Infectious Diseases Practice Questions

Q: What is the ideal mesh opening size for an effective mosquito net according to WHO standards?

1.2-1.7 mm mesh opening. ***1.2-1.7 mm mesh opening*** - The **World Health Organization (WHO)** recommends a mesh size of **1.2-1.5 mm (approximately 156 holes per square inch)** as the standard for effective mosquito nets. - This mesh opening size provides the **ideal balance** between blocking mosquito entry and maintaining adequate ventilation for comfortable sleeping. - It effectively prevents entry of **Anopheles** and **Culex** mosquitoes, the primary vectors for malaria and other mosquito-borne diseases, while allowing sufficient airflow. *2.5 mm mesh opening* - A mesh opening of **2.5 mm is too large** and would allow smaller mosquito species to pass through, particularly young adult mosquitoes. - This would **significantly reduce the protective efficacy** of the net against mosquito-borne diseases like malaria, dengue, and filariasis. - Such large mesh openings fail to meet WHO standards for insecticide-treated nets (ITNs) and long-lasting insecticidal nets (LLINs). *0.5 mm mesh opening* - This mesh size would be **unnecessarily fine** and would significantly restrict airflow, creating a hot and uncomfortable sleeping environment. - The **reduced ventilation** would decrease user compliance and acceptance, undermining the public health benefit. - It is not required for blocking standard mosquito species and would increase manufacturing costs without additional benefit. *3.0 mm mesh opening* - A mesh opening of **3.0 mm is far too large** to provide adequate protection against mosquitoes. - This would allow **easy passage of most mosquito species**, rendering the net essentially ineffective as a barrier. - Such nets would not meet any international standards for vector control and disease prevention.

Q: Which of the following is the most defining characteristic of Kyasanur Forest disease (KFD)?

It is zoonosis. ***It is zoonosis*** - **Kyasanur Forest disease (KFD)** is primarily a **zoonotic disease**, meaning it is transmitted from animals to humans. - The disease cycle involves forest animals, particularly **monkeys**, and is transmitted to humans through the bite of infected ticks. *Affects monkeys* - While **monkeys** are indeed affected by KFD and serve as an important amplifying host, this is a part of its zoonotic nature rather than the most defining characteristic itself. - The disease is devastating for monkey populations, but the broader concept of **zoonosis** more accurately defines its transmission to humans. *Caused by rickettsia* - KFD is caused by the **Kyasanur Forest disease virus (KFDV)**, which is a **flavivirus**, not a rickettsial organism. - **Rickettsial diseases** are caused by bacteria, and they are distinct from viral infections like KFD. *Caused by bacteria* - **Kyasanur Forest disease** is caused by a **virus (KFDV)**, belonging to the Flaviviridae family, not by bacteria. - Bacterial diseases and viral diseases have different etiologies, treatments, and often different clinical presentations.

Q: Chandler's index is used for -

Hookworm infestation. ***Hookworm infestation*** - **Chandler's index** is a measure used to assess the endemicity or prevalence of **hookworm infection** in a community. - It specifically calculates the average number of **hookworms per host** to estimate the severity of the infestation. *Malaria* - **Malaria** prevalence and incidence are assessed using parameters like **parasite rate**, **splenic index**, or **annual parasite index (API)**. - No specific index called Chandler's index is used for malaria. *Roundworm* - **Roundworm** (Ascaris lumbricoides) infestation is typically measured by prevalence or **intensity of infection** (e.g., eggs per gram of feces). - Chandler's index is not used for **ascariasis**. *Filaria* - **Filariasis** is assessed through microfilaremia rates, **antigen detection tests**, or clinical manifestations like **lymphoedema** and **hydrocele**. - **Chandler's index** is not a relevant measure in the context of filarial infections.

Q: Modes of disease transmission by vectors include all except?

Ingestion. ***Ingestion*** - While **ingestion** can be a mode of disease acquisition (e.g., contaminated food/water), it is not a direct mode of **disease transmission by a vector**. - Vectors primarily transmit pathogens through other mechanisms, such as biting or depositing infectious material. *Regurgitation* - This is a common mode of **vector-borne transmission** where the vector, often an insect, regurgitates partially digested blood containing pathogens during a subsequent meal. - Examples include the transmission of **Leishmania** by sandflies. *Rubbing of infected excrement* - This mode involves a vector depositing **infected feces** on the host's skin, which can then be rubbed into a bite wound or mucous membranes. - An example is the transmission of **Trypanosoma cruzi** (Chagas disease) by triatomine bugs. *Biting* - **Biting** is the most direct and common mode of vector-borne transmission, where the vector injects pathogens into the host's bloodstream during feeding. - This includes diseases like **malaria** (mosquitoes), **dengue** (mosquitoes), and **Lyme disease** (ticks).

Q: In Japanese encephalitis, which of the basic cycles of transmission mentioned below is not true-

Man-mosquito-man. ***Man-mosquito-man*** - Japanese encephalitis is a **zoonotic disease**, meaning humans are considered **dead-end hosts**. - While humans can be infected, the viral load in their blood is generally too low to infect mosquitoes, thus **this transmission cycle does not occur**. - This is the cycle that is **NOT true** for Japanese encephalitis. *Bird-mosquito-bird* - Wild birds, particularly wading birds like herons and egrets, are important **amplifying hosts** for Japanese encephalitis virus (JEV). - This cycle helps maintain the virus in nature, with mosquitoes (*Culex* species) transmitting the virus between birds. - This is a **true transmission cycle**. *Cattle-mosquito-cattle* - Cattle can be infected with JEV and can serve as hosts, though they are generally considered **less efficient amplifying hosts** compared to pigs. - While this cycle exists, it plays a **minor role** in maintaining the virus compared to the pig-mosquito-pig cycle. - This is a **true but less significant transmission cycle**. *Pig-mosquito-pig* - Pigs are the **most important amplifying hosts** for JEV, especially in endemic areas. - Mosquitoes, particularly *Culex tritaeniorhynchus*, frequently feed on pigs and readily become infected, producing high viremia that efficiently transmits the virus between pigs. - This cycle significantly contributes to human outbreaks and is the **primary transmission cycle**.

Q: Which of the following drugs are supplied free of cost to the government Hospital by NACO?

Zidovudine + Lamivudine + Nevirapine. ***Zidovudine + Lamivudine + Nevirapine*** - This combination represents the **first-line antiretroviral therapy (ART)** typically supplied by NACO (National AIDS Control Organization) for the free distribution to government hospitals. - Providing a **triple drug regimen** is crucial for effective viral suppression and preventing drug resistance in HIV-infected individuals [1].*Zidovudine* - While **Zidovudine** is an important antiretroviral drug, it is usually administered as part of a **combination therapy**, not as a single drug for initial treatment due to the risk of resistance. - NACO's strategy focuses on providing regimens for **optimal patient outcomes**, which involves multiple drugs.*Nevirapine + Zidovudine* - Although this is a **combination**, a complete first-line regimen typically includes three drugs from different classes to maximize efficacy and prevent resistance, such as the addition of **Lamivudine**. - A two-drug regimen would be **suboptimal** for initial treatment according to current ART guidelines.*Nevirapine* - **Nevirapine** is an antiretroviral drug, but like Zidovudine, it is part of a **combination therapy**. - Administering it as a single agent would lead to **rapid development of drug resistance**, rendering the treatment ineffective [1].

Q: Aedes transmit all except

West Nile fever. ***West Nile fever*** - **West Nile fever** is primarily transmitted by **Culex mosquitoes**, not Aedes mosquitoes. - While Aedes mosquitoes can be minor vectors in some situations, the main vector for West Nile virus is the **Culex** genus. *Rift Valley fever* - **Rift Valley fever** can be transmitted by several mosquito species, including those from the **Aedes** genus, particularly in epidemic settings. - It is a **zoonotic disease** that can also infect humans through contact with infected animal tissues or fluids. *Dengue* - **Dengue fever** is famously transmitted by **Aedes aegypti** and **Aedes albopictus** mosquitoes. - These mosquitoes are prevalent in tropical and subtropical regions worldwide, leading to millions of cases annually. *Yellow fever* - **Yellow fever** is primarily transmitted by the **Aedes aegypti** mosquito in urban areas and by other Aedes species in jungle environments. - It is a serious viral hemorrhagic disease endemic in parts of Africa and South America.

Q: Most efficient anti-larval measure to prevent urban malaria is:

Cover overhead tank. ***Cover overhead tank*** - **Overhead tanks** are common breeding grounds for **Anopheles stephensi**, the primary vector for **urban malaria**. Covering them prevents mosquitoes from laying eggs. - This measure directly targets the **larval stage** of the mosquito, effectively reducing the mosquito population. *Clean drainage and sewage system* - While important for general sanitation and preventing other diseases, **drainage and sewage systems** are less significant breeding sites for the specific mosquito species causing urban malaria than overhead tanks. - **Anopheles stephensi** prefers clean water collections, not typically polluted drainage. *Cover pits* - Covering pits is a good measure to reduce mosquito breeding in general, but **pits** are not the most common or impactful breeding sites for the primary urban malaria vector. - This method may address some potential breeding spots but not the most efficient in the context of urban malaria. *Filling cesspools and ditches* - **Cesspools and ditches** often contain stagnant, sometimes contaminated, water, which is not the preferred breeding environment for **Anopheles stephensi**. - While beneficial for controlling other mosquito species and improving hygiene, it is not the most efficient anti-larval measure specifically against urban malaria.

Q: In malarial eradication programme, the basis of using insecticide is to reduce lifespan of mosquito by less than:

10 days. ***10 days*** - The **extrinsic incubation period** for malaria parasites (*Plasmodium* species) in *Anopheles* mosquitoes is typically **10-14 days** (varying by species and temperature). - By reducing mosquito lifespan to **less than 10 days**, insecticides prevent the parasite from completing its development cycle and becoming infectious. - This is the **critical threshold** used in malaria eradication programs to break the transmission cycle. *6 days* - While this would prevent parasite development, 6 days is **not the established threshold** used in malaria control programs. - The target is specifically less than 10 days based on the minimum extrinsic incubation period. *3 days* - This duration is far **below the critical threshold** and is not the basis for insecticide use in eradication programs. - While it would prevent transmission, it does not represent the scientifically established target. *1 day* - A 1-day lifespan is **unrealistically short** and not a practical or biologically relevant target for malaria control. - The established threshold based on parasite biology is 10 days, not 1 day.

Q: According to DOTS, what is the minimum number of positive samples required for TB diagnosis?

1 out of 2 samples positive. ***Correct: 1 out of 2 samples positive*** - Under the **current NTEP (National TB Elimination Program)** guidelines in India, for **sputum smear microscopy-based diagnosis**, **two sputum specimens** are collected (one spot specimen and one early morning specimen). - A patient is diagnosed as **smear-positive pulmonary TB** if **at least one of these two specimens shows acid-fast bacilli (AFB)** on microscopic examination. - This criterion aligns with **WHO recommendations** and represents the updated approach from the older "2 out of 3" criterion. - **Clinical and radiological correlation** is essential to support the diagnosis. *Incorrect: 2 out of 3 samples positive* - This was the **older criterion** under the classical RNTCP/DOTS strategy when three sputum samples were routinely collected. - Current guidelines have **simplified the process** to two specimens, making this option outdated. - Modern TB diagnosis emphasizes **rapid molecular tests (CBNAAT/TrueNat)** as first-line tools, with microscopy playing a supplementary role. *Incorrect: 3 out of 3 samples positive* - This is **overly stringent** and would lead to significant **under-diagnosis** of TB cases. - The **sensitivity of sputum microscopy** is limited (50-60% in many settings), and even true TB cases may not show AFB in all samples. - Such a criterion would delay treatment initiation and worsen patient outcomes. *Incorrect: None of the options* - This is incorrect as **"1 out of 2 samples positive"** is the correct criterion under current NTEP guidelines for smear microscopy-based TB diagnosis.

Question 1

What is the ideal mesh opening size for an effective mosquito net according to WHO standards?

Accepted Answer

1.2-1.7 mm mesh opening

Answer

0.5 mm mesh opening

Answer

3.0 mm mesh opening

Answer

2.5 mm mesh opening

Question 2

Which of the following is the most defining characteristic of Kyasanur Forest disease (KFD)?

Accepted Answer

It is zoonosis

Answer

Affects monkeys

Answer

Caused by rickettsia

Answer

Caused by bacteria

Question 3

Chandler's index is used for -

Accepted Answer

Hookworm infestation

Answer

Malaria

Answer

Roundworm

Answer

Filaria

Question 4

Modes of disease transmission by vectors include all except?

Accepted Answer

Ingestion

Answer

Regurgitation

Answer

Rubbing of infected excrement

Answer

Biting

Question 5

In Japanese encephalitis, which of the basic cycles of transmission mentioned below is not true-

Accepted Answer

Man-mosquito-man

Answer

Bird-mosquito-bird

Answer

Cattle-mosquito-cattle

Answer

Pig-mosquito-pig

Question 6

Which of the following drugs are supplied free of cost to the government Hospital by NACO?

Accepted Answer

Zidovudine + Lamivudine + Nevirapine

Answer

Zidovudine

Answer

Nevirapine + Zidovudine

Answer

Nevirapine

Question 7

Aedes transmit all except

Accepted Answer

West Nile fever

Answer

Rift Valley fever

Answer

Dengue

Answer

Yellow fever

Question 8

Most efficient anti-larval measure to prevent urban malaria is:

Accepted Answer

Cover overhead tank

Answer

Clean drainage and sewage system

Answer

Cover pits

Answer

Filling cesspools and ditches

Question 9

In malarial eradication programme, the basis of using insecticide is to reduce lifespan of mosquito by less than:

Accepted Answer

10 days

Answer

1 day

Answer

6 days

Answer

3 days

Question 10

According to DOTS, what is the minimum number of positive samples required for TB diagnosis?

Accepted Answer

1 out of 2 samples positive

Answer

2 out of 3 samples positive

Answer

3 out of 3 samples positive

Answer

None of the options

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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