Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 71: What is considered the most dangerous type of diphtheria?

A. Facial
B. Laryngeal (Correct Answer)
C. Nasal
D. Cutaneous

Explanation: **Explanation:** **Laryngeal diphtheria** is considered the most dangerous form because it poses an immediate threat to the airway. The hallmark of diphtheria is the formation of a **pseudomembrane** (composed of fibrin, leukocytes, and dead epithelial cells). In the larynx, this membrane can cause mechanical obstruction of the narrow glottic opening. Furthermore, edema and the potential for the membrane to detach and be aspirated can lead to sudden asphyxia and death. **Analysis of Options:** * **Nasal Diphtheria:** Generally the mildest form. It is characterized by serosanguinous discharge but has low systemic toxin absorption. However, it is highly important from an epidemiological perspective as a source of infection. * **Faucial (Pharyngeal) Diphtheria:** This is the most common clinical type. While it can lead to severe "bull neck" appearance due to lymphadenopathy and high toxin absorption (causing myocarditis), it is statistically less likely to cause immediate fatal airway obstruction compared to the laryngeal type. * **Cutaneous Diphtheria:** Usually presents as non-healing ulcers. It is rarely fatal as systemic toxin absorption from the skin is minimal. **High-Yield Clinical Pearls for NEET-PG:** * **Agent:** *Corynebacterium diphtheriae* (Gram-positive, club-shaped, Chinese-letter pattern). * **Schick Test:** Used to demonstrate the immune status of an individual (susceptibility). * **Treatment:** Prompt administration of **Diphtheria Antitoxin (ADS)** is the priority to neutralize unbound toxins. * **Carrier State:** Nasal carriers are more dangerous than throat carriers in spreading the disease. * **Drug of Choice:** Erythromycin (to stop toxin production and clear the carrier state).

Question 72: As per RNTCP Category 1, what is the recommended drug regimen?

A. 4 drugs for 2 months and 2 drugs for 4 months
B. 3 drugs for 2 months and 2 drugs for 4 months
C. Includes retreatment cases (Correct Answer)
D. Treatment is given daily and directly observed

Explanation: ### Explanation Under the **Revised National Tuberculosis Control Programme (RNTCP)**, which has now transitioned into the **National TB Elimination Programme (NTEP)**, the categorization of TB patients was simplified to streamline treatment protocols. **Why Option C is Correct:** Historically, RNTCP divided patients into Category I (New cases) and Category II (Retreatment cases). However, under the updated **Daily Regimen guidelines (2017 onwards)**, the distinction between Category I and II was abolished. Currently, all patients—both **New and Previously Treated (Retreatment cases)**—are treated with the same standard four-drug regimen (HRZE). Therefore, the current "Category 1" equivalent essentially encompasses all cases, including retreatment cases. **Analysis of Incorrect Options:** * **Option A & B:** These describe the old intermittent (thrice-weekly) regimens. Under the current Daily Regimen, the standard treatment for drug-sensitive TB is **2HRZE + 4HRE** (4 drugs for 2 months, followed by 3 drugs for 4 months). Note that Ethambutol (E) is now continued in the continuation phase. * **Option D:** While treatment is indeed given **daily**, the concept of "Directly Observed" (DOT) has evolved. The program now emphasizes **Treatment Adherence Support** (using digital tools like Nikshay) rather than strict physical observation for every single dose, making this a less specific "defining" feature compared to the inclusion of retreatment cases in the unified category. **High-Yield Clinical Pearls for NEET-PG:** * **Standard Regimen:** 2 months of IP (HRZE) + 4 months of CP (HRE). * **Drug Dosages:** Fixed-Dose Combinations (FDCs) are administered based on **weight bands** (Adult bands: 25-34, 35-49, 50-64, 65+ kg). * **Pyridoxine (Vitamin B6):** Should be supplemented (10–25 mg/day) to prevent peripheral neuropathy caused by Isoniazid, especially in high-risk groups. * **Extension of IP:** There is no longer a provision to extend the Intensive Phase (IP) if the 2-month sputum is positive; instead, the patient is evaluated for drug resistance.

Question 73: Dengue is transmitted by?

A. Anopheles
B. Culex
C. Mansonia
D. Aedes (Correct Answer)

Explanation: **Explanation:** **Correct Answer: D. Aedes** Dengue fever is caused by the Dengue virus (DENV 1-4), a flavivirus transmitted primarily by the bite of an infected female **Aedes aegypti** mosquito (the primary vector) and, to a lesser extent, **Aedes albopictus**. These mosquitoes are "day-biters," with peak activity during early morning and late afternoon. They are characterized by white stripes on their legs and thorax, earning them the nickname "Tiger mosquito." **Why other options are incorrect:** * **Anopheles:** This genus is the primary vector for **Malaria**. Unlike Aedes, Anopheles mosquitoes typically bite at night and breed in clean, stagnant water. * **Culex:** These are vectors for **Japanese Encephalitis, Bancroftian Filariasis, and West Nile Virus**. They are known as "nuisance mosquitoes" and typically breed in dirty, polluted water. * **Mansonia:** This genus is the primary vector for **Malayan Filariasis (Brugia malayi)**. They are unique because their larvae attach to the submerged roots of aquatic plants (like *Pistia*) for respiration. **High-Yield Clinical Pearls for NEET-PG:** * **Extrinsic Incubation Period:** 8–10 days (the time the virus takes to develop inside the mosquito). * **Intrinsic Incubation Period:** 3–14 days (the time from the mosquito bite to the onset of symptoms in humans). * **Breeding Sites:** Aedes prefers artificial collections of clean water (coolers, flower pots, discarded tires). * **Aedes albopictus** is the maintenance vector in many areas and is known for its ability to survive in colder climates compared to *A. aegypti*.

Question 74: In the case of a dog bite, the biting animal should be observed for at least how many days?

A. 5 days
B. 10 days (Correct Answer)
C. 15 days
D. 3 weeks

Explanation: **Explanation:** The correct answer is **10 days (Option B)**. This duration is based on the pathogenesis of the Rabies virus. In mammals, the virus only appears in the saliva (making the animal infectious) shortly before the onset of clinical symptoms or death. If a dog or cat remains healthy and alive for 10 days following a bite, it confirms that the animal was not shedding the virus in its saliva at the time of the incident, and therefore, the victim is not at risk of Rabies from that specific exposure. **Analysis of Options:** * **Option A (5 days):** This is too short. While some animals may die within 5 days, the shedding of the virus can precede symptoms by 3–7 days; thus, a 5-day window does not sufficiently rule out infectivity. * **Option C & D (15 days / 3 weeks):** These periods are unnecessarily long. Global guidelines (WHO and National Guidelines on Rabies Prophylaxis) have standardized the observation period to 10 days as it provides a 100% safety margin for clinical decision-making. **High-Yield Clinical Pearls for NEET-PG:** * **Observation vs. Treatment:** Post-Exposure Prophylaxis (PEP) should be started **immediately** and should not be delayed while waiting for the observation period results, especially in Category II and III bites. If the animal remains healthy after 10 days, PEP can be discontinued. * **Species:** The 10-day observation rule applies specifically to **dogs, cats, and ferrets**. It does not apply to wild animals. * **Incubation Period:** While the observation period is 10 days, the incubation period in humans is highly variable (typically 1–3 months), depending on the site of the bite and viral load. * **Management:** Local wound washing with soap and water for 15 minutes is the most crucial first step in preventing Rabies.

Question 75: Which of the following diseases has man as the only reservoir?

A. Rabies
B. Measles (Correct Answer)
C. Typhoid
D. Japanese B encephalitis

Explanation: **Explanation:** In epidemiology, a **reservoir** is the natural habitat in which an infectious agent lives, grows, and multiplies. When a disease has **man as the only reservoir**, it implies there is no animal (zoonotic) or environmental source for the pathogen. This is a critical factor in public health because such diseases are theoretically candidates for **eradication**. **Why Measles is the Correct Answer:** Measles is caused by the Rubeola virus. It is an exclusively human disease with no known animal reservoir or subclinical carrier state. Once an individual recovers, they develop lifelong immunity. This "human-only" cycle is why global eradication of Measles is considered biologically feasible, similar to Smallpox. **Analysis of Incorrect Options:** * **Rabies (A):** This is a classic **zoonosis**. The reservoirs are primarily wild and domestic animals (dogs, bats, foxes). Humans are "dead-end hosts." * **Typhoid (C):** While humans are the only natural reservoir for *Salmonella Typhi*, the question asks for the most definitive example among the choices. However, Typhoid involves **chronic carriers** (e.g., gallbladder colonization) and can survive for short periods in contaminated water/food, making its transmission cycle more complex than the direct respiratory spread of Measles. (Note: In many exams, if Measles is present, it is the preferred answer for "only reservoir"). * **Japanese B Encephalitis (D):** This is an **extra-human cycle**. The virus is maintained in a cycle involving pigs (amplifier hosts) and water birds (reservoirs), transmitted to humans via *Culex* mosquitoes. **High-Yield Clinical Pearls for NEET-PG:** * **Other diseases with man as the only reservoir:** Smallpox (eradicated), Poliomyelitis, Mumps, Rubella, Pertussis, and Syphilis. * **Eradication vs. Elimination:** Eradication (global) is only possible if there is no animal reservoir. * **Measles Key Fact:** It is most infectious during the **prodromal stage** (before the rash appears). The presence of **Koplik spots** is pathognomonic.

Question 76: Which insecticide is effective in killing Phlebotomous argentipes?

A. Malathion
B. DDT (Correct Answer)
C. BHC
D. Pyrethrum

Explanation: **Explanation:** The correct answer is **DDT (Dichloro-Diphenyl-Trichloroethane)**. *Phlebotomus argentipes* is the primary vector for **Kala-azar (Visceral Leishmaniasis)** in the Indian subcontinent. The vector is highly susceptible to residual insecticides because it rests indoors in cracks and crevices of mud walls. **1. Why DDT is the Correct Answer:** DDT remains the **insecticide of choice** for the National Vector Borne Disease Control Programme (NVBDCP) in India for the control of Kala-azar. It is used in **Indoor Residual Spraying (IRS)** at a dosage of **1.0 g/m²**. The sandfly has not yet developed significant physiological resistance to DDT in most endemic areas, making it the most cost-effective and efficient tool for interrupting transmission. **2. Why Other Options are Incorrect:** * **Malathion:** While used for organophosphate-resistant mosquitoes (like *Anopheles*), it is not the primary choice for sandflies due to its shorter residual effect and odor. * **BHC (Benzene Hexachloride):** Previously used for malaria control, it has been largely phased out due to environmental persistence and the development of widespread resistance. * **Pyrethrum:** This is a **space spray** (knock-down agent) used for immediate killing of adult insects. It does not have the long-lasting residual action required for effective sandfly control in mud dwellings. **High-Yield Clinical Pearls for NEET-PG:** * **Vector Habitat:** *Phlebotomus* breeds in damp soil rich in organic matter (e.g., cattle sheds). * **IRS Strategy:** For Kala-azar, IRS with DDT should be done up to a height of **6 feet** from the floor. * **Drug of Choice for Kala-azar:** Liposomal Amphotericin B (single dose) is currently the first-line treatment. * **Post-Kala-azar Dermal Leishmaniasis (PKDL):** Occurs in about 5-10% of treated cases in India and acts as a reservoir for the parasite.

Question 77: A 25-year-old male tests positive for a hepatitis C infection. Which of the following is the most likely method of transmission?

A. Fecal-oral
B. Fomite
C. Intravenous drug use (needles) (Correct Answer)
D. Sexual transmission

Explanation: **Explanation:** **Hepatitis C Virus (HCV)** is primarily a **blood-borne pathogen**. The most efficient and common method of transmission is through direct percutaneous exposure to infected blood. In modern clinical practice, **Intravenous Drug Use (IVDU)** with the sharing of contaminated needles and syringes is the leading risk factor for HCV infection, accounting for the majority of new cases. Unlike Hepatitis B, the viral load of HCV in body fluids other than blood is relatively low, making blood-to-blood contact the most likely route. **Analysis of Incorrect Options:** * **A. Fecal-oral:** This is the primary route for **Hepatitis A and E** ("Vowels involve the bowels"). HCV is not transmitted via contaminated food or water. * **B. Fomite:** While HCV can survive on environmental surfaces for several days, transmission via inanimate objects (fomites) is clinically insignificant compared to direct blood exposure. * **D. Sexual transmission:** While possible, the risk of sexual transmission of HCV is considered **very low** (approximately 0-0.6% in monogamous heterosexual couples). It is significantly less efficient than the sexual transmission of Hepatitis B or HIV. **High-Yield Clinical Pearls for NEET-PG:** * **Post-Transfusion Hepatitis:** Historically, HCV was the most common cause of post-transfusion hepatitis; however, with modern screening, IVDU has surpassed it. * **Chronicity:** HCV has the highest rate of chronicity among hepatitis viruses (~75-85% of acute infections become chronic). * **Screening:** Anti-HCV antibody is the screening test of choice; **HCV-RNA (PCR)** is the gold standard for confirming active infection. * **Vaccine:** There is **no vaccine** available for Hepatitis C due to high antigenic variation (hypervariable region 1 of the E2 envelope glycoprotein).

Question 78: What percentage of patients infected with Mycobacterium tuberculosis will eventually develop active tuberculosis in their lifetime?

A. 5%
B. 10% (Correct Answer)
C. 15%
D. 20%

Explanation: **Explanation:** The correct answer is **10%**. This figure represents the lifetime risk of progression from Latent Tuberculosis Infection (LTBI) to active clinical disease in an immunocompetent individual. **Underlying Medical Concept:** When *Mycobacterium tuberculosis* enters the body, the immune system (specifically T-lymphocytes and macrophages) usually walls off the bacteria in a granuloma. In approximately **90%** of individuals, the infection remains dormant (Latent TB) for life. In the remaining **10%**, the bacteria eventually overcome the immune system, leading to active disease. This 10% risk is generally split: 5% occurs within the first two years post-infection (primary progression), and the remaining 5% occurs later in life (reactivation). **Analysis of Incorrect Options:** * **Option A (5%):** This represents the risk of developing active TB within the first two years of infection only, not the total lifetime risk. * **Option C & D (15% & 20%):** These percentages are higher than the average risk for an immunocompetent person. However, it is important to note that in HIV-positive individuals, the risk is significantly higher—approximately **10% per year**, rather than 10% per lifetime. **NEET-PG High-Yield Pearls:** * **The "Rule of 10":** 10% of those infected develop disease; of those, 50% develop it within 2 years. * **HIV Influence:** HIV is the most potent risk factor for the progression of LTBI to active TB. * **Infectivity:** An untreated smear-positive pulmonary TB patient can infect **10 to 15** people annually. * **Primary vs. Post-Primary:** In endemic areas like India, most adult TB cases are due to **reactivation** (Post-primary TB).

Question 79: The DTPB approach is included under which national health program?

A. National AIDS Control Programme
B. National Programme for Control of Blindness
C. National Strategic Plan for TB (Correct Answer)
D. National Malaria Elimination Programme

Explanation: ### Explanation The **DTPB approach** is a core component of the **National Strategic Plan (NSP) for Tuberculosis Elimination (2017–2025)** under the National TB Elimination Programme (NTEP). **Why the Correct Answer is Right:** DTPB stands for **D**etect, **T**reat, **P**revent, and **B**uild. This four-pronged strategy aims to achieve the ambitious goal of ending TB in India by 2025: * **Detect:** Early diagnosis of all TB cases, including drug-resistant and HIV-associated TB, through universal drug susceptibility testing (UDST). * **Treat:** Initiation of appropriate treatment for all patients, including those in the private sector, and ensuring adherence through ICT tools like Nikshay. * **Prevent:** Scaling up TB Preventive Treatment (TPT) for contacts and high-risk groups, and improving airborne infection control. * **Build:** Strengthening health systems, multisectoral collaboration, and adequate funding. **Analysis of Incorrect Options:** * **National AIDS Control Programme (NACP):** Focuses on the "95-95-95" targets and the "Test and Treat" policy, not the DTPB framework. * **National Programme for Control of Blindness (NPCB):** Focuses on reducing the prevalence of blindness through cataract surgeries and eye banking (Target: 0.3% prevalence by 2025). * **National Malaria Elimination Programme (NMEP):** Operates under the National Center for Vector Borne Diseases Control (NCVBDC) using strategies like LLINs, IRS, and the "High Burden to High Impact" (HBHI) approach. **High-Yield Clinical Pearls for NEET-PG:** * **Goal of NSP 2017-2025:** To eliminate TB by 2025 (5 years ahead of the global SDG target of 2030). * **Elimination Definition:** Incidence of less than 1 case per million population. * **Nikshay Poshan Yojana:** Provides ₹500/month nutritional support to all TB patients. * **TrueNat/CBNAAT:** Preferred first-line diagnostic tools under the "Detect" pillar.

Question 80: Pigs are an important source for which of the following diseases?

A. Japanese encephalitis (Correct Answer)
B. Kuru
C. Yellow fever
D. Rabies

Explanation: **Explanation:** **Japanese Encephalitis (JE)** is the correct answer because pigs play a critical role in its transmission cycle as **amplifier hosts**. In the natural cycle, the virus circulates between *Culex* mosquitoes (primarily *Culex tritaeniorhynchus*) and water birds (Ardeid birds). Pigs become infected and develop high-level viremia without showing clinical symptoms. This high viral load in pigs allows mosquitoes to easily pick up the virus and subsequently transmit it to humans (who are "dead-end hosts"). **Analysis of Incorrect Options:** * **Kuru:** This is a prion disease historically found in the Fore people of Papua New Guinea. It is transmitted through **ritualistic cannibalism** (consuming infected brain tissue), not animals. * **Yellow Fever:** The primary reservoirs are **monkeys** (in the jungle cycle) and humans (in the urban cycle). It is transmitted by *Aedes aegypti* mosquitoes. * **Rabies:** This is a viral zoonosis transmitted through the saliva of infected mammals, most commonly **dogs** (99% of human cases), bats, monkeys, and cats. **High-Yield Clinical Pearls for NEET-PG:** * **Amplifier Host:** Pigs (JE), whereas humans and horses are **Dead-end hosts** (viremia is insufficient to infect mosquitoes). * **Vector:** *Culex tritaeniorhynchus* (breeds in stagnant water/paddy fields). * **Vaccination:** Under the Universal Immunization Programme (UIP), the **SA-14-14-2** (live attenuated) vaccine is used in India. * **Control Strategy:** "Pig segregation" (keeping pigs >4-5 km from human dwellings) is a key preventive measure.

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Communicable Disease Control Principles

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Water-Borne Diseases

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HIV/AIDS Control Program

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Tuberculosis Control

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Leprosy Elimination

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Emerging and Re-emerging Infections

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Hospital-Acquired Infections

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