Infectious Diseases Practice Questions

Q: If a claw hand develops in a patient with Leprosy, what is the classification of the deformity?

Grade II. A **claw hand** deformity, characterized by hyperextension of the metacarpophalangeal joints and flexion of the interphalangeal joints, indicates a significant and **visible disability** but the affected part is still functional to a limited degree. In the context of leprosy, this observable and permanent deformity falls under **Grade II** on the WHO disability grading scale, signifying a clear and established disability. This grade indicates **no disability** or deformity related to leprosy. A patient with a claw hand has an obvious physical deformity and functional impairment, thus not fitting this classification. This grade refers to a **detectable impairment** but **no visible deformity**. A claw hand is a clearly visible deformity, making Grade I an inappropriate classification. While Grades are typically 0, I, and II in the WHO disability grading for leprosy, some classifications might refer to severe, non-functional deformities as higher grades. However, Grade II adequately captures **visible and significant deformities** like a claw hand, and a Grade III is not a standard or commonly used classification for a claw hand in leprosy in the WHO system.

Q: What is the primary electrolyte found in Oral Rehydration Salts (ORS) at a concentration of 75 mEq/L?

Sodium. ***Sodium*** - The primary electrolyte in **Oral Rehydration Salts (ORS)** is **sodium**, which is crucial for replacing losses due to diarrhea and facilitating water absorption in the intestines [1]. - The standard ORS formulation, recommended by the WHO, contains **75 mEq/L of sodium** to effectively rehydrate individuals with acute watery diarrhea [1]. *Potassium* - While **potassium** is an essential electrolyte found in ORS, its concentration is typically lower than sodium, usually around **20 mEq/L**. - Potassium helps replenish intracellular losses and supports normal cellular function, but it is not the primary electrolyte at the 75 mEq/L concentration. *Glucose* - **Glucose** is a crucial component of ORS, but it is a sugar, not an electrolyte. - Its role is to facilitate the co-transport of **sodium and water** across the intestinal wall, enhancing fluid absorption, but it does not contribute to the electrolyte concentration in mEq/L [1]. *Chloride* - **Chloride** is an electrolyte present in ORS, primarily to balance the charge of **sodium** and prevent hyynatremia. - Its concentration is typically around **65 mEq/L**, making it slightly less concentrated than sodium but still vital for maintaining electrolyte balance.

Q: What is the recommended amount of bleaching powder necessary to disinfect stools contaminated with cholera?

50 gm/liter. ***50 gm/liter*** - For effective disinfection of stools contaminated with cholera, a concentration of **50 gm of bleaching powder per liter** of stool is recommended to ensure the destruction of **Vibrio cholerae**. - This concentration typically provides a sufficient amount of available **chlorine** to inactivate the bacteria within a reasonable contact time. *75 gm/liter* - While this concentration would certainly disinfect, it is **higher than necessary** for routine cholera stool disinfection and leads to inefficient resource use. - Using excess bleaching powder can also create a **stronger odor** and possibly increase the risk of skin or respiratory irritation. *90 gm/liter* - This concentration is **excessive** and not the standard recommendation for cholera stool disinfection. - Higher concentrations contribute to **waste of resources** and do not offer significantly improved efficacy over the recommended dose for this specific application. *100 gm/liter* - This concentration is significantly **higher than required** for effective disinfection of cholera-contaminated stools. - Using such a high amount is **economically inefficient** and offers no additional benefit in terms of disinfection for this specific pathogen and application.

Q: Transovarian transmission is seen in which of the following infections?

Yellow fever. ***Yellow fever*** - **Transovarian transmission** refers to the passage of a pathogen from an adult female arthropod (like a mosquito) to her offspring via the eggs. This mechanism allows the virus to persist in the **vector population** even in the absence of infected vertebrate hosts. - **Yellow fever virus** is known to undergo transovarian transmission in its mosquito vectors, particularly *Aedes aegypti* and other *Aedes* species. *Plague* - Plague is caused by the bacterium *Yersinia pestis* and is primarily transmitted by **flea bites** from infected rodents to humans. - It does not involve transovarian transmission; the fleas acquire the bacteria during a **blood meal** from an infected host. *Ebola fever* - Ebola virus is transmitted through **direct contact** with blood or bodily fluids of infected humans or animals. - It is not an **arthropod-borne disease** and therefore does not exhibit transovarian transmission. *None of the options* - This option is incorrect because **Yellow Fever** clearly demonstrates transovarian transmission within its mosquito vector.

Q: Which vector is MOST commonly associated with transovarial transmission in diseases like Kyasanur Forest Disease and Crimean-Congo Hemorrhagic Fever?

Ticks. ***Ticks*** - Ticks are the primary **vectors** for transmitting **Kyasanur Forest Disease** (KFD virus) and **Crimean-Congo Hemorrhagic Fever** (CCHF virus), both relevant to India. - **Transovarial transmission** is a key mechanism where pathogens are passed from an infected female tick to her offspring via eggs, perpetuating the disease cycle within tick populations. - KFD is endemic to **Karnataka** (Western Ghats), while CCHF has been reported from various parts of India including Gujarat, Rajasthan, and Uttar Pradesh. *Mosquitoes* - Mosquitoes are known vectors for diseases like **malaria**, **dengue fever**, and **chikungunya**, but not for KFD or CCHF. - They primarily transmit pathogens through **salivary injection** during blood feeding, not typically via transovarial transmission for these specific tick-borne illnesses. *Fleas* - Fleas are vectors for diseases such as the **plague** (Yersinia pestis) and **murine typhus** (Rickettsia typhi). - They do not transmit KFD or CCHF, and their mode of transmission is typically through flea bites rather than transovarial mechanisms for these conditions. *Mites* - Mites can cause various skin conditions (e.g., **scabies**) and transmit **scrub typhus** (Orientia tsutsugamushi), which is relevant in India. - However, they are not associated with the transmission of KFD or CCHF.

Q: The primary reservoir for leptospirosis transmission is:

Rat. ***Correct Answer: Rat*** - **Rats** (and other rodents) are considered the primary natural reservoir for *Leptospira* bacteria worldwide and are **asymptomatic carriers**. - They excrete the bacteria in their urine, contaminating water and soil, which serves as the main source of human infection. *Incorrect: Cat* - While cats can become infected with *Leptospira*, they are **not typically considered significant reservoirs** for human transmission. - Their role in the epidemiologic cycle of leptospirosis is generally minor compared to rodents and some other mammals. *Incorrect: Dog* - **Dogs** can contract leptospirosis and excrete the bacteria in their urine, posing a risk to humans, but they are generally considered **incidental hosts or secondary reservoirs**, not the primary one. - Vaccination in dogs helps reduce their role in transmission. *Incorrect: Fish* - **Fish are not known to be reservoirs** for *Leptospira* bacteria. - Leptospirosis is primarily transmitted through contact with infected animal urine, not aquatic life like fish.

Q: Schistosomiasis is an example of which type of zoonosis that requires an intermediate host?

Meta-zoonoses. ***Meta-zoonoses*** - **Meta-zoonoses** are defined as zoonotic diseases that require an **intermediate invertebrate host** for the completion of the parasite's life cycle. - **Schistosomiasis** fits this definition as it involves fresh water snails acting as an intermediate host, where the parasite undergoes essential developmental stages. *Cyclo-zoonoses* - **Cyclo-zoonoses** require **more than one vertebrate host species** but no invertebrate host for the completion of the infectious agent's life cycle. - An example would be **Taeniasis**, which involves humans and cattle or pigs, but not an invertebrate. *Direct-zoonoses* - **Direct-zoonoses** are transmitted directly from an **infected vertebrate host to a susceptible vertebrate host** without the need for an intermediate host or vector. - Examples include **rabies** or **brucellosis**, which are passed directly from animals to humans. *Sporo-zoonoses* - **Sporo-zoonoses** are zoonoses where the infectious agent undergoes **sporogonic development in an invertebrate host**, but this term is not a standard or widely recognized category in the same way as direct, cyclo-, or meta-zoonoses. - The more appropriate term for diseases involving an invertebrate intermediate host is **meta-zoonoses**.

Q: Which disease is associated with a propagative cycle?

Filaria. ***Filaria*** - The **filarial worm** undergoes a **biological transmission cycle** in the mosquito vector where microfilariae develop through larval stages (L1 → L2 → L3) with multiplication. - This represents a **cyclopropagative cycle** (both development and multiplication occur in the vector). - In the context of this question and classical teaching, filaria is considered the standard example of biological transmission with vector multiplication. - The infective L3 larvae multiply from a single microfilaria, and multiple larvae can develop within one mosquito. *Plague* - **Plague** (*Yersinia pestis*) is transmitted by fleas through **mechanical transmission**. - Bacteria multiply in the flea's gut causing blockage (blocking transmission), but this is not considered a true biological cycle. - The pathogen does not undergo developmental stages in the vector. *Malaria* - **Malaria** (*Plasmodium* spp.) undergoes the **sporogonic cycle** in the mosquito, which is also a **cyclopropagative cycle**. - Gametocytes → ookinete → oocyst → sporozoites (development with multiplication). - While biologically similar to filaria, in classical epidemiology teaching, filaria is more commonly cited as the example for propagative transmission. *None of the options* - This option is incorrect as filaria demonstrates biological transmission with multiplication in the vector. - Both filaria and malaria technically undergo cyclopropagative cycles, but filaria is the conventional answer in medical education contexts.

Q: Which of the following diseases does not have a chronic carrier state?

Tetanus. ***Tetanus*** - Tetanus is caused by the toxin produced by *Clostridium tetani*, which is an **environmental bacterium** found in soil and does not establish a persistent infection within humans. - Humans are merely **accidental hosts** for this bacterium, meaning there is **no chronic carrier state** where an infected individual continuously harbors and transmits the pathogen. - The disease occurs through wound contamination with spores, not human-to-human transmission. *Measles* - Measles is an **acute viral infection** with no chronic carrier state in the classical sense. - After acute infection, the virus is cleared from the body in immunocompetent individuals. - While **subacute sclerosing panencephalitis (SSPE)** represents a rare persistent infection, this is **not a carrier state** as the virus is not transmissible from these individuals. - SSPE occurs years after initial infection but does not involve viral shedding or transmission. *Malaria* - Individuals infected with ***Plasmodium* parasites** can develop a **chronic carrier state**, particularly with *P. vivax* and *P. ovale*, which form hypnozoites in the liver. - These parasites can remain dormant and then reactivate, causing **relapses** and allowing for continued transmission to mosquitoes over extended periods. - Chronic asymptomatic carriers can serve as reservoirs for transmission in endemic areas. *Poliomyelitis* - Individuals infected with poliovirus can shed the virus in their stools for **several weeks to months** after infection. - In **immunodeficient individuals**, prolonged excretion can occur for years, creating chronic carriers. - This prolonged shedding allows for the **continued transmission** of the virus within a population.

Q: Which is the main vector of Dengue?

A. aegypti. ***A. aegypti*** - **Aedes aegypti** is the primary vector responsible for transmitting the **Dengue virus** to humans. - It is a **day-biting mosquito** found predominantly in tropical and subtropical regions. *Culex* - **Culex mosquitoes** are known vectors for diseases like **Japanese encephalitis**, **West Nile virus**, and **filariasis**. - They are generally **night-biting** and do not play a significant role in Dengue transmission. *Anopheles* - **Anopheles mosquitoes** are the primary vectors for **malaria** in humans. - They are not associated with the transmission of the Dengue virus. *Aedes scutellaris* - While part of the **Aedes genus**, **Aedes scutellaris** is a secondary vector for Dengue in the **Pacific region**. - The main vector for Dengue globally remains **Aedes aegypti**, followed by **Aedes albopictus** in some regions.

Question 1

If a claw hand develops in a patient with Leprosy, what is the classification of the deformity?

Accepted Answer

Grade II

Answer

Grade 0

Answer

Grade I

Answer

Grade III

Question 2

What is the primary electrolyte found in Oral Rehydration Salts (ORS) at a concentration of 75 mEq/L?

Accepted Answer

Sodium

Answer

Potassium

Answer

Glucose

Answer

Chloride

Question 3

What is the recommended amount of bleaching powder necessary to disinfect stools contaminated with cholera?

Accepted Answer

50 gm/liter

Answer

75 gm/liter

Answer

90 gm/liter

Answer

100 gm/liter

Question 4

Transovarian transmission is seen in which of the following infections?

Accepted Answer

Yellow fever

Answer

Plague

Answer

Ebola fever

Answer

None of the options

Question 5

Which vector is MOST commonly associated with transovarial transmission in diseases like Kyasanur Forest Disease and Crimean-Congo Hemorrhagic Fever?

Accepted Answer

Ticks

Answer

Mosquitoes

Answer

Fleas

Answer

Mites

Question 6

The primary reservoir for leptospirosis transmission is:

Accepted Answer

Rat

Answer

Cat

Answer

Dog

Answer

Fish

Question 7

Schistosomiasis is an example of which type of zoonosis that requires an intermediate host?

Accepted Answer

Meta-zoonoses

Answer

Cyclo-zoonoses

Answer

Direct-zoonoses

Answer

Sporo-zoonoses

Question 8

Which disease is associated with a propagative cycle?

Accepted Answer

Filaria

Answer

None of the options

Answer

Plague

Answer

Malaria

Question 9

Which of the following diseases does not have a chronic carrier state?

Accepted Answer

Tetanus

Answer

Malaria

Answer

Measles

Answer

Poliomyelitis

Question 10

Which is the main vector of Dengue?

Accepted Answer

A. aegypti

Answer

Culex

Answer

Anopheles

Answer

Aedes scutellaris

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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