Infectious Diseases Practice Questions

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: Following are examples of human "dead end" diseases except -

Bubonic plague. ***Bubonic plague (Plague)*** - The question refers to **plague in general**, which includes multiple clinical forms. - While **bubonic plague** (the most common form) is transmitted via **flea bites** from infected rodents and humans are typically dead-end hosts for this form, **pneumonic plague** (secondary complication or primary infection) allows **human-to-human transmission** via respiratory droplets. - This makes plague the **exception** among the listed diseases, as humans can serve as a source of infection to others in the pneumonic form, unlike true dead-end host situations. *Japanese encephalitis* - Humans are **dead-end hosts** for Japanese encephalitis virus. - Infected humans do not develop sufficient **viremia** to infect feeding mosquitoes. - The virus maintains its cycle between **Culex mosquitoes**, **pigs** (amplifying hosts), and **wading birds**, with humans being incidental hosts. *Hydatid disease* - Humans are **definitive dead-end hosts** for *Echinococcus granulosus* (causing cystic echinococcosis/hydatid disease). - The normal life cycle requires **definitive hosts** (dogs, canids) and **intermediate hosts** (sheep, cattle). - Humans develop **hydatid cysts** but cannot transmit the infection further as the parasite cannot complete its life cycle in humans. *Leishmaniasis* - In most forms of leishmaniasis, humans are considered **dead-end or accidental hosts**, particularly in **zoonotic cutaneous leishmaniasis** where animal reservoirs (rodents, dogs) maintain transmission. - However, in **anthroponotic visceral leishmaniasis** (*Leishmania donovani* in the Indian subcontinent), humans can serve as reservoir hosts. - For the purpose of this question, leishmaniasis is generally classified with dead-end diseases as the majority of leishmaniasis forms have zoonotic cycles where humans are incidental hosts with limited onward transmission.

Q: Which disease is classified as 'multibacillary'?

Leprosy. **Leprosy** - Leprosy, caused by *Mycobacterium leprae*, is classified by the **WHO** into **paucibacillary (PB)** and **multibacillary (MB)** forms based on bacterial load and number of skin lesions. - **Multibacillary leprosy** is defined as having more than 5 skin lesions with positive skin smears, requiring a longer treatment regimen (12 months of multidrug therapy with rifampicin, dapsone, and clofazimine). - This classification is specific to **leprosy** and is crucial for determining appropriate treatment duration and drug combinations. *Tuberculosis* - Tuberculosis is classified by **anatomical location** (pulmonary vs. extrapulmonary), **drug susceptibility** (drug-sensitive vs. drug-resistant), or **smear status** (smear-positive vs. smear-negative). - The term **'multibacillary'** is not used in TB classification, making this an incorrect option. *Trachoma* - Trachoma is a chronic **keratoconjunctivitis** caused by *Chlamydia trachomatis*, classified by **clinical stages** (TF, TI, TS, TT, CO) according to the WHO simplified grading system. - The paucibacillary/multibacillary classification does **not apply** to trachoma. *Tetanus* - Tetanus is a **toxin-mediated disease** caused by *Clostridium tetani*, manifesting as muscle spasms and lockjaw. - Classification is based on **clinical severity** (localized, generalized, cephalic, neonatal), not bacterial load, making the term 'multibacillary' inapplicable.

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: 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: Vector of scrub typhus in man?

Leptotrombidium deliense. ***Leptotrombidium deliense*** - This is the **chigger mite** species primarily responsible for transmitting **scrub typhus** to humans. - **Larval mites (chiggers)** of this species feed on human skin and transmit the bacterium *Orientia tsutsugamushi*. *O. tsutsugamushi* - This is the **causative agent** of scrub typhus, not the vector. - It is a **rickettsial bacterium** transmitted by infected chiggers. *Lice* - **Lice** (e.g., *Pediculus humanus corporis*) are vectors for diseases like **epidemic typhus** (caused by *Rickettsia prowazekii*) and **relapsing fever**, but not scrub typhus. - They are **blood-sucking insects** distinct from mites. *Pediculus humanus* - This refers to **human lice**, specifically *Pediculus humanus capitis* (head louse) or *Pediculus humanus corporis* (body louse). - As mentioned, lice transmit diseases like epidemic typhus, not **scrub typhus**.

Q: What is the most commonly reported bacterial sexually transmitted infection?

Chlamydia. ***Correct: Chlamydia*** - **Chlamydia trachomatis** is the most frequently reported bacterial STI in many countries, often being **asymptomatic** and thus easily spread - Its high prevalence is due to efficient transmission and the widespread use of sensitive diagnostic tests that detect infections in asymptomatic individuals - Accounts for the majority of reported bacterial STI cases globally *Incorrect: HSV* - **Herpes Simplex Virus (HSV)** is a **viral STI**, not bacterial, and is characterized by recurrent outbreaks of **genital ulcers** or sores - While common, it does not qualify as a bacterial infection and is often not laboratory-confirmed due to mild or subclinical presentations *Incorrect: HIV* - **Human Immunodeficiency Virus (HIV)** is also a **viral STI**, not bacterial, that attacks the immune system leading to AIDS - Although highly impactful, HIV is not a bacterial infection and has lower incidence rates compared to Chlamydia *Incorrect: Syphilis* - **Syphilis**, caused by the bacterium **Treponema pallidum**, is a serious bacterial STI that can have long-term complications if untreated - While its incidence has been increasing in some regions, it is significantly less common than **Chlamydia** in terms of overall reported cases

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: 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: 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

Which disease is associated with a propagative cycle?

Accepted Answer

Filaria

Answer

None of the options

Answer

Plague

Answer

Malaria

Question 2

Following are examples of human "dead end" diseases except -

Accepted Answer

Bubonic plague

Answer

Hydatid disease

Answer

Japanese encephalitis

Answer

Leishmaniasis

Question 3

Which disease is classified as 'multibacillary'?

Accepted Answer

Leprosy

Answer

Tuberculosis

Answer

Trachoma

Answer

Tetanus

Question 4

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 5

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

Accepted Answer

Tetanus

Answer

Malaria

Answer

Measles

Answer

Poliomyelitis

Question 6

Vector of scrub typhus in man?

Accepted Answer

Leptotrombidium deliense

Answer

O. tsutsugamushi

Answer

Lice

Answer

Pediculus humanus

Question 7

What is the most commonly reported bacterial sexually transmitted infection?

Accepted Answer

Chlamydia

Answer

HSV

Answer

HIV

Answer

Syphilis

Question 8

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 9

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 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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