APHA Vaccine-Preventable Diseases & Immunology 3 — Questions and Answers
Question 1: Which hepatitis virus is transmitted primarily through the fecal-oral route and does NOT cause chronic infection?
- Hepatitis B
- Hepatitis C
- Hepatitis A (Correct answer)
- Hepatitis D
Correct answer: Hepatitis A
Hepatitis A virus is transmitted via contaminated food and water (fecal-oral route) and causes only acute infection, never progressing to chronic hepatitis.
Question 2: In the context of immunology, what does 'seroconversion' mean?
- The process of a virus mutating to evade antibodies
- The development of detectable antibodies in serum following vaccination or infection (Correct answer)
- A decline in antibody titers over time requiring booster doses
- The transfer of maternal antibodies to a neonate
Correct answer: The development of detectable antibodies in serum following vaccination or infection
Seroconversion refers to the point at which detectable antibodies against a specific antigen first appear in a person's serum, indicating a successful immune response.
Question 3: Haemophilus influenzae type b (Hib) most commonly causes which serious invasive disease in unvaccinated young children?
- Whooping cough
- Bacterial meningitis (Correct answer)
- Tetanus
- Diphtheria
Correct answer: Bacterial meningitis
Before Hib vaccination, H. influenzae type b was the leading cause of bacterial meningitis in children under 5, along with epiglottitis, pneumonia, and septic arthritis.
Question 4: The polysaccharide capsule of Streptococcus pneumoniae is important in vaccine development because it:
- Causes direct tissue destruction through enzyme production
- Allows the bacterium to evade phagocytosis and serves as the target antigen in vaccines (Correct answer)
- Produces toxins that damage nerve endings leading to paralysis
- Enables viral replication within respiratory epithelium
Correct answer: Allows the bacterium to evade phagocytosis and serves as the target antigen in vaccines
The polysaccharide capsule prevents phagocytosis, making it a key virulence factor; pneumococcal vaccines target capsular polysaccharides to generate protective antibodies.
Question 5: Which statement best describes the concept of 'original antigenic sin' in immunology?
- The immune system always produces IgM antibodies before IgG antibodies
- Prior exposure to an antigen shapes future immune responses, sometimes to the detriment of responses to related antigens (Correct answer)
- Vaccines must be given in the exact sequence listed on the immunization schedule
- Live vaccines are always more immunogenic than inactivated vaccines
Correct answer: Prior exposure to an antigen shapes future immune responses, sometimes to the detriment of responses to related antigens
Original antigenic sin describes how the immune system preferentially recalls responses to previously encountered antigens, which may impair optimal responses to related but distinct antigens encountered later.
Question 6: Meningococcal disease caused by Neisseria meningitidis is particularly dangerous because:
- It is resistant to all known antibiotics
- It can progress from onset to death within 24–48 hours and causes septicemia with characteristic petechial rash (Correct answer)
- It exclusively affects immunocompromised individuals over age 65
- Vaccination provides only short-term protection lasting less than one month
Correct answer: It can progress from onset to death within 24–48 hours and causes septicemia with characteristic petechial rash
Meningococcal disease is a medical emergency that can cause death within 24–48 hours due to fulminant septicemia, often presenting with a characteristic non-blanching petechial or purpuric rash.
Question 7: Tetanus toxoid works as a vaccine by:
- Killing all Clostridium tetani bacteria in the body upon injection
- Stimulating antibody production against the tetanospasmin toxin, neutralizing it before it binds nerve tissue (Correct answer)
- Activating natural killer cells to destroy infected wound tissue
- Providing passive immunity through pooled human immunoglobulin
Correct answer: Stimulating antibody production against the tetanospasmin toxin, neutralizing it before it binds nerve tissue
Tetanus toxoid is a chemically inactivated form of tetanospasmin that induces the production of antitoxin antibodies capable of neutralizing the toxin before it irreversibly binds to nerve terminals.
APHA Vaccine-Preventable Diseases & Immunology 3
Which hepatitis virus is transmitted primarily through the fecal-oral route and does NOT cause chronic infection?