Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 301: 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 302: 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 303: 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 304: 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 305: 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 306: 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 307: 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 308: 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 309: 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.

Question 310: Zoonotic disease of viral etiology includes -

A. Q fever
B. Rickettsial disease
C. Rubella
D. Rabies (Correct Answer)

Explanation: ***Rabies*** - Rabies is a classic example of a **zoonotic disease** caused by the **rabies virus**, transmitted to humans primarily through the bite of an infected animal. - The virus affects the **central nervous system** and is almost invariably fatal once clinical symptoms appear. *Q fever* - Q fever is a **zoonotic disease**, but it is caused by the bacterium **Coxiella burnetii**, not a virus. - It is often transmitted from farm animals and can cause acute or chronic illness. *Rickettsial disease* - Rickettsial diseases are caused by various species of **Rickettsia bacteria**, which are spread by arthropod vectors like ticks, fleas, and lice. - These are bacterial infections and not viral in origin. *Rubella* - Rubella, also known as German measles, is a **viral disease** caused by the rubella virus, but it is typically spread directly from person to person through respiratory droplets. - It is **not considered a zoonotic disease** as it does not primarily originate in animals and transmit to humans.

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