Infectious Diseases Practice Questions

Q: All of the following are true about Typhoid fever except:

The highest incidence occurs in the 30-40 years age group. **Explanation:** The correct answer is **D**. In endemic areas like India, Typhoid fever (Enteric fever) primarily affects children and young adults. The highest incidence is typically observed in the **5–19 years age group**, not the 30–40 years group. By the fourth decade of life, many individuals have developed partial immunity due to repeated subclinical exposures. **Analysis of Options:** * **Option A:** The incubation period is typically **10–14 days**, though it can range from 3 days to 3 weeks depending on the dose of inoculum. * **Option B:** Epidemiological data shows a higher prevalence in **males** compared to females, often attributed to greater outdoor exposure and consumption of contaminated street food/water. * **Option C:** Chronic carriers (who harbor *S. typhi* in the gallbladder) can be treated with **Ampicillin or Amoxicillin** (4-6g/day) combined with Probenecid for 6 weeks. However, in the presence of gallstones, cholecystectomy is often required for a permanent cure. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir:** Man is the only known reservoir. * **Carrier State:** A "Chronic Carrier" excretes bacilli for more than **one year**. The **Ty21a** oral vaccine is a live attenuated strain, while the **Vi polysaccharide** is injectable. * **Clinical Signs:** Look for "Step-ladder pyrexia," "Rose spots" (2nd week), and "Relative bradycardia" (Faget’s sign). * **Diagnosis:** Use the **BASU** mnemonic for culture: **B**lood (1st week), **A**gglutination/Widal (2nd week), **S**tool (3rd week), **U**rine (4th week). Bone marrow culture is the most sensitive.

Q: Plague is what type of zoonosis?

Metazoonosis. ### Explanation The classification of zoonoses is based on the life cycle of the infecting organism and the necessity of different hosts for its maintenance. **Why Metazoonosis is Correct:** **Metazoonoses** are diseases transmitted biologically by **invertebrate vectors**. In these diseases, the agent multiplies, develops, or both, within the vector before being transmitted to a vertebrate host. **Plague** (*Yersinia pestis*) is a classic metazoonosis because it requires the **rat flea (*Xenopsylla cheopis*)** as a biological vector to transmit the bacteria from rodents to humans. **Analysis of Incorrect Options:** * **Direct Zoonosis:** These are maintained in a single vertebrate species (e.g., Rabies, Brucellosis, Anthrax). They are transmitted from an infected vertebrate to a susceptible one by contact or a mechanical vector. * **Cyclozoonosis:** These require **more than one vertebrate host** species (but no invertebrate host) to complete the agent’s life cycle. Examples include *Taenia solium* (requires humans and pigs) and Echinococcosis. * **Sapro-zoonosis:** These require a **non-animal environmental reservoir** (like soil or decaying organic matter) for the development of the agent. Examples include Tetanus and Histoplasmosis. **High-Yield Clinical Pearls for NEET-PG:** * **Vector of Plague:** *Xenopsylla cheopis* (Rat flea) is the most efficient vector. * **Mechanism:** The "Blocked Flea" phenomenon occurs when *Y. pestis* multiplies in the flea's proventriculus, preventing blood intake and forcing the flea to regurgitate bacteria into the host. * **Indicators:** The **Flea Index** (specifically the Cheopis index >1) is a critical epidemiological marker for an impending plague outbreak. * **Drug of Choice:** Streptomycin is traditionally the DOC, though Gentamicin and Doxycycline are also used.

Q: Which of the following is a rabies-free country?

Australia. **Explanation:** **Correct Answer: B. Australia** **Medical Concept:** A "rabies-free" country is defined by the World Health Organization (WHO) as a territory where no indigenous human or animal cases of rabies (caused by the classical *Rabies virus*) have been reported for at least two years, supported by a rigorous surveillance system and strict import/quarantine laws. Australia is historically recognized as rabies-free. While the **Australian Bat Lyssavirus (ABLV)** exists in local bat populations and can cause a rabies-like illness, the classical rabies virus (RABV) is not endemic to the continent. **Analysis of Incorrect Options:** * **A. China:** China remains one of the highest-burden countries for human rabies globally, primarily transmitted through domestic dogs. * **C. France:** While France has eliminated rabies in its terrestrial wildlife (like foxes) through oral vaccination programs, it is not classified as entirely rabies-free due to occasional imported cases and the presence of European Bat Lyssaviruses. * **D. Russia:** Rabies is endemic across Russia, with significant reservoirs in wild foxes, wolves, and stray dogs. **High-Yield NEET-PG Pearls:** * **Rabies-Free Areas:** Other notable rabies-free regions include the **United Kingdom, Japan, New Zealand, Iceland, and parts of Oceania.** * **Island Status:** Most rabies-free nations are islands, which allows for strict control over animal movement. * **India Context:** India has the highest incidence of rabies in the world (approx. 20,000 deaths/year). **Lakshadweep and the Andaman & Nicobar Islands** are the only parts of India considered rabies-free. * **Rule of 100:** Rabies is considered **100% fatal** once clinical symptoms appear, but **100% preventable** with timely Post-Exposure Prophylaxis (PEP).

Q: The human is the dead-end host for which of the following organisms?

Bubonic plague. ### Explanation **Correct Answer: C. Bubonic plague** In medical ecology, a **dead-end host** (or accidental host) is an organism from which an infectious agent cannot be transmitted to another susceptible host. This usually occurs because the pathogen does not reach a high enough concentration in the blood (bacteremia/viremia) or is not shed in sufficient quantities for a vector or environment to pick it up. In **Bubonic plague** (*Yersinia pestis*), the natural cycle involves rodents and fleas. Humans are infected via the bite of an infected rat flea (*Xenopsylla cheopis*). In the bubonic form, the bacteria proliferate in the lymph nodes (buboes) but do not typically reach high enough levels in the blood to infect a new flea. Therefore, the human cannot sustain the transmission cycle. *(Note: If the infection progresses to Pneumonic plague, humans can transmit it via respiratory droplets, but for the Bubonic form, they remain a dead-end host.)* **Why the other options are incorrect:** * **A. Malaria:** Humans are an essential part of the life cycle. The *Anopheles* mosquito picks up gametocytes from human blood to continue the cycle. * **B. Typhoid:** Humans are the **only** reservoir for *Salmonella typhi*. Transmission occurs via the feco-oral route from cases or chronic carriers. * **D. Filaria:** Humans are the definitive host. The *Culex* mosquito ingests microfilariae from human blood to facilitate the parasite's development. **High-Yield Clinical Pearls for NEET-PG:** * **Other Dead-end Hosts:** Humans are also dead-end hosts for **Japanese Encephalitis (JE)**, **Rabies**, **Hydatid disease** (*Echinococcus granulosus*), and **Toxoplasmosis**. * **Plague Vector:** The most efficient vector is *Xenopsylla cheopis* (Rat flea). * **Indicator:** A "Rat Fall" is a classic warning sign of an impending plague outbreak in a community.

Q: A 3-year-old male child presents with a bat bite on the face. Categorize the wound for rabies post-exposure prophylaxis.

Category 3. ### Explanation **Correct Answer: C. Category 3** The categorization of rabies exposure is based on the severity of contact and the risk of virus transmission. According to WHO and National Guidelines (NRCP), **Category 3** exposure includes: 1. Single or multiple transdermal bites or scratches. 2. Licks on broken skin. 3. Contamination of mucous membranes with saliva (licks on eyes/mouth). 4. **Direct contact with bats.** In this case, the child has a bat bite on the face. Any direct contact with bats is automatically classified as Category 3 due to the high risk of rabies transmission and the often-imperceptible nature of bat bites. Furthermore, bites on highly vascular areas like the **face, head, neck, and fingertips** are always treated with the highest priority. **Why other options are incorrect:** * **Category 1:** Refers to touching or feeding animals, or licks on intact skin. No prophylaxis is required. * **Category 2:** Refers to minor scratches or abrasions without bleeding, or nibbling of uncovered skin. This requires vaccination but not Rabies Immunoglobulin (RIG). * **Category 4:** There is no "Category 4" in the standard WHO/National Rabies classification system. **High-Yield Clinical Pearls for NEET-PG:** * **Management of Category 3:** Requires immediate local wound washing (15 mins with soap and water), **Rabies Vaccine (ARV)**, and **Rabies Immunoglobulin (RIG)** infiltrated into the wound. * **Bat Bites:** In many regions, bat bites are considered Category 3 even if the bite is not visible. * **Site Importance:** Bites on the face have a shorter incubation period because the virus reaches the CNS faster via cranial nerves. * **Rule of Thumb:** If it bleeds, it is Category 3. If it involves a bat, it is Category 3.

Q: What is the WHO ORS composition in mmol for Sodium (Na+)?

Sodium (Na+) - 75. The WHO recommended **Low Osmolarity ORS** is a cornerstone of pediatric gastroenterology and a high-yield topic for NEET-PG. The transition from the older "Standard ORS" to the current "Low Osmolarity" version was designed to reduce the risk of hypernatremia and decrease the need for unscheduled IV fluids. ### **Explanation of the Correct Answer** **D. Sodium (Na+) - 75 mmol/L:** The current WHO Low Osmolarity ORS contains **75 mmol/L** of Sodium. This concentration is optimal for the sodium-glucose cotransport mechanism in the small intestine, ensuring effective water absorption while maintaining a lower total osmolarity (245 mOsm/L) to prevent osmotic diarrhea. ### **Analysis of Incorrect Options** * **A. Glucose - 111 mmol/L:** This was the concentration in the **older Standard ORS**. The current Low Osmolarity ORS contains **75 mmol/L** of Glucose. A 1:1 molar ratio of Sodium to Glucose is maintained for optimal absorption. * **B. Potassium (K+) - 20 mmol/L:** While this value is **correct** for the concentration of Potassium in ORS, the question specifically asks for the composition of **Sodium (Na+)**. * **C. Chloride (Cl-) - 65 mmol/L:** This is the correct concentration for Chloride in the current formula, but it does not answer the question regarding Sodium. ### **High-Yield Clinical Pearls for NEET-PG** * **Total Osmolarity:** 245 mOsm/L (Previous was 311 mOsm/L). * **Trisodium Citrate:** 10 mmol/L (Used as a buffering agent to correct acidosis; it also increases the shelf life of ORS). * **ReSoMal:** Used specifically for children with **Severe Acute Malnutrition (SAM)**. It has lower Sodium (45 mmol/L) and higher Potassium (40 mmol/L). * **Zinc Supplementation:** Always given alongside ORS in diarrhea (20 mg/day for 10–14 days; 10 mg/day for infants <6 months) to reduce the duration and recurrence of episodes.

Q: What type of transmission is involved in the case of plague in rat flea?

Propagative. ### Explanation In vector-borne diseases, biological transmission occurs when the pathogen undergoes a necessary period of development or multiplication within the vector. This is categorized into three types based on how the pathogen behaves: **1. Why Propagative is Correct:** In **Propagative transmission**, the pathogen simply **multiplies** (increases in number) within the vector but undergoes **no change in form or morphology**. In the case of Plague (*Yersinia pestis*), the bacteria multiply extensively in the proventriculus of the rat flea (*Xenopsylla cheopis*), eventually causing a physical blockage. When the "blocked flea" attempts to feed, it regurgitates the multiplied bacteria into the host. Since the bacteria only increase in number without changing their biological stage, it is purely propagative. **2. Analysis of Incorrect Options:** * **Cyclo-developmental:** The pathogen undergoes **morphological change** (developmental stages) but **does not multiply**. * *Example:* Filarial parasite (*Wuchereria bancrofti*) in the mosquito. * **Cyclopropagative:** The pathogen undergoes **both** morphological change and an increase in number. * *Example:* Malaria parasite (*Plasmodium*) in the Anopheles mosquito. **3. NEET-PG High-Yield Pearls:** * **Plague Vector:** *Xenopsylla cheopis* (Rat flea) is the most efficient vector. * **Blockage Phenomenon:** This is the hallmark of plague transmission where the bacterial mass prevents blood from entering the flea's stomach, making the flea "hungry" and aggressive. * **Other Propagative Examples:** Yellow fever virus in mosquitoes and Arboviruses in general. * **Extrinsic Incubation Period:** The time required for the pathogen to develop/multiply in the vector before it becomes infective.

Q: The mass treatment of trachoma is undertaken if the prevalence in the community is:

5%. **Explanation:** The management of Trachoma (caused by *Chlamydia trachomatis*) follows the WHO-recommended **SAFE Strategy** (Surgery, Antibiotics, Facial cleanliness, and Environmental improvement). The decision to initiate community-wide mass treatment depends on the prevalence of **Trachomatous Inflammation—Follicular (TF)** in children aged 1–9 years. **Why 5% is the Correct Answer:** According to the current WHO guidelines, mass drug administration (MDA) with oral Azithromycin is indicated if the prevalence of TF in children (1–9 years) is **≥ 5%**. * If prevalence is **5% to <10%**, a single round of annual mass treatment is conducted, followed by a re-impact survey. * If prevalence is **≥ 10%**, annual mass treatment is mandatory for at least 3 years before re-evaluation. **Analysis of Incorrect Options:** * **A (3%):** This is below the threshold for mass intervention. At this level, treatment is usually targeted at individual cases and their household contacts rather than the whole community. * **C (6%):** While 6% qualifies for mass treatment, the **threshold** for initiating the program is 5%. In competitive exams, the minimum cutoff value is the standard answer. * **D (10%):** This was the historical threshold for mass treatment in older guidelines. However, the WHO updated the criteria to 5% to accelerate the elimination of blinding trachoma. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Single dose of **Oral Azithromycin (20 mg/kg up to 1g)**. Topical 1% Tetracycline eye ointment is an alternative. * **WHO Target:** The goal is the **Elimination of Trachoma as a public health problem**, defined as a TF prevalence of 15 years). * **SAFE Strategy:** "S" and "A" are the medical/surgical components, while "F" and "E" are the public health components.

Q: Which of the following statements regarding Anopheles Fluviatilis is INCORRECT?

It is restricted to the Andaman and Nicobar Islands.. ### Explanation **1. Why Option D is the Correct (Incorrect Statement):** *Anopheles fluviatilis* is one of the most important primary vectors of malaria in India, but it is **not** restricted to the Andaman and Nicobar Islands. It is widely distributed across the **foothills and hilly tracts** of mainland India, particularly in the Western Ghats, Nilgiris, and Central Indian ranges. The vector specifically restricted to the Andaman and Nicobar Islands is *Anopheles sundaicus*. **2. Analysis of Other Options:** * **Option A (Breeding):** This is a correct statement. *A. fluviatilis* typically breeds in **slow-moving, clear water** such as hill streams, irrigation channels, and seepage water. This distinguishes it from *A. stephensi*, which prefers stagnant water in urban containers. * **Option B (Vector Efficiency):** This is a correct statement. It is a highly efficient vector. Due to its high survival rate and frequent feeding habits, it can maintain malaria transmission even when its **population density is low**. * **Option C (Feeding Habit):** This is a correct statement. In most hilly regions, *A. fluviatilis* is **highly anthropophilic** (prefers human blood over animals), which contributes to its high "Vectorial Capacity." **3. High-Yield NEET-PG Pearls:** * **Primary Vector of Hilly Areas:** *Anopheles fluviatilis*. * **Primary Vector of Urban Malaria:** *Anopheles stephensi*. * **Primary Vector of Rural Malaria:** *Anopheles culicifacies* (responsible for 60-70% of cases in India). * **Primary Vector of Coastal Areas/Islands:** *Anopheles sundaicus*. * **Resting Habit:** *A. fluviatilis* is primarily **endophilic** (rests indoors), making it susceptible to Indoor Residual Spraying (IRS).

Q: Which of the following is not monitored in malaria surveillance currently?

Infant parasite rate. **Explanation:** In the current strategy of the **National Center for Vector Borne Diseases Control (NCVBDC)**, surveillance focuses on the active and passive detection of cases within the general population to monitor transmission intensity and program efficiency. **Why "Infant Parasite Rate" is the correct answer:** The **Infant Parasite Rate (IPR)** is defined as the percentage of infants (under 1 year) showing parasites in their blood. While it was historically considered the best indicator of **recent/current malaria transmission** in a locality, it is no longer used for routine monitoring under the current National Program. Modern surveillance shifted towards more comprehensive community-wide indices. **Analysis of Incorrect Options:** * **ABER (Annual Blood Examination Rate):** This monitors the **efficiency of the surveillance system**. It measures the number of slides examined per 100 population per year. A minimum ABER of 10% is generally required to ensure adequate case detection. * **API (Annual Parasite Incidence):** This is the **primary indicator** used to classify malaria endemicity in an area. It is calculated as (Total confirmed cases / Total population) × 1000. * **SPR (Slide Positivity Rate):** This measures the proportion of slides found positive among those examined. It is a sensitive indicator of the **prevalence of malaria** in a community at a given time. **High-Yield Pearls for NEET-PG:** * **API < 1** is the threshold for an area to enter the "Elimination Phase." * **Annual Falciparum Incidence (AFI)** and **Slide Falciparum Rate (SFR)** are used specifically to monitor the burden of *P. falciparum*. * **Active Surveillance:** Health workers visit houses (usually fortnightly) to detect fever cases. * **Passive Surveillance:** Cases are detected when patients voluntarily visit health facilities.

Question 1

All of the following are true about Typhoid fever except:

Accepted Answer

The highest incidence occurs in the 30-40 years age group

Answer

Incubation period is 10-14 days

Answer

It is most common among males

Answer

Carriers can be treated by ampicillin

Question 2

Plague is what type of zoonosis?

Accepted Answer

Metazoonosis

Answer

Cyclozoonosis

Answer

Direct zoonosis

Answer

Sapro-zoonosis

Question 3

Which of the following is a rabies-free country?

Accepted Answer

Australia

Answer

China

Answer

France

Answer

Russia

Question 4

The human is the dead-end host for which of the following organisms?

Accepted Answer

Bubonic plague

Answer

Malaria

Answer

Typhoid

Answer

Filaria

Question 5

A 3-year-old male child presents with a bat bite on the face. Categorize the wound for rabies post-exposure prophylaxis.

Accepted Answer

Category 3

Answer

Category 1

Answer

Category 2

Answer

Category 4

Question 6

What is the WHO ORS composition in mmol for Sodium (Na+)?

Accepted Answer

Sodium (Na+) - 75

Answer

Glucose - 111

Answer

Potassium (K+) - 20

Answer

Chloride (Cl-) - 65

Question 7

What type of transmission is involved in the case of plague in rat flea?

Accepted Answer

Propagative

Answer

Cyclopropagative

Answer

Cyclo-developmental

Answer

None

Question 8

The mass treatment of trachoma is undertaken if the prevalence in the community is:

Accepted Answer

5%

Answer

3%

Answer

6%

Answer

10%

Question 9

Which of the following statements regarding Anopheles Fluviatilis is INCORRECT?

Accepted Answer

It is restricted to the Andaman and Nicobar Islands.

Answer

It breeds in moving water.

Answer

It propagates malaria at lower densities compared to other Anopheles species.

Answer

It is highly anthropophilic.

Question 10

Which of the following is not monitored in malaria surveillance currently?

Accepted Answer

Infant parasite rate

Answer

ABER

Answer

Annual parasite incidence

Answer

Slide positivity rate

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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