Air-Borne Diseases — MCQs
Which of the following infectious diseases has the highest proportion of asymptomatic chronic carriers?
Koplik's spots occur in which phase of measles -
Which of the following statements is true regarding the epidemiology of influenza?
Which TB drug causes optic neuritis as a side effect?
All of the following statements regarding measles are true, except:
Which of the following statements about the influenza virus is NOT true?
True about measles
A patient with TB on DOTS develops orange-red discoloration of urine and tears. Which drug is responsible?
Which immunization is typically given at 6 months of age?
A child comes with fever, cold, cough, and a membrane over the tonsils; a nasal swab is taken. On which medium should the culture be done for the earliest diagnosis of diphtheria?
Air-Borne Diseases Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following infectious diseases has the highest proportion of asymptomatic chronic carriers?
- A. Measles
- B. Rabies
- C. Diphtheria
- D. Hepatitis B (Correct Answer)
Explanation: ***Hepatitis B*** - **Hepatitis B** infection has a significant proportion of **chronic asymptomatic carriers**, particularly when infection occurs perinatally or in early childhood. - In adults, approximately **5% develop chronic infection** after acute exposure, and many of these chronic carriers remain asymptomatic while maintaining infectivity. - Chronic carriers can harbor the virus for years or decades without clinical symptoms, making them an important reservoir for transmission. - This is a major public health concern as asymptomatic carriers can unknowingly transmit the virus. *Measles* - **Measles** is highly contagious and typically presents with **symptomatic disease** in nearly all infected individuals. - Clinical features include characteristic maculopapular rash, cough, coryza, conjunctivitis, and Koplik's spots. - Asymptomatic infection is **extremely rare** with measles virus. *Diphtheria* - While **asymptomatic pharyngeal carriage** of *Corynebacterium diphtheriae* can occur, it is not the predominant pattern. - Clinical diphtheria typically presents with pseudomembrane formation, sore throat, and potential systemic toxin effects. - Carrier rates vary but are not as epidemiologically significant as with Hepatitis B. *Rabies* - **Rabies** is almost **100% symptomatic** once the virus reaches the central nervous system. - There is **no chronic asymptomatic carrier state** in humans. - Once clinical symptoms appear (encephalitis, hydrophobia, paralysis), the disease is virtually always fatal.
Question 2: Koplik's spots occur in which phase of measles -
- A. Post exanthematous phase
- B. End of prodromal phase (Correct Answer)
- C. Recrudescence phase
- D. Exanthematous phase
Explanation: ***End of prodromal phase*** - **Koplik's spots**, pathognomonic for measles, typically appear 1-2 days before the onset of the **maculopapular rash**, marking the very end of the **prodromal phase**. - These are small, white spots with a bluish-white center on an erythematous base, found on the **buccal mucosa** opposite the molars. *Post exanthematous phase* - This phase occurs *after* the rash has faded and is characterized by **desquamation** and **cough**, not the appearance of Koplik's spots. - Koplik's spots would have long disappeared by this stage. *Recrudescence phase* - This term usually refers to the **reappearance of symptoms** after a period of improvement, which is not characteristic of Koplik's spots in measles. - Koplik's spots represent an initial diagnostic sign rather than a recurrent symptom. *Exanthematous phase* - The **exanthematous phase** is when the characteristic **maculopapular rash** appears and spreads, typically starting a few days *after* Koplik's spots have already emerged and are beginning to fade. - While overlap can occur, Koplik's spots are *most prominent* and diagnostic *before* the rash fully develops.
Question 3: Which of the following statements is true regarding the epidemiology of influenza?
- A. Pandemics cannot occur with influenza viruses.
- B. Incubation period is typically 7-10 days.
- C. Humans are the only reservoir for influenza.
- D. Asymptomatic cases can occur and may contribute to transmission. (Correct Answer)
Explanation: ***Asymptomatic cases can occur and may contribute to transmission.*** - Asymptomatic or mildly symptomatic individuals can shed the virus, contributing to the silent spread of influenza within a community. - This characteristic makes **influenza control** challenging, as not all infected individuals seek medical attention or are easily identified. *Incubation period is typically 7-10 days.* - The typical incubation period for influenza is much shorter, usually **1 to 4 days**, with an average of 2 days. - A 7-10 day incubation period is more characteristic of infections like **measles** or **mumps**, not influenza. *Pandemics cannot occur with influenza viruses.* - Influenza viruses are well-known for their potential to cause **pandemics** through antigenic shifts, leading to novel strains against which the population has little to no immunity. - Historically, there have been several major influenza pandemics, such as the **1918 Spanish Flu** and the 2009 H1N1 pandemic. *Humans are the only reservoir for influenza.* - While humans are a significant reservoir, influenza viruses also circulate in **animal reservoirs** such as birds (especially wild aquatic birds) and pigs. - These animal reservoirs can serve as sources for new human strains through **inter-species transmission** and genetic reassortment.
Question 4: Which TB drug causes optic neuritis as a side effect?
- A. Isoniazid
- B. Pyrazinamide
- C. Rifampicin
- D. Ethambutol (Correct Answer)
Explanation: ***Ethambutol*** - **Ethambutol** is known to cause **optic neuritis**, leading to **decreased visual acuity** and impaired **red-green color discrimination**. - This side effect is **dose-dependent** and usually **reversible** upon discontinuing the drug, though permanent damage can occur with prolonged use. *Isoniazid* - **Isoniazid** is primarily associated with **peripheral neuropathy** and **hepatotoxicity**, which can be mitigated with **pyridoxine (vitamin B6)** supplementation. - While visual disturbances can occur, **optic neuritis** is not its most characteristic or frequent ocular side effect. *Pyrazinamide* - The main side effects of **pyrazinamide** include **hepatotoxicity** and **hyperuricemia**, which can lead to **gouty arthritis**. - It does not typically cause **optic neuritis** or other significant ocular complications. *Rifampicin* - **Rifampicin** is well-known for causing **hepatotoxicity**, **red-orange discoloration of body fluids** (urine, tears, sweat), and various **drug interactions** due to enzyme induction. - Ocular side effects like **optic neuritis** are not a common or characteristic adverse effect of rifampicin.
Question 5: All of the following statements regarding measles are true, except:
- A. Koplik spot are seen on retina (Correct Answer)
- B. I-P is 10-14 days
- C. Long term complication may be seen in form of SSPE
- D. Caused by RNA virus
- E. Rash appears first on face
Explanation: ***Koplik spot are seen on retina*** - **Koplik spots** are pathognomonic for measles and are typically found on the **buccal mucosa** (inside the cheeks), not on the retina [1]. - These are small, white, or bluish-white lesions with a red halo, appearing before the characteristic rash. *I-P is 10-14 days* - The **incubation period (I-P)** for measles, from exposure to the onset of symptoms, typically ranges from **10 to 14 days**. - This period includes the initial prodromal symptoms before the rash appears. *Long term complication may be seen in form of SSPE* - **Subacute sclerosing panencephalitis (SSPE)** is a rare, but fatal, **late complication** of measles infection [1]. - It results from persistent measles virus infection in the central nervous system, often developing years after the initial infection [1]. *Caused by RNA virus* - Measles is caused by the **measles virus**, which is a **single-stranded RNA virus** belonging to the *Paramyxoviridae* family. - It is an enveloped virus that primarily infects respiratory epithelial cells and replicates in lymphoid tissues. *Rash appears first on face* - The characteristic **maculopapular rash** of measles typically begins on the **face and behind the ears**. - It then spreads downwards to the trunk and extremities, fading in the same order [1].
Question 6: Which of the following statements about the influenza virus is NOT true?
- A. Drift is the accumulation of point mutations.
- B. Only type A shows antigenic drift.
- C. All types exhibit antigenic shift. (Correct Answer)
- D. None of the above.
Explanation: ***All types exhibit antigenic shift.*** - This statement is **incorrect** (and thus the correct answer to this question asking for what is NOT true). - **Antigenic shift** is a major genetic reassortment event that occurs primarily in **Influenza A virus**, where entire gene segments are exchanged between different strains, potentially leading to pandemic strains. - **Influenza B** can undergo antigenic drift but does NOT typically exhibit antigenic shift due to its limited host range (primarily humans) and lack of reassortment opportunities. - **Influenza C** causes mild respiratory illness and shows minimal antigenic variation. *Only type A shows antigenic drift.* - This statement is **false**. Both **Influenza A and Influenza B** undergo **antigenic drift**. - Antigenic drift involves gradual accumulation of point mutations in hemagglutinin (HA) and neuraminidase (NA) genes, allowing immune evasion. - This is why this is also an incorrect statement, but the question asks for one answer, and "all types exhibit shift" is the more clearly false statement. *Drift is the accumulation of point mutations.* - This statement is **true**. - **Antigenic drift** results from **point mutations** in genes encoding surface proteins (HA and NA). - These minor changes allow the virus to evade existing immunity, causing seasonal epidemics. *None of the above.* - This option is incorrect because there IS a false statement among the options ("All types exhibit antigenic shift").
Question 7: True about measles
- A. Long term complication follows in form of SSPE (Correct Answer)
- B. Rash appear first on leg
- C. Koplik spots are seen in retina
- D. Caused by DNA virus
Explanation: ***Long term complication follows in form of SSPE*** - **Subacute sclerosing panencephalitis (SSPE)** is a rare, but fatal, progressive neurodegenerative disease that can develop years after a measles infection [1]. - It is caused by persistent measles virus in the brain, leading to **neurological deterioration** and eventually death [2]. *Rash appear first on leg* - The characteristic rash of measles typically appears first on the **face and behind the ears**, then spreads downward to the trunk and extremities [1]. - The rash is usually **maculopapular** and confluent, turning brownish and fading in the same order it appeared [1]. *Koplik spots are seen in retina* - **Koplik spots** are pathognomonic for measles and are found on the **buccal mucosa** (inside the cheeks), opposite the molars [1]. - They appear as small, white, or bluish-white spots with an erythematous base before the onset of the rash. *Caused by DNA virus* - Measles is caused by the **measles virus**, which is a **single-stranded RNA virus** belonging to the genus *Morbillivirus* in the family *Paramyxoviridae*. - It is not a DNA virus; this classification has significant implications for its replication cycle and vaccine development.
Question 8: A patient with TB on DOTS develops orange-red discoloration of urine and tears. Which drug is responsible?
- A. Ethambutol
- B. Rifampicin (Correct Answer)
- C. Pyrazinamide
- D. Isoniazid
Explanation: ***Rifampicin*** - **Rifampicin** is well-known for causing **orange-red discoloration** of urine, sweat, tears, and other body fluids due to its intrinsic color. - This side effect is benign and does not indicate liver damage or other serious toxicity, but patients should be informed about it. *Ethambutol* - **Ethambutol** is primarily associated with **optic neuritis**, leading to decreased visual acuity and red-green color blindness. - It does not cause discoloration of body fluids. *Pyrazinamide* - **Pyrazinamide** is commonly associated with **hepatotoxicity** and **hyperuricemia**, which can lead to gout. - It does not cause discoloration of body fluids. *Isoniazid* - **Isoniazid** is known to cause **peripheral neuropathy** (prevented by pyridoxine supplementation) and **hepatotoxicity**. - It does not cause discoloration of body fluids.
Question 9: Which immunization is typically given at 6 months of age?
- A. Measles vaccine
- B. DPT vaccine (Correct Answer)
- C. BCG vaccine
- D. None of the options
Explanation: **DPT vaccine** - The DPT (diphtheria, pertussis, and tetanus) vaccine is administered in multiple doses during infancy as part of the primary immunization series. - At **6 months of age**, the **third dose of DPT** is typically given (following doses at 6 weeks, 10 weeks, and 14 weeks according to the Indian immunization schedule). - Among the options provided, DPT is the only vaccine routinely administered at 6 months of age. - This vaccine protects against three serious bacterial infections: **diphtheria**, which can cause breathing problems; **pertussis (whooping cough)**, a severe respiratory illness; and **tetanus**, which causes painful muscle spasms. *Measles vaccine* - The measles vaccine (given as part of the **MMR vaccine** or as MR vaccine in India) is typically administered at **9 to 12 months of age** for the first dose, and a second dose between 15-18 months or 4-6 years. - It is not routinely given at 6 months, as maternal antibodies can interfere with its effectiveness at this younger age. *BCG vaccine* - The BCG (Bacillus Calmette-Guérin) vaccine protects against **tuberculosis** and is given at **birth** or in early infancy as a single dose. - It is not administered at 6 months of age. *None of the options* - This option is incorrect because the **DPT vaccine** (third dose) is a standard immunization given at 6 months of age according to the Indian immunization schedule. - Multiple vaccines are actually given at 6 months (including OPV, Hepatitis B, Hib, PCV), but among the listed options, only DPT is correct.
Question 10: A child comes with fever, cold, cough, and a membrane over the tonsils; a nasal swab is taken. On which medium should the culture be done for the earliest diagnosis of diphtheria?
- A. L. J. media
- B. MC Conkey's Agar
- C. Citrate media
- D. Loffler's serum slope (Correct Answer)
Explanation: ***Loffler's serum slope*** - This medium promotes the rapid growth of *Corynebacterium diphtheriae*, allowing for early identification based on characteristic microscopic morphology within 6-8 hours. - It enhances the production of **metachromatic granules** (Babes-Ernst bodies), which are key diagnostic features for diphtheria. *L. J. media* - **Lowenstein-Jensen (LJ) medium** is primarily used for the isolation and culture of **mycobacteria**, particularly *Mycobacterium tuberculosis*. - It is not suitable for the rapid growth or specific identification of *Corynebacterium diphtheriae*. *MC Conkey's Agar* - **MacConkey agar** is a selective and differential medium used for the isolation and differentiation of **Gram-negative enteric bacilli**. - It inhibits the growth of Gram-positive bacteria and is not appropriate for culturing *Corynebacterium diphtheriae*, which is Gram-positive. *Citrate media* - **Citrate media**, such as Simmons citrate agar, are used to test an organism's ability to utilize citrate as its sole source of carbon. - This is a biochemical test for bacterial differentiation and not a primary isolation medium for *Corynebacterium diphtheriae*.
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