Infectious Diseases Practice Questions

Q: Which of the following diseases worldwide is transmitted by Culex, Anopheles, and Aedes mosquitoes acting as vectors?

Filariasis. **Explanation:** The correct answer is **Filariasis** (specifically Lymphatic Filariasis caused by *Wuchereria bancrofti* and *Brugia malayi*). Unlike many other vector-borne diseases that are specific to one genus of mosquito, Lymphatic Filariasis is unique because it can be transmitted by a wide range of mosquito vectors across different geographical regions. * **Culex:** The primary vector for *W. bancrofti* in urban and semi-urban areas (specifically *Culex quinquefasciatus*). * **Anopheles:** A significant vector in rural areas, particularly in Africa and parts of Asia. * **Aedes:** Acts as a vector for the sub-periodic form of filariasis in certain Pacific Islands. **Analysis of Incorrect Options:** * **Malaria:** Transmitted exclusively by the female **Anopheles** mosquito. * **Dengue:** Transmitted primarily by **Aedes aegypti** and secondarily by *Aedes albopictus*. * **Yellow Fever:** Transmitted by **Aedes aegypti** (urban cycle) and *Haemagogus* species (sylvatic cycle). **NEET-PG High-Yield Pearls:** 1. **Culex quinquefasciatus** is known as the "nuisance mosquito" and breeds in dirty, stagnant water (drains, septic tanks). 2. **Drug of Choice:** Diethylcarbamazine (DEC) is the mainstay of treatment; however, it is contraindicated in patients with Onchocerciasis or heavy Loa loa infection. 3. **National Health Program:** India aims for the **Elimination of Lymphatic Filariasis (ELF)** using Mass Drug Administration (MDA) of DEC + Albendazole (and recently, the IDA regimen: Ivermectin + DEC + Albendazole). 4. **Diagnosis:** The best time to collect a blood sample for *W. bancrofti* is between **10 PM and 2 AM** due to nocturnal periodicity.

Q: What is the amount of Sodium chloride (NaCl) in reduced osmolarity Oral Rehydration Solution (ORS)?

2.6 gm/litre. The correct answer is **2.6 gm/litre**. ### **Explanation** The World Health Organization (WHO) and UNICEF transitioned from standard ORS to **Reduced Osmolarity ORS** to minimize the risk of hypernatremia and reduce stool output and vomiting. The total osmolarity was reduced from 311 mOsm/L to **245 mOsm/L**. In this formulation, the concentration of **Sodium Chloride (NaCl)** is specifically set at **2.6 gm/litre** to provide 75 mmol/L of Sodium and 65 mmol/L of Chloride. ### **Analysis of Options** * **A. 2.6 gm/litre (Correct):** This is the precise amount of NaCl in the current WHO-recommended reduced osmolarity ORS. * **B. 2.9 gm/litre (Incorrect):** This is the amount of **Trisodium Citrate** present in the ORS sachet. * **C. 3.5 gm/litre (Incorrect):** This was the amount of NaCl used in the **Old (Standard) WHO ORS** formulation. It is no longer recommended for routine diarrhea management. * **D. 2.7 gm/litre (Incorrect):** This is a distractor value; however, the total amount of **Anhydrous Glucose** in the sachet is 13.5 gm/litre. ### **High-Yield Facts for NEET-PG** To master ORS questions, remember the **"2.6, 2.9, 1.5, 13.5"** rule for a 1-liter packet: 1. **Sodium Chloride:** 2.6 gm 2. **Trisodium Citrate:** 2.9 gm (Replaced Sodium Bicarbonate to increase shelf life) 3. **Potassium Chloride:** 1.5 gm 4. **Glucose (Anhydrous):** 13.5 gm 5. **Total Weight:** 20.5 gm 6. **Total Osmolarity:** 245 mOsm/L (Glucose and Sodium are both 75 mmol/L, maintaining a 1:1 molar ratio for optimal absorption via SGLT-1 receptors).

Q: Which of the following is NOT true about varicella?

All stages of the rash are seen at one time. **Explanation** The correct answer is **A**, as the statement "All stages of the rash are seen at one time" is actually a **characteristic feature** of Varicella (Chickenpox), not a false statement. In the context of NEET-PG, this question is often framed to test the distinction between Varicella and Variola (Smallpox). 1. **Why Option A is the correct choice (as a true statement):** Varicella rash appears in successive crops. Because new lesions appear while older ones are healing, the rash is **pleomorphic**, meaning macules, papules, vesicles ("dewdrops on a rose petal"), and crusts are all visible simultaneously in the same anatomical area. In contrast, Smallpox lesions are monomorphic (all at the same stage). 2. **Option B (Humans are the only reservoir):** This is a true statement. There is no animal reservoir for Varicella-Zoster Virus (VZV), which makes it a candidate for theoretical eradication. 3. **Option C (Age group):** This is true. In temperate climates and pre-vaccination eras, chickenpox is primarily a childhood disease, most common in the 5–10 year age group. 4. **Option D (Infectivity):** This is true. The period of communicability extends from **48 hours before** the rash appears until **all vesicles have crusted over** (usually 5 days after onset). **High-Yield Clinical Pearls for NEET-PG:** * **Centripetal Distribution:** Varicella rash is denser on the trunk and sparse on the extremities (opposite of Smallpox). * **Tzanck Smear:** Shows **Multinucleated Giant Cells** with Cowdry Type A intranuclear inclusions. * **Secondary Infection:** The most common complication in children is secondary bacterial skin infection (Staph/Strep). * **Congenital Varicella Syndrome:** Highest risk if the mother is infected during the first 20 weeks of pregnancy (presents with limb hypoplasia and cicatricial skin scarring).

Q: What is the recommended glucose to sodium ratio in Oral Rehydration Solution (ORS)?

1:1. The correct answer is **A. 1:1**. ### **Explanation of the Correct Answer** The effectiveness of Oral Rehydration Solution (ORS) is based on the **SGLT-1 (Sodium-Glucose Linked Transporter)** mechanism in the small intestine. For every molecule of glucose absorbed, one molecule of sodium is actively transported across the intestinal epithelium. This creates an osmotic gradient that pulls water into the bloodstream. According to the WHO-UNICEF standard for **Low Osmolarity ORS**, the concentration of Glucose is **75 mmol/L** and Sodium is **75 mmol/L**. Therefore, the molar ratio is exactly **1:1**. This specific ratio ensures maximum water absorption while preventing osmotic diarrhea that could occur if glucose levels were too high. ### **Analysis of Incorrect Options** * **B (3:1):** This ratio would imply an excess of glucose. While some older formulations experimented with different ratios, a 3:1 ratio is not physiologically optimal for the SGLT-1 transporter. * **C (7:1) & D (10:1):** These ratios represent a significant excess of glucose. High concentrations of glucose in the intestinal lumen increase the intraluminal osmolarity, which can actually draw water *out* of the body and into the gut, worsening dehydration (osmotic diarrhea). ### **High-Yield Clinical Pearls for NEET-PG** * **Composition of Low Osmolarity ORS (per Liter):** * Sodium Chloride: 2.6 g * Glucose (Anhydrous): 13.5 g * Potassium Chloride: 1.5 g * Trisodium Citrate: 2.9 g * **Total Osmolarity:** 245 mOsm/L (The most frequently asked value). * **Zinc Supplementation:** Always given alongside ORS in pediatric diarrhea (20 mg/day for 10–14 days; 10 mg/day for infants <6 months) to reduce the duration and recurrence of episodes. * **Trisodium Citrate** is preferred over Bicarbonate because it increases the shelf life of ORS packets.

Q: Which of the following is NOT true about Dracunculiasis?

Man is the intermediate host.. **Explanation:** **Dracunculiasis (Guinea Worm Disease)** is a parasitic infection caused by *Dracunculus medinensis*. To answer this question, one must understand the specific life cycle of the parasite. 1. **Why Option B is the Correct Answer (The "NOT True" statement):** In the life cycle of *Dracunculus medinensis*, **Man is the Definitive Host**, not the intermediate host. The definitive host is where the parasite reaches maturity and undergoes sexual reproduction. The **Intermediate Host is the Cyclops** (water flea), which ingests the larvae. Humans become infected by drinking stagnant water containing these infected Cyclops. 2. **Analysis of Other Options:** * **Option A (No animal reservoir):** This is true. Dracunculiasis is one of the few parasitic diseases where humans are the only reservoir, making it a prime candidate for global eradication. * **Option C (India has eradicated the disease):** This is true. India was declared Dracunculiasis-free by the WHO in **February 2000**. The last case in India was reported in July 1996 in Rajasthan. * **Option D (Limited to tropical/subtropical regions):** This is true. The disease is historically associated with poor, rural communities in tropical regions (primarily Africa) where people rely on open stagnant water sources. **High-Yield Clinical Pearls for NEET-PG:** * **Agent:** *Dracunculus medinensis* (The "Fiery Serpent"). * **Vector/Intermediate Host:** Cyclops (specifically *Cyclops quadricornis*). * **Incubation Period:** Approximately 1 year (8–14 months). * **Diagnosis:** Visualizing the adult worm emerging from a skin ulcer (usually on the lower limbs). * **Prevention:** The most effective strategy is **straining water** through a fine mesh cloth or treating water with **Temephos (Abate)** to kill Cyclops. There is no vaccine or specific medicine to treat the disease.

Q: In a plague epidemic, all of the following measures are implemented for control, EXCEPT:

Vaccination of susceptible individuals. **Explanation:** The control of a plague epidemic focuses on rapid containment and interrupting transmission. **Vaccination (Option B)** is the correct answer because it is **not recommended** for controlling an ongoing outbreak. The plague vaccine (killed or live attenuated) provides short-term immunity, takes time to develop an immune response, and does not protect against primary pneumonic plague. Therefore, it is reserved for high-risk laboratory personnel or field workers, rather than the general population during an epidemic. **Analysis of other options:** * **Isolation of contacts (Option A):** This is a critical measure, especially for pneumonic plague. Contacts must be isolated and monitored for 6 days (the maximum incubation period) to prevent secondary transmission. * **Surveillance (Option C):** Active surveillance of both human cases and rodent populations (flea index monitoring) is essential to track the spread and effectiveness of control measures. * **Chemoprophylaxis (Option D):** Tetracycline or Doxycycline is the drug of choice for the chemoprophylaxis of contacts. It provides immediate protection, unlike vaccines. **NEET-PG High-Yield Pearls:** * **Drug of Choice (Treatment):** Streptomycin is the traditional DOC; Gentamicin is a preferred alternative. * **Chemoprophylaxis:** Doxycycline (preferred) or Tetracycline. * **Flea Index:** A "General Flea Index" of **>1** indicates a high risk of a plague outbreak. * **Quarantine:** The international quarantine period for Plague is **6 days**. * **Pneumonic Plague:** This is the most infectious form, transmitted via droplets, and is 100% fatal if untreated within 24 hours.

Q: As per the Revised National Tuberculosis Control Programme (RNTCP) Category-1 guidelines, what is the drug regimen?

Four drugs for two months and two drugs for four months. **Explanation:** Under the **Revised National Tuberculosis Control Programme (RNTCP)**, now integrated into the **National TB Elimination Programme (NTEP)**, Category-1 is indicated for new cases of tuberculosis (both pulmonary and extra-pulmonary). **1. Why Option A is correct:** The standard regimen for Category-1 consists of two phases: * **Intensive Phase (IP):** 2 months of four drugs—**HRZE** (Isoniazid, Rifampicin, Pyrazinamide, and Ethambutol). * **Continuation Phase (CP):** 4 months of two drugs—**HR** (Isoniazid and Rifampicin). The goal of the IP is to rapidly kill the bacterial load, while the CP eliminates semi-dormant bacilli to prevent relapse. **2. Why other options are incorrect:** * **Option B:** Three drugs are insufficient for the Intensive Phase in new cases; Ethambutol is essential to prevent resistance. * **Option C:** Category-1 is strictly for **New Cases**. Retreatment cases (Relapse, Treatment after default, Failure) were previously classified under Category-2 (which has since been phased out in favor of Universal Drug Susceptibility Testing). * **Option D:** While the program has transitioned to a **Daily Regimen**, the question specifically asks for the "drug regimen" (composition and duration). In the context of traditional RNTCP MCQ patterns, Option A defines the core pharmacological structure of Category-1. **High-Yield Clinical Pearls for NEET-PG:** * **Dosage:** Fixed-Dose Combinations (FDCs) are used based on weight bands. * **Pyridoxine (Vitamin B6):** Always co-administered (10–25 mg/day) to prevent Isoniazid-induced peripheral neuropathy. * **Extension:** There is no longer an extension of the Intensive Phase if the sputum is positive at 2 months; instead, the patient proceeds to CP and undergoes DST. * **CP Duration:** In cases of TB Meningitis or Bone/Joint TB, the CP may be extended to 7–10 months.

Q: Which form of plague is the most contagious?

Pneumonic plague. **Explanation:** **Pneumonic plague** is the most contagious and lethal form of the disease. Unlike other forms, it is the only one that can be transmitted directly from **person-to-person via respiratory droplets** (aerosol transmission). It has a very short incubation period (1–3 days) and, if untreated, a case fatality rate approaching 100%. Its ability to spread rapidly through coughing makes it a significant public health threat and a potential bioterrorism agent. **Analysis of Incorrect Options:** * **Bubonic Plague:** The most common clinical form, characterized by painful lymph node swelling (buboes). It is transmitted via the **bite of an infected rat flea** (*Xenopsylla cheopis*). It is not directly contagious between humans unless there is contact with suppurating buboes. * **Septicemic Plague:** Occurs when the bacteria (*Yersinia pestis*) multiply in the bloodstream. It can be a primary infection or a complication of bubonic plague. While highly fatal, it is not contagious through respiratory routes. * **Wild Plague:** Also known as Sylvatic plague, this refers to the infection circulating in wild rodent populations (e.g., marmots, ground squirrels) rather than a specific clinical manifestation in humans. **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agent:** *Yersinia pestis* (a Gram-negative coccobacillus showing characteristic **bipolar "safety-pin" staining**). * **Vector:** The Oriental rat flea (*Xenopsylla cheopis*) is the most efficient vector. * **Drug of Choice:** **Streptomycin** is the traditional DOC; Gentamicin and Doxycycline are effective alternatives. * **Chemoprophylaxis:** Doxycycline or Tetracycline is recommended for close contacts of pneumonic plague patients. * **Indicator:** A "Rat Fall" (sudden death of rats) is a precursor to a human bubonic plague outbreak.

Q: What is the recommended duration of prophylactic antibiotic treatment for pertussis contacts?

10 days. The correct answer is **10 days**. ### **Explanation** Pertussis (Whooping Cough), caused by *Bordetella pertussis*, is highly contagious. Post-exposure antimicrobial prophylaxis (PEP) is recommended for all household and close contacts, regardless of their age or vaccination status, to prevent secondary transmission. The drug of choice for both treatment and prophylaxis is **Azithromycin** (5 days) or **Clarithromycin** (7 days). However, according to the standard guidelines (CDC and Park’s Textbook of Preventive and Social Medicine), the traditional gold standard for chemoprophylaxis using **Erythromycin** is a duration of **10 to 14 days**. In the context of competitive exams like NEET-PG, **10 days** is the established standard duration cited for effective eradication of the bacteria from the nasopharynx of contacts. ### **Analysis of Incorrect Options** * **Options A (11 days) & C (12 days):** These are arbitrary numbers and do not align with any standardized clinical protocols for pertussis management. * **Option B (14 days):** While 14 days was previously the standard for Erythromycin, modern guidelines have shifted towards shorter, equally effective courses (7–10 days) to improve compliance and reduce gastrointestinal side effects. In a "single best answer" format, 10 days is currently preferred. ### **High-Yield Clinical Pearls for NEET-PG** * **Agent of Choice:** Macrolides (Azithromycin is preferred due to better compliance and fewer side effects). * **Infectivity Period:** Most infectious during the **catarrhal stage** and the first 3 weeks of the paroxysmal stage [1]. * **Chemoprophylaxis:** Should ideally be started within **21 days** of onset of cough in the index case. * **Vaccine:** The "aP" (acellular) component is preferred over "wP" (whole-cell) in older children and adults to minimize the risk of neurological complications.

Question 1

Which of the following diseases worldwide is transmitted by Culex, Anopheles, and Aedes mosquitoes acting as vectors?

Accepted Answer

Filariasis

Answer

Malaria

Answer

Dengue

Answer

Yellow Fever

Question 2

What is the amount of Sodium chloride (NaCl) in reduced osmolarity Oral Rehydration Solution (ORS)?

Accepted Answer

2.6 gm/litre

Answer

2.9 gm/litre

Answer

3.5 gm/litre

Answer

2.7 gm/litre

Question 3

Which of the following is NOT true about varicella?

Accepted Answer

All stages of the rash are seen at one time

Answer

Humans are the only known reservoir

Answer

Children between 5-10 years old are most commonly affected

Answer

Patients are infectious 48 hours before the onset of the vesicular rash and until all vesicles are crusted

Question 4

What is the most effective way to prevent vertical transmission of HIV?

Accepted Answer

Antiretroviral therapy (ART)

Answer

Nevirapine

Answer

Zidovudine

Answer

Elective cesarean section

Question 5

What is the recommended glucose to sodium ratio in Oral Rehydration Solution (ORS)?

Accepted Answer

1:1

Answer

3:1

Answer

7:1

Answer

10:1

Question 6

Which of the following is NOT true about Dracunculiasis?

Accepted Answer

Man is the intermediate host.

Answer

There is no animal reservoir.

Answer

India has eradicated the disease.

Answer

It is limited to tropical and subtropical regions.

Question 7

In a plague epidemic, all of the following measures are implemented for control, EXCEPT:

Accepted Answer

Vaccination of susceptible individuals

Answer

Isolation of contacts

Answer

Surveillance

Answer

Chemoprophylaxis with tetracycline

Question 8

As per the Revised National Tuberculosis Control Programme (RNTCP) Category-1 guidelines, what is the drug regimen?

Accepted Answer

Four drugs for two months and two drugs for four months

Answer

Three drugs for two months and two drugs for four months

Answer

Includes retreatment cases

Answer

The regimen is given daily

Question 9

Which form of plague is the most contagious?

Accepted Answer

Pneumonic plague

Answer

Bubonic plague

Answer

Septicemic plague

Answer

Wild plague

Question 10

What is the recommended duration of prophylactic antibiotic treatment for pertussis contacts?

Accepted Answer

10 days

Answer

11 days

Answer

14 days

Answer

12 days

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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