Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 351: Hepatitis B can be transmitted through all EXCEPT:

A. Milk
B. Blood
C. Stool (Correct Answer)
D. Semen

Explanation: ***Stool*** - Hepatitis B virus is primarily transmitted through **blood** and **body fluids**, not via the **fecal-oral route**. - While viral particles might theoretically be present in stool, the concentration is too low to cause an infection. *Milk* - **Breast milk** can contain the hepatitis B virus, allowing for mother-to-child transmission during breastfeeding. - This is a less common route than perinatal transmission at birth but is still possible. *Blood* - **Blood** is a major vehicle for hepatitis B transmission, occurring through shared needles, transfusions (less common now due to screening), or unprotected medical procedures. - Even microscopic amounts of infected blood can transmit the virus. *Semen* - **Semen** is a known bodily fluid that can transmit the hepatitis B virus during unprotected sexual intercourse. - This is a significant mode of transmission for adults.

Question 352: The most important sandfly-transmitted disease in India is-

A. Kala azar (Correct Answer)
B. Typhus
C. Relapsing fever
D. Plague

Explanation: ***Kala azar*** - **Kala azar**, or **visceral leishmaniasis**, is a severe parasitic disease endemic to India, transmitted primarily by *Phlebotomus argentipes* sandflies. - It is characterized by fever, **splenomegaly**, hepatomegaly, and can be fatal if untreated, making it a major public health concern. *Typhus* - **Typhus** is caused by Rickettsial bacteria and is typically transmitted by lice or fleas, not sandflies. - Symptoms include fever, rash, and headache, differing significantly from the visceral symptoms of Kala azar. *Relapsing fever* - **Relapsing fever** is caused by *Borrelia* bacteria and is transmitted by ticks or lice, not sandflies. - It is characterized by recurring episodes of fever, distinct from the progressive symptoms of Kala azar. *Plague* - **Plague** is caused by *Yersinia pestis* and is primarily transmitted by **fleas** carried by rodents. - It presents with buboes, fever, and sepsis, which are different from the clinical manifestations of sandfly-borne diseases.

Question 353: Following diseases are transmitted by mosquito except?

A. Dengue fever
B. Yellow fever
C. Plague (Correct Answer)
D. Japanese encephalitis

Explanation: ***Plague*** - **Plague** is primarily transmitted by the bite of infected **fleas**, which are often found on rodents like rats. - While humans can contract plague through contact with infected animals or respiratory droplets from pneumonic plague patients, **mosquitoes are not vectors** for its transmission. *Dengue fever* - **Dengue fever** is a well-known **mosquito-borne** viral infection, transmitted primarily by **Aedes aegypti** and **Aedes albopictus** mosquitoes. - These mosquitoes bite during the daytime and are responsible for spreading the dengue virus in tropical and subtropical regions. *Yellow fever* - **Yellow fever** is another significant **mosquito-borne viral disease**, primarily transmitted by infected **Aedes aegypti** mosquitoes. - It circulates in urban, savanna, and jungle environments, with mosquitoes acting as the primary vector for human infection. *Japanese encephalitis* - **Japanese encephalitis** is a serious **mosquito-borne viral infection** of the brain, transmitted mainly by **Culex mosquitoes**, particularly **Culex tritaeniorhynchus**. - These mosquitoes typically breed in rice paddies and feed on birds and pigs, which act as amplifying hosts, before transmitting the virus to humans.

Question 354: First step in control of cholera epidemic:

A. Chemoprophylaxis
B. Verification of diagnosis (Correct Answer)
C. Provision of safe water
D. ORS therapy

Explanation: ***Verification of diagnosis*** - The initial and crucial step in controlling any epidemic, including cholera, is to **confirm the diagnosis** to ensure that the public health response is appropriate for the identified pathogen. - This involves **laboratory confirmation** of *Vibrio cholerae* from patient samples, which guides subsequent interventions. *Chemoprophylaxis* - While **antibiotics** can be used as prophylaxis for close contacts in some cholera outbreaks, it is not the *first* step in controlling an epidemic. - Widespread chemoprophylaxis is generally not recommended due to concerns about **antibiotic resistance** and its limited impact on the overall epidemic curve. *Provision of safe water* - **Providing safe water** is a critical, long-term intervention for preventing and controlling cholera, addressing the root cause of transmission. - However, it typically follows diagnosis and other immediate containment measures, and its implementation can take time. *ORS therapy* - **Oral Rehydration Solution (ORS) therapy** is a cornerstone of cholera patient *management* to prevent dehydration and death. - While essential for affected individuals, it is a treatment for cases, not the first step in *controlling the epidemic* at a public health level.

Question 355: A common source of Staphylococcus in the hospital is:

A. Hands of hospital personnel
B. Bed linen
C. IV fluids
D. Infected wounds (Correct Answer)

Explanation: ***Infected wounds*** - Infected wounds, particularly those with purulent discharge, are a significant reservoir for **Staphylococcus** species. - These wounds can shed large numbers of bacteria into the environment, increasing the risk of transmission to other patients and healthcare workers. *Hands of hospital personnel* - While hands of hospital personnel are a common vector for transmitting **Staphylococcus**, the bacteria often originate from colonized or infected patients, not directly from the personnel themselves as the primary source. - Proper hand hygiene aims to interrupt this transmission, not to eliminate a primary source on the personnel. *Bed linen* - Bed linen can become contaminated with **Staphylococcus** from patient shedding, but it is typically a secondary contaminated surface rather than a primary source where the bacteria originate and thrive. - The bacterial load on bed linen, while a risk, is often less concentrated than in an active infection site. *IV fluids* - Intravenous fluids themselves are generally sterile and are not a common source of **Staphylococcus** unless they become externally contaminated during preparation or administration. - Contamination of IV fluids leading to bacteremia is a serious complication, but the fluid itself is rarely the origin of the bacterial colonization.

Question 356: Diseases associated with rodents include all except

A. Leptospirosis
B. Tularemia
C. Rat Bite fever
D. Oriental sore (Correct Answer)

Explanation: ***Oriental sore*** - **Oriental sore** is a form of **cutaneous leishmaniasis**, caused by Leishmania parasites transmitted by the bite of **sandflies**, not rodents. - This disease is characterized by chronic skin lesions that can develop into ulcers. *Leptospirosis* - **Leptospirosis** is a bacterial disease spread through the urine of infected animals, including **rodents**, often via contaminated water or soil. - Symptoms can range from mild flu-like illness to severe conditions like **Weil's disease**, affecting the liver and kidneys. *Tularemia* - **Tularemia**, also known as **rabbit fever**, is a bacterial disease that can be transmitted by **rodents**, rabbits, and other animals. - Transmission occurs through insect bites (ticks, deer flies), contact with infected animal carcasses, or contaminated food/water. *Rat Bite fever* - **Rat Bite fever** is caused by bacteria (usually *Streptobacillus moniliformis* or *Spirillum minus*) transmitted through a **rat bite** or scratch. - It is directly associated with rodent exposure and can cause fever, rash, and arthritis.

Question 357: Not true about aedes mosquito-

A. Eggs cannot survive more than 1 week without water (Correct Answer)
B. Transmits dengue fever
C. Are recurrent day time biters
D. Prefer breeding in stagnant water

Explanation: ***Eggs cannot survive more than 1 week without water*** - This statement is incorrect because **Aedes eggs** are known for their ability to survive long periods (months to even a year) of **desiccation** (drying out) in the absence of water. - This characteristic allows the eggs to **withstand dry seasons** and hatch when conditions become favorable with water. *Transmits dengue fever* - **Aedes aegypti** and **Aedes albopictus** are the primary vectors for **dengue virus**. - The mosquito acquires the virus by biting an infected person and then transmits it to other individuals through subsequent bites. *Are recurrent day time biters* - **Aedes mosquitoes** are primarily active and feed during the **daylight hours**, particularly in the early morning and late afternoon. - They are known for taking **multiple blood meals** from different individuals in a single gonotrophic cycle, making them efficient disease transmitters. *Prefer breeding in stagnant water* - **Aedes mosquitoes** lay their eggs in small collections of **stagnant water**, often in artificial containers around human dwellings. - Examples include water storage containers, discarded tires, flower pots, and gutters, which highlights their **domestic breeding habits**.

Question 358: Which of the following about cholera is true ?

A. Invasive
B. Endotoxin is released
C. Recent infections in India are of classical type
D. Vibriocidal antibody titre measures seroprevalence (Correct Answer)

Explanation: **Vibriocidal antibody titre measures seroprevalence** - The vibriocidal antibody test measures the level of antibodies that can kill *Vibrio cholerae* bacteria in a patient's serum, indicating **prior exposure or vaccination** and thus **seroprevalence**. - These antibodies target outer membrane antigens of the bacteria and are a key component of the immune response against cholera. *Invasive* - *Vibrio cholerae* is a **non-invasive bacterium** that colonizes the small intestine but does not penetrate the intestinal mucosa or enter the bloodstream. - Its pathogenesis primarily involves the production of **cholera toxin**, which acts locally on enterocytes. *Endotoxin is released* - *Vibrio cholerae* is a **Gram-negative bacterium**, which possesses **lipopolysaccharide (LPS)** in its outer membrane, commonly referred to as endotoxin. - However, the primary virulence factor responsible for the severe diarrhea in cholera is **cholera toxin**, an exotoxin, not the direct release of endotoxin in quantities sufficient to cause systemic endotoxic shock as seen in other Gram-negative infections. *Recent infections in India are of classical type* - The classical biotype of *Vibrio cholerae* is **rarely associated with recent outbreaks** globally, including in India. - Most recent cholera epidemics and infections worldwide, including in India, are caused by the **El Tor biotype** of *Vibrio cholerae* O1.

Question 359: What is the most common mode of transmission of Brucella?

A. Water
B. Air
C. Aerosol
D. Milk (Correct Answer)

Explanation: ***Milk*** - **Brucellosis** is primarily a **zoonotic disease** that can be transmitted to humans through the consumption of **unpasteurized milk** and dairy products from infected animals. - The bacteria *Brucella* can survive in milk and infect individuals once ingested. *Water* - While *Brucella* can potentially contaminate water, it is not considered the primary or most common mode of transmission for brucellosis in humans. - **Ingestion of contaminated water** is a less frequent route compared to exposure through dairy products or animal contact. *Air* - **Airborne transmission** is not a typical mode for *Brucella*; the bacteria are not commonly spread through respiratory droplets in the general population. - Though *Brucella* can be aerosolized in specific laboratory or occupational settings (e.g., slaughterhouses), this is not a common community transmission route. *Aerosol* - As mentioned, **aerosol transmission** of *Brucella* mainly occurs in specific high-risk environments, such as laboratories working with concentrated cultures or close contact with infected animal tissues during veterinary procedures. - It is not a significant mode of transmission for the vast majority of human brucellosis cases.

Question 360: Rickettsial pox is transmitted by:

A. Louse
B. Mite (Correct Answer)
C. Soft tick
D. Hard tick

Explanation: ***Mite*** - Rickettsialpox is caused by the bacterium *Rickettsia akari* and is primarily transmitted to humans through the bite of an infected **mite**, specifically the house mouse mite (*Liponyssoides sanguineus*). - The mite serves as both the **vector** and **reservoir** for the bacteria, perpetuating its life cycle between mice and occasionally humans. *Louse* - **Lice** are known vectors for other rickettsial diseases, such as **epidemic typhus** (*Rickettsia prowazekii*). - However, they are not involved in the transmission of **rickettsialpox**. *Soft tick* - **Soft ticks** (e.g., *Ornithodoros* species) are known to transmit various diseases, including **tick-borne relapsing fever**. - They are not associated with the transmission of **rickettsialpox**. *Hard tick* - **Hard ticks** (e.g., *Ixodes*, *Dermacentor* species) transmit a wide range of diseases, such as **Lyme disease**, **Rocky Mountain spotted fever**, and **ehrlichiosis**. - While they transmit other rickettsial diseases, **rickettsialpox** is not among them.

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Communicable Disease Control Principles

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Vector-Borne Diseases

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Water-Borne Diseases

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Air-Borne Diseases

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Zoonotic Diseases

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Sexually Transmitted Infections

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HIV/AIDS Control Program

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Tuberculosis Control

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Leprosy Elimination

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Emerging and Re-emerging Infections

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Hospital-Acquired Infections

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Integrated Disease Surveillance Project

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