Infectious Diseases Practice Questions

Q: Which of the following statements about mosquitoes is FALSE?

Mosquitoes are the definitive hosts in filariasis.. **Explanation** In parasitology, the **definitive host** is defined as the host in which the parasite undergoes its **sexual cycle** or reaches maturity. The **intermediate host** is where the asexual cycle or larval stages occur. 1. **Why Option B is False (The Correct Answer):** In **Filariasis** (*Wuchereria bancrofti*), the sexual cycle occurs within the human lymphatic system, making **Humans the definitive host**. Mosquitoes (Culex) serve only as the **intermediate host**, where the parasite undergoes developmental changes (L1 to L3 larvae) without multiplication (Cyclo-developmental transmission). 2. **Analysis of Other Options:** * **Option A:** In **Malaria**, the sexual cycle (sporogony) occurs in the midgut of the female Anopheles mosquito. Therefore, the **mosquito is the definitive host**, while humans are the intermediate host. * **Option C:** Under optimal conditions of temperature and humidity, the mosquito life cycle (Egg → Larva → Pupa → Adult) typically takes **7–10 days**, but it can extend up to **3 weeks** depending on environmental factors. * **Option D:** While most mosquitoes stay within 1–2 km of their breeding site, many species (like *Anopheles* and *Culex*) are capable of traveling up to **3 kilometers** or more, often aided by wind currents. **High-Yield NEET-PG Pearls:** * **Malaria:** Mosquito = Definitive Host; Human = Intermediate Host. * **Filariasis:** Human = Definitive Host; Mosquito = Intermediate Host. * **Extrinsic Incubation Period:** The time taken for the parasite to develop inside the mosquito (e.g., ~10–14 days for Malaria). * **Overwintering:** Mosquitoes can survive adverse seasons through "hibernation" in the adult or egg stage.

Q: Which of the following is NOT transmitted through the sexual route?

Hepatitis E. **Explanation:** The transmission of Hepatitis viruses is a high-yield topic for NEET-PG. To answer this correctly, one must distinguish between **Enteric** (fecal-oral) and **Parenteral/Sexual** routes. **Why Hepatitis E is the correct answer:** Hepatitis E (HEV) is primarily transmitted via the **fecal-oral route**, most commonly through contaminated drinking water. While Hepatitis A is also enteric, current medical literature and epidemiological studies (including CDC and WHO guidelines) indicate that Hepatitis E has **no documented sexual transmission** route. In contrast, Hepatitis A can be transmitted sexually, particularly through oral-anal contact (common in MSM populations). **Analysis of Incorrect Options:** * **Option A (Hepatitis A):** While primarily fecal-oral, HAV is recognized as a sexually transmitted infection (STI) among men who have sex with men (MSM) due to direct or indirect oral-anal contact. * **Option C (Hepatitis A & E):** This is incorrect because, as established, Hepatitis A *can* be transmitted sexually, whereas Hepatitis E cannot. * **Option D (Hepatitis D):** Hepatitis D (Delta virus) requires the presence of Hepatitis B (HBsAg) to replicate. It shares the same transmission routes as HBV, which includes percutaneous, mucosal, and **sexual contact**. **High-Yield Clinical Pearls for NEET-PG:** * **Vowels (A & E):** Transmitted via the **Enteric** route (Fecal-oral). * **Consonants (B, C, D):** Transmitted via **Blood**/Body fluids (Parenteral/Sexual). * **Pregnancy Warning:** Hepatitis E is notorious for causing high mortality (up to 20%) in pregnant women due to fulminant hepatic failure. * **Chronic Status:** Hepatitis A and E generally cause acute infection only (except HEV in immunocompromised hosts), while B, C, and D can lead to chronic carrier states.

Q: Following the identification of a case of acute flaccid paralysis (AFP), what is the next step in management?

Reporting the case to public health authorities. ### Explanation **Correct Answer: B. Reporting the case to public health authorities** **Concept:** Under the Global Polio Eradication Initiative, **Acute Flaccid Paralysis (AFP) surveillance** is the gold standard for detecting the transmission of wild poliovirus. In any surveillance system, the **immediate next step** upon identifying a suspected case is **notification/reporting**. In India, any case of AFP in a child under 15 years of age (or any person of any age if polio is suspected) must be reported to the District Immunization Officer within **24 hours**. This triggers the investigation process, including stool sample collection and mapping. **Analysis of Incorrect Options:** * **A. Administering OPV:** While vaccination is preventive, it is not the immediate management step for a patient already presenting with paralysis. Outbreak response immunization (mop-up rounds) occurs only after laboratory confirmation. * **C. Performing stool culture:** This is a critical part of the investigation (two "adequate" stool samples 24 hours apart within 14 days of onset), but it can only be initiated systematically *after* the case is reported and an investigation ID is generated. * **D. Initiating chemoprophylaxis:** There is no chemoprophylaxis available for Polio; it is a viral disease managed through supportive care and prevented via vaccination. **High-Yield Pearls for NEET-PG:** * **AFP Definition:** Sudden onset of flaccid paralysis in a child <15 years. * **Surveillance Indicators:** 1. **Non-Polio AFP Rate:** Should be $\geq$ 2 per 100,000 children <15 years (indicator of system sensitivity). 2. **Stool Adequacy:** $\geq$ 80% of reported cases should have two stool samples collected 24 hours apart within 14 days of paralysis onset. * **Zero Reporting:** Even if no cases are found, a "nil" report must be submitted weekly to ensure the surveillance system is active.

Q: Post-exposure prophylaxis is indicated in all of the following conditions EXCEPT:

Japanese encephalitis. **Explanation:** Post-exposure prophylaxis (PEP) is the administration of drugs or vaccines after a potential exposure to a pathogen to prevent the development of disease. **Why Japanese Encephalitis (JE) is the correct answer:** JE is a vector-borne viral disease transmitted by the *Culex* mosquito. There is **no recommended PEP** for JE because there is no evidence that post-exposure vaccination or antiviral therapy prevents the onset of the disease once a person has been bitten by an infected mosquito. Prevention relies solely on pre-exposure vaccination and vector control. **Analysis of other options:** * **HIV:** PEP is a standard of care involving a 28-day course of Antiretroviral Therapy (ART), ideally started within 2 hours (and no later than 72 hours) after needle-stick injuries or sexual exposure. * **Varicella Zoster:** PEP is indicated for susceptible individuals (e.g., immunocompromised, pregnant women, or neonates) using **Varicella-Zoster Immunoglobulin (VZIG)** or the Varicella vaccine within 3–5 days of exposure. * **Swine Influenza (H1N1):** Oseltamivir (Tamiflu) is indicated as PEP for high-risk individuals (e.g., household contacts with comorbidities) who have been exposed to a confirmed case. **High-Yield Clinical Pearls for NEET-PG:** * **Rabies:** The most critical PEP in India; involves wound cleaning, RIG (Immunoglobulin), and modern cell culture vaccines (ARV). * **Hepatitis B:** PEP involves HBIG and the Hep B vaccine series for unvaccinated individuals after percutaneous exposure. * **Meningococcal Meningitis:** Chemoprophylaxis with **Rifampicin** (drug of choice), Ciprofloxacin, or Ceftriaxone is indicated for close contacts.

Q: What is the recommended distance for vector control around an airport for yellow fever?

400 m. **Explanation:** The correct answer is **400 meters (Option A)**. This distance is a standard International Health Regulation (IHR) requirement aimed at preventing the transmission of Yellow Fever via its primary vector, the *Aedes aegypti* mosquito. **Why 400 meters?** The "Aedes-free zone" or "Sanitary zone" is established around airports and seaports to ensure that mosquitoes do not board aircraft or ships. The distance of 400 meters is chosen because it exceeds the typical flight range of the *Aedes aegypti* mosquito, which is generally limited to 100–200 meters. By maintaining a 400m buffer zone free of breeding sites, the risk of "imported" or "exported" yellow fever is significantly minimized. **Analysis of Incorrect Options:** * **Option B (200 m):** While this is the average flight range of the mosquito, it does not provide a sufficient safety margin for international quarantine standards. * **Option C (500 m) & Option D (100 m):** These distances are not recognized by the WHO or IHR for specific vector control perimeters regarding yellow fever. 100m is too short to be effective, and 500m is not the standardized regulatory figure. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Aedes aegypti* (Urban yellow fever) and *Haemagogus* (Sylvan/Jungle yellow fever). * **Vaccine:** 17D strain (Live attenuated). It becomes effective **10 days** after administration and provides **lifelong immunity** (as per 2016 WHO amendments). * **Validity of Certificate:** For international travel, the yellow fever vaccination certificate is valid for life, starting 10 days after vaccination. * **Incubation Period:** 3 to 6 days. * **India Status:** India is "Yellow Fever receptive" (vector is present, but the disease is not). Therefore, strict quarantine and vector control at entry points are mandatory.

Q: What is the primary reservoir for scrub typhus?

Rodents. **Explanation:** **Scrub Typhus** is a rickettsial zoonosis caused by *Orientia tsutsugamushi*. Understanding the transmission cycle is crucial for NEET-PG. **1. Why Rodents are the Correct Answer:** In the transmission cycle of scrub typhus, **rodents** (specifically field mice and rats) serve as the **primary reservoir** of the infection in nature. They maintain the bacteria in the environment, providing a persistent source of infection for the vectors. **2. Analysis of Incorrect Options:** * **Mites (Option A):** While mites (specifically the larval stage called **chiggers**) are the **vectors** that transmit the disease to humans, they are not the primary reservoir. However, they can maintain the bacteria through *transovarial transmission* (acting as a secondary reservoir). * **Humans (Option B):** Humans are **accidental, dead-end hosts**. We do not transmit the disease further and are not involved in maintaining the infection cycle in nature. * **Dogs (Option C):** Dogs are not involved in the epidemiological cycle of scrub typhus. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Larval stage of trombiculid mites (*Leptotrombidium deliense*). * **Pathognomonic Sign:** The **Eschar** (a painless, black crusty sore at the site of the mite bite) is the most important clinical diagnostic clue. * **Habitat:** "Mite islands" (areas of scrub vegetation where the vector and reservoir coexist). * **Drug of Choice:** **Doxycycline** is the gold standard treatment. Azithromycin is an alternative, especially in pregnancy. * **Diagnosis:** The **Weil-Felix test** (OX-K positive) is a classic but non-specific test; IgM ELISA is now the preferred diagnostic method.

Q: What is the concentration of sodium in mOsm/L in low osmolar ORS?

75. **Explanation:** The WHO and UNICEF recommended the shift from standard ORS to **Low Osmolar ORS** (Reduced Osmolarity ORS) to improve clinical outcomes. The primary goal was to reduce the risk of hypernatremia and decrease the need for unscheduled IV fluids by lowering the total osmolarity. **1. Why 75 mOsm/L is correct:** In the Reduced Osmolarity ORS formulation, the concentration of **Sodium is 75 mmol/L (or mOsm/L)** and **Glucose is 75 mmol/L**. This 1:1 molar ratio is critical because it optimizes the sodium-glucose cotransport mechanism in the small intestine, ensuring maximum water absorption while reducing stool output and vomiting compared to the older formula. **2. Analysis of Incorrect Options:** * **Option A (45):** This is too low for standard rehydration in diarrhea, though some specialized maintenance fluids or "ReSoMal" (used in severe acute malnutrition) have lower sodium levels (approx. 45 mmol/L). * **Option C (90):** This was the sodium concentration in the **Old/Standard WHO ORS**. While effective for cholera, it was found to increase the risk of hypernatremia in children with non-cholera diarrhea. * **Option D (60):** This does not correspond to the sodium concentration of any standard WHO-recommended ORS formulation. **High-Yield Clinical Pearls for NEET-PG:** * **Total Osmolarity of Low Osmolar ORS:** 245 mOsm/L (Old ORS was 311 mOsm/L). * **Composition Breakdown:** Sodium (75), Glucose (75), Potassium (20), Chloride (65), and Trisodium Citrate (10). * **Citrate vs. Bicarbonate:** Citrate is used because it increases the shelf life of the ORS packet and helps correct acidosis. * **Zinc Supplementation:** Always remember that Zinc (20mg/day for 14 days; 10mg for infants <6 months) is given alongside ORS to reduce the duration and severity of diarrhea.

Q: What is the recommended threshold for parasite prevalence (API) for initiating Malaria Mass Drug Administration?

Greater than 2. **Explanation:** In the context of Malaria control and elimination strategies, the **Annual Parasite Incidence (API)** is the most common indicator used to measure the malaria burden in a population. It is defined as the number of confirmed cases per 1,000 population per year. **Why Option B is Correct:** According to the National Framework for Malaria Elimination (NFME) in India and WHO guidelines, an **API > 2** is the critical threshold used to categorize "High Burden" areas (Category 3). In these high-transmission settings, **Mass Drug Administration (MDA)** or targeted mass treatments are recommended as a rapid intervention to reduce the parasite reservoir in the community, interrupt transmission, and prevent outbreaks. **Analysis of Incorrect Options:** * **Option A (API > 5):** While an API > 5 indicates very high transmission, the intervention threshold for aggressive measures like MDA is lower (at 2) to ensure early containment before the burden reaches such high levels. * **Option C (15) and D (25):** These values are significantly higher than the standard epidemiological thresholds used for public health decision-making in malaria elimination programs. An API of 15-25 would indicate a severe epidemic state rather than a strategic threshold for initiating MDA. **High-Yield Clinical Pearls for NEET-PG:** * **API Formula:** (Total number of positive slides / Total population) × 1000. * **API 10%** to ensure adequate surveillance. * **SPR (Slide Positivity Rate):** A more sensitive indicator of recent changes in transmission than API. * **MDA Drugs:** Usually involves a combination of an ACT (Artemisinin-based Combination Therapy) and a single dose of Primaquine (as a gametocytocide).

Question 1

Under the Revised National Tuberculosis Control Programme (RNTCP), for diagnosis of Multidrug-Resistant Tuberculosis (MDR TB), which drugs are currently used for drug sensitivity testing?

Accepted Answer

Rifampicin, Isoniazid, and Ethambutol

Answer

Rifampicin

Answer

Rifampicin and Isoniazid

Answer

Rifampicin, Isoniazid, and Pyrazinamide

Question 2

Which of the following statements about mosquitoes is FALSE?

Accepted Answer

Mosquitoes are the definitive hosts in filariasis.

Answer

Mosquitoes are the definitive hosts in malaria.

Answer

The life cycle of a mosquito can be completed in 3 weeks.

Answer

A female mosquito can travel up to 3 kilometers.

Question 3

Which of the following is an example of a zoonotic disease?

Accepted Answer

Anthrax

Answer

Brucellosis

Answer

Leptospirosis

Answer

Chagas disease

Question 4

Which of the following is NOT transmitted through the sexual route?

Accepted Answer

Hepatitis E

Answer

Hepatitis A

Answer

Hepatitis A & E

Answer

Hepatitis D

Question 5

Following the identification of a case of acute flaccid paralysis (AFP), what is the next step in management?

Accepted Answer

Reporting the case to public health authorities

Answer

Administering Oral Polio Vaccine (OPV)

Answer

Performing stool culture for enteroviruses

Answer

Initiating chemoprophylaxis

Question 6

Post-exposure prophylaxis is indicated in all of the following conditions EXCEPT:

Accepted Answer

Japanese encephalitis

Answer

HIV

Answer

Varicella zoster

Answer

Swine influenza

Question 7

What is the recommended distance for vector control around an airport for yellow fever?

Accepted Answer

400 m

Answer

200 m

Answer

500 m

Answer

100 m

Question 8

What is the primary reservoir for scrub typhus?

Accepted Answer

Rodents

Answer

Mites

Answer

Humans

Answer

Dogs

Question 9

What is the concentration of sodium in mOsm/L in low osmolar ORS?

Accepted Answer

75

Answer

45

Answer

90

Answer

60

Question 10

What is the recommended threshold for parasite prevalence (API) for initiating Malaria Mass Drug Administration?

Accepted Answer

Greater than 2

Answer

Greater than 5

Answer

15

Answer

25

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?