Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 661: What is the most commonly reported bacterial sexually transmitted infection?

A. HSV
B. HIV
C. Syphilis
D. Chlamydia (Correct Answer)

Explanation: ***Correct: Chlamydia*** - **Chlamydia trachomatis** is the most frequently reported bacterial STI in many countries, often being **asymptomatic** and thus easily spread - Its high prevalence is due to efficient transmission and the widespread use of sensitive diagnostic tests that detect infections in asymptomatic individuals - Accounts for the majority of reported bacterial STI cases globally *Incorrect: HSV* - **Herpes Simplex Virus (HSV)** is a **viral STI**, not bacterial, and is characterized by recurrent outbreaks of **genital ulcers** or sores - While common, it does not qualify as a bacterial infection and is often not laboratory-confirmed due to mild or subclinical presentations *Incorrect: HIV* - **Human Immunodeficiency Virus (HIV)** is also a **viral STI**, not bacterial, that attacks the immune system leading to AIDS - Although highly impactful, HIV is not a bacterial infection and has lower incidence rates compared to Chlamydia *Incorrect: Syphilis* - **Syphilis**, caused by the bacterium **Treponema pallidum**, is a serious bacterial STI that can have long-term complications if untreated - While its incidence has been increasing in some regions, it is significantly less common than **Chlamydia** in terms of overall reported cases

Question 662: Vector of scrub typhus in man?

A. O. tsutsugamushi
B. Leptotrombidium deliense (Correct Answer)
C. Lice
D. Pediculus humanus

Explanation: ***Leptotrombidium deliense*** - This is the **chigger mite** species primarily responsible for transmitting **scrub typhus** to humans. - **Larval mites (chiggers)** of this species feed on human skin and transmit the bacterium *Orientia tsutsugamushi*. *O. tsutsugamushi* - This is the **causative agent** of scrub typhus, not the vector. - It is a **rickettsial bacterium** transmitted by infected chiggers. *Lice* - **Lice** (e.g., *Pediculus humanus corporis*) are vectors for diseases like **epidemic typhus** (caused by *Rickettsia prowazekii*) and **relapsing fever**, but not scrub typhus. - They are **blood-sucking insects** distinct from mites. *Pediculus humanus* - This refers to **human lice**, specifically *Pediculus humanus capitis* (head louse) or *Pediculus humanus corporis* (body louse). - As mentioned, lice transmit diseases like epidemic typhus, not **scrub typhus**.

Question 663: Pediculosis is caused by?

A. Louse (Correct Answer)
B. Mite
C. Tick
D. Black Fly

Explanation: ***Louse*** - **Pediculosis** is a parasitic infestation of the skin by blood-feeding insects called **lice**. - There are different types of lice, including head lice (Pediculus humanus capitis), body lice (Pediculus humanus humanus), and pubic lice (Pthirus pubis), all of which cause pediculosis. *Mite* - **Mites** are responsible for infestations like **scabies**, which is caused by Sarcoptes scabiei. - While both lice and mites are arthropods, they cause distinct parasitic conditions with different clinical presentations and treatments. *Tick* - **Ticks** are known vectors for various diseases, including **Lyme disease** (Borrelia burgdorferi), **Rocky Mountain spotted fever** (Rickettsia rickettsii), and **tick-borne encephalitis**. - Ticks are arachnids, not insects, and their bites can cause localized reactions but not pediculosis. *Black Fly* - **Black flies** (Simulium species) are vectors for **onchocerciasis** (river blindness), caused by the parasitic nematode Onchocerca volvulus. - Their bites are typically painful and can cause localized swelling and allergic reactions, but they do not transmit pediculosis.

Question 664: What is the recommended amount of bleaching powder necessary to disinfect stools contaminated with cholera?

A. 50 gm/liter (Correct Answer)
B. 75 gm/liter
C. 90 gm/liter
D. 100 gm/liter

Explanation: ***50 gm/liter*** - For effective disinfection of stools contaminated with cholera, a concentration of **50 gm of bleaching powder per liter** of stool is recommended to ensure the destruction of **Vibrio cholerae**. - This concentration typically provides a sufficient amount of available **chlorine** to inactivate the bacteria within a reasonable contact time. *75 gm/liter* - While this concentration would certainly disinfect, it is **higher than necessary** for routine cholera stool disinfection and leads to inefficient resource use. - Using excess bleaching powder can also create a **stronger odor** and possibly increase the risk of skin or respiratory irritation. *90 gm/liter* - This concentration is **excessive** and not the standard recommendation for cholera stool disinfection. - Higher concentrations contribute to **waste of resources** and do not offer significantly improved efficacy over the recommended dose for this specific application. *100 gm/liter* - This concentration is significantly **higher than required** for effective disinfection of cholera-contaminated stools. - Using such a high amount is **economically inefficient** and offers no additional benefit in terms of disinfection for this specific pathogen and application.

Question 665: Which of the following is not typically screened for in blood donations?

A. HIV
B. HBV
C. HCV
D. Epstein-Barr Virus (EBV) (Correct Answer)

Explanation: ***Epstein-Barr Virus (EBV)*** ✓ - EBV is **NOT routinely screened** for in blood donations in India and most countries - While EBV is a common virus (>90% adults are seropositive), it is **not considered a major transfusion-transmitted infection** - The virus is primarily transmitted through saliva; transfusion-associated EBV transmission is **extremely rare and usually not clinically significant** in immunocompetent recipients - Risk-benefit analysis does not support routine screening due to **high prevalence, low clinical impact, and cost considerations** - EBV screening may only be considered for specific recipients (e.g., severely immunocompromised patients) *HIV* - **Routinely screened** in all blood donations worldwide - Screening includes HIV-1 and HIV-2 antibodies and/or HIV antigen/RNA testing - Transfusion-transmitted HIV causes AIDS with severe consequences - Mandatory screening under the Drugs and Cosmetics Act in India *HBV* - **Routinely screened** in all blood donations - Screening includes HBsAg (Hepatitis B surface antigen) testing, and often anti-HBc or HBV DNA - Can cause acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma - Mandatory screening in India and globally *HCV* - **Routinely screened** in all blood donations - Screening includes anti-HCV antibodies and/or HCV RNA (nucleic acid testing) - Major cause of chronic hepatitis, cirrhosis, and liver cancer - Mandatory screening under blood safety regulations

Question 666: What is the recommended Aedes Aegypti index for preventing Yellow Fever transmission?

A. Less than 1% (Correct Answer)
B. Less than 5%
C. Less than 10%
D. Less than 20%

Explanation: ***Less than 1%*** - An **Aedes Aegypti index** of **less than 1%** is the recommended threshold by WHO to effectively prevent Yellow Fever transmission. - Maintaining the vector index (House Index) below this critical level significantly reduces the chances of epidemic transmission. - This stringent target is essential for breaking the transmission cycle in endemic areas. *Less than 5%* - While an index of less than 5% represents moderate control, it is insufficient for reliable Yellow Fever prevention. - This threshold may be acceptable for the Breteau Index (measured differently), but for the House Index, 1% is the standard. - At this level, there remains significant risk of transmission during favorable conditions. *Less than 10%* - An index of **less than 10%** is considered inadequate for prevention of Yellow Fever transmission. - This level carries a substantial risk of outbreaks, as the vector population remains high enough to support sustained transmission. - Urgent vector control interventions are needed at this level. *Less than 20%* - An **Aedes Aegypti index** of less than 20% indicates a high-risk environment for Yellow Fever transmission. - This level is far above the recommended threshold and suggests a critical need for immediate and aggressive vector control measures. - At this level, epidemic transmission is highly likely if the virus is introduced.

Question 667: The primary reservoir for leptospirosis transmission is:

A. Rat (Correct Answer)
B. Cat
C. Dog
D. Fish

Explanation: ***Correct Answer: Rat*** - **Rats** (and other rodents) are considered the primary natural reservoir for *Leptospira* bacteria worldwide and are **asymptomatic carriers**. - They excrete the bacteria in their urine, contaminating water and soil, which serves as the main source of human infection. *Incorrect: Cat* - While cats can become infected with *Leptospira*, they are **not typically considered significant reservoirs** for human transmission. - Their role in the epidemiologic cycle of leptospirosis is generally minor compared to rodents and some other mammals. *Incorrect: Dog* - **Dogs** can contract leptospirosis and excrete the bacteria in their urine, posing a risk to humans, but they are generally considered **incidental hosts or secondary reservoirs**, not the primary one. - Vaccination in dogs helps reduce their role in transmission. *Incorrect: Fish* - **Fish are not known to be reservoirs** for *Leptospira* bacteria. - Leptospirosis is primarily transmitted through contact with infected animal urine, not aquatic life like fish.

Question 668: Schistosomiasis is transmitted by?

A. Fish
B. Snail (Correct Answer)
C. Cattle
D. Cyclops

Explanation: ***Snail*** - **Snails** act as the **intermediate host** for all species of Schistosoma, where the parasite undergoes asexual reproduction. - Humans become infected when they come into contact with water contaminated with **cercariae**, which are released from infected snails. *Cyclops* - **Cyclops** (a type of freshwater crustacean) are the intermediate hosts for parasites like **Dracunculus medinensis** (guinea worm) and **Diphyllobothrium latum** (fish tapeworm). - They are not involved in the life cycle or transmission of Schistosoma. *Fish* - Various fish can be intermediate hosts for parasites such as **Clonorchis sinensis** (Chinese liver fluke) or **Diphyllobothrium latum**. - Fish do not play a role in the transmission of schistosomiasis. *Cattle* - **Cattle** can serve as definitive hosts for certain parasites, such as **Taenia saginata** (beef tapeworm), where the larval stage (cysticerci) is found in their muscle tissue. - They are not involved in the life cycle or transmission of Schistosoma.

Question 669: Schistosomiasis is an example of which type of zoonosis that requires an intermediate host?

A. Meta-zoonoses (Correct Answer)
B. Cyclo-zoonoses
C. Direct-zoonoses
D. Sporo-zoonoses

Explanation: ***Meta-zoonoses*** - **Meta-zoonoses** are defined as zoonotic diseases that require an **intermediate invertebrate host** for the completion of the parasite's life cycle. - **Schistosomiasis** fits this definition as it involves fresh water snails acting as an intermediate host, where the parasite undergoes essential developmental stages. *Cyclo-zoonoses* - **Cyclo-zoonoses** require **more than one vertebrate host species** but no invertebrate host for the completion of the infectious agent's life cycle. - An example would be **Taeniasis**, which involves humans and cattle or pigs, but not an invertebrate. *Direct-zoonoses* - **Direct-zoonoses** are transmitted directly from an **infected vertebrate host to a susceptible vertebrate host** without the need for an intermediate host or vector. - Examples include **rabies** or **brucellosis**, which are passed directly from animals to humans. *Sporo-zoonoses* - **Sporo-zoonoses** are zoonoses where the infectious agent undergoes **sporogonic development in an invertebrate host**, but this term is not a standard or widely recognized category in the same way as direct, cyclo-, or meta-zoonoses. - The more appropriate term for diseases involving an invertebrate intermediate host is **meta-zoonoses**.

Question 670: Which of the following is a zoonotic disease?

A. Hydatid cyst (Correct Answer)
B. Malaria
C. Filariasis
D. Dengue fever

Explanation: ***Hydatid cyst*** - This disease is caused by the larval stage of the tapeworm **Echinococcus granulosus**, which completes its life cycle in dogs and sheep. - Humans can become infected by ingesting material contaminated with **Echinococcus eggs**, typically from contact with infected dogs or contaminated food/water, making it a zoonotic disease. *Malaria* - Malaria is transmitted by the **Anopheles mosquito** biting infected humans and then uninfected humans. - While it involves a vector, its primary reservoir is humans and it is not typically considered zoonotic as there is no animal-to-human transmission from a non-human primary reservoir. *Filariasis* - Filariasis is spread by various mosquito vectors (e.g., **Culex, Anopheles, Aedes**) that transmit parasitic worms to humans. - The life cycle primarily involves humans and mosquitos, and it is not classified as a zoonotic disease. *Dengue fever* - Dengue fever is a viral infection transmitted by **Aedes mosquitoes** (primarily *Aedes aegypti* and *Aedes albopictus*) between humans. - Similar to malaria, while it involves a vector, the primary reservoir is humans, and it is not considered zoonotic.

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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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