Infectious Diseases Practice Questions

Q: Which of the following exposures carries the maximum risk of transmission of HIV?

Blood transfusion. The risk of HIV transmission depends on the route of exposure, the viral load in the source fluid, and the volume of inoculum. **Correct Option: A. Blood Transfusion** Blood transfusion carries the highest risk of HIV transmission, estimated at approximately **90–92% per exposure**. This is because a large volume of infected blood is introduced directly into the recipient's systemic circulation. When a unit of blood contaminated with HIV is transfused, seroconversion is almost certain. **Explanation of Incorrect Options:** * **B. Sexual Intercourse:** While this is the most common mode of transmission globally, the risk per single act is relatively low. Receptive anal intercourse carries the highest risk among sexual acts (~1.38%), followed by receptive vaginal intercourse (~0.08%). * **C. Needle Prick:** The average risk of HIV transmission after a percutaneous exposure to HIV-infected blood (e.g., accidental needlestick) is approximately **0.3%**. For mucous membrane exposure, it is even lower (~0.09%). * **D. Transplacental:** Mother-to-child transmission (MTCT) can occur during pregnancy, delivery, or breastfeeding. Without intervention, the risk ranges from **15% to 45%**; however, with effective Antiretroviral Therapy (ART), this can be reduced to Vertical Transmission (without ART) > Receptive Anal Sex > Needle Prick > Receptive Vaginal Sex. * **Post-Exposure Prophylaxis (PEP):** Should be started as soon as possible, ideally within **2 hours** and no later than **72 hours**, continuing for **28 days**. * **Standard PEP Regimen:** Tenofovir (300mg) + Lamivudine (300mg) + Dolutegravir (50mg) once daily.

Q: Which of the following statements about measles is incorrect?

The infectivity of measles is low.. ### Explanation **Why Option C is the correct answer (Incorrect Statement):** Measles is one of the most highly contagious infectious diseases known to mankind. The infectivity of measles is **extremely high**, not low. It has a **Secondary Attack Rate (SAR) of >90%** among susceptible household contacts. The basic reproduction number ($R_0$) for measles is estimated to be between 12 and 18, meaning one infected individual can spread the virus to 12–18 non-immune people. **Analysis of other options:** * **Option A (Koplik's spots are pathognomonic):** This is a **correct** statement. Koplik’s spots (small white spots on a red background on the buccal mucosa opposite the lower second molars) appear during the pre-eruptive stage and are unique to measles. * **Option B (Source of infection is a case):** This is a **correct** statement. There are no known animal reservoirs or long-term carriers for measles. The infection is spread solely by human cases via respiratory droplets. * **Option D (Affects age group 1 to 3 years):** This is a **correct** statement. In endemic areas with high birth rates, measles primarily affects children aged 6 months to 3 years. Maternal antibodies usually protect the infant for the first 6 months of life. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Period:** From 4 days before to 5 days after the appearance of the rash. * **Incubation Period:** Typically 10 days from exposure to fever and 14 days to rash. * **Vitamin A:** Supplementation is mandatory in measles management to reduce mortality and complications like blindness. * **MC Complication:** Otitis media is the most common complication; however, **Pneumonia** is the most common cause of measles-related death. * **SSPE:** Subacute sclerosing panencephalitis is a rare, delayed, fatal neurological complication occurring years after the initial infection.

Q: Under the National Malaria Eradication Programme (NMEP), what is the minimum annual blood examination rate that should be achieved?

10%. **Explanation:** The **Annual Blood Examination Rate (ABER)** is a critical process indicator used to monitor the efficiency and operational coverage of malaria surveillance activities. It represents the percentage of the total population from which blood smears (thick and thin) are collected and examined for malaria parasites over one year. **1. Why 10% is Correct:** Under the National Malaria Eradication Programme (now integrated into the National Center for Vector Borne Diseases Control - NCVBDC), a **minimum ABER of 10%** is required to ensure adequate surveillance. This threshold is based on the epidemiological assumption that approximately 10% of the population in a malarious area will suffer from fever at least once a year. If the ABER falls below 10%, it indicates "poor surveillance," meaning cases are likely being missed, which could lead to an undetected outbreak. **2. Analysis of Incorrect Options:** * **B (12%) & C (14%):** While achieving a higher ABER (e.g., 15% or more) is encouraged in high-endemic areas to ensure no cases are missed, these are not the "minimum" statutory requirement set by the national guidelines. * **D (18%):** This value is significantly higher than the standard requirement and does not correspond to any specific surveillance target under the NMEP/NVBDCP. **3. High-Yield Clinical Pearls for NEET-PG:** * **ABER Formula:** (Number of blood slides examined in a year / Total population) × 100. * **API (Annual Parasite Incidence):** The most sensitive index to measure the malaria burden in a community. Formula: (Total confirmed cases in a year / Total population) × 1000. * **Surveillance Types:** ABER includes both **Active Case Detection (ACD)** (health workers visiting houses) and **Passive Case Detection (PCD)** (patients reporting to clinics). * **SPR (Slide Positivity Rate):** (Total slides positive / Total slides examined) × 100. This measures the validity of the surveillance.

Q: Safe injection practices can prevent which of the following diseases?

Hepatitis B. **Explanation:** The core concept behind this question is the **mode of transmission** of viral hepatitis. Safe injection practices are designed to prevent the transmission of **blood-borne pathogens** (infections spread through blood and body fluids). **Why Hepatitis B is correct:** Hepatitis B Virus (HBV) is primarily transmitted through parenteral routes, including contaminated needles, syringes, and medical equipment. Safe injection practices—such as using a sterile needle for every patient, preventing needle-stick injuries, and avoiding the reuse of multidose vials—directly interrupt this chain of transmission. Other blood-borne diseases prevented by these practices include Hepatitis C and HIV. **Why the other options are incorrect:** * **Hepatitis A and Hepatitis E:** These viruses are transmitted via the **fecal-oral route**, usually through contaminated food or water. While they are types of hepatitis, they are not typically associated with percutaneous (injection) exposure. * **Typhoid (Enteric Fever):** Caused by *Salmonella typhi*, this is also a water-borne/food-borne disease transmitted via the fecal-oral route. **High-Yield Clinical Pearls for NEET-PG:** * **HBV Infectivity:** HBV is highly infectious; the risk of transmission after a needle-stick injury from an HBeAg-positive source is approximately **30%** (compared to 3% for HCV and 0.3% for HIV). * **WHO Definition:** A safe injection is one that does not harm the recipient, does not expose the provider to any avoidable risk, and does not result in waste that is dangerous to the community. * **Injection Safety:** The use of **Auto-Disable (AD) syringes** is the gold standard recommended by the WHO to prevent reuse.

Q: A freshly prepared oral rehydration solution should not be used after how many hours?

24 hours. **Explanation:** The correct answer is **24 hours (Option D)**. **Why it is correct:** Oral Rehydration Solution (ORS) is a glucose-electrolyte solution used to prevent and treat dehydration. Once the ORS powder is dissolved in water, it becomes a potential medium for bacterial growth. The glucose in the solution acts as a substrate for microorganisms, and since the solution is often kept at room temperature in domestic settings, the risk of contamination increases over time. According to WHO and UNICEF guidelines, any unused portion of the prepared solution must be discarded after 24 hours to ensure safety and prevent secondary gastrointestinal infections. **Why other options are incorrect:** * **4, 6, and 12 hours (Options A, B, C):** While the solution is certainly safe during these intervals, discarding it this early would be wasteful, especially in resource-limited settings. The 24-hour mark is the standardized clinical threshold where the risk of microbial contamination outweighs the benefit of the solution. **High-Yield Clinical Pearls for NEET-PG:** * **Composition of WHO Reduced Osmolarity ORS:** Total osmolarity is **245 mOsm/L**. (Sodium: 75, Glucose: 75, Chloride: 65, Potassium: 20, Citrate: 10 mmol/L). * **Trisodium Citrate:** It is added to ORS to increase shelf life and help in the correction of acidosis. * **Zinc Supplementation:** Always given alongside ORS in diarrhea (20 mg/day for 14 days; 10 mg for infants <6 months) to reduce the duration and severity of the episode. * **Home-made ORS:** If commercial packets are unavailable, a solution of 6 teaspoons of sugar and 1/2 teaspoon of salt in 1 liter of water is recommended.

Q: Which of the following are vector-borne diseases?

Japanese encephalitis. **Explanation:** Vector-borne diseases are illnesses caused by pathogens (viruses, bacteria, or parasites) transmitted to humans by organisms like mosquitoes, ticks, or lice. **Japanese Encephalitis (JE)** is a classic vector-borne viral disease caused by a Flavivirus. It is transmitted to humans through the bite of infected **Culex mosquitoes** (primarily *Culex tritaeniorhynchus*). The virus cycles between vertebrate hosts (pigs and water birds) and mosquitoes, with humans acting as "dead-end" hosts. **Analysis of Options:** * **Epidemic Typhus (Option A):** While this is technically vector-borne (transmitted by the human body louse, *Pediculus humanus corporis*), in the context of standard NEET-PG questions, JE is often the prioritized answer for "vector-borne" unless multiple selections are allowed. However, if this were a single-choice question where JE is marked correct, it highlights JE's higher prevalence in the Indian public health context. * **Tetanus (Option C):** This is **not** vector-borne. It is caused by the contamination of wounds with spores of *Clostridium tetani*, typically found in soil or manure. * **Kyasanur Forest Disease (Option D):** KFD is also a vector-borne disease (transmitted by **Hard Ticks**, *Haemaphysalis spinigera*). If the question allows only one answer and JE is marked, it may be due to JE's status as a major National Health Program priority. **High-Yield Clinical Pearls for NEET-PG:** * **JE Vector:** *Culex* mosquitoes breed in stagnant water, specifically **irrigated rice fields**. * **JE Host:** Pigs are "amplifier hosts"; Ardeid birds are "reservoir hosts." * **KFD:** Known as "Monkey Fever"; localized to Karnataka and surrounding Western Ghats. * **Epidemic Typhus:** Caused by *Rickettsia prowazekii*; transmitted by lice (Brill-Zinsser disease is the recrudescent form).

Q: Diethyltoluamide is an effective agent against which of the following?

Repellent. **Explanation:** **Diethyltoluamide (DEET)** is the most widely used chemical **insect repellent** worldwide. It works by interfering with the chemoreceptors on the antennae of biting insects (such as mosquitoes, ticks, and fleas), effectively "masking" the host's scent or acting as an irritant that prevents the insect from landing or biting. * **Why Option C is Correct:** DEET is the gold standard for personal protection against vector-borne diseases. It is applied topically to skin or clothing. It does not kill the insect but prevents contact between the vector and the human host. * **Why Options A & B are Incorrect:** Larvicides (e.g., Temephos, Abate) and agents targeting pupae (e.g., Paris Green or mineral oils) are used for **source reduction** in water bodies. DEET has no efficacy in killing the immature stages of the mosquito life cycle. * **Why Option D is Incorrect:** Space sprays (e.g., Pyrethrum extract) are used for "knock-down" effects in indoor or outdoor environments to kill adult mosquitoes instantly. DEET is a personal protective measure, not an environmental spray. **High-Yield Facts for NEET-PG:** * **Duration of Action:** A 30% concentration of DEET typically provides protection for about 6 hours. * **Safety:** It is generally safe for adults and children over 2 months of age, but high concentrations should be avoided in infants due to the risk of neurotoxicity (encephalopathy). * **Other Repellents:** Dimethyl phthalate (DMP), Dibutyl phthalate, and Picaridin are other examples. * **Chemoprophylaxis vs. Repellent:** While DEET prevents the bite (mechanical), drugs like Doxycycline or Mefloquine provide pharmacological prophylaxis against the pathogen itself.

Question 1

Which of the following exposures carries the maximum risk of transmission of HIV?

Accepted Answer

Blood transfusion

Answer

Sexual intercourse

Answer

Needle prick

Answer

Transplacental

Question 2

Which of the following statements about measles is incorrect?

Accepted Answer

The infectivity of measles is low.

Answer

Koplik's spots are pathognomonic.

Answer

The source of infection is typically a case of measles.

Answer

Measles commonly affects the age group of 1 to 3 years.

Question 3

Filaria elimination is possible in the South-East Asian region due to all of the following reasons EXCEPT:

Accepted Answer

Humans are the only reservoir.

Answer

The parasite does not multiply in the intermediate host mosquito.

Answer

Larvae multiply in the human reservoir only.

Answer

Infectious larvae are deposited on the skin but most of them die before penetrating.

Question 4

Under the National Malaria Eradication Programme (NMEP), what is the minimum annual blood examination rate that should be achieved?

Accepted Answer

10%

Answer

12%

Answer

14%

Answer

18%

Question 5

Which of the following is NOT a mosquito-borne disease?

Accepted Answer

Tularemia

Answer

Yellow fever

Answer

Kala-azar

Answer

Dengue fever

Question 6

Safe injection practices can prevent which of the following diseases?

Accepted Answer

Hepatitis B

Answer

Hepatitis A

Answer

Typhoid

Answer

Hepatitis E

Question 7

A freshly prepared oral rehydration solution should not be used after how many hours?

Accepted Answer

24 hours

Answer

4 hours

Answer

6 hours

Answer

12 hours

Question 8

Which of the following are vector-borne diseases?

Accepted Answer

Japanese encephalitis

Answer

Epidemic typhus

Answer

Tetanus

Answer

Kyasanur Forest Disease (KFD)

Question 9

Diethyltoluamide is an effective agent against which of the following?

Accepted Answer

Repellent

Answer

Larvicidal

Answer

Agent against pupae of Anopheles

Answer

Space spray

Question 10

Which of the following is true for Directly Observed Treatment, Short-course (DOTS)?

Accepted Answer

Treatment is provided under direct supervision

Answer

All patients receive the exact same treatment regimen

Answer

Streptomycin is administered to every patient

Answer

The treatment regimen is administered daily

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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