Infectious Diseases Practice Questions

Q: Oral rehydration solution (ORS) contains how much potassium per liter?

20 mEq. **Explanation:** The WHO-recommended **Low Osmolarity ORS** is designed to optimize the co-transport of sodium and glucose while maintaining electrolyte balance during diarrheal diseases. Potassium is a critical component because significant amounts of intracellular potassium are lost in stool during diarrhea, which can lead to life-threatening hypokalemia and paralytic ileus. **Why 20 mEq is correct:** The standard formulation contains **1.5 grams of Potassium Chloride (KCl)** per liter. When dissociated, this provides exactly **20 mEq/L of Potassium ions**. This concentration is sufficient to replace ongoing losses without risking hyperkalemia in patients with transiently decreased renal perfusion. **Analysis of Incorrect Options:** * **30 mEq & 40 mEq:** These concentrations are too high for standard oral rehydration. While severe hypokalemia might require higher concentrations, these are typically managed via intravenous routes or supervised clinical settings to avoid cardiac arrhythmias. * **10 mEq:** This concentration is insufficient to compensate for the high potassium losses seen in secretory diarrheas like Cholera. **High-Yield Clinical Pearls for NEET-PG:** * **Composition of Low Osmolarity ORS (per liter):** * Sodium Chloride: 2.6 g (Na+: 75 mEq) * Glucose (Anhydrous): 13.5 g (Glucose: 75 mmol) * Potassium Chloride: 1.5 g (**K+: 20 mEq**) * Trisodium Citrate: 2.9 g (Citrate: 10 mEq) * **Total Osmolarity:** 245 mOsm/L (The previous "Standard" ORS was 311 mOsm/L). * **Role of Citrate:** It is added to correct metabolic acidosis and increases the shelf life of the ORS packet compared to bicarbonate. * **Zinc Supplementation:** Always remember that for children with diarrhea, Zinc (20 mg/day for 14 days) is given alongside ORS to reduce the duration and recurrence of episodes.

Q: What is the recommended prophylaxis for healthcare personnel working in a plague ward?

Vaccine. **Explanation:** The primary strategy for healthcare personnel (HCP) working in high-risk environments like a plague ward is active immunization. **1. Why Option A is Correct:** The **Killed Plague Vaccine** (formalin-killed *Yersinia pestis*) is recommended for individuals at high risk of exposure, including laboratory workers handling the bacteria and medical staff working in plague wards. While the vaccine does not provide 100% protection against primary pneumonic plague, it significantly reduces the severity of the disease and is the standard preventive measure for occupational exposure. **2. Why Other Options are Incorrect:** * **Options B & C (Tetracycline):** Tetracycline or Doxycycline is used for **chemoprophylaxis**, not routine prophylaxis. Chemoprophylaxis is strictly reserved for "close contacts" of a pneumonic plague case or those with a definite flea bite during an outbreak. It is administered for 7 days. Continuous use "throughout the duty period" is not a standard protocol due to the risk of side effects and resistance. * **Option D (Vaccine and Erythromycin):** Erythromycin is not the drug of choice for plague. Aminoglycosides (Streptomycin) are used for treatment, and Tetracyclines/Sulfonamides are used for prophylaxis. **High-Yield Pearls for NEET-PG:** * **Causative Agent:** *Yersinia pestis* (Gram-negative, safety-pin appearance/bipolar staining). * **Drug of Choice (Treatment):** Streptomycin is the gold standard; Gentamicin is an alternative. * **Chemoprophylaxis of Choice:** Tetracycline (or Doxycycline). * **Vaccine Type:** Killed vaccine (Haffkine's vaccine). It provides immunity for about 6 months and requires a booster. * **Quarantine:** The period for plague is **6 days**.

Q: Epidemics of typhus fever have been associated with war and famine for several centuries. What factor was most important in the control of such epidemics following the end of World War II?

Disinfestation by use of DDT. ### Explanation **Epidemic Typhus** is caused by *Rickettsia prowazekii* and is transmitted to humans by the **human body louse** (*Pediculus humanus corporis*). Historically, it has been a scourge during wars and famines due to overcrowding and lack of hygiene, which facilitate louse infestation. **Why Option D is Correct:** The most significant factor in controlling typhus epidemics post-WWII was the introduction of **DDT (Dichlorodiphenyltrichloroethane)**. DDT was used for mass **disinfestation** (delousing) of civilian and military populations. By applying DDT powder directly to clothing and bodies, the vector (the body louse) was eliminated, effectively breaking the chain of transmission. This was famously demonstrated in the 1843-44 Naples epidemic, where DDT halted the outbreak for the first time in history. **Why Other Options are Incorrect:** * **Option A:** *Anopheles* mosquitoes are vectors for Malaria, not Typhus. While DDT was also used for malaria control, it is irrelevant to typhus transmission. * **Option B & C:** While improved sanitation and food handling are vital for controlling enteric diseases (like Cholera or Typhoid), they do not directly target the body louse, which lives in the seams of clothing. **Clinical Pearls for NEET-PG:** * **Vector:** Human Body Louse (Note: Head lice and pubic lice are *not* significant vectors for typhus). * **Transmission:** Occurs via the **posterior station** (rubbing infected louse feces into the bite wound or mucous membranes), not the bite itself. * **Brill-Zinsser Disease:** A recrudescent (latent) form of epidemic typhus that occurs years after the primary attack. * **Drug of Choice:** Tetracyclines (Doxycycline) are the mainstay of treatment.

Q: Which mosquito species can fly the greatest distance?

Culex. **Explanation:** The flight range of mosquitoes is a critical factor in vector control and the planning of anti-larval operations. Among the common medically important vectors, **Culex** mosquitoes are known for their high dispersal capacity. **1. Why Culex is Correct:** Culex species (particularly *Culex quinquefasciatus*) are strong fliers. While their average daily flight is around 1–3 km, they are documented to fly distances of **up to 11 km** (and sometimes further depending on wind currents). This extensive range is why the "control zone" around human settlements for Culex must be wider than for other species. **2. Analysis of Incorrect Options:** * **Mansonia:** These mosquitoes generally have a limited flight range, usually staying within **1–2 km** of their breeding sites (aquatic plants like *Pistia*). * **Aedes:** Known as "day biters," Aedes aegypti is a very weak flier. It typically travels only **50–100 meters** and rarely exceeds 400 meters. This is why Aedes-borne diseases (Dengue/Zika) often show "cluster" distributions in specific households or streets. * **Anopheles:** Most Anopheles species have a flight range of **1.5 to 2 km**. While some can travel further if aided by wind, their standard effective flight range is significantly less than that of Culex. **3. NEET-PG High-Yield Pearls:** * **Flight Range Summary:** Aedes (Shortest: ~100m) < Mansonia (~1km) < Anopheles (~2km) < **Culex (Longest: Up to 11km).** * **Breeding Sites:** *Aedes* (Artificial containers), *Anopheles* (Clean standing water), *Culex* (Dirty/stagnant water/sewage), *Mansonia* (Water with floating vegetation). * **Resting Habit:** Culex is **exophilic** (rests outdoors) but **endophagic** (bites indoors), making it a persistent nuisance and a potent vector for Filariasis and Japanese Encephalitis.

Q: A patient is diagnosed with meningococcal meningitis after returning from abroad. What immediate chemoprophylaxis should be advised for the patient's close contacts?

Rifampicin 600 mg twice daily for 2 days. **Explanation:** **1. Why Option B is Correct:** Meningococcal meningitis, caused by *Neisseria meningitidis*, requires prompt chemoprophylaxis for close contacts to eliminate nasopharyngeal carriage and prevent secondary cases. The standard WHO and CDC recommended regimen for **Rifampicin** in adults is **600 mg twice daily (BD) for 2 days** (total of 4 doses). Rifampicin is the drug of choice because it achieves high concentrations in salivary secretions, effectively eradicating the carrier state. **2. Analysis of Incorrect Options:** * **Option A & D:** Rifampicin must be administered twice daily to maintain effective inhibitory concentrations against *N. meningitidis*. A once-daily regimen is insufficient for eradication and is more commonly associated with tuberculosis treatment. * **Option C:** The dosage of 300 mg is sub-therapeutic for adults (though it may be used for children based on weight, i.e., 10 mg/kg). Furthermore, the duration for meningococcal prophylaxis is strictly 2 days; a 3-day course is unnecessary and increases the risk of side effects. **3. High-Yield Clinical Pearls for NEET-PG:** * **Close Contacts:** Defined as household members, daycare center contacts, or anyone directly exposed to the patient's oral secretions (e.g., kissing, mouth-to-mouth resuscitation). * **Alternative Drugs:** If Rifampicin is contraindicated (e.g., pregnancy), the alternatives are **Ciprofloxacin (500 mg single dose)** or **Ceftriaxone (250 mg IM single dose)**. Ceftriaxone is the preferred choice for pregnant women. * **Timing:** Prophylaxis should ideally be administered within 24 hours of identifying the index case. * **Side Effect Note:** Advise patients that Rifampicin may turn urine, sweat, and tears orange-red; it also renders oral contraceptive pills less effective.

Q: Which test is done for tuberculosis screening?

Tuberculin test. **Explanation:** The correct answer is **C. Tuberculin test (Mantoux test)**. In epidemiology and community medicine, a **screening test** is used to identify asymptomatic individuals who may have a disease or infection within a large population. The Tuberculin Skin Test (TST) measures the delayed-type hypersensitivity reaction to Purified Protein Derivative (PPD). It is the standard tool for screening because it identifies "latent tuberculosis infection" (LTBI), even when no clinical disease is present. **Analysis of Incorrect Options:** * **A. Sputum microscopy:** This is a **diagnostic test** used to confirm active pulmonary tuberculosis in symptomatic patients (Presumptive TB). It is the primary tool for the National TB Elimination Program (NTEP) but is not used for screening the general asymptomatic population. * **B. Sputum culture:** This is the **"Gold Standard" for diagnosis**. It is highly specific and sensitive but takes 2–8 weeks for results, making it impractical for mass screening. * **C. Lymph node biopsy:** This is a diagnostic procedure used specifically for **Extrapulmonary TB** (Tubercular Lymphadenitis) to look for caseating granulomas. **High-Yield Clinical Pearls for NEET-PG:** * **Interpretation:** An induration of **≥10 mm** after 48–72 hours is generally considered positive in India. * **BCG Effect:** A prior BCG vaccination can cause a false-positive TST, though the reaction usually diminishes over time. * **Anergy:** False negatives can occur in immunocompromised states (HIV, malnutrition, miliary TB, or recent viral infections like Measles). * **IGRA:** Interferon-Gamma Release Assays (like QuantiFERON-TB Gold) are newer screening alternatives that do not cross-react with the BCG vaccine.

Q: Apart from dengue hemorrhagic fever, Aedes aegypti is a vector for the transmission of which disease?

Yellow fever. ### Explanation **Correct Answer: D. Yellow fever** **1. Why Yellow Fever is Correct:** *Aedes aegypti* is a highly efficient urban vector known for its "nervous biting" habit (biting multiple people to complete one blood meal). While it is the primary vector for **Dengue**, it is also the principal vector for **Yellow Fever**, **Chikungunya**, and **Zika virus**. In the context of Yellow Fever, *Aedes aegypti* facilitates the "Urban Cycle" of transmission between humans, whereas *Haemagogus* species are involved in the "Sylvatic (Jungle) Cycle." **2. Analysis of Incorrect Options:** * **A. Filaria:** In India, the primary vector for Lymphatic Filariasis (*Wuchereria bancrofti*) is the **Culex quinquefasciatus** mosquito, which breeds in dirty, stagnant water. * **B. Japanese Encephalitis (JE):** This is transmitted primarily by **Culex tritaeniorhynchus** and *Culex vishnui* group mosquitoes. They typically breed in irrigated rice fields. * **C. Kyasanur Forest Disease (KFD):** This is a viral hemorrhagic fever transmitted by **Hard Ticks** (*Haemaphysalis spinigera*), not mosquitoes. It is endemic to specific regions in Karnataka, India. **3. NEET-PG High-Yield Pearls:** * **Aedes aegypti Characteristics:** Known as the "Tiger Mosquito" (due to white stripes), it is a **daytime biter**, breeds in **artificial collections of clean water** (coolers, tires, flower pots), and has a flight range of usually less than 100 meters. * **Yellow Fever in India:** Although the vector (*Aedes aegypti*) is abundant in India, Yellow Fever is **not present** in India. This is a classic "vulnerable but not receptive" scenario. * **The "Aedes" Rule:** Remember the triad: **Dengue, Chikungunya, and Zika** are all transmitted by *Aedes*.

Q: Which fish is used for larval control of malaria?

Gambusia. **Explanation:** **Biological control** is a key component of Integrated Vector Management (IVM) for malaria. The use of larvivorous fish is an eco-friendly method to reduce the population of *Anopheles* mosquitoes by targeting them at the aquatic stage. **1. Why Gambusia is Correct:** *Gambusia affinis* (commonly known as the **Mosquitofish**) is the most widely used fish for this purpose. It is highly effective because it is hardy, prolific, and a single fish can consume about **100–300 larvae per day**. It prefers shallow waters where mosquito larvae typically breed. Another commonly used fish in India is *Poecilia reticulata* (Guppy). **2. Analysis of Incorrect Options:** * **Amphethis & Globerulis:** These are not recognized genera of larvivorous fish. They are distractor terms often used in exams to mimic biological nomenclature. * **None:** This is incorrect as *Gambusia* is the gold standard for biological larval control globally. **3. High-Yield Clinical Pearls for NEET-PG:** * **Preferred Species:** *Gambusia affinis* (Mosquitofish) and *Poecilia reticulata* (Guppy). * **Mechanism:** These fish are surface feeders, which aligns with the position of *Anopheles* larvae (which float parallel to the water surface). * **Environmental Impact:** While effective, *Gambusia* is considered an invasive species in some regions; therefore, it should ideally be introduced only in man-made containers, tanks, or wells rather than natural wetlands. * **Other Biological Agents:** *Bacillus thuringiensis israelensis* (Bti) and *Bacillus sphaericus* are bacterial agents used as biolarvicides. * **Chemical Alternative:** Temephos (Abate) is the organophosphate of choice for chemical larviciding in potable water.

Question 1

Oral rehydration solution (ORS) contains how much potassium per liter?

Accepted Answer

20 mEq

Answer

30 mEq

Answer

40 mEq

Answer

10 mEq

Question 2

What is the recommended prophylaxis for healthcare personnel working in a plague ward?

Accepted Answer

Vaccine

Answer

Tetracycline throughout the duty period

Answer

A course of tetracycline

Answer

Vaccine and Erythromycin

Question 3

Epidemics of typhus fever have been associated with war and famine for several centuries. What factor was most important in the control of such epidemics following the end of World War II?

Accepted Answer

Disinfestation by use of DDT

Answer

Eradication of Anopheles mosquitoes

Answer

Improved sanitation practices

Answer

Improved methods for handling food supplies

Question 4

Which of the following is the most appropriate treatment for a patient with tuberculosis in whom Mycobacterium is resistant to both isoniazid and rifampicin?

Accepted Answer

6 drugs for 6 months and 4 drugs for 18 months

Answer

6 drugs for 4 months and 4 drugs for 12 months

Answer

6 drugs for 6 months and 4 drugs for 4 months

Answer

5 drugs for 2 months, 4 drugs for one month, and 3 drugs for 5 months

Question 5

Which mosquito species can fly the greatest distance?

Accepted Answer

Culex

Answer

Mansonia

Answer

Aedes

Answer

Anopheles

Question 6

A patient is diagnosed with meningococcal meningitis after returning from abroad. What immediate chemoprophylaxis should be advised for the patient's close contacts?

Accepted Answer

Rifampicin 600 mg twice daily for 2 days

Answer

Rifampicin 600 mg once daily for 3 days

Answer

Rifampicin 300 mg twice daily for 3 days

Answer

Rifampicin 600 mg once daily for 2 days

Question 7

Which test is done for tuberculosis screening?

Accepted Answer

Tuberculin test

Answer

Sputum microscopy

Answer

Sputum culture

Answer

Lymph node biopsy

Question 8

Apart from dengue hemorrhagic fever, Aedes aegypti is a vector for the transmission of which disease?

Accepted Answer

Yellow fever

Answer

Filaria

Answer

Japanese encephalitis

Answer

Kyasanur forest disease

Question 9

All of the following are true about malaria, except?

Accepted Answer

Infant parasite rate is a poor indicator of malaria occurrence in a community.

Answer

The vector for transmission is the Anopheles mosquito.

Answer

Newborns are resistant to P. falciparum infection.

Answer

Anopheles culicifacies is common in rural areas.

Question 10

Which fish is used for larval control of malaria?

Accepted Answer

Gambusia

Answer

Amphethis

Answer

Globerulis

Answer

None

Infectious Diseases — MCQs

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