Infectious Diseases Practice Questions

Q: Acute flaccid paralysis is reported in a child aged -

0-15 years. ### Explanation **1. Why Option C is Correct:** Under the **Global Polio Eradication Initiative**, Acute Flaccid Paralysis (AFP) surveillance is the gold standard for detecting poliomyelitis. The operational definition for AFP surveillance includes any child **under the age of 15 years** who presents with recent onset of floppy weakness (including Guillain-Barré syndrome, transverse myelitis, or traumatic neuritis). Additionally, the surveillance system includes any person of any age if polio is strongly suspected by a clinician. The 0–15 age group is targeted because children in this bracket are most susceptible to paralytic poliomyelitis. **2. Why Other Options are Incorrect:** * **Option A (0-3 years) & B (0-5 years):** While children under 5 are at the highest risk for contracting the poliovirus, surveillance must be broader to ensure no cases are missed. Limiting surveillance to these ages would result in poor sensitivity and failure to detect late-childhood cases. * **Option D (0-25 years):** This range is too broad for routine AFP surveillance. While adults can contract polio, the epidemiological focus for eradication remains on the pediatric population where transmission is most active. **3. High-Yield Clinical Pearls for NEET-PG:** * **AFP Surveillance Goal:** To achieve a "Non-polio AFP rate" of at least **2 per 100,000** children under 15 years (an indicator of a sensitive surveillance system). * **Stool Collection:** Two "adequate" stool samples must be collected **24–48 hours apart** within **14 days** of the onset of paralysis. * **Zero Reporting:** This is a key component where health facilities must report "zero cases" weekly if no AFP cases are detected, ensuring active monitoring. * **India Status:** India was declared Polio-free by the WHO on **March 27, 2014** (last case reported in Jan 2011, Howrah, West Bengal).

Q: Case Fatality Rate (CFR) of Rabies is:

100%. ### Explanation **1. Understanding the Correct Answer (C. 100%)** Case Fatality Rate (CFR) is a measure of the **virulence** or killing power of a disease, calculated as the number of deaths divided by the total number of diagnosed cases. Rabies is unique in clinical medicine because once the virus enters the central nervous system and symptoms appear, it is considered **universally fatal**. There is no effective cure for clinical rabies, and death typically occurs within 2 to 10 days due to respiratory paralysis or cardiac arrest. Therefore, the CFR is mathematically and clinically 100%. **2. Analysis of Incorrect Options (A, B, D)** Options A (80%), B (90%), and D (95%) are incorrect because they suggest a possibility of survival or recovery after the onset of symptoms. While modern intensive care (e.g., the Milwaukee Protocol) has attempted to treat symptomatic patients, these cases are extreme statistical outliers and have not successfully altered the established 100% CFR in medical literature. **3. NEET-PG High-Yield Clinical Pearls** * **Definition of CFR:** It is a ratio (expressed as a percentage), not a rate, as it does not involve a time component in the denominator. * **Indicator of Virulence:** CFR is the best indicator of the virulence of an infectious agent. * **Rabies Prevention:** While the CFR is 100%, the disease is **100% preventable** through timely Post-Exposure Prophylaxis (PEP), including wound washing, Rabies Vaccine, and Rabies Immunoglobulin (RIG). * **Incubation Period:** Typically 1–3 months but can range from 1 year. * **Diagnostic Hallmark:** Presence of **Negri bodies** (intracytoplasmic inclusion bodies) in the hippocampus and cerebellum (post-mortem).

Q: A patient presents with a dog bite on the palm and fingers, with oozing of blood on the neck region. To which class of exposure does this situation belong?

Class III. **Explanation:** The classification of rabies exposure is based on the severity of the contact and the risk of viral transmission. This patient falls into **Class III (Category III)** exposure due to the nature and location of the injuries. **1. Why Class III is correct:** According to WHO and National Guidelines, Class III exposure involves: * **Single or multiple transdermal bites or scratches** (wounds that draw blood). * **Licks on broken skin** or contamination of mucous membranes with saliva. * **Exposure to bats.** * **High-risk locations:** Bites on highly innervated areas like the **palms, fingers, face, and neck** are automatically considered high-risk because the virus has a shorter distance to travel to the central nervous system. Since this patient has bleeding wounds on the palm/fingers and neck, it is a definitive Class III exposure requiring both **Rabies Vaccine** and **Rabies Immunoglobulin (RIG)**. **2. Why other options are incorrect:** * **Class I:** Involves touching or feeding animals, or licks on intact skin. No treatment is required. * **Class II:** Involves minor scratches or abrasions without bleeding, or nibbling of uncovered skin. These require immediate vaccination but usually do not require RIG. **High-Yield Clinical Pearls for NEET-PG:** * **Management of Class III:** Wound washing (15 mins) + Full course of Vaccine + RIG (infiltrated around the wound). * **Site of Injection:** Intramuscular (IM) vaccine is given in the **deltoid** (never the gluteal region). * **Post-Exposure Prophylaxis (PEP):** Modern cell culture vaccines (IDRV) follow the **Updated Thai Red Cross Schedule** (2-2-2-0-2) or the **Essen Schedule** (1-1-1-1-1). * **Rule of Thumb:** Any bite that draws blood is Category III. Any bite on the head, neck, or hands is treated with maximum caution.

Q: Larvae of which of the following lies parallel to the surface of water?

Anopheles. The correct answer is **Anopheles**. ### **Explanation** The orientation of mosquito larvae in water is a classic high-yield distinction in medical entomology. * **Anopheles:** The larvae lack a respiratory siphon. To breathe, they must lie **parallel (horizontal)** to the water surface to allow their posterior respiratory spiracles to make direct contact with the air. They are often referred to as "surface feeders." * **Culex and Aedes:** These larvae possess a **respiratory siphon** (a tube-like structure). This allows them to hang **at an angle (obliquely)** from the water surface while breathing, with only the tip of the siphon piercing the surface film. * **Sandfly:** This is a distractor. Sandflies (*Phlebotomus*) do not have an aquatic life cycle; their larvae develop in moist soil rich in organic matter, not in standing water. ### **High-Yield Clinical Pearls for NEET-PG** To differentiate these vectors quickly, remember these "Rule of Opposites": | Feature | Anopheles | Culex / Aedes | | :--- | :--- | :--- | | **Larva Position** | Parallel to surface | At an angle (Oblique) | | **Siphon Tube** | Absent | Present | | **Adult Resting** | At an angle (45°) | Parallel to surface | | **Eggs** | Laid singly with lateral floats | Rafts (Culex) / Singly without floats (Aedes) | | **Feeding Time** | Night biters | Day biters (Aedes) / Night biters (Culex) | **Key Disease Associations:** * **Anopheles:** Vector for Malaria. * **Culex:** Vector for Japanese Encephalitis, West Nile Virus, and Bancroftian Filariasis. * **Aedes:** Vector for Dengue, Chikungunya, Zika, and Yellow Fever.

Q: Which of the following drugs is used for mass prophylaxis for the prevention of meningococcal meningitis?

Ciprofloxacin. **Explanation:** The goal of prophylaxis in meningococcal meningitis is to eradicate the nasopharyngeal carriage of *Neisseria meningitidis*, thereby preventing the spread of the disease to close contacts and the community. **Why Ciprofloxacin is the Correct Answer:** **Ciprofloxacin** (500 mg, single oral dose) is currently the drug of choice for **mass prophylaxis**. It is highly effective in eliminating the carrier state, has the advantage of being a single-dose oral regimen, and is generally well-tolerated. In the context of public health and "mass" administration, its ease of use and cost-effectiveness make it superior to multi-dose regimens. **Analysis of Incorrect Options:** * **Rifampicin:** While historically the gold standard, it is no longer preferred for *mass* prophylaxis because it requires a 2-day course (four doses), induces cytochrome P450 enzymes (leading to drug interactions), and carries a high risk of developing rapid bacterial resistance. It also turns secretions orange, which can affect compliance. * **Ceftriaxone:** This is highly effective and is the drug of choice for prophylaxis in **pregnant women**. However, it must be administered via intramuscular injection, making it impractical for large-scale "mass" prophylaxis. * **Minocycline:** Although it can eradicate the carrier state, it is rarely used due to a high incidence of vestibular side effects (vertigo, dizziness, and nausea). **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (General/Mass):** Ciprofloxacin (Single dose). * **Drug of Choice (Pregnancy):** Ceftriaxone (Single IM injection). * **Alternative for Children:** Rifampicin or Ceftriaxone. * **Note:** Prophylaxis is indicated for close contacts (household, daycare) but is **not** recommended for casual contacts (school or office) unless an outbreak is confirmed.

Q: Which of the following diseases is NOT transmitted by milk?

Leishmaniasis. **Explanation:** The correct answer is **Leishmaniasis (Option D)**. This is because Leishmaniasis is a protozoan disease transmitted exclusively through the bite of an infected female **sandfly** (*Phlebotomus* species). It is a vector-borne disease and does not involve an oral-fecal or milk-borne route of transmission. **Why the other options are incorrect:** Milk can act as a vehicle for various bacterial and viral pathogens, usually through direct excretion from an infected udder or secondary contamination during handling. * **Tuberculosis (Option A):** *Mycobacterium bovis* causes bovine TB and is classically transmitted to humans via the consumption of unpasteurized milk from infected cows. * **Brucellosis (Option B):** Also known as "Undulant Fever," *Brucella* species are highly resilient in raw milk and dairy products (like fresh cheese). This is the most common route of transmission for humans. * **Q Fever (Option C):** Caused by *Coxiella burnetii*, the organism is excreted in high concentrations in the milk, urine, and feces of infected livestock (cattle, sheep, goats). While inhalation is the primary route, ingestion of raw milk is a recognized secondary route. **High-Yield Clinical Pearls for NEET-PG:** * **Milk-borne diseases** are classified into: 1. **Infections from the animal:** Bovine TB, Brucellosis, Q Fever, Salmonellosis, and Anthrax. 2. **Infections from human handling:** Typhoid, Cholera, Shigellosis, and Staphylococcal food poisoning. * **Pasteurization** (Holder’s method: 63°C for 30 mins or HTST: 72°C for 15 secs) is designed to kill the most heat-resistant milk-borne pathogen, *Coxiella burnetii*. * **Phosphatase Test** is used to check the efficiency of pasteurization.

Q: Which of the following statements is NOT true regarding the Annual Infection Rate (AIR) of tuberculosis?

A 1% increase in AIR is equivalent to 70 new cases of TB.. **Explanation** The **Annual Infection Rate (AIR)**, also known as the Annual Risk of Tuberculosis Infection (ARTI), is a critical epidemiological metric in TB control. **Why Option A is the Correct Answer (The False Statement):** The statement is mathematically incorrect. According to Styblo’s rule, a **1% AIR corresponds to approximately 50 new cases of smear-positive pulmonary tuberculosis** per 100,000 population, not 70. This ratio helps epidemiologists estimate the incidence of disease based on infection surveys. **Analysis of Other Options:** * **Option B:** AIR is indeed considered the **best indicator** for evaluating the TB problem and its trends in a community because it is less affected by the quality of diagnostic services compared to notification rates. * **Option C:** It represents the "attacking force" of TB because it measures the probability of a person being infected (or reinfected) with *M. tuberculosis* over the course of one year. * **Option D:** Historically, the AIR in India has been estimated at approximately **1.7%**, though this varies by region and has shown a declining trend in recent years due to the National Tuberculosis Elimination Program (NTEP) interventions. **High-Yield Clinical Pearls for NEET-PG:** * **Calculation:** AIR is typically measured using Tuberculin Skin Tests (Mantoux) in unvaccinated children (to avoid BCG interference). * **Prevalence vs. Incidence:** AIR reflects the *incidence of infection*, whereas the number of active cases reflects the *prevalence/incidence of disease*. * **Styblo’s Rule:** 1% ARTI ≈ 50 Smear +ve cases/1 lakh population. * **Primary Tool:** AIR is the most sensitive tool to monitor the long-term impact of TB control programs.

Q: All of the following statements are true about pertussis except:

Leukocytosis correlates with the severity of cough. **Explanation:** The correct answer is **C**. While pertussis (Whooping Cough) is characterized by a striking **absolute lymphocytosis**, the degree of leukocytosis does **not** correlate with the severity of the cough. Instead, the severity of lymphocytosis is a predictor of poor prognosis and the development of pulmonary hypertension in infants. **Analysis of Options:** * **Option A (True):** Pertussis is highly contagious among household contacts. The **Secondary Attack Rate (SAR)** is typically cited as **>90%** (some texts say 80-100%), making it one of the most infectious respiratory diseases. * **Option B (True):** Unlike many other bacterial infections, *Bordetella pertussis* does not have a recognized chronic carrier state. Humans are the only reservoir, and the infection is maintained by a cycle of transmission between symptomatic or mildly symptomatic individuals. * **Option D (True):** **Erythromycin** (or other Macrolides like Azithromycin/Clarithromycin) is the drug of choice. While it does not significantly alter the clinical course if started in the paroxysmal stage, it is crucial for eliminating the organism from the nasopharynx and limiting transmission. **High-Yield Clinical Pearls for NEET-PG:** * **Infectivity:** Maximum during the **catarrhal stage** (first 1-2 weeks). * **Diagnosis:** Gold standard is **Culture** (Regan-Lowe or Bordet-Gengou medium). PCR is now the preferred rapid test. * **Vaccination:** The "aP" in DTaP stands for acellular pertussis, which has fewer side effects than the whole-cell (wP) vaccine but may have shorter-lived immunity. * **Chemoprophylaxis:** Recommended for all household contacts regardless of vaccination status.

Q: Smallpox eradication was successful because of all the following factors except:

Cross-resistance existed with animal pox viruses. **Explanation:** The eradication of Smallpox (declared by the WHO on May 8, 1980) is a landmark achievement in public health. The correct answer is **Option D** because cross-resistance with animal pox viruses was **not** a factor that contributed to its eradication. In fact, the Variola virus (Smallpox) was strictly a human pathogen with no animal reservoir, which was a primary reason why eradication was possible. **Why the other options are incorrect (Factors that DID help eradication):** * **A. Subclinical cases do not transmit the disease:** Smallpox was always clinically apparent. Since there were no asymptomatic carriers or subclinical infections spreading the virus silently, health workers could easily identify, isolate, and trace contacts (the "Ring Vaccination" strategy). * **B. Highly effective vaccine:** The bifurcated needle and the heat-stable lyophilized vaccine allowed for easy administration and potency in tropical climates without a strict cold chain. * **C. Lifelong immunity:** A single infection or successful vaccination provided long-lasting, solid immunity, preventing re-infection within the population. **High-Yield NEET-PG Pearls:** * **Last Case:** The last naturally occurring case of *Variola major* was in **Rahima Banu** (Bangladesh, 1975); the last case of *Variola minor* was in **Ali Maow Maalin** (Somalia, 1977). * **Strategy Shift:** Eradication was achieved by shifting from "Mass Vaccination" to **"Surveillance and Containment"** (Ring Vaccination). * **Incubation Period:** 7–14 days (highly predictable). * **Key Biological Feature:** No animal reservoir and no chronic carrier state. If a virus cannot hide in animals or asymptomatic humans, it can be eliminated.

Question 1

Acute flaccid paralysis is reported in a child aged -

Accepted Answer

0-15 years

Answer

0-3 years

Answer

0-5 years

Answer

0-25 years

Question 2

Case Fatality Rate (CFR) of Rabies is:

Accepted Answer

100%

Answer

80%

Answer

90%

Answer

95%

Question 3

A patient presents with a dog bite on the palm and fingers, with oozing of blood on the neck region. To which class of exposure does this situation belong?

Accepted Answer

Class III

Answer

Class I

Answer

Class II

Answer

None of the above

Question 4

Larvae of which of the following lies parallel to the surface of water?

Accepted Answer

Anopheles

Answer

Culex

Answer

Aedes

Answer

Sandfly

Question 5

Which of the following drugs is used for mass prophylaxis for the prevention of meningococcal meningitis?

Accepted Answer

Ciprofloxacin

Answer

Rifampicin

Answer

Ceftriaxone

Answer

Minocycline

Question 6

Which of the following statements are true about Pertussis?

Accepted Answer

Incubation period is 7-14 days, it can affect any age, and the secondary attack rate in unimmunized persons is 90%.

Answer

Incubation period is 7-14 days, main source of infection is chronic carriers, and it can affect any age.

Answer

Main source of infection is chronic carriers and it can affect any age.

Answer

Main source of infection is chronic carriers, the secondary attack rate in unimmunized persons is 90%, and it is more common in summers.

Question 7

Which of the following diseases is NOT transmitted by milk?

Accepted Answer

Leishmaniasis

Answer

Tuberculosis

Answer

Brucellosis

Answer

Q Fever

Question 8

Which of the following statements is NOT true regarding the Annual Infection Rate (AIR) of tuberculosis?

Accepted Answer

A 1% increase in AIR is equivalent to 70 new cases of TB.

Answer

It is one of the best indicators for evaluating the tuberculosis problem and its trend.

Answer

It expresses the attacking force of tuberculosis in the community.

Answer

The AIR in India is 1.7%.

Question 9

All of the following statements are true about pertussis except:

Accepted Answer

Leukocytosis correlates with the severity of cough

Answer

Secondary attack rate is > 90%

Answer

There is no subclinical or chronic carrier state

Answer

The drug of choice is erythromycin

Question 10

Smallpox eradication was successful because of all the following factors except:

Accepted Answer

Cross-resistance existed with animal pox viruses

Answer

Subclinical cases do not transmit the disease

Answer

A highly effective vaccine was available

Answer

The disease conferred lifelong immunity

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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