Infectious Diseases Practice Questions

Q: Why has multidrug-resistant tuberculosis (MDR-TB) re-emerged as a major public health concern?

Poor treatment compliance and inadequate drug regimens. ***Poor treatment compliance and inadequate drug regimens*** - **MDR-TB** (resistance to at least **isoniazid** and **rifampicin**) primarily arises when patients do not complete their long-term treatment or take medications irregularly. - These factors exert **selective pressure** on the bacterial population, allowing resistant mutants to survive and multiply, leading to the failure of standard **DOTS** protocols. *Increased virulence of Mycobacterium tuberculosis strains* - While some strains like the **Beijing lineage** are highly transmissible, emergence of resistance is driven by **selective drug pressure** rather than inherent virulence. - Increased virulence affects the severity of the disease but does not fundamentally cause the **genetic mutations** associated with drug resistance. *Changes in bacterial cell wall structure* - While the **mycolic acid** layer provides a natural barrier to many antibiotics, **acquired resistance** in TB is typically due to specific **chromosomal mutations** (e.g., *katG* or *rpoB* genes). - Structural changes are generally a result of the resistance mechanism (like thickened cell walls in some variants) rather than the primary cause of the **MDR-TB epidemic**. *Development of new bacterial toxins* - *Mycobacterium tuberculosis* does not traditionally rely on **classic exotoxins** or **endotoxins** to cause disease or resist medications. - Resistance is a metabolic and genetic adaptation to **bactericidal agents**, and toxin production plays no known role in the resistance to **isoniazid** or **rifampicin**.

Q: Soil may act as a reservoir for all EXCEPT-

Brucellosis. **Explanation:** The core concept here is distinguishing between **soil-borne pathogens** (geophilic organisms) and **zoonotic pathogens** that require a living animal host for survival and transmission. **Why Brucellosis is the Correct Answer:** Brucellosis is a classic zoonotic disease caused by *Brucella* species. Its primary reservoir is **infected animals** (cattle, goats, sheep, and pigs). Humans are infected through direct contact with animal secretions, consumption of unpasteurized dairy, or inhalation of aerosols in slaughterhouses. While the bacteria can survive briefly in the environment, soil is **not** a natural reservoir or a significant source of infection for Brucellosis. **Analysis of Incorrect Options:** * **Tetanus (*Clostridium tetani*):** The soil is the primary reservoir. The organism exists as highly resistant spores that can survive in soil and manure for years. * **Anthrax (*Bacillus anthracis*):** Known as a "soil-borne" infection. Spores can remain viable in soil for decades, especially in "anthrax districts" with specific alkaline and calcium-rich soil conditions. * **Coccidioidomycosis:** This is a fungal infection caused by *Coccidioides immitis*. The fungus grows as a mold in the **soil** of arid regions (e.g., Southwestern US). **NEET-PG High-Yield Pearls:** * **Soil-transmitted Helminths (STH):** Remember the "ASH" mnemonic—*Ascaris*, *Strongyloides*, and Hookworm (*Ancylostoma*). * **Bacterial Soil Reservoirs:** *Clostridium tetani*, *Clostridium botulinum*, and *Bacillus anthracis*. * **Fungal Soil Reservoirs:** *Histoplasma capsulatum*, *Cryptococcus neoformans*, and *Coccidioides*. * **Brucellosis Key Fact:** It is often called "Undulant Fever" or "Malta Fever." The most common route of transmission in India is the consumption of raw milk.

Q: Which indicator best represents the vector's burden in human malaria transmission?

Man biting rate. ### Explanation **Correct Option: A. Man biting rate** The **Man Biting Rate (MBR)** is the most direct measure of the **vector's burden** in the transmission cycle. It is defined as the average number of bites received by a single person from a specific vector species per unit of time (usually per day). Since malaria transmission depends entirely on the frequency of contact between the mosquito and the human host, MBR is the primary indicator of the intensity of the vector's activity and the risk of exposure. **Analysis of Incorrect Options:** * **B. Inoculation Rate:** This measures the number of **infective** bites per person per unit of time. While it indicates transmission risk, it is a subset of the biting rate (only counting mosquitoes with sporozoites) and represents the "force of infection" rather than the overall vector burden. * **C. Slide Positive Rate (SPR):** This is a **parasitological indicator** derived from human surveillance (number of positive slides per 100 slides examined). It reflects the prevalence of the disease in the human population, not the vector's burden. * **D. Human Blood Index (HBI):** This measures the proportion of blood meals taken by a mosquito population from human hosts versus animals. It indicates the **host preference (anthropophily)** of the vector but does not quantify the frequency of biting or the total burden. **High-Yield Pearls for NEET-PG:** * **Annual Parasite Incidence (API):** The most sensitive index for measuring malaria burden in a community (used for planning under NCVBDC). * **Annual Blood Examination Rate (ABER):** Measures the efficiency of the surveillance system (Target: >10%). * **Entomological Inoculation Rate (EIR):** The best measure of the "force of infection" in an area (MBR × Sporozoite Rate). * **Infant Parasite Rate:** The best indicator of **recent/ongoing transmission** in a locality.

Q: Microfilaria in Culex depicts what kind of biological transmission?

Cyclo-developmental. ### Explanation In biological transmission, the disease agent undergoes essential changes or multiplication within the vector. The classification depends on whether the agent **develops** (changes stages) or **propagates** (increases in number). **1. Why Cyclo-developmental is Correct:** In the case of Microfilaria (*Wuchereria bancrofti*) within the *Culex* mosquito, the parasite undergoes essential developmental changes (from L1 to L3 larvae) but **does not multiply** in number. One microfilaria ingested results in only one infective larva. This combination of "cycle" (development) without "propagation" (multiplication) is termed **Cyclo-developmental transmission**. **2. Analysis of Incorrect Options:** * **Cyclo-propagative:** The agent undergoes both developmental changes and multiplication. * *Example:* *Plasmodium* (Malaria) in *Anopheles* mosquitoes. * **Propagative:** The agent only multiplies in number but undergoes no developmental change. * *Example:* Plague bacilli in rat fleas or Yellow fever virus in *Aedes* mosquitoes. * **Developmental:** This is a component of cyclo-developmental transmission but is not the standard epidemiological term used to describe this specific vector-parasite relationship. **3. NEET-PG High-Yield Clinical Pearls:** * **Extrinsic Incubation Period:** The time required for the parasite to complete its development inside the mosquito (approx. 10–14 days for Filaria). * **Mechanical Transmission:** Unlike biological transmission, the agent undergoes no change/multiplication (e.g., Housefly carrying Typhoid bacilli on its legs). * **Transovarial Transmission:** When the pathogen is passed from the adult vector to its offspring (e.g., Tick-borne relapsing fever, Scrub typhus). * **Key Mnemonic:** * *Malaria* = **CP** (Cyclo-Propagative) * *Filaria* = **CD** (Cyclo-Developmental) * *Plague/Viruses* = **P** (Propagative)

Q: What is true about citrate in Oral Rehydration Solution (ORS)?

It increases shelf life.. **Explanation:** The transition from the old WHO-ORS formula (containing Sodium Bicarbonate) to the current **Reduced Osmolarity ORS** involved replacing bicarbonate with **Trisodium Citrate**. **1. Why Option C is Correct:** The primary reason for using Trisodium Citrate is its **chemical stability**. Sodium bicarbonate is unstable in tropical climates; it reacts with glucose in the packet, causing the powder to turn brown (Maillard reaction) and decompose. Citrate is far more stable, which significantly **increases the shelf life** of ORS packets, making it ideal for storage and transport in developing countries. Clinically, citrate also promotes the intestinal absorption of sodium and water and is metabolized into bicarbonate to correct metabolic acidosis. **2. Why Other Options are Incorrect:** * **A. Cheaper:** Citrate is actually more expensive than bicarbonate, but the cost is offset by the reduced wastage due to longer shelf life. * **B. Nutritious:** ORS is a rehydration therapy, not a nutritional supplement. While it prevents dehydration-related complications, citrate itself provides no significant nutritional value. * **D. Tastier:** Citrate does not significantly improve the palatability of the solution. **High-Yield Clinical Pearls for NEET-PG:** * **Standard WHO ORS Osmolarity:** 245 mOsm/L (Reduced Osmolarity) [1]. * **Glucose Concentration:** 75 mmol/L (essential for the SGLT-1 transport mechanism) [1]. * **Sodium Concentration:** 75 mmol/L [1]. * **Potassium Concentration:** 20 mmol/L (to replace losses in stool) [1]. * **Citrate Concentration:** 10 mmol/L (equivalent to 30 mmol/L of bicarbonate) [1]. * **Zinc Supplementation:** Always given alongside ORS (20 mg/day for 14 days; 10 mg for infants <6 months) to reduce the duration and recurrence of diarrhea.

Q: Which of the following is considered a newly emerged infectious agent?

Nipah virus. **Explanation:** The concept of **Emerging Infectious Diseases (EIDs)** refers to infections that have newly appeared in a population or have existed but are rapidly increasing in incidence or geographic range. **Why Nipah Virus is Correct:** Nipah virus (NiV) is a classic example of a **newly emerged zoonotic virus**. It was first identified in **1998-1999** during an outbreak among pig farmers in Malaysia. It is a highly fatal Henipavirus (Paramyxoviridae family) transmitted by *Pteropus* bats (fruit bats). In the context of recent Indian outbreaks (notably in Kerala), it is categorized as a significant emerging public health threat. **Analysis of Incorrect Options:** * **Pneumocystis jirovecii (B):** This is a well-known opportunistic fungus. While it gained prominence during the 1980s HIV/AIDS epidemic, it is considered a "re-emerging" or established pathogen rather than a "newly emerged" agent in the current chronological context. * **Coronavirus (C):** This is a broad family of viruses (including those causing the common cold) that have been known for decades. The family itself is not "newly emerged." * **SARS (D):** While SARS-CoV was an emerging virus in 2003, it has been effectively eradicated from human circulation since 2004. In competitive exams, when compared to Nipah (which continues to cause periodic new outbreaks), Nipah is the preferred answer for "newly emerged." **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir:** Fruit bats (*Pteropus* species). * **Transmission:** Direct contact with infected pigs, contaminated date palm sap, or human-to-human via respiratory droplets. * **Clinical Presentation:** Severe encephalitis (high mortality rate ~40-75%) and atypical pneumonia. * **Diagnosis:** RT-PCR (Gold standard) and ELISA for IgM/IgG. * **Other Emerging Viruses to remember:** Zika, Ebola, MERS-CoV, and Crimean-Congo Hemorrhagic Fever (CCHF).

Q: Which species of Anopheles mosquito is responsible for urban malaria?

Anopheles stephensi. **Explanation:** The correct answer is **Anopheles stephensi**. In India, malaria transmission is highly dependent on the specific ecological niches of various *Anopheles* species. **1. Why Anopheles stephensi is correct:** *Anopheles stephensi* is the primary vector for **urban malaria**. It has uniquely adapted to city environments by breeding in artificial water containers such as overhead tanks, cisterns, fountain pools, and construction sites. Its ability to thrive in man-made containers allows it to maintain malaria transmission in densely populated urban centers. **2. Analysis of Incorrect Options:** * **Anopheles culicifacies:** This is the most important vector for **rural malaria** in India. It breeds in clean ground water like irrigation channels, pools, and borrow pits. It is responsible for nearly 60-70% of total malaria cases in the country. * **Anopheles sundaicus:** This species is restricted to **coastal areas**, particularly the Andaman and Nicobar Islands. It is known for breeding in brackish (salty) water. * **Anopheles fluviatilis:** This is a major vector in **hilly and forested areas** (especially in central and eastern India). It prefers breeding in slow-moving streams and is highly anthropophilic (prefers human blood). **High-Yield Clinical Pearls for NEET-PG:** * **Vector of Malaria in North-East India:** *Anopheles minimus* and *Anopheles dirus*. * **National Framework for Malaria Elimination (NFME):** India aims to eliminate malaria by **2030**. * **Urban Malaria Scheme (UMS):** Launched in 1971, it focuses on source reduction and anti-larval measures (like using *Gambusia* fish) specifically targeting *A. stephensi*. * **Bionomics:** Remember, *A. stephensi* is "Urban," while *A. culicifacies* is "Rural."

Q: Which of the following conditions does not typically require chemoprophylaxis?

Chickenpox. **Explanation:** The core concept of **chemoprophylaxis** involves the administration of specific drugs (including antibiotics and antivirals) to prevent the development of an infection in an exposed or high-risk individual. **Why Chickenpox (Option B) is the correct answer:** Chickenpox (Varicella-Zoster Virus) is primarily managed through **immunoprophylaxis** rather than chemoprophylaxis. Prevention post-exposure relies on the **Varicella vaccine** (within 3–5 days of exposure) or **Varicella-Zoster Immunoglobulin (VZIG)** for immunocompromised individuals. Antiviral drugs like Acyclovir are used for treatment or "pre-emptive therapy" in high-risk cases, but they are not routinely administered as standard chemoprophylaxis for the general population. **Analysis of Incorrect Options:** * **Typhoid (Option A):** While vaccination is the primary prevention, chemoprophylaxis (e.g., Ciprofloxacin or Azithromycin) may be indicated in specific outbreak settings or for household contacts in certain epidemiological contexts. * **Influenza (Option C):** Antiviral chemoprophylaxis with **Oseltamivir** (Tamiflu) or Zanamivir is a standard recommendation for high-risk individuals (e.g., nursing home residents) during an outbreak or post-exposure. * **Cholera (Option D):** Mass chemoprophylaxis is not recommended, but **selective chemoprophylaxis** (using Doxycycline or Tetracycline) is indicated for close household contacts to limit secondary transmission. **High-Yield NEET-PG Pearls:** * **Cholera:** Drug of choice for chemoprophylaxis is **Doxycycline** (single dose). * **Meningococcal Meningitis:** Drug of choice is **Rifampicin** (Ciprofloxacin or Ceftriaxone are alternatives). * **Leptospirosis:** Chemoprophylaxis for high-risk exposure is **Doxycycline** (200 mg weekly). * **Plague:** Chemoprophylaxis is done using **Tetracycline** or Doxycycline. * **Pertussis:** Erythromycin is used for household contacts.

Q: What is the drug of choice for chemoprophylaxis in contacts of a patient with pneumonic plague?

Tetracycline. **Explanation:** **Plague** is a zoonotic infection caused by *Yersinia pestis*. The pneumonic form is highly contagious and carries a high mortality rate, necessitating immediate chemoprophylaxis for close contacts (those within 2 meters of a patient). **1. Why Tetracycline is Correct:** **Tetracycline** (or Doxycycline) is the gold-standard drug of choice for chemoprophylaxis against plague. It is highly effective in preventing the progression of the disease in exposed individuals. The standard regimen is Tetracycline (500 mg four times daily) or Doxycycline (100 mg twice daily) for **7 days**. **2. Why Other Options are Incorrect:** * **Penicillin (A):** *Yersinia pestis* is naturally resistant to penicillins; they have no role in the treatment or prophylaxis of plague. * **Rifampicin (B):** This is primarily used for prophylaxis in Meningococcal meningitis and Leprosy, not for plague. * **Erythromycin (C):** While it has some activity against certain Gram-negative bacteria, it is significantly less effective than tetracyclines for *Y. pestis* and is not a recommended prophylactic agent. **3. High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for Treatment:** **Streptomycin** is the traditional DOC for treating bubonic and pneumonic plague. Gentamicin is a common alternative. * **Alternative Prophylaxis:** In children under 8 years or pregnant women (where tetracyclines are contraindicated), **Sulfadiazine** or **Trimethoprim-Sulfamethoxazole** can be used. * **Vector:** The primary vector is the **Rat Flea (*Xenopsylla cheopis*)**. * **Quarantine:** The international quarantine period for Plague is **6 days**.

Question 1

A state reports increased incidence of scrub typhus with unusual antibiotic resistance patterns. Molecular analysis reveals genetic recombination between different Orientia tsutsugamushi strains. Considering One Health approach, which integrated strategy would be most effective for long-term control?

Accepted Answer

Environmental modification, rodent control, public education, and surveillance strengthening

Answer

Development of new antibiotics for resistant strains as sole measure

Answer

Mass chemoprophylaxis with doxycycline during outbreak season only

Answer

Isolation of all suspected cases in specialized centers

Question 2

Why has multidrug-resistant tuberculosis (MDR-TB) re-emerged as a major public health concern?

Accepted Answer

Poor treatment compliance and inadequate drug regimens

Answer

Increased virulence of Mycobacterium tuberculosis strains

Answer

Changes in bacterial cell wall structure

Answer

Development of new bacterial toxins

Question 3

Soil may act as a reservoir for all EXCEPT-

Accepted Answer

Brucellosis

Answer

Tetanus

Answer

Anthrax

Answer

Coccidioidomycosis

Question 4

Which indicator best represents the vector's burden in human malaria transmission?

Accepted Answer

Man biting rate

Answer

Inoculation rate

Answer

Slide positive rate

Answer

Human blood index

Question 5

Microfilaria in Culex depicts what kind of biological transmission?

Accepted Answer

Cyclo-developmental

Answer

Cyclo-propagative

Answer

Developmental

Answer

Propagative

Question 6

What is true about citrate in Oral Rehydration Solution (ORS)?

Accepted Answer

It increases shelf life.

Answer

It is cheaper.

Answer

It is nutritious.

Answer

It is tastier.

Question 7

Which of the following is considered a newly emerged infectious agent?

Accepted Answer

Nipah virus

Answer

Pneumocystis jirovecii

Answer

Coronavirus

Answer

SARS

Question 8

Which species of Anopheles mosquito is responsible for urban malaria?

Accepted Answer

Anopheles stephensi

Answer

Anopheles culicifacies

Answer

Anopheles sundaicus

Answer

Anopheles fluviatilis

Question 9

Which of the following conditions does not typically require chemoprophylaxis?

Accepted Answer

Chickenpox

Answer

Typhoid

Answer

Influenza

Answer

Cholera

Question 10

What is the drug of choice for chemoprophylaxis in contacts of a patient with pneumonic plague?

Accepted Answer

Tetracycline

Answer

Penicillin

Answer

Rifampicin

Answer

Erythromycin

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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