Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 341: Influenza pandemics are most commonly caused by-

A. Influenza-A (Correct Answer)
B. Influenza-C
C. Influenza-D
D. Influenza-B

Explanation: ***Influenza-A*** - **Influenza A viruses** are responsible for causing **all known influenza pandemics** due to their ability to undergo **antigenic shift**. - Antigenic shift involves major genetic reassortment, particularly in the hemagglutinin (H) and neuraminidase (N) surface proteins, allowing the virus to evade host immunity and cause widespread infection. - Historical pandemics (1918 Spanish flu, 1957 Asian flu, 1968 Hong Kong flu, 2009 H1N1) were all caused by Influenza A. *Influenza-C* - **Influenza C viruses** are generally associated with **mild, self-limiting respiratory illnesses** and do not typically cause epidemics or pandemics. - The genome of Influenza C viruses is less prone to the significant genetic changes necessary to cause pandemics. *Influenza-D* - **Influenza D viruses** primarily infect **cattle and other livestock** and have not been shown to cause human infections. - They are not associated with human epidemics or pandemics. *Influenza-B* - While **Influenza B viruses** can cause seasonal epidemics, they do not undergo **antigenic shift** to the same extent as Influenza A. - Influenza B viruses only circulate in humans and lack the animal reservoir necessary for major reassortment events. - This limited genetic variability means they are **not typically associated with pandemics**.

Question 342: Transmission assessment survey is for?

A. Plasmodium falciparum
B. Plasmodium vivax
C. Leishmania donovani
D. Wuchereria bancrofti (Correct Answer)

Explanation: ***Wuchereria bancrofti*** - The **Transmission Assessment Survey (TAS)** is explicitly designed by the World Health Organization (WHO) to determine if **lymphatic filariasis (LF)**, primarily caused by *Wuchereria bancrofti*, has been successfully eliminated as a public health problem. - It uses specific thresholds of **microfilaria prevalence** in endemic areas to decide when mass drug administration (MDA) can be stopped. *Plasmodium falciparum* - This parasite causes **falciparum malaria**, and its transmission is assessed through methods like **malaria indicator surveys (MIS)**, entomological surveys, and case detection rates, not TAS. - The goal for *Plasmodium falciparum* is **malaria control** and elimination, but it doesn't utilize the TAS methodology. *Plasmodium vivax* - This parasite causes **vivax malaria**, similarly assessed by malaria-specific surveys and surveillance, including **passive and active case detection**, not a TAS for lymphatic filariasis. - While efforts are made for *Plasmodium vivax* elimination, it requires different diagnostic and surveillance strategies due to its hypnozoite stage. *Leishmania donovani* - This parasite is responsible for **visceral leishmaniasis (kala-azar)**, and its transmission is monitored through surveillance of human cases, vector control assessment, and serological surveys. - The elimination program for **kala-azar** in endemic areas uses **different indicators and survey methods** than the TAS for lymphatic filariasis.

Question 343: Vector for dengue fever is:

A. Culex
B. Female Anopheles
C. Male Anopheles
D. Aedes (Correct Answer)

Explanation: ***Aedes*** - The **Aedes aegypti** and **Aedes albopictus** mosquitoes are the primary vectors for the dengue virus. - These mosquitoes are typically **day-biting** and thrive in urban and semi-urban environments. *Culex* - **Culex mosquitoes** are known vectors for diseases such as **West Nile virus**, **Japanese encephalitis**, and **filariasis**. - They generally bite during **dusk and dawn**, and in the evening, unlike Aedes. *Female Anopheles* - The **female Anopheles mosquito** is the exclusive vector for **malaria** parasites. - They are primarily active during **nighttime hours**, differing from the typical biting habits of dengue vectors. *Male Anopheles* - **Male mosquitoes**, including male Anopheles, do **not bite humans** or transmit diseases. - They feed exclusively on **nectar and plant sap**, not blood.

Question 344: Lowest incidence of trachoma is seen in:

A. Odisha
B. Uttar Pradesh
C. Punjab (Correct Answer)
D. Rajasthan

Explanation: ***Punjab*** - Punjab is identified as having the **lowest incidence of trachoma** among the listed Indian states. This is attributed to better sanitation, living conditions, and access to healthcare. - The disease is primarily linked to **poor hygiene** and **lack of clean water**, which are less prevalent issues in Punjab compared to other regions. *Odisha* - Odisha has historically reported **higher rates of trachoma** due to environmental factors and socioeconomic conditions conducive to its spread. - Areas with limited access to **clean water** and sanitation often see a greater burden of infectious diseases like trachoma. *Uttar Pradesh* - Uttar Pradesh is a large state with significant rural populations where **trachoma has been endemic** in many districts. - Challenges like **population density** and variable access to health services contribute to sustained incidence of the disease. *Rajasthan* - Rajasthan is known for its arid climate and often faces issues with **water scarcity**, which can exacerbate hygiene problems leading to higher trachoma rates. - Some districts in Rajasthan have been identified as **highly endemic** for trachoma due to environmental and social factors.

Question 345: Bird-Arthropod-Man transmission is seen in

A. Paragonimus westermani
B. Plague
C. Plasmodium falciparum
D. Japanese encephalitis (Correct Answer)

Explanation: ***Japanese encephalitis*** - Japanese encephalitis virus typically cycles between **birds** (especially wading birds like herons) and **mosquitoes** (mainly *Culex* species), with humans and pigs being dead-end hosts. - The mosquito acts as the **arthropod vector** transmitting the virus from infected birds to humans. *Paragonimus westermani* - This is a **lung fluke** with a complex life cycle involving snails and crustaceans as intermediate hosts, and humans or carnivorous mammals as definitive hosts. - It does not involve a **bird-arthropod-man** transmission cycle. *Plague* - Plague is caused by the bacterium *Yersinia pestis* and is primarily transmitted by **fleas** (arthropods) from **rodents** (mammals) to humans. - While it involves arthropods and humans, birds are not part of its primary transmission cycle. *Plasmodium falciparum* - *Plasmodium falciparum* causes **malaria** and is transmitted between humans by **Anopheles mosquitos** (arthropods). - This transmission cycle is typically **human-mosquito-human**, with birds not being involved in the transmission to humans.

Question 346: The best approach to prevent cholera epidemic in a community is:

A. Health education
B. Mass chemoprophylaxis with tetracycline
C. Vaccination of all individuals
D. Safe water and sanitation (Correct Answer)

Explanation: ***Safe water and sanitation*** - Cholera is primarily transmitted through **fecally contaminated water** and food sources. Ensuring access to **safe drinking water** and proper **sanitation facilities** (e.g., latrines, waste management) is the most effective and sustainable way to break the chain of transmission. - These measures prevent the spread of the *Vibrio cholerae* bacteria in the environment, thereby stopping new infections and preventing large-scale outbreaks. *Health education* - While important for promoting good hygiene practices like handwashing and safe food preparation, **health education alone** is often insufficient to control a widespread cholera epidemic without concomitant improvements in infrastructure. - It may improve individual behaviors but does not address the fundamental environmental contamination that drives large outbreaks. *Mass chemoprophylaxis with tetracycline* - Administering antibiotics like **tetracycline** to entire communities is not a sustainable or practical strategy for epidemic prevention. - It can lead to **antibiotic resistance**, has limited effectiveness in preventing widespread transmission, and carries potential side effects. *Vaccination of all individuals* - **Oral cholera vaccines** are effective and can be used in conjunction with other measures, especially during outbreaks or in high-risk areas. - However, achieving **universal vaccination** quickly enough to prevent an ongoing epidemic can be challenging due to logistical hurdles, cost, and vaccine availability, making it less immediate and comprehensive than addressing water and sanitation.

Question 347: Most common source of diphtheria transmission is:

A. Both carriers and cases
B. Case
C. Carrier (Correct Answer)
D. None of the options

Explanation: ***Carrier*** - **Asymptomatic carriers** can harbor and shed *Corynebacterium diphtheriae* for extended periods, making them a significant reservoir. - They often remain undetected, thus facilitating the **silent spread** of the infection within a community. *Both carriers and cases* - While both contribute to transmission, **carriers** are often considered the most common source due to their asymptomatic nature and prolonged shedding, unlike acute cases who are usually identified and isolated. - This option is partially true, but **carriers** are particularly effective at sustaining endemic transmission. *Case* - **Diphtheria cases** do transmit the disease, but they are typically symptomatic, leading to quicker diagnosis and isolation, which limits their overall contribution to widespread transmission compared to unnoticed carriers. - Their period of infectivity is generally shorter than that of chronic carriers. *None of the options* - This option is incorrect as there are clear sources of diphtheria transmission. - **Carriers** specifically play a well-documented and crucial role in the epidemiology of diphtheria.

Question 348: Best method of preventing transmission of MRSA infection is

A. Hand wash (Correct Answer)
B. Disinfecting surfaces
C. Fumigation of the ward
D. Antibiotics

Explanation: ***Hand wash*** - **Hand hygiene**, particularly **vigorous hand washing** with soap and water or using alcohol-based hand rubs, is the single most effective measure to prevent the transmission of **MRSA** in healthcare settings. - This removes transient flora, including **MRSA**, from the skin, preventing its spread from patient to patient or from contaminated surfaces to patients. *Disinfecting surfaces* - While important for reducing environmental contamination, **surface disinfection** alone is insufficient to prevent **MRSA transmission** if hand hygiene is not consistently performed. - **MRSA can persist on surfaces**, but direct contact with healthcare worker hands is the primary route of transmission to patients. *Fumigation of the ward* - **Fumigation** is generally not a recommended or effective routine method for preventing the transmission of common healthcare-associated infections like **MRSA**. - It is often reserved for specific highly contagious pathogens or terminal disinfection in certain circumstances, and its efficacy for **MRSA** is limited compared to hand hygiene. *Antibiotics* - **Antibiotics** are used to treat **MRSA infections**, but they do not prevent its transmission, and their widespread or prophylactic use can even contribute to **antibiotic resistance**. - The focus for prevention is on infection control practices, not medical therapy.

Question 349: Under National Vector Borne Diseases Control Programme, operational efficiency of antimalarial measures is assessed by:

A. Infant parasite rate
B. Slide positivity rate
C. Annual Parasite Incidence (Correct Answer)
D. Annual Blood Examination Rate

Explanation: ***Annual Parasite Incidence*** - **Annual Parasite Incidence (API)** is a key indicator for assessing the operational efficiency of malaria control measures as it measures the **number of confirmed malaria cases per 1,000 population per year**. - A decrease in API over time suggests that antimalarial measures are effectively reducing the incidence of malaria in the population. *Infant parasite rate* - The **infant parasite rate** specifically focuses on malaria infection prevalence in infants, often reflecting recent transmission. - While important for understanding ongoing transmission, it may not reflect the overall operational efficiency of all antimalarial measures across all age groups. *Slide positivity rate* - The **slide positivity rate (SPR)** indicates the proportion of blood smears examined that are positive for malaria parasites. - SPR reflects the intensity of transmission and diagnostic efficiency, but a high SPR could also indicate poor case detection or treatment, making it less direct for assessing operational efficiency of control over a population. *Annual Blood Examination Rate* - The **Annual Blood Examination Rate (ABER)** indicates the proportion of the population whose blood is examined for malaria parasites within a year. - ABER reflects surveillance efforts and case detection, but a high ABER without a corresponding decrease in malaria cases does not necessarily signify efficient control measures for reducing disease burden.

Question 350: The arthropod vector BEST KNOWN for transovarian transmission of multiple pathogens is -

A. Fleas
B. Ticks (Correct Answer)
C. Sandfly
D. Mosquitoes

Explanation: ***Ticks*** - Ticks are well-known for their diverse modes of pathogen transmission, including **transovarian transmission**, where pathogens are passed from an infected female tick to her offspring through the eggs. - This mechanism is crucial for the maintenance and spread of several tick-borne diseases, such as **Rocky Mountain spotted fever (caused by *Rickettsia rickettsii*)** and **Babesiosis** (caused by *Babesia* species). *Fleas* - Fleas are primarily known for transmitting pathogens such as *Yersinia pestis* (causing **plague**) and *Rickettsia typhi* (causing **murine typhus**) through their bites, but transovarian transmission is not their primary mode. - They typically transmit pathogens through **regurgitation** during feeding or by their **feces** being rubbed into the bite wound. *Sandfly* - Sandflies are vectors for diseases like **leishmaniasis**, caused by parasitic protozoa of the genus *Leishmania*. - They transmit these pathogens through **saliva** during blood meals, but transovarian transmission is not a significant feature of their lifecycle. *Mosquitoes* - Mosquitoes are vectors for a wide range of diseases, including **malaria**, **dengue**, **Zika**, and **West Nile virus**, primarily through the **injection of saliva** during blood feeding. - While some arboviruses can exhibit transovarian transmission in mosquitoes, it is not as prominent or broadly impactful across multiple pathogens as it is in ticks.

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