Infectious Diseases — MCQs
On this page
Incubation period for diphtheria and salmonella gastroenteritis is:
In a case of meningitis, Neisseria meningitides was grown in culture after 48 hours. Which measure is to be taken immediately ?
Which of the following is Amphixenoses?
You are conducting a study on a new type of infectious disease and find that the case fatality rate is high. It means that:
Which of the following diseases is transmitted by Mansonia?
Where did the last case of Smallpox occur?
Spread of which disease cannot be controlled by isolation -
Not true about measles
The following vaccine is developed against cholera -
Relapsing fever is transmitted by -
Infectious Diseases Indian Medical PG Practice Questions and MCQs
Question 501: 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 502: 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 503: 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 504: 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 505: 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 506: 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 507: 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 508: 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 509: 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.
Question 510: Relapsing fever is transmitted by -
- A. Hard tick
- B. Sandfly
- C. Tsetse fly
- D. Soft tick (Correct Answer)
Explanation: ***Soft tick*** - **Relapsing fever** (especially endemic/spirochetal relapsing fever) is primarily transmitted by the bite of infected **soft ticks** (*Ornithodoros* species). - These ticks are often nocturnal feeders and brief, painless bites, making them difficult to detect. *Hard tick* - **Hard ticks** (families Ixodidae) are vectors for diseases such as **Lyme disease**, **Rocky Mountain spotted fever**, and **Babesiosis**, but not typically relapsing fever. - They tend to attach for longer periods (hours to days) to feed. *Sandfly* - **Sandflies** are vectors for diseases like **leishmaniasis** and **sandfly fever**, which are caused by protozoa or viruses, respectively. - They are not associated with the transmission of spirochetes causing relapsing fever. *Tsetse fly* - The **tsetse fly** is the primary vector for **African trypanosomiasis** (sleeping sickness), caused by parasitic protozoa. - Its transmission mechanism and the pathogens it carries are different from those involved in relapsing fever.
Practice by Chapter
Communicable Disease Control Principles
Practice Questions
Vector-Borne Diseases
Practice Questions
Water-Borne Diseases
Practice Questions
Air-Borne Diseases
Practice Questions
Zoonotic Diseases
Practice Questions
Sexually Transmitted Infections
Practice Questions
HIV/AIDS Control Program
Practice Questions
Tuberculosis Control
Practice Questions
Leprosy Elimination
Practice Questions
Emerging and Re-emerging Infections
Practice Questions
Hospital-Acquired Infections
Practice Questions
Integrated Disease Surveillance Project
Practice Questions
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free