Infectious Diseases — MCQs
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STDs are transmitted by
As per ICMR guidelines, which of the following are the criteria for SARS-COV-2 exposure for a pregnant female during the COVID-19 pandemic? 1. Travel to an affected country within previous 14 days 2. Close contact with a confirmed case within a distance of 1 metre for more than 15 minutes 3. Residing in a containment zone 4. Healthcare workers examining a confirmed case without adequate protection
Which one of the following mosquitoes is responsible for transmitting Japanese encephalitis?
Which of the following diseases has man as an incidental host with ‘Pig → Mosquito → Pig’ as the basic cycle of transmission?
What is the most important test to assess the prevalence of tuberculosis infection in a community?
What is the window period for HIV infection?
With reference to dengue virus, consider the following statements: 1. In India, all the four serotypes are found. 2. The reservoir of infection is both man and mosquito. 3. Adults usually have a milder disease than children. 4. Dengue hemorrhagic fever is caused by infection with more than one dengue virus. Which of the statements given above is/are correct?
Match List I with List II and select the correct answer using the codes given below the lists:
Which of the following statements is true about hydatid disease?
Consider the following features of food poisoning: 'Incubation period less than 24 hours, source of infection is milk products, and symptoms include diarrhoea and vomiting.' To which of the following does the above description apply? 1. Staphylococcal food poisoning 2. Salmonella food poisoning 3. Botulism Select the correct answer using the code given below:
Infectious Diseases Indian Medical PG Practice Questions and MCQs
Question 221: STDs are transmitted by
- A. Contact with soil
- B. Droplet infection
- C. Vector borne
- D. Direct contact (Correct Answer)
Explanation: ***Direct contact*** - **Sexually Transmitted Diseases (STDs)** are primarily spread through direct physical contact, most commonly during **sexual activity** (vaginal, anal, or oral sex). - This mode of transmission allows for the exchange of infected bodily fluids or skin-to-skin contact, leading to the spread of pathogens like bacteria, viruses, or parasites. *Contact with soil* - Diseases transmitted through contact with soil, such as **tetanus** or **hookworm infections**, typically involve pathogens that reside in the soil. - This is not a primary mode of transmission for common STDs. *Droplet infection* - **Droplet infection** involves the transmission of pathogens through respiratory droplets expelled during coughing, sneezing, or talking, like in **influenza** or **tuberculosis**. - STDs are generally not aerosolized and do not spread through this route. *Vector borne* - **Vector-borne diseases** are transmitted by an intermediate organism, often an insect (e.g., **mosquitoes** for malaria, **ticks** for Lyme disease). - STDs do not rely on vectors for transmission between human hosts.
Question 222: As per ICMR guidelines, which of the following are the criteria for SARS-COV-2 exposure for a pregnant female during the COVID-19 pandemic? 1. Travel to an affected country within previous 14 days 2. Close contact with a confirmed case within a distance of 1 metre for more than 15 minutes 3. Residing in a containment zone 4. Healthcare workers examining a confirmed case without adequate protection
- A. 1, 2 and 3
- B. 1, 2 and 4 (Correct Answer)
- C. 1, 3 and 4
- D. 2, 3 and 4
Explanation: ***1, 2 and 4*** - As per **ICMR guidelines for COVID-19 exposure assessment**, the criteria for direct SARS-CoV-2 exposure included: - **Travel to an affected country** within the previous 14 days (epidemiological link) - **Close contact with a confirmed case** (within 1 meter for more than 15 minutes without adequate protection) - **Healthcare workers examining confirmed cases** without adequate personal protective equipment - These represent **direct exposure pathways** requiring immediate testing and quarantine protocols for pregnant women. *1, 2 and 3* - While travel history and close contact are valid direct exposure criteria, **residing in a containment zone** represents an **area-based epidemiological risk factor** rather than a direct exposure event. - Containment zone residence warranted enhanced surveillance but did not constitute direct exposure unless accompanied by specific contact history or symptoms. - This option incorrectly omits criterion 4 (healthcare workers without protection), which was a critical direct occupational exposure pathway. *1, 3 and 4* - This option incorrectly includes containment zone residence while **omitting close contact with a confirmed case** (criterion 2). - Close contact was the **most common and direct mode of transmission**, making it a fundamental exposure criterion that cannot be excluded. - The distinction between area-based risk (containment zone) and person-to-person exposure (close contact) was operationally important for triage and testing priorities. *2, 3 and 4* - This option omits **travel to an affected country**, which was crucial especially in the **early pandemic phases** when imported cases were a primary concern. - Travel history was an essential screening criterion for all individuals, including pregnant women, requiring mandatory testing and quarantine. - Again, this incorrectly elevates containment zone residence to a direct exposure criterion equivalent to documented close contact or occupational exposure.
Question 223: Which one of the following mosquitoes is responsible for transmitting Japanese encephalitis?
- A. Aedes aegypti
- B. Anopheles stephensi
- C. Culex tritaeniorhynchus (Correct Answer)
- D. Mansonia
Explanation: ***Culex tritaeniorhynchus*** - This mosquito species is the **primary vector** for **Japanese encephalitis virus (JEV)** transmission in many endemic regions of Asia. - It typically breeds in **rice paddies** and other agricultural water sources, allowing for efficient transmission within populations. *Aedes aegypti* - This mosquito is the main vector for **Dengue**, **Chikungunya**, and **Zika** viruses. - It is not a significant vector for Japanese encephalitis. *Anopheles stephensi* - This mosquito is a major vector for **malaria**, particularly in urban areas of India. - It primarily transmits **Plasmodium parasites** and is not associated with Japanese encephalitis. *Mansonia* - Mosquitoes of the *Mansonia* genus are known vectors for **lymphatic filariasis** and some arboviruses. - They are not considered primary vectors for Japanese encephalitis.
Question 224: Which of the following diseases has man as an incidental host with ‘Pig → Mosquito → Pig’ as the basic cycle of transmission?
- A. Japanese encephalitis (Correct Answer)
- B. Handigodu syndrome
- C. Chikungunya
- D. Kyasanur forest disease
Explanation: ***Japanese encephalitis*** - **Japanese encephalitis** is a viral disease where humans are incidental dead-end hosts. - The established transmission cycle involves **pigs as amplifying hosts** and mosquitoes (primarily *Culex tritaeniorhynchus*) as vectors, which then infect other pigs, maintaining the "Pig → Mosquito → Pig" cycle. - Water birds serve as natural reservoir hosts, while pigs amplify the virus. *Handigodu syndrome* - **Handigodu disease** is another name for **Kyasanur Forest Disease (KFD)** or a related viral hemorrhagic fever from the same region in Karnataka, India. - It is a tick-borne viral disease, not mosquito-borne, with monkeys and small mammals as reservoir hosts. - There is no "Pig → Mosquito → Pig" transmission cycle involved. *Chikungunya* - **Chikungunya** is a viral disease transmitted primarily by *Aedes aegypti* and *Aedes albopictus* mosquitoes, with humans being the primary reservoir hosts. - The transmission cycle is "Human → Mosquito → Human," not involving pigs as amplifying hosts. *Kyasanur forest disease* - **Kyasanur forest disease (KFD)** is a viral hemorrhagic fever transmitted by *Haemaphysalis* ticks, with monkeys and small mammals serving as reservoir hosts. - The transmission cycle involves ticks and forest animals, not pigs and mosquitoes, and humans are incidental hosts.
Question 225: What is the most important test to assess the prevalence of tuberculosis infection in a community?
- A. Mass miniature radiography
- B. Tuberculin test (Correct Answer)
- C. Sputum examination of AFB
- D. Clinical examination
Explanation: ***Tuberculin test*** - The **tuberculin skin test (TST)**, or Mantoux test, measures the delayed-type hypersensitivity reaction to tuberculin, indicating prior exposure to *Mycobacterium tuberculosis*. - A positive TST reflects **tuberculosis infection**, whether latent or active, making it a valuable tool for assessing prevalence in a community. *Mass miniature radiography* - This method, now largely replaced by digital radiography, primarily detects **active pulmonary tuberculosis** by identifying lung lesions like infiltrates or cavities. - It is less effective for detecting **latent tuberculosis infection (LTBI)**, which represents the majority of infected individuals in a community. *Sputum examination of AFB* - This test is crucial for diagnosing **active pulmonary tuberculosis** by identifying acid-fast bacilli (AFB) in sputum. - However, it only detects individuals who are actively shedding bacteria and may not capture the broader prevalence of **latent infection** in a community. *Clinical examination* - A clinical examination primarily identifies individuals with **symptoms of active tuberculosis**, such as persistent cough, fever, or weight loss. - It is not a reliable method for assessing the overall **prevalence of tuberculosis infection**, particularly asymptomatic latent cases, in a community.
Question 226: What is the window period for HIV infection?
- A. 3 – 6 weeks
- B. 3 – 15 days
- C. 6 – 8 months
- D. 6 – 24 weeks (Correct Answer)
Explanation: ***6 – 24 weeks*** - The **window period** for HIV infection refers to the time after initial infection during which **antibodies have not yet developed** to a detectable level. - While it can vary depending on the testing method, the **6-24 week range** generally encompasses the period for traditional antibody tests to become positive. - This is the **conservative estimate** used for conventional HIV antibody testing, ensuring adequate time for seroconversion in most individuals. *3 – 6 weeks* - While many individuals will develop detectable antibodies within this timeframe, this range is **too narrow** to capture all cases of seroconversion. - Some individuals may take longer (up to 12 weeks or more) to develop detectable antibody levels, making this an **incomplete window period**. - The 6-24 week range provides a more **conservative and comprehensive** testing window. *3 – 15 days* - This timeframe is typically **too short** for the body to produce a detectable antibody response to HIV. - **Early HIV infection** during this period would likely be detected by more sensitive tests, such as **HIV RNA PCR**, which detect viral genetic material directly. - This represents the **eclipse period** rather than the full antibody window period. *6 – 8 months* - While some individuals may take longer to seroconvert, 6-8 months is generally considered **outside the typical window period** for most conventional HIV antibody tests. - Most people will develop detectable antibodies much earlier than this, usually within **3-12 weeks**. - This timeframe is excessively long and not reflective of standard testing protocols.
Question 227: With reference to dengue virus, consider the following statements: 1. In India, all the four serotypes are found. 2. The reservoir of infection is both man and mosquito. 3. Adults usually have a milder disease than children. 4. Dengue hemorrhagic fever is caused by infection with more than one dengue virus. Which of the statements given above is/are correct?
- A. 2, 3 and 4
- B. 4 only
- C. 1, 2 and 4 (Correct Answer)
- D. 1 and 2 only
Explanation: ***1, 2 and 4*** - **All four serotypes** (DEN-1, DEN-2, DEN-3, and DEN-4) of the dengue virus are endemic in India, contributing to the recurrent outbreaks seen across the country. - Dengue is a **vector-borne disease**, meaning the virus cycles between humans (the primary reservoir) and mosquitoes (specifically *Aedes aegypti* and *Aedes albopictus*), making both essential for its transmission. - **Dengue hemorrhagic fever (DHF)**, or severe dengue, is often associated with a **second infection by a different serotype** of the dengue virus due to antibody-dependent enhancement (ADE). *2, 3 and 4* - The statement that adults usually have a milder disease than children is **incorrect**; children often present with milder, non-specific symptoms, while adults are more likely to develop typical dengue fever or severe forms. - The other statements regarding the presence of all four serotypes, the reservoir, and the cause of DHF are correct. *4 only* - While statement 4 (DHF caused by infection with more than one serotype) is correct, it overlooks the accuracy of statements 1 and 2. - Omitting statements 1 and 2 makes this option incomplete as both are established facts about dengue. *1 and 2 only* - This option correctly identifies that all four serotypes exist in India and that humans and mosquitoes serve as reservoirs. - However, it **incorrectly excludes statement 4** regarding the etiology of dengue hemorrhagic fever (DHF), which results from sequential infection with a different serotype.
Question 228: Match List I with List II and select the correct answer using the codes given below the lists:
- A. A->2 B->1 C->3 D->4
- B. A->1 B->2 C->4 D->3
- C. A->2 B->1 C->4 D->3 (Correct Answer)
- D. A->1 B->2 C->3 D->4
Explanation: ***A->2 B->1 C->4 D->3*** **Correct Matching:** **A. Nosocomial → Hepatitis B viral infection (2)** - **Nosocomial infections** are hospital-acquired infections contracted in healthcare settings - **Hepatitis B** can be transmitted nosocomially through contaminated needles, medical equipment, blood products, or during invasive procedures - This is a classic example of nosocomial transmission **B. Opportunistic → Cytomegaloviral infection (1)** - **Opportunistic infections** occur in individuals with compromised immune systems - **CMV infection** is a prototypical opportunistic pathogen, commonly affecting: - HIV/AIDS patients with CD4 count <50 - Solid organ transplant recipients - Bone marrow transplant patients - Patients on immunosuppressive therapy **C. Iatrogenic → Influenza (4)** - **Iatrogenic conditions** are inadvertently caused by medical treatment or procedures - This pairing is clinically weak as influenza is primarily a community-acquired respiratory infection, not caused by medical intervention - This represents the official answer key matching for this PYQ **D. Epornithic → Aplastic anemia (3)** - **Epornithic** refers to epidemic disease outbreaks in bird populations - This pairing is clinically incorrect as aplastic anemia is a human bone marrow failure disorder - This represents the official answer key matching for this PYQ **Note:** This is a Past Year Question (UPSC-CMS-2016) where the official answer key indicates A->2 B->1 C->4 D->3. While pairings A and B are medically accurate, pairings C and D have clinical inconsistencies that students should be aware of. *Incorrect A->2 B->1 C->3 D->4* - While correctly matching Nosocomial→Hepatitis B and Opportunistic→CMV - Incorrectly pairs Iatrogenic→Aplastic anemia and Epornithic→Influenza - Does not match the official answer key *Incorrect A->1 B->2 C->4 D->3* - Incorrectly pairs Nosocomial→CMV (though CMV can be nosocomial, Hepatitis B is the better match here) - Incorrectly pairs Opportunistic→Hepatitis B (not typically classified as opportunistic) - Does not match the official answer key *Incorrect A->1 B->2 C->3 D->4* - All pairings are incorrect - Does not match the official answer key
Question 229: Which of the following statements is true about hydatid disease?
- A. It is a protozoal disease
- B. It is a zoonosis (Correct Answer)
- C. Man is the definitive host
- D. It is rare in sheep rearing countries
Explanation: ***Correct: It is a zoonosis*** - Hydatid disease is caused by the larval stage of **Echinococcus granulosus**, a **tapeworm**, and is transmitted from animals to humans - **Zoonoses** are diseases that can be transmitted from animals to humans, making this the correct statement - The primary reservoir includes dogs (definitive hosts) and sheep (intermediate hosts), with transmission to humans occurring through contact with contaminated dog feces *Incorrect: It is a protozoal disease* - Hydatid disease is caused by a **tapeworm** (cestode), specifically *Echinococcus granulosus*, not by a protozoan - Protozoal diseases are caused by single-celled eukaryotic organisms such as *Plasmodium* (malaria) or *Giardia* (giardiasis) - This is a helminthic infection, not a protozoal one *Incorrect: Man is the definitive host* - In the life cycle of *Echinococcus granulosus*, **dogs and other canines** are the **definitive hosts**, harboring the adult tapeworm in their intestines - Humans are **accidental intermediate hosts**, getting infected by ingesting eggs and developing hydatid cysts in organs (especially liver and lungs) - The natural cycle involves dogs eating infected offal from sheep, not humans being part of the natural transmission cycle *Incorrect: It is rare in sheep rearing countries* - Hydatid disease is **endemic** and more common in **sheep-rearing countries** including Mediterranean regions, Middle East, South America, Australia, and parts of Africa - Sheep act as important intermediate hosts in the life cycle of *Echinococcus granulosus* - The dog-sheep-dog cycle maintains high endemicity in pastoral communities where dogs have access to infected sheep viscera
Question 230: Consider the following features of food poisoning: 'Incubation period less than 24 hours, source of infection is milk products, and symptoms include diarrhoea and vomiting.' To which of the following does the above description apply? 1. Staphylococcal food poisoning 2. Salmonella food poisoning 3. Botulism Select the correct answer using the code given below:
- A. 1 only (Correct Answer)
- B. 2 only
- C. 1 and 3
- D. 1 and 2
Explanation: ***1 only*** - **Staphylococcal food poisoning** has a **very short incubation period** (1-6 hours), making it the most characteristic match for "less than 24 hours." - Commonly associated with contaminated **dairy products** (milk, cream, custards) and meats where the bacteria produce **preformed enterotoxins**. - Causes **sudden onset** of severe **nausea, vomiting**, and diarrhea due to preformed toxins. - The **rapid onset** (within hours) and strong association with **milk products** make this the best fit for all three criteria. *2 only* - **Salmonella food poisoning** typically has an incubation period of **6-72 hours** (average 12-36 hours), which is longer than the typical Staphylococcal onset. - While technically some cases can present within 24 hours, the **short incubation period** described is more characteristic of **toxin-mediated** rather than **infection-mediated** food poisoning. - Primary sources are **poultry, eggs**, and meat; while milk can be a vehicle, it's not the classic source. - Symptoms result from **bacterial invasion** of intestinal mucosa rather than preformed toxins. *1 and 3* - While **Staphylococcal food poisoning** aligns with the description, **Botulism** does not. - **Botulism** has an incubation period of **12-36 hours** (range 2 hours to 8 days) and is characterized by **neurological symptoms** (diplopia, dysphagia, descending paralysis) rather than prominent diarrhea and vomiting. - Source is typically **improperly canned or preserved foods**, not milk products. *1 and 2* - **Salmonella food poisoning** has a longer average incubation period and is more commonly associated with poultry and eggs, differentiating it from the described scenario. - The **very short incubation period** (< 24 hours, typically 1-6 hours) and **milk products** as source point specifically to **Staphylococcal food poisoning** with its preformed toxin mechanism. - Only **Staphylococcal food poisoning** matches all conditions most characteristically.
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