Infectious Diseases Practice Questions

Q: Mineral oils are used in mosquito control measures as a:

Larvicide. **Explanation:** The correct answer is **Larvicide**. Mineral oils (such as Malariol or Flit) are a classic method of anti-larval control used in environmental sanitation. **Why Larvicide is correct:** Mineral oils act through a physical mechanism rather than a chemical one. When sprayed on the surface of stagnant water, they form a thin, continuous film. This film serves two purposes: 1. **Suffocation:** It prevents the mosquito larvae and pupae from breathing by blocking their respiratory siphons (tubes) when they come to the surface for air. 2. **Toxicity:** Certain components of the oil may be directly toxic to the larvae upon contact. Because they target the aquatic stage of the mosquito life cycle, they are classified as larvicides. **Why other options are incorrect:** * **Personal protection method:** These include barriers like Mosquito nets (LLINs), repellents (DEET), and protective clothing, which prevent the mosquito from biting a human host. * **Adulticide:** These are chemicals (like DDT or Malathion) used to kill adult mosquitoes, typically through Indoor Residual Spraying (IRS). * **Space spray:** This involves dispersing fine droplets of insecticide into the air (fogging) to kill flying adult mosquitoes (e.g., Pyrethrum or Malathion fogging). **High-Yield NEET-PG Pearls:** * **Malariol:** A common mixture used for this purpose (Diesel + Kerosene + Castor oil). * **Dosage:** Approximately 10–15 gallons per acre of water surface is required. * **Limitation:** Mineral oils are not suitable for drinking water; for potable water, **Abate (Temephos)** is the larvicide of choice. * **Biological Larvicide:** *Gambusia affinis* (Guppy fish) is the preferred biological method for larval control.

Q: Which of the following diseases has humans as the only reservoir?

Measles. ### Explanation **Correct Option: C. Measles** Measles is a classic example of a disease where **humans are the only reservoir**. There is no known animal reservoir or non-human carrier state. This epidemiological characteristic is crucial because it makes Measles a potential candidate for global eradication. The virus is maintained in the community by a continuous chain of transmission from one susceptible human to another. **Analysis of Incorrect Options:** * **A. Rabies:** This is a viral zoonosis. The primary reservoirs are wild and domestic animals (dogs, bats, foxes). Humans are "dead-end" hosts. * **B. Tetanus:** The reservoir for *Clostridium tetani* is **soil** and the intestinal tracts of animals/humans. It is an environmental reservoir, meaning the disease cannot be eradicated. * **C. JE Virus (Japanese Encephalitis):** This virus follows a complex cycle involving **pigs** (amplifier hosts) and **water birds** (ardied birds/natural reservoirs). Humans are accidental, dead-end hosts. **NEET-PG High-Yield Pearls:** * **Human-only Reservoirs:** Other diseases with only human reservoirs include **Smallpox** (eradicated), **Polio**, **Mumps**, **Rubella**, **Typhoid**, and **Syphilis**. * **Measles Infectivity:** It is most infectious during the **prodromal stage** (before the rash appears). * **Secondary Attack Rate (SAR):** Measles has one of the highest SARs (>80%), reflecting its extreme contagiousness in susceptible populations. * **Eradication Criteria:** A disease can generally only be eradicated if it has no animal reservoir and an effective intervention (vaccine) is available.

Q: What is the breeding ground for the vectors of Japanese B virus?

Paddy field. ### Explanation **Correct Option: A. Paddy field** Japanese Encephalitis (JE) is caused by the Japanese B virus, a flavivirus. The primary vectors are mosquitoes of the **Culex vishnui group** (specifically *Culex tritaeniorhynchus*). These mosquitoes are "exophilic" (rest outdoors) and "zoophilic" (prefer animal blood). Their preferred breeding grounds are large bodies of stagnant water with vegetation, making **irrigated paddy fields** the most significant ecological niche for their proliferation. **Analysis of Incorrect Options:** * **B. Mixed garbage:** This is the typical breeding ground for **houseflies** (*Musca domestica*), which act as mechanical vectors for enteric diseases, not JE. * **C. Cooler water:** Stagnant water in desert coolers is the classic breeding site for ***Aedes aegypti***, the vector for Dengue, Chikungunya, and Zika. * **D. Stale food:** While stale food attracts pests like cockroaches and flies, it is not a breeding medium for the Culex mosquitoes responsible for JE transmission. **High-Yield Clinical Pearls for NEET-PG:** * **The Cycle:** JE follows a **Pig-Mosquito-Man** cycle. Pigs are the "amplifier hosts" (they develop high viral titers without getting sick), while Ardeid birds (herons, egrets) are the "natural reservoirs." * **Dead-end Host:** Humans are "dead-end hosts" because the level of viremia in humans is insufficient to infect a biting mosquito. * **Seasonality:** In India, JE cases typically peak during the **monsoon and post-monsoon** periods, coinciding with rice cultivation cycles. * **Vaccination:** The most commonly used vaccine in the National Immunization Schedule is the live attenuated **SA-14-14-2** strain.

Q: Chikungunya fever is transmitted by which mosquito?

Aedes. **Explanation** **Correct Answer: C. Aedes** Chikungunya is a viral disease caused by the Chikungunya virus (CHIKV), an RNA virus belonging to the genus *Alphavirus*. It is primarily transmitted to humans through the bite of infected mosquitoes of the **Aedes** genus, specifically ***Aedes aegypti*** and ***Aedes albopictus***. These mosquitoes are "day-biters," peaking in activity during early morning and late afternoon. They typically breed in stagnant water containers in urban and peri-urban settings. **Analysis of Incorrect Options:** * **Anopheles:** This genus is the primary vector for **Malaria**. While it transmits various parasitic and some viral diseases (like O'nyong'nyong fever), it does not transmit Chikungunya. * **Culex:** These mosquitoes are known vectors for **Japanese Encephalitis (JE)**, **Bancroftian Filariasis**, and West Nile Fever. They typically breed in dirty, stagnant water like drains and septic tanks. * **Any of the above:** Vector-virus relationships are highly specific; only Aedes mosquitoes possess the biological compatibility to harbor and transmit the Chikungunya virus. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad:** Fever, Rash, and severe **Arthralgia** (joint pain is often debilitating and can persist for months). * **Aedes albopictus:** Known as the "Asian Tiger Mosquito," it is increasingly responsible for outbreaks in temperate regions due to its ability to survive in cooler climates. * **Other Aedes-borne diseases:** Dengue, Zika virus, and Yellow Fever. * **Incubation Period:** Typically 3–7 days. * **Diagnosis:** RT-PCR (during the first week) or Serology (ELISA for IgM antibodies).

Q: An organism that multiplies and develops within a host is called:

Cyclopropagative. ### Explanation In Community Medicine and Parasitology, the classification of biological transmission depends on whether the parasite undergoes changes in form (development) or increases in number (multiplication) within the vector/host. **1. Why Cyclopropagative is correct:** The term **Cyclopropagative** is used when the organism undergoes **both** a change in form (developmental stages) and an increase in number (multiplication). * *Example:* Malaria parasite (*Plasmodium*) in the *Anopheles* mosquito. The parasite develops from a gametocyte to a sporozoite while multiplying significantly. **2. Analysis of Incorrect Options:** * **Cyclodevelopmental (Option B):** The organism undergoes a change in form/stage but **does not multiply**. * *Example:* Filarial parasite (*Wuchereria bancrofti*) in the *Culex* mosquito or Guinea worm in *Cyclops*. One microfilaria develops into one infective larva. * **Developmental (Option C):** This is a broader, less specific term. In the context of biological transmission, "Propagative" transmission is the counterpart where the organism multiplies but does **not** change in form (e.g., Plague bacilli in rat fleas). * **All of the above (Option D):** Incorrect because the three types of transmission are mutually exclusive based on the parasite's life cycle requirements. ### NEET-PG High-Yield Pearls: * **Propagative:** Multiplication only, no change in form (e.g., Plague, Yellow Fever virus in mosquitoes). * **Cyclodevelopmental:** Change in form only, no multiplication (e.g., Filariasis, Guinea worm). * **Cyclopropagative:** Both change in form and multiplication (e.g., Malaria). * **Mechanical Transmission:** The vector acts only as a carrier; no development or multiplication occurs (e.g., Housefly carrying Typhoid bacilli).

Q: Presence of an infectious agent on clothes or dressings is termed?

Contamination. **Explanation:** The presence of an infectious agent on the surface of a body, or on inanimate objects like clothes, dressings, water, or food, is termed **Contamination**. 1. **Why Contamination is Correct:** Contamination refers to the mere presence of pathogens on an external surface (fomites or skin) without the agent necessarily entering the tissues or multiplying. In this case, clothes and dressings act as **fomites**, serving as vehicles for potential transmission. 2. **Why the other options are incorrect:** * **Infection:** This is the entry, development, and multiplication of an infectious agent in the body of a human or animal. Unlike contamination, infection implies a biological interaction with the host's tissues. * **Infestation:** This term is specifically used for the lodgment, development, and reproduction of **arthropods** (e.g., lice, mites, ticks) on the surface of the body or in clothing (e.g., Pediculosis, Scabies). * **Contagion:** This is an older, less technical term referring to the transmission of disease by direct or indirect contact. It does not specifically define the presence of an agent on an object. **High-Yield Clinical Pearls for NEET-PG:** * **Pollution:** The presence of offensive but not necessarily infectious matter in the environment (e.g., chemicals in water). * **Host Defenses:** Contamination does not always lead to infection; the "Infectious Dose" and host immunity determine if the agent will successfully invade. * **Fomites:** Inanimate objects (like the clothes/dressings mentioned) that can transfer pathogens are classic examples of indirect transmission. * **Ectoparasites:** Always associate "Infestation" with ectoparasites like *Sarcoptes scabiei*.

Question 1

All are true for components of DOTS, except?

Accepted Answer

High compliance

Answer

Given under observation

Answer

Political commitment

Answer

Accountability

Question 2

What is the best step for malaria control in a high environmental temperature setting?

Accepted Answer

Eliminate breeding places

Answer

Wear full-sleeved clothing

Answer

Use indoor residual insecticide spraying

Answer

Provide early treatment for infected individuals

Question 3

Mineral oils are used in mosquito control measures as a:

Accepted Answer

Larvicide

Answer

Personal protection method

Answer

Adulticide

Answer

Space spray

Question 4

Which of the following diseases has humans as the only reservoir?

Accepted Answer

Measles

Answer

Rabies

Answer

Tetanus

Answer

JE virus

Question 5

What is the breeding ground for the vectors of Japanese B virus?

Accepted Answer

Paddy field

Answer

Mixed garbage

Answer

Cooler water

Answer

Stale food

Question 6

Chikungunya fever is transmitted by which mosquito?

Accepted Answer

Aedes

Answer

Anopheles

Answer

Culex

Answer

Any of the above

Question 7

In the heterosexual transmission of Human Immunodeficiency Virus (HIV) infection, what is the relative risk of transmission between partners?

Accepted Answer

There is a greater risk of transmission from the infected male to the uninfected female.

Answer

There is a greater risk of transmission from the infected female to the uninfected male.

Answer

The risk of transmission is equal in either direction.

Answer

HIV infection is not transmitted through heterosexual acts.

Question 8

An organism that multiplies and develops within a host is called:

Accepted Answer

Cyclopropagative

Answer

Cyclodevelopmental

Answer

Developmental

Answer

All of the above

Question 9

Which of the following conditions does NOT require isolation?

Accepted Answer

Pneumonic plague

Answer

Mumps

Answer

Measles

Answer

Hepatitis A

Question 10

Presence of an infectious agent on clothes or dressings is termed?

Accepted Answer

Contamination

Answer

Infection

Answer

Infestation

Answer

Contagion

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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