Infectious Diseases Practice Questions

Q: What is the true infectivity period of hepatitis A?

2-3 weeks before and 1 week after the onset of jaundice. **Explanation:** The infectivity of Hepatitis A Virus (HAV) is closely linked to the concentration of the virus excreted in the feces. The maximum viral shedding occurs during the late incubation period and the prodromal (pre-icteric) phase. **1. Why Option D is Correct:** According to standard epidemiological data (Park’s PSM), the period of maximum infectivity for Hepatitis A begins **2 to 3 weeks before** the onset of jaundice and continues for about **1 week after** the appearance of jaundice. By the time jaundice is clinically apparent, the viral titer in the stool begins to decline rapidly, and most patients are non-infectious by the end of the first week of the icteric phase. **2. Analysis of Incorrect Options:** * **Options A & C:** These suggest a 2-week post-jaundice infectivity period. While viral RNA can sometimes be detected longer, the "true infectivity" (the period where transmission is epidemiologically significant) typically ceases after 7 days of jaundice. * **Option B:** This underestimates the pre-icteric infectivity. The virus starts shedding significantly as early as 2-3 weeks before symptoms appear, making this the most dangerous period for community transmission. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mode of Transmission:** Primarily feco-oral; common in areas with poor sanitation. * **Secondary Attack Rate (SAR):** High among household contacts (approx. 20%). * **Diagnosis:** IgM anti-HAV is the gold standard for acute infection. * **Vaccination:** Live attenuated (H2 strain) or Inactivated vaccines are available. * **Post-exposure Prophylaxis:** Best given within 2 weeks of exposure (Vaccine or Immunoglobulin). * **Key Fact:** Hepatitis A does **not** cause chronic infection or a carrier state.

Q: Which of the following is NOT included in the 'SAFE' strategy?

Supplementation of vitamins. The **SAFE strategy** is a comprehensive public health approach recommended by the World Health Organization (WHO) for the elimination of **Trachoma**, the leading infectious cause of blindness worldwide. ### **Why "Supplementation of vitamins" is the correct answer:** Vitamin supplementation (specifically Vitamin A) is a core strategy for preventing Xerophthalmia and nutritional blindness, but it is **not** a component of the SAFE strategy. Trachoma is caused by *Chlamydia trachomatis* (serotypes A, B, Ba, and C), and its management focuses on surgical intervention, infection control, and hygiene rather than nutritional support. ### **Explanation of the SAFE Components:** * **S - Surgery:** To treat the blinding stage of the disease (Trachomatous Trichiasis) by correcting inward-turning eyelashes. * **A - Antibiotics:** Specifically the use of **Azithromycin** (single oral dose) or Tetracycline eye ointment to treat the active infection and reduce the community reservoir. * **F - Facial cleanliness:** Encouraging regular face washing, especially in children, to reduce the transmission of infected ocular and nasal secretions. * **E - Environmental improvement:** Improving access to water and sanitation (e.g., latrine construction) to reduce the population of **Musca sorbens** (eye-seeking flies) that act as vectors. ### **High-Yield Facts for NEET-PG:** * **Target:** The WHO "GET2020" initiative aimed to eliminate trachoma by 2020. * **Vector:** The common housefly (*Musca domestica*) and the eye-seeking fly (*Musca sorbens*). * **Drug of Choice:** Azithromycin (20 mg/kg up to 1g). * **India Status:** India was declared free from **infective trachoma** in 2017, though surveillance for trichiasis continues.

Q: Which of the following is NOT a component of the SAFE strategy?

Screening. The **SAFE strategy** is a comprehensive public health approach recommended by the WHO for the global elimination of **Trachoma** (caused by *Chlamydia trachomatis*). ### Why "Screening" is the Correct Answer The letter **'S'** in the SAFE acronym stands for **Surgery**, not Screening. While screening is a general public health activity, it is not a formal component of this specific management protocol. The goal of the 'S' component is to provide surgical correction (typically Bilamellar Tarsal Rotation) for individuals suffering from **trachomatous trichiasis** to prevent corneal opacity and blindness. ### Explanation of Incorrect Options * **Antibiotics (A):** This refers to the mass distribution of antibiotics (specifically **Azithromycin** 20mg/kg single dose or Tetracycline 1% eye ointment) to the entire community to treat active infection and reduce the reservoir of *C. trachomatis*. * **Facial hygiene (F):** This focuses on encouraging children and adults to wash their faces regularly. Clean faces reduce the transmission of infected ocular and nasal secretions. * **Environmental modification (E):** This involves improving access to clean water, proper sanitation, and **fly control** (specifically *Musca sorbens*), as flies are the primary mechanical vectors for the disease. ### High-Yield Clinical Pearls for NEET-PG * **Target Goal:** The WHO aims for the Global Elimination of Trachoma by the year **2030**. * **Vector:** *Musca sorbens* (the eye-seeking fly) is the most common vector. * **Drug of Choice:** Oral Azithromycin (Single dose) is the preferred treatment in the SAFE strategy. * **Trachoma Grading:** Remember the **WHO FISTO classification** (Follicular, Intense, Scarring, Trichiasis, Opacity) for clinical staging.

Q: If API is greater than 2, the vector is resistant to DDT. What is the recommended frequency for malathion spraying?

3 rounds of malathion every 3 months. ### Explanation **Concept & Correct Answer:** Under the **National Vector Borne Disease Control Programme (NVBDCP)**, the strategy for Indoor Residual Spraying (IRS) is determined by the **Annual Parasite Incidence (API)** and vector resistance patterns. When the **API is >2** and the vector (Anopheles mosquito) shows resistance to DDT, the program shifts to alternative insecticides. **Malathion** is an organophosphate used in such scenarios. Because Malathion has a shorter residual effect (approximately 6–8 weeks) compared to DDT, it requires more frequent applications to maintain effective coverage throughout the transmission season. The standard protocol for Malathion IRS is **3 rounds per year**, spaced at intervals of **every 3 months** (12 weeks). **Analysis of Incorrect Options:** * **Option B & D:** Monthly spraying is logistically impractical, expensive, and unnecessary for Malathion’s degradation profile. * **Option C:** 1–2 rounds are insufficient to cover the transmission period given Malathion's shorter residual efficacy. Two rounds are typically reserved for DDT (which lasts 6 months) or Synthetic Pyrethroids. **High-Yield Clinical Pearls for NEET-PG:** * **API Threshold:** API >2 is the cut-off for "High Risk" areas requiring mandatory IRS. * **Insecticide Rotation:** * **DDT:** 2 rounds/year (Residual effect: 6 months). * **Malathion:** 3 rounds/year (Residual effect: 2–3 months). * **Synthetic Pyrethroids (e.g., Deltamethrin):** 2 rounds/year. * **Dosage:** Malathion is applied at a dosage of **2 g/m²**. * **Malathion Fogging:** Used specifically during **outbreaks** or for Aedes (Dengue) control, whereas IRS is for routine Malaria control.

Q: What is considered the most dangerous type of diphtheria?

Laryngeal. **Explanation:** **Laryngeal diphtheria** is considered the most dangerous form because it poses an immediate threat to the airway. The hallmark of diphtheria is the formation of a **pseudomembrane** (composed of fibrin, leukocytes, and dead epithelial cells). In the larynx, this membrane can cause mechanical obstruction of the narrow glottic opening. Furthermore, edema and the potential for the membrane to detach and be aspirated can lead to sudden asphyxia and death. **Analysis of Options:** * **Nasal Diphtheria:** Generally the mildest form. It is characterized by serosanguinous discharge but has low systemic toxin absorption. However, it is highly important from an epidemiological perspective as a source of infection. * **Faucial (Pharyngeal) Diphtheria:** This is the most common clinical type. While it can lead to severe "bull neck" appearance due to lymphadenopathy and high toxin absorption (causing myocarditis), it is statistically less likely to cause immediate fatal airway obstruction compared to the laryngeal type. * **Cutaneous Diphtheria:** Usually presents as non-healing ulcers. It is rarely fatal as systemic toxin absorption from the skin is minimal. **High-Yield Clinical Pearls for NEET-PG:** * **Agent:** *Corynebacterium diphtheriae* (Gram-positive, club-shaped, Chinese-letter pattern). * **Schick Test:** Used to demonstrate the immune status of an individual (susceptibility). * **Treatment:** Prompt administration of **Diphtheria Antitoxin (ADS)** is the priority to neutralize unbound toxins. * **Carrier State:** Nasal carriers are more dangerous than throat carriers in spreading the disease. * **Drug of Choice:** Erythromycin (to stop toxin production and clear the carrier state).

Q: In the case of a dog bite, the biting animal should be observed for at least how many days?

10 days. **Explanation:** The correct answer is **10 days (Option B)**. This duration is based on the pathogenesis of the Rabies virus. In mammals, the virus only appears in the saliva (making the animal infectious) shortly before the onset of clinical symptoms or death. If a dog or cat remains healthy and alive for 10 days following a bite, it confirms that the animal was not shedding the virus in its saliva at the time of the incident, and therefore, the victim is not at risk of Rabies from that specific exposure. **Analysis of Options:** * **Option A (5 days):** This is too short. While some animals may die within 5 days, the shedding of the virus can precede symptoms by 3–7 days; thus, a 5-day window does not sufficiently rule out infectivity. * **Option C & D (15 days / 3 weeks):** These periods are unnecessarily long. Global guidelines (WHO and National Guidelines on Rabies Prophylaxis) have standardized the observation period to 10 days as it provides a 100% safety margin for clinical decision-making. **High-Yield Clinical Pearls for NEET-PG:** * **Observation vs. Treatment:** Post-Exposure Prophylaxis (PEP) should be started **immediately** and should not be delayed while waiting for the observation period results, especially in Category II and III bites. If the animal remains healthy after 10 days, PEP can be discontinued. * **Species:** The 10-day observation rule applies specifically to **dogs, cats, and ferrets**. It does not apply to wild animals. * **Incubation Period:** While the observation period is 10 days, the incubation period in humans is highly variable (typically 1–3 months), depending on the site of the bite and viral load. * **Management:** Local wound washing with soap and water for 15 minutes is the most crucial first step in preventing Rabies.

Q: What is true about the Mantoux test?

The test is usually read after 48-72 hours.. **Explanation:** The Mantoux test (Tuberculin Skin Test) is a classic example of a **Type IV (Delayed-type) Hypersensitivity reaction**. When Purified Protein Derivative (PPD) is injected intradermally, it triggers a T-cell mediated response. This reaction takes time to develop, peaking between **48 to 72 hours**, which is why the induration must be measured during this specific window. **Analysis of Options:** * **Option A is incorrect:** A reaction is measured in **millimeters (mm)**, not centimeters. Furthermore, a reaction <5 mm is generally considered negative. * **Option B is incorrect:** Once a person is sensitized to *M. tuberculosis*, the Mantoux test usually remains positive for life, even after successful treatment. It cannot be used to monitor treatment efficacy. * **Option C is incorrect:** A positive reaction in children under 5 years (especially <2 years) is of **greater clinical significance**. It indicates recent infection and a high risk of progression to severe forms like tubercular meningitis or miliary TB. * **Option D is correct:** This is the standard protocol for reading the induration (not erythema). **High-Yield NEET-PG Pearls:** * **Dose:** 0.1 ml of PPD containing 5 TU (Tuberculin Units) is injected intradermally on the volar aspect of the forearm. * **False Negatives (Anergy):** Can occur in HIV/AIDS (low CD4 count), miliary TB, malnutrition, or recent viral infections (e.g., Measles). * **False Positives:** Can occur due to prior BCG vaccination or infection with Non-Tuberculous Mycobacteria (NTM). * **Booster Phenomenon:** A second test done shortly after an initial negative test may be positive due to "re-awakening" of the immune memory.

Question 1

What is the true infectivity period of hepatitis A?

Accepted Answer

2-3 weeks before and 1 week after the onset of jaundice

Answer

1-2 weeks before and 2 weeks after the onset of jaundice

Answer

1-2 weeks before and 1 week after the onset of jaundice

Answer

2-3 weeks before and 2 weeks after the onset of jaundice

Question 2

Which of the following is NOT included in the 'SAFE' strategy?

Accepted Answer

Supplementation of vitamins

Answer

Antibiotics

Answer

Face washing

Answer

Improvement of the environment

Question 3

Which of the following is NOT a component of the SAFE strategy?

Accepted Answer

Screening

Answer

Antibiotics

Answer

Facial hygiene

Answer

Environmental modification

Question 4

If API is greater than 2, the vector is resistant to DDT. What is the recommended frequency for malathion spraying?

Accepted Answer

3 rounds of malathion every 3 months

Answer

2 rounds of malathion every month

Answer

1-2 rounds of malathion every 3 months

Answer

1 round of malathion every month

Question 5

What is considered the most dangerous type of diphtheria?

Accepted Answer

Laryngeal

Answer

Facial

Answer

Nasal

Answer

Cutaneous

Question 6

Which of the following is NOT true regarding malaria?

Accepted Answer

Infant parasite rate is a poor indicator of malaria occurrence in a community.

Answer

Aberration (ABER) is used as an operational approach.

Answer

Spleen rate is an important indicator of the endemisity of malaria.

Answer

Malaria is usually caused by Plasmodium vivax.

Question 7

Regarding the epidemiology of AIDS, all the following statements are true EXCEPT:

Accepted Answer

Maternofetal transmission is the most common mode of transmission.

Answer

In India, AIDS is mainly caused by HIV-1.

Answer

Intravenous drug abuse increases the risk of transmission.

Answer

Medical personnel are at higher risk of acquiring HIV infection.

Question 8

In the case of a dog bite, the biting animal should be observed for at least how many days?

Accepted Answer

10 days

Answer

5 days

Answer

15 days

Answer

3 weeks

Question 9

What is true about the Mantoux test?

Accepted Answer

The test is usually read after 48-72 hours.

Answer

A reaction less than 5 cm is always positive.

Answer

The test is usually negative after treatment.

Answer

A positive reaction in children less than 2 years old is less important than in adults.

Question 10

Which of the following statements is true about the epidemiology of leprosy?

Accepted Answer

Insects can transmit leprosy.

Answer

A high prevalence of cases in childhood indicates that the disease is under control.

Answer

Lepra bacilli cannot survive outside the human body.

Answer

The bacterial load is high in the tuberculoid variety of leprosy.

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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