?

Accepted Answer

Leptospira

Answer

Mycoplasma

Answer

Legionella

Answer

Listeria

Question 6

Which of the following is not transmitted transplacentally –

Accepted Answer

Mumps

Answer

Toxoplasma

Answer

Rubella

Answer

Syphilis

Question 7

Septic shock is primarily due to

Accepted Answer

Lipopolysaccharide

Answer

Protein

Answer

Peptidoglycan

Answer

Teichoic acid

Question 8

Genital ulcers are seen in all except:

Accepted Answer

H. aegyptius

Answer

H. ducreyi

Answer

HSV

Answer

Chlamydia

Question 9

Which of the following doesn't cause urethritis in males?

Accepted Answer

H. Ducreyi

Answer

Trichomonas vaginalis

Answer

Chlamydia trachomatis

Answer

N. gonorrhoeae

Question 10

Which microorganism causes pseudomembranous colitis?

Accepted Answer

C. difficile

Answer

Shigella

Answer

E. coli

Answer

Salmonella

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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