Infectious Diseases Practice Questions

Q: What is the most appropriate test to assess the prevalence of tuberculosis infection in a community?

Tuberculin test. **Explanation:** The **Tuberculin Skin Test (TST/Mantoux test)** is the gold standard for estimating the **prevalence of tuberculosis infection** in a community. It measures delayed-type hypersensitivity to Purified Protein Derivative (PPD). It is important to distinguish between "infection" (presence of bacilli in the body without clinical disease) and "disease" (active clinical symptoms). TST identifies individuals who have been infected at some point, making it the primary tool for calculating the **Annual Risk of Tuberculosis Infection (ARTI)**. **Analysis of Options:** * **Mass Miniature Radiography (MMR):** While useful for screening large groups for lung abnormalities, it is non-specific, expensive, and carries radiation risks. It detects structural changes (disease) but cannot confirm infection status. * **Sputum Examination:** This is the "Gold Standard" for diagnosing **active pulmonary tuberculosis (case detection)** and monitoring treatment response. However, it only identifies infectious cases (smear-positive) and misses latent infections. * **Clinical Examination:** This is highly subjective and lacks the sensitivity or specificity required to estimate prevalence, as many infected individuals remain asymptomatic (latent TB). **High-Yield Facts for NEET-PG:** * **ARTI (Annual Risk of TB Infection):** The best indicator of the TB transmission trend in a community; it is derived from TST surveys in children. * **Prevalence of Disease:** Best measured by a combination of Chest X-ray and Sputum culture. * **Incidence of Disease:** Best measured by notification data or longitudinal cohort studies. * **Cut-off:** In India, an induration of **≥10 mm** after 48–72 hours is generally considered positive.

Q: Which of the following statements regarding varicella infection is NOT true?

Scabs are highly infective. **Explanation:** The correct answer is **A (Scabs are highly infective)**. This statement is false because, in Varicella (Chickenpox), the virus is present in the vesicular fluid and respiratory secretions, but **not in the scabs/crusts**. Once the lesions have crusted over, the patient is no longer considered infectious. **Analysis of Options:** * **Option A (False):** Unlike Smallpox (where scabs are infectious), Varicella scabs are non-infectious. Infectivity lasts from 1–2 days before the rash appears until all vesicles have crusted (usually 5 days after rash onset). * **Option B (True):** Varicella is caused by **Varicella-Zoster Virus (VZV)**, which is Human Herpes Virus 3 (HHV-3), a member of the Alphaherpesvirinae subfamily. * **Option C (True):** The primary modes of transmission are inhalation of **respiratory droplets** (oro-pharyngeal secretions) and direct contact with the fluid from skin lesions. * **Option D (True):** The distribution of the rash is **centripetal**, meaning it appears first on the trunk (where it is most abundant) and then spreads to the face and extremities. **High-Yield Clinical Pearls for NEET-PG:** * **Pleomorphism:** "Dew-drop on a rose petal" appearance; lesions of all stages (papules, vesicles, crusts) are seen simultaneously. * **Secondary Attack Rate:** Very high (~90%) in susceptible household contacts. * **Congenital Varicella Syndrome:** Characterized by cicatricial skin scarring, limb hypoplasia, and chorioretinitis if the mother is infected during the first 20 weeks of pregnancy. * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusion bodies.

Q: Which of the following influenza virus types is NOT currently circulating in the world?

H5N1. **Explanation:** The question focuses on the distinction between **seasonal (human) influenza** viruses and **avian/zoonotic influenza** viruses. **Why H5N1 is the correct answer:** H5N1 is a highly pathogenic avian influenza (HPAI) virus. While it causes sporadic outbreaks in poultry and occasional "spillover" infections in humans, it has **not** achieved sustained human-to-human transmission. Therefore, it is not considered a "currently circulating" seasonal human influenza virus. In the context of public health surveillance, "circulating" refers to viruses regularly spreading within the human population. **Analysis of Incorrect Options:** * **H1N1:** This is a subtype of Influenza A. The A(H1N1)pdm09 strain has been circulating globally as a seasonal virus since the 2009 pandemic. * **H3N2:** This is another subtype of Influenza A that currently circulates globally among humans and often causes more severe seasonal epidemics compared to H1N1. * **Influenza B virus:** Unlike Influenza A, these are not divided into subtypes but into **lineages** (Victoria and Yamagata). Influenza B is a standard component of the seasonal flu burden in humans. **High-Yield NEET-PG Pearls:** 1. **Antigenic Shift vs. Drift:** Seasonal circulation is maintained by *Antigenic Drift* (point mutations). A pandemic occurs due to *Antigenic Shift* (genetic reassortment), which could potentially happen if a virus like H5N1 gains the ability for human-to-human spread. 2. **Current Seasonal Vaccine:** The WHO-recommended quadrivalent vaccine typically covers four strains: Influenza A (H1N1), Influenza A (H3N2), and two Influenza B lineages. 3. **Drug of Choice:** Oseltamivir (Neuraminidase inhibitor) remains the primary treatment for both seasonal and suspected avian influenza cases.

Q: Which of the following are direct zoonoses?

Rabies and Brucellosis. ### Explanation **Concept of Direct Zoonoses** Zoonoses are classified based on their life cycle and mode of transmission. **Direct Zoonoses** are diseases transmitted from an infected vertebrate host to a susceptible human host by direct contact, contact with a fomite, or by a mechanical vector. Crucially, the agent undergoes **no essential developmental change or propagation** during transmission. **Why Option D is Correct:** * **Rabies:** Transmitted directly via the bite of an infected animal (saliva). The virus does not require an intermediate host or developmental cycle outside the vertebrate host. * **Brucellosis:** Transmitted through direct contact with infected animal tissues, secretions, or the consumption of unpasteurized milk. * *Other examples include: Anthrax, Leptospirosis, and Q fever.* **Analysis of Incorrect Options:** * **Options A & C (Taeniasis and Hydatid disease):** These are classified as **Cyclozoonoses**. These diseases require more than one vertebrate host (e.g., humans and cattle for *T. saginata*; humans and dogs for *E. granulosus*) to complete their life cycle, but no invertebrate host. * **Option B:** While Rabies is a direct zoonosis, this option is incomplete as Brucellosis also fits the definition provided in the context of the question. **NEET-PG High-Yield Pearls:** 1. **Metazoonoses:** Require both a vertebrate and an **invertebrate host** (e.g., Plague, Malaria, Kala-azar). 2. **Saprozoonoses:** Require a vertebrate host and a **non-animal environmental reservoir** like soil or plants (e.g., Tetanus, Histoplasmosis). 3. **Ornithosis:** A term often used for Psittacosis (Chlamydia psittaci), which is a direct zoonosis transmitted from birds.

Q: A freshly prepared oral rehydration solution should not be used after how many hours?

24 hours. ### Explanation **Correct Answer: D. 24 hours** **Underlying Medical Concept:** Oral Rehydration Solution (ORS) is a non-sterile preparation containing glucose and electrolytes. Once the ORS powder is dissolved in water, it becomes a potential medium for bacterial growth, especially in tropical climates or unhygienic conditions. The glucose in the solution acts as a substrate for microorganisms. According to **WHO and UNICEF guidelines**, a freshly prepared ORS solution must be discarded after **24 hours** to prevent the risk of secondary bacterial contamination and potential worsening of diarrhea (iatrogenic gastroenteritis). **Analysis of Incorrect Options:** * **A, B, and C (4, 6, and 12 hours):** These timeframes are too short. While the solution is safest when used immediately, discarding it within 4–12 hours would lead to unnecessary wastage of resources, especially in community settings where access to clean water and ORS packets may be limited. The 24-hour mark is the standardized safety threshold. **High-Yield Clinical Pearls for NEET-PG:** * **Standard WHO ORS Composition (Reduced Osmolarity):** Sodium (75 mmol/L), Glucose (75 mmol/L), Chloride (65 mmol/L), Potassium (20 mmol/L), and Citrate (10 mmol/L). * **Total Osmolarity:** 245 mOsm/L (This is a frequent "image-based" or "value-based" question). * **Role of Citrate:** It increases the shelf life of the powder and helps in correcting acidosis. * **Zinc Supplementation:** Always used alongside ORS in pediatric diarrhea (20 mg/day for 14 days; 10 mg/day for infants <6 months) to reduce the duration and recurrence of episodes.

Q: Which of the following is NOT a zoonotic disease?

Rubella. **Explanation:** The core concept tested here is the definition of a **Zoonosis**, which is an infectious disease that is naturally transmitted from vertebrate animals to humans. **Why Rubella is the correct answer:** Rubella (German Measles) is **not** a zoonotic disease because humans are the **only known reservoir** for the Rubella virus. It is transmitted person-to-person via respiratory droplets. Since there is no animal involvement in its natural life cycle, it cannot be classified as a zoonosis. **Analysis of incorrect options:** * **Tuberculosis (A):** While *M. tuberculosis* is primarily human-to-human, *Mycobacterium bovis* causes **Bovine Tuberculosis**, which is a classic zoonosis transmitted to humans via unpasteurized milk. * **Q Fever (B):** Caused by *Coxiella burnetii*, this is a highly infectious zoonosis. The primary reservoirs are cattle, sheep, and goats. Humans are infected by inhaling contaminated dust or handling infected animal products. * **Taeniasis (C):** This is a parasitic zoonosis. *Taenia saginata* (beef tapeworm) and *Taenia solium* (pork tapeworm) require animal intermediate hosts to complete their life cycle before infecting humans. **NEET-PG High-Yield Pearls:** 1. **Anthropozoonoses:** Diseases transmitted from animals to man (e.g., Rabies, Leptospirosis, Plague). 2. **Zooanthroponoses:** Diseases transmitted from man to animals (e.g., Human Tuberculosis to cattle). 3. **Cyclozoonoses:** Require more than one vertebrate host species to complete the life cycle (e.g., Echinococcosis, Taeniasis). 4. **Metazoonoses:** Transmitted by an invertebrate vector (e.g., Plague, Arboviruses). 5. **Saprozoonoses:** Require a non-animal environmental reservoir like soil (e.g., Tetanus, Histoplasmosis).

Q: Which of the following diseases is not transmitted by Aedes mosquitoes?

Bancroftian filariasis. **Explanation:** The correct answer is **Bancroftian filariasis** because its primary vector is the **Culex mosquito** (specifically *Culex quinquefasciatus*), not the *Aedes* mosquito. While *Aedes* species can transmit certain types of filariasis (like *Brugia malayi* in specific regions), the classic Bancroftian filariasis caused by *Wuchereria bancrofti* is globally associated with *Culex* in urban and semi-urban settings. **Analysis of Options:** * **Yellow fever:** This is a viral hemorrhagic fever caused by a Flavivirus. It is primarily transmitted by *Aedes aegypti* (urban cycle) and *Haemagogus* species (sylvatic cycle). * **Dengue fever:** Caused by the Dengue virus (Flavivirus), it is the most common mosquito-borne viral disease in humans, transmitted predominantly by *Aedes aegypti* and *Aedes albopictus*. * **Chikungunya fever:** Caused by an Alphavirus (Togaviridae), it is transmitted to humans by the same *Aedes* vectors (*A. aegypti* and *A. albopictus*), often leading to outbreaks in the same geographical areas as Dengue. **High-Yield Clinical Pearls for NEET-PG:** * **Aedes Characteristics:** Known as "Day biters" (peak activity at dawn and dusk) and "Tiger mosquitoes" due to white stripes on their legs. They breed in artificial collections of clean water (e.g., flower pots, discarded tires). * **Vector Mnemonics:** * **Culex:** Bancroftian Filariasis, Japanese Encephalitis, West Nile Virus. * **Anopheles:** Malaria. * **Aedes:** Dengue, Chikungunya, Yellow Fever, Zika Virus. * **Wuchereria bancrofti:** Exhibits **nocturnal periodicity** (microfilariae appear in peripheral blood between 10 PM and 2 AM), correlating with the biting habits of the *Culex* mosquito.

Q: Before starting antiretroviral therapy, NACO recommends how many sessions of counseling?

2. **Explanation:** The National AIDS Control Organization (NACO) guidelines emphasize that **treatment preparedness** is the cornerstone of long-term success in Antiretroviral Therapy (ART). **Why 2 sessions are correct:** According to NACO protocols, a minimum of **two counseling sessions** are mandatory before initiating ART. 1. **Session 1 (Initial Counseling):** Focuses on the basics of HIV, the benefits of ART, the necessity of lifelong commitment, and identifying a treatment supporter. 2. **Session 2 (Follow-up/Readiness Assessment):** Conducted to reinforce the information from the first session, assess the patient's readiness, address potential barriers to adherence (like substance abuse or mental health issues), and ensure the patient understands that 95% adherence is required for viral suppression. **Analysis of Incorrect Options:** * **Option A (1 session):** A single session is considered insufficient to ensure the patient has fully grasped the complexities of lifelong therapy and the implications of drug resistance. * **Options C & D (3 or 4 sessions):** While additional sessions may be conducted if a patient is deemed "not ready" or has complex psychosocial issues, the *standard recommendation* for a stable patient is two sessions to avoid unnecessary delays in starting treatment. **High-Yield Clinical Pearls for NEET-PG:** * **Adherence Goal:** For ART to be effective and to prevent drug resistance, a minimum of **>95% adherence** is required. * **Treatment Supporter:** NACO recommends identifying a "Treatment Supporter" (usually a family member or friend) during these sessions to supervise drug intake. * **"Test and Treat" Policy:** Regardless of CD4 count or clinical stage, all HIV-positive individuals are now eligible for ART; however, the two-session preparedness rule still applies to ensure retention in care.

Question 1

Which of the following is true about resistant tuberculosis?

Accepted Answer

Clinical deterioration.

Answer

Sputum smear is positive after 5 months.

Answer

Culture is positive after 3 months.

Answer

Active disease in chest X-ray.

Question 2

What is the most appropriate test to assess the prevalence of tuberculosis infection in a community?

Accepted Answer

Tuberculin test

Answer

Mass miniature radiography

Answer

Sputum examination

Answer

Clinical examination

Question 3

Which of the following statements regarding varicella infection is NOT true?

Accepted Answer

Scabs are highly infective

Answer

Caused by a herpes virus

Answer

Transmitted by oro-pharyngeal secretions

Answer

Vesicles are centripetal in distribution

Question 4

Which of the following influenza virus types is NOT currently circulating in the world?

Accepted Answer

H5N1

Answer

H1N1

Answer

H3N2

Answer

Influenza B virus

Question 5

Which of the following are direct zoonoses?

Accepted Answer

Rabies and Brucellosis

Answer

Rabies and Taeniasis

Answer

Rabies

Answer

Rabies and Hydatid disease

Question 6

A freshly prepared oral rehydration solution should not be used after how many hours?

Accepted Answer

24 hours

Answer

4 hours

Answer

6 hours

Answer

12 hours

Question 7

Which of the following is NOT a zoonotic disease?

Accepted Answer

Rubella

Answer

Tuberculosis

Answer

Q fever

Answer

Taeniasis

Question 8

Which of the following diseases is not transmitted by Aedes mosquitoes?

Accepted Answer

Bancroftian filariasis

Answer

Yellow fever

Answer

Dengue fever

Answer

Chikungunya fever

Question 9

Before starting antiretroviral therapy, NACO recommends how many sessions of counseling?

Accepted Answer

2

Answer

1

Answer

3

Answer

4

Question 10

If a patient with tuberculosis who is sputum smear positive continues to be smear positive at the end of the intensive phase of Category I treatment under DOTS, what is the recommended further management?

Accepted Answer

Continue the intensive phase or treatment for one more month.

Answer

Restart Category I treatment.

Answer

Treat as a failure and initiate Category II treatment under DOTS.

Answer

Start the continuation phase under Category I.

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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