UPSC-CMS 2020 — Microbiology
3 Previous Year Questions with Answers & Explanations
Which of the following represent the properties of an ideal disinfectant? 1. It is broad spectrum 2. It is fast acting 3. It is non-toxic Select the correct answer using the code given below:
During the EARLY phase of a primary immune response, which of the following best describes the relationship between peak IgM and IgG antibody levels?
Which is the most specific causative agent of Rabies?
UPSC-CMS 2020 - Microbiology UPSC-CMS Practice Questions and MCQs
Question 1: Which of the following represent the properties of an ideal disinfectant? 1. It is broad spectrum 2. It is fast acting 3. It is non-toxic Select the correct answer using the code given below:
- A. 1 and 3 only
- B. 1, 2 and 3 (Correct Answer)
- C. 2 and 3 only
- D. 1 and 2 only
Explanation: ***Correct Answer: 1, 2 and 3*** An **ideal disinfectant** should possess all three properties: - **Broad spectrum activity** - It should effectively kill or inactivate a wide range of microorganisms, including bacteria, viruses, fungi, and spores - **Fast-acting** - It should achieve rapid antimicrobial effect after application, which is crucial in clinical settings to prevent pathogen spread and minimize exposure time - **Non-toxic** - It should be safe for humans and animals when used as directed, minimizing adverse effects on users, patients, and the environment Additional desirable properties include stability, solubility in water, non-corrosive nature, pleasant odor, and cost-effectiveness. *Incorrect: 1 and 3 only* - While broad spectrum and non-toxic nature are crucial, **fast action** is also an essential property for an ideal disinfectant to ensure rapid microbial elimination - A disinfectant that is not fast-acting would be less practical in situations requiring quick decontamination *Incorrect: 2 and 3 only* - A disinfectant that is fast-acting and non-toxic is insufficient without **broad-spectrum activity** - Without broad-spectrum activity, it may fail to eliminate certain pathogens, limiting its overall utility in infection control *Incorrect: 1 and 2 only* - Although broad spectrum and fast-acting properties are important, an ideal disinfectant must also be **non-toxic** - Toxicity would severely limit its application, especially in healthcare settings where human contact is frequent
Question 2: During the EARLY phase of a primary immune response, which of the following best describes the relationship between peak IgM and IgG antibody levels?
- A. 50 times more
- B. 100 times more (Correct Answer)
- C. 25 times more
- D. 10 times more
Explanation: ***100 times more*** - In the **early phase of a primary immune response**, **IgM** is the first antibody produced and reaches peak levels when **IgG** levels are still very low. - During this early period (approximately days 5-10), the **IgM concentration** can be significantly higher than IgG, with some references citing ratios up to 100-fold. - **Important note:** As the primary response matures, **IgG levels rise and eventually exceed IgM levels** through class switching. This question specifically addresses the early peak comparison. *50 times more* - While IgM does predominate early in the primary response, the 50-fold ratio underestimates the typical difference during the **early peak phase** when IgG production has just begun. - The most commonly cited ratio for early primary response is closer to 100-fold. *25 times more* - This ratio **underestimates** the relative abundance of **IgM** compared to **IgG** during the early peak of a primary immune response. - **IgG** levels are typically very low or just beginning to rise in the early stages, while IgM has reached peak levels. *10 times more* - This significantly **underestimates** the difference in antibody levels during the early primary immune response. - The rapid and robust initial production of **IgM** with delayed IgG production creates a much larger differential in the early phase. **Clinical Note:** In a **secondary immune response**, the pattern reverses dramatically—IgG is produced rapidly and in much higher quantities than IgM (often 100-1000 times more) due to memory B cell activation.
Question 3: Which is the most specific causative agent of Rabies?
- A. Rabies lyssavirus (RABV) (Correct Answer)
- B. Lagos bat lyssavirus (LBV)
- C. Mokola lyssavirus (MOKV)
- D. Duvenhage lyssavirus (DUVV)
Explanation: ***Rabies lyssavirus (RABV)*** - **Rabies lyssavirus (RABV)**, also known as the **classical rabies virus** or **genotype 1**, is the primary and most specific causative agent of rabies in humans and animals worldwide. - While other lyssaviruses (Lagos bat, Mokola, Duvenhage, Australian bat lyssavirus, etc.) can cause rabies-like illnesses, **RABV is overwhelmingly responsible** for the vast majority of documented rabies cases globally. - It is transmitted primarily through dog bites in endemic regions and causes acute, progressive, fatal encephalomyelitis. *Lagos bat lyssavirus (LBV)* - **Lagos bat lyssavirus (genotype 2)** is a distinct species within the *Lyssavirus* genus that can cause rabies-like disease, primarily in bats in Africa. - It is **rarely associated with human rabies** and is not the most common or specific cause globally. *Mokola lyssavirus (MOKV)* - **Mokola lyssavirus (genotype 3)** is another lyssavirus found in Africa, isolated from shrews, rodents, and rarely humans. - Although it can cause a fatal encephalomyelitis similar to rabies, human cases are **extremely rare**, and it is not considered the typical rabies virus. *Duvenhage lyssavirus (DUVV)* - **Duvenhage lyssavirus (genotype 4)** is a bat-associated lyssavirus found in Africa, first isolated in 1970. - Human cases are **exceptionally rare** (only a few documented cases), and it is not the primary causative agent of classic rabies.