Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 501: The limitation of movement of well persons or animals exposed to communicable diseases for a period usually not longer than the longest incubation period is known as:

A. Segregation
B. Isolation
C. Quarantine (Correct Answer)
D. Modified quarantine

Explanation: ***Quarantine*** - **Quarantine** refers to the **restriction of movement** for **healthy individuals** who have been exposed to a communicable disease. - This period lasts for the **longest incubation period** of the disease to monitor for symptom development and prevent further spread. - This is a key public health measure to control disease transmission from exposed but asymptomatic contacts. *Segregation* - **Segregation** in public health refers to the general separation of groups, but it is **not a specific epidemiological term** for managing disease exposure. - It lacks the specific temporal element (incubation period) and focus on exposed well persons that defines quarantine. - Segregation is a broader term that may apply to various forms of group separation but is not the standard terminology for this specific disease control measure. *Isolation* - **Isolation** is the separation of **sick individuals** with a communicable disease from healthy individuals to prevent transmission. - This typically applies to confirmed or suspected cases showing symptoms, not healthy exposed contacts. - Key difference: isolation is for the **symptomatic/infected**, while quarantine is for the **asymptomatic/exposed**. *Modified quarantine* - **Modified quarantine** allows for some flexibility in movement, often with monitoring or specific restrictions, rather than complete limitation of movement. - It's a less stringent form compared to the complete restriction described in the classic definition of quarantine. - Examples include allowing essential work with precautions while monitoring for symptoms.

Question 502: Incubation period for diphtheria and salmonella gastroenteritis is:

A. 2-6 days and 6-72 hours (Correct Answer)
B. 1-2 days and 1-3 days
C. 2-6 days and 1-3 days
D. 1-2 days and 6-72 hours

Explanation: ***Correct Answer: 2-6 days and 6-72 hours*** - **Diphtheria** has an incubation period of **2-6 days** (typically 2-5 days) - **Salmonella gastroenteritis** has an incubation period of **6-72 hours** (0.25-3 days) - Both values represent the standard, well-established incubation periods found in medical literature *Incorrect: 1-2 days and 1-3 days* - The incubation period of **1-2 days is too short for diphtheria**, which typically requires 2-6 days - While 1-3 days overlaps with Salmonella's range, it misses the shorter duration (as low as 6 hours) that can occur *Incorrect: 2-6 days and 1-3 days* - The diphtheria incubation period (2-6 days) is correct - However, expressing Salmonella's incubation as **1-3 days is less precise** than 6-72 hours, as it doesn't capture the shortest possible incubation period *Incorrect: 1-2 days and 6-72 hours* - The Salmonella incubation period (6-72 hours) is correct - However, **1-2 days is inadequate for diphtheria**, which requires a minimum of 2 days and typically extends to 5-6 days

Question 503: In a case of meningitis, Neisseria meningitides was grown in culture after 48 hours. Which measure is to be taken immediately ?

A. Antibiotic treatment of contacts (Correct Answer)
B. All of the options
C. Isolation of contacts
D. Vaccination of contacts

Explanation: ***Correct: Antibiotic treatment of contacts*** - **Chemoprophylaxis is the immediate priority** for close contacts of confirmed *Neisseria meningitidis* cases - Should be administered **within 24 hours** of case identification to prevent secondary cases - **Recommended antibiotics**: Rifampicin (2 days), Ciprofloxacin (single dose), or Ceftriaxone (single dose) - **Close contacts include**: household members, daycare contacts, anyone directly exposed to patient's oral secretions, healthcare workers exposed to respiratory secretions - This is the **most effective immediate measure** to prevent transmission as meningococcal disease has a 2-10 day incubation period *Incorrect: Isolation of contacts* - **Contacts do NOT require isolation** according to WHO and CDC guidelines - Only the **index patient** requires droplet precautions for 24 hours after starting appropriate antibiotics - Contacts can continue normal activities while on chemoprophylaxis and should monitor for symptoms - Isolating healthy contacts is not evidence-based and creates unnecessary social disruption *Incorrect: Vaccination of contacts* - Meningococcal vaccination is important for **long-term prevention** but not immediate post-exposure prophylaxis - Vaccines take **7-14 days** to develop protective immunity, too slow for immediate protection - Recommended in **outbreak settings** or for high-risk groups as an adjunct to chemoprophylaxis - Does not replace the need for immediate antibiotic prophylaxis *Incorrect: All of the options* - **Only antibiotic chemoprophylaxis** is the immediate measure required - Isolation of contacts is not standard practice for meningococcal disease - Vaccination is a secondary/long-term measure, not immediate - The question asks for the **immediate** measure, which is unequivocally chemoprophylaxis

Question 504: Which of the following is Amphixenoses?

A. Salmonella
B. Anthrax
C. Rabies
D. Trypanosoma cruzi (Correct Answer)

Explanation: ***Trypanosoma cruzi*** - **Amphixenoses** refers to infections that are naturally maintained in both wild (sylvatic) and domestic animal populations, with transmission occurring between these populations. - ***Trypanosoma cruzi***, the causative agent of **Chagas disease**, is a classic example of amphixenosis. - It cycles between **wild animals** (opossums, armadillos, rodents), **domestic animals** (dogs, cats), and **humans**, transmitted by **triatomine bugs (kissing bugs)**. - The disease is maintained in both wild and domestic cycles, making it a true amphixenosis. *Salmonella* - While **Salmonella** can infect both humans and animals, it is primarily classified as a **zoonosis** or **anthropozoonosis**. - It follows a fecal-oral transmission route and is not considered an **amphixenosis** in the classical epidemiological sense. *Anthrax* - **Anthrax (Bacillus anthracis)** is a classic **saprozoonosis** (or sapronosis). - The organism survives in soil (non-living reservoir) and infects herbivores through environmental spores. - Its epidemiology is linked to environmental contamination rather than sustained cycles in both wild and domestic animal populations. *Rabies* - **Rabies** is classified as a **zoonosis**, maintained primarily in wild carnivores (foxes, bats, raccoons) and domestic animals (dogs). - While it affects both wild and domestic animals, transmission is predominantly unidirectional (animal to human via bites), not bidirectional between wild and domestic animal populations as required for amphixenosis classification.

Question 505: You are conducting a study on a new type of infectious disease and find that the case fatality rate is high. It means that:

A. The disease is caused by a virulent organism (Correct Answer)
B. The disease is highly infective
C. The disease has a short incubation period
D. All of the options

Explanation: ***The disease is caused by a virulent organism*** - A **high case fatality rate** (CFR) indicates that a large proportion of **diagnosed cases** of the disease result in death, directly reflecting the **severity** and **virulence** of the causative pathogen. - **Virulence** is defined as the degree of pathogenicity of a microorganism, which means its ability to cause disease and, in this context, severe or fatal forms of the disease. *The disease is highly infective* - **Infectivity** refers to the ability of an organism to establish an infection, often measured by the **attack rate** or **secondary attack rate**, not the case fatality rate. - A highly infective disease might spread easily, but it does not necessarily mean it will cause severe or fatal outcomes in infected individuals. *The disease has a short incubation period* - The **incubation period** is the time between exposure to a pathogen and the onset of symptoms, and it is unrelated to the **case fatality rate**. - A short incubation period indicates how quickly symptoms appear, but not how severe or deadly the disease is once symptoms manifest. *All of the options* - As explained, only the claim that the disease is caused by a **virulent organism** is directly supported by a high **case fatality rate**. - High infectivity or a short incubation period are distinct epidemiological characteristics and do not automatically follow from a high CFR.

Question 506: Which of the following diseases is transmitted by Mansonia?

A. Chikungunya
B. Bancroftian filariasis (Correct Answer)
C. Japanese encephalitis
D. Dengue

Explanation: ***Bancroftian filariasis*** - **Bancroftian filariasis** (caused by *Wuchereria bancrofti*) is commonly transmitted by three mosquito genera: *Culex*, *Anopheles*, and *Mansonia*. - *Mansonia* mosquitoes are known vectors for the larvae of *Wuchereria bancrofti*, which mature into adult worms in the human lymphatic system. *Chikungunya* - Chikungunya virus is primarily transmitted by mosquitoes of the genus *Aedes*, particularly **_Aedes aegypti_** and **_Aedes albopictus_**. - *Mansonia* mosquitoes are not considered primary or significant vectors for the transmission of Chikungunya. *Japanese encephalitis* - Japanese encephalitis virus is mainly transmitted by mosquitoes of the genus _Culex_, specifically **_Culex tritaeniorhynchus_**. - While *Mansonia* mosquitoes may occasionally carry the virus, they are not primary vectors for its transmission to humans. *Dengue* - Dengue virus is primarily transmitted by **_Aedes aegypti_** and **_Aedes albopictus_** mosquitoes. - *Mansonia* mosquitoes are not implicated in the transmission cycle of Dengue fever.

Question 507: Where did the last case of Smallpox occur?

A. Uganda
B. Somalia (Correct Answer)
C. Sudan
D. Libya

Explanation: ***Somalia*** - The **last naturally occurring case** of **variola major** (a more severe form of smallpox) was reported in **Ali Maow Maalin** in **Somalia** in 1977. - This case marked a significant milestone in the global eradication campaign, as subsequent cases were either laboratory-related or variola minor (a milder form). *Uganda* - While smallpox was endemic in many African countries, **Uganda** was not the site of the last naturally occurring case. - The last outbreaks in Uganda preceded the final eradication efforts in other regions. *Sudan* - **Sudan** did experience smallpox outbreaks in the past, but it was not the location of the very last case. - Eradication efforts were extensive across Africa, with the final focus shifting to specific regions. *Libya* - **Libya** also had experience with smallpox, but it was not the country where the last naturally transmitted case was identified. - The global eradication strategy systematically targeted remaining pockets of disease.

Question 508: Spread of which disease cannot be controlled by isolation -

A. Diphtheria
B. Mumps
C. Cholera
D. Neonatal tetanus (Correct Answer)

Explanation: ***Neonatal tetanus*** - **Neonatal tetanus** is caused by spores of *Clostridium tetani* entering the umbilical stump, particularly in unhygienic birth practices. - Its spread is primarily through **environmental contamination** and unsterile wound care, not person-to-person transmission, making isolation ineffective. *Diphtheria* - **Diphtheria** is a highly contagious bacterial infection spread through respiratory droplets, making **isolation of infected individuals** crucial to prevent transmission. - Strict isolation and prompt antitoxin treatment are essential for controlling outbreaks. *Mumps* - **Mumps** is a viral infection that spreads easily through respiratory droplets from infected individuals. - **Isolation measures** and vaccination are highly effective in controlling its spread within communities. *Cholera* - **Cholera** is an acute diarrheal illness caused by ingestion of food or water contaminated with *Vibrio cholerae*. - While isolation can help prevent spread through direct contact in exceptional circumstances, primary control relies on **sanitation, safe water, and hygiene**, as well as careful management of bodily fluids.

Question 509: Not true about measles

A. Koplik spots are pathognomonic
B. Edmonston zagreb strain used for vaccine
C. Carriers are the source of infection (Correct Answer)
D. Incubation period is 2 weeks

Explanation: ***Carriers are the source of infection*** - Measles is transmitted through **respiratory droplets** from infected individuals during the **prodromal phase** and early rash, not through asymptomatic carriers. - While individuals can transmit the virus before symptoms fully develop, they are not considered **asymptomatic carriers** in the sense of long-term, symptom-free transmission. *Koplik spots are pathognomonic* - **Koplik spots** are indeed considered **pathognomonic** for measles, appearing as small, white, or bluish-white spots on the buccal mucosa. - Their presence helps in the **early clinical diagnosis** of measles, often before the characteristic rash appears. *Edmonston zagreb strain used for vaccine* - The **Edmonston-Zagreb strain** is one of the attenuated live virus strains used in some measles vaccines (e.g., in some MMR formulations), demonstrating its relevance in immunization. - Other attenuated strains, such as the **Schwarz** and **Moraten** strains, are also used in measles vaccines globally. *Incubation period is 2 weeks* - The typical incubation period for measles is around **10-14 days** (approximately 2 weeks) from exposure to the onset of symptoms like fever and rash. - This period allows for viral replication before the characteristic clinical signs of the disease become apparent.

Question 510: The following vaccine is developed against cholera -

A. Ty 21a oral
B. Dukoral (Correct Answer)
C. Rotavirus vaccine
D. Vi polysaccharide

Explanation: ***Dukoral*** - **Dukoral** is an **oral cholera vaccine** that contains inactivated *Vibrio cholerae* O1 and O139 bacteria and recombinant B subunit of cholera toxin, providing protection against cholera. - It is often recommended for travelers visiting areas where **cholera** is endemic. *Ty 21a oral* - **Ty21a oral** is an **attenuated live oral vaccine** used for the prevention of **typhoid fever**, caused by *Salmonella Typhi*. - It does not offer protection against cholera. *Rotavirus vaccine* - **Rotavirus vaccine** is an **oral vaccine** used to prevent severe **rotavirus gastroenteritis** in infants and young children. - While it protects against diarrheal disease, it is not effective against cholera, which is caused by *Vibrio cholerae*. *Vi polysaccharide* - **Vi polysaccharide vaccine** is an **injectable vaccine** used for the prevention of **typhoid fever**, targeting the Vi capsular polysaccharide of *Salmonella Typhi*. - Similar to Ty21a, it is effective against typhoid but not cholera.

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