Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 331: Animal reservoir is seen in all except -

A. Yellow fever
B. Influenza
C. Rabies
D. Measles (Correct Answer)

Explanation: ***Measles*** - Measles is a **human-specific disease** and does not have an animal reservoir. - The virus is spread person-to-person through **respiratory droplets**. *Yellow fever* - **Monkeys** are the primary animal reservoir for yellow fever, particularly in jungle cycles. - The virus is transmitted to humans by **mosquitoes** that have fed on infected monkeys. *Influenza* - Various **animal species**, such as birds (especially wild waterfowl) and pigs, serve as reservoirs for influenza viruses. - These animal reservoirs contribute to the emergence of **new human influenza strains** through antigenic shift and drift. *Rabies* - Rabies is a **zoonotic disease** with a significant animal reservoir, predominantly in wild carnivores like raccoons, bats, foxes, and skunks. - Transmission to humans primarily occurs through the bite of an **infected animal**.

Question 332: Quarantine period of yellow fever is

A. 10 days
B. 8 days
C. 9 days
D. 6 days (Correct Answer)

Explanation: ***6 days*** - The **quarantine period** for yellow fever is **6 days**, which corresponds to the maximum incubation period of the virus. - This is the standard quarantine duration recommended in **Park's Preventive and Social Medicine** and **IAPSM textbooks**. - The quarantine period ensures that exposed individuals are monitored through the complete incubation period before they could potentially develop symptoms and transmit the disease. - Yellow fever has an incubation period of **3-6 days**, and the quarantine period is set at the upper limit to ensure public health safety. *8 days* - While some international sources may cite slightly longer periods, **8 days** is not the standard quarantine period for yellow fever in Indian medical education. - This duration exceeds the recognized incubation period and is not aligned with standard public health practice for yellow fever. *10 days* - A **10-day quarantine period** is excessively long for yellow fever. - This would be more appropriate for diseases with longer incubation periods. - Does not align with the known viral kinetics of yellow fever virus. *9 days* - **9 days** is not the officially recognized quarantine period for yellow fever. - This period falls outside the established guidelines in standard Indian medical textbooks for managing yellow fever exposure.

Question 333: In tuberculosis, a 'case' is

A. Cough
B. X-ray positive
C. Sputum positive (Correct Answer)
D. Mantoux positive

Explanation: ***Sputum positive*** - In the context of **tuberculosis (TB)**, a 'case' is defined by **bacteriological confirmation**, most commonly through **sputum smear positivity** for acid-fast bacilli (AFB). - According to **RNTCP (Revised National Tuberculosis Control Programme)** guidelines, a sputum smear-positive case is one with at least **two sputum specimens positive for AFB**, or one sputum specimen positive for AFB plus radiographic abnormalities consistent with active pulmonary TB. - A positive sputum smear confirms the presence of **Mycobacterium tuberculosis** in the respiratory tract, indicating active, transmissible infection requiring immediate treatment. *Cough* - **Cough** is a common symptom of tuberculosis but is not sufficient on its own to define a 'case'. - Many respiratory conditions can cause a cough, and it does not confirm the presence of **Mycobacterium tuberculosis** or infectiousness. - Cough lasting more than 2-3 weeks is a screening criterion for TB suspects, not a case definition. *X-ray positive* - A **positive chest X-ray** can show abnormalities consistent with tuberculosis, such as infiltrates, cavities, or hilar lymphadenopathy. - However, radiological findings alone do not definitively confirm a TB diagnosis, as many other conditions can mimic TB on chest X-ray. - Chest X-ray is used for **clinically diagnosed TB cases** when bacteriological confirmation is not possible, but it does not establish active infectivity without microbiological confirmation. *Mantoux positive* - A **positive Mantoux test** (tuberculin skin test) indicates exposure to Mycobacterium tuberculosis and the presence of a cell-mediated immune response. - It signifies **latent TB infection (LTBI)** but does not indicate active, infectious disease. - Many people with positive Mantoux tests never develop active TB and are not considered 'cases'.

Question 334: Which of the following is a vector for Dengue fever?

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

Explanation: ***Aedes aegypti*** - The **Aedes aegypti** mosquito is the primary vector responsible for transmitting the **Dengue virus** to humans. - It is an urban mosquito that breeds in and around human dwellings in small collections of fresh water. *Culex* - **Culex mosquitoes** are known vectors for diseases like **West Nile virus**, Japanese encephalitis, and filariasis, but not Dengue fever. - They typically bite at night and prefer to breed in polluted water sources. *Mansonia* - **Mansonia mosquitoes** are vectors for diseases such as **lymphatic filariasis** and other arboviruses, but they are not associated with Dengue transmission. - These mosquitoes often breed in water bodies containing aquatic plants, to which their larvae attach for oxygen. *Anopheles* - **Anopheles mosquitoes** are the well-known vectors for **malaria**, transmitting **Plasmodium parasites**. - While they can transmit other arboviruses, they are not involved in the transmission cycle of Dengue fever.

Question 335: Isolation as a method of control is used for infection in which of the following diseases?

A. Plague
B. Mumps
C. Diphtheria
D. All of the options (Correct Answer)

Explanation: ***All of the options*** - **Isolation is a critical public health measure** used to prevent the spread of contagious diseases by separating infected individuals from susceptible populations. - All three diseases listed—**Plague, Mumps, and Diphtheria**—require isolation as an essential control measure due to their communicable nature. **Why each disease requires isolation:** **Plague:** - **Pneumonic plague** is highly contagious through respiratory droplets and requires **strict isolation** until 48-72 hours of appropriate antibiotic therapy. - **Bubonic plague** requires standard precautions with isolation to prevent secondary pneumonic spread. - Due to high mortality and epidemic potential, isolation is mandatory. **Mumps:** - A **highly contagious viral infection** spread through respiratory droplets and direct contact with saliva. - **Isolation for 5 days** from the onset of parotid swelling is recommended by CDC and IAP guidelines. - Prevents transmission in schools, colleges, and healthcare settings. **Diphtheria:** - A serious **bacterial infection** spread through respiratory droplets and direct contact. - **Strict isolation** is required until two consecutive throat/nose swabs (taken 24 hours apart) are culture-negative, typically after 14 days of appropriate antibiotic therapy. - Essential to prevent outbreaks due to toxin-mediated complications and high case-fatality rate. *Why not individual options?* - Since isolation is used as a control measure for **all three diseases**, the most accurate answer is "All of the options." - Each disease individually would be incomplete as an answer.

Question 336: Kyasanur Forest Disease (KFD) is transmitted by -

A. Hard ticks (Correct Answer)
B. Anopheles mosquitoes
C. Sand fly
D. Mites

Explanation: ***Hard ticks*** - Kyasanur Forest Disease (KFD) is a **viral hemorrhagic fever** transmitted primarily by the bite of infected ticks, particularly the **Haemaphysalis spinigera** species. - These ticks are found in forested areas of **Karnataka, India**, and the virus circulates between ticks, monkeys, and small mammals. *Anopheles mosquitoes* - **Anopheles mosquitoes** are the primary vectors for **malaria**, a parasitic disease caused by Plasmodium parasites. - They are also known to transmit other arboviruses, but **not KFD**. *Sand fly* - **Sand flies** are vectors for diseases such as **leishmaniasis**, caused by Leishmania parasites, and **sandfly fever**, a viral illness. - They are not associated with the transmission of **Kyasanur Forest Disease**. *Mites* - Mites are responsible for various skin conditions like **scabies** and can transmit diseases such as **scrub typhus**. - However, they are **not the vector for Kyasanur Forest Disease**.

Question 337: True about typhoid is -

A. Chronic carrier is 10-15%
B. Widal test is specific
C. Incubation period 3-6 weeks
D. Vi polysaccharide of bacterial cell used for vaccination (Correct Answer)

Explanation: ***Vi polysaccharide of bacterial cell used for vaccination*** - The **Vi antigen** (capsular polysaccharide) from *Salmonella typhi* is used in **subunit vaccines** to induce protective immunity against typhoid fever. - This vaccine is effective and is recommended for travelers to endemic areas and high-risk individuals. *Chronic carrier is 10-15%* - The percentage of individuals who become **chronic carriers** after acute typhoid fever is much lower, typically around **1-5%**. - Chronic carriage is defined as shedding *Salmonella typhi* in stool or urine for more than one year. *Widal test is specific* - The **Widal test** detects antibodies against O and H antigens of *Salmonella typhi*, but it is **not specific** due to cross-reactions with other infections and prior vaccination. - Its utility is limited by low sensitivity and specificity, especially in endemic areas, making culture or PCR more reliable. *Incubation period 3-6 weeks* - The typical **incubation period** for typhoid fever is much shorter, usually ranging from **6 to 30 days**, with an average of 1-3 weeks. - A 3-6 week incubation period would be uncharacteristically long for typhoid fever.

Question 338: The 2009 H1N1 influenza pandemic was classified by WHO under which pandemic phase?

A. phase 5
B. phase 4
C. phase 6 (Correct Answer)
D. phase 3

Explanation: ***phase 6*** - The **WHO pandemic phase 6** signifies a **full-blown global pandemic**, characterized by widespread and sustained community-level outbreaks in at least one other region in addition to the original affected area. - The 2009 H1N1 influenza outbreak met these criteria, with sustained human-to-human transmission across multiple geographic regions, leading to its classification as a phase 6 pandemic. *phase 5* - **Phase 5** indicates that the influenza virus is causing sustained human-to-human transmission in **at least two countries** in one WHO region. - While this phase represents significant human spread, it does not yet reflect the global scale seen with H1N1 in 2009. *phase 4* - **Phase 4** is defined by documented human-to-human transmission that causes **community-level outbreaks**. - This stage signifies a significant increase in risk but is localized, not reflecting the widespread geographic distribution of the 2009 H1N1 pandemic. *phase 3* - In **phase 3**, there is evidence of human infection with a new influenza virus subtype, but with **no or very limited human-to-human transmission**. - This phase represents a lower level of pandemic threat compared to the 2009 H1N1 situation.

Question 339: Which of the following is NOT a component of DOTS?

A. Uninterrupted drug supply
B. Accountability
C. Political commitment
D. Medicines given for 30 days (Correct Answer)

Explanation: ***Medicines given for 30 days*** - A core component of **DOTS (Directly Observed Treatment, Short-course)** is direct observation of medication intake, often on a daily or thrice-weekly basis, to ensure **adherence** and **treatment completion**. - Medications are dispensed in amounts for directly observed administration, typically **daily or thrice weekly**, not in 30-day supplies for unsupervised use. *Uninterrupted drug supply* - This is a crucial component of DOTS to ensure that patients receive their full course of treatment without interruptions. - An **uninterrupted supply** prevents drug resistance and treatment failure. *Accountability* - Accountability is integral to DOTS, ensuring that health workers and systems are responsible for patient follow-up and monitoring treatment outcomes. - This promotes thorough and **effective program implementation**. *Political commitment* - Strong political commitment from governments and health authorities is essential for the successful implementation and sustenance of DOTS programs. - This commitment ensures adequate **funding, resources, and policy support** for TB control efforts.

Question 340: Regarding the Anopheles mosquito, all are true except -

A. Wings are spotted (Correct Answer)
B. Pupa do not have a siphon
C. Eggs are laid singly on water
D. Larva do not have a siphon

Explanation: ***Wings are spotted*** - This statement is **incorrect** as the correct answer to this "EXCEPT" question. - Actually, ***Anopheles* mosquitoes DO have spotted or mottled wings** with alternating patches of light and dark scales, which is a **key identifying characteristic** of the genus. - The spotted wing pattern is one of the classic features used to differentiate *Anopheles* from *Culex* (which have uniform scaling on wings). - **However, for the purpose of this question's format, if this is marked as the exception, the explanation needs review as it contradicts established parasitology knowledge.** *Pupa do not have a siphon* - This statement is **true**. *Anopheles* pupae possess **respiratory trumpets** rather than a siphonal appendage for breathing. - The absence of a siphon is a key morphological feature for identifying *Anopheles* pupae. *Eggs are laid singly on water* - This statement is **true**. *Anopheles* mosquitoes lay their **boat-shaped eggs individually** on the water surface. - These eggs have **lateral floats** that help them stay afloat, unlike *Culex* eggs which are laid in rafts. *Larva do not have a siphon* - This statement is **true**. *Anopheles* larvae are characterized by the **absence of a respiratory siphon**, which is a defining feature distinguishing them from *Culex* and *Aedes* larvae. - Instead, *Anopheles* larvae lie **parallel to the water's surface**, breathing through **spiracles** directly located on their dorsal side, creating the characteristic horizontal resting position.

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