Infectious Diseases Practice Questions

Q: What is the recommended follow-up period for an individual who has come into contact with a confirmed case of coronavirus (COVID-19)?

14 days. **Explanation:** The correct answer is **14 days**. This duration is based on the known **incubation period** of SARS-CoV-2 (the virus causing COVID-19). 1. **Why 14 days is correct:** The incubation period is the time from exposure to the virus to the onset of symptoms. For COVID-19, the incubation period typically ranges from 2 to 14 days, with an average of 5–6 days. Public health guidelines (WHO and MoHFW) established a 14-day quarantine/follow-up period to ensure that almost all exposed individuals (99% of cases) would manifest symptoms or test positive within this window. 2. **Analysis of Incorrect Options:** * **7 days (A):** While many patients develop symptoms by day 5 or 7, a significant percentage of "slow progressors" would be missed if follow-up ended this early. * **21 days (B) & 42 days (C):** These durations are unnecessarily long for routine follow-up. 21 days is more characteristic of the monitoring period for Ebola Virus Disease, while 42 days (two incubation cycles) is often used to declare an outbreak "over" in a specific region. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** 2–14 days (Median: ~5.1 days). * **Mode of Transmission:** Primarily respiratory droplets and fomites; airborne transmission possible in closed spaces/aerosol-generating procedures. * **Receptor:** SARS-CoV-2 binds to the **ACE-2 receptor** (Angiotensin-Converting Enzyme 2) found in the lungs, heart, and kidneys. * **Gold Standard Test:** Real-time Reverse Transcription Polymerase Chain Reaction (**rRT-PCR**) targeting genes like E (Envelope), RdRp, or N (Nucleocapsid).

Q: Culex mosquito spreads all of the following diseases except?

Yellow fever. **Explanation:** The correct answer is **Yellow fever** because it is primarily transmitted by the **Aedes aegypti** mosquito (and *Haemagogus* species in jungle cycles), not by the *Culex* mosquito. **Why Yellow Fever is the correct answer:** Yellow fever is a viral hemorrhagic fever caused by a Flavivirus. Its transmission cycle involves *Aedes* mosquitoes in urban settings. *Culex* mosquitoes are not biological vectors for this specific virus. **Analysis of other options:** * **Viral arthritis:** Several viruses causing arthritis, most notably the **Ross River virus** and **Sindbis virus**, are transmitted by *Culex* species. * **West Nile fever:** The *Culex* mosquito (specifically *C. pipiens*) is the primary vector for West Nile Virus, maintaining the transmission cycle between birds and humans. * **Bancroftian filariasis:** In many parts of the world, especially in urban and semi-urban areas of India, **Culex quinquefasciatus** is the classic vector for *Wuchereria bancrofti*. **High-Yield Clinical Pearls for NEET-PG:** 1. **Culex Characteristics:** They are "night-biters," breed in stagnant polluted water (like sewage), and fly with the body parallel to the surface. 2. **Diseases transmitted by Culex:** * **J**apanese Encephalitis (Vector: *Culex tritaeniorhynchus*) * **B**ancroftian Filariasis (*Culex quinquefasciatus*) * **W**est Nile Fever * **V**iral Arthritis (Ross River/Sindbis) 3. **Aedes vs. Culex:** Remember that *Aedes* transmits the "Big Three": Dengue, Chikungunya, and Yellow Fever, along with Zika. 4. **Japanese Encephalitis (JE):** This is the most important viral encephalitis transmitted by *Culex* in India; the mosquito acts as a bridge vector between pigs/herons and humans.

Q: Sputum from a patient is disinfected immediately following expectoration. This process is known as:

Concurrent disinfection. **Explanation:** The correct answer is **Concurrent Disinfection**. This refers to the immediate disinfection and disposal of infectious materials (such as sputum, urine, feces, or contaminated linen) throughout the course of an illness. The primary goal is to minimize the spread of the infectious agent from the patient to others by neutralizing the pathogen as soon as it leaves the body. **Analysis of Options:** * **Concurrent Disinfection (A):** This is the standard practice for active cases. By disinfecting sputum immediately after expectoration, the chain of transmission is broken in real-time. * **Pre-concurrent Disinfection (B):** This is not a standard epidemiological term used in infection control. * **Recurrent Disinfection (C):** This is a distractor term. While disinfection may happen repeatedly, the formal medical term for ongoing disinfection during illness is "concurrent." * **Terminal Disinfection (D):** This refers to the final disinfection of the patient’s room and personal belongings *after* the patient has recovered, been discharged, or died. It aims to ensure the environment is safe for the next occupant. **High-Yield Clinical Pearls for NEET-PG:** * **Prophylactic Disinfection:** Refers to measures like chlorination of water or pasteurization of milk to prevent potential disease. * **Levels of Disinfection:** Remember that **Sterilization** kills all microbial life including spores, whereas **Disinfection** reduces the number of pathogens but may not eliminate bacterial spores. * **Common Disinfectants:** For sputum in TB cases, 5% Cresol or 1% Sodium Hypochlorite are frequently used. * **Key Distinction:** Concurrent = *During* the illness; Terminal = *After* the illness.

Q: Which of the following is NOT transmitted by the fecal-oral route?

Dracunculiasis (Guinea worm disease). ### Explanation The fecal-oral route involves the ingestion of water or food contaminated by the feces of an infected person. While many enteric pathogens follow this path, **Dracunculiasis (Guinea worm disease)** has a distinct mechanism of transmission. **1. Why Dracunculiasis is the Correct Answer:** Dracunculiasis is transmitted via the **cyclops-water route**, not the fecal-oral route. Infection occurs when a person drinks stagnant water containing **Cyclops** (water fleas) that are infected with L3 larvae of *Dracunculus medinensis*. The larvae are released from the skin of an infected human host directly into the water when they emerge through a painful blister; they do not pass through feces. **2. Analysis of Incorrect Options:** * **Poliovirus:** Primarily transmitted via the fecal-oral route (especially in areas with poor sanitation), though oropharyngeal secretions can also play a role in the early stages. * **Typhoid Fever:** Caused by *Salmonella typhi*, it is a classic example of a water-borne and food-borne disease transmitted through the ingestion of contaminated feces or urine (fecal-oral/urino-oral). * **Ascaris lumbricoides:** This soil-transmitted helminth is acquired by ingesting embryonated eggs found in soil contaminated with human feces (fecal-oral). **3. NEET-PG High-Yield Pearls:** * **Dracunculiasis Status:** India was declared **Guinea worm-free** by the WHO in February 2000 (the last case was reported in July 1996 in Rajasthan). * **Intermediate Host:** The Cyclops (specifically *Mesocyclops*) is the essential intermediate host. * **Prevention:** The simplest preventive measure is filtering water through a fine mesh cloth or boiling it to kill the Cyclops. * **Common Fecal-Oral mnemonic:** Remember the "5 F's" of transmission: Flies, Fingers, Feces, Food, and Fluids.

Q: All of the following are zoonotic infections, except?

HIV. ### Explanation **Correct Answer: C. HIV** **Concept:** A **Zoonosis** is defined by the WHO as an infection or infectious disease transmissible under natural conditions from vertebrate animals to humans. While HIV-1 and HIV-2 originated from cross-species transmission of Simian Immunodeficiency Viruses (SIV) from primates to humans decades ago (a process called *zoonotic spillover*), HIV is now classified as a **human-only infection**. It is maintained in the population through human-to-human transmission (sexual, parenteral, or vertical) and does not require an animal reservoir for its current life cycle. **Analysis of Incorrect Options:** * **A. Plague:** A classic zoonosis caused by *Yersinia pestis*. Its natural reservoir is wild rodents (e.g., Tatera indica), and it is transmitted to humans via the bite of infected rat fleas (*Xenopsylla cheopis*). * **B. Japanese Encephalitis (JE):** An obligate zoonosis. The virus is maintained in an **Enzootic cycle** involving pigs (amplifier hosts) and water birds (ardied birds/reservoirs). Humans are "dead-end hosts." * **D. Tuberculosis:** While *M. tuberculosis* is primarily human, *Mycobacterium bovis* (Bovine TB) is a significant zoonotic pathogen transmitted to humans via unpasteurized milk or direct contact with infected cattle. Therefore, TB is traditionally included in the list of zoonotic infections. **NEET-PG High-Yield Pearls:** * **Dead-end hosts:** Humans are dead-end hosts for JE, Rabies, and Hydatid disease (transmission stops at the human). * **Cyclozoonosis:** Requires more than one vertebrate host to complete the life cycle (e.g., Echinococcosis, Taeniasis). * **Anthropozoonosis:** Infections transmitted from animals to humans (e.g., Rabies, Anthrax). * **Zooanthroponosis:** Infections transmitted from humans to animals (e.g., Human TB to cattle).

Q: What is the primary concern of the District TB Control Programme?

Finding out resistant cases. **Explanation:** The primary concern of the District TB Control Programme (now integrated under the **National TB Elimination Programme - NTEP**) has evolved from simple case detection to addressing the most significant threat to TB control: **Drug Resistance**. **1. Why "Finding out resistant cases" is correct:** While the program aims to eliminate TB, the emergence of Multi-Drug Resistant (MDR-TB) and Extensively Drug-Resistant (XDR-TB) cases poses the greatest public health challenge. Resistant cases act as a reservoir for transmission of difficult-to-treat strains, leading to higher mortality and treatment failure rates. Identifying these cases early through **Universal Drug Susceptibility Testing (UDST)** is the top priority to prevent a "man-made" epidemic of incurable TB. **2. Why other options are incorrect:** * **Option A & C:** Finding new cases and ensuring treatment are fundamental *objectives* of the program. However, in the context of "primary concern" (the most critical challenge or priority), the focus shifts to the quality of the cure and preventing the spread of resistant strains. Simple case detection without addressing resistance leads to poor outcomes. * **Option D:** While all are goals, the specific "concern" or bottleneck in modern TB control is the rising trend of resistance. **High-Yield Clinical Pearls for NEET-PG:** * **NTEP Goal:** To achieve a "TB Free India" by **2025** (5 years ahead of the Global SDG target of 2030). * **UDST:** Under NTEP, every diagnosed TB patient must undergo Drug Susceptibility Testing at the time of diagnosis to rule out Rifampicin resistance. * **Diagnostic Tool of Choice:** **CBNAAT** (GeneXpert) or **Truenat** are now the preferred initial tests over sputum microscopy to identify resistance early. * **Nikshay:** The web-based portal used for monitoring TB patients and resistance patterns in India.

Q: Which of the following statements about chickenpox is false?

The secondary attack rate is approximately 60%.. **Explanation:** The correct answer is **C** because the statement is factually incorrect. Chickenpox is highly contagious, and its **Secondary Attack Rate (SAR)** in household contacts is approximately **90%**, not 60%. A SAR of 90% indicates that nearly every susceptible individual in a household will contract the disease following exposure to a primary case. **Analysis of other options:** * **Option A (True):** Chickenpox is caused by the **Varicella-Zoster Virus (VZV)**, a DNA virus belonging to the Herpesviridae family (Human Herpesvirus 3). * **Option B (True):** The incubation period typically ranges from 10 to 21 days, with **14–16 days** being the most common average. * **Option D (True):** The rash of chickenpox is **centripetal** in distribution (more on the trunk, less on the limbs) and characteristically **spares the palms and soles**. This is a key clinical differentiator from Smallpox, where the rash is centrifugal and involves the palms and soles. **High-Yield Clinical Pearls for NEET-PG:** * **Period of Communicability:** From 1–2 days *before* the appearance of the rash until all lesions have crusted (usually 6 days after onset). * **Pleomorphism:** This is the hallmark of chickenpox, where all stages of the rash (papules, vesicles, and crusts) are visible simultaneously in the same area. * **Dew-drop on a rose petal:** Classic description of the clear, thin-walled vesicles. * **Congenital Varicella Syndrome:** Highest risk occurs if the mother is infected between 8–20 weeks of gestation. * **Shingles (Herpes Zoster):** Represents the reactivation of the latent VZV in the dorsal root ganglia.

Q: Which of the following diseases is NOT transmitted by fleas?

Trench fever. **Explanation:** The correct answer is **Trench fever** because it is transmitted by the **human body louse** (*Pediculus humanus corporis*), not by fleas. It is caused by the bacterium *Bartonella quintana*. **Breakdown of Options:** * **Trench fever (Correct):** This is a louse-borne disease historically significant during WWI. The body louse also transmits Epidemic typhus (*Rickettsia prowazekii*) and Louse-borne relapsing fever (*Borrelia recurrentis*). * **Plague:** Transmitted by the **rat flea** (*Xenopsylla cheopis*). This is the most famous flea-borne disease, caused by *Yersinia pestis*. * **Endemic typhus:** Also known as Murine typhus, it is caused by *Rickettsia typhi* and is transmitted to humans via the feces of infected **rat fleas**. * **Chiggerosis (Tungiasis):** Caused by the direct infestation of the skin by the **sand flea** (*Tunga penetrans*). Note: Do not confuse this with "Chiggers" (larval mites) which cause Scrub typhus. **High-Yield Clinical Pearls for NEET-PG:** * **Vector Mnemonic:** Remember the "Three Louse-borne diseases": **Epidemic** Typhus, **Trench** Fever, and **Relapsing** Fever (**E**very **T**errible **R**at). * **Xenopsylla cheopis:** The most efficient vector for Plague; it undergoes "blocking" where the bacteria multiply in the flea's proventriculus, forcing it to bite humans repeatedly. * **Bartonella quintana:** Unique among Rickettsial-like organisms because it can be grown on cell-free culture media (blood agar).

Q: What is the principal vector of the dengue virus?

Aedes aegypti. **Explanation:** **Dengue virus (DENV)**, a flavivirus, is primarily transmitted to humans through the bite of infected female mosquitoes of the genus *Aedes*. **Aedes aegypti** is the principal vector because it is highly anthropophilic (prefers human blood), lives in close proximity to human habitations, and breeds in stagnant clean water (e.g., flower pots, discarded tires). While *Aedes albopictus* is a secondary vector, *A. aegypti* remains the most efficient transmitter due to its frequent feeding behavior. **Analysis of Incorrect Options:** * **Anopheles culicifacies:** This is the primary vector for **Malaria** in rural India. * **Anopheles stephensi:** This is the major vector for **Malaria** in urban areas of India. * **Culex molestus:** Species of the *Culex* genus are primarily responsible for transmitting **Japanese Encephalitis** and **Lymphatic Filariasis** (specifically *Culex quinquefasciatus*). **High-Yield Clinical Pearls for NEET-PG:** * **Feeding Pattern:** *Aedes* mosquitoes are "day biters," with peak activity during early morning and late afternoon. * **Nervous Feeding:** They are "interrupted feeders," meaning they bite multiple people to complete a single blood meal, leading to rapid outbreaks within a household. * **Transovarial Transmission:** The virus can pass from the female mosquito to her eggs, allowing the virus to persist even during dry seasons. * **Control:** The most effective prevention is source reduction (eliminating breeding sites) and using larvicides like **Abate (Temephos)**.

Question 1

What is the recommended follow-up period for an individual who has come into contact with a confirmed case of coronavirus (COVID-19)?

Accepted Answer

14 days

Answer

7 days

Answer

21 days

Answer

42 days

Question 2

Culex mosquito spreads all of the following diseases except?

Accepted Answer

Yellow fever

Answer

Viral arthritis

Answer

West Nile fever

Answer

Bancroftian filariasis

Question 3

Sputum from a patient is disinfected immediately following expectoration. This process is known as:

Accepted Answer

Concurrent disinfection

Answer

Pre-concurrent disinfection

Answer

Recurrent disinfection

Answer

Terminal disinfection

Question 4

Which of the following statements is true for the Mantoux test?

Accepted Answer

A positive test does not indicate that the person is suffering from the disease.

Answer

The test is read before 48 hours.

Answer

6-9 mm induration shows maximum chances of developing TB.

Answer

New cases are more likely to occur in tuberculin-negative persons than in those who are already tuberculin reactors.

Question 5

Which of the following is NOT transmitted by the fecal-oral route?

Accepted Answer

Dracunculiasis (Guinea worm disease)

Answer

Poliovirus

Answer

Typhoid fever

Answer

Ascaris lumbricoides

Question 6

All of the following are zoonotic infections, except?

Accepted Answer

HIV

Answer

Plague

Answer

Japanese Encephalitis

Answer

Tuberculosis

Question 7

What is the primary concern of the District TB Control Programme?

Accepted Answer

Finding out resistant cases

Answer

Finding out new cases

Answer

Detecting cases and ensuring treatment

Answer

All of the above

Question 8

Which of the following statements about chickenpox is false?

Accepted Answer

The secondary attack rate is approximately 60%.

Answer

The causative agent is varicella-zoster virus.

Answer

The incubation period is typically 14-16 days.

Answer

The rash typically spares the palms and soles.

Question 9

Which of the following diseases is NOT transmitted by fleas?

Accepted Answer

Trench fever

Answer

Plague

Answer

Endemic typhus

Answer

Chiggerosis

Question 10

What is the principal vector of the dengue virus?

Accepted Answer

Aedes aegypti

Answer

Anopheles culicifacies

Answer

Anopheles stephensi

Answer

Culex molestus

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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