Infectious Diseases Practice Questions

Q: What is the annual infection rate of tuberculosis?

Percentage of new patients positive for tuberculin test. ***Percentage of new patients positive for tuberculin test*** - The **annual infection rate of tuberculosis (AIRT)** is defined as the percentage of individuals (typically children aged 1-9 years) who show **tuberculin conversion** (from negative to positive) in a given year. - Among the given options, this is the **closest representation** as it focuses on **newly infected individuals** rather than prevalent cases. - AIRT is a key epidemiological indicator reflecting **ongoing transmission** and the **annual risk of tuberculous infection** in a community. - This measure helps assess TB control program effectiveness and disease burden. *Percentage of total patients positive for tuberculin test* - This represents the **prevalence of tuberculosis infection** in the population, including both old and new infections. - It does not specifically measure the **annual rate of acquiring new infections**, which is what AIRT captures. *Percentage of sputum positive total patients* - This indicates the **prevalence of active, infectious pulmonary tuberculosis** in a population. - It refers to individuals with **active TB disease** who are shedding bacteria in sputum, not latent infection detected by tuberculin testing. *Percentage of sputum positive new patients* - This represents the **incidence of new, active, infectious tuberculosis cases** (case detection rate). - While important for TB surveillance, it measures **active disease** rather than **infection rate** detected by tuberculin skin test.

Q: In which condition is a night blood survey performed?

Lymphatic filariasis. ***Lymphatic filariasis*** - A **night blood survey** is crucial for diagnosing lymphatic filariasis because the microfilariae of species like *Wuchereria bancrofti* and *Brugia malayi* exhibit **nocturnal periodicity**, meaning they are most abundant in peripheral blood between 10 PM and 2 AM. - Collecting blood at night maximizes the chance of detecting these parasites, which are responsible for the disease. *Typhoid fever* - Diagnosis of **typhoid fever** primarily relies on **blood cultures** taken during the febrile phase, or stool/urine cultures later in the disease. - A night blood survey is not relevant for detecting the causative bacterium, *Salmonella Typhi*. *Malaria infection* - While a **blood smear** is essential for diagnosing malaria, the timing of blood collection is less critical than for filariasis, although peak parasite density can vary. - **Malaria parasites** are typically detected in blood samples taken during symptomatic periods, regardless of specific time of day. *Visceral leishmaniasis* - **Visceral leishmaniasis** is diagnosed by detecting parasites in samples from **bone marrow**, spleen, or lymph nodes, or through serological tests for antibodies. - A night blood survey is not used in the diagnosis of *Leishmania donovani* infection.

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: Which of the following diseases is NOT transmitted by sandflies?

Relapsing fever. ***Relapsing fever*** - **Relapsing fever** is primarily transmitted by **ticks** (tick-borne relapsing fever) or **lice** (louse-borne relapsing fever), not sandflies. - It is caused by **spirochetes** of the genus *Borrelia*, which are distinct from the *Leishmania* parasites transmitted by sandflies. *Cutaneous Leishmaniasis* - **Cutaneous leishmaniasis** is a **sandfly-borne disease** caused by *Leishmania* parasites, leading to skin sores. - Sandflies (genus **Phlebotomus** in the Old World and **Lutzomyia** in the New World) transmit these parasites. *Visceral Leishmaniasis* - **Visceral leishmaniasis**, also known as **kala-azar**, is a severe form of leishmaniasis transmitted by the bite of **infected female sandflies**. - It affects internal organs like the **spleen**, **liver**, and **bone marrow**. *Oriental sore* - **Oriental sore** is another name for **cutaneous leishmaniasis**, indicating that it is also transmitted by **sandflies**. - It refers to the characteristic **skin lesions** caused by *Leishmania* parasites following a sandfly bite.

Q: Which of the following insects has shown the least widespread development of resistance to DDT?

Tsetse flies. ***Tsetse flies*** - **Tsetse flies** have shown the least widespread development of **resistance to DDT**, likely due to their specific life cycles and limited exposure in widespread application campaigns. - This has made DDT, or its successor compounds, remain effective in certain tsetse control programs where other insects have developed high resistance. *Mosquitoes* - **Mosquitoes** have developed **widespread resistance to DDT** globally, significantly impacting malaria control efforts. - Their rapid breeding cycles and extensive exposure to DDT over decades led to the selection and proliferation of resistant strains. *Fleas* - **Fleas** have also developed **significant resistance to DDT**, especially in regions where it was heavily used for pest control in homes and livestock. - This resistance is a major factor in the continued prevalence of flea-borne diseases in certain areas. *Ticks* - **Ticks** have shown considerable development of **resistance to DDT** and other acaricides due to widespread use in livestock and agricultural settings. - Their resistance has complicated efforts to control tick-borne diseases and protect animal health.

Q: Infectivity period of chickenpox is ?

1 day before and 4 days after appearance of rash. ***1 day before and 4 days after appearance of rash*** - The infectivity period of **chickenpox (varicella)** begins approximately **1-2 days (24-48 hours) before the rash appears**. - It extends until **all lesions have crusted over**, which typically occurs around **5-6 days after rash onset**, though some sources cite **4-5 days**. - This option represents the **commonly accepted timeframe** taught in Indian medical curricula and NEET PG examinations. *4 days before and 5 days after appearance of rash* - The **pre-rash infectivity period is too long** in this option; chickenpox is infectious for only **1-2 days before rash**, not 4 days. - While the "5 days after" is medically accurate, the incorrect pre-rash duration makes this option wrong. *Only when scab falls* - This statement is **incorrect**; infectivity starts much earlier, **1-2 days before the rash appears**. - By the time scabs fall, the person is **no longer infectious**, as crusted lesions contain non-infectious material. - This option ignores the critical **pre-rash and early rash infectious period**. *Entire incubation period* - The **incubation period** for chickenpox is usually **10-21 days**, during which the individual is **not infectious** for most of this time. - Infectivity begins only in the **last 1-2 days of incubation** (just before rash onset) and continues into the eruptive phase, not for the entire duration.

Q: All of the following are anthropozoonosis except

Schistosomiasis. ***Schistosomiasis*** - This is a **human-to-human** disease, even though it involves an intermediate **snail host**. - Its life cycle does not involve transmission of pathogens from vertebrate animals to humans. *Rabies* - Rabies is a classic **anthropozoonosis**, transmitted to humans primarily through the saliva of infected animals, most commonly **dogs** and **bats**. - It involves a pathogen (rabies virus) that cycles between animals and can be transmitted to humans. *Plague* - Plague is an **anthropozoonosis** caused by *Yersinia pestis*, typically transmitted from **rodents** (e.g., rats) to humans via flea bites. - The disease maintains a natural reservoir in wild rodent populations, making it a prime example of animal-to-human transmission. *Anthrax* - Anthrax is an **anthropozoonosis** caused by *Bacillus anthracis*, transmitted to humans from infected **livestock** (e.g., cattle, sheep). - Humans usually acquire the infection through contact with infected animals or their products, or by inhaling spores.

Q: The international quarantine period for yellow fever as approved by the Government of India is ?

6 days. ***6 days*** - The **incubation period** for yellow fever is typically 3-6 days, and the 6-day quarantine period is internationally accepted to cover this range. - This period is established to prevent the importation and spread of the disease by ensuring that individuals arriving from endemic areas do not develop symptoms after arrival. *9 days* - This duration is **longer than the internationally recognized incubation period** for yellow fever and is not the standard quarantine period. - Implementing a 9-day quarantine would be excessive and not based on the typical disease progression. *10 days* - A 10-day quarantine period is also **not the standard** for yellow fever as approved by international health regulations or by the Government of India. - While some diseases may require a 10-day quarantine, yellow fever's incubation period makes 6 days sufficient. *12 days* - A 12-day quarantine is **significantly longer** than necessary for yellow fever, as virtually all cases would manifest symptoms within the first 6 days. - This period is typically associated with diseases with much longer incubation periods, which is not the case for yellow fever.

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.

Question 1

What is the annual infection rate of tuberculosis?

Accepted Answer

Percentage of new patients positive for tuberculin test

Answer

Percentage of total patients positive for tuberculin test

Answer

Percentage of sputum positive total patients

Answer

Percentage of sputum positive new patients

Question 2

Which of the following statements best describes the operational definition of onchocerciasis elimination?

Accepted Answer

Transmission of O. volvulus has been reduced to a level where it cannot sustain itself in the population.

Answer

All interventions have been successfully implemented.

Answer

There is no recrudescence of the disease after a defined period.

Answer

All of the options are true.

Question 3

In which condition is a night blood survey performed?

Accepted Answer

Lymphatic filariasis

Answer

Typhoid fever

Answer

Malaria infection

Answer

Visceral leishmaniasis

Question 4

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 5

Which of the following diseases is NOT transmitted by sandflies?

Accepted Answer

Relapsing fever

Answer

Visceral Leishmaniasis

Answer

Oriental sore

Answer

Cutaneous Leishmaniasis

Question 6

Which of the following insects has shown the least widespread development of resistance to DDT?

Accepted Answer

Tsetse flies

Answer

Mosquitoes

Answer

Fleas

Answer

Ticks

Question 7

Infectivity period of chickenpox is ?

Accepted Answer

1 day before and 4 days after appearance of rash

Answer

Only when scab falls

Answer

Entire incubation period

Answer

4 days before and 5 days after appearance of rash

Question 8

All of the following are anthropozoonosis except

Accepted Answer

Schistosomiasis

Answer

Rabies

Answer

Plague

Answer

Anthrax

Question 9

The international quarantine period for yellow fever as approved by the Government of India is ?

Accepted Answer

6 days

Answer

9 days

Answer

10 days

Answer

12 days

Question 10

The primary reservoir for leptospirosis transmission is:

Accepted Answer

Rat

Answer

Cat

Answer

Dog

Answer

Fish

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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