Infectious Diseases Practice Questions

Q: What amount of bleaching powder is necessary to disinfect choleraic stools?

50 gm/lit. **Explanation:** The disinfection of excreta, particularly in the context of highly infectious diseases like Cholera, is a critical component of **terminal disinfection** in Community Medicine. **Why 50 gm/lit is correct:** For the disinfection of stools and vomit in a cholera outbreak, the standard recommendation is to use **bleaching powder (Calcium Hypochlorite)** at a concentration of **50 grams per liter** (or 5% solution). This high concentration is necessary because organic matter (fecal material) rapidly neutralizes free chlorine. A lower dose would be insufficient to penetrate the organic load and achieve the required germicidal effect to kill *Vibrio cholerae*. The mixture should be allowed to stand for at least **2 hours** for complete disinfection. **Analysis of Incorrect Options:** * **75 gm/lit & 90 gm/lit:** These concentrations are unnecessarily high. While they would certainly disinfect the stool, they are not the standard public health recommendation and would lead to wastage of resources and increased chemical irritation. * **100 gm/lit:** This represents a 10% solution. While 10% bleach is sometimes used for large blood spills in laboratory settings, it is not the standard protocol for choleraic stool management in field epidemiology. **High-Yield Clinical Pearls for NEET-PG:** * **Contact Time:** Always remember that for stool disinfection, the contact time is **2 hours**. * **Urine Disinfection:** For disinfecting urine, the same concentration (50 gm/lit) is used, but the contact time can be reduced to **10 minutes**. * **Chlorine Demand:** The reason we use such a high dose (50g) compared to water disinfection (where we use milligrams) is the high **"Chlorine Demand"** of organic matter. * **Bleaching Powder Composition:** Fresh bleaching powder contains approximately **33% available chlorine**. It is unstable and loses chlorine content on exposure to air, light, or moisture.

Q: Culex tritaenorrhynchus transmits which of the following diseases?

Japanese encephalitis. **Explanation:** The correct answer is **Japanese encephalitis (JE)**. *Culex tritaenorrhynchus* is the primary vector for Japanese encephalitis in India and Southeast Asia. This mosquito species typically breeds in stagnant water, such as irrigated rice fields and shallow ditches. The transmission cycle involves an **enzootic cycle** where the virus circulates between mosquitoes and "amplifier hosts" (primarily pigs and water birds like herons and egrets). Humans are "dead-end hosts" because the level of viremia in humans is insufficient to infect a biting mosquito. **Analysis of Incorrect Options:** * **A & B (Dengue and Yellow Fever):** These are transmitted by the **Aedes aegypti** mosquito (and *Aedes albopictus* for Dengue). *Aedes* mosquitoes are "container breeders" that bite during the day, unlike the nocturnal *Culex*. * **C (Kyasanur Forest Disease):** KFD is a viral hemorrhagic fever transmitted by **Hard ticks** (*Haemaphysalis spinigera*). It is geographically restricted to the Western Ghats of India. **High-Yield Clinical Pearls for NEET-PG:** * **Vector Characteristics:** *Culex tritaenorrhynchus* is a **zoophilic** mosquito (prefers animal blood) and a **nocturnal** biter. * **JE Vaccine:** The live-attenuated **SA-14-14-2** strain is commonly used in the Universal Immunization Programme (UIP) in endemic districts. * **Culex as a Vector:** Remember the mnemonic **"C-B-F"** for *Culex*—it transmits **C**ulex (Japanese Encephalitis), **B**ancroftian Filariasis, and **F**ebrile illnesses like West Nile Fever. * **Control:** The most effective environmental control for JE is intermittent irrigation of rice fields to disrupt the mosquito breeding cycle.

Q: All of the following are true about Roll Back Malaria except?

Developing new insecticides. **Explanation:** The **Roll Back Malaria (RBM)** partnership was launched in 1998 by WHO, UNICEF, UNDP, and the World Bank. Its primary goal is to reduce the malaria burden through the implementation of evidence-based strategies and strengthening health systems, rather than focusing on basic laboratory research like developing new chemicals. **Why Option C is the Correct Answer:** Developing new insecticides is a function of **Research and Development (R&D)** and chemical industries, not a core operational strategy of the Roll Back Malaria initiative. RBM focuses on the **scaling up** of existing, proven interventions and ensuring they reach the populations in need. **Analysis of Incorrect Options:** * **Option A (Insecticide-treated bed nets):** This is one of the four main technical strategies of RBM. Long-Lasting Insecticidal Nets (LLINs) are the gold standard for vector control. * **Option B & D (Strengthening health systems & Training health workers):** RBM emphasizes sustainable development. This includes improving healthcare infrastructure, ensuring a steady supply of Artemisinin-based Combination Therapy (ACT), and training community health workers for early diagnosis and prompt treatment (EDPT). **NEET-PG High-Yield Pearls:** * **RBM Strategies:** 1. Evidence-based interventions (LLINs, IRS, ACTs); 2. Strengthening health systems; 3. Multi-sectoral partnership; 4. Movement for social mobilization. * **Global Target:** The current "Global Technical Strategy for Malaria 2016–2030" aims for a **90% reduction** in malaria incidence and mortality rates by 2030. * **World Malaria Day:** Observed on **April 25th**. * **Drug of Choice:** ACT is the mainstay for *P. falciparum*, while Primaquine is added for *P. vivax* to prevent relapse (except in G6PD deficiency).

Q: Transmission of cholera is primarily through which route?

All of the above. **Explanation:** Cholera, caused by the bacterium *Vibrio cholerae*, is a classic example of a disease transmitted via the **fecal-oral route**. While contaminated water is the most common vehicle for large-scale outbreaks, the transmission dynamics are broader, involving any medium contaminated with the pathogen. 1. **Why "All of the above" is correct:** *Vibrio cholerae* is shed in massive quantities (up to $10^{12}$ organisms per liter) in the "rice-water" stools and vomitus of infected patients. * **Contaminated Water (Option B):** This is the primary reservoir. In areas with poor sanitation, feces enter the water supply, leading to explosive epidemics. * **Contaminated Food (Option A):** Food can be contaminated via "fingers, flies, and fluids." Vegetables grown with sewage water or shellfish harvested from contaminated estuaries are common sources. * **Vomitus (Option C):** A high-yield fact often overlooked is that the **vomitus** of a cholera patient is also infectious. If vomitus contaminates food or surfaces handled by others, it can transmit the disease. 2. **Clinical Pearls for NEET-PG:** * **Infective Dose:** High ($10^8$–$10^{11}$ cells) because the organism is acid-sensitive and must survive the gastric acid barrier. * **Haldane’s Rule:** Cholera is more severe in individuals with **Blood Group O**. * **Stool Characteristics:** Non-offensive, "rice-water" appearance with mucus flakes; contains high concentrations of Potassium and Bicarbonate. * **Gold Standard Diagnosis:** Stool culture on **TCBS (Thiosulfate Citrate Bile Salts Sucrose) agar**, where it forms yellow colonies. * **Treatment Priority:** Aggressive rehydration (ORS/IV fluids) is the mainstay; Doxycycline is the drug of choice to reduce the duration of shedding.

Q: What is the quarantine period for yellow fever?

6 days. **Explanation:** The correct answer is **6 days**. In public health and international health regulations, the quarantine period for a disease is traditionally defined as the **maximum incubation period** of that specific infection. For Yellow Fever, the incubation period typically ranges from 3 to 6 days. Therefore, to ensure that an individual arriving from an endemic zone is not carrying the virus, they must be quarantined for the maximum duration of 6 days from the date of last possible exposure. **Analysis of Options:** * **A & B (1-2 days):** These are incorrect as they are shorter than the minimum incubation period; symptoms would likely not have manifested yet. * **C (6 days):** This is the **correct** answer, representing the maximum incubation period as per WHO International Health Regulations (IHR). * **D (10 days):** While the Yellow Fever vaccine becomes legally valid and provides immunity **10 days** after administration, this is not the quarantine period. **High-Yield Clinical Pearls for NEET-PG:** * **Vaccine Validity:** The Yellow Fever vaccine (17D strain) is valid for **life** (as per WHO 2016 update), but for international travel certificates, it becomes valid **10 days after vaccination**. * **Vector:** Primarily *Aedes aegypti* (Urban cycle) and *Haemagogus* (Jungle cycle). * **India Status:** India is "Yellow Fever receptive" (has the vector but not the virus). Hence, strict quarantine rules apply to travelers from the African and South American endemic belts. * **Contraindication:** The vaccine is a live attenuated vaccine and is contraindicated in infants <6 months, pregnant women, and immunocompromised individuals.

Q: Which of the following considerations regarding Dracunculosis eradication is NOT true?

DDT. **Explanation:** Dracunculiasis (Guinea Worm Disease) is a parasitic infection caused by *Dracunculus medinensis*. It is unique because it is transmitted solely through drinking water contaminated with **Cyclops** (water fleas) harboring the infective larvae. India was declared Dracunculiasis-free by the WHO in February 2000. **Why DDT is the correct answer (NOT true):** DDT is a residual insecticide used primarily for controlling adult mosquitoes (vectors for Malaria) or sandflies. Since Dracunculiasis is **not** transmitted by an insect vector but by a crustacean (Cyclops) in water, DDT has no role in its eradication. The chemical of choice for killing Cyclops in drinking water is **Abate (Temephos)**. **Analysis of other options:** * **Drinking piped water/Hand pumps:** This is a primary prevention strategy. Providing safe water sources eliminates the need for people to use open "step-wells" or ponds where transmission occurs. * **Health education:** Crucial for behavioral change, such as teaching communities to filter water using fine cloth (nylon mesh) and preventing infected individuals from entering water bodies. * **Control of Cyclops:** This is the mainstay of environmental control. It involves chemical treatment of water (Temephos) or biological control (introducing larvivorous fish like Gambusia). **High-Yield Facts for NEET-PG:** * **Intermediate Host:** Cyclops (Water flea). * **Infective Stage:** 3rd stage L3 larva. * **Definitive Host:** Humans (No animal reservoir). * **Incubation Period:** 10–14 months. * **Eradication Strategy:** India used the "Guinea Worm Eradication Programme" (GWEP) launched in 1983-84. * **Last Case in India:** Reported in July 1996 (Jodhpur, Rajasthan).

Q: Ultra low volume fogging is done for which of the following agents?

Malathion. **Explanation:** **Ultra-Low Volume (ULV) Fogging** is a specialized vector control technique where concentrated liquid insecticide is dispersed as a fine mist of tiny droplets (5–50 microns). This allows the chemical to remain suspended in the air longer, effectively killing adult mosquitoes on contact. 1. **Why Malathion is Correct:** **Malathion** (an organophosphate) is the insecticide of choice for ULV fogging, especially during outbreaks of Dengue, Chikungunya, and Malaria. It is used in technical grade (95% concentration) at very low dosages (approx. 0.5 liters per hectare). Its efficacy in rapid "knock-down" of adult mosquitoes makes it the gold standard for emergency vector control. 2. **Why Other Options are Incorrect:** * **DDT (Option A):** A chlorinated hydrocarbon used primarily for **Indoor Residual Spraying (IRS)**. It is a persistent insecticide applied to walls to kill mosquitoes when they rest; it is not used for fogging. * **Pyrethroids (Option C):** While some synthetic pyrethroids (like Deltamethrin) can be used for space sprays, Malathion remains the classic and most frequently cited agent for ULV fogging in standard public health textbooks (Park’s PSM). * **Abate/Temephos (Option D):** This is a **larvicide**. It is applied to stagnant water bodies to kill mosquito larvae and is never used for aerial fogging or space spraying. **High-Yield Pearls for NEET-PG:** * **Space Sprays:** Include Fogging (thermal) and ULV (cold) sprays. * **Dose of Malathion for ULV:** 0.5 liters/hectare. * **Dose of Malathion for IRS:** 2g/m² (used when there is resistance to DDT). * **Biological Control:** *Gambusia affinis* (Mosquito fish) and *Lebistes reticulatus* (Guppy fish) are used for larval control.

Q: What is the period of isolation for Salmonella infection?

3 consecutive stool cultures are negative. ### Explanation The correct answer is **C: 3 consecutive stool cultures are negative.** **Why it is correct:** Salmonella (specifically *Salmonella Typhi* and *Paratyphi*) is primarily transmitted via the fecal-oral route. Clinical recovery does not always coincide with the cessation of pathogen shedding. To ensure a patient is no longer infectious and to prevent the development of a "carrier state," public health guidelines require microbiological evidence of clearance. Isolation or exclusion from high-risk activities (like food handling) is maintained until **three consecutive stool cultures**, taken at least 24 hours apart, are negative. **Analysis of Incorrect Options:** * **A. 72 hours after chemotherapy:** While symptoms may improve shortly after starting antibiotics (chemotherapy), the patient can still shed the bacteria in feces, posing a transmission risk. * **B. Widal test negative:** The Widal test measures antibodies (H and O agglutinins), not the presence of the bacteria itself. Titers can remain high long after the infection has cleared, making it an invalid tool for determining the end of isolation. * **D. Urine culture is negative twice:** While *S. Typhi* can be found in urine (especially in cases associated with Schistosomiasis), stool culture is the gold standard for confirming the end of the communicable period. **High-Yield Facts for NEET-PG:** * **Carrier State:** Defined as the excretion of *S. Typhi* in stool/urine for **more than one year**. * **Chronic Carrier Site:** The **Gallbladder** is the most common site for chronic fecal carriage (often associated with gallstones). * **Urinary Carrier Site:** Associated with **Schistosoma haematobium** infection in the bladder. * **Culture Timing:** Stool cultures are most likely to be positive in the **2nd and 3rd weeks** of illness, whereas blood cultures are best in the **1st week**.

Question 1

If a patient with tuberculosis who is sputum smear positive continues to be smear positive at the end of the intensive phase of Category I treatment under DOTS, what is the recommended further management?

Accepted Answer

Continue the intensive phase or treatment for one more month.

Answer

Restart Category I treatment.

Answer

Treat as a failure and initiate Category II treatment under DOTS.

Answer

Start the continuation phase under Category I.

Question 2

What amount of bleaching powder is necessary to disinfect choleraic stools?

Accepted Answer

50 gm/lit

Answer

75 gm/lit

Answer

90 gm/lit

Answer

100 gm/lit

Question 3

Culex tritaenorrhynchus transmits which of the following diseases?

Accepted Answer

Japanese encephalitis

Answer

Dengue fever

Answer

Yellow fever

Answer

Kyasanur Forest Disease (KFD)

Question 4

All of the following are true about Roll Back Malaria except?

Accepted Answer

Developing new insecticides

Answer

Insecticide-treated bed nets

Answer

Strengthening the health system

Answer

Training health workers

Question 5

Transmission of cholera is primarily through which route?

Accepted Answer

All of the above

Answer

Contaminated food with fecal matter

Answer

Contaminated water with fecal matter

Answer

Contaminated food with vomitus from an infected individual

Question 6

What is the quarantine period for yellow fever?

Accepted Answer

6 days

Answer

1 day

Answer

2 days

Answer

10 days

Question 7

In an area with an annual parasite index of less than 2, what is the recommended course of action?

Accepted Answer

Monthly blood smears for all positive cases

Answer

Passive surveillance only

Answer

Two rounds of DDT application annually

Answer

Entomological surveillance

Question 8

Which of the following considerations regarding Dracunculosis eradication is NOT true?

Accepted Answer

DDT

Answer

Drinking piped water and installation of hand pumps

Answer

Health education and awareness of the public

Answer

Control of Cyclops

Question 9

Ultra low volume fogging is done for which of the following agents?

Accepted Answer

Malathion

Answer

DDT

Answer

Pyrethroid

Answer

Abate

Question 10

What is the period of isolation for Salmonella infection?

Accepted Answer

3 consecutive stool cultures are negative

Answer

72 hours after chemotherapy

Answer

Widal test negative

Answer

Urine culture is negative twice

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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