Infectious Diseases Practice Questions

Q: Japanese B encephalitis virus is transmitted by which mosquito?

Culex tritaeniorhynchus. **Explanation:** Japanese Encephalitis (JE) is a major public health concern in India, caused by a Group B Arbovirus (Flavivirus). The correct answer is **Culex tritaeniorhynchus**, which is the primary vector for JE in India and Southeast Asia. **1. Why Culex tritaeniorhynchus is correct:** These mosquitoes are "exophilic" (outdoor resters) and "zoophilic" (prefer animal blood). They breed primarily in irrigated rice fields and shallow ditches. The virus follows a **Pig-Mosquito-Man** cycle. Pigs act as the "amplifier hosts," allowing the virus to multiply to high titers without getting sick, which the Culex mosquito then transmits to humans. **2. Analysis of Incorrect Options:** * **Aedes aegypti:** This is the primary vector for Dengue, Chikungunya, Yellow Fever, and Zika virus. It is a day-biter and breeds in stagnant clean water. * **Culex fatigans (C. quinquefasciatus):** This is the principal vector for **Bancroftian Filariasis**. While it belongs to the same genus, it is not the primary vector for JE. * **Hard tick (Ixodid ticks):** These are vectors for diseases like Kyasanur Forest Disease (KFD), Indian Tick Typhus, and Tularemia, but not JE. **High-Yield Clinical Pearls for NEET-PG:** * **Dead-end Host:** Humans are dead-end hosts for JE because the viraemia in humans is insufficient to infect a biting mosquito. * **Incidental Host:** Man is an incidental host; the natural cycle is between mosquitoes, pigs, and water birds (Ardeid birds like herons and egrets). * **Vaccination:** The most common vaccine used in the Universal Immunization Programme (UIP) in India is the **SA-14-14-2** (Live attenuated vaccine), given at 9 months and 16–24 months. * **Seasonality:** JE outbreaks typically coincide with the monsoon and post-monsoon periods due to increased mosquito breeding in paddy fields.

Q: What is false about pertussis?

Maternal antibody provides protection in infants.. **Explanation:** The correct answer is **A (Maternal antibody provides protection in infants)** because this statement is false. Unlike diseases like Measles, maternal antibodies against *Bordetella pertussis* do not cross the placenta in sufficient quantities to provide passive immunity to the newborn. Consequently, infants are susceptible to pertussis from birth, which is why the disease is most severe and carries the highest mortality in this age group. **Analysis of other options:** * **Option B:** Pertussis is primarily spread via **droplet infection**. While the bacteria can survive for short periods on surfaces, **fomites play a negligible/small role** in transmission compared to direct respiratory contact. * **Option C:** Pertussis is **commonly seen in infants** and young children (under 5 years). In fact, the "shift to the right" (older age groups) is seen only in highly vaccinated populations, but globally, infants remain the primary risk group. * **Option D:** Epidemiologically, pertussis shows **no significant gender predilection**; both males and females are affected equally, although some studies historically suggested a slightly higher incidence/mortality in females. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** 7–14 days (Range: 5–21 days). * **Infectivity:** Highest during the **catarrhal stage**. * **Drug of Choice:** Erythromycin (or other Macrolides like Azithromycin) for 7–14 days. * **Vaccination:** The "P" in DPT. To overcome the lack of maternal immunity, the WHO and National Immunization Schedule recommend starting the primary series at **6 weeks** of age. * **Secondary Attack Rate (SAR):** Very high, approximately **80–90%** in susceptible household contacts.

Q: What is the recommended duration for the use of long-lasting insecticidal nets?

3 years. ### Explanation **Correct Answer: C. 3 years** **1. Why it is correct:** Long-Lasting Insecticidal Nets (LLINs) are a core intervention in the Global Malaria Program. Unlike traditional Insecticide-Treated Nets (ITNs) that require re-treatment every 6–12 months, LLINs are manufactured by permanently incorporating or coating insecticide (usually pyrethroids) into the fibers. According to WHO guidelines and the National Vector Borne Disease Control Programme (NVBDCP), an LLIN is designed to maintain its biological efficacy against mosquitoes for **at least 3 years** or 20 standard washes under field conditions. **2. Why the other options are incorrect:** * **A & B (6 months / 1 year):** These durations are typical for conventional ITNs, which lose their insecticide concentration rapidly after a few washes and require periodic "dipping" in insecticide. * **D (10 years):** No current LLIN technology guarantees insecticide stability or physical integrity (resistance to tearing) for a decade. Using a net beyond its efficacy period increases the risk of malaria transmission. **3. High-Yield Clinical Pearls for NEET-PG:** * **Insecticide Used:** Primarily **Pyrethroids** (e.g., Permethrin, Deltamethrin, Alpha-cypermethrin). * **Mechanism:** LLINs provide a "double-action" protection—a **physical barrier** and a **chemical repellent/killing effect** (knockdown effect). * **Target Population:** Under the National Framework for Malaria Elimination in India, LLINs are distributed free of cost in high-burden areas (API > 2). * **Maintenance:** LLINs should be washed with cold water and mild soap and dried in the **shade** (direct sunlight degrades the insecticide). * **The "3-20" Rule:** Remember LLINs for **3** years or **20** washes.

Q: In an epidemic of hepatitis E, infection in which of the following groups carries a poor prognosis?

Pregnant women. **Explanation:** Hepatitis E Virus (HEV), a single-stranded RNA virus transmitted via the feco-oral route, is generally a self-limiting disease with a low case fatality rate (0.5–3%). However, it is notorious for its **high mortality rate (up to 20–25%) in pregnant women**, particularly during the **third trimester**. **Why Pregnant Women?** The poor prognosis in pregnancy is attributed to a combination of factors: * **Hormonal Changes:** High levels of estrogen and progesterone suppress cell-mediated immunity. * **Cytokine Shift:** A shift from Th1 to Th2 immune response makes the mother more susceptible to viral replication. * **Complications:** HEV in pregnancy frequently leads to **Fulminant Hepatic Failure (FHF)**, Disseminated Intravascular Coagulation (DIC), and obstetric complications like premature delivery or postpartum hemorrhage. **Analysis of Incorrect Options:** * **A & C (Malnourished/Anaemic Males):** While malnutrition and anemia can impair general immunity, they do not specifically predispose an individual to the fulminant hepatic failure characteristic of HEV infection. * **D (Postmenopausal Women):** The specific immunological and hormonal milieu of pregnancy is absent in postmenopausal women; their risk profile remains similar to the general population. **High-Yield Clinical Pearls for NEET-PG:** * **Virus Family:** Hepeviridae (Non-enveloped RNA virus). * **Transmission:** Feco-oral (Water-borne epidemics). * **Zoonotic Potential:** HEV Genotype 3 and 4 are associated with consumption of undercooked pork. * **Chronic Infection:** HEV can cause chronic hepatitis in **organ transplant recipients** and immunocompromised patients. * **Diagnosis:** IgM anti-HEV is the gold standard for acute infection.

Q: Chandler index is used for the diagnosis of which condition?

Ancylostomiasis. **Explanation:** The **Chandler Index** is a specific epidemiological tool used to measure the intensity of infection in a community for **Ancylostomiasis (Hookworm infestation)**. It is calculated by taking the average number of hookworm eggs per gram of feces across a sampled population. * **Why Option A is correct:** The Chandler Index assesses the "worm burden." It is clinically significant because the severity of iron-deficiency anemia in hookworm disease is directly proportional to the number of worms present. An index of **less than 200** is considered low, while an index **greater than 250** indicates a significant public health problem where clinical anemia is likely prevalent in the community. * **Why other options are incorrect:** * **Ascariasis (B):** Diagnosis is typically made via stool microscopy for eggs or the passage of adult worms; there is no specific "index" named after Chandler for this. * **Dracunculiasis (C):** Diagnosis is clinical (visualizing the emerging Guinea worm). * **Filariasis (D):** Epidemiological assessment uses the **Microfilaria Rate**, **Density**, and the **Mosquito Infection/Infectivity Rate**, not the Chandler Index. **High-Yield Clinical Pearls for NEET-PG:** * **Hookworm species:** *Ancylostoma duodenale* (consumes ~0.15 ml blood/day) and *Necator americanus* (consumes ~0.03 ml blood/day). * **Stoll’s Egg Counting Technique:** Another method used to estimate worm load. * **Key Association:** Ground itch (at entry site) and Loeffler’s syndrome (during pulmonary migration).

Q: Which of the following genera includes the 'tiger mosquito'?

Aedes. **Explanation:** The correct answer is **C. Aedes**. The **Aedes mosquito** (specifically *Aedes albopictus*) is popularly known as the **'Tiger Mosquito'** due to the characteristic bold, white transverse stripes on its black body and legs. This species, along with *Aedes aegypti*, is a highly efficient vector for several viral diseases. **Why the other options are incorrect:** * **Anopheles:** Known as the vector for **Malaria**. They are typically identified by their spotted wings and the fact that they rest at a 45-degree angle to the surface. * **Mansonia:** These mosquitoes are the primary vectors for **Brugian Filariasis**. They are unique because their larvae attach to the submerged roots of aquatic plants (like *Pistia*) to breathe. * **Culex:** Often called the "nuisance mosquito," it is the vector for **Bancroftian Filariasis** and **Japanese Encephalitis**. They typically breed in dirty, stagnant water. **High-Yield Clinical Pearls for NEET-PG:** 1. **Aedes Characteristics:** They are **"day biters"** (peak activity early morning and evening) and **"container breeders"** (preferring clean, stagnant water in flower pots, tires, or coolers). 2. **Diseases Transmitted:** Dengue (Break-bone fever), Chikungunya, Zika virus, and Yellow Fever. 3. **Flight Range:** Aedes has a very short flight range (usually <100 meters), making localized source reduction the most effective control strategy. 4. **Nervousness:** Aedes is known as a "nervous feeder," often biting multiple people to complete a single blood meal, which leads to rapid outbreaks.

Q: Which geographical region in India was identified as being suitable for mass DEC-medicated salt treatment for lymphatic filariasis due to its safety, low cost, and effectiveness?

Lakshadweep islands. **Explanation:** The correct answer is **Lakshadweep islands**. **Why Lakshadweep is correct:** Mass administration of **Diethylcarbamazine (DEC)-medicated salt** is a specialized strategy for the elimination of lymphatic filariasis. This method involves replacing common salt with salt fortified with 0.1% to 0.4% DEC. The **Lakshadweep islands** were identified as the ideal geographical region for this intervention because the islands are geographically isolated, have a closed market for salt supply (making it easier to monitor and control the distribution), and have a high endemicity of filariasis. Studies conducted here demonstrated that medicated salt is safe, inexpensive, and highly effective in reducing microfilaria rates compared to annual mass drug administration (MDA) alone. **Why other options are incorrect:** * **Goa, Daman and Diu:** While these are coastal areas where filariasis may be endemic, they are not geographically isolated "closed systems." The open trade routes and multiple sources of salt supply make the logistics of ensuring 100% coverage with medicated salt nearly impossible. * **Andaman and Nicobar islands:** Although isolated, the landmark pilot studies and successful large-scale implementation specifically cited in Indian public health literature and the National Health Programs focus on the Lakshadweep experience as the primary model for DEC-salt efficacy. **High-Yield Clinical Pearls for NEET-PG:** * **DEC-Salt Concentration:** Usually **0.1% to 0.2% w/w** is used for 6–12 months. * **Advantages:** No "side effects" typically seen with bolus doses (like the Mazzotti reaction) because the drug dose is low and continuous. * **Drug of Choice:** DEC is the drug of choice for Lymphatic Filariasis (except in cases of co-infection with Onchocerciasis). * **National Target:** India aims for the elimination of Lymphatic Filariasis by **2027** (three years ahead of the global target).

Q: What is the modified plan of operation for Malaria based on?

API (Annual Parasite Incidence). ### Explanation The **Modified Plan of Operation (MPO)** was launched in **1977** under the National Malaria Eradication Programme (NMEP) after a massive resurgence of malaria in India. Its primary objective was to prevent deaths and reduce morbidity through a decentralized approach. **Why API is the correct answer:** The MPO shifted the strategy from "eradication" to "control." The intensity of anti-malarial activities (specifically Indoor Residual Spraying or IRS) was determined by the **Annual Parasite Incidence (API)**. * Areas with an **API of 2 or above** were classified as high-risk and received regular insecticidal spraying. * Areas with an **API below 2** received focal spraying only. API is calculated as: *(Total number of positive slides in a year / Total population)* × 1000. **Analysis of Incorrect Options:** * **B. ABER (Annual Blood Examination Rate):** This measures the efficiency of the surveillance system (operational efficiency). While crucial for monitoring, it is not the criteria used to categorize areas for the MPO strategy. * **C. Spleen Rate:** This is a measure of **endemicity** (prevalence) in a community, traditionally used in children aged 2–9 years. It does not guide the current operational planning of the national program. * **D. Infant Parasite Rate:** This is the most sensitive index to measure the **recent transmission** of malaria in a locality. If the IPR is zero for three consecutive years, it indicates the absence of malaria transmission. **High-Yield NEET-PG Pearls:** * **API ≥ 2:** Threshold for regular IRS under MPO. * **ABER:** Should ideally be **10% or more** to ensure adequate surveillance. * **SPR (Slide Positivity Rate):** Used to monitor the trend of the disease in a specific area. * **Pf% (P. falciparum percentage):** Vital for monitoring the shift toward the more dangerous species of malaria.

Q: The definition of extensively drug-resistant TB includes resistance to all of the following drugs, EXCEPT:

Ethambutol. **Explanation:** The definition of **Extensively Drug-Resistant Tuberculosis (XDR-TB)** was updated by the WHO in 2021 to reflect changes in treatment regimens. According to the current definition, XDR-TB is TB caused by *Mycobacterium tuberculosis* strains that fulfill the following criteria: 1. **MDR-TB/RR-TB:** Resistance to **Rifampicin** (with or without resistance to **Isoniazid**). 2. **Resistance to any Fluoroquinolone** (e.g., Levofloxacin or Moxifloxacin). 3. **Resistance to at least one additional Group A drug:** This includes **Bedaquiline** or **Linezolid**. **Why Ethambutol is the correct answer:** Ethambutol is a first-line antitubercular drug. While it is often part of the background resistance profile in MDR/XDR cases, its resistance is **not** a defining criterion for the classification of XDR-TB. **Analysis of Incorrect Options:** * **Rifampicin & Isoniazid (Options A & C):** Resistance to these two drugs defines Multi-Drug Resistant TB (MDR-TB). Since XDR-TB is a more severe form of MDR-TB, resistance to these (specifically Rifampicin) is a mandatory prerequisite. * **Amikacin (Option D):** Under the **older (pre-2021) WHO definition**, XDR-TB was defined as MDR-TB plus resistance to any fluoroquinolone and at least one of the three second-line injectable drugs (Amikacin, Capreomycin, or Kanamycin). While no longer a primary defining criterion in the 2021 update, it was historically a core component of the definition. **High-Yield Clinical Pearls for NEET-PG:** * **MDR-TB:** Resistance to at least Isoniazid (H) and Rifampicin (R). * **Pre-XDR-TB:** MDR-TB plus resistance to any Fluoroquinolone. * **Group A Drugs (WHO 2019):** Levofloxacin/Moxifloxacin, Bedaquiline, and Linezolid. These are now the most potent drugs for drug-resistant TB. * **True XDR (2021 Update):** MDR + Fluoroquinolone resistance + (Bedaquiline OR Linezolid) resistance.

Q: Chandler index is an important tool in epidemiology. Which of the following is its least likely use?

Determining case severity and prognosis. **Explanation:** The **Chandler Index** is a classic epidemiological tool used specifically for **Hookworm infection** (*Ancylostoma duodenale* and *Necator americanus*). It represents the average number of eggs per gram (EPG) of stool calculated from a representative sample of the community. **Why Option A is the correct answer:** The Chandler Index is a **population-based metric**, not a clinical one. While it measures the "worm burden" of a community, it is **not used to determine individual case severity or prognosis**. Clinical severity in an individual depends on factors like nutritional status, iron stores, and host immunity, rather than just the egg count. Prognosis is determined by clinical response to anthelmintic treatment and iron supplementation. **Analysis of Incorrect Options:** * **B. Impact of control programme:** By comparing the Chandler Index before and after an intervention (e.g., mass drug administration or improved sanitation), health authorities can quantify the effectiveness of the program. * **C. Endemicity:** The index categorizes the level of infection in a region. A Chandler Index ** 500** indicates a significant public health problem. * **D. Load of infection in the community:** This is the primary definition of the index. It estimates the total intensity of the parasite reservoir within a specific population. **High-Yield Clinical Pearls for NEET-PG:** * **Formula:** Chandler Index = (Total number of eggs in all samples) / (Total number of samples). * **Hookworm & Anemia:** The primary morbidity is **Microcytic Hypochromic Anemia** due to chronic blood loss (Ancylostoma: 0.15–0.2 ml/day; Necator: 0.03 ml/day). * **Ground Itch:** The allergic reaction at the site of larval entry (L3 - Filariform larva). * **Drug of Choice:** Albendazole (400 mg single dose).

Question 1

Japanese B encephalitis virus is transmitted by which mosquito?

Accepted Answer

Culex tritaeniorhynchus

Answer

Aedes aegypti

Answer

Culex fatigans

Answer

Hard tick

Question 2

What is false about pertussis?

Accepted Answer

Maternal antibody provides protection in infants.

Answer

Fomites play a small role in the spread of disease.

Answer

It is commonly seen in infants.

Answer

Males and females are equally affected.

Question 3

What is the recommended duration for the use of long-lasting insecticidal nets?

Accepted Answer

3 years

Answer

6 months

Answer

1 year

Answer

10 years

Question 4

In an epidemic of hepatitis E, infection in which of the following groups carries a poor prognosis?

Accepted Answer

Pregnant women

Answer

Malnourished male

Answer

Anaemic male

Answer

Postmenopausal women

Question 5

Chandler index is used for the diagnosis of which condition?

Accepted Answer

Ancylostomiasis

Answer

Ascariasis

Answer

Dracunculiasis

Answer

Filariasis

Question 6

Which of the following genera includes the 'tiger mosquito'?

Accepted Answer

Aedes

Answer

Anopheles

Answer

Mansonia

Answer

Culex

Question 7

Which geographical region in India was identified as being suitable for mass DEC-medicated salt treatment for lymphatic filariasis due to its safety, low cost, and effectiveness?

Accepted Answer

Lakshadweep islands

Answer

Goa

Answer

Daman and Diu

Answer

Andaman and Nicobar islands

Question 8

What is the modified plan of operation for Malaria based on?

Accepted Answer

API (Annual Parasite Incidence)

Answer

ABER (Age-Based Expectation Rate)

Answer

Spleen rate

Answer

Infant parasite rate

Question 9

The definition of extensively drug-resistant TB includes resistance to all of the following drugs, EXCEPT:

Accepted Answer

Ethambutol

Answer

Rifampicin

Answer

Isoniazide

Answer

Amikacin

Question 10

Chandler index is an important tool in epidemiology. Which of the following is its least likely use?

Accepted Answer

Determining case severity and prognosis

Answer

Impact of control programme

Answer

Endemicity

Answer

Load of infection in the community

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?