Infectious Diseases Practice Questions

Q: Aedes aegypti transmits which of the following?

Yellow fever. **Explanation:** The correct answer is **Yellow fever**. *Aedes aegypti* is a highly efficient vector for several viral diseases, primarily because it is anthropophilic (prefers human blood) and breeds in stagnant water around human dwellings. **1. Why Yellow Fever is Correct:** Yellow fever is caused by a Flavivirus and is transmitted to humans by the bite of infected *Aedes aegypti* mosquitoes (urban cycle) or *Haemagogus* mosquitoes (sylvatic/jungle cycle). *Aedes* mosquitoes are known for being "day-biters" and are characterized by white markings on their legs (lyre-shaped). **2. Analysis of Incorrect Options:** * **Japanese Encephalitis (JE):** Transmitted by **Culex** mosquitoes (primarily *Culex tritaeniorhynchus*). These mosquitoes breed in rice fields and irrigation canals. * **Kyasanur Forest Disease (KFD):** This is a tick-borne viral hemorrhagic fever. The principal vector is the hard tick, **Haemaphysalis spinigera**. * **Filaria:** Lymphatic filariasis in India is primarily transmitted by **Culex quinquefasciatus**. While *Aedes* can transmit certain types of filariasis (like *Brugia*), *Culex* is the classic vector associated with *Wuchereria bancrofti*. **3. NEET-PG High-Yield Pearls:** * **Diseases transmitted by *Aedes aegypti*:** Remember the mnemonic **"DYD"** — **D**engue, **Y**ellow Fever, **D**engue Hemorrhagic Fever, **Chikungunya**, and **Zika** virus. * **Control Measure:** The most effective way to control *Aedes* is "Source Reduction" (eliminating stagnant water). * **Yellow Fever Vaccine:** The **17D vaccine** is a live attenuated vaccine providing immunity for life (as per revised WHO guidelines), though international travel certificates are valid for 10 years to life.

Q: Which of the following is not a control measure for diphtheria?

Treatment of carriers with antitoxin. **Explanation:** The correct answer is **B. Treatment of carriers with antitoxin**. In Diphtheria management, **Diphtheria Antitoxin (ADS)** is used only for the treatment of **clinical cases** to neutralize the circulating toxin. It has no role in the treatment of carriers because carriers harbor the organism (*Corynebacterium diphtheriae*) but do not produce the toxin in a way that causes systemic illness. Therefore, giving antitoxin to a carrier is physiologically unnecessary and carries a risk of hypersensitivity. Carriers are managed solely with a 10-day course of oral **Erythromycin** (or Penicillin) to eliminate the focus of infection. **Analysis of other options:** * **A. Treatment of cases with erythromycin:** This is a standard control measure. While antitoxin is the priority for cases, antibiotics are essential to stop further toxin production and prevent the spread of the bacilli to others. * **C. Isolation of cases:** Diphtheria is highly contagious. Isolation (for at least 14 days or until two consecutive nose/throat swabs are negative) is a fundamental public health measure to limit the reservoir of infection. * **D. Regular immunization:** This is the most effective long-term control measure. Maintaining high herd immunity through the primary series (Pentavalent/DPT) and boosters is the cornerstone of preventing outbreaks. **High-Yield NEET-PG Pearls:** * **Schick Test:** Used to distinguish between susceptible individuals and those immune to diphtheria. * **Carrier Treatment:** Erythromycin is the drug of choice for carriers (10 days). * **Contact Management:** Close contacts should receive a prophylactic dose of Erythromycin and a booster dose of the vaccine. * **Incubation Period:** Usually 2–5 days. * **Virulence Test:** Elek's gel precipitation test is used to detect toxigenicity.

Q: Genito-ulcerative (non-herpetic) diseases are coded under which color in the Standard Treatment Guidelines (STG) kits?

White. ### Explanation The National AIDS Control Organization (NACO) in India utilizes a **Syndromic Management** approach for Sexually Transmitted Infections (STIs). This method uses color-coded kits to provide immediate, standardized treatment based on clinical presentation rather than waiting for laboratory confirmation. **1. Why White is Correct:** The **White Kit** is specifically designed for **Genital Ulcerative Disease (Non-Herpetic)**. It is used when a patient presents with a non-vesicular ulcer [1]. * **Contents:** Injection Benzathine Penicillin (2.4 million units) and Tablet Azithromycin (1g). **2. Analysis of Incorrect Options:** * **Grey (Option A):** Used for **Urethral Discharge, Cervical Discharge, and Anorectal Discharge**. It contains Azithromycin (1g) and Cefixime (400mg). * **Blue (Option B):** Used for **Vaginal Discharge** (Bacterial Vaginosis and Trichomoniasis). It contains Metronidazole (2g) and Secnidazole (2g) or Clindamycin. * **Red (Option D):** Used for **Genital Ulcerative Disease (Herpetic)**. It contains Acyclovir (400mg) to treat Herpes Simplex Virus (HSV-2) [1]. **3. Clinical Pearls for NEET-PG:** * **Green Kit:** Used for **Vaginal Discharge** (specifically Candidiasis). Contains Fluconazole (150mg) [1]. * **Yellow Kit:** Used for **Lower Abdominal Pain** (Pelvic Inflammatory Disease). * **Black Kit:** Used for **Inguinal Bubo**. Contains Azithromycin and Doxycycline. * **High-Yield Tip:** If a genital ulcer is painful and soft, think **Chancroid** (*H. ducreyi*); if painless and hard, think **Syphilis** (*T. pallidum*). Both are covered by the **White Kit**.

Q: What is the recommended dose of chloroquine for children aged 4-8 years?

300 mg. **Explanation:** The treatment of uncomplicated malaria with Chloroquine follows a standardized weight-based or age-based regimen. For pediatric patients, the total dose is **25 mg/kg** of chloroquine base spread over three days (10 mg/kg on Day 1 & 2, and 5 mg/kg on Day 3). **Why 300 mg is correct:** In the context of age-based dosing (often used in public health programs like NVBDCP), children are categorized into specific brackets. For the **4–8 years** age group, the recommended dose is **300 mg** (base). This typically corresponds to 2 tablets of 150 mg chloroquine base. **Analysis of Incorrect Options:** * **150 mg (Option B):** This is the dose for children aged **1–4 years**. It is also the standard strength of one "base" tablet. * **450 mg (Option C):** This dose is reserved for children aged **9–14 years** (3 tablets). * **600 mg (Option D):** This is the standard adult loading dose (4 tablets) for a 60 kg adult on Day 1 of treatment. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Inhibits heme polymerase (biocrystallization), leading to the accumulation of toxic heme in the parasite food vacuole. * **Drug of Choice:** Still the DOC for sensitive *P. falciparum* and all *P. vivax* (except in resistant pockets). It is also the DOC for malaria in **pregnancy**. * **Adverse Effects:** Pruritus (common in dark-skinned individuals), bull’s eye retinopathy (chronic use), and QTc prolongation. * **Resistance:** Mediated by the **pfcrt** gene (Chloroquine Resistance Transporter), which pumps the drug out of the parasite's food vacuole.

Q: Soil acts as a source as well as a reservoir for which of the following diseases?

Tetanus. **Explanation:** The correct answer is **Tetanus**. In epidemiology, a **reservoir** is the natural habitat where an infectious agent lives, grows, and multiplies, while a **source** is the object or person from which the agent passes to the host. For **Tetanus**, the causative organism *Clostridium tetani* exists in the soil as highly resilient spores. The soil acts as a **reservoir** because the bacteria can persist there for years. It also acts as the **source** of infection when these spores enter the human body through a contaminated wound or injury. **Analysis of Incorrect Options:** * **A. Rabies:** The reservoir is primarily animals (dogs, bats, monkeys). Soil plays no role in its transmission. * **C. Typhoid:** The reservoir is exclusively human (cases or carriers). While soil can be contaminated by feces, the primary source is contaminated food or water. * **D. Measles:** This is a strictly human disease. The reservoir and source are infected human cases; the virus cannot survive in the environment/soil. **NEET-PG Clinical Pearls:** * **Soil-transmitted pathogens:** Other examples where soil acts as a reservoir include *Anthrax*, *Gas gangrene*, and various *Soil-Transmitted Helminths* (STH) like Hookworm. * **Tetanus Spores:** They are resistant to boiling and common disinfectants; autoclaving at 121°C for 20 minutes is required for sterilization. * **Epidemiological Fact:** Tetanus is one of the few infectious diseases that is **non-communicable** (it does not spread from person to person).

Q: Which of the following should be injected in and around the wound in a class III rabies bite?

Anti-rabies serum. **Explanation:** The management of a Category III rabies bite (single or multiple transdermal bites, scratches, or contamination of mucous membranes with saliva) requires immediate local wound treatment, active immunization (vaccine), and passive immunization. **1. Why Anti-rabies Serum (RIG) is correct:** The primary goal in Category III bites is to neutralize the virus at the site of entry before it can invade the peripheral nerves. **Rabies Immunoglobulin (RIG)** or Anti-rabies serum provides immediate, pre-formed antibodies. According to WHO and National guidelines, as much of the calculated dose of RIG as anatomically feasible must be **infiltrated in and around the wound(s)**. This creates a "protective barrier" of antibodies at the exact site of viral inoculation. **2. Why other options are incorrect:** * **Tetanus toxoid:** While tetanus prophylaxis is part of wound management, it is administered intramuscularly (usually in the deltoid), not infiltrated into the bite wound. * **Antibiotic solution:** Routine infiltration of antibiotics into a bite wound is not recommended. Systemic antibiotics may be prescribed orally if the wound appears infected or is deep, but they do not prevent rabies. **Clinical Pearls for NEET-PG:** * **Dosage:** Human RIG (HRIG) is 20 IU/kg; Equine RIG (ERIG) is 40 IU/kg. * **Site:** If any serum remains after infiltration, it should be injected IM at a site distant from the vaccine injection site. * **Timing:** RIG should be administered as soon as possible (Day 0). It is not recommended beyond 7 days after the first dose of the vaccine, as the body begins producing its own antibodies by then. * **Wound Suturing:** Should be avoided. If necessary, it must be done only after infiltrating RIG and delayed by a few hours.

Q: Measles is infective for how many days before the onset of rash?

4 days. ### Explanation **Correct Option: B (4 days)** The period of communicability for Measles (Rubeola) is defined as **4 days before to 5 days after** the appearance of the rash. This period coincides with the peak of viral shedding from the respiratory tract. The infectivity is highest during the **prodromal stage** (pre-eruptive phase), characterized by the "3 Cs" (Cough, Coryza, Conjunctivitis) and Koplik spots, even before the characteristic maculopapular rash appears. **Analysis of Incorrect Options:** * **Option A (10 days):** This is too long. While the incubation period of Measles is approximately 10–14 days, the patient is not infectious during the early incubation phase. * **Option C (1 day):** This underestimates the window of transmission. Viral shedding begins significantly earlier than 24 hours before the rash. * **Option D (Same day):** This is clinically dangerous to assume. Measles is most contagious *before* the rash appears; by the time the rash is visible, the patient has already been infectious for several days. **High-Yield Clinical Pearls for NEET-PG:** * **Secondary Attack Rate (SAR):** Measles has one of the highest SARs (>90%) among susceptible household contacts. * **Koplik Spots:** These are pathognomonic and appear 1–2 days before the rash on the buccal mucosa opposite the lower second molars. * **Isolation:** A child with measles should be isolated for at least 4 days after the rash appears to prevent transmission. * **Vaccination:** The Measles vaccine is a live attenuated vaccine (Edmonston-Zagreb strain in India) usually given at 9 months and 16–24 months. * **Vitamin A:** Supplementation is recommended for all children with acute measles to prevent complications like blindness and pneumonia.

Q: Amphixenosis is best described as:

An infection caused by Trypanosoma cruzi. **Explanation:** **Understanding the Concept:** Zoonoses are classified based on the direction of transmission between hosts. **Amphixenosis** refers to an infection that is maintained in nature by both humans and lower vertebrate animals, where the transmission can occur in either direction (Humans ↔ Animals). **Why Option D is Correct:** * **Trypanosoma cruzi (Chagas Disease):** This is a classic example of amphixenosis. It circulates among a wide range of wild and domestic animals (reservoirs) and humans, with the Triatomine bug acting as the vector. The infection cycle is equally sustainable in both human and animal populations. **Analysis of Incorrect Options:** * **Option A & C (Enterobius vermicularis & Ascaris lumbricoides):** These are **Anthroponoses**. These infections are restricted to humans; they do not have an animal reservoir and are transmitted from human to human. * **Option B (Bacillus anthracis):** This is an **Anthropozoonosis**. This term refers to infections that are primarily maintained in animals and are transmitted from animals to humans (Animals → Humans). Humans are usually "dead-end" hosts. **High-Yield Clinical Pearls for NEET-PG:** * **Zooanthroponosis:** Infections transmitted from humans to animals (e.g., Human Tuberculosis to cattle). * **Cyclozoonosis:** Requires more than one vertebrate host species to complete the life cycle (e.g., *Taenia saginata*, *Echinococcus granulosus*). * **Metazoonosis:** Transmitted to humans via an invertebrate vector (e.g., Plague, Arboviruses). * **Saprozoonosis:** Requires a non-animal environmental reservoir like soil or water (e.g., Histoplasmosis, Larva migrans).

Question 1

Aedes aegypti transmits which of the following?

Accepted Answer

Yellow fever

Answer

Japanese Encephalitis (JE)

Answer

Kyasanur Forest Disease (KFD)

Answer

Filaria

Question 2

Which of the following is not a control measure for diphtheria?

Accepted Answer

Treatment of carriers with antitoxin

Answer

Treatment of cases with erythromycin

Answer

Isolation of cases

Answer

Regular immunization of under-fives

Question 3

Genito-ulcerative (non-herpetic) diseases are coded under which color in the Standard Treatment Guidelines (STG) kits?

Accepted Answer

White

Answer

Grey

Answer

Blue

Answer

Red

Question 4

Which of the following is NOT transmitted by the rat flea?

Accepted Answer

Salmonellosis

Answer

Plague

Answer

Hymenolopsis

Answer

Endemic typhus

Question 5

What is the recommended dose of chloroquine for children aged 4-8 years?

Accepted Answer

300 mg

Answer

150 mg

Answer

450 mg

Answer

600 mg

Question 6

Soil acts as a source as well as a reservoir for which of the following diseases?

Accepted Answer

Tetanus

Answer

Rabies

Answer

Typhoid

Answer

Measles

Question 7

Which of the following should be injected in and around the wound in a class III rabies bite?

Accepted Answer

Anti-rabies serum

Answer

Tetanus toxoid

Answer

Antibiotic solution

Answer

None of the above

Question 8

Measles is infective for how many days before the onset of rash?

Accepted Answer

4 days

Answer

10 days

Answer

1 day

Answer

On the same day

Question 9

Which of the following is NOT helpful for the elimination of Filariasis?

Accepted Answer

Larvae are deposited on the skin surface where they cannot survive.

Answer

Microfilariae do not multiply in vectors.

Answer

Microfilariae multiply in humans.

Answer

None of the above.

Question 10

Amphixenosis is best described as:

Accepted Answer

An infection caused by Trypanosoma cruzi

Answer

An infection caused by Enterobius vermicularis

Answer

An infection caused by Bacillus anthracis (Anthrax)

Answer

An infection caused by Ascaris lumbricoides

Infectious Diseases — MCQs

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