Epidemiology Practice Questions

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 is NOT a live attenuated vaccine?

Oral polio vaccine. **Explanation:** The question asks to identify which option is **NOT** a live attenuated vaccine. However, there is a technical discrepancy in the provided key: **Oral Polio Vaccine (Sabin), Yellow Fever, and Measles are all classic examples of live attenuated vaccines.** The correct answer to "Which is NOT a live vaccine" among these options is **D. Influenza vaccine**, specifically the injectable form (IIV), which is inactivated. **1. Why Option D (Influenza) is the most appropriate answer:** While a Live Attenuated Influenza Vaccine (LAIV) exists as a nasal spray, the standard influenza vaccine administered globally is the **Inactivated Influenza Vaccine (IIV)**. In the context of standard MCQ patterns, if a vaccine has both live and killed versions, and the other options are exclusively live, the one with a killed version is the intended answer. **2. Analysis of Incorrect Options (Live Vaccines):** * **A. Oral Polio Vaccine (Sabin):** A live attenuated vaccine. It induces both systemic (IgG) and local intestinal immunity (IgA). * **B. Yellow Fever Vaccine:** A live attenuated vaccine (17D strain). It is one of the most effective vaccines available. * **C. Measles Vaccine:** A live attenuated vaccine (Edmonston-Zagreb strain in India). It is highly heat-sensitive. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Live Vaccines:** "**B**oy **R**omeo **G**ive **M**y **L**ove **T**o **P**ollywood **S**tar" (**B**CG, **R**otavirus, **G**ermany Measles/Rubella, **M**easles/Mumps, **L**ive Influenza, **T**yphoid (Ty21a), **P**olio (Sabin), **S**mallpox/Yellow Fever). * **Contraindications:** Live vaccines are generally contraindicated in **pregnancy** and **immunocompromised** states (except HIV patients before clinical AIDS develops). * **Storage:** Most live vaccines are freeze-dried (lyophilized) and must be stored in the freezer compartment (except OPV, which is the most heat-sensitive).

Q: What is the term for a disease introduced to a country for the first time?

Exotic disease. ### Explanation **Correct Answer: A. Exotic disease** **Why it is correct:** An **exotic disease** is defined as a disease which is imported into a country in which it does not otherwise occur. The term is derived from the fact that the pathogen is "foreign" or "alien" to the local geographical area. A classic example in the Indian context is **Yellow Fever**; although the vector (*Aedes aegypti*) is present, the disease itself is not endemic, making any introduction "exotic." **Why the other options are incorrect:** * **B. Epidemic:** This refers to the occurrence of cases of an illness in a community or region clearly in **excess of normal expectancy**. It relates to the *frequency* of the disease, not its origin. * **C. Endemic:** This refers to the **constant presence** of a disease or infectious agent within a given geographic area or population group without external importation (e.g., Typhoid in India). * **D. Hyperendemic:** This describes a situation where a disease is constantly present at a **high incidence and/or prevalence** rate and affects all age groups equally (e.g., Malaria in certain African regions). **NEET-PG High-Yield Pearls:** * **Sporadic:** Scattered cases occurring irregularly and haphazardly (e.g., Tetanus). * **Pandemic:** An epidemic that spreads across several countries or continents, usually affecting a large number of people (e.g., COVID-19, Influenza). * **Enzootic/Epizootic:** These are the animal equivalents of endemic and epidemic, respectively. * **Epornithic:** An epidemic occurring in a bird population. * **Zoonosis:** An infection transmissible under natural conditions from vertebrate animals to man (e.g., Rabies, Brucellosis).

Q: What is the term for a disease imported into a country that was not otherwise present?

Exotic disease. ### Explanation **Correct Answer: C. Exotic disease** **1. Why it is correct:** In epidemiology, an **exotic disease** is defined as a disease that is imported into a country or geographic region where it does not otherwise occur. These diseases are introduced from the outside, often through international travel, trade, or migration. A classic example in the Indian context is **Yellow Fever**; while the vector (*Aedes aegypti*) is present in India, the disease itself is not endemic and is considered exotic. **2. Analysis of Incorrect Options:** * **A. Epornitic disease:** This refers to an epidemic or outbreak of disease occurring within a **bird population**. It is the avian equivalent of an "epizootic." * **B. Zoonotic disease:** These are infections that are naturally transmissible from **vertebrate animals to humans** (e.g., Rabies, Brucellosis, Plague). The term describes the source of infection, not its geographic status. * **C. Epizootic disease:** This refers to an outbreak of disease that rapidly affects a large number of **animals** in a specific area at the same time (e.g., Anthrax or Foot and Mouth Disease). It is the animal equivalent of an "epidemic" in humans. **3. NEET-PG High-Yield Pearls:** * **Enzootic:** A disease that is constantly present in an animal population (equivalent to "endemic" in humans). * **Epornithic:** An outbreak in birds. * **Yellow Fever Prevention:** To prevent the introduction of this exotic disease into India, strict international health regulations (IHR) require travelers from endemic zones to possess a valid **Yellow Fever Vaccination Certificate** (valid for life, starting 10 days after vaccination). * **Zoonoses Classification:** * *Orthozoonoses:* Cycle maintained in one vertebrate (e.g., Rabies). * *Cyclozoonoses:* Requires more than one vertebrate host (e.g., Echinococcosis). * *Metazoonoses:* Requires an invertebrate vector (e.g., Plague).

Q: In a population, the incidence of an autosomal recessive disease is 1/250,000. What is the carrier frequency in this population?

1/250. ### Explanation This question is based on the **Hardy-Weinberg Principle**, which is a high-yield topic in Epidemiology and Genetics. The principle uses the equation: **$p^2 + 2pq + q^2 = 1$**, where: * **$q^2$** = Frequency of the disease (homozygous recessive individuals) * **$2pq$** = Frequency of carriers (heterozygous individuals) * **$p$** = Frequency of the normal allele **1. Why Option A is Correct:** * **Step 1:** Find $q$. The incidence ($q^2$) is given as $1/250,000$. $q = \sqrt{1/250,000} = 1/500$. * **Step 2:** Find $p$. Since $p + q = 1$, and $q$ is very small, $p$ is approximately $1$. * **Step 3:** Calculate carrier frequency ($2pq$). $2 \times 1 \times (1/500) = 2/500 = \mathbf{1/250}$. **2. Why Other Options are Incorrect:** * **Option B (1/500):** This represents $q$ (the gene frequency of the abnormal allele), not the carrier frequency ($2pq$). * **Option C (1/1000):** This is a calculation error, likely from forgetting to multiply by 2 in the $2pq$ formula. * **Option D (1/5000):** This value is mathematically unrelated to the square root of the given incidence. **3. Clinical Pearls for NEET-PG:** * **Shortcut:** For rare autosomal recessive diseases, if the incidence is $1/X$, the carrier frequency is approximately $2/\sqrt{X}$. * **Hardy-Weinberg Equilibrium** assumes a large population, random mating, and no selection, mutation, or migration. * **Application:** This formula is used in genetic counseling to estimate the risk of a couple having an affected child when one or both are asymptomatic carriers.

Question 1

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 2

Which of the following statements are true about HIV epidemiology?

Accepted Answer

Children are rarely affected; Southern Africa has 72% of the total global burden; seminal secretions are more infectious than vaginal secretions; HIV cases can infect during the window period.

Answer

Children are rarely affected; less than 10% of HIV-infected persons progress to AIDS; seminal secretions are more infectious than vaginal secretions; HIV cases can infect during the window period.

Answer

Less than 10% of HIV-infected persons progress to AIDS; Southern Africa has 72% of the total global burden; seminal secretions are more infectious than vaginal secretions; HIV cases can infect during the window period.

Answer

Children are rarely affected; less than 10% of HIV-infected persons progress to AIDS; Southern Africa has 72% of the total global burden; HIV cases can infect during the window period.

Question 3

Mass chemoprophylaxis is indicated for which of the following conditions?

Accepted Answer

Filaria

Answer

Plague

Answer

Cholera

Answer

Measles

Question 4

Which of the following is NOT a live attenuated vaccine?

Accepted Answer

Oral polio vaccine

Answer

Yellow fever vaccine

Answer

Measles vaccine

Answer

Influenza vaccine

Question 5

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 6

What is the primary purpose of an interventional study?

Accepted Answer

Hypothesis Confirmation

Answer

Hypothesis Formulation

Answer

Hypothesis Testing

Answer

Hypothesis Manipulation

Question 7

ELISA is performed on a population with low prevalence. What would be the result of performing double screening ELISA tests?

Accepted Answer

Increased specificity and positive predictive value

Answer

Increased sensitivity and positive predictive value

Answer

Increased sensitivity and negative predictive value

Answer

Increased specificity and negative predictive value

Question 8

What is the term for a disease introduced to a country for the first time?

Accepted Answer

Exotic disease

Answer

Epidemic

Answer

Endemic

Answer

Hyperendemic

Question 9

What is the term for a disease imported into a country that was not otherwise present?

Accepted Answer

Exotic disease

Answer

Epornitic disease

Answer

Zoonotic disease

Answer

Epizootic disease

Question 10

In a population, the incidence of an autosomal recessive disease is 1/250,000. What is the carrier frequency in this population?

Accepted Answer

1/250

Answer

1/500

Answer

1/1000

Answer

1/5000

Epidemiology — MCQs

Epidemiology — MCQs

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