Infectious Diseases Practice Questions

Q: Incubation period for diphtheria and salmonella gastroenteritis is:

2-6 days and 6-72 hours. ***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

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

Antibiotic treatment of contacts. ***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

Q: Which of the following is Amphixenoses?

Trypanosoma cruzi. ***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.

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

The disease is caused by a virulent organism. ***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.

Q: Which of the following diseases is transmitted by Mansonia?

Bancroftian filariasis. ***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.

Q: Where did the last case of Smallpox occur?

Somalia. ***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.

Q: Spread of which disease cannot be controlled by isolation -

Neonatal tetanus. ***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.

Q: Not true about measles

Carriers are the source of infection. ***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.

Q: The following vaccine is developed against cholera -

Dukoral. ***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.

Q: Relapsing fever is transmitted by -

Soft tick. ***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.

Question 1

Incubation period for diphtheria and salmonella gastroenteritis is:

Accepted Answer

2-6 days and 6-72 hours

Answer

1-2 days and 1-3 days

Answer

2-6 days and 1-3 days

Answer

1-2 days and 6-72 hours

Question 2

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

Accepted Answer

Antibiotic treatment of contacts

Answer

All of the options

Answer

Isolation of contacts

Answer

Vaccination of contacts

Question 3

Which of the following is Amphixenoses?

Accepted Answer

Trypanosoma cruzi

Answer

Salmonella

Answer

Anthrax

Answer

Rabies

Question 4

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

Accepted Answer

The disease is caused by a virulent organism

Answer

The disease is highly infective

Answer

The disease has a short incubation period

Answer

All of the options

Question 5

Which of the following diseases is transmitted by Mansonia?

Accepted Answer

Bancroftian filariasis

Answer

Chikungunya

Answer

Japanese encephalitis

Answer

Dengue

Question 6

Where did the last case of Smallpox occur?

Accepted Answer

Somalia

Answer

Uganda

Answer

Sudan

Answer

Libya

Question 7

Spread of which disease cannot be controlled by isolation -

Accepted Answer

Neonatal tetanus

Answer

Diphtheria

Answer

Mumps

Answer

Cholera

Question 8

Not true about measles

Accepted Answer

Carriers are the source of infection

Answer

Koplik spots are pathognomonic

Answer

Edmonston zagreb strain used for vaccine

Answer

Incubation period is 2 weeks

Question 9

The following vaccine is developed against cholera -

Accepted Answer

Dukoral

Answer

Ty 21a oral

Answer

Rotavirus vaccine

Answer

Vi polysaccharide

Question 10

Relapsing fever is transmitted by -

Accepted Answer

Soft tick

Answer

Hard tick

Answer

Sandfly

Answer

Tsetse fly

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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