Infectious Diseases Practice Questions

Q: Identify the disease represented in the image.

Japanese encephalitis. ***Japanese encephalitis*** - The image likely depicts a mosquito vector, specifically from the *Culex* genus, which is the primary vector for **Japanese encephalitis virus**. - Common vectors of Japanese encephalitis are **Culex tritaeniorhynchus** and **Culex vishnui**. *Dengue* - Dengue virus is primarily transmitted by mosquitoes from the *Aedes* genus, especially **Aedes aegypti** and **Aedes albopictus**. - These mosquitoes are characterized by **distinctive white bands** on their legs and bodies. *Chikungunya* - Chikungunya is also transmitted by *Aedes* mosquitoes, mainly **Aedes aegypti** and **Aedes albopictus**. - The distinguishing feature of these vectors is not evident in the context of the question's focus on the depicted image. *Zika virus* - Zika virus is primarily transmitted by **Aedes aegypti**, the same mosquito responsible for dengue and chikungunya. - The image does not provide enough specific morphological details to differentiate it from other *Aedes*-borne diseases without additional context.

Q: In which disease is a healthy carrier commonly seen?

Meningococcal meningitis. ***Meningococcal meningitis*** - A significant proportion of the population can carry *N. meningitidis* in their **nasopharynx** without developing symptoms, serving as a reservoir for transmission. - This **asymptomatic carriage** is crucial for the spread and persistence of the disease in communities. *Measles* - Measles is highly contagious and typically causes **clear symptoms** in infected individuals; the concept of a healthy, asymptomatic carrier is not relevant. - Individuals with measles are infectious during the **prodromal phase** and until several days after rash onset. *Rubella* - Rubella, while often mild, does not typically involve a **healthy carrier state** where individuals harbor and transmit the virus without symptoms. - Infected individuals usually exhibit a **rash** and mild symptoms, and are contagious during that period. *Influenza* - While individuals can have **asymptomatic or very mild influenza infections**, they are not generally considered **healthy carriers** in the same way as meningococcal disease. - Asymptomatic influenza shedding is usually for a **shorter duration** compared to the prolonged carriage seen with *N. meningitidis*.

Q: What is the recommended mesh size for mosquito nets to effectively prevent mosquito bites?

156 holes per square inch. ***156 holes per square inch*** - This mesh size, equivalent to a **hole dimension of 1.5mm x 1.5mm**, is recommended by the **WHO** for insecticide-treated nets (ITNs) to effectively prevent mosquito entry. - It provides a balance between sufficient air circulation and preventing even smaller mosquito species from passing through. *50 holes per square inch* - This mesh size is too large and would allow **smaller mosquito species** to easily pass through, rendering the net ineffective. - It would not provide adequate **protection** against mosquito bites and disease transmission. *100 holes per square inch* - While better than 50 holes, this mesh size might still be insufficient to block all mosquito species, especially very small ones. - It does not meet the **WHO guidelines** for optimal protection. *200 holes per square inch* - Although this size would effectively block mosquitoes, it might excessively restrict **airflow**, making the net uncomfortable to sleep under in warm climates. - Higher mesh counts can also lead to **increased production costs** and potential issues with durability.

Q: Range of flight of Aedes mosquito is?

400 m. ***400 m*** - *Aedes* mosquitoes have a **typical flight range of up to 400 meters** from their breeding sites, which is well-established in vector control literature. - This flight range is a critical factor in planning **control measures and source reduction strategies**, as interventions need to cover a 400m radius around cases. - Most *Aedes aegypti* prefer to stay within **50-100 meters** but can disperse up to 400m when searching for blood meals or oviposition sites. *Less than 100 m* - While many *Aedes* mosquitoes do stay within **100 meters** of their breeding sites under normal conditions, this represents their **preferred range** rather than maximum capability. - The **maximum flight range** extends beyond this distance, making this answer too restrictive for vector control planning. *1 km* - A flight range of **1 km** exceeds the typical dispersal distance for *Aedes* mosquitoes under normal circumstances. - While occasional long-distance dispersal has been documented, this is not the standard flight range used in epidemiological planning. *10 km* - This distance is far too great for *Aedes* mosquitoes, which are relatively weak fliers. - Such long distances would require **passive transport** (vehicles, wind) rather than active flight.

Q: Best indicator for spread of TB in a community?

Annual infection rate. ***Annual infection rate*** - The **Annual Infection Rate (ARI)** is the gold standard indicator for measuring TB spread in a community - It measures the rate at which new TB infections occur in a tuberculin-negative population over one year - ARI directly reflects **recent transmission** and the force of infection in the community - WHO and Park's Textbook recommend ARI as the best epidemiological indicator for TB transmission - Calculated through tuberculin surveys showing conversion from negative to positive - An ARI of 1% indicates 1% of uninfected individuals become infected per year *Incidence of new cases* - Incidence measures new **disease cases** (active TB), not new infections - Only 5-10% of TB infections progress to active disease, often after years of latency - Incidence is affected by case detection rates, diagnostic capacity, and healthcare access - It underestimates actual transmission occurring in the community *Prevalence of infection* - **Prevalence** indicates total existing cases (both old and new) at a point in time - Influenced by both new infections and duration of infection/disease - Does not specifically measure the rate of ongoing transmission *Case rate* - **Case rate** refers to the number of active disease cases per population - Similar to prevalence, it doesn't isolate new transmission events - Less sensitive for detecting changes in transmission dynamics

Q: Which is the only infectious disease that has been eradicated worldwide?

Smallpox. ***Smallpox*** - **Smallpox** was declared eradicated by the World Health Organization in **1980**, following a successful global vaccination campaign. - This was possible due to its **human-only reservoir**, characteristic clinical features, and an effective vaccine. *Polio* - While significant progress has been made towards **polio eradication**, it is not yet fully eradicated, with cases still reported in a few endemic countries. - The disease is caused by the **poliovirus** and is preventable by vaccination, but challenges like vaccine hesitancy and conflict impede full eradication. *Diphtheria* - **Diphtheria** is a serious bacterial infection that is preventable by vaccination and has seen a drastic reduction in cases, but it has not been eradicated worldwide. - Outbreaks still occur in regions with low vaccination coverage, demonstrating its continued presence. *Measles* - **Measles** is a highly contagious viral disease that is preventable by a safe and effective vaccine, but it is far from eradicated. - Outbreaks regularly occur in many parts of the world, especially in areas with suboptimal vaccination rates.

Q: Infectivity of convalescent carrier of cholera lasts for?

2-3 weeks. ***2-3 weeks*** - The infectivity of a **convalescent carrier** of cholera typically lasts for about **2 to 3 weeks** after recovery, according to **Park's Textbook of Preventive and Social Medicine**. - During this period, individuals can still shed **Vibrio cholerae** in their feces, posing a risk of transmission. - This is the **standard duration** taught in Indian medical education for examination purposes. *1-5 days* - This timeframe is too short for the infectivity of a **convalescent carrier**, as bacterial shedding extends well beyond the acute phase. - While symptoms may resolve within this period, the organism continues to be excreted for much longer. *1-2 weeks* - While many individuals may stop shedding within this period (per WHO/CDC data), for examination purposes, the convalescent carrier period is defined as **2-3 weeks**. - This option represents the **lower range** but underestimates the full duration taught in standard Indian textbooks. *4-5 weeks* - This period is too long for the typical infectivity duration of a **convalescent carrier** of cholera. - **Chronic carriers** (rare in cholera, <1% of cases) can shed for months, but this does not represent the convalescent carrier period.

Q: Varicella zoster virus infection is more likely to occur in which of the following months?

March. ***March*** - Varicella-zoster virus (VZV) infections, particularly **chickenpox**, show a peak incidence during **late winter and spring months**. - This seasonality is attributed to changes in human behavior and environmental factors that facilitate transmission. *August* - **August** is typically a summer month in many regions, and VZV infections are less common during warmer periods. - Reduced indoor crowding and increased exposure to UV light may contribute to lower transmission rates. *October* - While October marks the beginning of autumn, it generally precedes the peak season for VZV infections. - Transmission rates start to increase but are usually not as high as in late winter or early spring. *November* - November, late autumn or early winter, sees an increase in respiratory and viral infections due to colder weather and increased indoor gatherings. - However, the peak incidence for VZV is typically observed a few months later, in late winter and early spring.

Q: Major reservoir of KFD?

Squirrels. ***Squirrels*** - **Squirrels** are considered a major reservoir for the Kyasanur Forest Disease (KFD) virus because they can carry the virus without showing severe symptoms themselves, allowing for viral persistence in nature. - The virus can be transmitted from infected squirrels to ticks, which then can spread the infection to other animals or humans. *Human* - Humans are considered **incidental hosts** for KFD, meaning they can become infected but do not typically play a significant role in maintaining the virus in nature. - While humans can experience severe disease, they do not serve as a reservoir for further transmission to other vectors or hosts. *Cattle* - **Cattle** are not typically considered a reservoir for the Kyasanur Forest Disease virus. - They can be exposed to KFD but are not known to sustain the viral cycle or transmit it effectively to ticks or other animals. *Monkey* - While KFD is often associated with **monkey deaths** (especially black-faced langurs and bonnet macaques), these animals are considered **amplifying hosts** rather than primary reservoirs. - Monkeys experience severe disease and high mortality, making them good indicators of viral activity but not long-term carriers for sustained transmission.

Q: Which insecticide is commonly used for insecticide-treated bed nets (ITBN) in malaria control?

Deltamethrin. ***Deltamethrin*** - **Deltamethrin** is a synthetic pyrethroid, widely favored for its **low mammalian toxicity** and high efficacy against mosquitoes, making it ideal for ITBNs. - Its **residual action** ensures long-lasting protection against mosquito bites, crucial for effective malaria prevention. *Malathion* - **Malathion** is an organophosphate insecticide and is generally used for **outdoor mosquito control** as a spray, but not typically impregnated into bed nets due to its odor and faster degradation. - It has a higher **acute toxicity** profile compared to pyrethroids, making it less suitable for direct prolonged human contact via bed nets. *Lindane* - **Lindane** (gamma-hexachlorocyclohexane) is an organochlorine insecticide which has been largely **phased out** for public health use due to its persistence in the environment and concerns about its potential neurotoxicity. - It is currently **not recommended** for ITBNs given environmental and health concerns as well as the availability of safer alternatives. *Fenitrothion* - **Fenitrothion** is another organophosphate insecticide primarily used in **agriculture** and for indoor residual spraying (IRS), but it is not commonly used for ITBNs. - Its **higher volatility** and less favorable safety profile compared to pyrethroids limit its use in materials that have direct and prolonged contact with people.

Question 1

Identify the disease represented in the image.

Accepted Answer

Japanese encephalitis

Answer

Dengue

Answer

Chikungunya

Answer

Zika virus

Question 2

In which disease is a healthy carrier commonly seen?

Accepted Answer

Meningococcal meningitis

Answer

Measles

Answer

Rubella

Answer

Influenza

Question 3

What is the recommended mesh size for mosquito nets to effectively prevent mosquito bites?

Accepted Answer

156 holes per square inch

Answer

50 holes per square inch

Answer

100 holes per square inch

Answer

200 holes per square inch

Question 4

Range of flight of Aedes mosquito is?

Accepted Answer

400 m

Answer

1 km

Answer

Less than 100 m

Answer

10 km

Question 5

Best indicator for spread of TB in a community?

Accepted Answer

Annual infection rate

Answer

Prevalence of infection

Answer

Incidence of new cases

Answer

Case rate

Question 6

Which is the only infectious disease that has been eradicated worldwide?

Accepted Answer

Smallpox

Answer

Polio

Answer

Diphtheria

Answer

Measles

Question 7

Infectivity of convalescent carrier of cholera lasts for?

Accepted Answer

2-3 weeks

Answer

1-5 days

Answer

1-2 weeks

Answer

4-5 weeks

Question 8

Varicella zoster virus infection is more likely to occur in which of the following months?

Accepted Answer

March

Answer

August

Answer

October

Answer

November

Question 9

Major reservoir of KFD?

Accepted Answer

Squirrels

Answer

Human

Answer

Cattle

Answer

Monkey

Question 10

Which insecticide is commonly used for insecticide-treated bed nets (ITBN) in malaria control?

Accepted Answer

Deltamethrin

Answer

Malathion

Answer

Fenitrothion

Answer

Lindane

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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