Typhoid Flashcards
What is the causative agent of typhoid fever?
Salmonella Typhi (S. Typhi).
How is typhoid fever transmitted?
Through ingestion of contaminated food or water, often via the fecal-oral route.
What is the incubation period of typhoid fever?
It varies from 6 to 30 days, with an average of 8-14 days.
What are the key virulence factors of S. Typhi?
Vi capsule, Typhi toxin, and pathogenicity islands (SPI-1 and SPI-2).
What are the available vaccines for typhoid?
- Ty21a (oral live attenuated vaccine)
- Vi polysaccharide vaccine (Vi-PS, unconjugated polysaccharide vaccine)
- Typhoid conjugate vaccine (TCV, conjugated to tetanus toxoid for better immunity)
Mary Mallon (Typhoid Mary) was an asymptomatic carrier responsible for
multiple typhoid outbreaks.
Typhoid fever is a strictly human disease, unlike Salmonella Enteritidis, which is
zoonotic.
The Vi capsule helps S. Typhi evade
opsonization and phagocytosis.
S. Typhi has a lower infectious dose (~100 organisms) compared to
non-typhoidal Salmonella (>10^6 organisms).
Chronic carriers of S. Typhi harbor the bacteria in the
gallbladder and shed it in feces.
Typhoid fever has a shorter incubation period than non-typhoidal Salmonella infections.
False
The Vi capsule is essential for S. Typhi to cause infection.
False – Vi-negative strains can still cause typhoid.
Typhoid fever can lead to chronic carrier status in some individuals.
True
S. Typhi is capable of cross-species transmission like other Salmonella species.
False
S. Typhi is a strictly ______________ pathogen.
Human
The primary mode of transmission for typhoid fever is ______________.
Fecal-oral route via contaminated food or water
The ______________ vaccine is a live-attenuated oral typhoid vaccine.
Ty21a
The Vi capsule of S. Typhi helps evade ______________ by the immune system.
Opsonization and phagocytosis
Which of the following is NOT a characteristic of S. Typhi?
a) Strictly human pathogen
b) Produces Vi capsule
c) Zoonotic transmission
d) Causes systemic infection
A: (c) Zoonotic transmission
Which virulence factor allows S. Typhi to invade deeper tissues?
a) Flagella
b) SPI-1 and SPI-2
c) Biofilm formation
d) Pili
A: (b) SPI-1 and SPI-2
Which vaccine provides the longest-lasting immunity against typhoid fever?
a) Ty21a
b) Vi-PS vaccine
c) Typhoid conjugate vaccine (TCV)
d) Oral cholera vaccine
A: (c) Typhoid conjugate vaccine (TCV)
A patient presents with a stepwise fever, constipation, and a rose-colored rash on the abdomen. What is the likely diagnosis and how is it confirmed?
Typhoid fever, confirmed via blood culture, stool culture, or Widal test.
A restaurant experiences a typhoid outbreak, and investigations trace it to a food handler who appears healthy. What does this suggest?
The food handler is a chronic carrier of S. Typhi, shedding bacteria without symptoms.
A traveler returns from an endemic area and falls ill with prolonged fever and fatigue. What preventive measures could have reduced their risk?
Vaccination (Ty21a or TCV), avoiding untreated water, and maintaining good hygiene.
Typhoid Fever:
A systemic bacterial infection caused by Salmonella Typhi.
Carrier State:
A condition in which an individual harbors and sheds a pathogen without symptoms.
Vi Capsule:
A polysaccharide capsule that helps S. Typhi evade immune responses.
Pathogenicity Islands (SPI-1 & SPI-2):
Genetic regions encoding virulence factors for invasion and immune evasion.
Fecal-Oral Transmission:
Infection spread through ingestion of food or water contaminated with fecal matter.
