Infectious Diseases Practice Questions

Q: A malarial survey is conducted in 50 villages having a population of one lakh. Out of 20,000 slides examined, 500 turned out to be malaria positive. What is the annual parasite incidence?

0.50%. ### Educational Explanation **Understanding Annual Parasite Incidence (API)** The Annual Parasite Incidence (API) is a crucial epidemiological index used under the National Vector Borne Disease Control Programme (NVBDCP) to measure the incidence of malaria in a community. It represents the number of confirmed malaria cases per 1,000 population per year. **Calculation:** The formula for API is: $$\text{API} = \frac{\text{Total number of positive slides in a year}}{\text{Total population}} \times 1000$$ Given in the question: * Total Population = 1,00,000 (One Lakh) * Total Positive Slides = 500 * (Note: The number of slides examined is used for the Annual Blood Examination Rate, not API). $$\text{API} = \frac{500}{1,00,000} \times 1000 = 5$$ An API of 5 per 1,000 population is equivalent to **0.5%** (since $5/1000 = 0.005$, and $0.005 \times 100 = 0.5\%$). Therefore, **Option C** is the correct answer. **Analysis of Incorrect Options:** * **Option A (20%):** This is mathematically incorrect and does not correlate with any standard malaria metric. * **Option B (5%):** This is a calculation error where the "per 1000" factor was likely confused with "per 100." * **Option D (0.40%):** This value is obtained if one incorrectly uses the number of slides examined (20,000) as the denominator instead of the total population. **High-Yield Clinical Pearls for NEET-PG:** * **API 10%**. * **Slide Positivity Rate (SPR):** (Total Positives / Total Slides Examined) × 100. In this case, SPR would be 2.5%. * **Slide Falciparum Rate (SFR):** (Total *P. falciparum* Positives / Total Slides Examined) × 100.

Q: Insecticide-treated bed nets (ITBNs) are typically treated with which class of insecticides?

Pyrethroids (e.g., Deltamethrin, Cyfluthrin). **Explanation:** **1. Why Pyrethroids are the Correct Choice:** Pyrethroids (e.g., **Deltamethrin, Cyfluthrin, Alpha-cypermethrin**) are the only class of insecticides currently recommended by the WHO for treating Long-Lasting Insecticidal Nets (LLINs). They are preferred because of their unique combination of **high efficacy** against mosquitoes, **rapid knockdown effect** (excito-repellent property), and **low mammalian toxicity**. They are stable enough to remain effective on the fabric even after multiple washes (usually up to 20 washes or 3 years). **2. Analysis of Incorrect Options:** * **B. Diethyltoluamide (DEET):** This is a chemical **repellent** applied to the skin or clothes to prevent bites; it does not kill insects and is not used for treating bed nets. * **C. Natural Pyrethrins:** While derived from the Chrysanthemum flower and insecticidal, they are highly **unstable** when exposed to light and heat (photo-labile), making them unsuitable for long-term use on bed nets. * **D. Organophosphates (e.g., Malathion):** These are primarily used for **Indoor Residual Spraying (IRS)** or space spraying (fogging). They are generally too toxic for the close, prolonged skin contact associated with sleeping under a bed net. **3. NEET-PG High-Yield Pearls:** * **LLIN vs. ITBN:** LLINs (Long-Lasting Insecticidal Nets) are the current standard; they are factory-treated and do not require re-treatment, unlike older ITBNs. * **The "Halo Effect":** Large-scale use of ITBNs provides community-wide protection by reducing the overall mosquito population, not just protecting the individual sleeper. * **Target:** ITBNs are a core strategy for **Malaria** and **Lymphatic Filariasis** control. * **Mechanism:** Pyrethroids work by prolonging the opening of sodium channels in the insect's nervous system, leading to paralysis and death.

Q: What is the most common cause of epidemic infective hepatitis?

Hepatitis E Virus (HEV). **Explanation:** The correct answer is **Hepatitis E Virus (HEV)**. In the context of public health and epidemiology, "epidemic" refers to a sudden increase in cases within a population. HEV is the most common cause of large-scale, water-borne epidemics of infective hepatitis in developing countries, including India. It is primarily transmitted via the **fecal-oral route**, often through contaminated drinking water. **Analysis of Options:** * **Hepatitis E (HEV):** It is the leading cause of both sporadic and epidemic viral hepatitis in India. It typically affects young adults and is notorious for causing high mortality (up to 20%) in **pregnant women** due to fulminant hepatic failure. * **Hepatitis A (HAV):** While also transmitted via the fecal-oral route, HAV is more commonly associated with **sporadic cases** and small clusters/outbreaks among children. In endemic areas, most children develop immunity early in life, making large-scale adult epidemics less common than HEV. * **Hepatitis B (HBV) & C (HCV):** These are transmitted via parenteral, sexual, or perinatal routes. They do not cause water-borne epidemics; instead, they are major causes of **chronic** hepatitis, cirrhosis, and hepatocellular carcinoma. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of acute viral hepatitis in India:** HEV (followed by HAV). * **Incubation Period:** HEV (2–8 weeks); HAV (2–6 weeks). * **Pregnancy Warning:** HEV in the 3rd trimester carries the highest risk of fulminant hepatitis. * **Zoonotic potential:** HEV Genotype 3 and 4 are associated with consumption of undercooked pork. * **Chronicity:** HEV generally does not cause chronic infection, except in immunocompromised individuals (e.g., organ transplant recipients).

Q: Which of the following is an anti-adult mosquito insecticide?

DDT. **Explanation:** The control of mosquitoes is categorized into measures targeting the aquatic stages (larvae/pupae) and those targeting the terrestrial stage (adults). **1. Why DDT is the Correct Answer:** **DDT (Dichlorodiphenyltrichloroethane)** is a classic **Adulticide**. It is a chlorinated hydrocarbon used primarily for **Indoor Residual Spraying (IRS)**. Its mechanism involves acting as a contact poison that disrupts the nervous system of adult mosquitoes when they rest on sprayed surfaces. Although resistance is widespread, it remains a hallmark example of an anti-adult measure in public health entomology. **2. Analysis of Incorrect Options:** * **Paris Green (Copper acetoarsenite):** This is a stomach poison used specifically as a **Larvicide**. It is emerald green in color and is effective against *Anopheles* larvae because they are surface feeders. * **Mineral Oil (e.g., Malariol):** These are **Larvicides** that act physically. When sprayed on water, they form a thin film that cuts off the air supply, suffocating the larvae and pupae. * **Fenthion:** This is an organophosphorus compound used as a potent **Larvicide**, particularly effective in polluted waters (like drains and septic tanks) against *Culex* mosquitoes. **3. High-Yield NEET-PG Pearls:** * **Adulticides:** Include Organochlorines (DDT), Organophosphates (Malathion), and Pyrethroids (Deltamethrin). * **Larvicides:** Include Mineral oils, Paris green, Synthetic insecticides (Abate/Temephos, Fenthion), and Biological agents (*Gambusia* fish, *Bacillus thuringiensis*). * **Space Sprays:** Used for rapid knockdown of adults during epidemics (e.g., Pyrethrum extract). * **Drug of Choice for Larviciding:** **Temephos (Abate)** is the preferred chemical for treating potable (drinking) water containers.

Q: Chemoprophylaxis is not required in which of the following conditions?

Typhoid. **Explanation:** **Chemoprophylaxis** refers to the administration of drugs to prevent the development of an infection or its progression to clinical disease. **Why Typhoid is the Correct Answer:** Chemoprophylaxis is **not recommended** for Typhoid fever (Enteric fever). Prevention relies primarily on food and water sanitation, personal hygiene, and **vaccination** (e.g., Vi polysaccharide, Ty21a, or Typhoid Conjugate Vaccine). Using antibiotics as prophylaxis for typhoid is ineffective, promotes antimicrobial resistance, and does not prevent the carrier state. **Analysis of Incorrect Options:** * **Meningococcal Meningitis:** Chemoprophylaxis is mandatory for close contacts of a confirmed case to eliminate nasopharyngeal carriage. The drug of choice (DOC) is **Rifampicin** (Ciprofloxacin or Ceftriaxone are alternatives). * **Bacterial Conjunctivitis:** Topical antibiotic drops (e.g., Erythromycin or Sulfacetamide) are used prophylactically, especially in newborns (**Ophthalmia Neonatorum**), to prevent infection from birth canal pathogens. * **Malaria:** Chemoprophylaxis is a standard protocol for travelers moving from non-endemic to endemic areas. Common drugs include **Chloroquine** (if sensitive), **Doxycycline**, or **Mefloquine**. **High-Yield Clinical Pearls for NEET-PG:** * **DOC for Chemoprophylaxis:** * **Cholera:** Doxycycline (Adults), Tetracycline (Children). * **Pertussis/Diphtheria:** Erythromycin. * **Leptospirosis:** Doxycycline (200mg weekly). * **Rheumatic Fever:** Benzathine Penicillin G (every 3 weeks). * **Plague:** Doxycycline or Tetracycline. * **Note:** Chemoprophylaxis is generally used for diseases with a short incubation period and high secondary attack rates among contacts.

Q: Which type of mosquito larvae lie horizontal on the water surface, resting parallel to it?

Anopheles. ### Explanation The correct answer is **Anopheles**. The orientation of mosquito larvae at the water surface is a classic morphological feature used in entomological identification. **1. Why Anopheles is correct:** Anopheles larvae lack a long respiratory siphon. Instead, they possess **palmate hairs** on their abdominal segments and a pair of small respiratory spiracles on the 8th abdominal segment. To breathe, they must lie **parallel (horizontal)** to the water surface to keep these spiracles in contact with the air. **2. Why the other options are incorrect:** * **Culex:** These larvae possess a long, narrow respiratory siphon. They hang **at an angle (obliquely)** to the water surface, with only the tip of the siphon touching the surface film. * **Aedes:** Similar to Culex, Aedes larvae have a short, stout respiratory siphon and hang **at an angle** (head down) from the surface. * **Mansonides:** These are unique because they do not come to the surface to breathe. Their specialized siphon **pierces the underwater roots/stems** of aquatic plants (like *Pistia*) to extract oxygen. **3. High-Yield Clinical Pearls for NEET-PG:** * **Adult Resting Posture:** Anopheles adults rest at an angle (45°) to the surface, while Culex and Aedes rest parallel to it (the opposite of their larval stages). * **Eggs:** Anopheles eggs are laid singly and have **lateral floats**. Culex eggs are laid in "rafts," and Aedes eggs are cigar-shaped and laid singly. * **Disease Association:** * *Anopheles:* Malaria. * *Culex:* Japanese Encephalitis, Bancroftian Filariasis. * *Aedes:* Dengue, Chikungunya, Zika, Yellow Fever. * *Mansonides:* Brugian Filariasis (Malayan Filariasis).

Q: Modified ZN Stain is used under which of the following programs?

NLEP. **Explanation:** The correct answer is **NLEP (National Leprosy Eradication Programme)**. **1. Why NLEP is correct:** Modified Ziehl-Neelsen (ZN) staining is the standard laboratory technique used to identify *Mycobacterium leprae*, the causative agent of Leprosy. Unlike *M. tuberculosis*, *M. leprae* is **less acid-fast**. Therefore, the concentration of the decolorizing agent (Sulphuric acid) is reduced from the standard 25% (used in TB) to **5%** (or even 1% for certain specimens) to prevent over-decolorization of the bacilli. This modification is essential for calculating the **Bacteriological Index (BI)** and **Morphological Index (MI)** in leprosy patients. **2. Why other options are incorrect:** * **RNTCP (now NTEP):** Uses the **Standard ZN Stain** (with 25% $H_2SO_4$) or Fluorescence microscopy for detecting *M. tuberculosis*. * **NVBDCP:** Focuses on vector-borne diseases like Malaria and Filariasis. Diagnosis typically involves peripheral blood smears (Leishman/Giemsa stain) or Rapid Diagnostic Tests (RDTs), not acid-fast staining. * **IMNCI:** This is a strategy for the integrated management of childhood illnesses (Pneumonia, Diarrhea, Measles, etc.) and relies on clinical algorithms rather than specific acid-fast staining techniques. **Clinical Pearls for NEET-PG:** * **Acid-fastness levels:** * *M. tuberculosis*: 25% $H_2SO_4$ * *M. leprae*: 5% $H_2SO_4$ * *Nocardia*: 1% $H_2SO_4$ * *Cryptosporidium/Isospora*: 0.25% $H_2SO_4$ * **Slit-skin smear:** The primary method for sample collection in NLEP; sites usually include earlobes and active skin lesions. * **NLEP Goal:** The current focus has shifted from "Eradication" to "Elimination" (defined as <1 case per 10,000 population).

Question 1

A malarial survey is conducted in 50 villages having a population of one lakh. Out of 20,000 slides examined, 500 turned out to be malaria positive. What is the annual parasite incidence?

Accepted Answer

0.50%

Answer

20%

Answer

5%

Answer

0.40%

Question 2

Insecticide-treated bed nets (ITBNs) are typically treated with which class of insecticides?

Accepted Answer

Pyrethroids (e.g., Deltamethrin, Cyfluthrin)

Answer

Diethyltoluamide (DEET)

Answer

Natural Pyrethrins

Answer

Organophosphates (e.g., Malathion)

Question 3

What is the most common cause of epidemic infective hepatitis?

Accepted Answer

Hepatitis E Virus (HEV)

Answer

Hepatitis A Virus (HAV)

Answer

Hepatitis B Virus (HBV)

Answer

Hepatitis C Virus (HCV)

Question 4

Which of the following is an anti-adult mosquito insecticide?

Accepted Answer

DDT

Answer

Paris green

Answer

Mineral oil

Answer

Fenthion

Question 5

Chemoprophylaxis is not required in which of the following conditions?

Accepted Answer

Typhoid

Answer

Meningococcal meningitis

Answer

Bacterial conjunctivitis

Answer

Malaria

Question 6

Which of the following statements are true about the epidemiology of leprosy?

Accepted Answer

Leprosy bacilli cannot survive outside the human body and the relapse rate is an indicator of the efficacy of the drug regimen.

Answer

Leprosy bacilli cannot survive outside the human body and the bacterial load is high in the tuberculoid variety.

Answer

The bacterial load is high in the tuberculoid variety, and insects can transmit the disease.

Answer

The bacterial load is high in the tuberculoid variety, and the relapse rate is an indicator of the efficacy of the drug regimen.

Question 7

Class II exposure in animal bites includes which of the following?

Accepted Answer

Scratches without oozing of blood

Answer

Bites from wild animals

Answer

Licks on a fresh wound

Answer

Scratch with oozing of blood

Question 8

Which of the following is NOT included in the syndromic approach to sexually transmitted diseases?

Accepted Answer

Dysuria in women

Answer

Genital ulcers

Answer

Urethral discharge in males

Answer

Vaginal discharge

Question 9

Which type of mosquito larvae lie horizontal on the water surface, resting parallel to it?

Accepted Answer

Anopheles

Answer

Aedes

Answer

Culex

Answer

Mansonides

Question 10

Modified ZN Stain is used under which of the following programs?

Accepted Answer

NLEP

Answer

RNTCP

Answer

NVBDCP

Answer

IMNCI

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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