Infectious Diseases Practice Questions

Q: Which of the following associations represents the least infectious type of tuberculosis?

TB in HIV patients. **Explanation:** The infectivity of Tuberculosis (TB) is directly proportional to the bacterial load in the sputum and the force of the cough. **Why Option D is Correct:** In patients with HIV, the immune system (specifically CD4+ T-cells) is severely compromised. This prevents the formation of well-defined **granulomas** and **cavities**. Cavitation is essential for the multiplication of large numbers of bacilli and their subsequent release into the airways. Consequently, TB in HIV patients is frequently **pauci-bacillary** or **extra-pulmonary**, making them significantly less infectious to others compared to immunocompetent individuals with cavitary disease. **Analysis of Incorrect Options:** * **A. Cavitary pulmonary disease:** This is the **most infectious** form. Cavities provide an oxygen-rich environment for massive mycobacterial replication and direct access to the bronchial tree for aerosolization. * **B. Laryngeal TB:** This is highly infectious because the bacilli are located at the exit of the respiratory tract, and vocalization/coughing easily disperses them. * **C. Sputum with 1,00,000 AFB/ml:** Infectivity is a function of bacterial density. Sputum positivity (especially >10⁴ bacilli/ml) indicates high transmissibility. **High-Yield Pearls for NEET-PG:** * **Most important determinant of infectivity:** Presence of cough and sputum AFB positivity. * **HIV-TB Paradox:** While HIV patients are at the highest risk of *developing* TB, they are the *least infectious* due to lack of cavitation. * **Household contacts:** The risk of infection is highest in the first few months of exposure to a smear-positive index case. * **Effective Treatment:** Infectivity reduces drastically within 2 weeks of starting appropriate Anti-Tubercular Treatment (ATT).

Q: Rabies can be transmitted by all of the following routes except?

Ingestion. ### Explanation **Correct Option: C (Ingestion)** **Reasoning:** Rabies is caused by the **Lyssavirus Type 1** (a neurotropic RNA virus). The virus is highly fragile and is inactivated by gastric acid (low pH) and digestive enzymes. Therefore, the ingestion of milk or meat from a rabid animal does not transmit the disease, as the virus cannot survive the gastrointestinal environment to reach the nervous system. **Analysis of Other Options:** * **Bites (Option B):** This is the most common route (over 99% of human cases). The virus is present in the saliva of the rabid animal and is inoculated into the host via a bite. * **Licks (Option D):** Transmission occurs if the saliva of a rabid animal comes into contact with **pre-existing scratches, open wounds, or intact mucous membranes** (eyes, mouth). This is classified as a Category II or III exposure depending on the severity. * **Aerosol (Option A):** Though rare, transmission can occur via inhalation of virus-laden aerosols. This has been documented in specific laboratory accidents and among individuals exploring caves heavily populated by infected bats (guano-rich environments). **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** Typically 1–3 months (Range: 1 year). It depends on the distance of the bite from the CNS and the viral load. * **Organ Transplant:** Rabies can be transmitted via **corneal or solid organ transplants** from infected donors. * **Diagnosis:** The presence of **Negri bodies** (intracytoplasmic inclusions) in the hippocampus or cerebellum is pathognomonic (post-mortem). * **Category III Exposure:** Includes single/multiple transdermal bites, licks on broken skin, or contamination of mucous membranes with saliva. This requires both **Vaccine and Rabies Immunoglobulin (RIG)**.

Q: Mass chemoprophylaxis is not given for which of the following conditions?

Scabies. **Explanation:** The concept of **Mass Chemoprophylaxis** involves the administration of specific drugs to an entire population (or a defined high-risk group) to prevent the occurrence or spread of a disease, regardless of whether individuals show symptoms. **Why Scabies is the Correct Answer:** Scabies is a parasitic infestation caused by *Sarcoptes scabiei*. While it is highly contagious, the standard public health approach is **Contact Treatment** (treating the index case and all close household contacts simultaneously) rather than mass administration to an entire community. Mass treatment is only considered in specific, extreme institutional outbreaks or hyper-endemic isolated communities, but it is not a standard national strategy like the other options. **Analysis of Incorrect Options:** * **Lymphatic Filariasis:** Mass Drug Administration (MDA) using **DEC and Albendazole** (or IDA regimen: Ivermectin, DEC, and Albendazole) is the cornerstone of the Global Programme to Eliminate Lymphatic Filariasis. * **Plague:** During an outbreak, mass chemoprophylaxis with **Tetracycline or Doxycycline** is recommended for the entire community in the affected area to break the chain of transmission. * **Vitamin A Deficiency:** The National Prophylaxis Programme against Nutritional Blindness involves mass administration of high-dose Vitamin A solution to all children aged 6 months to 5 years. **High-Yield Clinical Pearls for NEET-PG:** * **Trachoma:** Mass distribution of **Azithromycin** (SAFE strategy) is indicated if the prevalence of active trachoma in children is >10%. * **Meningococcal Meningitis:** Chemoprophylaxis (Rifampicin/Ciprofloxacin) is given to **close contacts**, not the whole community, unless an epidemic occurs in a closed community (e.g., barracks). * **Drug of Choice for Chemoprophylaxis:** * Cholera: Doxycycline * Leptospirosis: Doxycycline * Rheumatic Fever: Benzathine Penicillin (Long-term)

Q: Which of the following is true regarding malaria diagnosis?

A thick smear is used to identify the parasite.. ### Explanation **1. Why Option A is Correct:** In malaria microscopy, the **thick smear** is the gold standard for **identifying the presence of the parasite** (screening). Because it uses a larger volume of blood concentrated in a small area, it is approximately 20–40 times more sensitive than a thin smear, making it ideal for detecting low-density parasitemia. (Note: The *thin smear* is subsequently used for species identification and quantification). **2. Why the Other Options are Incorrect:** * **Option B:** **ABER** stands for **Annual Blood Examination Rate**, not a basophil ratio. It is a key indicator of surveillance efficiency under the National Center for Vector Borne Diseases Control (NCVBDC). For an area to be considered under effective surveillance, the ABER should be **at least 10%** (10 per 100 population per year), not 100. * **Option C:** Incubation periods vary significantly by species: *P. falciparum* (12 days), *P. vivax* (14 days), *P. ovale* (14 days), and *P. malariae* (28 days). * **Option D:** Fluorescent antibodies (Indirect Fluorescent Antibody test) typically become positive **2–3 weeks** after the onset of infection, not 1 week. They are used more for epidemiological surveys than acute diagnosis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard:** Light microscopy of Giemsa-stained peripheral blood smears. * **RDTs:** Rapid Diagnostic Tests usually detect **HRP-2** (for *P. falciparum*) and **pLDH** (for all species). * **Best Time for Smear:** During the peak of fever (though in practice, it should be done immediately upon suspicion). * **Drug of Choice:** **Artesunate Combination Therapy (ACT)** is the first-line treatment for Falciparum malaria in India, except in pregnancy (1st trimester).

Q: A 7-year-old child presents with a dog bite from the neighborhood. On examination, there is a small superficial abrasion without oozing of blood. How would you classify this bite?

Category 2. ### Explanation The classification of dog bites is based on the **WHO Rabies Exposure Categories**, which determine the required post-exposure prophylaxis (PEP). **Why Category 2 is correct:** Category 2 exposure is defined as **minor scratches or abrasions without bleeding**, or nibbling of uncovered skin. In this case, the child has a superficial abrasion without oozing of blood, which fits the criteria perfectly. * **Management:** Immediate local wound washing and administration of the Anti-Rabies Vaccine (ARV). Rabies Immunoglobulin (RIG) is generally not required for Category 2. **Analysis of Incorrect Options:** * **Category 1:** This involves touching or feeding animals, or licks on intact skin. Since there is an abrasion (break in skin), it cannot be Category 1. No treatment is required. * **Category 3:** This involves single or multiple transdermal bites/scratches with **bleeding**, licks on broken skin, or contamination of mucous membranes with saliva (e.g., licks on eyes/mouth). It also includes all exposures to bats. * **Category 4:** There is no "Category 4" in the WHO classification for rabies exposure. **High-Yield Clinical Pearls for NEET-PG:** 1. **Wound Management:** The most important first step is washing the wound with soap and running water for at least **15 minutes**. 2. **RIG Rule:** Category 3 exposures require **both** ARV and Rabies Immunoglobulin (RIG). RIG should be infiltrated into and around the wound. 3. **Site of Injection:** ARV is given Intramuscularly (Deltoid) or Intradermally. **Never** give the vaccine in the gluteal region as fat reduces vaccine efficacy. 4. **Suturing:** Avoid suturing rabies-infected wounds. If necessary, it should be done only after RIG infiltration and delayed by 24–48 hours.

Q: All of the following are true regarding acute attack of Polio, except?

Three consecutive stool samples are positive.. ### Explanation **Why Option B is the Correct Answer (The "Except" Statement):** In the surveillance of Acute Flaccid Paralysis (AFP) for Polio, the standard protocol requires **two** "adequate" stool samples, not three. These samples must be collected **24 to 48 hours apart** and within **14 days** of the onset of paralysis. A single positive sample is sufficient for a diagnosis; it is not a requirement for all consecutive samples to be positive to confirm the case. **Analysis of Other Options:** * **Option A:** Poliovirus is thermolabile. To maintain the "Reverse Cold Chain," stool samples must be transported at **2–8°C** in a cold box with ice packs to ensure the virus remains viable for culture. * **Option C:** Rapid notification is critical. Under the Global Polio Eradication Initiative, an AFP case should ideally be investigated within **48 hours** of reporting to ensure timely sample collection and contact tracing. * **Option D:** While stool is the primary specimen for surveillance due to prolonged viral shedding (up to 6 weeks), the poliovirus can be isolated from **throat swabs** during the first week of the illness (pre-paralytic and early paralytic phases). **High-Yield Clinical Pearls for NEET-PG:** * **AFP Surveillance:** The gold standard for Polio diagnosis is the isolation of the Wild Poliovirus (WPV) from stool in a WHO-accredited laboratory. * **Reverse Cold Chain:** This refers to the process of transporting clinical specimens from the field to the laboratory under cold conditions (the opposite of vaccine delivery). * **Stool Sample Criteria:** "Adequate" samples mean 2 samples, collected 24 hours apart, within 14 days of onset, arriving at the lab in good condition (no leakage/desiccation) with ice present. * **Most Common Site of Paralysis:** Spinal Polio typically affects the **lower limbs** asymmetrically (proximal muscles more than distal).

Q: All of the following are arthropod-borne diseases except:

Dracunculosis. **Explanation:** The core concept of this question lies in distinguishing between diseases transmitted by **arthropod vectors** (insects, arachnids) and those transmitted via **water-borne intermediate hosts**. **Why Dracunculosis is the correct answer:** Dracunculosis (Guinea worm disease) is **not** an arthropod-borne disease. It is a water-borne parasitic infection caused by *Dracunculus medinensis*. It is transmitted by drinking water containing **Cyclops** (water fleas). While Cyclops is a crustacean, it acts as an **intermediate host** in water, not a vector that actively bites or deposits the pathogen onto a human host. * *Note:* India was certified free of Dracunculosis by the WHO in February 2000. **Why the other options are incorrect:** * **Malaria:** A classic arthropod-borne disease transmitted by the bite of an infected female **Anopheles mosquito**. * **Filariasis:** Transmitted by various mosquito vectors, most commonly **Culex quinquefasciatus** (for *Wuchereria bancrofti*). * **Dengue:** A viral disease transmitted by the **Aedes aegypti** mosquito. **High-Yield Clinical Pearls for NEET-PG:** 1. **Cyclops** is the intermediate host for: Dracunculosis, Fish Tapeworm (*Diphyllobothrium latum*), and Gnathostomiasis. 2. **Biological Transmission types:** * *Propagative:* Plague (bacilli multiply in flea). * *Cyclo-propagative:* Malaria (parasite multiplies and changes stages in mosquito). * *Cyclo-developmental:* Filariasis (parasite changes stages but does not multiply in mosquito). 3. **Extrinsic Incubation Period:** The time required for the pathogen to develop inside the arthropod vector before it becomes infective to humans.

Question 1

Which of the following associations represents the least infectious type of tuberculosis?

Accepted Answer

TB in HIV patients

Answer

Cavitary pulmonary disease

Answer

Laryngeal TB

Answer

Sputum with 1,00,000 AFB/ml

Question 2

According to the new WHO 2013 malaria treatment guidelines, which of the following statements is true?

Accepted Answer

Primaquine is contraindicated in infants and pregnant women.

Answer

Artemisinin-based combination therapy (ACT) is not used in falciparum malaria.

Answer

Presumptive treatment with chloroquine should be given.

Answer

Primaquine is to be given for 7 days in falciparum malaria.

Question 3

Rabies can be transmitted by all of the following routes except?

Accepted Answer

Ingestion

Answer

Aerosol

Answer

Bites

Answer

Licks

Question 4

Mass chemoprophylaxis is not given for which of the following conditions?

Accepted Answer

Scabies

Answer

Lymphatic filariasis

Answer

Plague

Answer

Vitamin A deficiency

Question 5

Which of the following is true regarding malaria diagnosis?

Accepted Answer

A thick smear is used to identify the parasite.

Answer

An ABER (Absolute Basophil Eosinophil Ratio) reveals positivity by 100.

Answer

All types of malaria have the same incubation period.

Answer

Fluorescein antibodies become positive within 1 week of infection.

Question 6

A 7-year-old child presents with a dog bite from the neighborhood. On examination, there is a small superficial abrasion without oozing of blood. How would you classify this bite?

Accepted Answer

Category 2

Answer

Category 1

Answer

Category 3

Answer

Category 4

Question 7

All of the following are true regarding acute attack of Polio, except?

Accepted Answer

Three consecutive stool samples are positive.

Answer

Fecal sample is carried in a cold box.

Answer

Investigation is done within 48 hours.

Answer

Throat swab is taken for diagnosis.

Question 8

All of the following are arthropod-borne diseases except:

Accepted Answer

Dracunculosis

Answer

Malaria

Answer

Filariasis

Answer

Dengue

Question 9

Which of the following statements about whooping cough is false?

Accepted Answer

Asymptomatic carriers are the most important source of infection.

Answer

It commonly affects children under 1 year of age.

Answer

Primary cases are the most important source of infection.

Answer

The secondary attack rate is high.

Question 10

School closure is recommended during an outbreak of swine flu. All of the following support this recommendation except:

Accepted Answer

Closure of school will not lead to a reduction in contact between children.

Answer

Children are the most commonly affected population by swine flu.

Answer

Increased rates of transmission due to more opportunities for contact.

Answer

Playing together of students increases transmission.

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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