Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 51: A patient with chickenpox should be isolated for how long?

A. 6 days (Correct Answer)
B. 10 days
C. 12 days
D. 14 days

Explanation: **Explanation:** The isolation period for chickenpox (Varicella) is determined by the period of communicability. A patient is infectious from **1–2 days before the appearance of the rash** until all lesions have **crusted (scabbed) over**. **Why 6 days is the correct answer:** In most clinical cases, the rash appears in successive crops over 3–5 days. By the **6th day after the onset of the rash**, the majority of vesicles have typically crusted. Since the virus is not present in the scabs (it is only found in the vesicular fluid), the patient is no longer considered infectious once crusting is complete. Therefore, the standard isolation period recommended is **6 days after the onset of the rash**. **Analysis of Incorrect Options:** * **10, 12, and 14 days:** These durations significantly exceed the standard period of communicability for an uncomplicated case. While the incubation period of Varicella is 14–16 days (range 10–21 days), isolation is based on the duration of active viral shedding, which ceases once lesions dry up. **High-Yield NEET-PG Pearls:** * **Secondary Attack Rate (SAR):** Very high, approximately 90%. * **Incubation Period:** 14–16 days (Commonly tested). * **Characteristic Rash:** Centripetal distribution (more on trunk), pleomorphic (all stages—papule, vesicle, crust—seen simultaneously), and "dew-drop on a rose petal" appearance. * **Congenital Varicella Syndrome:** Highest risk if maternal infection occurs between 8–20 weeks of gestation. * **Scabs:** Unlike Smallpox, the scabs of Chickenpox are **not infectious**.

Question 52: What is the average lifespan of a cyclops?

A. 1 month
B. 2 months
C. 3 months (Correct Answer)
D. 4 months

Explanation: **Explanation:** **Cyclops** (also known as the "Water Flea") is a crustacean that serves as the essential intermediate host for *Dracunculus medinensis* (Guinea worm) and *Diphyllobothrium latum* (Fish tapeworm). **1. Why the Correct Answer is Right:** The average lifespan of a cyclops is approximately **3 months (Option C)**. This duration is significant in epidemiology because it influences the transmission window of Dracunculiasis. If a water source is left undisturbed and the cyclops die out naturally without a human host re-infecting the water, the cycle of transmission is broken. **2. Analysis of Incorrect Options:** * **Option A (1 month):** This is too short. While individual survival depends on water temperature and food availability, the average population survival extends beyond 4 weeks. * **Option B (2 months):** While some cyclops may die by this time, it does not represent the standard average lifespan cited in standard preventive medicine textbooks (like Park’s PSM). * **Option D (4 months):** This exceeds the typical average lifespan. Most cyclops populations in tropical stagnant water sources diminish before reaching this duration. **3. High-Yield Clinical Pearls for NEET-PG:** * **Size:** Cyclops measures roughly 0.5–2.0 mm. * **Dracunculiasis Cycle:** Humans get infected by drinking unfiltered water containing cyclops infected with **L3 larvae**. * **Chemical Control:** The drug of choice to kill cyclops in water bodies is **Abate (Temephos)** at a dosage of 1 mg/L. * **Physical Control:** Straining water through a fine cloth (mesh size <100 micrometers) or boiling water is effective. * **India Status:** India was declared **Guinea Worm free** by the WHO in February 2000 (last case reported in 1996 in Rajasthan).

Question 53: What is the incubation period of Diphtheria?

A. 2-6 days (Correct Answer)
B. 2-6 hours
C. 2-6 weeks
D. 2-6 months

Explanation: **Explanation:** **1. Why Option A is Correct:** The incubation period of Diphtheria, caused by *Corynebacterium diphtheriae*, is typically **2 to 6 days**. This short duration reflects the rapid colonization of the upper respiratory tract (or skin) and the subsequent production of the potent diphtheria exotoxin. The toxin acts locally to cause tissue necrosis and the formation of the characteristic "pseudomembrane," while systemic absorption can lead to myocarditis and polyneuritis. **2. Why Other Options are Incorrect:** * **Option B (2-6 hours):** This is characteristic of pre-formed bacterial toxins in food poisoning, such as *Staphylococcus aureus* or *Bacillus cereus* (emetic type). * **Option C (2-6 weeks):** This is too long for Diphtheria. Such durations are typical for diseases like Hepatitis A, Typhoid, or the early stages of Syphilis. * **Option D (2-6 months):** This prolonged period is seen in slow-growing infections like Hepatitis B, Rabies (variable), or certain filarial infections. **3. High-Yield Clinical Pearls for NEET-PG:** * **Causative Agent:** *Corynebacterium diphtheriae* (Gram-positive, club-shaped, Chinese-letter pattern). * **Schick Test:** Used to demonstrate susceptibility/immunity to Diphtheria. * **Culture Media:** **Löffler's serum slope** (rapid growth) and **Potassium Tellurite agar** (black colonies). * **Case Definition:** Presence of a greyish-white adherent pseudomembrane; attempting to remove it causes bleeding. * **Public Health:** The period of communicability is usually 14–28 days without antibiotics. Cases are considered non-infectious after **two consecutive negative cultures** taken 24 hours apart.

Question 54: Which of the following is also known as Monkey disease?

A. Japanese Encephalitis
B. Kyasanur forest disease (Correct Answer)
C. Rickettsial Disease
D. Rabies

Explanation: **Kyasanur Forest Disease (KFD)**, also known as **Monkey Fever** or Monkey Disease, is a viral hemorrhagic fever endemic to the Western Ghats of India (first identified in the Kyasanur Forest of Karnataka in 1957). ### Why B is Correct: The disease is caused by the **KFD virus (Flavivirus)**. It is called "Monkey Disease" because it was first discovered following an investigation into a large-scale die-off of monkeys (*Presbytis entellus* and *Macaca radiata*) in the forest. Monkeys act as **amplifying hosts**; their death is often the first sign of an impending human outbreak (sentinel event). Humans are accidental, dead-end hosts, usually infected via the bite of the principal vector, the hard tick **Haemaphysalis spinigera**. ### Why Other Options are Incorrect: * **A. Japanese Encephalitis:** Caused by a Flavivirus but transmitted by *Culex* mosquitoes. Its natural cycle involves pigs (amplifier hosts) and water birds (reservoirs). * **C. Rickettsial Disease:** These are a group of diseases (like Scrub Typhus) caused by Rickettsiae and transmitted by mites, lice, or ticks, but they are not associated with monkey epizootics. * **D. Rabies:** A lyssavirus infection typically transmitted through the saliva of infected mammals (dogs, bats). While monkeys can carry rabies, it is not termed "Monkey Disease." ### NEET-PG High-Yield Pearls: * **Vector:** *Haemaphysalis spinigera* (Hard tick). * **Reservoirs:** Rodents, shrews, and monkeys. * **Clinical Feature:** Biphasic fever, severe headache, myalgia, and hemorrhagic manifestations. * **Prevention:** Formalin-inactivated KFDV vaccine is used in endemic areas (given to individuals aged 7–65 years). * **Diagnosis:** PCR (early stage) or IgM ELISA.

Question 55: A 5-year-old child presents with rashes all over the body and was diagnosed with chickenpox. What feature helps differentiate chickenpox rash from smallpox rash?

A. Centrifugal distribution
B. Pleomorphic rash (Correct Answer)
C. Non-pleomorphic rash
D. Palms and soles are involved

Explanation: ### Explanation The correct answer is **B. Pleomorphic rash**. **1. Why Pleomorphic Rash is Correct:** Chickenpox (caused by the Varicella-Zoster virus) is characterized by **pleomorphism**, meaning that different stages of the rash (papules, vesicles, and crusts/scabs) are visible simultaneously in the same anatomical area. This occurs because the rash appears in successive "crops" over several days. In contrast, smallpox is **non-pleomorphic**; all lesions in a specific area evolve at the same rate and appear identical in stage. **2. Analysis of Incorrect Options:** * **A. Centrifugal distribution:** This is a hallmark of **Smallpox**, where the rash is more dense on the face and distal extremities. Chickenpox follows a **centripetal** distribution, being most dense on the trunk and sparse on the extremities. * **C. Non-pleomorphic rash:** This is characteristic of **Smallpox**, where all lesions are at the same stage of development. * **D. Palms and soles are involved:** This is a classic feature of **Smallpox**. In Chickenpox, the palms and soles are typically **spared**. **3. High-Yield NEET-PG Clinical Pearls:** * **Dew-drop on a rose petal:** Classic description of the thin-walled varicella vesicle on an erythematous base. * **Rapid Evolution:** Chickenpox lesions evolve rapidly (within 24 hours), whereas smallpox lesions evolve slowly. * **Incubation Period:** Chickenpox is typically 14–16 days (Range: 10–21 days). * **Infectivity:** A patient is infectious from 1–2 days *before* the rash appears until all vesicles have crusted over (usually 6 days after onset). * **Scabs:** In chickenpox, scabs fall off quickly (within 14 days) and do not contain the virus, unlike smallpox scabs which are highly infectious.

Question 56: Which of the following has the highest chance of transmission of HIV?

A. Anal intercourse
B. Transfusion of blood products (Correct Answer)
C. Kidney transplant
D. Transplacental transmission

Explanation: **Explanation:** The risk of HIV transmission depends on the **viral load** in the source fluid and the **route of exposure**. **1. Why Option B is Correct:** Transfusion of infected blood or blood products has the highest transmission efficiency, estimated at **>90% (approximately 92.5%)**. This is because a large volume of the virus is introduced directly into the recipient's bloodstream, bypassing all natural mucosal barriers. In the context of NEET-PG, blood transfusion is always considered the most efficient mode of transmission per single act of exposure. **2. Analysis of Incorrect Options:** * **Anal Intercourse (Option A):** While this is the most common mode of sexual transmission (specifically for the receptive partner), the risk per act is significantly lower, estimated at **1% to 1.4% (138 per 10,000 exposures)**. * **Kidney Transplant (Option C):** Organ transplantation carries a high risk, but it is statistically lower than a direct whole-blood transfusion. Furthermore, rigorous screening protocols make this a rare event compared to other modes. * **Transplacental Transmission (Option D):** Vertical transmission (Mother-to-Child) has a risk of **20–45%** in the absence of any intervention (ART). While high, it does not reach the near-certainty of a contaminated blood transfusion. **3. High-Yield Clinical Pearls for NEET-PG:** * **Order of Transmission Risk (Per act):** Blood Transfusion (>90%) > Vertical Transmission (20-45%) > Receptive Anal Intercourse (1%) > Needle Stick Injury (0.3%) > Receptive Vaginal Intercourse (0.08%). * **Most common route worldwide:** Heterosexual transmission. * **Most common route in India:** Heterosexual transmission. * **Needle Stick Injury Risk:** The risk of transmitting HIV via a needle stick is **0.3%**, whereas Hepatitis B (HBV) is much higher at **30%** and Hepatitis C (HCV) is **3%** (Rule of 3: 0.3, 3, 30).

Question 57: What is the estimated rate of mother-to-child transmission of HIV without any intervention?

A. 25% (Correct Answer)
B. 50%
C. 60%
D. 75%

Explanation: **Explanation:** The risk of Mother-to-Child Transmission (MTCT) of HIV, also known as vertical transmission, varies depending on the timing and interventions. In the absence of any medical intervention (no antiretroviral therapy, vaginal delivery, and breastfeeding), the transmission rate is estimated to be between **25% and 30%**. **Breakdown of Transmission Risk (Without Intervention):** * **In-utero (during pregnancy):** 5–10% * **During Labor/Delivery:** 10–15% (The period of highest risk per hour) * **Breastfeeding:** 5–20% **Why the other options are incorrect:** * **Option B (50%):** This is an overestimation. While the risk is significant, more than half of infants born to untreated HIV-positive mothers will remain HIV-negative. * **Options C & D (60% and 75%):** These values are far above the documented epidemiological rates for HIV vertical transmission. **High-Yield Clinical Pearls for NEET-PG:** 1. **With Intervention:** With modern Prevention of Mother-to-Child Transmission (PMTCT) protocols (ART for the mother, prophylaxis for the infant, and viral load suppression), the risk can be reduced to **less than 1–2%**. 2. **Most Common Route:** Intrapartum (during labor) is the most common time for transmission due to exposure to maternal blood and vaginal secretions. 3. **PPTCT Protocol (India):** All pregnant women are screened for HIV. If positive, the mother is started on lifelong ART (regardless of CD4 count) and the infant receives Nevirapine prophylaxis for 6 weeks (extendable to 12 weeks). 4. **Breastfeeding:** In India, exclusive breastfeeding for the first 6 months is recommended even for HIV-positive mothers, provided they are on ART. Mixed feeding should be strictly avoided.

Question 58: All of the following are true about Dengue hemorrhagic fever EXCEPT:

A. Lamivudine is the drug of choice. (Correct Answer)
B. Malnutrition is protective.
C. It is transmitted by Aedes mosquitoes.
D. The causative agent belongs to the Flaviviridae group.

Explanation: ### Explanation **1. Why Option A is the correct answer (The "Except" statement):** There is **no specific antiviral drug** for Dengue or Dengue Hemorrhagic Fever (DHF). Management is primarily **supportive**, focusing on judicious fluid resuscitation (isotonic crystalloids) and monitoring for plasma leakage. **Lamivudine** is a nucleoside reverse transcriptase inhibitor (NRTI) used in the treatment of **HIV and Hepatitis B**, not Dengue. **2. Analysis of Incorrect Options:** * **Option B (Malnutrition is protective):** This is a unique epidemiological feature of DHF. Clinical studies have observed that DHF/DSS (Dengue Shock Syndrome) occurs more frequently in **well-nourished children**. Malnutrition appears to be "protective," possibly because a robust immune system is required to trigger the massive cytokine storm (immunopathology) responsible for plasma leakage. * **Option C (Transmitted by Aedes):** Dengue is primarily transmitted by the bite of an infected **_Aedes aegypti_** (principal vector) or **_Aedes albopictus_** mosquito. These are "day-biters" that breed in artificial collections of clean water. * **Option D (Flaviviridae group):** The Dengue virus (DENV 1-4) is a single-stranded RNA virus belonging to the genus **Flavivirus** and family **Flaviviridae**. ### High-Yield Clinical Pearls for NEET-PG: * **Pathogenesis:** DHF occurs due to **Antibody-Dependent Enhancement (ADE)**, usually during a secondary infection with a different serotype. * **The "Critical Phase":** Occurs during defervescence (when fever drops). This is when plasma leakage and shock typically manifest. * **Vector Characteristics:** _Aedes aegypti_ is a "nervous feeder" (bites multiple people to complete one meal) and undergoes **transovarial transmission** of the virus. * **Diagnosis:** NS1 Antigen (Day 1-5); IgM/IgG ELISA (after Day 5). * **Tourniquet Test:** A positive test (≥10-20 petechiae per square inch) suggests capillary fragility, a hallmark of DHF.

Question 59: What is the target cure rate for multibacillary leprosy under the programme implementation plan for the 12th plan period?

A. > 85%
B. > 80%
C. >75%
D. > 95% (Correct Answer)

Explanation: ### Explanation The National Leprosy Eradication Programme (NLEP) set specific performance indicators during the **12th Five-Year Plan (2012–2017)** to monitor the quality of Multi-Drug Therapy (MDT) services and ensure effective disease control. **1. Why Option D is Correct:** The target **Cure Rate** (also known as the Treatment Completion Rate) for both **Multibacillary (MB)** and **Paucibacillary (PB)** leprosy was set at **> 95%**. This high threshold ensures that the vast majority of patients complete their full course of MDT (12 months for MB; 6 months for PB), which is critical to breaking the chain of transmission and preventing the emergence of drug resistance. **2. Why Other Options are Incorrect:** * **Options A, B, and C:** While 80% or 85% are common targets for other public health programs (like the initial cure rate targets for TB under RNTCP), they are considered insufficient for Leprosy. Because leprosy has a long incubation period and social stigma leads to concealment, the NLEP mandates a more stringent completion target (> 95%) to achieve elimination status. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Elimination Definition:** Prevalence rate of **< 1 case per 10,000 population**. * **MDT Regimen (Adult MB):** Rifampicin (600mg once monthly), Clofazimine (300mg once monthly + 50mg daily), and Dapsone (100mg daily) for **12 months**. * **MDT Regimen (Adult PB):** Rifampicin (600mg once monthly) and Dapsone (100mg daily) for **6 months**. * **Accompanied MDT:** To improve the cure rate, the full course of MDT is provided to the patient at the start if they cannot visit the clinic monthly. * **Current Goal:** The NLEP now focuses on "Leprosy Mukt Bharat" (Leprosy Free India), aiming for zero transmission by 2027.

Question 60: Targeted intervention for HIV is recommended for which of the following groups, except?

A. Commercial sex workers
B. Migrant laborers
C. Street children
D. Industrial workers (Correct Answer)

Explanation: **Explanation:** The concept of **Targeted Intervention (TI)** under the National AIDS Control Programme (NACP) focuses on providing prevention and care services to specific populations who are at a higher risk of acquiring and transmitting HIV. These groups are categorized based on their behavior or social vulnerability. **Why Industrial Workers is the correct answer:** Industrial workers are generally considered part of the "General Population." While they may face occupational hazards, they do not inherently belong to the high-risk or bridge populations defined by NACP for Targeted Interventions. HIV programs for this group usually fall under "Workplace Interventions" rather than the specific TI model. **Analysis of other options:** * **Commercial Sex Workers (CSWs):** Classified as a **Core High-Risk Group (HRG)**. They have the highest risk of transmission due to multiple sexual partners and are the primary focus of TIs. * **Migrant Laborers:** Classified as a **Bridge Population**. They act as a "bridge" for the virus, contracting it from HRGs at their work destination and transmitting it to their spouses in their rural hometowns. * **Street Children:** Classified as a **Vulnerable Population**. Due to lack of supervision, poverty, and high risk of substance abuse or sexual exploitation, they are included in TI strategies. **Clinical Pearls for NEET-PG:** * **Core High-Risk Groups (HRGs):** Female Sex Workers (FSW), Men who have Sex with Men (MSM), and Injecting Drug Users (IDU). * **Bridge Populations:** Migrants and Long-distance Truckers. * **Components of TI:** Behavioral Change Communication (BCC), Condom promotion, STI management, and creating an enabling environment. * **NACP Phase V (Current):** Aims to reduce new HIV infections and AIDS-related deaths by 80% by 2030 (The "95-95-95" targets).

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