Infectious Diseases Practice Questions

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.

Q: Cyclopropagative type of life cycle is seen in?

Malaria. ***Malaria*** - The **cyclopropagative** life cycle involves both reproduction (propagation) and developmental changes (cyclic) within the **arthropod vector**. - In malaria, the *Plasmodium* parasite undergoes asexual reproduction in the human host and then **sexual reproduction** (sporogony) with **developmental changes** in the **Anopheles mosquito**. - This combination of multiplication and development in the vector defines cyclopropagative transmission. *Filaria* - Filarial parasites, such as *Wuchereria bancrofti*, exhibit a **cyclodevelopmental** life cycle in the arthropod vector, meaning they undergo developmental changes but **do not reproduce** within the vector. - The microfilariae ingested by the mosquito develop into infective larvae, which are then transmitted to a new human host without multiplying inside the mosquito. *Cholera* - **Cholera** is caused by the bacterium *Vibrio cholerae*, which has a **direct life cycle** and is primarily transmitted through contaminated water or food. - There is no arthropod vector involved in the transmission or part of its life cycle. *Plague* - **Plague** is caused by the bacterium *Yersinia pestis*, primarily transmitted by **flea vectors** (e.g., *Xenopsylla cheopis*). - In the flea, the bacteria multiply in the gut (propagative transmission), but there is **no developmental/cyclic change** in the pathogen's form. - This is **propagative only**, not cyclopropagative, as it lacks the developmental component required for cyclopropagative transmission.

Q: You are the MO in charge in a PHC and there has been a plague epidemic in your area. Which of the following measures is the LEAST appropriate for controlling epidemic?

Vaccination of all susceptible individuals. ***Vaccination of all susceptible individuals*** - While beneficial for prevention, mass vaccination during an ongoing plague epidemic is **logistically challenging** and **too slow** to effectively control the immediate spread. - The incubation period of plague is short, and an effective vaccine often requires multiple doses and time to induce immunity, making it less suitable for **rapid epidemic containment**. *Isolation of contacts* - **Isolating contacts** helps prevent the disease from spreading further by separating potentially infected individuals who may be asymptomatic or in the incubation period. - This measure is crucial in **breaking chains of transmission** and limiting the epidemic's reach. *Rapid treatment of cases with streptomycin* - **Early and rapid treatment** of confirmed plague cases with effective antibiotics like **streptomycin** is a cornerstone of epidemic control, significantly reducing mortality and infectivity. - This intervention quickly minimizes the source of infection, preventing further transmission to others. *Early diagnosis and notification* - **Early diagnosis** allows for prompt initiation of treatment and isolation, while **notification** triggers public health responses such as contact tracing and surveillance. - These steps are essential for understanding the scope of the epidemic and implementing appropriate control measures efficiently.

Q: Tuberculin test is positive in general population (immunocompetent individuals with no specific risk factors) if induration is?

>10mm. >10mm - For **immunocompetent** individuals without specific risk factors, a tuberculin skin test (TST) induration of **≥10 mm** is considered positive. - This threshold indicates a likely **exposure to Mycobacterium tuberculosis** and a cellular immune response. *>7mm* - This is not a standard threshold for a positive TST in any risk group. - TST interpretation is based on specific **induration sizes** corresponding to different risk factors. *>5mm* - An induration of **≥5 mm** is considered positive for individuals with compromised immunity, those in close contact with active TB cases, or those with fibrotic changes on chest X-ray. - This lower threshold is used for **high-risk groups** due to their increased susceptibility to developing active tuberculosis. *>2mm* - An induration of **≥2 mm** is not typically used as a positive threshold for the tuberculin test in any established guidelines. - Such a small induration is generally considered **negative** or clinically insignificant.

Q: Sodium content in mmol/L in WHO oral rehydration solution is

75. ***75*** - The **WHO oral rehydration solution (ORS)** has been reformulated to a lower osmolarity to improve efficacy, with a sodium content of **75 mmol/L**. - This lower sodium concentration helps reduce the risk of **hypernatremia** and is effective in managing dehydration due to diarrhea. *90* - An ORS with **90 mmol/L** sodium content was part of the **original WHO ORS formula**. - While effective, this higher sodium concentration was associated with a greater risk of **hypernatremia** in some patients. *20* - A sodium content of **20 mmol/L** is significantly lower than recommended for effective rehydration in most diarrheal diseases. - This concentration would be insufficient to replace the **sodium losses** typically experienced during dehydration. *111* - A sodium content of **111 mmol/L** is considerably higher than the current WHO recommendation. - Such a high concentration would increase the risk of **hypernatremia** and potentially worsen dehydration at the cellular level due to high osmolarity.

Q: For the prevention of human rabies, immediate flushing and washing the wound(s) in animal bite cases, with plenty of soap and water, under running tap should be carried out for how much time?

15 minutes. ***15 minutes*** - **Immediate and thorough wound cleansing** with soap and water for at least 15 minutes is crucial for reducing the risk of rabies infection after an animal bite. - This physical removal of the *rabies virus* from the wound site is the **most effective first-aid measure** in preventing the disease. *5 minutes* - While some cleansing is better than none, five minutes may not be sufficient for **maximal removal of viral particles**, especially from deeper or more contaminated wounds. - The extended duration of 15 minutes ensures a more **thorough decontamination** and increased safety margin. *2 minutes* - This short duration of washing is **inadequate** for effective removal of the rabies virus from the wound. - It significantly increases the **risk of viral persistence** in the wound, undermining the primary goal of immediate first aid. *1 minute* - Washing for only one minute is **grossly insufficient** and offers minimal protective benefit against rabies transmission following an animal bite. - **Thorough mechanical scrubbing** and flushing for a longer period are essential.

Q: Kala azar is spread by –

Sand–fly. ***Sand–fly*** - Kala-azar, also known as **visceral leishmaniasis**, is transmitted to humans through the bite of an infected female **Phlebotomine sandfly**. - The sandfly acts as a **biological vector**, harboring the **Leishmania parasites** in its gut. *Black–fly* - **Black flies** are vectors for **onchocerciasis** (river blindness), caused by the parasite *Onchocerca volvulus*. - They are typically found near **fast-flowing water** and their bites often lead to skin nodules and eye lesions. *Tsetse–fly* - The **tsetse fly** is the vector for **African trypanosomiasis** (sleeping sickness), caused by species of *Trypanosoma*. - This disease primarily affects central nervous system function, leading to changes in sleep patterns. *House–fly* - **House flies** are primarily **mechanical vectors** for various pathogens, meaning they can transfer microbes from contaminated surfaces to food. - They are not known to transmit specific diseases like Kala-azar through a bite.

Q: Risk of transmission from single percutaneous exposure to blood for HIV is:-

0.1 - 0.36%. ***0.1 - 0.36%*** - The risk of **HIV transmission** from a single percutaneous exposure (e.g., needle stick injury) to infected blood is approximately **0.3%** (range 0.1% to 0.36%) according to CDC guidelines. - This relatively low risk is due to the small inoculum size and lower viral concentration in needle stick injuries compared to other exposures. - Post-exposure prophylaxis (PEP) can further reduce this already low transmission risk. *2.7-10%* - This range is significantly **higher** than the established risk for percutaneous HIV transmission. - This percentage is more aligned with **Hepatitis C virus (HCV)** transmission risk, which is approximately 1.8% (range 0-7%). *6-30%* - This range is substantially **overstated** for HIV transmission from percutaneous exposure. - These percentages reflect the transmission risk for **Hepatitis B virus (HBV)**, which has a much higher transmission rate (6-30%) from needle stick injuries. *0.4-5%* - While 0.4% is close to some reported upper limits, the 5% figure is **much higher** than established estimates for percutaneous HIV transmission. - This range incorrectly combines different risk estimates and does not accurately represent single percutaneous HIV exposure risk.

Q: In which of the following infections is the mosquito the main vector?

Yellow fever. ***Yellow fever*** - Yellow fever is a **viral hemorrhagic fever** transmitted by infected **_Aedes aegypti_ mosquitoes**. - The disease causes symptoms ranging from mild fever to severe illness with **jaundice** and internal **bleeding**. *Leprosy* - Leprosy is a **chronic bacterial infection** caused by **_Mycobacterium leprae_**. - It is primarily transmitted through **respiratory droplets** from prolonged close contact with an infected person. *Cholera* - Cholera is an **acute diarrheal disease** caused by infection of the intestine with **_Vibrio cholerae_ bacteria**. - It is typically spread through **contaminated water** or food sources. *Hepatitis - A* - Hepatitis A is a **viral liver disease** caused by the **Hepatitis A virus (HAV)**. - It is primarily transmitted via the **fecal-oral route**, often through contaminated food or water.

Question 1

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 2

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

Question 3

Cyclopropagative type of life cycle is seen in?

Accepted Answer

Malaria

Answer

Filaria

Answer

Cholera

Answer

Plague

Question 4

You are the MO in charge in a PHC and there has been a plague epidemic in your area. Which of the following measures is the LEAST appropriate for controlling epidemic?

Accepted Answer

Vaccination of all susceptible individuals

Answer

Isolation of contacts

Answer

Rapid treatment of cases with streptomycin

Answer

Early diagnosis and notification

Question 5

Tuberculin test is positive in general population (immunocompetent individuals with no specific risk factors) if induration is?

Accepted Answer

>10mm

Answer

>7mm

Answer

>5mm

Answer

>2mm

Question 6

Sodium content in mmol/L in WHO oral rehydration solution is

Accepted Answer

75

Answer

90

Answer

20

Answer

111

Question 7

For the prevention of human rabies, immediate flushing and washing the wound(s) in animal bite cases, with plenty of soap and water, under running tap should be carried out for how much time?

Accepted Answer

15 minutes

Answer

5 minutes

Answer

2 minutes

Answer

1 minute

Question 8

Kala azar is spread by –

Accepted Answer

Sand–fly

Answer

Black–fly

Answer

Tsetse–fly

Answer

House–fly

Question 9

Risk of transmission from single percutaneous exposure to blood for HIV is:-

Accepted Answer

0.1 - 0.36%

Answer

2.7-10%

Answer

6-30%

Answer

0.4-5%

Question 10

In which of the following infections is the mosquito the main vector?

Accepted Answer

Yellow fever

Answer

Leprosy

Answer

Cholera

Answer

Hepatitis - A

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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