Infectious Diseases Practice Questions

Q: Which of the following statements about Legionella is most accurate?

Aerosol inhalation is a common mode of transmission.. ***Aerosol inhalation is a common mode of transmission.*** - **Legionella pneumophila** is primarily transmitted through **inhalation of aerosolized water droplets** containing the bacteria - Common sources include **cooling towers, air conditioning systems, hot tubs, showerheads**, and decorative fountains - This is the **most defining and clinically important characteristic** of Legionella transmission - Understanding aerosol transmission is crucial for **outbreak control and prevention strategies** *There is no human-to-human transmission.* - This statement is **medically accurate** - Legionella does NOT spread from person to person - However, this is a secondary characteristic compared to the primary transmission mode - The question asks for the **most accurate** statement, making aerosol transmission more definitive *Prolonged carriers are common.* - This is **INCORRECT** - Legionella does NOT cause a chronic carrier state in humans - The bacteria **colonizes environmental water systems and amoebae** (like *Acanthamoeba* and *Naegleria*), not human hosts - Humans are accidental hosts through aerosol exposure *All of the options are true* - This is **INCORRECT** because "Prolonged carriers are common" is false - Only two of the three substantive statements are true

Q: Brill-Zinsser disease is a recrudescent form of which infection?

Recrudescence of R prowazekii infection. **Recrudescence of R prowazekii infection** - Brill-Zinsser disease is a **late-onset complication** of **epidemic typhus**, caused by *Rickettsia prowazekii*. - It occurs years after the initial infection, due to **reactivation of dormant bacteria** in the body. *Recrudescence of R typhi infection* - *Rickettsia typhi* causes **murine typhus**, but its recrudescent form is not referred to as Brill-Zinsser disease. - Murine typhus is typically a **milder disease** compared to epidemic typhus. *Recrudescence of Coxiella burnetii infection* - *Coxiella burnetii* causes **Q fever**, which can have a chronic form but is not a recrudescence of a typhus infection. - Q fever presents with different clinical manifestations, such as **endocarditis** or **hepatitis**, not typically a rash or neurological symptoms seen in typhus. *None of the options* - This option is incorrect because the specific recrudescent form described in the question clearly points to *Rickettsia prowazekii*.

Q: Patient came from Nagaland and shows positive test with OXK antigen. Diagnosis is?

Scrub typhus. ***Scrub typhus*** - A **positive Weil-Felix test** for the **OXK antigen** is highly suggestive of scrub typhus, particularly if the patient is from an endemic region like Nagaland. - Scrub typhus is caused by **_Orientia tsutsugamushi_**, transmitted by **chiggers** (larval mites), often presenting with fever and an **eschar**. *Trench fever* - Caused by **_Bartonella quintana_** and transmitted by the **human body louse**. - It does not typically show a positive Weil-Felix test for the OXK antigen. *Endemic typhus* - Also known as **murine typhus**, it is caused by **_Rickettsia typhi_** and transmitted by **fleas** (e.g., rat flea). - While it causes a positive Weil-Felix test, it usually involves the **OX19 antigen**, not OXK. *Epidemic typhus* - Caused by **_Rickettsia prowazekii_** and transmitted by the **human body louse**. - It yields a positive Weil-Felix test for the **OX19 and OX2 antigens**, but typically not for OXK.

Q: An 18-year-old girl in an endemic area presents with acute watery diarrhea. Considering the common infectious agents, what is the most likely causative agent?

V. cholerae. ***V. cholerae*** - **Cholera** presents with **acute watery diarrhea**, often described as "rice water stools," which can lead to rapid dehydration. - The patient resides in an **endemic area**, significantly increasing the likelihood of *Vibrio cholerae* infection. *Rotavirus* - While *Rotavirus* causes acute watery diarrhea, it is more common in **infants and young children** (under 5 years old), making it less likely in an 18-year-old. - *Rotavirus* infections are typically seasonal in temperate climates and less tied to endemic area status in adults. *Salmonella* - *Salmonella* infections typically present with **bloody-mucoid diarrhea** (dysentery), fever, and abdominal cramps, rather than purely watery diarrhea. - While *Salmonella* can cause watery diarrhea, the classic presentation often involves more systemic symptoms and an inflammatory response. *Shigella* - *Shigella* infections also typically cause **dysentery**, characterized by **bloody diarrhea**, fever, and tenesmus, due to invasion of the intestinal mucosa. - The absence of blood in the stool and the description of "acute watery diarrhea" make *Shigella* less probable than *V. cholerae*.

Q: The most common causative organism for traveler's diarrhea is which of the following?

E. coli. ***Correct: E. coli*** - **Enterotoxigenic Escherichia coli (ETEC)** is the most frequent cause of **traveler's diarrhea** worldwide, accounting for **30-40% of cases**. - It produces heat-labile (LT) and heat-stable (ST) enterotoxins that lead to **watery diarrhea** without significant fever or bloody stools. - Particularly common in travelers to **developing countries** in Latin America, Africa, and South Asia. *Incorrect: Shigella* - While it can cause severe diarrheal illness (dysentery) characterized by **bloody stools**, it accounts for only **5-10% of traveler's diarrhea cases**. - **Shigella infection** is more often associated with person-to-person spread and outbreaks in crowded settings. *Incorrect: Norwalk virus* - Also known as **Norovirus**, it is a very common cause of **gastroenteritis** globally, affecting people of all ages. - However, it is primarily responsible for widespread outbreaks, often in cruise ships or institutions, rather than being the predominant cause of individual traveler's diarrhea cases. *Incorrect: Rotavirus* - This virus is a major cause of **severe dehydrating diarrhea** in **infants and young children** worldwide. - While it can affect travelers, it is less common in adults and generally not considered the predominant cause of traveler's diarrhea in the general traveling population.

Q: Prusiner was awarded the Nobel Prize in 1997 for his work in:

Prion proteins. ***Prion proteins*** - Dr. Stanley B. Prusiner received the Nobel Prize in Physiology or Medicine in 1997 for his discovery of **prions**—infectious protein particles responsible for transmissible spongiform encephalopathies. - His work revolutionized our understanding of how certain diseases can be transmitted by **misfolded proteins** without genetic material. *Gene therapy techniques* - Gene therapy involves introducing genetic material into cells to treat diseases and was developed through the work of multiple scientists over several decades. - While a significant advancement, this was not the specific area for which Prusiner was awarded the Nobel Prize. *Neurodegenerative disorders* - While prions cause **neurodegenerative disorders** (e.g., Creutzfeldt-Jakob disease), Prusiner's groundbreaking work was specifically on the nature of the infectious agent itself (prions), not the general category of neurodegenerative disorders. - Many scientists contribute to understanding neurodegenerative diseases, but Prusiner's unique contribution was identifying a novel infectious mechanism. *Insulin production methods* - Insulin was first isolated and identified by Banting and Macleod in the early 20th century, leading to a Nobel Prize in 1923. - Modern methods for insulin production, including recombinant DNA technology, were developed by other researchers and companies at different times.

Q: Among the following E. coli variants, which is most commonly associated with persistent diarrhea in adults?

Enteroaggregative Escherichia coli (EAEC). ***Enteroaggregative Escherichia coli (EAEC)*** - EAEC is characterized by its distinctive **aggregative adherence** to intestinal cells, leading to chronic inflammation and persistent diarrhea, particularly in adults and immunocompromised individuals. - It produces **enteroaggregative heat-stable toxin (EAST1)** and **pet-like cytotoxins** that contribute to fluid secretion and mucosal damage. *Enteropathogenic Escherichia coli (EPEC)* - EPEC is a major cause of **infant diarrhea**, especially in developing countries, but is generally not associated with persistent diarrhea in adults. - It forms characteristic **attaching and effacing (A/E) lesions** on intestinal epithelial cells, destroying microvilli and impairing absorption. *Enterotoxigenic Escherichia coli (ETEC)* - ETEC is the most common cause of **traveler's diarrhea** and primarily causes acute, watery diarrhea due to the production of **heat-labile (LT)** and/or **heat-stable (ST) toxins**. - While it can cause significant dehydrating diarrhea, it is typically self-limiting and rarely leads to persistent symptoms in adults. *Enteroinvasive Escherichia coli (EIEC)* - EIEC causes a disease similar to **shigellosis**, characterized by **fever, cramps, and dysentery** (bloody, mucoid stools), by invading and destroying intestinal epithelial cells. - It is not commonly associated with persistent diarrhea but rather with an acute, inflammatory colonic infection.

Q: Which organism does not require a vector for transmission?

Coxiella burnetii. ***Coxiella burnetii*** - This organism causes **Q fever** and does not require an arthropod vector; it is primarily transmitted via **aerosols** from infected animals. - Humans usually acquire the infection by inhaling **contaminated aerosols** from infected livestock (cattle, sheep, goats). *Rickettsia prowazekii* - This bacterium is the causative agent of **epidemic typhus** and is transmitted by the **human body louse** (*Pediculus humanus corporis*). - The louse acts as a **biological vector**, acquiring the organism from an infected human and transmitting it through its feces, which are then scratched into the skin. *Rickettsia rickettsii* - This organism causes **Rocky Mountain Spotted Fever (RMSF)** and is transmitted by **ticks**, primarily the American dog tick (*Dermacentor variabilis*) and the Rocky Mountain wood tick (*Dermacentor andersoni*). - Ticks serve as both **vectors** and **reservoirs** for *Rickettsia rickettsii*. *Borrelia recurrentis* - This spirochete causes **louse-borne relapsing fever** and is transmitted by the **human body louse** (*Pediculus humanus corporis*). - Transmission occurs when the louse is crushed and its hemolymph, containing the bacteria, comes into contact with broken skin or mucous membranes.

Q: Which of the following viruses is not spread by the fecal-oral route?

Hepatitis B virus (HBV). ***Hepatitis B virus (HBV)*** - HBV is primarily transmitted through **percutaneous** or **mucosal exposure** to infectious blood or body fluids, such as during sex, sharing needles, or from mother to child. - It is not typically spread via the **fecal-oral route**. *Hepatitis E virus (HEV)* - HEV is a common cause of **acute viral hepatitis** and is predominantly transmitted through the **fecal-oral route**, often via contaminated drinking water. - High viral loads are shed in the feces of infected individuals, leading to environmental contamination. *Rotavirus* - Rotavirus is a major cause of **severe diarrheal disease** in infants and young children, and its transmission occurs almost exclusively through the **fecal-oral route**. - The virus is highly stable in the environment and can spread rapidly in settings with poor hygiene. *Norwalk virus (Norovirus)* - Norovirus is a highly contagious virus that causes **gastroenteritis** and is notorious for outbreaks in crowded settings; its primary mode of transmission is the **fecal-oral route**. - It can also spread through contaminated food and water, or direct contact with infected individuals.

Q: Which of the following conditions is most commonly classified as a sexually transmitted disease?

Chlamydia. ***Chlamydia*** - **Chlamydia trachomatis** is a bacterial infection that is exclusively transmitted through **sexual contact**, making it a classic sexually transmitted disease. - It often presents with **asymptomatic infections** but can lead to serious complications if untreated, such as pelvic inflammatory disease (PID) and infertility. *Trichomoniasis* - Caused by the **protozoan Trichomonas vaginalis**, it is also a sexually transmitted infection. - While sexually transmitted, **Chlamydia** is generally more prevalent and often considered the *most commonly* classified or reported bacterial STD. *Giardiasis* - Caused by the parasite **Giardia lamblia**, it is typically acquired through the ingestion of contaminated water or food. - It is primarily an **enteric infection** and not classified as a sexually transmitted disease, although anal-oral contact can be a route of transmission in some cases. *Amoebiasis* - Caused by the parasite **Entamoeba histolytica**, it is spread through the fecal-oral route, usually via contaminated food or water. - **Amoebiasis** is an infection of the intestines and liver, and it is not considered a sexually transmitted disease.

Question 1

Which of the following statements about Legionella is most accurate?

Accepted Answer

Aerosol inhalation is a common mode of transmission.

Answer

Prolonged carriers are common.

Answer

There is no human-to-human transmission.

Answer

All of the options are true

Question 2

Brill-Zinsser disease is a recrudescent form of which infection?

Accepted Answer

Recrudescence of R prowazekii infection

Answer

Recrudescence of R typhi infection

Answer

None of the options

Answer

Recrudescence of Coxiella burnetii infection

Question 3

Patient came from Nagaland and shows positive test with OXK antigen. Diagnosis is?

Accepted Answer

Scrub typhus

Answer

Trench fever

Answer

Endemic typhus

Answer

Epidemic typhus

Question 4

An 18-year-old girl in an endemic area presents with acute watery diarrhea. Considering the common infectious agents, what is the most likely causative agent?

Accepted Answer

V. cholerae

Answer

Rotavirus

Answer

Salmonella

Answer

Shigella

Question 5

The most common causative organism for traveler's diarrhea is which of the following?

Accepted Answer

E. coli

Answer

Shigella

Answer

Norwalk virus

Answer

Rotavirus

Question 6

Prusiner was awarded the Nobel Prize in 1997 for his work in:

Accepted Answer

Prion proteins

Answer

Gene therapy techniques

Answer

Neurodegenerative disorders

Answer

Insulin production methods

Question 7

Among the following E. coli variants, which is most commonly associated with persistent diarrhea in adults?

Accepted Answer

Enteroaggregative Escherichia coli (EAEC)

Answer

Enteropathogenic Escherichia coli (EPEC)

Answer

Enterotoxigenic Escherichia coli (ETEC)

Answer

Enteroinvasive Escherichia coli (EIEC)

Question 8

Which organism does not require a vector for transmission?

Accepted Answer

Coxiella burnetii

Answer

Rickettsia rickettsii

Answer

Borrelia recurrentis

Answer

Rickettsia prowazekii

Question 9

Which of the following viruses is not spread by the fecal-oral route?

Accepted Answer

Hepatitis B virus (HBV)

Answer

Rotavirus

Answer

Hepatitis E virus (HEV)

Answer

Norwalk virus (Norovirus)

Question 10

Which of the following conditions is most commonly classified as a sexually transmitted disease?

Accepted Answer

Chlamydia

Answer

Trichomoniasis

Answer

Giardiasis

Answer

Amoebiasis

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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