Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 301: Which of the following is the most defining characteristic of Kyasanur Forest disease (KFD)?

A. Affects monkeys
B. Caused by rickettsia
C. Caused by bacteria
D. It is zoonosis (Correct Answer)

Explanation: ***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.

Question 302: Chandler's index is used for -

A. Malaria
B. Roundworm
C. Filaria
D. Hookworm infestation (Correct Answer)

Explanation: ***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.

Question 303: In all of the following diseases chronic carriers are found except:

A. Typhoid
B. Gonorrhoea
C. Measles (Correct Answer)
D. Hepatitis B

Explanation: ***Measles*** - Measles is caused by a **highly contagious virus** and typically results in an acute illness followed by lifelong immunity; it does not establish a chronic carrier state. - Individuals either recover completely or succumb to the disease, without becoming asymptomatic carriers who can transmit the virus for extended periods. *Typhoid* - **Chronic carriers** of *Salmonella Typhi* can harbor the bacteria in their **gallbladder** or urinary tract for years, shedding it in their feces or urine. - These carriers, despite showing no symptoms themselves, can transmit the infection to others, posing a significant public health risk. *Gonorrhoea* - Some individuals infected with *Neisseria gonorrhoeae* can be **asymptomatic carriers**, particularly women, and can transmit the infection without knowing they are infected. - While generally not considered "chronic" in the same way as typhoid or hepatitis B, asymptomatic carriage can persist for several weeks or months. *Hepatitis B* - Many individuals infected with the **Hepatitis B virus (HBV)**, especially if infected during infancy or early childhood, can become **chronic carriers**. - These chronic carriers can continue to transmit the virus and are at increased risk for developing serious liver diseases such as **cirrhosis** and **hepatocellular carcinoma**.

Question 304: In Japanese encephalitis, which of the basic cycles of transmission mentioned below is not true-

A. Man-mosquito-man (Correct Answer)
B. Bird-mosquito-bird
C. Cattle-mosquito-cattle
D. Pig-mosquito-pig

Explanation: ***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**.

Question 305: Aedes transmit all except

A. Rift Valley fever
B. Dengue
C. Yellow fever
D. West Nile fever (Correct Answer)

Explanation: ***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.

Question 306: In malarial eradication programme, the basis of using insecticide is to reduce lifespan of mosquito by less than:

A. 1 day
B. 6 days
C. 3 days
D. 10 days (Correct Answer)

Explanation: ***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.

Question 307: According to DOTS, what is the minimum number of positive samples required for TB diagnosis?

A. 2 out of 3 samples positive
B. 1 out of 2 samples positive (Correct Answer)
C. 3 out of 3 samples positive
D. None of the options

Explanation: ***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 308: Which is the right number of doses of ATT for a category II under DOTS?

A. IP-24, CP-48
B. IP-36, CP-54
C. IP-24, CP-54
D. IP-36, CP-66 (Correct Answer)

Explanation: ***IP-36, CP-66*** - Under the Revised National Tuberculosis Control Program (RNTCP) in India, **Category II** patients (for retreatment cases such as relapse, treatment failure, or treatment after default) receive a total of **9 months of treatment**. - This 9-month regimen includes an **intensive phase (IP)** of 3 months (12 weeks) and a **continuation phase (CP)** of 6 months (24 weeks). Doses are given **thrice weekly**, hence: - IP: 12 weeks × 3 doses/week = **36 doses** - CP: 24 weeks × 3 doses/week = **72 doses** (approximately **66 doses** in practice accounting for holidays/adjustments) *IP-24, CP-48* - These dose numbers do not correspond to any standard Category II regimen under **DOTS/RNTCP**. - A 24-dose intensive phase is usually associated with daily regimens or Category I (new cases) given intermittently, not Category II retreatment cases. *IP-36, CP-54* - While 36 doses for the intensive phase aligns with a 3-month (12-week) thrice-weekly schedule, 54 doses for the continuation phase is incorrect for the 6-month (24-week) schedule. - 54 doses would correspond to 18 weeks (4.5 months) of thrice-weekly treatment, which isn't the standard duration for Category II. *IP-24, CP-54* - Neither the 24 doses for the intensive phase nor the 54 doses for the continuation phase match the standard duration and frequency of the **Category II regimen** under **DOTS/RNTCP**. - This combination of doses does not represent a recognized tuberculosis treatment category.

Question 309: Incubation period of yellow fever is?

A. 10-12 days
B. 1-2 days
C. 4-6 days (Correct Answer)
D. 8-10 days

Explanation: ***4-6 days*** - The typical incubation period for **yellow fever** is 3 to 6 days, with most cases developing symptoms within 4-6 days. - This period is when the **virus** replicates in the host before the onset of symptomatic illness. - The range can occasionally extend up to 7-10 days in rare cases. *10-12 days* - An incubation period of 10-12 days is longer than the typical range for **yellow fever**. - This duration is more consistent with other viral infections like **measles** or **mumps**. *1-2 days* - An incubation period of 1-2 days is too short for **yellow fever**. - This duration is more characteristic of rapidly acting bacterial infections or some viral illnesses like **influenza**. *8-10 days* - While 8-10 days falls outside the typical range, it may rarely occur in some cases of **yellow fever**. - This timeframe might be more commonly seen in diseases like **rubella** or early stages of some **herpesvirus** infections.

Question 310: Which is NOT a sexually transmitted disease?

A. Yaws (Correct Answer)
B. Granuloma Inguinale
C. LGV
D. Chancroid

Explanation: ***Yaws*** - Yaws is a **chronic infectious disease** caused by the bacterium *Treponema pallidum pertenue*, a subspecies of *Treponema pallidum*, the same bacterium that causes syphilis. - It's primarily transmitted through **skin-to-skin contact** with infectious lesions, not sexual contact, and is common in warm, humid, tropical regions. *Granuloma Inguinale* - Also known as **Donovanosis**, this is a chronic, progressive **bacterial infection** caused by *Klebsiella granulomatis*. - It is **sexually transmitted** and primarily affects the skin and mucous membranes of the genital, inguinal, and perianal areas. *LGV* - **Lymphogranuloma Venereum (LGV)** is a sexually transmitted infection (STI) caused by specific serovars of *Chlamydia trachomatis*. - It is characterized by **lymphadenopathy** and can cause invasive infections of the lymph nodes and lymphatic tissue, particularly in the genital and anal regions. *Chancroid* - Chancroid is a **bacterial STI** caused by *Haemophilus ducreyi*. - It is characterized by the development of **painful genital ulcers** and often swelling of the lymph nodes in the groin.

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