Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 421: Rat flea transmits:

A. Lassa fever
B. Trachoma
C. Endemic typhus (Correct Answer)
D. Rabies

Explanation: ***Endemic typhus*** - **Endemic typhus**, also known as **murine typhus**, is transmitted by the **rat flea (Xenopsylla cheopis)**, which carries the bacterium **Rickettsia typhi**. - The flea bites humans after feeding on infected rats, transmitting the bacteria. *Lassa fever* - **Lassa fever** is a **viral hemorrhagic fever** transmitted to humans primarily through contact with food or household items contaminated with urine or feces of **infected multimammate rats**. - It is not transmitted by fleas. *Trachoma* - **Trachoma** is a chronic infectious eye disease caused by the bacterium **Chlamydia trachomatis**. - It is transmitted through direct or indirect contact with eye and nose discharge of infected individuals, often via **flies (Musca sorbens)** that land on the eyes. *Rabies* - **Rabies** is a **viral disease** that is transmitted to humans through the saliva of infected animals, most commonly via a **bite** from an infected mammal such as a **dog, bat, or fox**. - It is not transmitted by fleas.

Question 422: All of the following are true about measles except?

A. I.P. = 7-14 days
B. Best age for immunization is 9-12 months
C. Maximum incidence in 6m-3 year age group
D. Secondary attack rate is 30% (Correct Answer)

Explanation: ***Secondary attack rate is 30%*** - The **secondary attack rate** for measles is extremely high, typically around **90%** in susceptible household contacts, making it one of the most contagious infectious diseases. - A rate of 30% would imply a much lower transmissibility than what is characteristically observed for measles. *I.P. = 7-14 days* - The **incubation period (I.P.)** for measles is typically 7-14 days from exposure to the onset of fever. - This is a well-established and accurate timeframe for the disease. *Best age for immunization is 9-12 months* - The **first dose** of the measles-mumps-rubella (MMR) vaccine is generally recommended between **9-12 months** of age in many parts of the world, especially in endemic areas, to provide early protection. - This timing balances the waning of maternal antibodies with the need for effective immunization. *Maximum incidence in 6m-3 year age group* - In areas with lower vaccination coverage, measles incidence is indeed highest in **preschool-aged children**, particularly those between 6 months and 3 years, as maternal antibodies wane and they become more exposed. - This age group is highly susceptible due to their developing immune systems and social interactions.

Question 423: Vertical transmission of pathogens from parent vector to offspring vector is called:

A. Mechanical transmission
B. Transovarian (Correct Answer)
C. Cyclodevelopmental transmission
D. Propagative transmission

Explanation: ***Transovarian*** - **Transovarian transmission** refers to the passage of a pathogen from an infected adult female vector directly into her offspring, often via the ova. - This mode of transmission ensures disease persistence in subsequent generations of vectors without requiring re-infection from an external host. *Mechanical transmission* - **Mechanical transmission** involves a pathogen being carried on the exterior of a vector (e.g., on legs or proboscis) from an infected host to a susceptible one, without replication or development within the vector. - The vector serves as a "flying syringe" or a simple carrier, not allowing for biological multiplication or development of the pathogen. *Cyclodevelopmental transmission* - In **cyclodevelopmental transmission**, the pathogen undergoes both developmental changes and multiplication within the vector. - An example is **filarial worms** in mosquitoes, where the parasite develops into the infective stage and also multiplies in the vector. *Propagative transmission* - **Propagative transmission** involves the pathogen multiplying within the vector but not undergoing any significant developmental changes. - A classic example is the **Arbovirus** replication within mosquitoes, where the virus replicates to high titers in the vector's tissues.

Question 424: Intensified malaria control under the national framework for malaria elimination is defined as:

A. No longer a health problem
B. Zero incidence of malaria
C. States with API >=1 (Correct Answer)
D. 3 consecutive years no local transmission in the state

Explanation: ***States with API >=1*** - Intensified malaria control under a national elimination framework targets regions with an **Annual Parasite Index (API) of 1 or greater**, indicating a significant burden of malaria requiring focused intervention. - This threshold helps prioritize resources and strategies to areas where malaria transmission is still active and potentially high, moving towards reduction and eventual elimination. *No longer a health problem* - This definition would classify an area as having achieved **malaria elimination**, which is a far more advanced stage than intensified control. - Intensified control is implemented when malaria is still a health problem, albeit one that is being actively managed to reduce its impact. *Zero incidence of malaria* - Zero incidence signifies **complete interruption of local malaria transmission**, meaning no new cases are occurring locally. - While the ultimate goal, intensified control aims to *reduce* incidence significantly, not necessarily achieve zero incidence immediately. *3 consecutive years no local transmission in the state* - This criterion typically defines **malaria elimination**, not intensified control. - Elimination is declared when there has been no local transmission for a sustained period, indicating a successful control program has halted the disease.

Question 425: Which of the following is the LEAST important step in the national TB control program?

A. Treatment of sputum positive cases
B. BCG vaccination (Correct Answer)
C. Isolation of sputum positive cases
D. Treatment of contacts

Explanation: ***BCG vaccination*** - While BCG vaccination offers some protection against severe forms of TB, particularly in children, it has **limited efficacy** against adult pulmonary TB, which is the primary driver of transmission. - The national TB control program's main focus is on **interrupting transmission** by identifying and effectively treating infectious cases. *Treatment of sputum positive cases* - This is a cornerstone of TB control because **sputum-positive cases** are the primary source of airborne transmission. - Effective treatment rapidly renders patients **non-infectious**, preventing further spread of the disease within the community. *Isolation of sputum positive cases* - **Isolation** of highly infectious individuals helps to prevent the immediate spread of *Mycobacterium tuberculosis* to others in close contact. - This is a crucial **infection control measure**, especially in healthcare settings and within households. *Treatment of contacts* - Treating contacts, especially those with **latent TB infection (LTBI)** or who are at high risk of progression to active disease (e.g., immunocompromised individuals), is vital for preventing the development of new active cases. - This strategy targets the **prevention of future active disease** in individuals already exposed to the bacterium.

Question 426: True statement about Japanese Encephalitis is:

A. No vaccine for JE
B. Cross reacts with Dengue virus
C. Mortality less than 10%.
D. Pigs are amplifier hosts (Correct Answer)

Explanation: ***Pigs are amplifier hosts*** - **Pigs** serve as the primary **amplifier hosts** for the Japanese Encephalitis virus, increasing the viral load in the environment and facilitating transmission to mosquitoes. - This amplification is crucial in the **epidemiology** of Japanese Encephalitis, as pigs sustain the transmission cycle between mosquitoes and maintain high viral loads. - This is the **most definitive and unique** characteristic statement about JE epidemiology. *No vaccine for JE* - This statement is incorrect; there are **effective vaccines available** for Japanese Encephalitis, recommended for travelers to endemic areas and high-risk populations. - Examples include inactivated vaccines (Ixiaro) and live-attenuated vaccines (SA 14-14-2, widely used in India's Universal Immunization Programme). *Cross reacts with Dengue virus* - While this statement is technically true, both Japanese Encephalitis virus (JEV) and Dengue virus (DENV) are **flaviviruses** and share common epitopes causing **serological cross-reactivity** in IgM/IgG tests. - However, this cross-reactivity is a **diagnostic challenge** rather than a defining epidemiological feature of JE itself. - This cross-reactivity is a property shared by multiple flaviviruses (including Zika, Yellow Fever, West Nile), making it less specific to JE. *Mortality less than 10%* - This statement is incorrect. The **case fatality rate** for symptomatic Japanese Encephalitis is significant, typically ranging from **20% to 30%**. - Even among survivors, severe neurological or psychiatric sequelae are common, affecting 30-50% of patients.

Question 427: Best strategy for leprosy eradication programme is

A. Early diagnosis and treatment (Correct Answer)
B. Mass chemotherapy
C. High risk chemotherapy
D. Health education

Explanation: ***Early diagnosis and treatment*** - **Early detection** of leprosy cases and prompt initiation of **multidrug therapy (MDT)** is the cornerstone of leprosy control and eradication programs. - This approach stops transmission by rendering patients non-infectious quickly, preventing further spread of the disease and reducing the incidence of disability. *Mass chemotherapy* - **Mass chemotherapy** involves treating a large population indiscriminately, which is generally not efficient or sustainable for leprosy control. - It could lead to **drug resistance** and unnecessary side effects in individuals who are not infected. *High risk chemotherapy* - **High-risk chemotherapy** typically targets specific populations with known high exposure or vulnerability, which might be a component of control but not the *best* overall strategy for eradication. - It might miss undetected cases outside the defined "high-risk" groups, allowing continued transmission. *Health education* - **Health education** is crucial for increasing awareness, reducing stigma, and promoting early presentation, but by itself, it cannot *control* or *eradicate* the disease. - It is a supportive measure that enhances the effectiveness of medical interventions by encouraging community participation and compliance with treatment.

Question 428: All are included in acute flaccid paralysis surveillance, except -

A. Transient weakness (Correct Answer)
B. Age
C. No cause
D. Tone

Explanation: ***Transient weakness*** - **Surveillance for acute flaccid paralysis (AFP)** focuses on persistent flaccid weakness, not temporary or transient weakness. The goal is to identify and investigate cases that could be **poliomyelitis** or other serious neurological conditions causing lasting paralysis. - While transient weakness might be a symptom in some conditions, it is not a criterion for inclusion in standard AFP surveillance, which specifically looks for **acute onset** and progressive or sustained flaccidity. *Age* - **Age** is a crucial component of AFP surveillance, particularly because poliomyelitis primarily affects **children under 15 years old**. Surveillance systems often target this age group to maximize the chances of detecting polio cases. - Data on the age of affected individuals is used to track epidemiological patterns and assess the effectiveness of **vaccination programs**. *No cause* - Cases where **no cause** is immediately apparent are specifically included in AFP surveillance to ensure that all potential cases of **poliomyelitis** are investigated. This is particularly important in regions working towards polio eradication. - Investigating cases with no obvious cause helps to rule out polio and identify other **etiologies of flaccid paralysis**, contributing to a broader understanding of neurological diseases. *Tone* - The assessment of **muscle tone** is fundamental to defining flaccid paralysis. **Reduced or absent muscle tone (flaccidity)** is a defining characteristic of AFP. - **Tone** helps differentiate AFP from other forms of paralysis (e.g., spastic paralysis) and guides the diagnostic workup for conditions like **Guillain-Barré Syndrome** or poliomyelitis.

Question 429: Which is not used in ORS:

A. Glucose with salt
B. Glucose without salt (Correct Answer)
C. Na+
D. All of the options

Explanation: ***Glucose without salt*** - **Oral Rehydration Solution (ORS)** formulations specifically include both **glucose and salts (electrolytes)**, as the sodium-glucose co-transport mechanism is crucial for optimal water and electrolyte absorption in the gut. - Using glucose alone without salts would be far less effective for rehydration and replenishing electrolyte losses during conditions like diarrhea. *Glucose with salt* - This combination is the **fundamental basis** of ORS, as **glucose facilitates sodium absorption** and, by extension, water absorption, into the body. - The presence of both glucose and various salts (like sodium chloride, potassium chloride, and sodium citrate) is essential for the efficacy of ORS in **rehydrating and correcting electrolyte imbalances**. *Na+* - **Sodium (Na+)** is a critical electrolyte included in ORS to replace losses and is vital for maintaining fluid balance and various physiological functions. - The correct balance of sodium, along with glucose, is essential for the **co-transport mechanism** that drives water absorption in the intestines. *All of the options* - This option is incorrect because both **glucose with salt (the combination)** and **Na+** are integral components of a standard ORS formulation. - The specific exclusion stated in the question (glucose without salt) is the feature that is *not* used in ORS.

Question 430: Which microorganism is considered the MOST significant agent for use as a weapon in biological terrorism?

A. Smallpox (Correct Answer)
B. Influenza
C. Ebola
D. Rabies

Explanation: ***Smallpox*** - **Smallpox** is considered a high-priority biological weapon agent due to its **high infectivity**, person-to-person transmission, and high mortality rate. - The discontinuation of global vaccination has led to a population with **minimal immunity**, making it a potent bioweapon. *Influenza* - While influenza viruses are highly transmissible and can cause significant illness, their **mortality rate is generally lower** than agents specifically chosen for biological warfare. - Widespread immunity from natural exposure and annual vaccination campaigns limits its effectiveness as a primary bioweapon. *Ebola* - **Ebola virus** causes severe hemorrhagic fever with a high fatality rate but is typically **less easily transmitted** than agents like smallpox through airborne routes. - Its outbreaks are usually localized, and containment measures are effective in preventing widespread pandemic spread, making it less ideal for mass casualty scenarios compared to smallpox. *Rabies* - **Rabies virus** is transmitted primarily through the bite of an infected animal and is **not easily spread from person to person**. - Its **incubation period is long**, and post-exposure prophylaxis is highly effective, making it an impractical agent for widespread biological terrorism.

Practice by Chapter

Communicable Disease Control Principles

Practice Questions

Vector-Borne Diseases

Practice Questions

Water-Borne Diseases

Practice Questions

Air-Borne Diseases

Practice Questions

Zoonotic Diseases

Practice Questions

Sexually Transmitted Infections

Practice Questions

HIV/AIDS Control Program

Practice Questions

Tuberculosis Control

Practice Questions

Leprosy Elimination

Practice Questions

Emerging and Re-emerging Infections

Practice Questions

Hospital-Acquired Infections

Practice Questions

Integrated Disease Surveillance Project

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free