Infectious Diseases Practice Questions

Q: Which mosquito transmits Tritu enorrhynchus?

Japanese encephalitis. ### Explanation **Correct Answer: D. Japanese Encephalitis** The question refers to the vector species **Culex tritaeniorhynchus**, which is the primary vector for **Japanese Encephalitis (JE)**. In the transmission cycle of JE, this mosquito acts as the bridge vector, carrying the virus from the amplifying hosts (primarily pigs and water birds) to humans. These mosquitoes typically breed in stagnant water, such as rice paddies and irrigation ditches, which explains the higher prevalence of JE in rural, agricultural areas. **Analysis of Incorrect Options:** * **A. Dengue Fever:** Transmitted primarily by **Aedes aegypti** (and secondarily by *Aedes albopictus*). These are "day-biters" that breed in clean, artificial water containers. * **B. Yellow Fever:** Also transmitted by the **Aedes aegypti** mosquito in urban cycles and *Haemagogus* species in jungle cycles. * **C. Kyasanur Forest Disease (KFD):** This is a viral hemorrhagic fever transmitted by **Hard ticks (Haemaphysalis spinigera)**, not mosquitoes. It is geographically limited to parts of Karnataka, India. **High-Yield Clinical Pearls for NEET-PG:** * **Vector Characteristics:** *Culex tritaeniorhynchus* is a **night-biter** (zoophilic) and prefers outdoor resting. * **Amplifying Host:** **Pigs** are the most important amplifying hosts for JE; humans are **dead-end hosts** because they do not develop sufficient viremia to infect mosquitoes. * **Diagnosis:** The gold standard for JE diagnosis is the detection of **IgM antibodies in CSF** or serum using MAC-ELISA. * **Vaccination:** The **Jenvac** (indigenous inactivated) and **SA-14-14-2** (live attenuated) vaccines are key preventive measures in endemic zones.

Q: Which insecticide is effective in killing Phlebotomous argentipes?

DDT. **Explanation:** The correct answer is **DDT (Dichloro-Diphenyl-Trichloroethane)**. *Phlebotomus argentipes* is the primary vector for **Kala-azar (Visceral Leishmaniasis)** in the Indian subcontinent. The vector is highly susceptible to residual insecticides because it rests indoors in cracks and crevices of mud walls. **1. Why DDT is the Correct Answer:** DDT remains the **insecticide of choice** for the National Vector Borne Disease Control Programme (NVBDCP) in India for the control of Kala-azar. It is used in **Indoor Residual Spraying (IRS)** at a dosage of **1.0 g/m²**. The sandfly has not yet developed significant physiological resistance to DDT in most endemic areas, making it the most cost-effective and efficient tool for interrupting transmission. **2. Why Other Options are Incorrect:** * **Malathion:** While used for organophosphate-resistant mosquitoes (like *Anopheles*), it is not the primary choice for sandflies due to its shorter residual effect and odor. * **BHC (Benzene Hexachloride):** Previously used for malaria control, it has been largely phased out due to environmental persistence and the development of widespread resistance. * **Pyrethrum:** This is a **space spray** (knock-down agent) used for immediate killing of adult insects. It does not have the long-lasting residual action required for effective sandfly control in mud dwellings. **High-Yield Clinical Pearls for NEET-PG:** * **Vector Habitat:** *Phlebotomus* breeds in damp soil rich in organic matter (e.g., cattle sheds). * **IRS Strategy:** For Kala-azar, IRS with DDT should be done up to a height of **6 feet** from the floor. * **Drug of Choice for Kala-azar:** Liposomal Amphotericin B (single dose) is currently the first-line treatment. * **Post-Kala-azar Dermal Leishmaniasis (PKDL):** Occurs in about 5-10% of treated cases in India and acts as a reservoir for the parasite.

Q: A 25-year-old male tests positive for a hepatitis C infection. Which of the following is the most likely method of transmission?

Intravenous drug use (needles). **Explanation:** **Hepatitis C Virus (HCV)** is primarily a **blood-borne pathogen**. The most efficient and common method of transmission is through direct percutaneous exposure to infected blood. In modern clinical practice, **Intravenous Drug Use (IVDU)** with the sharing of contaminated needles and syringes is the leading risk factor for HCV infection, accounting for the majority of new cases. Unlike Hepatitis B, the viral load of HCV in body fluids other than blood is relatively low, making blood-to-blood contact the most likely route. **Analysis of Incorrect Options:** * **A. Fecal-oral:** This is the primary route for **Hepatitis A and E** ("Vowels involve the bowels"). HCV is not transmitted via contaminated food or water. * **B. Fomite:** While HCV can survive on environmental surfaces for several days, transmission via inanimate objects (fomites) is clinically insignificant compared to direct blood exposure. * **D. Sexual transmission:** While possible, the risk of sexual transmission of HCV is considered **very low** (approximately 0-0.6% in monogamous heterosexual couples). It is significantly less efficient than the sexual transmission of Hepatitis B or HIV. **High-Yield Clinical Pearls for NEET-PG:** * **Post-Transfusion Hepatitis:** Historically, HCV was the most common cause of post-transfusion hepatitis; however, with modern screening, IVDU has surpassed it. * **Chronicity:** HCV has the highest rate of chronicity among hepatitis viruses (~75-85% of acute infections become chronic). * **Screening:** Anti-HCV antibody is the screening test of choice; **HCV-RNA (PCR)** is the gold standard for confirming active infection. * **Vaccine:** There is **no vaccine** available for Hepatitis C due to high antigenic variation (hypervariable region 1 of the E2 envelope glycoprotein).

Q: The last case of smallpox was reported in the world in which year?

1977. **Explanation:** Smallpox (caused by the *Variola* virus) holds a significant place in public health history as the first disease to be eradicated globally. **Why Option A is Correct:** The last **naturally occurring** case of smallpox (*Variola minor*) was reported in **Ali Maow Maalin** in Merca, **Somalia**, on **October 26, 1977**. This date marks the definitive end of natural transmission of the virus in the human population. **Analysis of Incorrect Options:** * **Option B (1978):** This year is significant because the **last fatal case** of smallpox occurred due to a **laboratory accident** in Birmingham, UK (Janet Parker). It was not a naturally occurring case. * **Option C (1979):** On December 9, 1979, the Global Commission for the Certification of Smallpox Eradication signed the document certifying that smallpox had been eradicated worldwide. * **Option D (1982):** This date is irrelevant to smallpox milestones. The official declaration of eradication by the World Health Assembly (WHA) occurred earlier, in **May 1980**. **High-Yield Clinical Pearls for NEET-PG:** * **Last case in India:** Reported on May 24, 1975 (Bhanumati Bhattacharya in Bihar). * **India declared Smallpox free:** April 1977. * **Global Eradication Declaration:** May 8, 1980 (33rd WHA). * **Vaccine:** Smallpox vaccine was the first vaccine (Edward Jenner, 1796) and utilized the **Bifurcated needle**. * **Eradication Strategy:** Shifted from mass vaccination to **"Surveillance and Containment."**

Q: Which of the following statements regarding Rabies infection is FALSE?

Human Rabies immunoglobulin dose is 10 IU/kg.. **Explanation:** The correct answer is **D**, as the statement is incorrect. The standard dose for **Human Rabies Immunoglobulin (HRIG)** is **20 IU/kg** body weight. For Equine Rabies Immunoglobulin (ERIG), the dose is 40 IU/kg. HRIG is administered to provide immediate passive immunity by neutralizing the virus at the wound site before the vaccine-induced active immunity develops. **Analysis of other options:** * **A. Dead-end infection:** This is **True**. Humans do not typically transmit rabies to other humans or animals (except via rare organ transplants), as the viral load in human saliva is insufficient for transmission. * **B. Aerosol transmission:** This is **True**. While rare, rabies can be transmitted via aerosols in specific environments like bat-infested caves or through laboratory accidents. * **C. Suturing:** This is **True** (in the context of general management). Suturing of rabies-prone wounds should ideally be **avoided**. If functionally necessary, it must be delayed by 24–48 hours and performed only after infiltrating the wound with Rabies Immunoglobulin (RIG) to prevent "seeding" the virus deeper into nerves. **High-Yield Clinical Pearls for NEET-PG:** * **Negri Bodies:** Pathognomonic intracytoplasmic eosinophilic inclusions found in the hippocampus (Ammon’s horn) and cerebellum (Purkinje cells). * **Incubation Period:** Typically 1–3 months; depends on the distance of the bite from the CNS. * **Post-Exposure Prophylaxis (PEP):** Includes wound washing (15 mins with soap/water), RIG, and the modern vaccine schedule (Essen: 0, 3, 7, 14, 28 days or IDRV: 0, 3, 7, 28 days). * **Category III Bites:** Always require both Vaccine and RIG.

Q: All the following diseases are spread by Hard Ticks except?

Relapsing fever. **Explanation:** The correct answer is **Relapsing fever** because it is primarily transmitted by **Soft Ticks** (*Ornithodoros*) or **Lice**, rather than Hard Ticks. 1. **Why Relapsing Fever is the correct answer:** * **Endemic Relapsing Fever** is caused by *Borrelia duttoni* and is transmitted by the **Soft Tick** (*Ornithodoros moubata*). * **Epidemic Relapsing Fever** is caused by *Borrelia recurrentis* and is transmitted by the **Human Body Louse**. * Hard ticks (*Ixodidae*) do not serve as vectors for these specific pathogens. 2. **Analysis of Incorrect Options (Diseases spread by Hard Ticks):** * **Kyasanur Forest Disease (KFD):** A viral hemorrhagic fever transmitted by the hard tick *Haemaphysalis spinigera*. It is highly relevant in the Indian context (Karnataka). * **Tularemia:** Caused by *Francisella tularensis*, it can be transmitted by various hard ticks (e.g., *Dermacentor*, *Amblyomma*), as well as deer flies and direct animal contact. * **Tick Paralysis:** Caused by a neurotoxin in the saliva of certain female hard ticks (e.g., *Dermacentor andersoni*). It presents as an ascending flaccid paralysis. **High-Yield Clinical Pearls for NEET-PG:** * **Hard Ticks (Ixodidae):** Remember the mnemonic **"K-B-R-T"** (KFD, Babesiosis, Rocky Mountain Spotted Fever/Rickettsioses, Tularemia). They have a dorsal shield (scutum) and feed for long periods. * **Soft Ticks (Argasidae):** They lack a scutum and feed rapidly. The most important medical association is **Endemic Relapsing Fever**. * **Lyme Disease:** Also transmitted by a hard tick (*Ixodes ricinus/scapularis*).

Q: What is the recommended content of Sodium chloride in WHO Oral Rehydration Solution (ORS)?

2-5 gm. **Explanation:** The World Health Organization (WHO) Oral Rehydration Solution (ORS) is a life-saving formulation designed to treat dehydration by utilizing the **sodium-glucose co-transport mechanism** in the small intestine. **1. Why Option A is Correct:** The current **WHO Reduced Osmolarity ORS** formulation contains exactly **2.6 grams** of Sodium Chloride (NaCl) per liter of water. This falls within the range of **2–5 gm** provided in the options. This specific concentration is calculated to provide 75 mmol/L of Sodium, which is optimal for maximizing water absorption while minimizing the risk of osmotic diarrhea or hypernatremia. **2. Analysis of Incorrect Options:** * **Option B (1.5 gm):** This is too low. Insufficient sodium would fail to correct the sodium deficit caused by diarrhea and would not provide enough solute to drive the co-transport mechanism effectively. * **Option C & D (10 gm & 20 gm):** These concentrations are dangerously high. Excessive sodium intake leads to hypernatremia and can cause "osmotic pull," drawing water out of the cells and into the gut, thereby worsening dehydration. **3. High-Yield Clinical Pearls for NEET-PG:** * **Total Osmolarity:** The WHO Reduced Osmolarity ORS has a total osmolarity of **245 mOsm/L** (the older formulation was 311 mOsm/L). * **Composition per Liter:** * Sodium Chloride: **2.6 g** * Glucose (Anhydrous): **13.5 g** * Potassium Chloride: **1.5 g** * Trisodium Citrate: **2.9 g** * **Role of Citrate:** It is added to correct metabolic acidosis and increases the shelf life of the ORS packet. * **Zinc Supplementation:** Always remember that for pediatric diarrhea, Zinc (20 mg/day for 14 days; 10 mg for infants <6 months) is recommended alongside ORS to reduce the duration and severity of the episode.

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.

Question 1

Which of the following diseases has man as the only reservoir?

Accepted Answer

Measles

Answer

Rabies

Answer

Typhoid

Answer

Japanese B encephalitis

Question 2

Which mosquito transmits Tritu enorrhynchus?

Accepted Answer

Japanese encephalitis

Answer

Dengue fever

Answer

Yellow fever

Answer

Kyasanur Forest Disease (KFD)

Question 3

Which insecticide is effective in killing Phlebotomous argentipes?

Accepted Answer

DDT

Answer

Malathion

Answer

BHC

Answer

Pyrethrum

Question 4

A 25-year-old male tests positive for a hepatitis C infection. Which of the following is the most likely method of transmission?

Accepted Answer

Intravenous drug use (needles)

Answer

Fecal-oral

Answer

Fomite

Answer

Sexual transmission

Question 5

The last case of smallpox was reported in the world in which year?

Accepted Answer

1977

Answer

1978

Answer

1979

Answer

1982

Question 6

Which of the following statements regarding Rabies infection is FALSE?

Accepted Answer

Human Rabies immunoglobulin dose is 10 IU/kg.

Answer

Rabies is a dead-end infection in humans.

Answer

Rabies can be transmitted by aerosols.

Answer

Suturing is usually recommended for local wounds.

Question 7

All the following diseases are spread by Hard Ticks except?

Accepted Answer

Relapsing fever

Answer

Kyasanur Forest Disease (KFD)

Answer

Tularemia

Answer

Tick paralysis

Question 8

What is the recommended content of Sodium chloride in WHO Oral Rehydration Solution (ORS)?

Accepted Answer

2-5 gm

Answer

1.5 gm

Answer

10 gm

Answer

20 gm

Question 9

Which indicator is used in the Revised National Tuberculosis Control Programme (RNTCP) to measure the impact of control measures?

Accepted Answer

Annual infection rate

Answer

Prevalence of infection

Answer

Incidence of new cases

Answer

Number of people having access to DOTS

Question 10

"Nuisance mosquito" refers to which of the following?

Accepted Answer

Culex

Answer

Anopheles

Answer

Tsetse fly

Answer

None of the above

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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