Infectious Diseases Practice Questions

Q: What is the best method for immunoprophylaxis of leprosy?

Killed ICRC bacillus. **Explanation:** The immunoprophylaxis of Leprosy involves the use of specific mycobacterial vaccines to stimulate cell-mediated immunity (CMI) against *Mycobacterium leprae*. **Why Killed ICRC Bacillus is Correct:** The **ICRC vaccine** (Indian Cancer Research Centre) is a first-generation vaccine derived from a cultivable mycobacterium belonging to the *M. avium-intracellulare* group, isolated from human lepromata. It shares significant antigenic determinants with *M. leprae*. Clinical trials in India have demonstrated that it provides significant protection and induces lepromin conversion in lepromatous leprosy patients and their contacts. Other vaccines used in leprosy include the **Mycobacterium w (Mw)** vaccine (now known as Leprovac) and the BCG vaccine (which offers variable protection). **Analysis of Incorrect Options:** * **A. MMR vaccine:** This is a live attenuated vaccine used for Measles, Mumps, and Rubella. It has no antigenic similarity to mycobacteria and provides no protection against leprosy. * **C. Plague bacillus vaccine:** This is used for *Yersinia pestis*. It is a killed vaccine (though newer versions exist) and is unrelated to leprosy prophylaxis. * **D. Anthrax bacillus vaccine:** This is used for *Bacillus anthracis*, primarily for high-risk individuals (veterinarians/military). It has no role in mycobacterial immunity. **High-Yield Pearls for NEET-PG:** * **BCG Vaccine:** While primarily for TB, BCG offers 20-40% protection against leprosy. Adding killed *M. leprae* to BCG increases its efficacy. * **Mycobacterium w (Mw):** Developed in India by Dr. G.P. Talwar; it is used as an immunotherapeutic adjunct to MDT. * **Chemoprophylaxis:** The current WHO recommendation for contacts of leprosy patients is a **Single Dose of Rifampicin (SDR)**. * **Most common site of leprosy:** Skin and peripheral nerves.

Q: Pleomorphism is seen in which of the following conditions?

Chickenpox. **Explanation:** **Pleomorphism** is a hallmark clinical feature of **Chickenpox** (caused by the Varicella-Zoster virus). In this context, pleomorphism refers to the simultaneous presence of skin lesions at **different stages of development** in the same anatomical area. Within a single cluster, one can observe macules, papules, vesicles ("dewdrops on a rose petal"), and crusts/scabs. This occurs because the rash appears in successive crops over 3–5 days. **Analysis of Options:** * **A. Chickenpox (Correct):** Characterized by a rapid progression of lesions, centripetal distribution (more on the trunk), and distinct pleomorphism. * **B. Rubella:** Presents with a discrete maculopapular rash that starts on the face and spreads downwards (cephalocaudal). It disappears in the order it appeared and does not show pleomorphism. * **C. Smallpox:** Unlike chickenpox, smallpox lesions are **monomorphic**. This means all lesions in a particular area are at the same stage of development. The rash is centrifugal (more on extremities) and lesions are deep-seated. * **D. Toxocara:** A parasitic infection (Visceral Larva Migrans) that typically presents with eosinophilia, hepatomegaly, or ocular involvement, but not a pleomorphic vesicular rash. **High-Yield Clinical Pearls for NEET-PG:** * **Distribution:** Chickenpox is **centripetal** (trunk > face > limbs); Smallpox is **centrifugal** (limbs/face > trunk). * **Axilla:** Chickenpox characteristically involves the axilla; Smallpox typically spares it. * **Scabs:** In Chickenpox, scabs begin to form 4–7 days after the rash appears and are **not infectious**. * **Incubation Period:** Chickenpox is usually 14–16 days (Range: 10–21 days). * **Secondary Attack Rate (SAR):** Very high for Chickenpox (approx. 90%), making it highly contagious.

Q: Which patient with positive sputum requires quarantine?

Children below 6 years of age. **Explanation:** The correct answer is **Children below 6 years of age**. In the context of infectious disease control, specifically regarding **Tuberculosis (TB)** under the National Tuberculosis Elimination Program (NTEP) guidelines, the management of household contacts is crucial. While "quarantine" in the strictest sense (restricting movement of healthy individuals) is rarely used for TB, the term here refers to the specific clinical protocol for **Chemoprophylaxis**. **Why Option D is correct:** Children under 6 years of age living in the same household as a sputum-positive TB patient are at the highest risk of developing severe, disseminated forms of the disease (like TB Meningitis or Miliary TB) due to their immature immune systems [1]. Regardless of their BCG vaccination status, if they are asymptomatic, they must receive **Isoniazid Preventive Therapy (IPT)** for 6 months (5mg/kg). This "medical quarantine" or protective cover is a high-yield preventive strategy. **Why other options are incorrect:** * **A & B (Pregnant women & Elderly):** While these groups are vulnerable, they are not routinely put under mandatory prophylactic "quarantine" or chemoprophylaxis solely based on contact, unless they are immunocompromised (e.g., HIV positive). * **C (Children above 6 years):** The risk of life-threatening primary complications decreases as the child grows. Routine IPT is prioritized for the <6 age group [1]. **High-Yield Clinical Pearls for NEET-PG:** * **IPT Dosage:** Isoniazid 5 mg/kg daily for 6 months. * **HIV Exception:** All HIV-positive contacts, regardless of age, must receive IPT if active TB is ruled out. * **Reverse Quarantine:** This term is often used for protecting the vulnerable (elderly/infants) from the infected, which is the principle applied here. * **Chemoprophylaxis vs. Treatment:** Always rule out active TB (via symptom screening/X-ray) before starting prophylaxis to prevent drug resistance.

Q: What is the approximate risk of mother-to-child transmission of HIV?

25%. **Explanation:** The risk of Mother-to-Child Transmission (MTCT) of HIV, also known as vertical transmission, occurs in the absence of any medical intervention (antiretroviral therapy, elective cesarean section, or avoidance of breastfeeding). **1. Why 25% is correct:** In untreated cases, the transmission rate is generally estimated to be between **20% and 30%** (averaging approximately **25%**). The transmission occurs at three stages: * **In-utero (Antenatal):** 5–10% * **During Labor/Delivery (Intranatal):** 10–15% (This is the period of highest risk per hour) * **Breastfeeding (Postnatal):** 5–20% **2. Why other options are incorrect:** * **50%, 60%, and 75%:** These values are significantly higher than the biological reality of HIV transmission. Even with high viral loads, the placental barrier and maternal immune factors prevent the majority of fetuses from contracting the virus. A 50-75% risk would imply that transmission is the "rule" rather than a 1-in-4 statistical probability. **High-Yield Clinical Pearls for NEET-PG:** * **With Intervention:** With Effective ART (Antiretroviral Therapy), viral suppression, and proper postnatal care, the risk of MTCT can be reduced to **less than 2%**. * **PPTCT Protocol (India):** The current WHO/NACO recommendation is **Option B** (Lifelong ART for all pregnant and breastfeeding women regardless of CD4 count). * **Drug of Choice:** **Tenofovir (TDF) + Lamivudine (3TC) + Dolutegravir (DTG)** is the preferred regimen. * **Infant Prophylaxis:** Nevirapine syrup is typically given to the infant for 6 weeks. * **Most common route:** The most common route of pediatric HIV infection worldwide is vertical transmission.

Q: What is the most common mode of transmission of HIV worldwide?

Heterosexual contact. **Explanation:** The transmission of Human Immunodeficiency Virus (HIV) occurs through the exchange of specific body fluids (blood, semen, vaginal secretions, and breast milk). **1. Why Heterosexual Contact is Correct:** Globally, **heterosexual contact** is the most common mode of transmission, accounting for the vast majority of new infections. This is particularly driven by high prevalence rates in Sub-Saharan Africa and parts of Asia. In the Indian context as well, heterosexual transmission remains the primary route of spread (responsible for over 85% of cases according to NACO data). **2. Analysis of Incorrect Options:** * **Homosexual contact (MSM):** While this is the predominant mode of transmission in many high-income countries (like the USA), it does not represent the majority of cases on a global scale. * **Intravenous Drug Abuse (IVDU):** This is a high-risk behavior due to direct blood-to-blood contact via shared needles, but it accounts for a smaller percentage of the global burden compared to sexual transmission. * **Contaminated blood products:** This is the **most efficient** mode of transmission (nearly 90-100% risk per exposure), but due to mandatory screening of blood banks, it is now the least common mode of transmission. **Clinical Pearls for NEET-PG:** * **Efficiency vs. Frequency:** Do not confuse "most common" (Heterosexual) with "most efficient" (Blood transfusion). * **Vertical Transmission:** The risk of mother-to-child transmission (MTCT) is approximately 30% without intervention, but can be reduced to HCV (3%) > HIV (0.3%).

Q: The SAFE strategy is used in the management of which condition?

Trachoma. **Explanation:** The **SAFE strategy** is a comprehensive public health approach recommended by the World Health Organization (WHO) for the elimination of **Trachoma**, which is caused by *Chlamydia trachomatis* (serotypes A, B, Ba, and C). Trachoma is the leading infectious cause of blindness worldwide. The acronym **SAFE** stands for: * **S – Surgery:** To correct trichiasis (inward-turning eyelashes) and prevent corneal scarring. * **A – Antibiotics:** Specifically, mass drug administration (MDA) of **Azithromycin** (single dose) or topical Tetracycline to treat the active infection. * **F – Facial cleanliness:** To reduce transmission via eye and nose secretions. * **E – Environmental improvement:** Improving access to water and sanitation (e.g., fly control) to break the cycle of reinfection. **Analysis of Incorrect Options:** * **Inclusion conjunctivitis:** Caused by *C. trachomatis* (serotypes D-K). While it is related to Trachoma, it is a sexually transmitted infection treated individually, not via the community-based SAFE strategy. * **Ophthalmia neonatorum:** Neonatal conjunctivitis occurring within the first month of life. Management focuses on prophylaxis (Povidone-iodine) and systemic treatment of the mother and infant, not environmental strategies. * **Haemorrhagic conjunctivitis:** Usually caused by Picornaviruses (Enterovirus 70). It is a self-limiting viral infection that does not require the multi-pronged SAFE approach. **High-Yield Clinical Pearls for NEET-PG:** * **WHO Grading (FISTO):** Trachomatous **F**ollicular, **I**ntense, **S**carring, **T**richiasis, and **O**pacity. * **Drug of Choice:** Oral Azithromycin (20 mg/kg up to 1g). * **Vector:** *Musca sorbens* (the eye-seeking fly) is the primary vector. * **India Status:** India was declared free from "infective trachoma" in 2017, but surveillance for trichiasis continues.

Q: Which household insecticide is commonly used for malaria control?

Malathion. **Explanation:** **Malathion (Option A)** is the correct answer because it is a widely used organophosphorus insecticide employed in public health programs for **Indoor Residual Spraying (IRS)** and ultra-low volume (ULV) fogging to control adult *Anopheles* mosquitoes. It acts by inhibiting acetylcholinesterase, leading to the paralysis and death of the vector. In India, under the National Vector Borne Disease Control Programme (NVBDCP), Malathion is specifically used in areas where vectors have developed resistance to DDT. **Analysis of Incorrect Options:** * **Pyrethrum (Option B):** This is a natural insecticide derived from Chrysanthemum flowers. While it is a potent "knock-down" agent used in space sprays, it lacks the residual efficacy required for long-term household malaria control compared to Malathion. * **Paris Green (Option C):** This is an emerald-green copper-acetoarsenite compound. It is a **larvicide** (stomach poison) used specifically to kill *Anopheles* larvae in stagnant water; it is not used as a household insecticide for adult mosquitoes. * **Permethrin (Option D):** This is a synthetic pyrethroid primarily used for **Insecticide-Treated Nets (ITNs)** and Long-Lasting Insecticidal Nets (LLINs) rather than as a primary household residual spray in the same capacity as Malathion. **High-Yield Facts for NEET-PG:** * **DDT:** Still the first-line agent for IRS in many parts of India unless resistance is documented. * **Space Spraying:** Pyrethrum is the drug of choice for "knock-down" effect during epidemics. * **Larvicides:** Abate (Temephos) is the preferred chemical larvicide for potable water; Paris Green is for non-potable water. * **Biological Control:** *Gambusia affinis* (Mosquito fish) and *Poecilia reticulata* (Guppy fish) are used for larval control.

Q: Which of the following statements is true about the rash of chickenpox?

Centripetal distribution. ### Explanation **Chickenpox (Varicella)** is caused by the Varicella-Zoster Virus (VZV). Understanding the characteristics of its rash is a high-yield topic for NEET-PG. **Why Option A is Correct:** The rash of chickenpox follows a **centripetal distribution**. This means the lesions are most dense on the trunk (center) and less dense on the extremities (periphery). The rash typically starts on the trunk and then spreads to the face and limbs. **Analysis of Incorrect Options:** * **B. Deep-seated lesions:** Chickenpox lesions are **superficial** and thin-walled, often described as "dewdrops on a rose petal." Deep-seated, firm lesions are characteristic of Smallpox. * **C. Affects palms:** Chickenpox typically **spares the palms and soles**. If a rash involves the palms and soles, clinicians should consider Smallpox, Syphilis, or Hand-Foot-Mouth Disease. * **D. Slow to evolve:** The rash is **rapidly evolving**. It progresses from macule to papule, vesicle, and scab within 24 hours. **Clinical Pearls for NEET-PG:** * **Pleomorphism:** This is the hallmark of chickenpox. Lesions at all stages of development (papules, vesicles, and crusts) are seen simultaneously in the same area. * **Fever:** In chickenpox, the fever usually appears with the onset of the rash (prodromal stage is very short or absent in children). * **Infectivity:** Patients are infectious from 48 hours *before* the rash appears until all lesions have crusted over. * **Scabs:** Unlike Smallpox, the scabs of chickenpox are **not infectious**.

Q: What is the recommended prophylaxis for health personnel working in a plague ward?

A course of tetracycline. **Explanation:** The correct answer is **C. A course of tetracycline**. **Medical Concept:** Plague, caused by *Yersinia pestis*, is a highly infectious disease. Health personnel working in plague wards are at high risk of exposure to pneumonic plague, which spreads via respiratory droplets. For post-exposure prophylaxis (PEP) or for those in close contact with patients, **chemoprophylaxis** is the gold standard. A short course (usually 7 days) of **Tetracycline** (or Doxycycline) is recommended to prevent the onset of the disease. **Analysis of Options:** * **A. Vaccine:** Plague vaccines (killed or live attenuated) are primarily used for pre-exposure prophylaxis in high-risk laboratory workers. They are **not** effective for immediate protection in an outbreak or ward setting because they take time to induce immunity and do not protect against pneumonic plague effectively. * **B. Tetracycline throughout the duty:** Chemoprophylaxis is administered as a fixed **course** (7 days) rather than indefinitely throughout the duty period to minimize toxicity and the risk of antibiotic resistance. * **D. Vaccine and Erythromycin:** Erythromycin is not the first-line drug for plague prophylaxis. Tetracyclines and Sulfonamides are preferred. As mentioned, the vaccine has no role in immediate post-exposure management. **High-Yield Pearls for NEET-PG:** * **Drug of Choice (DOC) for Treatment:** Streptomycin (Gentamicin is an alternative). * **DOC for Prophylaxis:** Tetracycline or Doxycycline. * **Vector:** Rat flea (*Xenopsylla cheopis*). * **Quarantine Period:** 6 days (International Health Regulations). * **Diagnostic Test:** Wayson stain (shows characteristic "safety-pin" appearance).

Q: What is the average number of fleas of each species per rodent called?

Specific Flea Index. ### Explanation In the study of plague epidemiology, flea indices are critical metrics used to monitor the risk of disease transmission from rodents to humans. **1. Why "Specific Flea Index" is correct:** The **Specific Flea Index** is defined as the average number of fleas of a **particular species** found per rodent host. For example, calculating the average number of *Xenopsylla cheopis* per rat gives the "Cheopis Index." This is a vital indicator because different flea species have varying efficiencies as plague vectors. A Cheopis Index greater than **1.0** is considered the critical threshold for an increased risk of a plague outbreak. **2. Why the other options are incorrect:** * **General Flea Index:** This refers to the average number of fleas of **all species** found per rodent. It provides a broad measure of infestation but does not account for the vector efficiency of specific species. * **Incidence of Flea Species:** This is not a standard epidemiological term in malariology or plague control. Incidence typically refers to the number of new cases of a disease in a population over a period. * **Flea Infestation Rate:** This is the **percentage** of rodents infested with fleas (of any species). It measures how widespread the infestation is among the host population, rather than the density of fleas per host. **3. High-Yield Facts for NEET-PG:** * **Vector of Plague:** *Xenopsylla cheopis* (Oriental rat flea) is the most efficient vector. * **Critical Threshold:** A Cheopis Index **> 1** indicates a potential plague epidemic. * **Blocking Phenomenon:** This occurs when *Yersinia pestis* multiplies in the flea's proventriculus, preventing blood from entering the stomach. The "blocked" flea bites repeatedly in an attempt to feed, thereby transmitting the bacteria. * **Total Flea Index:** Another name for the General Flea Index.

Question 1

What is the best method for immunoprophylaxis of leprosy?

Accepted Answer

Killed ICRC bacillus

Answer

MMR vaccine

Answer

Plague bacillus vaccine

Answer

Anthrax bacillus vaccine

Question 2

Pleomorphism is seen in which of the following conditions?

Accepted Answer

Chickenpox

Answer

Rubella

Answer

Smallpox

Answer

Toxocara

Question 3

Which patient with positive sputum requires quarantine?

Accepted Answer

Children below 6 years of age

Answer

Pregnant women

Answer

Elderly individuals

Answer

Children above 6 years of age

Question 4

What is the approximate risk of mother-to-child transmission of HIV?

Accepted Answer

25%

Answer

50%

Answer

60%

Answer

75%

Question 5

What is the most common mode of transmission of HIV worldwide?

Accepted Answer

Heterosexual contact

Answer

Homosexual contact

Answer

Intravenous drug abuse

Answer

Contaminated blood products

Question 6

The SAFE strategy is used in the management of which condition?

Accepted Answer

Trachoma

Answer

Inclusion conjunctivitis

Answer

Ophthalmia neonatorum

Answer

Haemorrhagic conjunctivitis

Question 7

Which household insecticide is commonly used for malaria control?

Accepted Answer

Malathion

Answer

Pyrethrum

Answer

Paris green

Answer

Permethrin

Question 8

Which of the following statements is true about the rash of chickenpox?

Accepted Answer

Centripetal distribution

Answer

Deep seated lesions

Answer

Affects palms

Answer

Slow to evolve

Question 9

What is the recommended prophylaxis for health personnel working in a plague ward?

Accepted Answer

A course of tetracycline

Answer

Vaccine

Answer

Tetracycline throughout the duty

Answer

Vaccine and Erythromycin

Question 10

What is the average number of fleas of each species per rodent called?

Accepted Answer

Specific Flea Index

Answer

General Flea Index

Answer

Incidence of Flea Species

Answer

Flea Infestation Rate

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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