Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 81: Donovanosis is caused by

A. H. ducreyi
B. Calymmatobacter granulomatis (Correct Answer)
C. Chlamydia trachomatis
D. Treponema pallidum

Explanation: ***Calymmatobacter granulomatis*** - **Donovanosis**, also known as granuloma inguinale, is a sexually transmitted infection primarily caused by the bacterium ***Calymmatobacterium granulomatis*** (now reclassified as *Klebsiella granulomatis*). - The disease is characterized by chronic, progressive ulcerative lesions of the **genitalia** and **perianal area**. *H. ducreyi* - ***Haemophilus ducreyi*** is the causative agent of **chancroid**, another sexually transmitted infection. - Chancroid typically presents as painful **genital ulcers** with associated **inguinal lymphadenopathy** (buboes). *Chlamydia trachomatis* - ***Chlamydia trachomatis*** is a common cause of several sexually transmitted infections, including **chlamydia**, **lymphogranuloma venereum (LGV)**, and **trachoma**. - Its clinical manifestations can range from **urethritis** and **cervicitis** to more severe systemic disease like LGV with invasive lymphadenopathy. *Treponema pallidum* - ***Treponema pallidum*** subspecies *pallidum* is the bacterium responsible for **syphilis**. - Syphilis progresses through distinct stages: **primary (chancre)**, secondary (rash, mucocutaneous lesions), and tertiary (neurosyphilis, cardiovascular syphilis, gummas).

Question 82: Which of the following is NOT transmitted sexually?

A. Gonorrhoea
B. T. pertenue (Correct Answer)
C. Syphilis
D. Candida

Explanation: ***T. pertenue*** - *T. pertenue* causes **yaws**, a chronic infection primarily affecting the skin, bones, and joints. - Yaws is transmitted through **direct skin-to-skin contact** with infectious lesions (non-sexual contact), making it distinctly **not a sexually transmitted infection**. - It is endemic in tropical regions and primarily affects children. *Gonorrhoea* - **Gonorrhoea** is a common **sexually transmitted infection (STI)** caused by the bacterium *Neisseria gonorrhoeae*. - It primarily affects the genitals, rectum, and throat, and is transmitted through **sexual contact**. *Syphilis* - **Syphilis** is a sexually transmitted infection caused by the bacterium *Treponema pallidum subspecies pallidum*. - It is transmitted through **direct contact with a syphilitic sore** (chancre) during sexual activity. *Candida* - While **vulvovaginal candidiasis** is often due to overgrowth of normal flora (influenced by hormonal changes, antibiotic use, or immunosuppression), *Candida* species **can be transmitted through sexual contact**. - Candida is recognized as a **sexually transmissible infection**, though it has multiple modes of transmission beyond sexual activity.

Question 83: Which disease is transmitted by all components of blood?

A. Malaria (Correct Answer)
B. Syphilis
C. Toxoplasma
D. Hepatitis B

Explanation: ***Malaria*** - **Malaria** is caused by *Plasmodium* parasites and is uniquely transmissible through **all blood components** including whole blood, packed RBCs, platelets, fresh frozen plasma, and cryoprecipitate - The parasites exist within **red blood cells** during the blood stage and can also be present as **free merozoites** in plasma during rupture of RBCs - **Critical for blood bank safety**: Even small volumes of any blood component from an infected donor can transmit malaria - Blood donations require extensive screening for malaria in endemic areas and from donors with travel history *Hepatitis B* - **Hepatitis B virus (HBV)** is highly transmissible through blood and present in plasma, but modern blood banking practice includes **universal HBsAg screening** which has virtually eliminated transmission - While technically present in multiple components, the question emphasizes diseases where **all components** pose equal transmission risk without modern screening *Syphilis* - **Syphilis** caused by *Treponema pallidum* can be transmitted via blood transfusion, but the organism is **fragile** and does not survive beyond 72-96 hours in refrigerated blood - Transmission risk is significantly reduced by standard blood storage conditions and routine serological screening - Not efficiently transmitted through all stored blood components *Toxoplasma* - **Toxoplasma gondii** transmission occurs primarily through **leukocyte-containing products** (whole blood, platelet concentrates) - Transmission via **cell-free plasma** or washed RBCs is uncommon - Does not have the same broad transmission profile across all blood components as malaria

Question 84: An infection becomes apparent only after a certain incubation period. Shortest incubation period is seen in:

A. Rubella
B. Hepatitis B
C. Influenza (Correct Answer)
D. Hepatitis A

Explanation: ***Correct Option: Influenza*** - The incubation period for influenza is typically **1 to 4 days**, with an average of 2 days, making it one of the shortest among common infectious diseases. - This **short incubation** contributes to its rapid spread during outbreaks. *Incorrect Option: Rubella* - The incubation period for rubella is significantly longer, typically ranging from **14 to 21 days**. - This longer period means symptoms appear much later after exposure compared to influenza. *Incorrect Option: Hepatitis B* - Hepatitis B has a very long incubation period, usually ranging from **60 to 150 days**, with an average of 90 days. - The prolonged asymptomatic phase allows for potential unaware transmission. *Incorrect Option: Hepatitis A* - The incubation period for Hepatitis A is also relatively long, ranging from **15 to 50 days**, with an average of 28 days. - This allows for viral shedding and potential transmission before symptoms become apparent.

Question 85: Traveller’s diarrhoea is most commonly caused by

A. Salmonella
B. EPEC
C. S. dysenteriae
D. ETEC (Correct Answer)

Explanation: ***ETEC*** - **Enterotoxigenic Escherichia coli (ETEC)** is the most frequent cause of traveler's diarrhoea worldwide. - It produces toxins that cause **fluid secretion** in the intestine, leading to watery diarrhoea. *Salmonella* - While a common cause of food poisoning, **Salmonella** typically presents with more severe symptoms like fever, abdominal cramps, and sometimes bloody stool, and is not the most common cause of traveler's diarrhoea. - Salmonella infections are often associated with consumption of contaminated poultry, eggs, or dairy products. *EPEC* - **Enteropathogenic Escherichia coli (EPEC)** causes diarrhoea primarily in infants and young children, leading to destruction of intestinal microvilli. - It is not a common cause of traveler's diarrhoea in adults. *S. dysenteriae* - **Shigella dysenteriae** is known for causing bacillary dysentery, characterized by severe, often bloody diarrhoea, high fever, and abdominal cramps. - While it can cause severe illness, it is not the most common cause of the more general traveller's diarrhoea.

Question 86: The difference between contamination and infection is that in infection

A. Infectious agent is on body surface (arthropods)
B. Infectious agent is on body surface or on non-human objects
C. Infectious agent is on clothes
D. Infectious agent is in the body of human (Correct Answer)

Explanation: ***Infectious agent is in the body of human*** - **Infection** implies that microorganisms have successfully **invaded the host tissues** and are replicating within the body, potentially causing a host response or disease. - The presence of the pathogen *inside* the body, beyond just surface adherence, is the defining characteristic of infection. *Arthropods on the body surface* - This describes an **infestation** (e.g., lice, mites), where the arthropods are physically present on the body surface but may not have *invaded* tissues in the same way bacteria or viruses do during an infection. - While some arthropods can transmit infectious agents, their mere presence on the surface is not synonymous with an internal infection. *Infectious agent is on body surface or on non-human objects* - This scenario describes **contamination**, where microorganisms are present on surfaces (either human skin or inanimate objects) but have not yet penetrated or established themselves within host tissues. - Contamination is a potential precursor to infection but is not an infection itself. *Infectious agents on clothes* - This is a clear example of **fomite contamination**, where infectious agents are present on inanimate objects like clothing. - The microorganisms are external to the body and are not causing an infection in the person wearing the clothes unless they are transferred and subsequently invade the host.

Question 87: A college student is surprised one morning by painful urination and a cream-colored exudate. Any person who acquires the gram-negative microbe that causes this infection is most likely to have acquired it via which of the following?

A. Nasal tract
B. Genitourinary tract (Correct Answer)
C. GI tract
D. Respiratory tract

Explanation: ***Genitourinary tract*** - The symptoms of **painful urination (dysuria)** and a **cream-colored purulent exudate** are pathognomonic for **urethral gonorrhea**, caused by *Neisseria gonorrhoeae*, a gram-negative diplococcus. - *Neisseria gonorrhoeae* is **exclusively acquired through direct sexual contact** (vaginal, anal, or oral) with an infected individual, making the **genitourinary tract the primary route of acquisition and site of infection**. - The organism has a predilection for **columnar epithelium** of the urethra, endocervix, rectum, pharynx, and conjunctiva. *Nasal tract* - The nasal tract is **not a route of acquisition** for *N. gonorrhoeae*. - Pathogens acquired via the nasal route include **respiratory viruses** (influenza, rhinovirus) and some causes of bacterial meningitis (e.g., *N. meningitidis*), which present with **respiratory or CNS symptoms**, not genitourinary symptoms. *GI tract* - The gastrointestinal tract is the entry point for **foodborne and waterborne pathogens** causing gastroenteritis (e.g., *Salmonella*, *Shigella*, *E. coli*). - While pharyngeal gonorrhea can occur from oral sexual contact, the **GI tract is not the primary acquisition route** for the urethral infection described, and gonorrhea does not cause primary GI symptoms. *Respiratory tract* - The respiratory tract is the acquisition route for infections like **tuberculosis** (*Mycobacterium tuberculosis*), **pneumonia** (*Streptococcus pneumoniae*), and **influenza**. - These infections present with **cough, dyspnea, fever, and respiratory distress**, not the genitourinary symptoms described in this case.

Question 88: Traveller's diarrhoea is caused by:

A. E. histolytica
B. E. coli (Correct Answer)
C. Giardia lamblia
D. Shigella

Explanation: ***E. coli*** - **Enterotoxigenic E. coli (ETEC)** is the most common cause of **traveler's diarrhea**, producing toxins that lead to watery stools. - The disease is typically acquired through ingestion of **contaminated food or water**, particularly in regions with poor sanitation. *E. histolytica* - This parasite causes **amoebiasis**, which can lead to **dysentery** (bloody diarrhea) or liver abscesses. - While it can cause diarrhea in travelers, it is not the most frequent pathogen associated with typical traveler's diarrhea. *Giardia lamblia* - **Giardiasis** typically results in **chronic, greasy, foul-smelling stools**, bloating, and malabsorption rather than acute watery diarrhea. - It's a common cause of **protracted diarrhea** in travelers but not the most frequent cause of acute onset. *Shigella* - This bacterium causes **shigellosis**, characterized by **dysentery (bloody, mucoid stools)**, fever, and abdominal cramps. - While a cause of bacterial diarrhea in travelers, it is less common than ETEC and presents with a more severe, invasive illness.

Question 89: NOT a cause of bacterial community acquired pneumonia:

A. Streptococcus pneumoniae
B. Mycoplasma pneumoniae
C. Blastomyces (Correct Answer)
D. Moraxella catarrhalis

Explanation: ***Blastomyces*** - *Blastomyces*, a **dimorphic fungus**, causes **blastomycosis**, which is a **fungal infection**, not a bacterial infection. - While it can cause community-acquired pneumonia with pulmonary symptoms, it is **NOT a bacterial pathogen** and therefore not a cause of **bacterial community-acquired pneumonia**. - The question asks specifically about bacterial causes, making this the correct answer. *Streptococcus pneumoniae* - **_Streptococcus pneumoniae_** is the **most common bacterial cause** of **community-acquired pneumonia (CAP)**. - Infection typically presents with **acute onset** of fever, chills, productive cough, and lobar consolidation on chest X-ray. *Mycoplasma pneumoniae* - **_Mycoplasma pneumoniae_** is a common cause of **atypical bacterial community-acquired pneumonia**, often referred to as "**walking pneumonia**". - It typically causes milder symptoms, including a **persistent dry cough** and malaise, and is prevalent in younger adults and children. *Moraxella catarrhalis* - **_Moraxella catarrhalis_** is a **bacterial pathogen** that causes **community-acquired pneumonia**, especially in patients with **chronic obstructive pulmonary disease (COPD)**. - It can also cause **bronchitis**, otitis media, and sinusitis.

Question 90: Chronic carrier state is seen in all except

A. Gonorrhea
B. Diphtheria
C. Typhoid
D. Measles (Correct Answer)

Explanation: ***Measles*** - Measles virus typically causes an **acute, self-limiting infection** and does not establish a chronic carrier state. - After infection, individuals develop **lifelong immunity**, and the virus is cleared from the body. *Gonorrhea* - **Asymptomatic carriers** of *Neisseria gonorrhoeae* are common, particularly in women, who can shed the bacteria for months or even years. - This carrier state can lead to continued transmission and spread of the infection without the individual being aware. *Diphtheria* - Some individuals who recover from diphtheria, or who are exposed to *Corynebacterium diphtheriae* but do not develop active disease, can become **asymptomatic carriers**. - These carriers harbor the bacteria in their **nasopharynx** and can transmit it to susceptible individuals. *Typhoid* - A significant percentage of individuals who recover from typhoid fever, especially those with gallstones, can become **chronic carriers** of *Salmonella Typhi*. - These carriers continuously shed the bacteria in their feces, acting as a major silent reservoir for the transmission of the disease.

Practice by Chapter

Respiratory Tract Infections

Practice Questions

Urinary Tract Infections

Practice Questions

Gastrointestinal Infections

Practice Questions

Skin and Soft Tissue Infections

Practice Questions

Central Nervous System Infections

Practice Questions

Bone and Joint Infections

Practice Questions

Cardiovascular Infections

Practice Questions

Sexually Transmitted Infections

Practice Questions

Zoonotic Infections

Practice Questions

Bloodstream Infections and Sepsis

Practice Questions

Fever of Unknown Origin

Practice Questions

Infections in Immunocompromised Host

Practice Questions

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