Infectious Diseases Practice Questions

Q: Which strain of influenza was declared as a pandemic?

H1N1. **Explanation:** The correct answer is **A. H1N1**. In June 2009, the World Health Organization (WHO) declared the **H1N1 "Swine Flu"** strain as the first global influenza pandemic in 41 years. This occurred due to **Antigenic Shift**, a major genetic change resulting in a new subtype to which the general population had little to no immunity. Historically, H1N1 was also responsible for the devastating 1918 "Spanish Flu" pandemic. **Analysis of Incorrect Options:** * **B. H5N1:** Known as **Avian Influenza (Bird Flu)**. While it has a high mortality rate in humans, it has not yet achieved efficient human-to-human transmission required to be declared a pandemic. It remains an epizootic/enzootic threat. * **C. H7N7:** Another strain of Avian Influenza. It has caused outbreaks in poultry and sporadic infections in humans (primarily conjunctivitis), but no sustained community transmission. * **D. H3N3:** This is a subtype found in birds and pigs but is not a significant human pathogen and has never caused a pandemic. (Note: **H3N2** was the cause of the 1968 Hong Kong Flu pandemic). **High-Yield Clinical Pearls for NEET-PG:** * **Antigenic Shift:** Sudden, major change (reassortment) leading to **Pandemics**. * **Antigenic Drift:** Gradual, point mutations leading to **Epidemics** and the need for annual vaccine updates. * **Pandemic Criteria:** A new virus emerges, infects humans, and causes sustained person-to-person transmission across multiple WHO regions. * **Drug of Choice:** Oseltamivir (Tamiflu) is the preferred neuraminidase inhibitor for H1N1.

Q: Breteau Index is used for the identification of breeding sites of which mosquito?

Aedes aegypti. **Explanation:** The **Breteau Index (BI)** is a key entomological indicator used in the surveillance of **Aedes aegypti**, the primary vector for Dengue, Chikungunya, and Zika virus. It is defined as the **number of positive containers (with larvae or pupae) per 100 houses inspected**. It is considered the most useful index for estimating the density of Aedes mosquitoes in a community because it establishes a relationship between positive containers and houses. **Analysis of Options:** * **Aedes aegypti (Correct):** Along with the Breteau Index, other indices used for Aedes include the **House Index** (percentage of houses positive for larvae) and the **Container Index** (percentage of water-holding containers positive for larvae). * **Anopheles (Incorrect):** Surveillance for Anopheles (Malaria vector) typically involves the **Spleen Index**, **Parasite Index**, or **Annual Parasite Incidence (API)**. Larval density is measured using the "Density per dip" method. * **Culex (Incorrect):** Culex (Filariasis/Japanese Encephalitis vector) is monitored using the **Density Index** (average number of mosquitoes collected per man-hour) or the **Percentage of positive pools**. * **Hookworm (Incorrect):** This is a helminthic infection, not a mosquito. Prevalence is measured via stool examination (eggs per gram). **High-Yield Clinical Pearls for NEET-PG:** * **Aedes aegypti** is known as the "Tiger Mosquito" (due to white stripes) and is a "day biter." * **Critical Threshold:** A Breteau Index **> 20** is generally considered a high risk for the transmission of Dengue fever in a community. * **Aedes** breeds in clean, stagnant water (artificial containers like tires, coolers, and flower pots), whereas **Culex** breeds in dirty, polluted water.

Q: What is the concentration of sodium in reduced osmolarity ORS (in mmol/litre)?

75. **Explanation:** The correct answer is **75 mmol/L**. This reflects the World Health Organization (WHO) and UNICEF recommendation for **Reduced Osmolarity ORS**, which was introduced to replace the older, high-osmolarity formula. **1. Why 75 mmol/L is correct:** The standard Reduced Osmolarity ORS is designed to optimize the co-transport of sodium and glucose in the small intestine. By lowering the sodium concentration to **75 mmol/L** and the total osmolarity to **245 mOsm/L**, the solution effectively reduces stool output, decreases the incidence of vomiting, and minimizes the risk of hypernatremia compared to the older formula. **2. Analysis of Incorrect Options:** * **Option A (50 mmol/L):** This is the sodium concentration found in **ReSoMal** (Rehydration Solution for Malnutrition), specifically designed for children with severe acute malnutrition (SAM) to avoid sodium overload. * **Option C (65 mmol/L):** This is the concentration of **Chloride** in the reduced osmolarity ORS, not sodium. * **Option D (20 mmol/L):** This is the concentration of **Potassium** in the reduced osmolarity ORS. **Clinical Pearls for NEET-PG:** * **Composition of Reduced Osmolarity ORS (mEq/L or mmol/L):** * Sodium: 75 * Chloride: 65 * Glucose (Anhydrous): 75 * Potassium: 20 * Citrate: 10 * **Total Osmolarity: 245 mOsm/L** * **High-Yield Fact:** The glucose-to-sodium ratio in the current ORS is **1:1**, which is the physiological ideal for the sodium-glucose luminal transporter (SGLT-1). * **Contraindications for ORS:** Paralytic ileus, intestinal obstruction, and altered sensorium (risk of aspiration).

Q: Chandler's endemic index is used in the diagnosis or assessment of which condition?

Hookworm infestation. **Explanation:** **Chandler’s Index** is a specific epidemiological tool used to assess the **severity of Hookworm infestation** in a community. Unlike simple prevalence rates, this index measures the "worm burden" by calculating the **average number of eggs per gram (EPG) of stool** across a population sample. * **Why it is correct:** Hookworm pathogenicity is directly related to the number of worms present (intensity of infection) rather than just their presence. Chandler’s Index categorizes the public health significance: an index below 200-250 is considered low, while an index above 500 indicates a significant public health problem where clinical hookworm anemia is likely prevalent. **Analysis of Incorrect Options:** * **A. Dengue Hemorrhagic Fever:** Monitored using entomological indices like the House Index, Container Index, and Breteau Index (measuring *Aedes aegypti* density). * **B. Malaria:** Assessed using the Annual Parasite Incidence (API), Annual Blood Examination Rate (ABER), and Splenic Index. * **C. Cholera:** Monitored through surveillance of "Acute Diarrheal Diseases" and confirmed via stool culture (Gold Standard) or the presence of "Rice water stools." **High-Yield Clinical Pearls for NEET-PG:** * **Hookworm Species:** *Ancylostoma duodenale* (causes more blood loss, ~0.15ml/day) and *Necator americanus* (~0.03ml/day). * **Clinical Feature:** The hallmark is **Iron Deficiency Anemia** (Microcytic Hypochromic). * **Treatment of Choice:** Albendazole (400mg single dose). * **Public Health Strategy:** Periodic deworming (National Deworming Day) and improving sanitation to prevent skin penetration (Ground itch).

Q: Which of the following is not a zoonotic disease?

Typhoid. **Explanation:** The correct answer is **Typhoid (A)**. A zoonotic disease is defined as an infection or infestation that is naturally transmissible from vertebrate animals to humans. **Why Typhoid is the correct answer:** Typhoid fever is caused by *Salmonella typhi*. It is an **anthroponotic** disease, meaning humans are the only natural reservoir and host. Transmission occurs via the feco-oral route through contaminated food or water, typically originating from a human case or a chronic carrier (e.g., "Typhoid Mary"). There is no animal involvement in its natural life cycle. **Analysis of incorrect options:** * **Brucellosis:** A classic zoonosis (also known as Malta Fever) transmitted to humans through contact with infected livestock (cattle, goats, sheep) or consumption of unpasteurized dairy products. * **Q Fever:** Caused by *Coxiella burnetii*, it is a zoonotic infection primarily associated with cattle, sheep, and goats. Humans usually get infected by inhaling contaminated dust or aerosols from animal birth products. * **Plague:** Caused by *Yersinia pestis*, it is a famous zoonosis maintained in a cycle involving wild rodents and transmitted to humans via the bite of an infected rat flea (*Xenopsylla cheopis*). **High-Yield NEET-PG Pearls:** * **Reverse Zoonosis:** When a disease is transmitted from humans to animals (e.g., Human tuberculosis to cattle). * **Cyclozoonosis:** Requires more than one vertebrate host to complete the life cycle (e.g., Echinococcosis, Taeniasis). * **Saprozoonosis:** Has a vertebrate host and a non-animal reservoir like soil or plants (e.g., Tetanus, Histoplasmosis). * **Key Anthroponoses:** Typhoid, Cholera, Amoebiasis, Measles, and Polio.

Q: Which type of mosquito is depicted?

Culex. ***Culex*** - Female **palpi are shorter** than the proboscis, as visible in the depicted mosquito. - Wings are **unspotted**, distinguishing it from Anopheles. - Lacks the **white/silver banding** on legs and abdomen characteristic of Aedes. - Wings show **uniform brown scales without the distinctive pale and dark scale patches** seen in Mansonoides, providing a positive visible feature distinguishing Culex from Mansonoides in the image. *Anopheles* - Female **palpi are equal in length** to the proboscis and wings often have **spotted patterns**. - Characteristic **45-degree resting posture** with head and proboscis angled downward. *Aedes* - Distinguished by **white/silver bands** on legs and abdomen, creating a striped appearance — absent in the depicted mosquito. - Has **short palpi** compared to proboscis length. *Mansonoides* - Less commonly encountered genus with **palpi shorter** than proboscis in females. - Lacks the characteristic **angled resting posture** and **wing spotting** of Anopheles. - Distinguished from Culex by **mottled wing scales** (alternating pale and dark patches on the wings) — absent in the depicted mosquito, which shows plain, uniformly scaled wings.

Question 1

Which strain of influenza was declared as a pandemic?

Accepted Answer

H1N1

Answer

H5N1

Answer

H7N7

Answer

H3N3

Question 2

Breteau Index is used for the identification of breeding sites of which mosquito?

Accepted Answer

Aedes aegypti

Answer

Anopheles

Answer

Culex

Answer

Hookworm

Question 3

What is the concentration of sodium in reduced osmolarity ORS (in mmol/litre)?

Accepted Answer

75

Answer

50

Answer

65

Answer

20

Question 4

Which of the following is true about meningococcal meningitis?

Accepted Answer

Treatment in the first 2 days can save the lives of 95% of cases.

Answer

Case fatality rate is less than 10% in untreated cases.

Answer

Cases are the main source of infection.

Answer

Rifampicin is the drug of choice for treatment.

Question 5

Which of the following statements about leprosy is false?

Accepted Answer

MDT is contraindicated during pregnancy.

Answer

It has been eliminated from India.

Answer

It can be transmitted through breast milk.

Answer

Lepromin test is not a diagnostic test.

Question 6

Isolation is indicated in which of the following conditions?

Accepted Answer

Tuberculosis (TB)

Answer

Cholera

Answer

Measles

Answer

Typhoid

Question 7

Chandler's endemic index is used in the diagnosis or assessment of which condition?

Accepted Answer

Hookworm infestation

Answer

Dengue hemorrhagic fever

Answer

Malaria

Answer

Cholera

Question 8

Which of the following is not a zoonotic disease?

Accepted Answer

Typhoid

Answer

Brucellosis

Answer

Q fever

Answer

Plague

Question 9

Which type of mosquito is depicted?

Accepted Answer

Culex

Answer

Aedes

Answer

Anopheles

Answer

Mansonoides

Question 10

What is the microfilaria endemicity index?

Accepted Answer

% of persons showing microfilaria in blood among diseased individuals

Answer

% of persons showing microfilaria in blood

Answer

Number of microfilaria in the blood

Answer

Average number of persons with positive slides

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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