Infectious Diseases Practice Questions

Q: What is the best disinfectant for cholera stool?

Cresol. ### Explanation In the management of a Cholera outbreak, the immediate disinfection of excreta (stool and vomit) is a critical step in breaking the chain of transmission. **Why Cresol is the Correct Answer:** **Cresol (5% solution)** is considered the disinfectant of choice for cholera stool. The primary reason is its high efficacy in the presence of **organic matter**. Cholera stools are voluminous and contain significant organic debris; while many disinfectants are neutralized by organic loads, Cresol retains its germicidal activity. It requires a contact time of approximately **1 hour** for complete disinfection. **Analysis of Incorrect Options:** * **Bleaching Powder (Calcium Hypochlorite):** While excellent for water disinfection, it is less effective for bulk stool because the organic matter rapidly consumes the free chlorine, rendering it ineffective unless used in very high, impractical concentrations. * **Phenol:** Although a standard antiseptic, it is generally less potent than its derivative, Cresol (which has a higher phenol coefficient). Cresol is preferred in public health practice for crude disinfection tasks. * **Lime (Slaked Lime):** Historically used for disinfecting gutters or feces in pits, it is less reliable and slower-acting compared to chemical germicides like Cresol for immediate bedside disinfection. **High-Yield Clinical Pearls for NEET-PG:** * **Best disinfectant for Cholera stool:** Cresol (5%). * **Best disinfectant for Water (Cholera):** Bleaching powder (Chlorine). * **Contact time for stool disinfection:** Minimum 1 hour. * **Concurrent Disinfection:** This refers to the immediate disinfection of all infectious excreta and soiled articles (linen) during the course of the illness. * **Terminal Disinfection:** Disinfection of the patient’s environment after they have recovered or died.

Q: Which of the following diseases involves a transmission chain with birds, arthropods, and humans?

Japanese encephalitis. **Explanation:** **Japanese Encephalitis (JE)** is the correct answer because it follows a complex **zoonotic transmission cycle** involving three key components: 1. **Birds:** Ardeid birds (herons and egrets) act as the **natural reservoir** hosts. 2. **Arthropods:** The primary vector is the **Culex tritaeniorhynchus** mosquito, which breeds in stagnant water like rice fields. 3. **Humans:** Humans act as **accidental, dead-end hosts** because the viremia in humans is insufficient to infect a biting mosquito. *Note: Pigs are the most important "amplifier hosts" in this cycle, but the bird-arthropod-human chain is a classic description of JE ecology.* **Why the other options are incorrect:** * **Malaria:** Involves an **Anopheles** mosquito and **Humans** only. There is no avian (bird) reservoir involved in human malaria. * **Paragonimus (Lung Fluke):** A parasitic infection involving a complex cycle with snails (1st intermediate host), crustaceans/crabs (2nd intermediate host), and humans/mammals. It does not involve birds or arthropod vectors. * **Plague:** Primarily involves **Rodents** (rats) and the **Rat Flea** (*Xenopsylla cheopis*). While birds are not part of the cycle, humans are accidental hosts. **High-Yield NEET-PG Pearls:** * **Vector:** *Culex tritaeniorhynchus* (Night biter, rice field breeder). * **Amplifier Host:** Pig (shows no symptoms but produces high viral titers). * **Dead-end Hosts:** Humans and Horses. * **Vaccine:** Live attenuated **SA-14-14-2** is commonly used in the Universal Immunization Programme (UIP) in endemic districts of India. * **Seasonality:** Peak incidence coincides with the rainy season and post-harvest periods.

Q: Which mosquito species is recognized as the principal secondary vector for Zika virus transmission globally?

Aedes albopictus. ***Aedes albopictus*** - This mosquito, commonly known as the **Asian tiger mosquito**, is recognized as the **principal secondary vector** for Zika virus transmission globally. - It is a competent vector capable of transmitting **Zika**, **Dengue**, and **Chikungunya** viruses across multiple continents including Asia, Europe, Africa, and the Americas. - While *Aedes aegypti* remains the primary vector, *Aedes albopictus* plays a significant role in Zika transmission, particularly in temperate regions where *Ae. aegypti* is less prevalent. - Its adaptability to diverse climates and ability to breed in natural and artificial water containers make it epidemiologically important. *Aedes polynesiensis* - This species is primarily known as a vector for **lymphatic filariasis** (*Wuchereria bancrofti*) in Pacific islands. - While it was involved in Zika virus transmission during the **French Polynesia outbreak (2013-2014)**, it is geographically restricted and not considered a principal vector for global Zika transmission. - Its role is limited to specific Pacific island populations. *Aedes australis* - This species is endemic to Australia and transmits **Ross River virus** and other Australian arboviruses. - It is **not** a recognized vector for Zika virus transmission. - Its geographical distribution and host preferences exclude it from the Zika transmission cycle. *Aedes mitchellae* - This species is not documented in major public health literature as a vector for Zika virus. - It belongs to a mosquito species complex with no established role in arboviral transmission to humans. - Epidemiologically insignificant for Zika virus transmission.

Q: What is the usual method of collecting a sample of urine to detect UTI?

Midstream catch. ***Midstream catch*** - This technique is the *standard, non-invasive method* for routine urine culture as it minimizes **contamination** from bacteria residing in the distal urethra and periurethral area. - By discarding the initial urine (starting stream) and collecting the middle portion, the sample is more representative of the urine contained within the **bladder**. *Early morning sample* - While an early morning sample is often preferred for optimal concentration (e.g., detecting **proteinuria** or **casts**), it is not the methodology for *minimizing contamination*. - The collection technique (midstream) is more critical than the time of day for ensuring a reliable sample for **UTI culture**. *Suprapubic catheter* - Suprapubic aspiration (SPA) provides an **uncontaminated specimen** (often considered the gold standard), but it is an invasive procedure requiring a needle insertion into the bladder. - It is reserved for specific situations, such as neonates or patients with ambiguous results, and is not the **usual** collection method. *Starting stream collection* - The starting stream is most likely to be contaminated with **urethral flora** (e.g., *Staphylococcus epidermidis* or environmental organisms). - Collecting the starting stream significantly increases the chance of **false positive** culture results, confusing the diagnosis of a true **UTI**.

Q: Identify A and B in the image of the mosquito larvae given

A-Anopheles, B-Culex. ***A-Anopheles, B-Culex*** - Larva A is identified as **Anopheles** because it rests **parallel** to the water surface and lacks a respiratory **siphon**; Anopheles larvae lack a siphon and breathe through posterior spiracles while lying parallel to the water surface; palmate hairs assist flotation. - Larva B is identified as **Culex** as it hangs at an **angle** to the water surface and breathes through a long, narrow respiratory **siphon**. *A-Culex, B-Aedes* - This is incorrect as larva A exhibits the characteristics of **Anopheles** (no siphon, parallel resting), not **Culex**. - While **Aedes** larvae also hang at an angle, larva B's long siphon is more typical of **Culex**; **Aedes** larvae usually have a shorter, stouter siphon. *A-Culex, B-Anopheles* - This option incorrectly reverses the identities. Larva A is **Anopheles** and larva B is **Culex** based on their distinct resting postures and respiratory structures. - The key differentiating feature is the presence of a **siphon** in B (**Culex**) and its absence in A (**Anopheles**). *A-Anopheles, B-Mansonia* - Although the identification of A as **Anopheles** is correct, larva B is not **Mansonia**. - **Mansonia** larvae are unique as they attach to the roots of aquatic plants to obtain oxygen and do not hang from the surface, unlike the larva shown in B.

Q: The SAFE strategy given by WHO forms the mainstream of the management of Trachoma. What does the S in the acronym represent?

Surgery. ***Surgery*** - The 'S' in the WHO's SAFE strategy for Trachoma management stands for **Surgery**, which is essential for correcting **trichiasis** (in-turned eyelashes). - Surgery prevents irreversible vision loss by stopping the eyelashes from rubbing against and scarring the **cornea**. *Symptom* - Management of specific **symptoms** is generally an element of clinical treatment but does not represent a component of the comprehensive population-level intervention strategy known as SAFE. - The SAFE approach focuses on addressing the **infectious agent** (Antibiotics) and transmission factors (Facial cleanliness, Environmental improvement) for elimination. *Spectacles* - **Spectacles** are used for correcting refractive errors (like myopia or hyperopia) and are not a therapeutic measure for active **Chlamydia trachomatis** infection or trichiasis. - The goal of SAFE is elimination of the infectious cause and treatment of the blinding sequelae, not visual **refractive correction**. *Symbol* - A **symbol** is an abstract representation and does not constitute a concrete public health or clinical intervention necessary for the elimination of trachoma. - The other components (**Antibiotics**, **Facial cleanliness**, **Environmental improvement**) are tangible actions aimed at disease control and prevention.

Q: Which of the following is correctly matched for vectors and diseases? Vector: A. Louse, B. Mite, C. Flea, D. Tick. Disease: I. Scrub typhus, II. Endemic typhus, III. Rocky Mountain spotted fever, IV. Epidemic typhus.

A-IV, B-I, C-II, D-III. ***A-IV, B-I, C-II, D-III (Correct)*** - **Louse (A)** transmits **Epidemic typhus (IV)**, caused by *Rickettsia prowazekii*, typically occurring in overcrowded, unhygienic environments. - **Mite (B)** (chigger) transmits **Scrub typhus (I)**, caused by *Orientia tsutsugamushi*. - **Flea (C)** (rat flea) transmits **Endemic typhus (II)**, caused by *Rickettsia typhi*. - **Tick (D)** transmits **Rocky Mountain spotted fever (III)**, caused by *Rickettsia rickettsii*. *A-I, B-III, C-IV, D-II (Incorrect)* - Incorrectly matches Louse (A) with Scrub typhus (I); scrub typhus is transmitted by **mites** (chiggers), not lice. - Incorrectly matches Mite (B) with Rocky Mountain spotted fever (III); RMSF is transmitted by **ticks**, not mites. *A-II, B-III, C-IV, D-I (Incorrect)* - Incorrectly matches Louse (A) with Endemic typhus (II); endemic typhus is transmitted by **fleas** (rat flea), not lice. - Incorrectly matches Flea (C) with Epidemic typhus (IV); epidemic typhus is transmitted by **lice**, not fleas. *A-IV, B-III, C-I, D-II (Incorrect)* - While A-IV is correct (Louse-Epidemic typhus), this option incorrectly matches Mite (B) with Rocky Mountain spotted fever (III), which is transmitted by **ticks**. - Incorrectly matches Flea (C) with Scrub typhus (I); scrub typhus is transmitted by **mites**, not fleas.

Q: Which of the following is not classified under High-Risk Groups for HIV as per NACO guidelines?

Truck drivers. ***Truck drivers*** - While considered a **Bridge Population** or a vulnerable group due to high mobility and potential for engaging in high-risk behavior, they are not categorized as a primary **High-Risk Group (HRG)** by NACO. - **Bridge Populations** facilitate the transmission of HIV between high-risk groups and the general population. ***Men having sex with men (MSM)*** - **MSM** is designated as a core **High-Risk Group (HRG)** due to a significantly higher prevalence of HIV compared to the general population. - The mode of transmission (anal intercourse) carries a higher risk and is considered a key factor in NACO's classification. ***Female sex workers (FSW)*** - **FSW** is classified as a core **High-Risk Group (HRG)** because of high exposure risk and the potential for greater onward transmission to the general population. - They are a major focus of targeted interventions under the National AIDS Control Programme (NACP). ***Injecting drug users (IDUs)*** - **IDUs** are a vital **High-Risk Group (HRG)** primarily due to the sharing of contaminated needles and syringes, leading to immediate blood-to-blood transmission (Parenteral route). - Targeted interventions focus on harm reduction strategies like Needle and Syringe Exchange Programmes (NSEP).

Q: According to WHO, which rapid molecular test is recommended as the initial diagnostic investigation for tuberculosis (TB) spine?

CBNAAT. ***CBNAAT*** - The **WHO** strongly recommends **CBNAAT (GeneXpert or Truenat)** as the **initial rapid molecular diagnostic test** for extrapulmonary TB (EPTB), including **TB spine (Pott's disease)**, due to its rapid turnaround time and high sensitivity. - CBNAAT simultaneously detects **Mycobacterium tuberculosis** DNA and identifies resistance to **Rifampicin**, providing critical information for prompt treatment initiation, typically within 2 hours. - This rapid molecular test is preferred over traditional methods for initial diagnosis to enable early treatment decisions. *Incorrect: X-ray* - X-rays are imaging studies useful for detecting features like **vertebral destruction**, **paraspinal shadow**, and collapse leading to **gibbus deformity**, but they are not molecular diagnostic tests. - While X-rays are included in the diagnostic workup, they cannot confirm the presence of the organism or detect drug resistance, which is why they are not the WHO-recommended initial molecular test. *Incorrect: CT scan* - CT scans offer superior visualization of subtle bony changes, extent of destruction, and delineating **paraspinal cold abscesses**, often used for staging and guiding intervention. - Like X-ray, CT is an **imaging modality** that assists in identifying structural changes but is not a molecular diagnostic test and cannot provide microbiological confirmation or drug resistance information. *Incorrect: Culture and sensitivity* - **Culture (e.g., Lowenstein-Jensen, MGIT)** is considered the **gold standard** for definitive diagnosis and comprehensive Drug Susceptibility Testing (DST). - However, culture results are slow (taking 4–8 weeks), which delays crucial management decisions, leading the WHO to prioritize **rapid molecular tests** like CBNAAT for **initial diagnosis** over culture, though culture remains important for comprehensive DST.

Q: Which mosquito larva has no siphon and rests parallel to the water surface?

Anopheles. ***Anopheles*** - **Anopheles** larvae lack a **siphon** (breathing tube) and breathe through spiracles located on the dorsal surface of the abdomen. - This absence of a siphon causes them to rest **parallel** to the water surface, which is a key identifying feature for species differentiation. *Aedes* - **Aedes** larvae possess a **siphon**, which is relatively shorter and stouter compared to *Culex*. - They hang down from the water surface at an angle, utilizing the siphon for air intake, not lying parallel to the surface. *Culex* - **Culex** larvae possess a long, distinct **siphon** (breathing tube) at the posterior end of the abdomen. - Due to the siphon, they rest at an **angle** (typically 45-60 degrees) to the water surface for breathing. *Mansonia* - **Mansonia** larvae have a modified, sharp **siphon** used to pierce the submerged **stems of aquatic plants** for oxygen extraction. - They remain attached to these plants underwater and do not float on or rest parallel to the water surface.

Question 1

What is the best disinfectant for cholera stool?

Accepted Answer

Cresol

Answer

Bleaching powder

Answer

Phenol

Answer

Lime

Question 2

Which of the following diseases involves a transmission chain with birds, arthropods, and humans?

Accepted Answer

Japanese encephalitis

Answer

Malaria

Answer

Paragonimus

Answer

Plague

Question 3

Which mosquito species is recognized as the principal secondary vector for Zika virus transmission globally?

Accepted Answer

Aedes albopictus

Answer

Aedes polynesiensis

Answer

Aedes australis

Answer

Aedes mitchellae

Question 4

What is the usual method of collecting a sample of urine to detect UTI?

Accepted Answer

Midstream catch

Answer

Starting stream collection

Answer

Early morning sample

Answer

Suprapubic catheter

Question 5

Identify A and B in the image of the mosquito larvae given

Accepted Answer

A-Anopheles, B-Culex

Answer

A-Anopheles, B-Mansonia

Answer

A-Culex, B-Aedes

Answer

A-Culex, B-Anopheles

Question 6

The SAFE strategy given by WHO forms the mainstream of the management of Trachoma. What does the S in the acronym represent?

Accepted Answer

Surgery

Answer

Spectacles

Answer

Symbol

Answer

Symptom

Question 7

Which of the following is correctly matched for vectors and diseases? Vector: A. Louse, B. Mite, C. Flea, D. Tick. Disease: I. Scrub typhus, II. Endemic typhus, III. Rocky Mountain spotted fever, IV. Epidemic typhus.

Accepted Answer

A-IV, B-I, C-II, D-III

Answer

A-II, B-III, C-IV, D-I

Answer

A-IV, B-III, C-I, D-II

Answer

A-I, B-III, C-IV, D-II

Question 8

Which of the following is not classified under High-Risk Groups for HIV as per NACO guidelines?

Accepted Answer

Truck drivers

Answer

Men having sex with men (MSM)

Answer

Injecting drug users (IDUs)

Answer

Female sex workers (FSW)

Question 9

According to WHO, which rapid molecular test is recommended as the initial diagnostic investigation for tuberculosis (TB) spine?

Accepted Answer

CBNAAT

Answer

X-ray

Answer

CT scan

Answer

Culture and sensitivity

Question 10

Which mosquito larva has no siphon and rests parallel to the water surface?

Accepted Answer

Anopheles

Answer

Aedes

Answer

Mansonia

Answer

Culex

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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