Infectious Diseases Practice Questions

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.

Q: When did the WHO declare the global eradication of smallpox?

8th May 1980. **Explanation:** The correct answer is **8th May 1980**. This date marks a monumental milestone in public health history when the **33rd World Health Assembly** officially declared the global eradication of smallpox. Smallpox remains the only human infectious disease to be completely eradicated through vaccination. **Analysis of Options:** * **8th May 1980 (Correct):** The official date of the WHO declaration of global eradication. * **26th October 1977:** This is the date of the **last naturally occurring case** of Smallpox (*Variola minor*) in the world, reported in Ali Maow Maalin in Merca, Somalia. * **5th July 1975:** This marks the date of the **last case of Smallpox in India** (specifically, the last case of *Variola major* in a patient named Rahima Banu in Bangladesh occurred later in Oct 1975, but India was declared smallpox-free in April 1977). * **17th May 1975:** This is a distractor date often confused with the timeline of the National Smallpox Eradication Programme (NSEP) in India. **High-Yield Clinical Pearls for NEET-PG:** * **Eradication vs. Elimination:** Eradication refers to the global extinction of the pathogen (Smallpox), while elimination refers to the interruption of transmission in a specific geographic area (e.g., Polio in India). * **Vaccine Type:** The Smallpox vaccine used the **Live Vaccinia virus** (not Variola). * **Last Case (Lab Accident):** The absolute last human case occurred in **1978** due to a laboratory accident in Birmingham, UK (Janet Parker). * **Bifurcated Needle:** The specific tool used for the "Multiple Puncture Method" of vaccination, which was crucial for the eradication campaign.

Q: What is the reservoir of plague?

Wild rat. **Explanation:** In the epidemiology of Plague (*Yersinia pestis*), it is crucial to distinguish between the **reservoir** (where the pathogen lives and multiplies long-term) and the **vector** (which transmits the pathogen). **Why Wild Rats are the Correct Answer:** Wild rodents (such as gerbils and marmots) are the **natural reservoir** of plague. They maintain the infection in nature through a cycle known as the **Sylvatic (Wild) Cycle**. These animals have a high degree of resistance to the bacteria, allowing the pathogen to persist in these populations for long periods without causing total extinction of the host. **Analysis of Incorrect Options:** * **Domestic Rat (Option A):** While domestic rats (e.g., *Rattus rattus*) are highly susceptible to plague, they are considered **incidental hosts** or "amplifying hosts" rather than the primary reservoir. When domestic rats die off in large numbers (epizootic), the fleas are forced to seek human hosts, leading to urban outbreaks. * **Rat Flea (Option C):** *Xenopsylla cheopis* is the **vector**, not the reservoir. It transmits the bacteria from rodents to humans via the "blocked flea" mechanism. * **Man (Option D):** Humans are **accidental hosts** and represent a "dead-end" for the bacteria (except in pneumonic plague, where human-to-human transmission occurs via droplets). **High-Yield NEET-PG Pearls:** * **Primary Vector:** *Xenopsylla cheopis* (most efficient). * **Index of Transmission:** The **Flea Index** (specifically the Cheopis index >1 is considered a danger signal for plague outbreaks). * **Quarantine Period:** 6 days. * **Drug of Choice:** Streptomycin (Treatment); Tetracycline/Doxycycline (Prophylaxis). * **Vaccine:** No longer recommended by the WHO for routine use; control focuses on flea and rodent management.

Question 1

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 2

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

Accepted Answer

Anopheles

Answer

Culex

Answer

Aedes

Answer

Sandfly

Question 3

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 4

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 5

Which of the following diseases is NOT transmitted by milk?

Accepted Answer

Leishmaniasis

Answer

Tuberculosis

Answer

Brucellosis

Answer

Q Fever

Question 6

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 7

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 8

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

Question 9

When did the WHO declare the global eradication of smallpox?

Accepted Answer

8th May 1980

Answer

26th October 1977

Answer

5th July 1975

Answer

17th May 1975

Question 10

What is the reservoir of plague?

Accepted Answer

Wild rat

Answer

Domestic rat

Answer

Rat flea

Answer

Man

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?