Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 401: Louse-borne typhus fever is:

A. Epidemic typhus (Correct Answer)
B. Rickettsialpox
C. Endemic typhus
D. Scrub typhus

Explanation: ***Epidemic typhus*** - **Epidemic typhus** is caused by **Rickettsia prowazekii** and is primarily transmitted by the **human body louse** (Pediculus humanus corporis). - This form of typhus is associated with overcrowding and poor hygiene, often leading to large outbreaks. *Rickettsialpox* - **Rickettsialpox** is caused by **Rickettsia akari** and is transmitted by the **house mouse mite**, not lice. - It typically presents with an **initial papulovesicular lesion** (eschar) followed by a generalized rash. *Endemic typhus* - **Endemic typhus**, also known as murine typhus, is caused by **Rickettsia typhi** and is transmitted by the **rat flea**, not lice. - It is generally milder than epidemic typhus and is associated with sporadic cases rather than large epidemics. *Scrub typhus* - **Scrub typhus** is caused by **Orientia tsutsugamushi** and is transmitted by the bite of infected **chiggers** (larval mites), not lice. - It is characterized by an **eschar** at the bite site and involves symptoms like fever, headache, and rash, primarily in rural areas of Asia and the Pacific.

Question 402: Chemoprophylaxis can be done for the following except:

A. Meningococcal meningitis
B. Typhoid fever (Correct Answer)
C. Cholera
D. Influenza

Explanation: ***Typhoid fever*** - **Typhoid fever** is primarily controlled through **vaccination** (Vi polysaccharide vaccine, Ty21a oral vaccine) and **improved sanitation** (safe water supply, proper sewage disposal). - **Chemoprophylaxis is NOT routinely recommended** for typhoid fever, even for travelers to endemic areas. Vaccination and food/water precautions are the mainstay of prevention. - Unlike other diseases requiring post-exposure prophylaxis, typhoid contacts are monitored rather than given prophylactic antibiotics. *Meningococcal meningitis* - **Chemoprophylaxis is essential** for close contacts of meningococcal disease cases. - **Rifampicin, ciprofloxacin, or ceftriaxone** are given to household contacts, healthcare workers exposed to respiratory secretions, and other close contacts. - This prevents secondary cases and interrupts transmission in high-risk individuals. *Cholera* - During cholera outbreaks, **chemoprophylaxis with doxycycline or azithromycin** may be used for household contacts and high-risk groups. - This is a **targeted intervention** during acute public health emergencies to prevent rapid spread. - Not routine, but justified in outbreak settings when transmission risk is high. *Influenza* - **Chemoprophylaxis with oseltamivir or zanamivir** is recommended for high-risk unvaccinated individuals exposed to confirmed influenza cases. - Used in institutional outbreaks, for immunocompromised patients, and during the window period before vaccine takes effect. - Particularly important when circulating strain doesn't match vaccine or vaccine is contraindicated.

Question 403: Animal to man transmission (zoonosis) is seen in -

A. Tuberculosis
B. Measles
C. Rabies (Correct Answer)
D. HIV

Explanation: ***Rabies*** - **Rabies** is a classic zoonotic disease, primarily transmitted to humans through the bite or scratch of an infected animal, most commonly **dogs, bats, or other wild carnivores**. - The virus travels from the site of infection to the central nervous system, leading to characteristic neurological symptoms. *Tuberculosis* - While certain strains of **Mycobacterium bovis** can cause zoonotic tuberculosis, the question implies common human tuberculosis (**Mycobacterium tuberculosis**), which is primarily transmitted person-to-person via airborne droplets. - While bovine TB is zoonotic, general "Tuberculosis" in this context usually refers to the human-to-human transmitted form. *Measles* - **Measles** is a highly contagious disease caused by the **measles virus**, which is a **human paramyxovirus**. - It is spread exclusively from **person to person** through respiratory droplets and has no known animal reservoir. *HIV* - **HIV (Human Immunodeficiency Virus)** is thought to have originated from **simian immunodeficiency virus (SIV)** in non-human primates, thus representing a historic zoonotic jump. - However, current and continued transmission of HIV is almost exclusively through **human-to-human contact**, not ongoing animal-to-human transmission.

Question 404: Reduviid bug is a vector for the transmission of:

A. Relapsing fever
B. Scrub typhus
C. Chagas disease (Correct Answer)
D. Lyme disease

Explanation: ***Chagas disease*** - Reduviid bugs, specifically the **Triatominae subfamily (kissing bugs)**, are the vectors for the transmission of **Trypanosoma cruzi**, the parasite that causes Chagas disease. - The parasite is transmitted through the bug's feces, which are often deposited on the skin near the bite site, and then rubbed into the wound or mucous membranes. *Relapsing fever* - Relapsing fever is primarily transmitted by **soft ticks (Ornithodoros species)**, for the endemic form, or by **lice (Pediculus humanus humanus)** for the epidemic form. - The causative agents are spirochetes from the genus **Borrelia**. *Scrub typhus* - Scrub typhus is transmitted by the larvae of **chigger mites (trombiculid mites)**, specifically those belonging to the genus Leptotrombidium. - The causative agent is **Orientia tsutsugamushi**. *Lyme disease* - Lyme disease is transmitted by **hard ticks** from the genus **Ixodes**, commonly known as deer ticks or black-legged ticks. - The causative agent is the spirochete **Borrelia burgdorferi**.

Question 405: Elimination of leprosy is defined as prevalence rate of:

A. < 1 per 1 lakh
B. < 1 per 100
C. < 1 per 1000
D. < 1 per 10000 (Correct Answer)

Explanation: ***< 1 per 10,000*** - The World Health Organization (WHO) defines **elimination of leprosy as a public health problem** as achieving a prevalence rate of **less than 1 case per 10,000 population** at the national level. - This target was set to highlight significant progress in disease control and public health efforts. - India achieved this milestone in December 2005. *< 1 per 1 lakh (100,000)* - This rate is significantly lower than the internationally accepted threshold for leprosy elimination and is not the standard definition. - A prevalence rate of less than 1 per 100,000 population indicates a level beyond elimination, often nearing eradication. *< 1 per 100* - A prevalence rate of less than 1 per 100 population (1%) is still a high prevalence and does not constitute elimination of leprosy. - This level would indicate a substantial burden of disease within the population. *< 1 per 1,000* - While a reduction from higher prevalence, a rate of less than 1 per 1,000 population is not the defined threshold for leprosy elimination. - This rate still suggests an ongoing public health concern that has not met the global elimination target.

Question 406: According to WHO, leprosy is considered a major public health problem when the prevalence is:

A. 1%
B. 0.50%
C. 0.10%
D. 0.01% (Correct Answer)

Explanation: ***0.01% or more (≥ 1 case per 10,000 population)*** - The World Health Organization (WHO) defines **elimination of leprosy as a public health problem** when prevalence falls **below 1 case per 10,000 population** (< 0.01%). - Conversely, leprosy **remains a public health problem** when prevalence is **≥ 1 case per 10,000 population** (≥ 0.01%). - This threshold is used for global monitoring to assess disease control and elimination targets. *1%* - A prevalence of 1% (100 cases per 10,000 population) would indicate a **severe hyperendemic** situation, far exceeding the WHO threshold. - This represents **uncontrolled transmission** and would be seen in areas with no leprosy control programs. *0.50%* - A prevalence of 0.50% (50 cases per 10,000 population) is significantly high, indicating a **major endemic burden**. - This is **50 times higher** than the WHO elimination threshold and represents poor disease control. *0.10%* - A prevalence of 0.10% (10 cases per 10,000 population) is **10 times higher** than the WHO threshold. - While indicating substantial burden requiring intervention, it is not the specific WHO-defined threshold for public health problem status.

Question 407: Incubation period of which disease is less than 7 days?

A. Measles
B. Mumps
C. Cholera (Correct Answer)
D. Leishmaniasis

Explanation: ***Cholera*** - Cholera has a very short incubation period, typically ranging from **a few hours to 5 days**, often within 2 to 3 days. - This rapid onset is due to the quick action of **Vibrio cholerae toxin** on the intestinal lining. *Measles* - The incubation period for measles is generally **10 to 14 days** from exposure to the onset of fever. - The characteristic rash appears several days after the initial fever. *Mumps* - Mumps typically has an incubation period of **16 to 18 days**, with a range of 12 to 25 days. - This longer period precedes the onset of symptoms like fever and **parotid gland swelling**. *Leishmaniasis* - The incubation period for leishmaniasis can be highly variable, ranging from **weeks to months or even years**, depending on the species and form of the disease (visceral, cutaneous). - This lengthy period reflects the complex life cycle of the **Leishmania parasite** within the host.

Question 408: Incubation period of Salmonella typhi -

A. 3-21 days (Correct Answer)
B. 2-5 days
C. 14-25 days
D. 0-60 days

Explanation: ***3-21 days*** - The typical incubation period for **Salmonella Typhi**, the bacterium causing typhoid fever, ranges from **3 to 21 days**. - This period allows the bacteria to multiply in the host before symptoms such as fever, headache, and malaise begin to appear. *2-5 days* - This incubation period is generally too short for **typhoid fever**, which typically has a longer course due to the pathogen's systemic spread. - Shorter incubation periods are more characteristic of other forms of **salmonellosis**, such as gastroenteritis. *14-25 days* - While overlap exists, a consistent range of **14 to 25 days** tends to skew towards the longer end of the typical incubation period, potentially missing earlier presentations. - The **3-21 day range** is more commonly cited in medical literature as the average window. *0-60 days* - An incubation period of **0-60 days** is excessively broad and lacks clinical precision for **typhoid fever**. - While rare cases might fall outside the typical range, this option includes an implausible immediate onset (0 days) and an overly protracted maximum duration.

Question 409: Which of the following is true about Endemic typhus?

A. Reservoir is humans
B. Vector is flea (Correct Answer)
C. Cause is Rickettsia prowazekii
D. Tetracycline is not useful for treatment

Explanation: ***Vector is flea*** - **Endemic typhus**, also known as **murine typhus**, is transmitted to humans by the **rat flea** (*Xenopsylla cheopis*). - The flea becomes infected by feeding on rodents (primarily rats) that carry the causative bacteria. *Reservoir is humans* - The primary **reservoir** for **endemic typhus** is **rodents**, particularly rats, not humans. - Humans are considered **accidental hosts** and do not typically perpetuate the transmission cycle. *Cause is Rickettsia prowazekii* - The causative agent of **endemic typhus** is **Rickettsia typhi**. - **Rickettsia prowazekii** is the causative agent of **epidemic typhus**, which is distinct from endemic typhus. *Tetracycline is not useful for treatment* - **Tetracyclines**, particularly **doxycycline**, are the **first-line treatment** for endemic typhus and are highly effective. - Other effective antibiotics include **chloramphenicol** and **fluoroquinolones**.

Question 410: Chiggerosis is due to

A. Louse
B. Chigger (Correct Answer)
C. Tick
D. Bed bug

Explanation: ***Chigger (Trombiculid mite larva)*** - **Chiggerosis**, also known as **trombiculosis**, is an intensely itchy dermatitis caused by the bite of the larval stage of **trombiculid mites**. - These larvae attach to the skin, inject digestive enzymes, and feed on liquefied tissue, causing characteristic **pruritic red papules**. *Louse* - **Lice** (e.g., *Pediculus humanus* or *Pthirus pubis*) cause **pediculosis**, characterized by pruritus, excoriations, and nits attached to hair shafts. - Their bites are typically small, red papules, but do not produce the intense, persistent inflammatory reaction associated with chigger bites. *Tick* - **Ticks** are larger arachnids that burrow their mouthparts into the skin to feed on blood, which can transmit various **pathogens** (e.g., Lyme disease, Rocky Mountain spotted fever). - While tick bites can cause localized irritation, they do not typically result in the widespread, intensely itchy rash seen in chiggerosis. *Bed bug* - **Bed bugs** (*Cimex lectularius*) are nocturnal insects that feed on human blood, typically producing small, **itchy red welts** often arranged in a linear pattern ("breakfast, lunch, and dinner"). - The rash is distinct from chiggerosis, which presents as highly inflammatory, localized papules often found in skin folds or tight clothing areas.

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HIV/AIDS Control Program

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