Infectious Diseases — MCQs

An army jawan posted in a remote forest area presented with fever and headache. His fever was 104°F and pulse was 70 per minute. He had an erythematous lesion of about 1 cm on the leg surrounded by small vesicles, along with generalized lymphadenopathy at the time of presentation to the referral hospital. His blood sample was collected to perform serology for the diagnosis of Rickettsial disease. Which one of the following results in the Weil-Felix reaction will be diagnostic in this clinical setting?

Q99

All of the following are sexually transmitted, except?

Q100

Which of the following bacterial organisms does not cause invasive diarrhea?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 91: Man is the only reservoir for

A. Salmonella typhi (Correct Answer)
B. Campylobacter jejuni
C. E. histolytica
D. Y. enterocolitica

Explanation: ***Salmonella typhi*** - *Salmonella typhi* (and *S. paratyphi*) are **unique among Salmonella** species in that **humans are the only natural reservoir**. - Transmission occurs through the **fecal-oral route** via contaminated food or water from infected individuals or chronic carriers. - This is in contrast to non-typhoidal Salmonella, which have extensive **animal reservoirs**. *E. histolytica* - While *Entamoeba histolytica* primarily infects **humans**, it can occasionally infect **non-human primates and dogs**. - Humans serve as the **principal reservoir**, but not the exclusive one, making this option technically incorrect. *Campylobacter jejuni* - **Poultry** (especially chickens), **cattle**, and other animals are common reservoirs for *Campylobacter jejuni*. - Humans become infected primarily through consumption of **contaminated food or water**, particularly undercooked poultry. *Y. enterocolitica* - **Pigs** are a significant reservoir for *Yersinia enterocolitica*, along with other animals like rodents and livestock. - Transmission to humans often occurs via **contaminated pork products** or unpasteurized milk.

Question 92: Which of the following is an example of a nonvenereal disease –

A. Gonorrhea
B. Chancroid
C. LGV
D. Endemic syphilis (Correct Answer)

Explanation: ***Endemic syphilis*** - **Endemic syphilis** (also known as bejel or non-venereal syphilis) is a **nonvenereal treponemal infection** that affects the skin, mucous membranes, and bones. - It is typically spread through **direct skin-to-skin contact** or shared eating utensils, particularly among children in specific endemic regions, rather than sexual contact. *Gonorrhea* - **Gonorrhea** is a **classic sexually transmitted infection (STI)** caused by the bacterium *Neisseria gonorrhoeae*. - It primarily affects the **mucous membranes** of the reproductive tract, urethra, rectum, and pharynx, and is transmitted through sexual contact. *Chancroid* - **Chancroid** is a **sexually transmitted infection (STI)** caused by the bacterium *Haemophilus ducreyi*. - It is characterized by **painful genital ulcers** and often **swollen lymph nodes** in the groin, and is spread exclusively through sexual contact. *LGV* - **LGV (lymphogranuloma venereum)** is a **sexually transmitted infection (STI)** caused by specific serovars of *Chlamydia trachomatis*. - It is characterized by **small, painless genital ulcers** followed by painful swelling of the lymph nodes in the groin, and is transmitted through sexual contact.

Question 93: Which is not transmitted by arthropod?

A. Rickettsia rickettsii
B. Coxiella burnetii (Correct Answer)
C. Rickettsia akari
D. Rickettsia prowazakii

Explanation: ***Coxiella burnetii*** - *Coxiella burnetii* causes **Q fever**, which is primarily transmitted to humans through inhalation of **contaminated aerosols** from infected animals, particularly **cattle, sheep, and goats**. - While *Coxiella burnetii* can infect ticks, **tick bites are not the primary mode of transmission** to humans; instead, it's considered an occupational hazard for those working with livestock. *Rickettsia rickettsii* - *Rickettsia rickettsii* is the causative agent of **Rocky Mountain spotted fever**, which is transmitted to humans through the bite of infected **ticks**. - Ticks, such as the **American dog tick** and **Rocky Mountain wood tick**, are the primary vectors for this pathogen. *Rickettsia akari* - *Rickettsia akari* causes **rickettsialpox**, which is transmitted to humans by the bite of the **house mouse mite**. - The house mouse acts as the **reservoir**, and mites acquire the bacteria from feeding on infected mice. *Rickettsia prowazakii* - *Rickettsia prowazakii* is the cause of **epidemic typhus**, primarily transmitted to humans by the bite and feces of the **human body louse**. - The bacteria are rubbed into the skin through scratching or inhaled from dried louse feces.

Question 94: Acute meningitis in adolescents and young adults is caused by -

A. N. meningitidis (Correct Answer)
B. H. influenzae
C. E. coli
D. Streptococcus

Explanation: ***N. meningitidis*** - **_Neisseria meningitidis_** is the most common cause of **bacterial meningitis** in adolescents and young adults, often occurring in outbreaks within close-living communities like dormitories. - It can lead to severe illness, including **sepsis** and **neurological complications**, and rapid diagnosis and treatment are crucial. *H. Influenzae* - **_Haemophilus influenzae_** type b (Hib) was a major cause of bacterial meningitis in **infants and young children** before the widespread introduction of the Hib vaccine. - While it can still cause meningitis particularly in unvaccinated individuals, it is **less common** in adolescents and young adults compared to _N. meningitidis_. *E. coli* - **_Escherichia coli_** is a significant cause of meningitis primarily in **neonates** (newborns), often acquired during passage through the birth canal. - It is **rarely a cause** of meningitis in healthy adolescents and young adults. *Streptococcus* - **_Streptococcus pneumoniae_** (Pneumococcus) and **Group B Streptococcus** (_S. agalactiae_) are important causes of meningitis, but they typically affect different age groups more predominantly. - _S. pneumoniae_ primarily affects **young children and older adults**, while _S. agalactiae_ is a leading cause of **neonatal meningitis**.

Question 95: Systemic miliary TB occurs when the spread of Mycobacterium tuberculosis happens via which route?

A. Direct dissemination
B. Hematogenous (Correct Answer)
C. Lymphatic
D. Aerial

Explanation: ***Hematogenous*** - **Miliary TB** is characterized by the widespread dissemination of *Mycobacterium tuberculosis* to multiple organs via the **bloodstream (hematogenous route)**. - Hematogenous spread allows bacilli to be carried throughout the systemic circulation, leading to the formation of small, millet-seed-sized lesions in various tissues including lungs, liver, spleen, bone marrow, and other organs. - This typically occurs when bacilli from a primary focus erode into a blood vessel and gain access to the circulation. *Direct dissemination* - This route involves the local spread of infection from one tissue or organ directly to an adjacent one, without entering the bloodstream. - It does not account for the widespread, systemic involvement seen in miliary TB. *Lymphatic* - **Lymphatic spread** typically leads to involvement of regional lymph nodes and can contribute to dissemination, but it is not the primary route for the widespread, systemic involvement characteristic of miliary TB. - While bacilli can reach the bloodstream via the thoracic duct, the key mechanism for systemic miliary spread is direct hematogenous dissemination. *Aerial* - **Aerial spread** primarily refers to the transmission of *Mycobacterium tuberculosis* from person to person via airborne droplets, or the initial infection of the lungs. - It is the route of initial infection for pulmonary TB, not the mechanism for systemic dissemination within an infected individual leading to miliary disease.

Question 96: Acute intravascular hemolysis can be caused by infection due to all of the following organisms except:

A. Bartonella bacilliformis
B. Plasmodium falciparum
C. Clostridium tetani (Correct Answer)
D. Babesia microti

Explanation: ***Clostridium tetani*** - This organism causes **tetanus**, characterized by muscle spasms and lockjaw due to exotoxins, but it does **not directly cause intravascular hemolysis**. - Its pathology is primarily neurological, affecting neurotransmitter release at inhibitory synapses. *Bartonella bacilliformis* - This bacterium is the causative agent of **Carrion's disease**, which has two phases: an acute **hemolytic anemic phase** (Oroya fever) and a chronic eruptive phase (verruga peruana). - The acute phase is characterized by severe **intravascular hemolysis**, which can be life-threatening. *Plasmodium falciparum* - This parasite, responsible for the most severe form of malaria, infects **red blood cells**, leading to their lysis and causing **intravascular hemolysis**. - The destruction of red blood cells by the parasite directly contributes to **anemia** and other severe complications of malaria. *Babesia microti* - This is an intraerythrocytic parasite that causes **babesiosis**, a tick-borne disease. - Infections with *Babesia microti* are known to cause **hemolytic anemia** due to the parasite's replication within and subsequent destruction of red blood cells.

Question 97: True about prions are all except -

A. Can be transmitted by corneal transplant
B. Can occur sporadically
C. Cannot be inherited (Correct Answer)
D. Can be transmitted by human growth hormone preparation

Explanation: ***Cannot be inherited*** - This statement is **false** because prion diseases, such as **familial Creutzfeldt-Jakob disease (fCJD)** and **Gerstmann-Sträussler-Scheinker syndrome (GSS)**, can indeed be inherited due to mutations in the **PRNP gene**. - These genetic mutations lead to the production of an abnormal prion protein, PrPSc, which can then misfold and cause disease. *Can be transmitted by corneal transplant* - **Prion diseases** can be transmitted through corneal transplants, as the **cornea** can harbor infectious prions. - This route of transmission is an example of **iatrogenic CJD**, highlighting the importance of cautious donor screening. *Can occur sporadically* - The most common form of human prion disease, **sporadic Creutzfeldt-Jakob disease (sCJD)**, occurs without any known genetic mutation or environmental exposure. - This accounts for about 85-90% of all CJD cases, where the initial misfolding of the prion protein is spontaneous. *Can be transmitted by human growth hormone preparation* - **Iatrogenic Creutzfeldt-Jakob disease (iCJD)** has been linked to the use of human growth hormone preparations derived from cadaveric pituitary glands. - Before the advent of recombinant human growth hormone, these preparations could transmit prions from infected donors.

Question 98: An army jawan posted in a remote forest area presented with fever and headache. His fever was 104°F and pulse was 70 per minute. He had an erythematous lesion of about 1 cm on the leg surrounded by small vesicles, along with generalized lymphadenopathy at the time of presentation to the referral hospital. His blood sample was collected to perform serology for the diagnosis of Rickettsial disease. Which one of the following results in the Weil-Felix reaction will be diagnostic in this clinical setting?

A. High OX - 19 and OX - 2
B. High OX - 2
C. High OX - K (Correct Answer)
D. High OX - 19

Explanation: **High OX - K** - The clinical presentation (fever, headache, erythematous lesion with vesicles, rural exposure) is highly suggestive of **Scrub typhus**, which is caused by *Orientia tsutsugamushi*. - A **high OX-K titer** in the Weil-Felix reaction is characteristic for **Scrub typhus**, as this rickettsial species shares antigens with *Proteus mirabilis* OX-K. *High OX - 19 and OX - 2* - A high titer for both OX-19 and OX-2 would generally suggest **typhus group rickettsiae** (e.g., epidemic or endemic typhus), which is less likely given the specific lesion described (eschar with vesicles) and the forest setting. - This combination is not typically associated with the classic presentation of **Scrub typhus**. *High OX - 2* - A high OX-2 titer alone is less specific and can be elevated in some cases of **spotted fever group rickettsiae**, but it is not the primary indicator for Scrub typhus. - It would not definitively diagnose the clinical picture, which points strongly to Scrub typhus due to the characteristic skin lesion and rural exposure. *High OX - 19* - A high OX-19 titer is primarily indicative of **typhus group rickettsiae** like **epidemic typhus** (*Rickettsia prowazekii*) or **murine typhus** (*Rickettsia typhi*). - This finding is not consistent with the typical presentation of Scrub typhus, which is associated with the OX-K antigen.

Question 99: All of the following are sexually transmitted, except?

A. Echinococcus granulosus (Correct Answer)
B. Candida albicans
C. Molluscum contagiosum
D. Group B streptococcus

Explanation: ***Echinococcus granulosus*** - ***Echinococcus granulosus*** is a **tapeworm** that causes hydatid cyst disease (echinococcosis) - Transmitted via the **fecal-oral route** through ingestion of eggs from infected canid (dog) feces - Humans are accidental intermediate hosts; **definitive hosts are dogs and other canids** - **NOT sexually transmitted** - this is the correct answer *Candida albicans* - While ***Candida albicans*** can occasionally be transmitted through sexual contact, it is **NOT classified as a sexually transmitted infection (STI)** - Most candidiasis cases arise from **overgrowth of endogenous commensal flora**, not from sexual transmission - Primary risk factors include antibiotic use, diabetes, immunosuppression, and hormonal changes - Sexual transmission is rare and not the primary mode of acquisition *Molluscum contagiosum* - **Molluscum contagiosum** is a **poxvirus infection** transmitted through direct skin-to-skin contact - In adults, it is **commonly sexually transmitted** and lesions appear in the genital, lower abdominal, and inner thigh regions - Classified as an STI when transmitted through sexual contact in adults - In children, transmission occurs through non-sexual contact *Group B streptococcus* - **Group B streptococcus (GBS)** is a **commensal organism** that colonizes the gastrointestinal and genitourinary tracts in 10-30% of healthy adults - While it can be found in the genital tract, it is **NOT classified as a sexually transmitted infection** - Colonization is typically endogenous, not acquired through sexual contact - Important as a cause of neonatal sepsis and meningitis through vertical transmission during delivery

Question 100: Which of the following bacterial organisms does not cause invasive diarrhea?

A. Shigella
B. Campylobacter jejuni
C. Bacillus cereus (Correct Answer)
D. Aeromonas sp

Explanation: ***Bacillus cereus*** - *Bacillus cereus* typically causes **food poisoning** through the production of **exotoxins**, leading to either emetic (vomiting) or diarrheal syndromes. - Its pathogenic mechanism does not involve invasion of the intestinal mucosa, differentiating it from causes of invasive diarrhea. *Shigella* - **Shigella** species are well-known causes of **bacillary dysentery**, characterized by invasive diarrhea with bloody and mucous stools. - They invade the **colonic epithelial cells**, leading to inflammation, ulceration, and destruction of the mucosa. *Campylobacter jejuni* - **Campylobacter jejuni** is a leading cause of **bacterial gastroenteritis**, often resulting in invasive diarrhea. - It invades and damages the **intestinal epithelial cells**, particularly in the jejunum, ileum, and colon, causing inflammation and bloody stools. *Aeromonas sp* - **Aeromonas species** are recognized as opportunistic pathogens that can cause **gastroenteritis**, including invasive diarrheal disease. - They are capable of invading the intestinal mucosa and producing enterotoxins, contributing to symptoms of dysentery.

Practice by Chapter

Respiratory Tract Infections

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Urinary Tract Infections

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Gastrointestinal Infections

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Skin and Soft Tissue Infections

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Central Nervous System Infections

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Bone and Joint Infections

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Cardiovascular Infections

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Sexually Transmitted Infections

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Zoonotic Infections

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Bloodstream Infections and Sepsis

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Fever of Unknown Origin

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Infections in Immunocompromised Host

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