Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 361: Not true about Aedes mosquito

A. Larvae has siphon tube (Correct Answer)
B. Boat shaped eggs
C. Has stripes on body
D. Also known as tiger mosquito

Explanation: ***Larvae has siphon tube*** - Aedes larvae do not possess a long **siphon tube** for respiration; instead, they have a short, broad siphon or no siphon at all. - The presence of a long siphon tube is characteristic of **Culex mosquito** larvae, which helps them breathe by piercing the water surface. *Boat shaped eggs* - **Aedes mosquito** eggs are typically oval and laid singly on damp surfaces, not boat-shaped. - **Anopheles mosquitos** are known for laying boat-shaped eggs with floats. *Has stripes on body* - **Aedes aegypti** and **Aedes albopictus** (the tiger mosquito) are known for their distinct black and white stripes or bands on their legs and body. - This characteristic "striped" appearance is a key identification feature of adult Aedes mosquitoes. *Also known as tiger mosquito* - One of the most prevalent species, **Aedes albopictus**, is indeed widely known as the **Asian tiger mosquito** due to its distinctive striped appearance. - This common name helps differentiate it from other mosquito species and reflects its aggressive biting habits during the day.

Question 362: Sputum positive TB patients on chemotherapy should be isolated for at least:

A. 2 weeks (Correct Answer)
B. 3 weeks
C. 4 weeks
D. 6 weeks

Explanation: ***2 weeks*** - Patients with **sputum smear-positive TB** are generally considered infectious until they have received **2 weeks of effective anti-TB treatment** with appropriate anti-tubercular therapy. - After this period, the **bacterial load significantly decreases**, making transmission much less likely and allowing for discontinuation of strict isolation precautions. - This is the standard recommendation in **WHO guidelines, CDC guidelines, and Indian NTEP (National TB Elimination Programme)** for drug-susceptible TB. - Isolation can be discontinued after **2 weeks** if the patient shows **clinical improvement** and is on appropriate treatment. *3 weeks* - While some institutions may use a 3-week period as a **conservative margin**, this is **not the standard minimum** recommended by guidelines. - The infectious period typically ends within 2 weeks of effective chemotherapy for drug-susceptible TB. *4 weeks* - Isolating for four weeks is **unnecessarily prolonged** for most patients with drug-susceptible TB. - This leads to **increased healthcare costs** and extended hospital stays without substantial additional public health benefit. *6 weeks* - Such a long isolation period is typically reserved for cases of **multidrug-resistant TB (MDR-TB)** or extensively drug-resistant TB (XDR-TB) due to prolonged infectivity. - For standard sputum-positive drug-susceptible TB, this duration is excessive and does not align with current guidelines.

Question 363: Under RNTCP, the target for case detection through quality sputum microscopy is at least:

A. 70% (Correct Answer)
B. 95%
C. 85%
D. 60%

Explanation: ***70%*** - The **Revised National Tuberculosis Control Programme (RNTCP)** aimed for a minimum of **70% case detection** by identifying infectious smear-positive TB cases. - This target ensures that a significant proportion of **tuberculosis cases** are diagnosed and brought under treatment, thereby reducing transmission. *95%* - While 95% is a very high target, it was not the initial or primary target set by RNTCP for sputum microscopy case detection. - Such a high rate is often an ideal goal for **treatment success** or **cure rates**, rather than initial case detection. *85%* - The **85% target** was set for the **treatment success rate** for smear-positive pulmonary TB cases under RNTCP, not for initial case detection. - Achieving this target ensures effective treatment outcomes and prevents the development of **drug resistance**. *60%* - A 60% detection rate would be considered **insufficient** for effective TB control, as it would leave a large number of infectious individuals undiagnosed. - This low target would not adequately address the public health burden of **tuberculosis**.

Question 364: What is the most appropriate management step for a rat bite?

A. Administer rabies vaccine
B. Administer tetanus toxoid if vaccination status is unclear
C. Administer rabies immunoglobulin
D. Wash the wound thoroughly with soap and water (Correct Answer)

Explanation: ***Wash the wound thoroughly with soap and water*** - **Immediate wound cleansing** with soap and water is the most crucial first step in managing animal bites to remove saliva, dirt, and reduce bacterial load. - This simple mechanical irrigation significantly **reduces the risk of infection**, including bacterial infections and potential viral transmission, and should be performed before any other interventions. *Administer rabies vaccine* - While rabies is a concern with animal bites, **rats are very rarely vectors for rabies**, and routine post-exposure prophylaxis for rabies is usually not indicated for rat bites unless the animal is symptomatic or in a high-risk area. - The rabies vaccine is part of a **post-exposure prophylaxis (PEP)** regimen, which is initiated after initial wound care and risk assessment. *Administer tetanus toxoid if vaccination status is unclear* - Tetanus prophylaxis is important for any bite wound, especially if the patient's vaccination status is unknown or incomplete, but it is not the **immediate first step** before wound cleansing. - Tetanus toxoid administration aims to prevent **Clostridium tetani infection** and is a secondary step after initial wound care. *Administer rabies immunoglobulin* - **Rabies immunoglobulin (RIG)** provides immediate passive immunity and is part of the rabies post-exposure prophylaxis, but like the vaccine, it is generally not indicated for rat bites due to their extremely low risk of rabies transmission. - RIG is typically infiltrated around the wound site along with the first dose of rabies vaccine for high-risk exposures.

Question 365: The infectivity of chicken pox lasts for -

A. 6 days after onset of rash (Correct Answer)
B. 3 days after onset of rash
C. Till the fever subsides
D. Till the last scab falls off

Explanation: ***6 days after onset of rash*** - The infectious period for **chickenpox** (varicella) typically starts 1-2 days before the rash appears and lasts until all lesions have **crusted over**, which usually takes about 6 days after the onset of the rash. - This timeframe is crucial for **infection control** as the virus is highly contagious during this period. *3 days after onset of rash* - This period is **too short** to cover the entire infectious phase of chickenpox. - Many lesions may still be in the vesicular stage and highly contagious at only 3 days after rash onset. *Till the fever subsides* - While fever is a common symptom, the cessation of fever **does not reliably indicate** the end of the infectious period for chickenpox. - Patients can still be contagious even after their fever has gone down if lesions are still active. *Till the last scab falls off* - This duration is **longer** than the actual infectious period. Once all lesions have **crusted over**, the risk of transmission significantly decreases, even if the scabs have not yet fallen off. - The crusted lesions are generally not considered infectious.

Question 366: Plague is transmitted by all EXCEPT?

A. Culex (Correct Answer)
B. Pulex irritans
C. X. astia
D. X. cheopis

Explanation: ***Culex*** - **Culex** mosquitoes are known vectors for diseases like **West Nile virus**, **Japanese encephalitis**, and **filariasis**. - They are **not involved** in the transmission of **plague**, which is primarily a flea-borne disease. *Pulex irritans* - **Pulex irritans**, also known as the **human flea**, is a known vector for **plague** (*Yersinia pestis*). - It can transmit the bacteria from infected hosts, including humans and animals, to others through its bite. *X. astia* - **Xenopsylla astia** is an oriental rat flea, found predominantly in tropical regions like India, and is a significant vector for **plague**. - This flea species plays a crucial role in maintaining **enzootic plague** among rodent populations and transmitting it to humans. *X. cheopis* - **Xenopsylla cheopis**, the **oriental rat flea**, is the **primary vector** for **bubonic plague** worldwide. - It transmits *Yersinia pestis* from infected rodents (like rats) to humans through its bite, contributing to flea-borne epidemics.

Question 367: True about Anopheles mosquito?

A. Larvae have siphon tube
B. Larvae are bottom feeder
C. Larvae are surface feeder (Correct Answer)
D. Larvae lie at an angle to water surface

Explanation: ***Larvae are surface feeder*** - **Anopheles larvae** lie horizontally at the water surface and feed on surface scum and microbes, which is a **key distinguishing feature** in mosquito identification - Their specialized mouthparts are adapted for **grazing along the water's surface** - This characteristic differentiates them from other mosquito genera *Larvae have siphon tube* - **Anopheles larvae do not possess a respiratory siphon tube**; they breathe directly through spiracles on their eighth abdominal segment - The presence of a **siphon tube is characteristic of Culex and Aedes** mosquito larvae, not Anopheles *Larvae lie at an angle to water surface* - Mosquito larvae that hang at an angle from the water surface, using a respiratory siphon, are typically **Culex or Aedes species** - **Anopheles larvae lie parallel to the water surface**, not at an angle - this is another key identification feature *Larvae are bottom feeder* - While some aquatic insect larvae are bottom feeders, **Anopheles larvae are specifically adapted for surface feeding** - They primarily consume organisms and debris present in the **surface film** of the water, not from the bottom

Question 368: Most crucial part of tuberculosis control programme is -

A. Treatment of X-ray positive cases
B. BCG vaccination
C. Contact tracing
D. Treatment of sputum positive cases (Correct Answer)

Explanation: ***Treatment of sputum positive cases*** - Treating **sputum-positive cases** is paramount because these individuals are the primary source of **transmission** of *Mycobacterium tuberculosis* in the community. - Effective treatment of these highly infectious cases directly **reduces the bacterial load**, preventing further spread and significantly impacting the *R0* (basic reproduction number) of the disease. *Treatment of X-ray positive cases* - While X-ray findings can indicate active tuberculosis, they do not always correlate with **infectivity** as strongly as sputum positivity. - Many X-ray positive cases, especially those with **non-cavitary lesions**, may have low or no sputum positivity. *BCG vaccination* - **BCG vaccination** primarily protects against severe forms of tuberculosis, such as **meningitis** and **miliary TB**, in children. - It has variable efficacy against **pulmonary TB** in adults and does not prevent the transmission of the disease from already infected individuals to others. *Contact tracing* - **Contact tracing** is crucial for identifying individuals who have been exposed to TB and may be at risk for developing the disease, allowing for prophylaxis or early treatment. - However, without effectively treating the primary sources (sputum-positive cases), new infections will continue to occur, making contact tracing a reactive rather than a primary preventative measure.

Question 369: The high risk groups for transmission of HIV include the following except

A. Children of HIV mothers
B. Haemophiliacs
C. Men who have sex with men (MSM)
D. Health care workers (Correct Answer)

Explanation: ***Health care workers*** - While **health care workers** can be exposed to HIV through occupational activities (e.g., needlestick injuries), they are generally not considered a high-risk group for transmission if standard precautions are followed. - The risk of transmission through occupational exposure is relatively low (approximately 0.3% for needlestick injury), especially with proper safety measures and post-exposure prophylaxis. *Children of HIV mothers* - Children born to **HIV-positive mothers** are at high risk of acquiring the virus through vertical transmission during pregnancy, childbirth, or breastfeeding. - Without intervention, the transmission rate ranges from 15-45%, making this a recognized high-risk group. *Haemophiliacs* - Before the implementation of routine screening for blood products (pre-1985), **haemophiliacs** were at very high risk of contracting HIV through contaminated factor VIII and IX concentrates, which were essential for their treatment. - While current blood products are safe, haemophiliacs are historically recognized as a high-risk group. *Men who have sex with men (MSM)* - **Men who have sex with men** are a high-risk group due to unprotected receptive anal intercourse, which is an efficient mode of HIV transmission. - This demographic has historically been, and continues to be, disproportionately affected by the HIV epidemic globally.

Question 370: Which of the following diseases is transmitted by rat flea?

A. Oriental sore
B. Endemic typhus (Correct Answer)
C. Trench fever
D. Chagas disease

Explanation: ***Endemic typhus*** - **Endemic (murine) typhus** is caused by *Rickettsia typhi* and is primarily transmitted to humans by the **rat flea** (*Xenopsylla cheopis*) - The rat flea typically acquires the bacteria by feeding on infected rodents (e.g., rats), and then transmits it to humans through its feces while feeding. *Oriental sore* - **Oriental sore** refers to cutaneous leishmaniasis, caused by *Leishmania* parasites. - It is transmitted by the bite of infected **sandflies**, not rat fleas. *Trench fever* - **Trench fever** is caused by *Bartonella quintana* and is transmitted to humans by **human body lice** (*Pediculus humanus corporis*). - This disease is historically associated with crowded and unsanitary conditions, particularly during wartime. *Chagas disease* - **Chagas disease** (American trypanosomiasis) is caused by the parasite *Trypanosoma cruzi*. - It is primarily transmitted by the feces of infected **reduviid bugs** (also known as kissing bugs), which typically bite humans around the face.

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