Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 521: Bioterrorism is associated with all, except:

A. Plague
B. Chicken pox (Correct Answer)
C. Clostridia
D. Ebola virus

Explanation: ***Chicken pox*** - While contagious, **chickenpox (varicella-zoster virus)** is generally a mild childhood illness with widespread vaccination available. - It does not possess the high morbidity, mortality, or widespread panic potential that would make it a primary agent for **bioterrorism**. *Plague* - **Plague**, caused by *Yersinia pestis*, has historically been used as a bioterrorism agent due to its high mortality rate, especially the pneumonic form. - It can be easily disseminated and is capable of causing **widespread infection** in a susceptible population, leading to significant public health emergencies. *Clostridia* - **Clostridia** species, particularly *Clostridium botulinum* (producing botulinum toxin), are considered significant bioterrorism threats. - **Botulinum toxin** is one of the most potent neurotoxins known, capable of causing severe **paralysis and death** with minute quantities. *Ebola virus* - The **Ebola virus** causes severe hemorrhagic fever with a high fatality rate. - Its high transmissibility, severe symptoms, and lack of readily available treatments or vaccines make it a potent biological weapon.

Question 522: Brucellosis can be transmitted by all of the following modes, except -

A. Inhalation of infected dust or aerosol
B. Person to person transmission (Correct Answer)
C. Contact with infected placenta
D. Ingestion of unpasteurized milk and dairy products

Explanation: ***Person to person transmission*** - **Person-to-person transmission is NOT a significant route** for brucellosis and is the correct answer for this "except" question. - Brucellosis is primarily a **zoonotic disease**, transmitted from infected animals to humans. - While extremely rare instances have been reported (sexual transmission, organ transplantation, breastfeeding), these are **not epidemiologically significant** routes. - The disease does **not spread readily between humans** like typical communicable diseases. *Inhalation of infected dust or aerosol* - **Inhalation** of contaminated aerosols is a well-documented transmission route. - Common among **abattoir workers, laboratory personnel, and veterinarians** handling infected animal specimens. - The bacteria can enter through the **respiratory tract** and cause infection. *Contact with infected placenta* - **Direct contact with infected animal tissues** (placentas, aborted fetuses, birth fluids) is a **major transmission route**. - Occupational exposure for **farmers, veterinarians, and slaughterhouse workers**. - Bacteria enter through **skin abrasions or mucous membranes**. *Ingestion of unpasteurized milk and dairy products* - **Ingestion of contaminated food** is the **most common transmission route** worldwide. - Unpasteurized **milk, cheese, and other dairy products** from infected animals (cattle, goats, sheep) are the primary vehicles. - This is why **pasteurization** is critical for preventing brucellosis in the general population.

Question 523: The infectivity of a convalescent case of cholera lasts for

A. 7-14 days (Correct Answer)
B. 14-21 days
C. 21-28 days
D. Less than 7 days

Explanation: ***7-14 days*** - The infectivity of a convalescent case of **cholera** typically lasts for **7 to 14 days** after the onset of symptoms, during which time the individual continues to shed *Vibrio cholerae* in their feces. - This is the **most common duration** of bacterial shedding in convalescent cholera patients, as documented in standard epidemiological references including Park's Textbook of Preventive and Social Medicine. - This period is critical for public health measures, as convalescent carriers can still transmit the disease, especially in areas with poor sanitation. - After appropriate antibiotic treatment, the duration may be shortened to **3-5 days**. *14-21 days* - While some individuals may continue to shed *Vibrio cholerae* for **14-21 days**, this represents an **extended or atypical duration** rather than the typical convalescent period. - This longer shedding period may occur in patients with delayed treatment or incomplete antibiotic therapy, but is not the standard expected duration. - The typical duration of infectivity is shorter, usually resolving within **2 weeks**. *Less than 7 days* - While antibiotic treatment (especially with doxycycline or azithromycin) can significantly shorten the duration of bacterial shedding to **3-5 days**, most untreated or partially treated convalescent cases continue to shed for at least a week. - This duration is **too short** to represent the typical convalescent carrier period without aggressive antimicrobial therapy. *21-28 days* - Shedding beyond **21 days** is uncommon and represents **chronic carrier status**, which is rare with cholera (unlike typhoid fever where chronic carriers are more common). - Prolonged shedding for 3-4 weeks may occur in immunocompromised individuals or those with underlying gallbladder disease, but this is not the typical pattern for convalescent cholera cases. - The vast majority of patients clear the organism within **2 weeks** of symptom onset.

Question 524: True about scrub typhus is?

A. Incubation period is 3-4 days
B. Caused by Rickettsia typhi
C. Eschar is pathognomonic and diagnostic on its own
D. Transmitted by larva of trombiculid mite (Correct Answer)

Explanation: ***Transmitted by larva of trombiculid mite*** - Scrub typhus is transmitted to humans through the bite of the **larval form of trombiculid mites**, commonly known as chiggers. - These chiggers carry the bacteria *Orientia tsutsugamushi* within their salivary glands. - This is the **correct answer**. *Incubation period is 3-4 days* - The typical incubation period for scrub typhus ranges from **6 to 21 days**, with an average of 10 to 12 days. - An incubation period of 3-4 days is generally **too short** for scrub typhus. *Caused by Rickettsia typhi* - Scrub typhus is caused by **Orientia tsutsugamushi**, an obligate intracellular bacterium. - *Rickettsia typhi* is the causative agent of **murine typhus**, a different rickettsial disease. *Eschar is pathognomonic and diagnostic on its own* - An **eschar** is a characteristic and highly suggestive finding in scrub typhus, appearing at the site of the chigger bite in 50-80% of cases. - However, eschar is **not pathognomonic** - it can occur in other rickettsial diseases and conditions. - Definitive diagnosis requires laboratory confirmation such as **IgM ELISA**, **PCR**, or **serological tests** (Weil-Felix test) to identify *Orientia tsutsugamushi*.

Question 525: Tuberculin test is a cheap and easily available test. In which of the following situations there is high failure in the interpretation of the test?

A. Low prevalence of HIV infection in the population
B. High proportion of individuals vaccinated with BCG (Correct Answer)
C. Low prevalence of environmental mycobacterium exposure
D. High prevalence of tuberculosis in the population

Explanation: **High proportion of individuals vaccinated with BCG** - The **Bacillus Calmette-Guérin (BCG) vaccine** uses a live attenuated strain of *Mycobacterium bovis*, stimulating a cell-mediated immune response. - This immune response can lead to a **false-positive tuberculin skin test (TST)** result, as the immune system reacts to the PPD antigens, making it difficult to differentiate true TB infection from vaccination effects. *Low prevalence of HIV infection in the population* - A low HIV prevalence would generally **improve the interpretability of the tuberculin test**, as HIV infection causes immunosuppression, which can lead to false-negative results in infected individuals. - With fewer immunocompromised individuals, the test is more likely to accurately reflect exposure to *Mycobacterium tuberculosis*. *Low prevalence of environmental mycobacterium exposure* - A low prevalence of **non-tuberculous mycobacteria (NTM)** exposure would actually **reduce interference** with TST interpretation. - Exposure to NTM can sometimes cause cross-reactivity and false-positive TST results, so its low prevalence would enhance test specificity. *High prevalence of tuberculosis in the population* - A high prevalence of tuberculosis means that a **positive TST result is more likely to represent true infection**, increasing the test's positive predictive value. - While it doesn't cause failure in interpretation, it highlights the importance of the test in such settings.

Question 526: In Guinea worm prophylaxis, all are true, except -

A. Identification of carriers
B. Mass treatment with anti-helminthic drugs (Correct Answer)
C. Acute search of new cases
D. Health education to people to use a sieve for straining drinking water

Explanation: ***Mass treatment with anti-helminthic drugs*** - Guinea worm disease (Dracunculiasis) is caused by the parasite *Dracunculus medinensis*, which is transmitted through contaminated drinking water containing **copepods (water fleas)** harboring larvae. - Unlike many other helminthic infections, Guinea worm disease **does not respond to anti-helminthic drugs** for treatment or prevention, making mass treatment ineffective. *Identification of carriers* - Identifying and containing individuals who are actively expelling worms is crucial to prevent further contamination of water sources. - This strategy focuses on interrupting the parasite's life cycle by preventing infected individuals from entering communal water bodies. *Acute search of new cases* - Active surveillance and rapid detection of new cases enable prompt intervention, such as safe containment of the emerging worm and prevention of water source contamination. - This helps in monitoring incidence and targeting interventions effectively to achieve eradication. *Health education to people to use a sieve for straining drinking water* - This is a cornerstone of Guinea worm prophylaxis, as it directly addresses the mode of transmission by filtering out the **copepods** from drinking water. - Providing **cloth filters** or using fine-mesh sieves is a simple and effective way to ensure safe drinking water and interrupt the life cycle.

Question 527: Which of the following is a mosquito-borne infection?

A. HIV
B. Plague
C. Leprosy
D. Japanese encephalitis (Correct Answer)

Explanation: ***Japanese encephalitis*** * **Japanese encephalitis** is a viral disease primarily transmitted to humans through the bite of infected mosquitos, particularly those belonging to the **Culex species**. * The virus is maintained in a cycle involving mosquitos, pigs, and wading birds, with humans being **incidental hosts**. *HIV* * **HIV (Human Immunodeficiency Virus)** is primarily transmitted through direct contact with infected bodily fluids, such as during **sexual intercourse**, sharing of **contaminated needles**, and from **mother to child** during pregnancy, childbirth, or breastfeeding. * There is **no evidence** that HIV is transmitted by mosquitos or other insects, as the virus cannot replicate within the mosquito. *Plague* * **Plague** is a bacterial infection caused by *Yersinia pestis*, primarily transmitted to humans through the bite of **infected fleas** that have fed on infected rodents. * It is **not transmitted by mosquitos**; the primary vector is the flea, particularly the oriental rat flea (*Xenopsylla cheopis*). *Leprosy* * **Leprosy** is a chronic infectious disease caused by *Mycobacterium leprae*, primarily affecting the skin, peripheral nerves, upper respiratory tract, eyes, and testes. * It is believed to be transmitted via **droplets from the nose and mouth** during close and frequent contact with an untreated infected person, and **not through mosquito bites**.

Question 528: The natural life cycle of the Japanese encephalitis (JE) virus occurs between which of the following?

A. Pigs and Humans
B. Cattle and Birds
C. Pigs and Mosquitoes (Correct Answer)
D. Birds and Pigs

Explanation: ***Pigs and Mosquitoes*** - The primary **enzootic cycle** of Japanese encephalitis virus (JEV) occurs between **pigs** (amplifying hosts) and **Culex mosquitoes** (primarily *Culex tritaeniorhynchus*). - **Pigs** develop high levels of viremia (up to 10^5-10^7 infectious units/mL) without showing severe clinical signs, making them the most important **amplifying hosts**. - **Mosquitoes** acquire the virus after feeding on infected pigs and then transmit it to other pigs, humans, and incidental hosts, maintaining the transmission cycle in endemic areas. - While birds serve as **reservoir hosts**, the **pig-mosquito cycle** is the predominant pathway for viral amplification and human exposure. *Pigs and Humans* - Humans are **dead-end hosts** who typically do not develop viremia levels high enough (usually <10^5 infectious units/mL) to infect feeding mosquitoes. - There is **no direct human-to-human or pig-to-human transmission** without the mosquito vector. - The natural life cycle does not occur between pigs and humans alone. *Cattle and Birds* - **Birds** (particularly wading birds like herons and egrets) serve as **reservoir hosts** and can maintain the virus in nature, but they are not the primary amplifying hosts. - **Cattle** are generally not significant hosts or reservoirs for JEV transmission and do not develop sufficient viremia to contribute to the cycle. *Birds and Pigs* - While both birds and pigs can be infected, the transmission between them still requires a **mosquito vector** to complete the natural cycle. - The question asks about what the cycle occurs "between," which refers to the **direct transmission pair**: mosquitoes and pigs, not the broader ecological network.

Question 529: Which of the following strategies are part of the National Leprosy Control Programme?

A. Early detection of cases and short course multi-drug therapy (Correct Answer)
B. Chemoprophylaxis with dapsone and rehabilitation
C. Short course multi-drug therapy and chemoprophylaxis
D. Rehabilitation and early detection of cases

Explanation: ***Early detection of cases and short course multi-drug therapy*** - The primary strategy of the National Leprosy Control Programme (NLCP) is to actively identify new cases early to prevent disabilities. - **Multi-drug therapy (MDT)**, a short-course regimen, is administered to cure the disease and interrupt transmission. - This combination represents the **core control strategy** of NLCP. *Chemoprophylaxis with dapsone and rehabilitation* - **Chemoprophylaxis with dapsone** is not a standard strategy under NLCP due to concerns about resistance and limited effectiveness for mass prevention. - **Rehabilitation** is important for disability management but is a secondary/tertiary prevention strategy, not a primary control measure. *Short course multi-drug therapy and chemoprophylaxis* - While **MDT** is a cornerstone of NLCP, **chemoprophylaxis** is not included as a widespread intervention. - The focus remains on treating diagnosed cases rather than mass preventive drug administration. *Rehabilitation and early detection of cases* - **Early detection** is indeed a key component, but pairing it with **rehabilitation** alone misses the critical treatment component. - The core control strategy requires both early detection **and MDT treatment**, not just detection and rehabilitation.

Question 530: In RNTCP, one Tuberculosis Unit covers how much population?

A. 500000 (Correct Answer)
B. 400000
C. 600000
D. 200000

Explanation: ***500000*** - In the context of the **Revised National Tuberculosis Control Programme (RNTCP)** in India (now known as **National Tuberculosis Elimination Programme - NTEP** since 2020), one **Tuberculosis Unit (TU)** is designed to cover a population of approximately **500,000** individuals in plain areas and 250,000 in difficult terrains. - This population coverage ensures that diagnosis and treatment services for tuberculosis are accessible and effectively managed within a defined geographical area. *400000* - This value is less than the standard population covered by a single **Tuberculosis Unit (TU)** under the **RNTCP** guidelines for plain areas. - While exact coverage can vary slightly in specific contexts, 400,000 is not the benchmark figure for plain areas. *600000* - This figure is higher than the typical population covered by one **Tuberculosis Unit (TU)** in plain areas as per **RNTCP** norms. - Over-coverage could potentially strain resources and affect the quality of services provided within that unit. *200000* - This figure is lower than the standard population covered by a **Tuberculosis Unit (TU)** in plain areas and is typically closer to the coverage for **difficult or tribal geographical areas** (which is usually 250,000). - Such low coverage in plain areas would imply an inefficient allocation of resources if not justified by specific topographical or demographic challenges.

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HIV/AIDS Control Program

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Emerging and Re-emerging Infections

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Integrated Disease Surveillance Project

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