Infectious Diseases Practice Questions

Q: What is the primary reservoir of Clostridium tetani?

Soil. **Explanation:** **Clostridium tetani** is an anaerobic, Gram-positive, spore-forming bacillus. The primary reservoir for this organism is the **soil**, particularly soil enriched with manure. The spores are highly resilient and can survive for years in the environment, resisting heat and common disinfectants. * **Why Soil is Correct:** *C. tetani* spores are ubiquitous in the environment. They are commonly found in the intestines of herbivorous animals (like horses and cattle) and are excreted in feces, leading to heavy contamination of the soil. When these spores enter a human body through a contaminated wound, the anaerobic environment triggers germination into vegetative forms that produce the potent neurotoxin, **tetanospasmin**. * **Why other options are incorrect:** * **Humans:** While *C. tetani* can occasionally be found in the human transient flora (intestines), humans are considered accidental hosts, not the primary reservoir. * **Water:** While spores can contaminate water, it is not the natural habitat or primary source of infection. * **Hospital waste:** While a potential source of various nosocomial infections, it is not the primary ecological niche for tetanus spores. **High-Yield Clinical Pearls for NEET-PG:** * **Mode of Transmission:** Contamination of wounds (lacerations, animal bites, or umbilical stumps in neonates) with soil or dust containing spores. * **Toxin:** Tetanospasmin acts by blocking the release of inhibitory neurotransmitters (**GABA and Glycine**) at the motor nerve endings, leading to spastic paralysis. * **Clinical Sign:** The first sign is often **Trismus** (lockjaw) due to masseter muscle spasm, followed by **Risus Sardonicus** (characteristic grin) and **Opisthotonus** (arch-like body posture). * **Prevention:** Tetanus is a non-communicable disease; herd immunity does not apply. Individual protection via active immunization (Tetanus Toxoid) is the only way to prevent the disease.

Q: All of the following methods are antilarval measures except?

Malathion. **Explanation:** The core of this question lies in distinguishing between **anti-larval measures** (targeting the aquatic stage of the mosquito) and **anti-adult measures** (targeting the flying stage). **Why Malathion is the correct answer:** Malathion is an organophosphorus compound primarily used as an **adulticide**. In public health programs, it is used for **Residual Insecticide Spraying (RIS)** or as **Ultra-Low Volume (ULV)** fogging during outbreaks (e.g., Dengue or Malaria). It targets the adult mosquito, not the larvae; hence, it is not an anti-larval measure. **Analysis of Incorrect Options:** * **Intermittent Irrigation (Environmental Control):** This is a source reduction technique. By drying out paddy fields for 1–2 days a week, the larval cycle is disrupted, preventing them from maturing into adults. * **Paris Green (Chemical Control):** Copper acetoarsenite (Paris Green) is a stomach poison specifically used as a larvicide. When dusted on water surfaces, surface-feeding larvae (like *Anopheles*) ingest it and die. * **Gambusia affinis (Biological Control):** Known as the "Mosquito fish," it is a biological agent that predates on mosquito larvae. A single fish can consume 100–300 larvae per day. **High-Yield NEET-PG Pearls:** 1. **Abate (Temephos):** The most common chemical larvicide used for potable (drinking) water. 2. **Biological Agents:** Apart from *Gambusia*, *Poecilia reticulata* (Guppy fish) and *Bacillus thuringiensis israelensis* (Bti) are high-yield anti-larval agents. 3. **Space Sprays:** Pyrethrum is the drug of choice for "knock-down" effect in indoor spaces, while Malathion is used for large-scale outdoor fogging.

Q: What is the recommended drug for intermittent preventive therapy during pregnancy in malaria?

Sulfadoxine-pyrimethamine. **Explanation:** **Sulfadoxine-Pyrimethamine (SP)** is the drug of choice for **Intermittent Preventive Therapy in pregnancy (IPTp)**. According to WHO and National Guidelines, IPTp-SP is administered to all pregnant women in malaria-endemic areas starting from the second trimester. It works by inhibiting folic acid synthesis in the parasite, providing a "post-treatment prophylaxis" effect due to its long half-life. It reduces the risk of maternal anemia, low birth weight, and neonatal mortality. **Analysis of Options:** * **Proguanil (A):** While safe in pregnancy, it has a very short half-life and requires daily dosing, making it unsuitable for "intermittent" therapy. * **Pyrimethamine-dapsone (B):** Also known as Maloprim, this combination is associated with a risk of neonatal hemolysis and methemoglobinemia; it is not the standard for IPTp. * **Quinine (D):** This is a rapidly acting schizonticide used for the **treatment** of severe malaria or chloroquine-resistant malaria in the first trimester. It is never used for prophylaxis or intermittent therapy due to its short half-life and high toxicity (Cinchonism). **High-Yield NEET-PG Pearls:** * **Timing:** IPTp-SP should be started in the **second trimester** (after quickening). It should NOT be given in the first trimester due to the theoretical risk of teratogenicity (folate antagonism). * **Dosing:** At least 3 doses of SP are recommended, each at least one month apart. * **Contraindication:** SP is contraindicated in women with G6PD deficiency or known sulfonamide allergy. * **Folic Acid Interaction:** High doses of folic acid (≥5 mg) can interfere with SP efficacy; standard prenatal doses (0.4 mg) are safe.

Q: Blanket or mass treatment is indicated in all of the following conditions EXCEPT:

Dengue fever. **Explanation:** The concept of **Mass Treatment** (or Blanket Treatment) involves treating every individual in a defined community, regardless of whether they show symptoms, to eliminate the reservoir of infection. This strategy is typically employed for diseases that are highly contagious, have a high prevalence, or lack an effective vaccine. **Why Dengue Fever is the correct answer:** Dengue is a viral disease transmitted by the *Aedes aegypti* mosquito. There is **no specific antiviral treatment** for Dengue; management is purely supportive (fluid resuscitation and monitoring). Furthermore, treating an asymptomatic human does not prevent the spread, as the primary control strategy relies on **vector control** (source reduction and insecticides) rather than mass chemotherapy. **Analysis of Incorrect Options:** * **Trachoma:** Mass antibiotic distribution (Azithromycin) is a core component of the WHO **SAFE** strategy when the prevalence of active trachoma in children is >5%. * **Malaria:** Mass Drug Administration (MDA) is indicated in specific scenarios, such as during epidemics, in complex emergencies, or for the elimination of *P. falciparum* in isolated areas to rapidly reduce the parasite reservoir. * **Yaws:** Under the **Morgues Strategy**, mass treatment with a single dose of Azithromycin is the standard protocol for eradication in endemic communities. **High-Yield Clinical Pearls for NEET-PG:** * **Mass Treatment vs. Selective Treatment:** Mass treatment is for the whole community; selective treatment targets only those with positive diagnostic tests. * **Other diseases requiring Mass Treatment:** Lymphatic Filariasis (DEC + Albendazole), Onchocerciasis (Ivermectin), and Schistosomiasis (Praziquantel). * **Total Mass Treatment (TMT):** In Yaws, if the prevalence is >5%, the entire community is treated. If <5%, "Juvenile Mass Treatment" (treating all children <15 years) is performed.

Q: What is true about Japanese encephalitis?

Caused by Group A arbovirus. Japanese Encephalitis (JE) is a major public health concern in Southeast Asia and a high-yield topic for NEET-PG. **Explanation of the Correct Answer:** * **Option B (Caused by Group A arbovirus):** This is the **incorrect** statement among the options, making it the "correct" choice for this specific question format (assuming the question asks for the *false* statement). Japanese Encephalitis virus belongs to the **Flaviviridae** family, which are classified as **Group B Arboviruses**. Group A arboviruses (Alphaviruses) include viruses like Chikungunya and Eastern Equine Encephalitis. **Analysis of Other Options (True Statements):** * **Option A (Transmitted by Culex mosquito):** This is **true**. The primary vector is *Culex tritaeniorhynchus*, which breeds in stagnant water like rice fields. * **Option C (Pig is an amplifier host):** This is **true**. Pigs develop high-titer viremia without showing clinical signs, allowing mosquitoes to pick up the virus and spread it. They are essential for the maintenance of the transmission cycle. * **Option D (Man is an incidental host):** This is **true**. Humans are "dead-end" hosts because the level of viremia in humans is insufficient to infect a biting mosquito. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir Host:** Ardeid birds (herons, egrets). * **Amplifier Host:** Pigs (also known as "Link hosts"). * **Incubation Period:** 5 to 15 days. * **Vaccination:** The **SA-14-14-2** (Live attenuated) vaccine is used under the Universal Immunization Programme (UIP) in endemic districts of India, given at 9 months and 16–24 months. * **Seasonality:** Peak incidence usually occurs during the rainy season and post-harvest period.

Q: Mass chemoprophylaxis is indicated for which of the following conditions?

Filaria. **Explanation:** **Mass Chemoprophylaxis** refers to the administration of drugs to an entire population (regardless of infection status) in a defined geographical area to interrupt disease transmission. **Why Filaria is Correct:** Lymphatic Filariasis is the classic example where **Mass Drug Administration (MDA)** is the cornerstone of the National Vector Borne Disease Control Programme (NVBDCP). In endemic districts, a single annual dose of **DEC (Diethylcarbamazine) + Albendazole** (or the triple-drug regimen **IDA**: Ivermectin + DEC + Albendazole) is administered to the entire eligible population. The goal is to reduce the microfilarial load in the community to sub-periodic levels, thereby preventing transmission by mosquitoes. **Why Other Options are Incorrect:** * **Plague:** Chemoprophylaxis (Tetracycline or Doxycycline) is indicated only for **contacts** (selective/ring prophylaxis) and high-risk health workers, not the entire mass population. * **Cholera:** Mass chemoprophylaxis is **never recommended** by the WHO because it promotes drug resistance, gives a false sense of security, and diverts resources from sanitation and rehydration. It is only considered for household contacts. * **Measles:** There is no chemoprophylaxis for measles. Prevention is achieved through **active immunization** (vaccine) or post-exposure prophylaxis using Vitamin A and Immunoglobulins in specific cases. **High-Yield Clinical Pearls for NEET-PG:** * **Mass Chemoprophylaxis** is also indicated for **Trachoma** (Azithromycin) and **Onchocerciasis** (Ivermectin). * **Selective Chemoprophylaxis** (for contacts/high-risk groups) is used in Meningococcal meningitis, H. influenzae, and Pertussis. * **MDA for Filariasis** excludes children <2 years, pregnant women, and severely ill individuals.

Q: Which of the following statements about mosquitoes is FALSE?

Mosquitoes are the definitive hosts in filariasis.. **Explanation** In parasitology, the **definitive host** is defined as the host in which the parasite undergoes its **sexual cycle** or reaches maturity. The **intermediate host** is where the asexual cycle or larval stages occur. 1. **Why Option B is False (The Correct Answer):** In **Filariasis** (*Wuchereria bancrofti*), the sexual cycle occurs within the human lymphatic system, making **Humans the definitive host**. Mosquitoes (Culex) serve only as the **intermediate host**, where the parasite undergoes developmental changes (L1 to L3 larvae) without multiplication (Cyclo-developmental transmission). 2. **Analysis of Other Options:** * **Option A:** In **Malaria**, the sexual cycle (sporogony) occurs in the midgut of the female Anopheles mosquito. Therefore, the **mosquito is the definitive host**, while humans are the intermediate host. * **Option C:** Under optimal conditions of temperature and humidity, the mosquito life cycle (Egg → Larva → Pupa → Adult) typically takes **7–10 days**, but it can extend up to **3 weeks** depending on environmental factors. * **Option D:** While most mosquitoes stay within 1–2 km of their breeding site, many species (like *Anopheles* and *Culex*) are capable of traveling up to **3 kilometers** or more, often aided by wind currents. **High-Yield NEET-PG Pearls:** * **Malaria:** Mosquito = Definitive Host; Human = Intermediate Host. * **Filariasis:** Human = Definitive Host; Mosquito = Intermediate Host. * **Extrinsic Incubation Period:** The time taken for the parasite to develop inside the mosquito (e.g., ~10–14 days for Malaria). * **Overwintering:** Mosquitoes can survive adverse seasons through "hibernation" in the adult or egg stage.

Question 1

What is the primary reservoir of Clostridium tetani?

Accepted Answer

Soil

Answer

Humans

Answer

Water

Answer

Hospital waste

Question 2

All of the following methods are antilarval measures except?

Accepted Answer

Malathion

Answer

Intermittent irrigation

Answer

Paris green

Answer

Gambusia affinis

Question 3

Isolation has a definitive value in all except:

Accepted Answer

Hepatitis E

Answer

Diphtheria

Answer

Cholera

Answer

Pneumonic Plague

Question 4

If a new sputum smear positive patient of tuberculosis continues to be smear positive at the end of the intensive phase of category I treatment under DOTS, what should be the further management of this patient?

Accepted Answer

Continue the intensive phase of treatment for one more month

Answer

Start category I treatment again

Answer

Treat as failure and start category II treatment under DOTS

Answer

Start continuation phase under category I

Question 5

What is the recommended drug for intermittent preventive therapy during pregnancy in malaria?

Accepted Answer

Sulfadoxine-pyrimethamine

Answer

Proguanil

Answer

Pyrimethamine-dapsone

Answer

Quinine

Question 6

Blanket or mass treatment is indicated in all of the following conditions EXCEPT:

Accepted Answer

Dengue fever

Answer

Trachoma

Answer

Malaria

Answer

Yaws

Question 7

What is true about Japanese encephalitis?

Accepted Answer

Caused by Group A arbovirus

Answer

Transmitted by Culex mosquito

Answer

Pig is an amplifier host

Answer

Man is an incidental host

Question 8

Mass chemoprophylaxis is indicated for which of the following conditions?

Accepted Answer

Filaria

Answer

Plague

Answer

Cholera

Answer

Measles

Question 9

Under the Revised National Tuberculosis Control Programme (RNTCP), for diagnosis of Multidrug-Resistant Tuberculosis (MDR TB), which drugs are currently used for drug sensitivity testing?

Accepted Answer

Rifampicin, Isoniazid, and Ethambutol

Answer

Rifampicin

Answer

Rifampicin and Isoniazid

Answer

Rifampicin, Isoniazid, and Pyrazinamide

Question 10

Which of the following statements about mosquitoes is FALSE?

Accepted Answer

Mosquitoes are the definitive hosts in filariasis.

Answer

Mosquitoes are the definitive hosts in malaria.

Answer

The life cycle of a mosquito can be completed in 3 weeks.

Answer

A female mosquito can travel up to 3 kilometers.

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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