Infectious Diseases Practice Questions

Q: "Nuisance mosquito" refers to which of the following?

Culex. **Explanation:** The term **"Nuisance Mosquito"** is specifically attributed to **Culex fatigans** (also known as *Culex quinquefasciatus*). This designation arises from its pervasive behavior; it is a ubiquitous, domestic mosquito that breeds prolifically in polluted stagnant water, such as open drains and septic tanks. Unlike other species, Culex is a persistent biter, particularly active at night, causing significant irritation and sleep disturbance to humans, even in the absence of disease transmission. **Analysis of Options:** * **Culex (Correct):** Beyond being a "nuisance," it is the primary vector for **Bancroftian Filariasis** and **Japanese Encephalitis**. It is characterized by its "sit-down" posture (body parallel to the surface) and its preference for dirty water. * **Anopheles (Incorrect):** Known as the vector for **Malaria**. It is often referred to as the "clean water breeder." While it bites humans, it is not colloquially termed the nuisance mosquito in public health literature. * **Tsetse fly (Incorrect):** This is not a mosquito; it is a large biting fly found in Africa, responsible for transmitting **African Trypanosomiasis** (Sleeping Sickness). **High-Yield Clinical Pearls for NEET-PG:** * **Breeding Habitats:** Culex = Dirty/stagnant water; Anopheles = Clean/fresh water; Aedes = Artificial containers (man-made collections). * **Resting Posture:** Anopheles rests at an angle (45°); Culex and Aedes rest parallel to the surface. * **Flight Range:** Culex is a strong flier (up to 11 km), whereas Aedes has a very short range (<100 meters). * **Control:** The most effective way to control "nuisance" mosquitoes is through environmental sanitation and improving drainage systems.

Q: A child is suffering from varicella (fever & rash) and the child's aunt is pregnant. What is the earliest time the aunt can meet the child?

When the lesions have crusted. **Explanation:** The core medical concept here is the **period of communicability** of the Varicella-Zoster Virus (VZV). Varicella (Chickenpox) is highly contagious and is transmitted via respiratory droplets or direct contact with vesicle fluid. **Why Option A is correct:** A patient with varicella is infectious from **1–2 days before the onset of the rash** until **all lesions have crusted (scabbed) over**. Once the vesicles have crusted, the virus is no longer present in a transmissible form. For a pregnant woman, who is at high risk for complications (like pneumonia) and whose fetus is at risk for Congenital Varicella Syndrome, avoiding contact until the "crusting stage" is the absolute minimum safety requirement. **Why other options are incorrect:** * **Option B & C:** These are incorrect because the child is actively shedding the virus during the vesicular stage. Meeting "immediately" or based on "favoritism" ignores the high risk of transmission, which can lead to severe maternal morbidity or fetal anomalies. * **Option D:** While this is the safest social approach, it is not the *earliest* medical requirement. Once the lesions are crusted, the child is no longer a source of infection, making it medically safe for the aunt to visit before delivery. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** 10–21 days (Average 14–15 days). * **Congenital Varicella Syndrome:** Highest risk if maternal infection occurs between **8–20 weeks** of gestation (features: limb hypoplasia, cicatricial skin scarring, microcephaly). * **Perinatal Varicella:** If the mother develops a rash 5 days before to 2 days after delivery, the neonate must receive **Varicella-Zoster Immunoglobulin (VZIG)** due to lack of maternal antibody transfer. * **Treatment of choice in pregnancy:** Oral Acyclovir is generally recommended to reduce maternal complications.

Q: All of the following drugs are used in the management of MDR-TB under RNTCP except?

PAS. **Explanation:** The management of **MDR-TB (Multidrug-Resistant Tuberculosis)**—defined as resistance to at least Isoniazid and Rifampicin—has evolved significantly under the National TB Elimination Program (NTEP, formerly RNTCP). **Why PAS is the correct answer:** While **Para-aminosalicylic acid (PAS)** is an effective second-line anti-TB drug, it is currently classified by the WHO and NTEP as a **Group C** drug (Add-on agents). In the standard **Shorter MDR-TB Regimen** (9–11 months) and the **All-Oral Longer Regimen** (18–20 months), PAS is generally reserved as a drug of last resort when a core regimen cannot be constructed using more effective or less toxic drugs. In the context of standard RNTCP/NTEP protocols for MDR-TB, the other options are prioritized higher in the hierarchy. **Analysis of Incorrect Options:** * **Levofloxacin (Option A):** Fluoroquinolones (Levofloxacin or Moxifloxacin) are the **backbone** of MDR-TB treatment (Group A drugs). They are mandatory unless there is documented resistance. * **Ethionamide (Option C):** This is a key component of the **Shorter MDR-TB Regimen** used in India, acting as a core second-line agent. * **Cycloserine (Option D):** Classified as a Group B drug, it is a preferred second-line agent included in most MDR-TB regimens due to its efficacy and lack of cross-resistance with other drugs. **High-Yield Clinical Pearls for NEET-PG:** * **MDR-TB Definition:** Resistance to Isoniazid (H) and Rifampicin (R). * **XDR-TB Definition:** MDR-TB plus resistance to any Fluoroquinolone AND at least one of the Group A drugs (Bedaquiline or Linezolid). * **Bedaquiline:** Inhibits mycobacterial **ATP synthase**; it is now a cornerstone of all-oral MDR-TB regimens. * **Drug of Choice for MDR-TB:** Fluoroquinolones (specifically Levofloxacin/Moxifloxacin) are considered the most important component.

Q: Which of the following may not be used as candidate vaccine(s) in Leprosy?

BCG Vaccine + M.vaccae. **Explanation:** The question asks for the combination that is **not** used as a candidate vaccine for Leprosy. While several mycobacterial strains have been studied for cross-reactivity, the combination of **BCG + M. vaccae** is not a standard or recognized candidate vaccine for leprosy prevention in major clinical trials or national programs. **Analysis of Options:** * **BCG Vaccine (Option A):** It is the most widely studied vaccine for leprosy. It provides varying degrees of protection (20% to 80%) against leprosy due to the antigenic similarity between *M. tuberculosis* and *M. leprae*. * **Killed M. leprae + BCG (Option B):** This combination was extensively studied in trials (e.g., the ICRC trial in India). It aims to enhance the cell-mediated immune response specifically against *M. leprae* antigens. * **M. indicus pranii (Option C):** Formerly known as **Mw (Mycobacterium w)**, this is an indigenous vaccine developed in India. It is an approved immunotherapeutic and immunoprophylactic agent used as an adjunct to MDT in multibacillary leprosy. * **BCG + M. vaccae (Option D):** While *M. vaccae* has been researched for immunotherapy in tuberculosis and certain cancers, it is not a standard candidate vaccine for leprosy, especially not in combination with BCG for this specific purpose. **High-Yield Clinical Pearls for NEET-PG:** 1. **M. indicus pranii (Mw):** The first vaccine in the world for leprosy, developed by G.P. Talwar in India. 2. **ICRC Vaccine:** Developed at the Indian Cancer Research Centre, it uses a cultivable strain of *M. leprae*-like mycobacteria. 3. **Protective Efficacy:** BCG provides better protection against Leprosy than it does against Tuberculosis. 4. **MDT (Multi-Drug Therapy):** Remember that vaccines are considered "immunotherapy" (adjunct to MDT) or "immunoprophylaxis" (prevention).

Q: What is the best disinfectant for cholera stools?

Cresol. **Explanation:** The correct answer is **Cresol** (Option C). **Why Cresol is the correct answer:** In the management of infectious diseases like cholera, the disinfection of excreta (stools and vomit) is critical. **Cresol (Liquor Saponis Antisepticus/Lysol)** is considered the disinfectant of choice for cholera stools because it is highly effective against *Vibrio cholerae* and maintains its efficacy even in the presence of high organic matter. For effective disinfection, a 5% cresol solution should be used with a contact time of at least 1–2 hours. **Analysis of Incorrect Options:** * **Bleaching powder (A):** While it is the gold standard for disinfecting water (chlorination), it is less effective for stools because organic matter rapidly neutralizes free chlorine, rendering it ineffective unless used in very high concentrations. * **Coal-tar (B):** This is a crude source of phenolic compounds but is not used in standardized clinical practice for stool disinfection compared to its refined derivative, cresol. * **Formalin (D):** Formalin is primarily used for preserving tissues (histopathology) or fumigation (as a gas). It is not practical or standard for the routine disinfection of large volumes of liquid excreta due to its pungent odor and irritant properties. **High-Yield Clinical Pearls for NEET-PG:** * **Cholera Stool Disinfection:** Cresol (5%) or Bleaching powder (if cresol is unavailable, but requires longer contact). * **Sputum Disinfection:** Burning (best) or Cresol/Autoclaving. * **HIV/Hepatitis B Spills:** Sodium Hypochlorite (1% for small spills, 10% for large blood spills). * **Cystoscope/Endoscope:** 2% Glutaraldehyde (Cidex) is the agent of choice. * **Vibrio cholerae** is highly sensitive to acids but survives well in alkaline media (pH 8.5–9.5).

Question 1

"Nuisance mosquito" refers to which of the following?

Accepted Answer

Culex

Answer

Anopheles

Answer

Tsetse fly

Answer

None of the above

Question 2

A child is suffering from varicella (fever & rash) and the child's aunt is pregnant. What is the earliest time the aunt can meet the child?

Accepted Answer

When the lesions have crusted

Answer

Immediately

Answer

Anytime as the child is aunt's favourite

Answer

After the delivery of the baby

Question 3

What is true regarding Diphtheria?

Accepted Answer

Nasal carriers are more dangerous than cases

Answer

Immunization prevents the carrier state

Answer

Cases are the most important source of infection

Answer

Hemagglutination test has been replaced by the Schick test

Question 4

All of the following drugs are used in the management of MDR-TB under RNTCP except?

Accepted Answer

PAS

Answer

Levofloxacin

Answer

Ethionamide

Answer

Cycloserine

Question 5

What is true about Swine flu?

Accepted Answer

Older bird influenza vaccine is equally effective in swine flu.

Answer

Oseltamivir is effective in prevention.

Answer

Zanamivir can be used for treatment.

Answer

Influenza vaccine provides immunity just after vaccination.

Question 6

A 30-year-old female has sputum-positive tuberculosis. Her child is 3 years old. What is the recommended chemoprophylaxis for the child?

Accepted Answer

Isoniazid 5 mg/kg for 6 months

Answer

Isoniazid 3 mg/kg for 3 months

Answer

Isoniazid 5 mg/kg for 3 months

Answer

Isoniazid 3 mg/kg for 6 months

Question 7

Which of the following may not be used as candidate vaccine(s) in Leprosy?

Accepted Answer

BCG Vaccine + M.vaccae

Answer

BCG Vaccine

Answer

Killer M.leprae + BCG Vaccine

Answer

M.indicus pranii

Question 8

All of the following statements about Japanese Encephalitis are true, EXCEPT:

Accepted Answer

All individuals bitten by infected mosquitoes develop the disease.

Answer

Two to three cases per village may suggest an epidemic.

Answer

Children are more frequently affected than adults.

Answer

The ratio of inapparent to apparent infection is greater than 100:1.

Question 9

What is the best disinfectant for cholera stools?

Accepted Answer

Cresol

Answer

Bleaching powder

Answer

Coal-tar

Answer

Formalin

Question 10

Which of the following statements is NOT true regarding Japanese encephalitis?

Accepted Answer

A bite from an infected mosquito always leads to the disease.

Answer

Approximately 80% of patients are children below 5 years of age.

Answer

During epidemics, cases are scattered, with no more than 1-2 cases per village.

Answer

The ratio of asymptomatic to apparent cases is approximately 1:100.

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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