Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 671: Schistosomiasis is transmitted by?

A. Fish
B. Snail (Correct Answer)
C. Cattle
D. Cyclops

Explanation: ***Snail*** - **Snails** act as the **intermediate host** for all species of Schistosoma, where the parasite undergoes asexual reproduction. - Humans become infected when they come into contact with water contaminated with **cercariae**, which are released from infected snails. *Cyclops* - **Cyclops** (a type of freshwater crustacean) are the intermediate hosts for parasites like **Dracunculus medinensis** (guinea worm) and **Diphyllobothrium latum** (fish tapeworm). - They are not involved in the life cycle or transmission of Schistosoma. *Fish* - Various fish can be intermediate hosts for parasites such as **Clonorchis sinensis** (Chinese liver fluke) or **Diphyllobothrium latum**. - Fish do not play a role in the transmission of schistosomiasis. *Cattle* - **Cattle** can serve as definitive hosts for certain parasites, such as **Taenia saginata** (beef tapeworm), where the larval stage (cysticerci) is found in their muscle tissue. - They are not involved in the life cycle or transmission of Schistosoma.

Question 672: 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 673: Which of the following diseases does not have a chronic carrier state?

A. Malaria
B. Tetanus (Correct Answer)
C. Measles
D. Poliomyelitis

Explanation: ***Tetanus*** - Tetanus is caused by the toxin produced by *Clostridium tetani*, which is an **environmental bacterium** found in soil and does not establish a persistent infection within humans. - Humans are merely **accidental hosts** for this bacterium, meaning there is **no chronic carrier state** where an infected individual continuously harbors and transmits the pathogen. - The disease occurs through wound contamination with spores, not human-to-human transmission. *Measles* - Measles is an **acute viral infection** with no chronic carrier state in the classical sense. - After acute infection, the virus is cleared from the body in immunocompetent individuals. - While **subacute sclerosing panencephalitis (SSPE)** represents a rare persistent infection, this is **not a carrier state** as the virus is not transmissible from these individuals. - SSPE occurs years after initial infection but does not involve viral shedding or transmission. *Malaria* - Individuals infected with ***Plasmodium* parasites** can develop a **chronic carrier state**, particularly with *P. vivax* and *P. ovale*, which form hypnozoites in the liver. - These parasites can remain dormant and then reactivate, causing **relapses** and allowing for continued transmission to mosquitoes over extended periods. - Chronic asymptomatic carriers can serve as reservoirs for transmission in endemic areas. *Poliomyelitis* - Individuals infected with poliovirus can shed the virus in their stools for **several weeks to months** after infection. - In **immunodeficient individuals**, prolonged excretion can occur for years, creating chronic carriers. - This prolonged shedding allows for the **continued transmission** of the virus within a population.

Question 674: Which of the following diseases have incubation period <10 days?

A. Influenza
B. Plague
C. Cholera
D. All of the options (Correct Answer)

Explanation: ***All of the options*** - Cholera, Influenza, and Plague all have incubation periods less than 10 days. **Cholera** - Incubation period: Few hours to 5 days (commonly 2-3 days) - This rapid onset is due to the quick replication of *Vibrio cholerae* and toxin production in the intestinal tract - The short incubation period contributes to explosive outbreaks in endemic areas **Influenza** - Incubation period: 1-4 days (average 2 days) - This short period contributes to its high transmissibility during seasonal outbreaks - Patients can be infectious before symptom onset **Plague** - Bubonic plague: 2-6 days incubation - Pneumonic plague: 1-3 days (even shorter, facilitating rapid progression) - The short incubation period, especially for pneumonic form, makes plague a serious public health concern All three diseases qualify as having incubation periods under 10 days, making "All of the options" the correct answer.

Question 675: A 5-year-old child presented with fever, fatigue, abdominal pain, and vomiting. On further history evaluation, he had a habit of eating dog feces. Investigations show visceral larva migrans. Which animal is the most likely source of this infection in this child?

A. Pig
B. Monkeys
C. Cows
D. Dogs (Correct Answer)

Explanation: ***Dogs*** - The history of eating **dog feces** directly links to the transmission of **Toxocara canis** eggs, the primary cause of visceral larva migrans. - Humans, especially children, can get infected by ingesting infective eggs from contaminated soil or dog feces. *Pig* - While pigs can harbor parasites like **Taenia solium** (pork tapeworm) and **Trichinella spiralis**, these do not typically cause visceral larva migrans. - Transmission from pigs usually involves consumption of undercooked pork, not direct contact with feces in the context of visceral larva migrans. *Monkeys* - Monkeys are not a common source of parasites causing human visceral larva migrans. - Parasitic infections associated with monkeys in humans are generally rare and usually specific to certain geographical contexts or exotic pet exposure. *Cows* - Cows can be hosts for parasites such as **Taenia saginata** (beef tapeworm), but they are not associated with visceral larva migrans caused by *Toxocara* species. - Ingestion of raw or undercooked beef is the typical mode of transmission for cow-related parasitic infections.

Question 676: What is the purpose of 'ring vaccination' in disease control?

A. A strategy to create lesions for disease identification.
B. Vaccination administered within a specific radius around a confirmed case. (Correct Answer)
C. Vaccination given to all individuals in a one-mile radius of a case.
D. A mass vaccination campaign targeting the entire population of a region.

Explanation: ***Vaccination administered within a specific radius around a confirmed case.*** - **Ring vaccination** is a targeted disease control strategy that focuses on immunizing individuals who are *most likely to be infected* due to direct or indirect contact with a confirmed case. - This strategy creates a **"ring" of immunized individuals** around the infected person, forming a protective barrier to prevent further disease transmission. - Commonly used for diseases like **smallpox** (historical eradication) and **Ebola outbreaks**, where rapid containment is critical. *A strategy to create lesions for disease identification.* - Ring vaccination is a **preventive immunization strategy**, not a diagnostic method. - Lesions are symptoms of infection, not artificially created for disease identification purposes. *Vaccination given to all individuals in a one-mile radius of a case.* - While ring vaccination does involve proximity-based targeting, the **"one-mile radius" is too specific and inflexible**. - The actual radius is determined by **disease transmissibility, contact tracing results, and population density**, not a fixed distance. *A mass vaccination campaign targeting the entire population of a region.* - Ring vaccination is a **targeted, focused strategy**, not a mass campaign. - Mass vaccination campaigns aim for broad population coverage, whereas ring vaccination specifically targets **contacts and contacts of contacts** around known cases for rapid containment.

Question 677: What is the recommended number of openings per square inch for a standard mosquito net to ensure effective mosquito control?

A. 150 openings (Correct Answer)
B. 100 openings
C. 250 openings
D. 175 openings

Explanation: ***150 openings*** - A minimum of **150-156 openings per square inch** is the **WHO-recommended standard** for mosquito nets to effectively prevent mosquito penetration while maintaining adequate ventilation. - This mesh size corresponds to approximately **1.2-1.5 mm** aperture, which blocks all medically important mosquito species including *Anopheles*, *Aedes*, and *Culex*. - This specification is fine enough to provide reliable protection against vector-borne diseases like malaria, dengue, and filariasis. *100 openings* - This mesh size is **too coarse** and would allow smaller mosquitoes to pass through, significantly reducing the net's effectiveness. - It does not meet public health standards and would not provide adequate protection against disease-transmitting mosquito species. *175 openings* - While this would provide effective mosquito exclusion, it is **not the standard recommendation** and represents an unnecessarily fine mesh. - The additional fineness provides minimal benefit over the standard 150-156 openings while potentially reducing airflow slightly. *250 openings* - This mesh is **excessively fine** and significantly **reduces airflow and ventilation**, making the net uncomfortable for users, especially in hot, humid climates. - The very fine mesh accumulates dust and debris more rapidly, requiring frequent cleaning without providing meaningful additional protection over the standard mesh size. - Poor ventilation may reduce user compliance and acceptance of bed net use.

Question 678: Which of the following infectious diseases has the LEAST structured WHO surveillance system?

A. Malaria
B. Relapsing fever (Correct Answer)
C. Polio
D. Viral encephalitis

Explanation: ***Relapsing fever*** - **Relapsing fever** caused by *Borrelia* species, often lacks a dedicated, highly structured global surveillance system compared to other diseases due to its more sporadic and localized outbreaks in many regions. - While it is a reportable disease in some areas, the **WHO's efforts are not as extensively coordinated or funded globally** as for diseases targeted for eradication or high-priority control. *Polio* - The **Global Polio Eradication Initiative (GPEI)**, led by WHO, maintains one of the most comprehensive and structured surveillance systems worldwide, with active case finding and laboratory confirmation. - This system includes robust environmental surveillance and aims for **zero cases** globally, requiring meticulous data collection and reporting. *Malaria* - WHO maintains a highly structured and extensive global surveillance system for **malaria**, particularly through its **Global Malaria Programme**, which focuses on controlling and eventually eradicating the disease. - Surveillance includes tracking case incidence, analyzing drug resistance, monitoring vector populations, and evaluating intervention effectiveness in **endemic regions**. *Viral encephalitis* - **Viral encephalitis** is a group of diseases with various etiologies, and while not all forms have individual structured global surveillance, severe forms like **Japanese encephalitis** and **West Nile virus** are under significant surveillance by WHO and national health agencies. - Surveillance often involves tracking outbreaks, identifying causal agents, and monitoring for emerging threats due to its potential for **epidemics** and severe neurological outcomes.

Question 679: Which of the following is not a vector-borne disease?

A. KFD
B. JE
C. Brucella (Correct Answer)
D. Plague

Explanation: ***Brucella*** - **Brucellosis** is primarily transmitted through the consumption of infected, unpasteurized dairy products or direct contact with infected animal tissues, making it a **food-borne** or **contact-borne** disease, not vector-borne. - The bacteria can also be acquired through inhalation of aerosols in occupational settings, but a biological vector is not involved in its transmission to humans. *KFD* - **Kyasanur Forest Disease** (KFD) is a **tick-borne viral hemorrhagic fever** endemic to India. - It is transmitted to humans through the bite of infected ticks, making it a classic example of a **vector-borne disease**. *JE* - **Japanese Encephalitis** (JE) is a **mosquito-borne flaviviral infection** and is the most important cause of viral encephalitis in Asia. - It is transmitted by **Culex mosquitoes**, particularly *Culex tritaeniorhynchus*, confirming its vector-borne nature. *Plague* - **Plague** is a severe bacterial infection caused by *Yersinia pestis*, primarily transmitted to humans through the bites of **infected fleas** (a type of vector). - These fleas often carry the bacteria from infected rodents, making it a definitive **vector-borne disease**.

Question 680: Polio is transmitted by:

A. Blood
B. Skin contact
C. Inhalational
D. Fecal-oral (Correct Answer)

Explanation: **Fecal-oral** - **Polioviruses** are transmitted primarily through the ingestion of material contaminated with the feces of an infected person. - This route facilitates the virus's entry into the **gastrointestinal tract**, where it replicates and can then spread. - This is the **primary mode of transmission**, especially in areas with poor sanitation and hygiene. *Blood* - While it's theoretically possible for polio to be transmitted via blood transfusions if a donor is acutely viremic, it is **not a primary or common route** of transmission. - Bloodborne transmission is **not the main mechanism** for the spread of polio in populations. *Skin contact* - **Direct skin contact** does not typically facilitate the transmission of poliovirus. - Poliovirus requires entry into the body via the **mucous membranes**, primarily the mouth, which is not achieved through simple skin contact. *Inhalational* - **Inhalational transmission** through respiratory droplets or aerosols is not the primary mode of poliovirus spread. - While some viruses can spread this way, polio's primary entry point is the **gastrointestinal system** via the fecal-oral route.

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HIV/AIDS Control Program

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Emerging and Re-emerging Infections

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