Infectious Diseases Practice Questions

Q: Sputum positive TB patients on chemotherapy should be isolated for at least:

2 weeks. ***2 weeks*** - Patients with **sputum smear-positive TB** are generally considered infectious until they have received **2 weeks of effective anti-TB treatment** with appropriate anti-tubercular therapy. - After this period, the **bacterial load significantly decreases**, making transmission much less likely and allowing for discontinuation of strict isolation precautions. - This is the standard recommendation in **WHO guidelines, CDC guidelines, and Indian NTEP (National TB Elimination Programme)** for drug-susceptible TB. - Isolation can be discontinued after **2 weeks** if the patient shows **clinical improvement** and is on appropriate treatment. *3 weeks* - While some institutions may use a 3-week period as a **conservative margin**, this is **not the standard minimum** recommended by guidelines. - The infectious period typically ends within 2 weeks of effective chemotherapy for drug-susceptible TB. *4 weeks* - Isolating for four weeks is **unnecessarily prolonged** for most patients with drug-susceptible TB. - This leads to **increased healthcare costs** and extended hospital stays without substantial additional public health benefit. *6 weeks* - Such a long isolation period is typically reserved for cases of **multidrug-resistant TB (MDR-TB)** or extensively drug-resistant TB (XDR-TB) due to prolonged infectivity. - For standard sputum-positive drug-susceptible TB, this duration is excessive and does not align with current guidelines.

Q: Under RNTCP, the target for case detection through quality sputum microscopy is at least:

70%. ***70%*** - The **Revised National Tuberculosis Control Programme (RNTCP)** aimed for a minimum of **70% case detection** by identifying infectious smear-positive TB cases. - This target ensures that a significant proportion of **tuberculosis cases** are diagnosed and brought under treatment, thereby reducing transmission. *95%* - While 95% is a very high target, it was not the initial or primary target set by RNTCP for sputum microscopy case detection. - Such a high rate is often an ideal goal for **treatment success** or **cure rates**, rather than initial case detection. *85%* - The **85% target** was set for the **treatment success rate** for smear-positive pulmonary TB cases under RNTCP, not for initial case detection. - Achieving this target ensures effective treatment outcomes and prevents the development of **drug resistance**. *60%* - A 60% detection rate would be considered **insufficient** for effective TB control, as it would leave a large number of infectious individuals undiagnosed. - This low target would not adequately address the public health burden of **tuberculosis**.

Q: Plague is transmitted by all EXCEPT?

Culex. ***Culex*** - **Culex** mosquitoes are known vectors for diseases like **West Nile virus**, **Japanese encephalitis**, and **filariasis**. - They are **not involved** in the transmission of **plague**, which is primarily a flea-borne disease. *Pulex irritans* - **Pulex irritans**, also known as the **human flea**, is a known vector for **plague** (*Yersinia pestis*). - It can transmit the bacteria from infected hosts, including humans and animals, to others through its bite. *X. astia* - **Xenopsylla astia** is an oriental rat flea, found predominantly in tropical regions like India, and is a significant vector for **plague**. - This flea species plays a crucial role in maintaining **enzootic plague** among rodent populations and transmitting it to humans. *X. cheopis* - **Xenopsylla cheopis**, the **oriental rat flea**, is the **primary vector** for **bubonic plague** worldwide. - It transmits *Yersinia pestis* from infected rodents (like rats) to humans through its bite, contributing to flea-borne epidemics.

Q: True about Anopheles mosquito?

Larvae are surface feeder. ***Larvae are surface feeder*** - **Anopheles larvae** lie horizontally at the water surface and feed on surface scum and microbes, which is a **key distinguishing feature** in mosquito identification - Their specialized mouthparts are adapted for **grazing along the water's surface** - This characteristic differentiates them from other mosquito genera *Larvae have siphon tube* - **Anopheles larvae do not possess a respiratory siphon tube**; they breathe directly through spiracles on their eighth abdominal segment - The presence of a **siphon tube is characteristic of Culex and Aedes** mosquito larvae, not Anopheles *Larvae lie at an angle to water surface* - Mosquito larvae that hang at an angle from the water surface, using a respiratory siphon, are typically **Culex or Aedes species** - **Anopheles larvae lie parallel to the water surface**, not at an angle - this is another key identification feature *Larvae are bottom feeder* - While some aquatic insect larvae are bottom feeders, **Anopheles larvae are specifically adapted for surface feeding** - They primarily consume organisms and debris present in the **surface film** of the water, not from the bottom

Q: Most crucial part of tuberculosis control programme is -

Treatment of sputum positive cases. ***Treatment of sputum positive cases*** - Treating **sputum-positive cases** is paramount because these individuals are the primary source of **transmission** of *Mycobacterium tuberculosis* in the community. - Effective treatment of these highly infectious cases directly **reduces the bacterial load**, preventing further spread and significantly impacting the *R0* (basic reproduction number) of the disease. *Treatment of X-ray positive cases* - While X-ray findings can indicate active tuberculosis, they do not always correlate with **infectivity** as strongly as sputum positivity. - Many X-ray positive cases, especially those with **non-cavitary lesions**, may have low or no sputum positivity. *BCG vaccination* - **BCG vaccination** primarily protects against severe forms of tuberculosis, such as **meningitis** and **miliary TB**, in children. - It has variable efficacy against **pulmonary TB** in adults and does not prevent the transmission of the disease from already infected individuals to others. *Contact tracing* - **Contact tracing** is crucial for identifying individuals who have been exposed to TB and may be at risk for developing the disease, allowing for prophylaxis or early treatment. - However, without effectively treating the primary sources (sputum-positive cases), new infections will continue to occur, making contact tracing a reactive rather than a primary preventative measure.

Q: The high risk groups for transmission of HIV include the following except

Health care workers. ***Health care workers*** - While **health care workers** can be exposed to HIV through occupational activities (e.g., needlestick injuries), they are generally not considered a high-risk group for transmission if standard precautions are followed. - The risk of transmission through occupational exposure is relatively low (approximately 0.3% for needlestick injury), especially with proper safety measures and post-exposure prophylaxis. *Children of HIV mothers* - Children born to **HIV-positive mothers** are at high risk of acquiring the virus through vertical transmission during pregnancy, childbirth, or breastfeeding. - Without intervention, the transmission rate ranges from 15-45%, making this a recognized high-risk group. *Haemophiliacs* - Before the implementation of routine screening for blood products (pre-1985), **haemophiliacs** were at very high risk of contracting HIV through contaminated factor VIII and IX concentrates, which were essential for their treatment. - While current blood products are safe, haemophiliacs are historically recognized as a high-risk group. *Men who have sex with men (MSM)* - **Men who have sex with men** are a high-risk group due to unprotected receptive anal intercourse, which is an efficient mode of HIV transmission. - This demographic has historically been, and continues to be, disproportionately affected by the HIV epidemic globally.

Q: Which of the following diseases is transmitted by rat flea?

Endemic typhus. ***Endemic typhus*** - **Endemic (murine) typhus** is caused by *Rickettsia typhi* and is primarily transmitted to humans by the **rat flea** (*Xenopsylla cheopis*) - The rat flea typically acquires the bacteria by feeding on infected rodents (e.g., rats), and then transmits it to humans through its feces while feeding. *Oriental sore* - **Oriental sore** refers to cutaneous leishmaniasis, caused by *Leishmania* parasites. - It is transmitted by the bite of infected **sandflies**, not rat fleas. *Trench fever* - **Trench fever** is caused by *Bartonella quintana* and is transmitted to humans by **human body lice** (*Pediculus humanus corporis*). - This disease is historically associated with crowded and unsanitary conditions, particularly during wartime. *Chagas disease* - **Chagas disease** (American trypanosomiasis) is caused by the parasite *Trypanosoma cruzi*. - It is primarily transmitted by the feces of infected **reduviid bugs** (also known as kissing bugs), which typically bite humans around the face.

Q: All of the following are zoonosis, except:

HIV. ***HIV*** - While HIV originated from **simian immunodeficiency virus (SIV)** in non-human primates, it is **no longer considered a zoonosis** because transmission now occurs exclusively **human-to-human**. - The virus has fully adapted to **human hosts**, and there is **no ongoing animal reservoir** contributing to the current epidemic. - Zoonotic diseases require **active animal-to-human transmission**, which does not apply to HIV in its current form. *Japanese Encephalitis* - This is a **mosquito-borne viral disease** that primarily circulates between **mosquitoes, pigs, and birds**. - Humans are **accidental dead-end hosts**, making this a true **zoonotic disease**. *Plague* - Caused by **Yersinia pestis**, which naturally infects **small mammals (rodents)** and their fleas. - Humans become infected through **flea bites** or direct contact with infected animals, making it a **classic zoonosis**. *Tuberculosis* - While most human TB is caused by **M. tuberculosis** (human-to-human), **M. bovis** causes **zoonotic TB**. - Transmitted from **infected cattle** to humans via **unpasteurized dairy products** or close contact with infected animals. - This animal-to-human transmission qualifies TB as a **zoonotic disease**.

Q: What should the Aedes aegypti index be to effectively control yellow fever?

An index below 5%.. ***An index below 5%.*** - For effective yellow fever control, the *Aedes aegypti* index needs to be **below 5%** according to WHO guidelines and standard public health practices. - This threshold is considered adequate to significantly reduce the risk of yellow fever transmission and prevent outbreaks. - The 5% threshold applies to House Index (HI) or Breteau Index measurements of *Aedes aegypti* presence. *An index below 1%.* - An index below 1% is the **stringent threshold for dengue control**, not yellow fever. - Dengue requires a lower vectorial capacity threshold because it has higher transmission efficiency even at lower mosquito densities. - While achieving below 1% would also control yellow fever, it is **not the standard target** specified for yellow fever programs. *An index below 10%.* - An index below 10% indicates **moderate to high risk** for *Aedes*-borne disease transmission. - This level is **insufficient for effective yellow fever control** and would still allow significant transmission potential. - Control programs aim for much lower indices to prevent epidemic spread. *An index below 20%.* - An index below 20% indicates a **very high risk** of transmission for yellow fever and other *Aedes*-borne diseases. - This level is **far from adequate** for any meaningful vector control and suggests imminent outbreak risk. - Urgent intervention would be needed at this threshold level.

Q: The most sensitive index for surveillance of malaria transmission is -

Infant parasite rate. ***Infant parasite rate*** - The **infant parasite rate**, specifically in children aged 0-11 months, is considered the most sensitive indicator of active malaria transmission. - This is because these infants have had minimal exposure to malaria, and a positive parasite finding indicates recent and ongoing transmission within the community. *Proportional case rate* - The **proportional case rate** indicates the proportion of all diseases that are malaria, which is useful for understanding disease burden but less sensitive for transmission changes. - It does not specifically target a population group directly reflecting recent transmission as accurately as the infant parasite rate. *Spleen rate* - The **spleen rate** (percentage of children with enlarged spleens) reflects cumulative exposure to malaria over a longer period, acting as a historical indicator. - It is a good measure of endemicity but does not rapidly capture recent changes or sensitivities in ongoing transmission. *Parasite density index* - **Parasite density index** measures the average number of parasites per unit of blood in infected individuals. - While it reflects the intensity of infection, it is not as direct or sensitive an indicator of current transmission events within a community as the infant parasite rate.

Question 1

Sputum positive TB patients on chemotherapy should be isolated for at least:

Accepted Answer

2 weeks

Answer

3 weeks

Answer

4 weeks

Answer

6 weeks

Question 2

Under RNTCP, the target for case detection through quality sputum microscopy is at least:

Accepted Answer

70%

Answer

95%

Answer

85%

Answer

60%

Question 3

Plague is transmitted by all EXCEPT?

Accepted Answer

Culex

Answer

Pulex irritans

Answer

X. astia

Answer

X. cheopis

Question 4

True about Anopheles mosquito?

Accepted Answer

Larvae are surface feeder

Answer

Larvae have siphon tube

Answer

Larvae are bottom feeder

Answer

Larvae lie at an angle to water surface

Question 5

Most crucial part of tuberculosis control programme is -

Accepted Answer

Treatment of sputum positive cases

Answer

Treatment of X-ray positive cases

Answer

BCG vaccination

Answer

Contact tracing

Question 6

The high risk groups for transmission of HIV include the following except

Accepted Answer

Health care workers

Answer

Children of HIV mothers

Answer

Haemophiliacs

Answer

Men who have sex with men (MSM)

Question 7

Which of the following diseases is transmitted by rat flea?

Accepted Answer

Endemic typhus

Answer

Oriental sore

Answer

Trench fever

Answer

Chagas disease

Question 8

All of the following are zoonosis, except:

Accepted Answer

HIV

Answer

Japanese Encephalitis

Answer

Plague

Answer

Tuberculosis

Question 9

What should the Aedes aegypti index be to effectively control yellow fever?

Accepted Answer

An index below 5%.

Answer

An index below 10%.

Answer

An index below 20%.

Answer

An index below 1%.

Question 10

The most sensitive index for surveillance of malaria transmission is -

Accepted Answer

Infant parasite rate

Answer

Proportional case rate

Answer

Spleen rate

Answer

Parasite density index

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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