Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 661: Which is the main vector of Dengue?

A. A. aegypti (Correct Answer)
B. Culex
C. Anopheles
D. Aedes scutellaris

Explanation: ***A. aegypti*** - **Aedes aegypti** is the primary vector responsible for transmitting the **Dengue virus** to humans. - It is a **day-biting mosquito** found predominantly in tropical and subtropical regions. *Culex* - **Culex mosquitoes** are known vectors for diseases like **Japanese encephalitis**, **West Nile virus**, and **filariasis**. - They are generally **night-biting** and do not play a significant role in Dengue transmission. *Anopheles* - **Anopheles mosquitoes** are the primary vectors for **malaria** in humans. - They are not associated with the transmission of the Dengue virus. *Aedes scutellaris* - While part of the **Aedes genus**, **Aedes scutellaris** is a secondary vector for Dengue in the **Pacific region**. - The main vector for Dengue globally remains **Aedes aegypti**, followed by **Aedes albopictus** in some regions.

Question 662: What is the most commonly reported bacterial sexually transmitted infection?

A. HSV
B. HIV
C. Syphilis
D. Chlamydia (Correct Answer)

Explanation: ***Correct: Chlamydia*** - **Chlamydia trachomatis** is the most frequently reported bacterial STI in many countries, often being **asymptomatic** and thus easily spread - Its high prevalence is due to efficient transmission and the widespread use of sensitive diagnostic tests that detect infections in asymptomatic individuals - Accounts for the majority of reported bacterial STI cases globally *Incorrect: HSV* - **Herpes Simplex Virus (HSV)** is a **viral STI**, not bacterial, and is characterized by recurrent outbreaks of **genital ulcers** or sores - While common, it does not qualify as a bacterial infection and is often not laboratory-confirmed due to mild or subclinical presentations *Incorrect: HIV* - **Human Immunodeficiency Virus (HIV)** is also a **viral STI**, not bacterial, that attacks the immune system leading to AIDS - Although highly impactful, HIV is not a bacterial infection and has lower incidence rates compared to Chlamydia *Incorrect: Syphilis* - **Syphilis**, caused by the bacterium **Treponema pallidum**, is a serious bacterial STI that can have long-term complications if untreated - While its incidence has been increasing in some regions, it is significantly less common than **Chlamydia** in terms of overall reported cases

Question 663: The primary reservoir for leptospirosis transmission is:

A. Rat (Correct Answer)
B. Cat
C. Dog
D. Fish

Explanation: ***Correct Answer: Rat*** - **Rats** (and other rodents) are considered the primary natural reservoir for *Leptospira* bacteria worldwide and are **asymptomatic carriers**. - They excrete the bacteria in their urine, contaminating water and soil, which serves as the main source of human infection. *Incorrect: Cat* - While cats can become infected with *Leptospira*, they are **not typically considered significant reservoirs** for human transmission. - Their role in the epidemiologic cycle of leptospirosis is generally minor compared to rodents and some other mammals. *Incorrect: Dog* - **Dogs** can contract leptospirosis and excrete the bacteria in their urine, posing a risk to humans, but they are generally considered **incidental hosts or secondary reservoirs**, not the primary one. - Vaccination in dogs helps reduce their role in transmission. *Incorrect: Fish* - **Fish are not known to be reservoirs** for *Leptospira* bacteria. - Leptospirosis is primarily transmitted through contact with infected animal urine, not aquatic life like fish.

Question 664: What is the recommended Aedes Aegypti index for preventing Yellow Fever transmission?

A. Less than 1% (Correct Answer)
B. Less than 5%
C. Less than 10%
D. Less than 20%

Explanation: ***Less than 1%*** - An **Aedes Aegypti index** of **less than 1%** is the recommended threshold by WHO to effectively prevent Yellow Fever transmission. - Maintaining the vector index (House Index) below this critical level significantly reduces the chances of epidemic transmission. - This stringent target is essential for breaking the transmission cycle in endemic areas. *Less than 5%* - While an index of less than 5% represents moderate control, it is insufficient for reliable Yellow Fever prevention. - This threshold may be acceptable for the Breteau Index (measured differently), but for the House Index, 1% is the standard. - At this level, there remains significant risk of transmission during favorable conditions. *Less than 10%* - An index of **less than 10%** is considered inadequate for prevention of Yellow Fever transmission. - This level carries a substantial risk of outbreaks, as the vector population remains high enough to support sustained transmission. - Urgent vector control interventions are needed at this level. *Less than 20%* - An **Aedes Aegypti index** of less than 20% indicates a high-risk environment for Yellow Fever transmission. - This level is far above the recommended threshold and suggests a critical need for immediate and aggressive vector control measures. - At this level, epidemic transmission is highly likely if the virus is introduced.

Question 665: What is the recommended amount of bleaching powder necessary to disinfect stools contaminated with cholera?

A. 50 gm/liter (Correct Answer)
B. 75 gm/liter
C. 90 gm/liter
D. 100 gm/liter

Explanation: ***50 gm/liter*** - For effective disinfection of stools contaminated with cholera, a concentration of **50 gm of bleaching powder per liter** of stool is recommended to ensure the destruction of **Vibrio cholerae**. - This concentration typically provides a sufficient amount of available **chlorine** to inactivate the bacteria within a reasonable contact time. *75 gm/liter* - While this concentration would certainly disinfect, it is **higher than necessary** for routine cholera stool disinfection and leads to inefficient resource use. - Using excess bleaching powder can also create a **stronger odor** and possibly increase the risk of skin or respiratory irritation. *90 gm/liter* - This concentration is **excessive** and not the standard recommendation for cholera stool disinfection. - Higher concentrations contribute to **waste of resources** and do not offer significantly improved efficacy over the recommended dose for this specific application. *100 gm/liter* - This concentration is significantly **higher than required** for effective disinfection of cholera-contaminated stools. - Using such a high amount is **economically inefficient** and offers no additional benefit in terms of disinfection for this specific pathogen and application.

Question 666: What is the significance of a 2-year post-treatment surveillance period in paucibacillary leprosy?

A. To monitor for treatment compliance during active therapy
B. To assess the effectiveness of multibacillary leprosy treatment protocols
C. To detect early signs of drug resistance in ongoing treatment
D. To identify relapses, reactions, and neurological complications after treatment completion (Correct Answer)

Explanation: ***To identify relapses, reactions, and neurological complications after treatment completion*** - The 2-year post-treatment surveillance period for **paucibacillary leprosy** is crucial for monitoring for **relapses** which can occur even after successful multidrug therapy (MDT). - It also allows for the early detection and management of **leprosy reactions** (e.g., Type 1 reversal reactions) and **neurological complications** such as nerve damage, which can develop or progress after treatment completion. *To monitor for treatment compliance during active therapy* - Monitoring for **treatment compliance** occurs *during* the active 6-month MDT period for paucibacillary leprosy, not primarily in the 2-year post-treatment surveillance phase. - While compliance is essential for successful treatment, the post-treatment period is focused on after-effects. *To assess the effectiveness of multibacillary leprosy treatment protocols* - This surveillance period is specifically for **paucibacillary leprosy**, which has a different treatment regimen and surveillance duration (6 months MDT followed by 2 years surveillance) compared to multibacillary leprosy (12 months MDT followed by 5 years surveillance). - The effectiveness of multibacillary treatment protocols would be assessed over a longer period following completion of its own specific MDT. *To detect early signs of drug resistance in ongoing treatment* - Detection of **drug resistance** is typically assessed *during* treatment if a patient is not responding clinically or shows signs of worsening, or in cases of relapse where drug resistance might be suspected as the cause. - While possible, the primary purpose of post-treatment surveillance is broader than just drug resistance; it encompasses all potential adverse long-term outcomes.

Question 667: What is the Chandler's Index for Hookworm that indicates a significant health problem?

A. > 200
B. > 100
C. > 300
D. > 50 (Correct Answer)

Explanation: ***> 50*** - A Chandler's Index of **> 50** indicates a significant public health problem due to **hookworm infection**. - **Chandler's Index** is calculated as the **average egg count per person in a community** (total hookworm eggs counted ÷ number of persons examined), used to assess the population-level burden of hookworm infection. - A value **> 50** suggests that the community has a significant hookworm problem requiring public health intervention. *> 300* - This value is significantly higher than the threshold for a significant public health problem and would indicate an **extremely severe burden of infection**. - While this represents a very high Chandler's Index, it's not the standard cut-off for defining a "significant" health problem (which is the lower threshold of >50). *> 200* - A Chandler's Index of **> 200** would denote a very high intensity of hookworm infection in the community. - However, this is not the standard threshold used to define when hookworm becomes a "significant" public health issue - the threshold is lower at >50. *> 100* - A Chandler's Index of **> 100** represents a substantial level of hookworm infection within a population. - However, the widely recognized cutoff for a "significant health problem" is **> 50**, indicating public health concern even at this moderate level of community infection burden.

Question 668: What is the osmolarity of the new Oral Rehydration Solution (ORS)?

A. 270
B. 245 (Correct Answer)
C. 290
D. 310

Explanation: ***245*** - The **new ORS (reduced osmolarity ORS)** has an osmolarity of **245 mOsmol/L**. - This reduced osmolarity formulation has been shown to be more effective in reducing stool output, vomiting, and duration of diarrhea compared to the standard ORS. *270* - While 270 mOsmol/L is closer to the target, it is not the exact osmolarity of the **new ORS formulation**. - The precise osmolarity of the new ORS is specifically designed for optimal water and electrolyte absorption. *290* - The **standard (or traditional) ORS** had an osmolarity of **310 mOsmol/L**, which is higher than 290 mOsmol/L. - An osmolarity of 290 mOsmol/L does not correspond to a recognized standard or new ORS formulation. *310* - The **standard (or traditional) ORS** formulation had an osmolarity of **310 mOsmol/L**. - The move to a new ORS with reduced osmolarity was to improve efficacy and reduce the risk of hypernatremia in some patients.

Question 669: Which of the following is the primary transmission route for Hepatitis E?

A. Contaminated water (Correct Answer)
B. Blood and bodily fluids
C. Airborne transmission
D. Vertical transmission (mother to child)

Explanation: ***Contaminated water*** - **Hepatitis E virus (HEV)** is primarily transmitted through the **fecal-oral route**, with contaminated drinking water being the most common vehicle. - This mode of transmission is particularly prevalent in regions with poor sanitation and hygiene, leading to **waterborne outbreaks**. - HEV is responsible for **epidemic hepatitis** in developing countries, especially during floods and monsoons. *Blood and bodily fluids* - This is the primary transmission route for other hepatitis viruses like **Hepatitis B** and **Hepatitis C**, but not for Hepatitis E. - While rare cases of **transfusion-transmitted HEV** have been reported in endemic areas, it is not the main mode of spread. *Vertical transmission (mother to child)* - Vertical transmission can occur but is **not the primary route** for HEV. - When it does occur in pregnant women (especially in third trimester), it can lead to **severe outcomes** including fulminant hepatitis with high mortality (15-25%). *Airborne transmission* - **Hepatitis E** is not an **airborne disease**; it is not spread through respiratory droplets or aerosols. - This route of transmission is associated with respiratory infections, not enteric viruses like HEV.

Question 670: Which of the following is not typically screened for in blood donations?

A. HIV
B. HBV
C. HCV
D. Epstein-Barr Virus (EBV) (Correct Answer)

Explanation: ***Epstein-Barr Virus (EBV)*** ✓ - EBV is **NOT routinely screened** for in blood donations in India and most countries - While EBV is a common virus (>90% adults are seropositive), it is **not considered a major transfusion-transmitted infection** - The virus is primarily transmitted through saliva; transfusion-associated EBV transmission is **extremely rare and usually not clinically significant** in immunocompetent recipients - Risk-benefit analysis does not support routine screening due to **high prevalence, low clinical impact, and cost considerations** - EBV screening may only be considered for specific recipients (e.g., severely immunocompromised patients) *HIV* - **Routinely screened** in all blood donations worldwide - Screening includes HIV-1 and HIV-2 antibodies and/or HIV antigen/RNA testing - Transfusion-transmitted HIV causes AIDS with severe consequences - Mandatory screening under the Drugs and Cosmetics Act in India *HBV* - **Routinely screened** in all blood donations - Screening includes HBsAg (Hepatitis B surface antigen) testing, and often anti-HBc or HBV DNA - Can cause acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma - Mandatory screening in India and globally *HCV* - **Routinely screened** in all blood donations - Screening includes anti-HCV antibodies and/or HCV RNA (nucleic acid testing) - Major cause of chronic hepatitis, cirrhosis, and liver cancer - Mandatory screening under blood safety regulations

Practice by Chapter

Communicable Disease Control Principles

Practice Questions

Vector-Borne Diseases

Practice Questions

Water-Borne Diseases

Practice Questions

Air-Borne Diseases

Practice Questions

Zoonotic Diseases

Practice Questions

Sexually Transmitted Infections

Practice Questions

HIV/AIDS Control Program

Practice Questions

Tuberculosis Control

Practice Questions

Leprosy Elimination

Practice Questions

Emerging and Re-emerging Infections

Practice Questions

Hospital-Acquired Infections

Practice Questions

Integrated Disease Surveillance Project

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free