Infectious Diseases Practice Questions

Q: Smallpox eradication was successful due to all factors except:

Cross-resistance with animal pox viruses existed. Smallpox remains the only human infectious disease to be globally eradicated (declared by the WHO on May 8, 1980). Its eradication was possible due to specific epidemiological features of the Variola virus. ### **Explanation of the Correct Answer** **Option D** is the correct answer because it is a **false statement**. While the Smallpox vaccine was derived from the Vaccinia virus (a related orthopoxvirus), there was **no natural cross-resistance** from animal pox viruses that protected the human population. In fact, the lack of an animal reservoir was a primary reason for eradication success; the virus lived only in humans, meaning once human transmission was broken, the virus had nowhere to hide. ### **Analysis of Incorrect Options (Reasons for Eradication Success)** * **Option A:** Subclinical (asymptomatic) cases were virtually non-existent. Every infected person showed a characteristic rash, making cases easy to identify and isolate. Since subclinical cases did not transmit the disease, "surveillance-containment" was highly effective. * **Option B:** The bifurcated needle and the heat-stable freeze-dried vaccine allowed for easy administration and potency in tropical climates without a strict cold chain. * **Option C:** The vaccine provided long-lasting immunity, and a visible vaccination scar allowed health workers to easily identify immune individuals in a community. ### **NEET-PG High-Yield Pearls** * **Last Case (World):** Ali Maow Maalin in Somalia (1977) - *Variola minor*. * **Last Case (India):** Saiban Bibi in West Bengal (May 1975) - *Variola major*. * **India declared Smallpox Free:** April 1977. * **Strategy used:** Initially "Mass Vaccination," later shifted to **"Surveillance and Containment"** (Ring Vaccination), which led to final eradication. * **Incubation Period:** 10–14 days; patients are infectious from the onset of rash until the last scab falls off.

Q: Kyasanur forest disease is transmitted by:

Tick. **Explanation:** **Kyasanur Forest Disease (KFD)**, commonly known as "Monkey Fever," is a viral hemorrhagic fever endemic to the South Indian state of Karnataka. **1. Why Tick is the Correct Answer:** KFD is caused by the Kyasanur Forest Disease Virus (KFDV), a member of the *Flaviviridae* family. The primary vector for transmission is the **Hard Tick (*Haemaphysalis spinigera*)**. Humans typically contract the disease through the bite of an infected nymphal tick or via contact with an infected animal, most notably monkeys (Langurs and Bonnet macaques), which act as amplifier hosts. **2. Why Other Options are Incorrect:** * **Mite:** Mites are vectors for diseases like **Scrub Typhus** (*Leptotrombidium* mite). They are not involved in the transmission of KFD. * **Mosquito:** While mosquitoes transmit many flaviviruses (like Dengue, Zika, and Yellow Fever), they do not carry KFDV. * **None:** This is incorrect as the tick vector is well-established in medical literature. **3. High-Yield Clinical Pearls for NEET-PG:** * **Reservoirs:** Wild rodents and shrews are the natural reservoirs; monkeys are the "sentinel" animals (their deaths often signal an outbreak). * **Seasonality:** Peak incidence occurs during the dry season (January to June) when human activity in forests increases. * **Clinical Presentation:** Characterized by sudden onset high fever, frontal headache, severe myalgia, and hemorrhagic manifestations. A "biphasic" fever pattern is sometimes noted. * **Prevention:** A **formalin-inactivated KFDV vaccine** is used in endemic areas for individuals aged 7–65 years. * **Diagnosis:** Confirmed via PCR (early stage) or ELISA (IgM) for antibodies.

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

Taeniasis. **Explanation:** The core concept of a **zoonosis** is a disease or infection that is naturally transmissible from vertebrate animals to humans. **Why Taeniasis is the correct answer:** Taeniasis (specifically caused by *Taenia saginata* and *Taenia solium*) is classified as an **anthropozoonosis** or more specifically, a cycle involving humans as the definitive host. While animals (cattle and pigs) are intermediate hosts, the disease is maintained by the human-to-animal-to-human cycle. According to the WHO classification, diseases where the human is an essential link in the life cycle (like Taeniasis or Schistosomiasis) are often excluded from the strict definition of "zoonotic diseases," which typically refers to infections where humans are accidental hosts. **Analysis of Incorrect Options:** * **Plague:** A classic zoonosis caused by *Yersinia pestis*. It is primarily a disease of rodents, transmitted to humans via the bite of an infected rat flea (*Xenopsylla cheopis*). * **Rabies:** A viral zoonosis transmitted through the saliva of infected mammals (dogs, bats, monkeys). Humans are "dead-end" hosts. * **Brucellosis:** A bacterial zoonosis (undulant fever) transmitted to humans through direct contact with infected livestock or consumption of unpasteurized dairy products. **NEET-PG High-Yield Pearls:** * **Classification:** * *Orthozoonoses:* Cycle maintained in one reservoir (e.g., Rabies). * *Cyclozoonoses:* Require more than one vertebrate host (e.g., Taeniasis, Echinococcosis). * *Metazoonoses:* Require an invertebrate vector (e.g., Plague). * **Emerging Zoonoses:** Keep an eye on Nipah virus, Ebola, and Kyasanur Forest Disease (KFD) for recent exam trends. * **Dead-end hosts:** Humans are dead-end hosts for Rabies, Hydatid disease, and Japanese Encephalitis.

Q: What is the standard dose of Tuberculin used in the Mantoux test?

1 TU in 0.1 ml. ### Explanation **1. Understanding the Correct Answer (B):** The Mantoux test (Tuberculin Skin Test) is the standard method for identifying latent *Mycobacterium tuberculosis* infection. The standard dose recommended by the WHO and used in India (RNTCP/NTEP guidelines) is **1 TU (Tuberculin Unit) of PPD RT23**. This dose is contained in a volume of **0.1 ml**, which is injected **intradermally** on the volar aspect of the forearm using a tuberculin syringe. This specific volume is chosen because it creates a discrete 6–10 mm wheal, allowing for the standardized delivery of the antigen to the dermis. **2. Analysis of Incorrect Options:** * **Option A (1 TU in 1 ml):** This is incorrect because 1 ml is a very large volume for an intradermal injection; it would cause significant tissue trauma and would not allow for the localized delayed-type hypersensitivity reaction required for the test. * **Option C (0.1 TU in 1 ml):** This is incorrect as the dosage is too low (sub-therapeutic for a reaction) and the volume is too high. * **Option D (0.1 TU in 0.1 ml):** While the volume is correct, the concentration is insufficient. 0.1 TU is not potent enough to elicit a reliable diagnostic response in most individuals. **3. High-Yield Clinical Pearls for NEET-PG:** * **Standard Antigen:** PPD RT23 with Tween 80 (stabilizer) is most commonly used. * **Reading the Test:** Results must be read **48 to 72 hours** after injection. * **Measurement:** Only the **induration** (palpable hardening) is measured, not the erythema (redness). * **Interpretation:** In India, an induration of **≥10 mm** is generally considered positive. In HIV-positive individuals, **≥5 mm** is considered positive. * **False Negative:** Can occur in miliary TB, malnutrition, sarcoidosis, or recent viral infections (e.g., Measles). * **False Positive:** Can occur due to prior BCG vaccination or infection with Non-Tuberculous Mycobacteria (NTM).

Q: All of the following infections have carrier states, EXCEPT:

Measles. **Explanation:** The concept of a **carrier state** refers to an individual who harbors a specific infectious agent without having clinical disease but serves as a potential source of infection for others. **1. Why Measles is the Correct Answer:** Measles is caused by a highly contagious virus that follows an **"all-or-none" phenomenon**. Once infected, an individual either develops the clinical disease or gains lifelong immunity. There is **no chronic or subclinical carrier state** in Measles. Furthermore, the virus does not persist in the body after the acute phase (except in the rare, late-onset complication of SSPE, which is not considered a carrier state for transmission). **2. Analysis of Incorrect Options:** * **Diphtheria:** Known for having both **convalescent and healthy carriers**. Carriers are more common than clinical cases and are significant reservoirs for spreading the infection in the community. * **Typhoid (Enteric Fever):** Famous for the **chronic carrier state** (e.g., "Typhoid Mary"). The bacteria (*S. typhi*) can persist in the gallbladder or biliary tract for years, shedding the organism in feces. * **Gonorrhea:** Frequently presents with **asymptomatic/subclinical carriers**, especially in females. These individuals do not show symptoms but can transmit the infection to sexual partners. **High-Yield Clinical Pearls for NEET-PG:** * **Diseases with NO carrier state:** Measles, Pertussis, Rabies, Smallpox, and Plague. * **Epidemiological Importance:** Diseases without a carrier state are generally easier to eradicate (e.g., Smallpox) because there is no "hidden" reservoir in the population. * **Incubatory Carrier:** Someone who sheds the pathogen during the incubation period (e.g., Measles, Mumps, Polio, Hepatitis B). Note: While Measles has an *incubatory* phase of shedding, it does not have a *chronic* carrier state.

Q: Which of the following is not a zoonosis?

Amoebiasis. **Explanation:** A **zoonosis** is defined as an infection or infectious disease transmissible under natural conditions from vertebrate animals to humans. **Why Amoebiasis is the correct answer:** Amoebiasis, caused by *Entamoeba histolytica*, is an **anthroponosis**. The primary reservoir of infection is the human case or carrier (specifically the "cyst passer"). Transmission occurs via the fecal-oral route from human to human. While some animals can be experimentally infected, they do not play a role in the natural maintenance or transmission of the disease to humans. **Analysis of incorrect options:** * **Leptospirosis:** A classic zoonosis caused by *Leptospira interrogans*. Humans are accidental hosts, usually infected through contact with water contaminated by the urine of reservoir animals like rats (rodents). * **Rabies:** A viral zoonosis transmitted to humans through the bite or scratch of an infected animal (most commonly dogs in India, but also bats, monkeys, and cats). * **Hydatid Disease:** Caused by *Echinococcus granulosus*. It is a cyclozoonosis where the life cycle requires more than one vertebrate host (Dogs as definitive hosts and sheep/cattle as intermediate hosts). Humans are accidental "dead-end" hosts. **High-Yield Clinical Pearls for NEET-PG:** * **Anthroponoses:** Diseases where the reservoir is exclusively human (e.g., Amoebiasis, Typhoid, Cholera, Polio, Measles). * **Reverse Zoonosis (Zooanthroponosis):** Diseases transmitted from humans to animals (e.g., Human tuberculosis to cattle). * **Most common zoonosis in India:** Brucellosis is often cited as a major underdiagnosed bacterial zoonosis, while Rabies remains the most fatal. * **Leptospirosis** is often associated with occupational exposure (sewer workers, rice field workers) and post-monsoon outbreaks.

Q: Epidemic typhus is transmitted by which of the following vectors?

Louse. **Explanation:** **Epidemic typhus** is caused by the bacterium *Rickettsia prowazekii*. The correct answer is **Louse (Option A)**, specifically the human body louse (*Pediculus humanus corporis*). The transmission occurs when the louse feeds on an infected human, and the bacteria multiply in the louse's gut. When the louse moves to a new host, it defecates while feeding; the host then inadvertently rubs the infected feces into the bite wound or other abrasions. **Analysis of Incorrect Options:** * **Soft tick (Option B):** These are the primary vectors for **Endemic Relapsing Fever** (*Borrelia* species). * **Hard tick (Option C):** These transmit diseases such as **Indian Tick Typhus** (*Rickettsia conorii*), Kyasanur Forest Disease (KFD), and Rocky Mountain Spotted Fever. * **Rat flea (Option D):** This is the vector for **Endemic (Murine) typhus** (*Rickettsia typhi*) and Bubonic Plague (*Yersinia pestis*). **High-Yield Clinical Pearls for NEET-PG:** 1. **Brill-Zinsser Disease:** This is a recrudescent form of epidemic typhus that occurs years after the primary infection, as the bacteria can remain latent in lymphoid tissue. 2. **The "Rickettsial Rule":** * Epidemic Typhus = Louse (*R. prowazekii*) * Endemic Typhus = Rat Flea (*R. typhi*) * Scrub Typhus = Trombiculid Mite/Chigger (*Orientia tsutsugamushi*) 3. **Treatment:** Doxycycline is the drug of choice for all rickettsial infections. 4. **Epidemiology:** Epidemic typhus is often associated with overcrowding, war, and famine where hygiene is poor.

Q: Which of the following is NOT true about Japanese Encephalitis (JE)?

Case fatality rate is 80-90%. **Explanation:** Japanese Encephalitis (JE) is a major public health concern in India, particularly in the North-Eastern and Terai regions. The question asks for the **incorrect** statement regarding JE. **1. Why Option C is the correct answer (The False Statement):** The Case Fatality Rate (CFR) of Japanese Encephalitis is typically **20% to 30%**, not 80-90%. While JE is a severe disease, the majority of those who survive (about 30-50%) are left with significant neurological or psychiatric sequelae. A CFR of 80-90% is more characteristic of diseases like untreated Rabies or certain Ebola outbreaks. **2. Analysis of Incorrect Options (True Statements):** * **Option A:** JE is primarily transmitted by **Culex mosquitoes**, specifically the *Culex tritaeniorhynchus* group. These mosquitoes breed in stagnant water, such as rice fields. * **Option B:** In fatal cases, death typically occurs within the first **7 to 9 days** of the onset of symptoms, usually due to severe cerebral edema or secondary complications. * **Option D:** The disease progression starts with a **prodromal stage** lasting **1 to 6 days**, characterized by fever, headache, and nausea, before progressing to the encephalitic stage (altered sensorium, convulsions). **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir/Host:** Pigs and Ardeid birds (herons, egrets) are the main reservoirs. Pigs are called **"Amplifier Hosts"** because they allow the virus to multiply without getting sick. * **Incubation Period:** 5 to 15 days. * **Vaccination:** Under the Universal Immunization Programme (UIP) in endemic districts, the **SA-14-14-2** (Live Attenuated) vaccine is given at 9 months and 16-24 months. * **Vector Bionomics:** Culex mosquitoes are "exophilic" (outdoor resters) and "exophagic" (outdoor biters), primarily active during dusk and night.

Q: What are the true targets for DOTS in terms of case finding and cure rate?

Case finding 70%, cure rate 85%. ### Explanation The **Directly Observed Treatment, Short-course (DOTS)** strategy, launched by the WHO in the 1990s and adopted by India’s Revised National Tuberculosis Control Programme (RNTCP), established specific global targets to ensure effective TB control. **1. Why Option D is Correct:** The global targets set for DOTS were specifically designed to break the chain of transmission. * **Case Finding (70%):** The goal was to detect at least 70% of the estimated new sputum smear-positive cases in the community. * **Cure Rate (85%):** The goal was to achieve a cure rate of at least 85% among those detected. Mathematical modeling suggests that achieving these two specific benchmarks simultaneously leads to a significant decline in the prevalence and incidence of Tuberculosis. **2. Why Other Options are Incorrect:** * **Options A & B:** These overestimate the initial case-finding target. While higher detection is always desirable, the official DOTS benchmark was set at 70%. * **Option C:** This underestimates the cure rate. A cure rate of 75% is insufficient to prevent the emergence of Multi-Drug Resistant TB (MDR-TB) and does not adequately reduce the pool of infectious patients. **3. High-Yield Clinical Pearls for NEET-PG:** * **Evolution of Targets:** Under the current **National Strategic Plan (2017-2025)** and the **Nikshay** ecosystem, India has moved beyond these 70/85 targets toward "Elimination" (defined as <1 case per million population). * **DOTS Five Pillars:** 1. Political commitment, 2. Good quality microscopy (Diagnosis), 3. Uninterrupted supply of drugs, 4. Direct observation of treatment, 5. Systematic recording and reporting. * **Success Indicator:** The most sensitive indicator of the success of the RNTCP/NTEP is the **Cure Rate**.

Question 1

Smallpox eradication was successful due to all factors except:

Accepted Answer

Cross-resistance with animal pox viruses existed

Answer

Subclinical cases do not transmit the disease

Answer

A highly effective vaccine was available

Answer

The vaccine conferred lifelong immunity

Question 2

Kyasanur forest disease is transmitted by:

Accepted Answer

Tick

Answer

Mite

Answer

Mosquito

Answer

None

Question 3

Which of the following is NOT an example of a zoonotic disease?

Accepted Answer

Taeniasis

Answer

Plague

Answer

Rabies

Answer

Brucellosis

Question 4

What is the standard dose of Tuberculin used in the Mantoux test?

Accepted Answer

1 TU in 0.1 ml

Answer

1 TU in 1 ml

Answer

0.1 TU in 1 ml

Answer

0.1 TU in 0.1 ml

Question 5

All of the following infections have carrier states, EXCEPT:

Accepted Answer

Measles

Answer

Diphtheria

Answer

Typhoid

Answer

Gonorrhea

Question 6

Which of the following is not a zoonosis?

Accepted Answer

Amoebiasis

Answer

Leptospirosis

Answer

Rabies

Answer

Hydatid disease

Question 7

Epidemic typhus is transmitted by which of the following vectors?

Accepted Answer

Louse

Answer

Soft tick

Answer

Hard tick

Answer

Rat flea

Question 8

All of the following factors contribute to the resurgence of malaria, except:

Accepted Answer

Drug resistance in the host

Answer

Drug resistance in the parasite

Answer

Drug resistance in vectors

Answer

Antigenic variations in the parasite

Question 9

Which of the following is NOT true about Japanese Encephalitis (JE)?

Accepted Answer

Case fatality rate is 80-90%

Answer

Transmitted by Culex mosquitoes

Answer

Death typically occurs within 9 days

Answer

Duration of prodromal symptoms is 1-6 days

Question 10

What are the true targets for DOTS in terms of case finding and cure rate?

Accepted Answer

Case finding 70%, cure rate 85%

Answer

Case finding 80%, cure rate 85%

Answer

Case finding 80%, cure rate 80%

Answer

Case finding 70%, cure rate 75%

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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